Isoconversional methods are usually used in thermal degradation kinetic studies. These methods give the values of e�ective activation energy as a function of conversion in associa-tion with various thermoanalytical data like TGA. The main advantage of isoconversional methods is the determination of activation energy independent of the reaction model. For non-isothermal data, isoconversional methods require a series of experiments at di�erent temperature programs. Three of the most used procedures are represented by the di�eren-tial method of Friedman (FR) and the integral methods Ozawa-Flynn-Wall (OFW) and Kissinger-Akahira-Sunose (KAS), the last one used in this work.Starting from the general form of global degradation rate reaction:

α – conversion degree; A – preexponential factor;

E – activation energy; f(α) – reaction model

the mathematical model of KAS method is:

where βi – heating rates and

The activation energy is determined from the slope of linear representations of the left side of these equations vs. 1/Tα,i

The thermogravimetric measurements of each sample were performed at four di�erent heating rates (2, 5, 10, 20 °C/min) from ambient temperature up to 600°C, in nitrogen atmo-sphere. The samples weight was 2.0 ± 0.1 mg.

)(exp αα fRTEA

dtd

⋅

−⋅=

∫=α

ααα

0 )()(

fdg

Isoconversional kinetic methods

[ ]ii

i

TREg

ERA

T ,2,

1)(lnlnlnα

α

α

α

α

αβ⋅−−

≅

THERMAL DEGRADATION OF POLY(N-ISOPROPYLACRYL-AMIDE-co-5,6-BENZO-2-METHYLENE-1,3-DIOXEPANE)

STATISTICAL COPOLYMERS: A KINETIC ANALYSISPaul O. Stanescua *, Gabriel Turturicaa, Maria Andreia, Constantin Draghicib, Dumitru Mircea Vulugab, Anamaria Zahariac, Andrei Sârbuc, Mircea Teodorescua *

a)Department of Bioresources and Polymer Science, Faculty of Applied Chemistry and Materials Science, Polytechnic University, 1 Gh. Polizu Street, 022453 Bucharest, Romania; b)Center of Organic Chemistry of the Romanian Academy, 202B Splaiul Independentei, 060023 Bucharest, Romania

c)National Institute of Research and Development for Chemistry and Petrochemistry - ICECHIM, 202 Splaiul Independentei, 06002, Bucharest, Romania

IntroductionThermosensitive water-soluble polymers have been intensely researched within the last de-cades due to both their biomedical and industrial applications, based on their tempera-ture-triggered hydrophilic-hydrophobic transition in aqueous solutions. Amongst them, poly(N-isopropylacrylamide) (PNIPAM) is maybe the most well known, largely involved in bio-medical research due to its lower critical solution temperature (LCST ≈ 32°C) close to body tem-perature and abrupt thermal response . However, PNIPAM is a non-biodegradable polymer be-cause of the backbone being made up only of C-C bonds and therefore, di�cult to be removed from the body, which seriously limits its biomedical applications. To overcome this, degradable PNIPAM polymers containing hydrolizable ester groups within the backbone have been pre-pared recently by free-radically copolymerizing NIPAM with cyclic ketene acetals, like 5,6-ben-zo-2-methylene-1,3-dioxepane.In this work, the solid state thermal degradation of the PNIPAM - BMDO statistical polymers was investigated by thermogravimetric analysis. Activation energies of the degradation process were calculated using isoconversional methods.

CHCH2 CHCH2n

nNHC

CH3CH3

CHO NHC

CH3CH3

CHO

O

O+ m CH2 COO CH2CH2 m

BMDO

NIPAM

R

poly(NIPAM-co-BMDO)

Figure 1. Copolymerization of NIPAM and BMDO and structure of the resulting statistical copolymers

Statistical copolymer poly(NIPAM-co-BMDO) of various composition, were obtained by radical adition-fragmentation polymerization ( RAFT ), in the presence of S-1-dodecyl-S’’-(α,α’-dimethyl-α’’-acetic acid trithiocarbonate ( TTC ) as RAFT agent. The polymerisation was conducted at 120 °C, in a 10 ml Schlenk flask, charged with 0.6-0.8 g of monomer, TTC, initiator and solvent ( 1,2-Dichlorobenzene ) under nitrogen ( the solvent was prebubbled with N2

for 25 min then the calculated amount of initiator - DTBP was added and bubbled for an extra 5 min ).

Experimental

Results

1. The NIPAM – BMDO statistical copolymers displayed a lower stability than the correspond-ing homopolymers, i.e. PNIPAM and PBMDO.2. The activation energy of the global degradation process increases with conversion and also with NIPAM units content.

Conclