A Comparative Study of Oxygen Permeabilities of Film-Forming Polymers by Quenching of Platinum Porphyrin Phosphorescence

Full Paper

A Comparative Study of Oxygen Permeabilitiesof Film-Forming Polymers by Quenching ofPlatinum Porphyrin Phosphorescence

Dedicated to Professor H. W. Spiess on the occasion of his 65th birthday

Sandra Hess, Alfons Becker, Stanislav Baluschev, Vladimir Yakutkin,Gerhard Wegner*

Oxygen permeabilities of different polymers were determined by using two differentmethodsbased on quenching of an excited phosphorescent dye by oxygen. In the first method, thephosphorescent dye platinum octaethylporphyrin is directly dissolved in the polymer film ofinterest whereas in the second method a sensorfilm is used which is separated from the film ofinterest by a spacer. The polymers investigatedare PMMA, PVC, PVAc, cellulose acetate, PEMA,and PS. The resulting oxygen permeability co-efficients are compared with data reported inthe literature. It was found that oxygen per-meation strongly depends on the protocol ofpreparation and thermal history of the films.

Introduction

Information on oxygen permeabilities through polymer

films is essential for many different kinds of application,

most importantly for the development of barrier materials

suitable for packaging of, e.g., electronic devices[1,2] as well

as for the improvement of membranes for gas separation

processes like air separation.[3,4] A commonly usedmethod

to measure gas permeabilities is the so-called time lag

method.[5] The polymer film of interest separates two

chambers which are both initially evacuated. One side of

the film (the feed side) is suddenly exposed to a defined

S. Hess, A. Becker, S. Baluschev, V. Yakutkin, G. WegnerMax Planck Institute for Polymer Research, Ackermannweg 10,55128 Mainz, GermanyFax: þ49 6131 379 100; E-mail: [email protected]

Macromol. Chem. Phys. 2007, 208, 2173–2188

� 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

pressure or partial pressure of the desired gas. From this

moment on, the the pressure in the calibrated volume of

the second chamber (the permeate chamber) is measured

as a function of time by using a pressure sensor. Hereby, a

time lag occurs before the permeating component reaches

the receiving chamber. After this period, a constant flow

of the gas through the film occurs. From this steady-state

flux the desired permeability can be determined. Draw-

backs of this method are that large areas of free-standing

films without any defects and with a uniform thickness

are needed which are not always easy to prepare from

research materials. Further, the receiving volume must be

relatively large due to the dimensions of the necessary

pressure sensor. Moreover, the assessment of polymers

which exhibit high barrier properties can be very time

consuming and inaccurate due to the limited sensitivity of

the pressure sensors.

DOI: 10.1002/macp.200700196 2173

S. Hess, A. Becker, S. Baluschev, V. Yakutkin, G. Wegner

Figure 1. Structure of PtOEP.

2174 �

In the case of oxygen as permeating species, the mass

transport through polymers can be investigated by using

spectroscopic techniques, provided the polymers under

investigation are transparent. For instance, Petrak[6] as

well as Holland et al.[7] have determined oxygen perme-

abilities by placing the polymer film of interest on top of a

sensing layer. This sensing layer contains a sensitizer

which converts the oxygen molecules which have passed

the test film into singlet oxygen by photoexcitation. In the

next step, the singlet oxygen reacts with an oxygen

acceptor also present in the layer. The disappearance of the

absorbance of this oxygen acceptor was spectroscopically

monitored as a function of time and the data were used to

calculate the desired permeability.

A more commonly used technique rests on the ability of

oxygen to quench the luminescence of a photoexcited

sensor dye. Optical oxygen sensors based on this principle

have higher sensitivities compared to other sensing

techniques. They are widely used to detect oxygen

pressures and concentrations, e.g., in biosensing[8,9] or

barometry (pressure-sensitive paints[10]) and they are also

used to investigate oxygen transport through polymers.

Methods to determine diffusion coefficients of oxygen in

thin polymer films aswell as their shortcomings have been

briefly reviewed in the recent literature.[11,12]

The present paper is focused on the determination of

permeabilities. Therefore, previous literature which

describes direct determination of permeability coefficients

is briefly reviewed in the following.

In 1968, Jones[13] investigated the permeation of oxygen

through a PMMAfilmwhich contained naphthalene as the

phosphorescent dye by performing lifetime measure-

ments exposing the sample to different oxygen pressures.

The obtained Stern-Volmer relationship was combined

with the kinetics of diffusion-controlled reactions result-

ing in an expression to achieve the desired permeability.

This approach has found widespread acceptance and we

cite the work of Winnik et al.[14–18] as an example. In most

cases, the permeability coefficient was determined from a

Stern-Volmer plot of the lifetimes of the emitters or by

measurements of the integral intensity of phosphores-

cence. For the latter case, commercial fluorescence spectro-

meters were frequently used and the sample was exposed

to nitrogen and atmospheric air. Among others, Winnik

et al. used this principle to characterize different poly

(alkylaminothiophenylphosphazenes) for their possible

application as pressure-sensitive paint.[14,15] Platinum

porphyrins were used as dye, but rhenium and iridium

complexes were tested, as well.[16] The same group also

characterized core-shell soft sphere ionic liquids using this

method[17] as well as polymer silica composite films.[18]

A further variation of this technique to measure oxygen

permeability was developed by Rharbi et al.[19] It is similar

to conventional permeation and time-lag methods. The


2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

film of interest separates the feed chamber from a

receiving chamber of defined volume. However, instead

of a pressure sensor, a highly permeable polymer film

containing a phosphorescent dye is used as the sensor.

Thus, in contrast to the quenching method mentioned

above, sensor and film of interest are separated.

Two methods based on phosphorescence intensity

quenching to determine oxygen permeabilities through

polymer films are used in the current work. For both

methods the same dye as sensing material was taken. To

be suitable for oxygen sensing the dye has to fulfill certain

requirements.[20,21] It should have a high quantum yield

for photoexcitation and, of course, the excited dye should

be quenched by collision with an oxygen molecule

resulting in a loss in intensity of the emitted light. In

general, sensors based on phosphorescence quenching can

detect oxygen with higher sensitivity compared to

fluorescence techniques: the long lifetime of such lumo-

phores enables their interaction with the diffusing oxygen

molecules which will reach the dye while it is in the

excited state resulting in a high quenching efficiency.

Therefore, less sophisticated detection systems can be used

in this case. Additionally, the longer excitation and

emission wavelengths of such dyes are more compatible

to available optical instrumentation. Finally, the Stokes

shift of the dye should be in the order of 100 nm ormore to

prevent reabsorption of the emitted light. The phosphor-

escent dye chosen for this work is platinum octaethylpor-

phyrin (PtOEP, Figure 1) which is widely used for

oxygen-sensing systems[8,9,20–23] and is one of the most

intense emitters among metalloporphyrin dyes.[21] PtOEP

absorbs in the visible region at 535 nm and phosphores-

cence emission appears at 646 nm. The lifetime of PtOEP in

DOI: 10.1002/macp.200700196

A Comparative Study of Oxygen Permeabilities of Film-Forming Polymers . . .

films is in the range of 100 ms, the exact value depending

on the chemical nature of the polymer matrix.

Method A used in the present work is similar to the

method applied in refs.[13–18], however, instead of lifetimes

intensities were monitored. The luminescent dye is

directly embedded in the polymer film of interest. After

monitoring the phosphorescence intensity of the film in

the absence of oxygen, the film is exposed to a defined

oxygen partial pressure and allowed to equilibrate. The

oxygen molecules permeating through the film collide

with the excited dye molecules and quench their excess

energy. As a consequence, a loss in intensity of phosphor-

escence can be observed. The change of luminescence

intensity is monitored at different oxygen partial pres-

sures. The resulting Stern-Volmer plot can be used to

determine the oxygen permeability provided that the

lifetime in the absence of oxygen is known (see below).

Advantages of this method are that only small film areas

are needed and the method is not affected by holes in the

film. Furthermore, no free-standing films are necessary

and even fluid materials can be investigated.[15,17] How-

ever, some drawbacks exist: when examining high-barrier

materials it is possible that the presence of dye molecules

influences the permeability of the gas. Another point is

that thismethod can only be applied if the dye is soluble in

the polymer, and a uniform distribution without any

aggregation of it in the film must be achieved. To dissolve

the dye in the polymer material both substances should

be soluble in a common solvent fromwhich the film can be

cast or spin-coated.

It is assumed that the presence of the sensor dye does

not influence the free volume of the film material nor the

distribution of free volume. In our studies, we use the dye

in such low concentrations that such effects are improb-

able and, actually, a change in glass transition because the

dye could act as plasticizer has not been seen.

A secondmethod, B,was triedwhich is similar to the one

described by Rharbi et al.[19] As described above, the sensor

and the polymer film of interest are separated by using a

spacer which creates a defined receiving volume between

the film and sensor. In our case, the sensor is made of

a polystyrene (PS) film of 3–4 mm thickness containing

0.5 wt.-% PtOEP on a glass substrate. It is important that

the polymer used for the sensor has a much higher

permeability than the films under investigation, other-

wise the permeability of the sensor layer itself would be

detected. The samples are prepared in an inert atmosphere,

therefore, no oxygen is present in the receiving volume.

Exposing the sample to oxygen at time zero, the gas

molecules passing through the film enter the receiving

volume and cause quenching of photoexcited dye in the

sensor film. The time-dependent decrease in phosphores-

cence intensity is monitored and used to calculate the

desired permeability.



To measure the change in intensities by exposing the

samples to oxygen, a new setup was developed which

enables to conduct both methods. Compared to a conven-

tional fluorescence spectrometer the device constructed is

more versatile. The device contains a temperature-

controlled measurement chamber which is removable to

be able to pick up samples stored in an inert atmosphere.

So, sampleswithout any previous contact to oxygen can be

investigated at the start of the measurement. Using a

gas-mixing chamber, the sample can be exposed to oxygen

at different partial pressures as well as to pure oxygen. It is

also possible to attach a water vapor supply to the mixing

chamber, therefore, investigations under defined relative

humidities are possible as well.

In the following, we present first the theoretical back-

ground of themethods used. Next, a detailed description of

the sample preparation and the setup is given, followed by

the results and their discussion. Different kinds of polymer

films were investigated by applying method A. Hereby,

measurements were performed with a N2/O2 mixture as

well as pure O2 as feed. The obtained permeabilities are

comparedwith reference data found in the literature. More

detailed investigations were performed with PS and

poly(methyl methacrylate) (PMMA) films including the

investigation of different dye contents in such films, dif-

ferent film thicknesses, and temperature-dependent mea-

surements were performed. Finally, the suitability of

method B was tested using a poly(vinyl chloride) (PVC) as

well as a PMMA film. In summary, we present a com-

parative study meant to validate the photophysical

method of determination of the oxygen permeability for

a broad range of prototypical polymers against literature

data based on similar or other methods.

Background

Permeability

The permeation of a penetrant through a dense polymer

film can be characterized by the permeability coefficient P,

which is generally defined as the steady-state flux J of the

penetratingmolecules through the filmnormalized by film

thickness d and pressure difference Dp¼ p1�p2 of the gas

component between feed side 1 and permeate side 2 of the

film.

P ¼ Jd

p1 � p2ð Þ (1)

It is believed that permeation through polymers is a

solution-diffusion process, and the permeability coeffi-

cient can be expressed as a product of a diffusion co-

efficient D and a solubility coefficient S provided that the

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2176 �

diffusion coefficient is a constant and thus independent of

penetrant concentration in the film.

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2007

P ¼ DS (2)

The solubility coefficient S is determined by the con-

densability of the penetrants, by the polymer/penetrant

interactions and by the fraction of free volume existing in

the polymer. The diffusion coefficient is a measure of

mobility of the penetrant, and it is influenced by the

packing and dynamics of the polymer chains and by the

shape and size of the permeating molecules. A lot of

models exist to describe the mass transport through

polymers based on the free volume of the polymer,

statistical or energetic considerations.[24] Most suitable are

theories which take the structure of the polymer chains

into account, describing the mass transport as jumps of

the penetrant between microvoids through temporary

channels caused by thermal motions of the polymer

chains. Many computer simulations are based on this

approach.[24–26]

Method A

By using thismethod, experiments are performed inwhich

the oxygen concentration in the film is allowed to reach

equilibrium. Therefore, a uniform distribution of oxygen in

the film can be assumed. As a consequence, the

diffusion-controlled (or dynamic) quenching of phosphor-

escence can be described by the Stern-Volmer equation

I0I¼ t0

t¼ 1þ kqt0½O2� (3)

where I denotes the intensity and t the phosphorescence

lifetime of the dye in the presence of oxygenwhile I0 and t0are the corresponding values in the absence of oxygen. kq is

the bimolecular quenching rate constant and [O2] the

concentration of oxygen. A relation between the intensity

and the oxygen partial pressure pO2 as well as the

solubility coefficient S can be obtained by applying

Henry’s law

I0I¼ t0

t¼ 1þ kqt0S pO2 (4)

For dynamic quenching processes the quenching rate

constant kq can be related to the diffusion controlled rate

constant kdiff for the formation of the encounter complex

between oxygen and the excited dye molecule. kdiff is

described in terms of Smoluchowski’s diffusion encounter

theory,[27,28] and as a consequence kq can be expressed as

kq ¼ akdiff ¼ a4pNAsD (5)

ol. Chem. Phys. 2007, 208, 2173–2188

WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Here a is the probability of quenching in an encounter

complex of the excited dye/quencher, s the diameter of the

encounter complex, and NA Avogadro’s number. D is the

sum of the diffusion coefficients of the interacting species.

However, due to the fact that the diffusion of oxygen in a

polymer is much higher than the one of the dye, D is set

equal to the diffusion coefficient of oxygen. Substitution of

Equation (5) in (4) yields the following expression:

I0I¼ t0

t¼ 1þ 4pNAst0ð Þ DSð ÞpO2 (6)

By combining Equation (6) and Equation (2), the desired

permeability can be calculated from the slope of the

Stern-Volmer plot provided that t0, a, and s are known.

Unfortunately, several uncertainties exist using this

method. In the strict sense, the above mentioned for-

malism is only valid in fluid media. Difficulties can occur

by applying the theory for rigid polymeric systems

because of the possible presence of microscopic inhomo-

geneities in the polymer matrix.[12,15] The magnitude of

quenching probability a as well as the magnitude of the

encounter complex s are further critical parameters. The

quenching probability a can be calculated by using spin

statistics. For the quenching process of a triplet state, an a

value of 1/9 has been obtained.[29,30] However, in a poly-

mer matrix multiple re-encounters between the oxygen

and the dye are possible because the oxygen is trapped in

the free volume surrounding the polymer and dye mole-

cule. Therefore, the magnitude of a can approach unity for

the quenching of triplets.[14,17] For the diameter of en-

counter complex often the sum of the van der Waals radii

of the dye and an oxygen molecule is used. However, the

true magnitude of this value can be expected to be smaller

because the dye molecule is not a sphere and active

collisions are dependent on the direction of the arriving

oxygen molecules.

Despite such considerations the route of previous

authors is followed in this work assuming a value of

1 nm for the product of a and s.[14,17]

Method B

Method B is in principle equal to the time-lag method

described above. The permeability coefficient can be

calculated from the slope of the steady-state part of the

obtained pressure versus time curve using Equation (1)

which can be expressed as follows:

P ¼ dQ

dt

d

Ap1¼ dp2

dt

V2

RT

d

Ap1(7)

where p1 denotes the pressure at the feed side of the film,

p2¼pO2 the pressure of the permeated gas component in

DOI: 10.1002/macp.200700196


the receiving chamber, V2 the volume of the receiving

chamber, R the gas constant, and T the temperature.

However, instead of a pressure sensor a phosphorescent

sensor is used to detect the concentration of oxygen in the

receiving chamber. Therefore, Equation (4) can be used to

calculate the time-dependent change of the oxygen

pressure from the steady-state slope of a I0/I� 1 versus

pO2 curve

Macrom

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dpO2

dt¼ d I0=I � 1ð Þ

dt

1

KSV(8)

Hereby, the Stern-Volmer constant KSV(¼kqt0S) can be

derived from the slope of the Stern-Volmer plot of the

emission from the sensor film used. By combining

Equation (7) and (8) the desired permeability coefficient

can be obtained.

Experimental Part

Materials

All polymers and solvents were used without further purification.

PVC (Mr¼48000) and cellulose acetate (CA, Mr¼ 61000, 40%

acetyl groups) were obtained from Fluka, Germany. Poly(vinyl

acetate) (PVAc, Mw ¼ 237100), PS (Mw ¼280000), poly(ethyl

methacrylate) (PEMA, Mw ¼515000), PMMA (Mw ¼120000) as

well as the solvents (p.a. quality) toluene, tetrahydrofurane (THF),

and 1,4-dioxane were obtained from Sigma-Aldrich (Germany).

The dye PtOEP was purchased from Frontier Scientific (UK).

Oxygen (99.999 vol.-%) and nitrogen (99.998 vol.-%) were

purchased from Westfalen Reinstgas (Germany).

Film Preparation

Method A

In general a 15wt.-% polymer solutionwas prepared and 0.5wt.-%

(related to the weight of polymer) of PtOEP was added. PVAc, PS,

PMMA, and PEMA were dissolved in toluene while for PVC (10

Figure 2. Experimental setup.

wt.-%) THF and for CA (8 wt.-%) 1,4-dioxane

was used. All solutions were stirred in the

dark until the polymer and PtOEP were

completely dissolved. Films were prepared

by spin-coating of 0.4 mL of the respective

solution at 1 000 rpm for 60 s resulting in

films of thicknesses between 3 and 5 mm

depending on the kind of polymer (the

thicknesses were measured using a Tencor

P-10 step profiler). Pieces of carefully cleaned

microscope slides of approximately 6.5 cm2

were used as substrates. The films were

stored in the dark in an evacuated desiccator

for at least 24 h. Before measurement the

films were evacuated under ultra-high

vacuum using a turbo molecular pump for

at least 12 h.

ol. Chem. Phys. 2007, 208, 2173–2188


Method B

Free-standing films of the polymer of interest were prepared by

casting a solution of 3 wt.-% polymer onto a glass plate onwhich a

Teflon ring with a smooth bottom was placed. After evaporating

the solvent the resulting film was removed from the glass plate

and dried in vacuo at 50 8C for 48 h.

The sensor filmwas prepared as described inmethodA by using

a solution of 15 wt.-% PS in toluene containing 0.5 wt.-% PtOEP. A

grommet (thickness 2 mm, inner diameter 10 mm) was fixed on

top of the sensor layer as a spacer by using an epoxy adhesive

(endfest 300, Uhu, Germany). Then the sensor film was put into a

glove box. An appropriate piece of the free-standing film was

placed on top of the spacer the next day and fixed by using the

same adhesive.

Setup

The apparatus constructed is shown in Figure 2. It consists of a

high vacuummeasurement cell inwhich a temperature controlled

sample holder is mounted. Additionally, at the sample holder an

oxygen sensor (Electrovac GmbH, type SO-K-D12-60-250) is

attached. The measurement cell is connected by a valve with a

big tube diameter to a turbo molecular pump (Pfeiffer vacuum,

TSH071E and TMH071P) to ensure a high vacuum in the cell. The

measurement cell is removable to be able to pick up samples from

a glove box.

The sample holder is placed in the optical path of the beam of a

helium/neon laser (Lasos, 548 nm, 5 mW). The laser beam passes

an aperture, a self-made automatic chopper and an interference

filter (Owis GmbH, CWL 535�2 nm) before reaching the sample.

The resulting phosphorescence emission is separated from the

excitation beam by using an interference filter (Owis GmbH, CWL

646�2 nm), and it is focused by a lens on an optical fiber. This

fiber is connected to a grating spectrograph (EGþG, Digital Triple

Grating Spectrograph, Model 1235) and a Peltier cooled photo-

multiplier (Products of Research, Inc.). With a self-made data

acquisition the time-dependent change in phosphorescence

intensity during the measurement procedure can be monitored.

To expose the sample to a defined oxygen partial pressure the

measurement cell is connected by a valve to a gas mixing system.



Figure 3. Decay of phosphorescence emission (PS film containing0.5 wt.-% PtOEP).

2178 �

It consists of a mixing chamber made of stainless steel in which a

second oxygen sensor is mounted, a pressure sensor (SensSym,

19C030P, 0–30 psi), and several valves to dose the desired ratio of

gas components and to fill the measurement cell. A three-way

valve connects the nitrogen supply to the measurement cell and

the connecting tubes to be able to flush them with pure nitrogen

to remove residual oxygen before the measurement starts.

Measurement Procedures and Data Evaluation

Method A

Prior to measurement the sample placed in the sample holder is

evacuated for at least 12 h by using a turbo molecular pump to

remove oxygen and residual traces of solvent. Then the

phosphorescence intensity of the sample under vacuum and

under continuous illumination is monitored to check, if the

intensity decreases within the first few minutes. This phenom-

enon can occur when using the dye PtOEP and is ascribed to

limited photodecomposition. In such cases, it was observed that

after 10 min continuous illumination a stable phosphorescence

intensitywill be detectedwhich remains constant formany hours.

This observation was also made by Lee and Okura.[21] All

measurements are performed after such a ‘‘conditioning’’ period.

Nevertheless, to protect the sample from unwanted photodecom-

position and to prevent heating of the sample, for the measure-

ment itself a chopperwas used illuminating the sample for 0.5 s in

an interval of 20 s. The measurement starts by detecting the

phosphorescence intensity under vacuum for at least 5 min.

Meanwhile, in the mixing chamber the desired oxygen/nitrogen

mixture is prepared and a small defined overpressure is applied.

(The overpressure is chosen in such a way that after the filling

process atmospheric pressure is achieved inside the measurement

cell.) Then the valve to the pump is closed and the valve to the

mixing chamber is opened to fill the measurement chamber. Now

phosphorescence quenching occurs and a loss in intensity can be

observed until steady-state intensity is reached. After several

minutes the chamber is evacuated again to start the next

measurement cycle. A typical dataset of such ameasurement cycle

is shown in Figure 3. Usually, the measurement of one sample

consists of five such cycles by applying different gas mixtures at

oxygen contents between 2.5 and 20%. From the slope of

Stern-Volmer plots the desired permeability was evaluated using

Equation (9):

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2007

P ¼ slope

4pNAast0(9)

A value of 1 nm was assumed for the product as as stated

above.

The values for t0 were determined by performing pulsed

excitation experiments. For that purpose, the sample, placed

in vacuo was excited by a 5 ms laser pulse (<1 mW) and the

emission decay was monitored using a photomultiplier. The

experimentally obtained values of t0 for the different types of

polymers used in this work are listed in Table 1.

The standard deviation of several measurements of PMMA films

of similar thickness containing 0.5 wt.-% PtOEP allows to estimate

ol. Chem. Phys. 2007, 208, 2173–2188


an error of 10% in themagnitude of P for thismethod. The sensitivity

limit is based on distinguishable values of I0 and I in the intensity

versus time plots (Figure 3). Therefore, as a lower limit, an oxygen

permeability of approximately 10�16 cm3(STP) � cm � cm�2 � s�1 � Pa�1

can be estimated.

Method B

The sample is mounted into the sample holder inside a nitrogen

glove box to ensure an oxygen-free environment in the measure-

ment cell. After placing the cell in the set up and after the

above-described illumination conditioning of the sensor film,

the phosphorescence intensity under nitrogen is measured

time-dependently. Again the chopper was used to suppress

possible side-effects by photodecomposition. Then the measure-

ment cell is evacuated carefully by using amembrane pump. After

closing the valve to the pump the valve to the mixing chamber

containing the desired mixture of oxygen and nitrogen is opened

to fill the measurement chamber. From this moment on the

time-dependent change in intensity is monitored. By plotting

the normalized intensity versus time from the slope of the

steady-state region of the curve the permeability coefficient can be

calculated using Equation (7) and (8) provided KSV of the sensor

film is known. As described in Method A in the Section

Permeability this constant can be obtained from the slope of

Stern-Volmer plot of the sensor film

I0I� 1 ¼ KSVpO2 (10)

Results and Discussion

Sensor Molecules Dissolved inthe Polymer (Method A)

In this section, polymer films are investigated in which the

sensor dye is dissolved. The permeation behavior of

DOI: 10.1002/macp.200700196


Table 1. Summary of oxygen permeability coefficients for the polymers investigated found in the literature and determined in the presentwork (bold).

Polymer Tg t0 P T Film preparation Ref.

-C ms 10S13 cm3(STP) � cm �cmS2 � sS1 �PaS1

-C

PMMA 99a) 0.065 35 Only blends preparation described:

cast from THF-solution,

film dried 1 week at 75 -C,

second week at 130 -C,

then quenched to room

temperature (rt)

[31]

0.075 25 Not described [32]


0.078 Cast from CH2Cl2 solution,

drying at rt

[34]

0.116 34 Commercial sample,

probably slightly

crosslinked

[35]

0.162 25 Dye added during

polymerization, 10 mm slices

cut from polymer rod,

degassed at 105 -C

[13]

0.26

(calculated

from Table 2)

22 Cast from CH2Cl2 solution,

dried over night under

vacuum at 100 -C

[36]

99.1 0.083 (S)b) 22 Spin-coated from toluene

solution, drying for 24 h at

rt, annealed at 105 -C

for 12 h, then ultra-high

vacuum for 12 h

This

work

PVC 83[40] 0.023–0.089 23 Not described [37]

0.034 25 Supplied by American

Hoechst Corp., annealed

above Tg under

high vacuum for 12 h

[38]



0.060 25 Only blends preparation described:

cast from THF solution,

stored in desiccator over

phosphorus pentoxide,

100–250mm

[39]

0.083

(calculated

from Table 2)

22 Cast from CH2Cl2 solution,

dried overnight under

vacuum at 100 -C

[36]


� 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.mcp-journal.de 2179


Table 1. (Continued)



-C

0.093 25 Cast from THF-solution,

film dried under reduced

pressure at rt for 2 h,

vacuum over night

(35–65 mm)

[40]

0.195 25 Cast from THF solution [41]

0.210

(20 -C)

0.182

(120 -C)

25 Cast from THF solution,

preheated samples at

different T, 100mm

[42]

0.338–0.090

(aging)

25 Cast from THF-solution,

film dried under reduced

pressure at rt for 2 h,

vacuum over night

(35–65 mm)

[43]

89.7 0.046

(0.046)b)Spin-coated from THF

solution, drying 24 h at rt,

then ultra-high vacuum

for 12 h

This

work

PVAc 30[45] 0.136 10 Cast from acetone solution,

dried under high vacuum

at T up to 70 -C for weeks

[44]


0.269 25 Cast from THF solution,

few days of air drying,

then dried under vacuum

at T between boiling

point of solvent and Tg

[45]

0.288 25 Cast from acetone solution,



[44]




[44]

0.375 35 Only prepared for mixed matrix

membranes as

described: cast from

CH2Cl2 solution, dried

under vacuum overnight,

annealed at 50 -C under

vacuum for 1 d

[46]

2180Macromol. Chem. Phys. 2007, 208, 2173–2188

� 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/macp.200700196




-C ms 10S13 cm3(STP) � cm �cmS2 � sS1 � PaS1

-C

97.0 0.223

(0.235)b)22 Spin-coated from toluene

solution, drying 24 h

at rt, then ultra-high

vacuum for 12 h

This

work

97.0 0.122

(0.128)b)22 Same film, annealed at

rt for 3 months

This

work

CA

(40% acetyl

groups)

61–66[45] 0.348 25 Cast from acetone solution,



at T between boiling point

of solvent and Tg

[45]

(Acetyl group

content not

mentioned)


(Acetyl group

content not

mentioned)

0.585 30 Lumarith p-912 Celanese

(plasticized) (25mm)

[47]

(Acetyl group

content not

mentioned)

0.788 35 Only blends prep. described:

cast from CH2Cl2/THF (1:3)

solution, slow evaporation

(5–7 d), film dried under

vacuum 35–100mm

[48]

(40% acetyl

groups)

91.7 0.320

(0.339)b)22 Spin-coated from

1,4-dioxane solution,

drying 24 h at rt, then ultra-high

vacuum for 12 h

This

work

PEMA 63a) 1.178 25 Cast from acetone solution,




of solvent and Tg

[45]


dried under vacuum at

T raising up to 130 8C (3 d)

[49]

1.932 35 Cast from CH3Cl-solution

or compression molded,

annealed at 90 8C

[50]

0.522



then ultra-high vacuum

for 12 h

This

work


� 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.mcp-journal.de 2181





-C

PS 100a) 1.3 25 Not described [37]

1.5 25 Preparation of pure films

not described, maybe

dichlorobenzene/PS

casting solution, film

dried under reduced

pressure at rt for 12 h

[51]

1.60 25 Cast from CH2Cl2 solution,




of solvent and Tg

[45]

1.8 25 Molding in carver press

at 140 -C, cooled to rt

over 20 min,

110 and 250 mm

[19]



3.8 rt Chloroform/PS casting

solution, evaporation

of solvent, 62–245mm

[52]

3.7

6.3

3.79 22 Cast from CH2Cl2 solution,

dried over night

under vacuum

at 100 -C,7–57 mm

[36]

89.5 0.896



then ultra-high

vacuum for 12 h

This

work

a)Measured by suppliers.; b)In parentheses: P data obtained from measurements using N2/O2 mixtures (present work).

2182 �

oxygen through different kinds of polymers is analyzed by

performing N2/O2 mixed gas measurements at 22 8C using

oxygen contents from 0 to 20% as well as pure gas

experiments with different pressures of pure oxygen as

feed (up to 200 hPa). The obtained permeability coeffi-

cients are compared with permeability data found in

literature (Table 1).[31–52]



PMMA

To figure out suitable measurement conditions, different

PMMA films varying in dye contents as well as in film

thickness were analyzed. Therefore, films with thicknesses

of 3.22, 1.37, and 0.37 mm were prepared containing

0.75 wt.-% PtOEP each. As expected, no influence of the

DOI: 10.1002/macp.200700196


Table 2. Oxygen permeability coefficients of PMMA films with0.75 wt.-% dye content and different thicknesses.

Thickness of

PMMA film

p

mm 10S13 cm3(STP) � cm �cmS2 � sS1 �PaS1

3.22 0.263

1.37 0.294

0.37 0.275

thickness on the permeability data are observed (Table 2).

The permeability coefficients are all the same within the

experimental error. By investigating films containing 0.1,

0.5, 0.75, and 1.0 wt.-% PtOEP, respectively, related to the

weight of the polymer, no changes in the oxygen perme-

ability coefficients were observed (Table 3). However, a

lower lifetime of 86.7 ms was found for the film containing

1% dye compared to the lifetimes of films with a lower dye

content (averaged value 99.1 ms). This observation indi-

cates the occurrence of aggregation of the dye molecules.

An excited dye molecule can be deactivated by interaction

with a non-excited dye leading to the observed reduction

of lifetime (self-quenching). However, the influence of this

effect on the permeability coefficients is negligible. There-

fore, for further experiments, films of thicknesses between

3 and 5 mm thickness containing 0.5 wt.-% dye were used.

By investigating the oxygen permeation through PMMA

films, an averaged permeability coefficient of 0.291�10�13 cm3(STP) � cm � cm�2 � s�1 � Pa�1 was obtained. Hereby

N2/O2 mixtures with different oxygen partial pressures

were used to obtain the desired Stern-Volmer plots.

Additionally, experiments with pure oxygen as feed

were performed. Comparing the non-bracketed data with

the data given in parentheses (Table 1), nearly no differ-

ence compared to the mixed gas results can be found.

Therefore, it can be concluded that nitrogen molecules

Table 3. Oxygen permeability coefficients and t0 values of PMMAfilms with different dye contents and same thickness of approxi-mately 3.5 mm.

PtOEP content

of PMMA film

t0 P

wt.-% ms 10S13 cm3(STP) � cm �cmS2 � sS1 �PaS1

0.10 98.9 0.334

0.50 99.4 0.325

0.75 99.1 0.330

1.00 86.7 0.327



present in the gas mixture do not affect the oxygen

permeation in the film.

However, compared to the data found in the literature

(Table 1) the oxygen permeability coefficient found in this

work is significantly higher. In this work, freshly prepared

films were used after drying at room temperature under

reduced pressure. Considering the measurement condi-

tions used in the references it was found that the drying

procedures – if reported – differ from the one used in this

work. Jones[13] and Charlesworth and Gan[36] dried their

films at temperatures very close to or at the glass

transition temperature of PMMA, and Chiou and Paul[31]

stored their films even at 130 8C for a week. Therefore, a

sample was investigated with and without annealing

before measuring the oxygen permeability at 23 8C(Figure 4). For the non-annealed sample which had been

treated as described above an oxygen permeability of

0.298� 10�13 cm3(STP) � cm � cm�2 � s�1 � Pa�1 was found.

The same sample was then annealed at 105 8C for 12 h.

After quenching to room temperature the sample was as

usual evacuated for 12 h using a turbo molecular pump,

then themeasurementwas conducted. Now a significantly

lower oxygen permeability was observed: a value of

0.083� 10�13 cm3(STP) � cm � cm�2 � s�1 � Pa�1 was found in

this case. This value matches much better to the data

reported in the literature. Therefore, it is important to

describe the history of the film forwhich permeability data

are to be evaluated in order to make the data obtained

comparable. Due to annealing of the sample the packing

density of the polymer chains increases resulting in a

decrease in free volume. Since the permeability coefficient

strongly depends on the free volume content of the

polymer, a small reduction in the free volume can lead to a

significant decrease in permeability.

Figure 4. Stern-Volmer plots for PtOEP in PMMA: not annealed(&) and annealed at 105 8C for 12 h (&).



Figure 5. Stern-Volmer plots for PtOEP in PMMA (annealed at105 8C) and pure O2 permeation, measured at 23 8C (&), at 40 8C(�), and at 60 8C (~).

2184 �

The temperature dependence of the oxygen perme-

ability was investigated using the annealed sample.

An increase in segmental motion of the polymer chains

with increasing temperature is expected to result in

larger permeability coefficients. In fact, as shown in

Figure 5 the slopes of the Stern-Volmer plots increase with

increasing temperature (from 23 up to 60 8C), resulting in

oxygen permeabilities of 0.083� 10�13 cm3( STP ) � cm �cm�2 � s�1 � Pa�1 at 23 8C, 0.105� 10�13 cm3( STP ) � cm �cm�2 � s�1 � Pa�1 at 40 8C, and 0.145� 10�13 cm3(STP) � cm �cm�2 � s�1 � Pa�1 at 60 8C. We note in passing that PtOEP is

stable against the temperature used here: the lifetime

under absence of oxygen was measured at the tempera-

tures chosen, and it resulted in exactly the same value of

96.2 ms at all temperatures. The activation energy of

permeation was estimated as 12.3 kJ �mol�1.

PVC

A commercial nonplasticized PVC was investigated, the

film was prepared as described in Method A in Film

Preparation section. Pure gas and mixed gas measure-

ments gave exactly the same permeability coefficients. A

value of 0.046� 10�13 cm3(STP) � cm � cm�2 � s�1 � Pa�1

was obtained. This value is comparable to the data

reported in the literature. However, as shown in Table 1,

the literature data presented there can be classified

into two groups. Data of the first group are in the range

between 0.023� 10�13 and 0.093� 10�13 cm3 (STP) � cm �cm�2 � s�1 � Pa�1; the value found in this work ranks among

the data in this group.[32,33,36–40] The second group[41,42]

presents a ten-fold higher oxygen permeabilities of around

0.2� 10�13 cm3(STP) � cm � cm�2 � s�1 � Pa�1. However, due

to the lack of detailed descriptions of the film preparation,

it is difficult to figure out possible reasons for these dif-

ferences. The samples of the first group had been exposed

to temperatures above Tg beforemeasurement, therefore, a



lower oxygen permeation can be expected as shown

above. However, also for the second group Rabek et al.[42]

have investigated annealed samples, e.g., obtaining a

permeability coefficient of 0.182� 10�13 cm3(STP) �cm � cm�2 � s�1 � Pa�1 for a sample which had been an-

nealed at 120 8C for 6 h before measurement.

Additionally, Stern-Volmer plots of PtOEP in PVC

published in the literature were analyzed: Theoretically,

from the slopes of these plots the permeability coefficient

should be calculable using Equation (9) provided that the

product of a and s is known. Again a value of 1.0 nm was

assumed for this product. Lee and Okura[21] has published a

Stern-Volmer plot of a PVC film which was prepared by

casting from a methylethylketone solution onto glass

slides. After drying at room temperature under vacuum for

1 d the sample was heated at 60 8C for 5 h. From the slope

of the straight line of this plot a permeability coefficient of

0.074� 10�13 cm3(STP) � cm � cm�2 � s�1 � Pa�1 can be calcu-

lated assuming a total pressure of 1 013.25 hPa (only

oxygen percentages are presented) and using a t0 value of

89.7 ms as determined in the present work. The perme-

ability coefficient obtained fits well to the first group of

data as mentioned above.

Analyzing a Stern-Volmer plot published by Eaton

and Douglas[53] a permeability coefficient of 0.231�10�13 cm3(STP) � cm � cm�2 � s�1 � Pa�1 was obtained, with

again t0¼ 89.7 ms. The film had been prepared by spin-

coating of a PVC/THF solution in which PtOEP in dichloro-

methane was added. No drying conditions are mentioned

in this reference. This value belongs to the second group of

permeability coefficients reported in the literature.

In contrast to classical measurement methods, the

permeability coefficients obtained by analyzing Stern-

Volmer plots are independent of holes and microdefects in

the films. Therefore, possible defects as explanation for the

higher values in the second group can be excluded.

Tiemblo et al.[43] have already recognized this disagree-

ment in literature values. They have shown that diffusion

as well as permeation coefficients are strongly time-

dependent. Investigating the diffusion coefficients of

different gases in PVC films of thicknesses between 35 and

65 mm they found that even after months an equilibrium

value for the diffusion coefficients was not found, and

the apparent value decreased almost by an order of

magnitude within this time. For the oxygen permeation, a

permeability coefficient of about 0.34� 10�13 cm3 (STP) �cm � cm�2 � s�1 � Pa�1 was reported for the first day, decreas-

ing to a value of approximately 0.09� 10�13 cm3(STP) �cm � cm�2 � s�1 � Pa�1 after 100 d.

This observation can be explained by a physical aging

process (free volume relaxation) of the glassy polymer[43,54,55]

as already mentioned when the results of our studies on

PMMA (see above) were discussed. This physical aging is not

only time- but also temperature-dependent, i.e., it can be

DOI: 10.1002/macp.200700196


accelerated by annealing the sample as seen in the Section

PMMA in Sensor Molecules Dissolved in the Polymer

(Method A).

In the present work, the oxygen permeation measure-

ment was conducted 3 d after the film had been prepared,

and values even lower than those obtained by Tiemblo

et al.[43] after 100 d were found. However, much thinner

filmswere used in the present study.McCaig and Paul[56,57]

investigated the effect of film thicknesses on the physical

aging of a glassy polyacrylate. They observed that for

thicker films (d> 2.5 mm in their case) the decrease in

oxygen permeability is very small and seems to be in-

dependent of film thickness. However, in contrast to our

studies for PMMA, for thinner films a significant loss in

oxygen permeation and a strong dependence on film

thickness was found. They hypothesized that physical

aging is caused by two distinct but simultaneous mecha-

nisms, which both result in a decrease in free volume. The

first one was assigned to a lattice contraction which

seemed to be independent of film thickness and was

completed rather quickly. The second one was described

as diffusion of free volume out of the polymer film. This

process was assumed to be dependent on thickness: the

thinner the film the faster the loss in free volume.

However, such an interpretation is not backed by generally

accepted rules and theories on free volume relaxation.

We would rather assume that partial crystallization of

PVC contributes strongly to the permeation behavior. The

group of lowermagnitude of Pmust be assigned to films in

which crystallization has occurred to its typical extent

while the films in which crystallization was delayed give

an approximately ten-fold higher value.

Figure 6. Stern-Volmer plots for PtOEP in PVAc:mixed gas (&) andpure gas measurement (&) of a freshly prepared sample as wellas mixed gas (~) and pure gas measurement (~) of a samplewhich was kept at room temperature for 3 month.



PVAc

As shown in Figure 6 from the slope of the Stern-

Volmer plot very similar oxygen permeability values

were found for the mixed gas and pure gas measure-

ment of PVAc (0.235� 10�13 and 0.223� 10�13 cm3 (STP) �cm � cm�2 � s�1 � Pa�1, respectively). The measurement was

conducted at 22 8C and the values agree very well with

those published by Salame[32] measured at 25 8C, also with

the other data shown in Table 1 taking into account the

higher temperature used there during measurement. By

repeating the measurement with the same sample after it

had been kept for 3 months at room temperature, a signi-

ficant decrease in the magnitudes of the permeability

coefficients (up to 46%) was found. This is again attributed

to physical aging of the polymer.

CA

A CA sample containing approximately 40% acetyl groups

was investigated. Again similar results were obtained by

conducting mixed and pure gas measurements: oxygen

permeability coefficients of 0.339� 10�13 and 0.320�10�13 cm3(STP) � cm � cm�2 � s�1 � Pa�1, respectively, were

found. The data agree well with the value obtained by

Haraya and Hwang[45] for the same polymer measured at

25 8C. Most of the other references mentioned in Table 1

report values obtained at higher temperatures, and as

expected higher permeabilities were found. However, in

these cases the content of acetyl groups in CA was not

mentioned, thus these values are probably not comparable

with the ones obtained in this work.

PEMA

The measurement of a PEMA sample for N2/O2 mixtures

gave a permeability of 0.532� 10�13 cm3(STP) � cm � cm�2 �s�1 � Pa�1. However, the literature quotes data in the range

of 1.2–1.4� 10�13 cm3(STP) � cm � cm�2 � s�1 � Pa�1, which is

more than two-foldmagnitude.[45,49,50] The literature deals

with samples which had been exposed to higher tem-

peratures before measurement: Haraya and Hwang[45]

heated the sample at temperatures between 56 8C and the

glass transition temperature of 63 8C of PEMA. Chiou and

Paul[49] annealed the sample even at 130 8C for 3 d,

whereas Stannett and Williams[50] used a temperature of

90 8C to anneal the sample.

In our case the samples were not preheated, only dried

in vacuo at room temperature. However, even then a lower

permeability coefficient was obtained compared to the

literature values.

PS

An averaged value for the oxygen permeability coefficient

of 0.854� 10�13 cm3(STP) � cm � cm�2 � s�1 � Pa�1 was found

for PS. However, as in the case of PEMA the data obtained



2186 �

in this work are significantly lower compared to the data

reported in the literature (Table 1). Therefore, more

detailed investigations were performed. Again, an influ-

ence of different film thicknesses (analyzing films with

thicknesses of 4.86, 2.22, and 0.59mm) or of the dye content

(ranging from 0.1 up to 1.5 wt.-% related to the weight of

polymer) on the oxygen permeability coefficients was not

observed. Within the experimental error the permeability

coefficients calculated are identical. The same behavior

was observed by Charlesworth and Gan,[36] who analyzed

films containing camphorquinone as the sensor dye.

The literature quotes permeability coefficients for oxy-

gen in PS determined by conventional measurement

methods (based, e.g., on the time-dependent pressure

change at the permeate side) in the range of (1.3–2.0)�10�13 cm3(STP) � cm � cm�2 � s�1 � Pa�1 (Table 1). Our value is

nearly half as large. However, analyzing the data obtained

from luminescence quenching of a dye mixed with PS it is

found that they differ from those obtained by classical

methods.

Charlesworth and Gan[36] investigated the kinetics of

the quenching of camphorquinone by oxygen in different

glassy polymer matrices including PS. The samples were

free-standing films cast from CH2Cl2 solution with thick-

nesses between 7 and 57 mm containing 10 wt.-% of

ketone. All films used in that work were dried overnight in

a vacuum oven at 100 8C. From the rate constant para-

meters, the solubility coefficients and the lifetimes of the

dye in the matrix in the absence of oxygen as well as from

an a value of 0.47 and a s value of 0.58 nm determined in

that work, an oxygen permeability coefficient of 3.8�10�13 cm3(STP) � cm � cm�2 � s�1 � Pa�1 can be estimated,

which is double as high as the data obtained by classical

methods.

Nowakowska et al.[52] investigated the fluorescence

quenching of different dyes embedded in PS by oxygen in

the steady state. The free-standing films with thicknesses

between 62 and 245 mm were obtained by casting a

chloroform solution on a glass plate. The dyes used were

naphthalene, triphenylene, and perylene. Here, a can be

assumed to be unity because of quenching of the excited

singlet state of the dyes. For s a value of 1.1 nmwas assumed.

As already calculated from Yekta et al.[12] the permeability

coefficients were 3.8� 10�13, 3.7� 10�13, and 6.3� 10�13

cm3(STP) � cm � cm�2 � s�1 � Pa�1, respectively, again higher

than expected from conventional measurements.

Furthermore, Stern-Volmer plots of PtOEP in PS pub-

lished in the literature were analyzed: Shinar et al.[58]

reported some Stern-Volmer plots for PtOEP-doped PS

films, fromwhich oxygen permeabilities of approximately

0.984� 10�13 and 1.31� 10�13 cm3(STP) � cm � cm�2 � s�1 �Pa�1 can be estimated, choosing a t0-value of 89.5 ms found

in the present work and a total pressure of 1 013.25 hPa. In

these investigations, two different commercial batches of



PtOEPwere used resulting in slightly different slopes of the

Stern-Volmer plots. The films had been prepared by drop

casting of a toluene/PS solution onto cleaned glass slides.

The resulting filmswere allowed to dry for several hours in

air in the dark at ambient temperature or at 60 8C. Thepermeability data obtained from the reported Stern-

Volmer plots are very similar to those obtained in the

present work.

Lee and Okura[21] have published a Stern-Volmer plot

obtained by intensity measurements. From the slope of

the straight line shown in that reference, a permeability

coefficient of 0.424� 10�13 cm3(STP) � cm � cm�2 � s�1 � Pa�1

can be estimated using again the t0-value 89.5 ms found in

the present work. As only oxygen percentages are pre-

sented in their plot, for the calculation a total pressure of

1 013.25 hPa was assumed. The film was prepared by

casting a toluene solution on glass slides. The film was

dried at room temperature under vacuum for 1 d, then it

was dried at 60 8C for 5 h.

From the slope of the intensity Stern-Volmer plot

published from Eaton and Douglas,[53] an oxygen perme-

ability coefficient of 0.437� 10�13 cm3(STP) � cm � cm�2

� s�1 � Pa�1 can be calculated, again using the lifetime

reported in the present article. In this case the PS film was

obtained by casting a dichloromethane solution on a plate;

unfortunately, no drying conditions are reported in that

reference.

The differences in oxygen permeability coefficients

determined by Stern-Volmer plots found in the literature

and obtained in the present work for PS are surprising. An

explanation for these discrepancies cannot be given at the

moment.

Sensor Film is Separated from PolymerFilm of Interest (Method B)

A free-standing PVC film with a thickness of 50.0 mm was

investigated using method B. Here, the film of interest is

separated by a spacer from the sensor film in which the

dye is dissolved. The sample is exposed to a N2/O2 mixture

with an oxygen partial pressure of 200 hPa. The oxygen

molecules pass the polymer film and penetrate into the

sensor film resulting in a loss in phosphorescence emission

of the excited dye embedded there. The intensity change

was monitored time dependently. From the slope of

the steady-state part of the curve obtained (Figure 7) an

oxygen permeability coefficient of (0.039� 0.009)�10�13 cm3(STP) � cm � cm�2 � s�1 � Pa�1 can be calculated

which agrees well with the data reported in the literature

(group one) and is marginally lower compared to the value

obtained by using method A.

A second free-standing film was analyzed as well,

namely a PMMA film of 52.8 mm thickness (Figure 7).

DOI: 10.1002/macp.200700196


Figure 7. Plot of I0/I� 1 versus time investigating the oxygenpermeation through a PVC film (&) and through a PMMA film(&) according to method B (see text).

However, in this case the film was dried only at 35 8Cfor 48 h before preparing the spacer sample. By apply-

ing again an oxygen partial pressure of 200 hPa, an

oxygen permeability coefficient of (0.282� 0.091)�10�13 cm3(STP) � cm � cm�2 � s�1 � Pa�1 was obtained. This

value is similar to the data found from method A for

samples which were not subjected to free volume

relaxation.

Conclusion

Two different methods to measure oxygen permeabilities

based on phosphorescence quenching of the excited state

of a sensor dye were used in the current work. In method A

the dye is directly dissolved in the polymer of interest.

Even if separate lifetime measurements in the absence of

oxygen are necessary, it is a very fast method to screen

different transparent polymers. The permeation measure-

ment itself lasts only up to 2 h. In most cases, the results

obtained fit very well to data reported in the literature.

However, in the case of PEMA and PS lower values were

found. A detailed explanation for these discrepancies

cannot be given at present. However, literature also gives a

wide range of different data for oxygen permeabilities for

the same polymer. Experience gained in the course of this

investigation points towards incomplete free volume

relaxation as the origin of the many disagreements found

in the literature.

Applying method B, the sensor was separated from the

film of interest using a spacer. The oxygen permeability

coefficients obtained agree well with reference values

from literature and the coefficients resulting frommethod

A for the few cases we have investigated. For this method



defect-free films are needed; however, only very small

areas are necessary. Thus, in contrast to the classical

methods, no large areas of defect-free films have to be

prepared.

To compare permeability data, it is important to take

the protocol of preparation and the thermal history of the

samples into account. Important points affecting gas

permeability are the drying procedures used as well as the

aging of the samples. Due to the non-equilibrium state of

glassy polymers at temperatures below the glass transi-

tion temperature, physical aging occurs which in all cases

influences the permeability data significantly. Addition-

ally, the solvent used for the filmpreparation can affect the

permeation of gases, especially in cases where the solvent

acts as a plasticizer and cannot be removed completely

from the sample. Thus, many factors can influence the

permeation of gases through polymers and comparison of

permeability data should be carried out very carefully.

Acknowledgements: The authors thank M. Thum for his supportby building up the setup and for conducting the first testmeasurements.

Received: April 3, 2007; Revised: June 29, 2007; Accepted: July 2,2007; DOI: 10.1002/macp.200700196

Keywords: oxygen permeability; phosphorescence; poly(methylmethacrylate); polystyrene; poly(vinyl chloride)

[1] I. Lange, Y. Wyser, Packag. Technol. Sci. 2003, 16, 149.[2] J. S. Lewis, M. S. Weaver, IEEE J. Select. Topics Quant. Electron.

2004, 10, 45.[3] R. Prasad, F. Notaro, D. R. Thomson, J. Membr. Sci. 1994, 94,

225.[4] R. W. Baker, ‘‘Membrane Technology and Applications’’, 2nd

edition, John Wiley & Sons, Chichester 2004, pp. 331–338.[5] C. E. Rogers, ‘‘Permeation of Gases and Vapours in Polymers’’,

in: Polymer Permeability, 1st edition, J. Comyn, Ed., ElsevierApplied Science Publishers, London, New York 1985, pp.21–27.

[6] K. Petrak, J. Appl. Polym. Sci. 1979, 23, 2365.[7] R. V. Holland, M. L. Rooney, R. A. Santangelo, Angew. Makro-

mol. Chem. 1988, 88, 209.[8] D. B. Papkovsky, J. Olah, I. V. Troyanovsky, N. A. Sadovsky,

V. D. Rumyantseva, A. F. Mironov, A. I. Yaropolov,A. P. Savitsky, Biosens. Bioelectron. 1991, 7, 199.

[9] D. B. Papkovsky, Sens. Actuators B 1995, 29, 213.[10] J. Kavandi, J. Callis, M. Gouterman, G. Khalil, D. Wright,

E. Green, D. Burns, B. McLachlan, Rev. Sci. Instrum. 1990,61, 3340.

[11] K. A. Kneas, J. N. Demas, B. Nguyen, A. Lockhart, W. Xu,B. A. DeGraff, Anal. Chem. 2002, 74, 1111.

[12] A. Yekta, Z. Masoumi, M. A. Winnik, Can. J. Chem. 1995, 73,2021.

[13] P. F. Jones, Polym. Lett. 1968, 6, 487.



2188 �

[14] Z. Masoumi, V. Stoeva, A. Yekta, Z. Pang, I. Manners,M. A. Winnik, Chem. Phys. Lett. 1996, 261, 551.

[15] C. N. Jayarajah, A. Yekta, I. Manners, M. A. Winnik, Macro-molecules 2000, 33, 5693.

[16] L. Huynh, Z. Wang, J. Yang, V. Stoeva, A. Lough, I. Manners,M. A. Winnik, Chem. Mater. 2005, 17, 4765.

[17] B.-H. Han, M. A. Winnik, A. B. Bourlinos, E. P. Giannelis, Chem.Mater. 2005, 17, 4001.

[18] X. Lu, I. Manners, M. A. Winnik, Macromolecules 2001, 34,1917.

[19] Y. Rharbi, A. Yekta, M. A. Winnik, Anal. Chem. 1999, 71,5045.

[20] I. Okura, ‘‘Photosensitization of Porphyrins and Phthalocya-nines’’, 1st edition, Gordon and Breach Science Publishers,Amsterdam 2000, p. 154 ff.

[21] S.-K. Lee, I. Okura, Spectrochim. Acta Part A 1998, 54, 91.[22] P. Douglas, K. Eaton, Sens. Actuators B 2002, 82, 200.[23] Y. Amao, K. Asai, I. Okura, H. Shinohara, H. Nishide, Analyst

2000, 125, 1911.[24] S. A. Stern, J. Membr. Sci. 1994, 94, 1.[25] A. A. Gusev, F. Muller-Plathe,W. F. van Gunsteren, U.W. Suter,

‘‘Dynamics of Small Molecules in Bulk Polymers’’, in:Advances in Polymer Science, Vol. 116, Springer-Verlag, Hei-delberg 1994, pp. 207–247.

[26] M. L. Greenfield, D. N. Theodorou, Macromolecules 2001, 34,8541.

[27] M. Smoluchowski, Z. Phys. Chem. 1917, 92, 129.[28] J. E. Guillet, ‘‘Mass Diffusion in Solid Polymers’’, in: Photo-

physical and Photochemical Tools in Polymer Science,M. A. Winnik, Ed., D. Reidel Publishing Company, Dordrecht1986, p. 487.

[29] J. E. Guillet, M. Andrews, Macromolecules 1992, 25, 2752.[30] J. B. Birks, Luminescence 1970, 1, 2, 154.[31] J. S. Chiou, D. R. Paul, J. Appl. Polym. Sci. 1987, 34, 1037.[32] M. Salame, J. Polym. Sci. : Symp. 1973, 41, 1.[33] W. J. Koros, M. Moaddeb, ‘‘Gas Barrier Polymers’’, in: Poly-

meric Materials Encyclopedia, Vol. 4, J. C. Salamone, Ed., CRCPress, Boca Raton p. 2700 f.

[34] A. Boersma, D. Cangialosi, S. J. Picken, Polymer 2003, 44,2463.



[35] W.-H. Yang, V. F. Smolen, N. A. Peppas, J. Membr. Sci. 1981,9, 53.

[36] J. M. Charlesworth, T. H. Gan, J. Phys. Chem. 1996, 100, 14922.[37] W. A. Combellick, ‘‘Barrier Polymers’’, in: Encyclopedia for

Polymer Science and Engineering, 2nd edition, Vol. 2,H. F. Mark, Ed., JohnWiley and Sons, New York 1985, p. 177ff.

[38] B. P. Tikhomirov, H. B. Hopfenberg, V. Stannett, J. L. Williams,Makromol. Chem. 1968, 118, 177.

[39] S. Marais, E. Bureau, F. Gouanve, E. Ben Salem, Y. Hirata,A. Andrio, C. Cabot, H. Atmani, Polym. Test. 2004, 23, 475.

[40] P. Tiemblo, E. Saiz, J. Guzman, E. Riande, Macromolecules2002, 35, 4167.

[41] R. W. Roberts, K. Kammermeyer, J. Appl. Polym. Sci. 1963, 7,2183.

[42] J. F. Rabek, Y. J. Shur, B. Ranby, J. Polym. Sci: Polym. Chem. Ed.1975, 13, 1285.

[43] P. Tiemblo, J. Guzman, E. Riande, C. Mijangos, H. Reinecke,Polymer 2001, 42, 4817 and corrigendum, Polymer 2001, 42,8321.

[44] P. Meares, J. Am. Chem. Soc. 1954, 76, 3415.[45] K. Haraya, S.-T. Hwang, J. Membr. Sci. 1992, 71, 13.[46] R. Mahajan, W. J. Koros, Ind. Eng. Chem. Res. 2000, 39, 2692.[47] R. Waack, N. H. Alex, H. L. Frisch, V. Stannett, M. Szwarc, Ind.

Eng. Chem. 1955, 47, 2524.[48] J. Li, K. Nagai, T. Nakagawa, S. Wang, J. Appl. Polym. Sci. 1995,

58, 1455.[49] J. S. Chiou, D. R. Paul, J. Membr. Sci. 1989, 45, 167.[50] V. Stannett, J. S. Williams, J. Polym. Sci. C 1965, 10, 45.[51] A. Higuchi, T. Agatsuma, S. Uemiya, T. Kojima, K. Mizoguchi,

I. Pinnau, K. Nagai, B. D. Freeman, J. Appl. Polym. Sci. 2000, 77,529.

[52] M. Nowakowska, J. Najbar, B. Waligora, Eur. Polym. J. 1976,12, 387.

[53] K. Eaton, P. Douglas, Sens. Actuators B 2002, 82, 94.[54] Y. Huang, D. R. Paul, Polymer 2004, 45, 8377.[55] J. M. Hutchinson, Prog. Polym. Sci. 1995, 20, 703.[56] M. S. McCaig, D. R. Paul, Polymer 2000, 41, 629.[57] M. S. McCaig, D. R. Paul, Polymer 2000, 41, 639.[58] R. Shinar, Z. Zhou, B. Choudhury, J. Shinar, Anal. Chim. Acta

2006, 568, 190.

DOI: 10.1002/macp.200700196

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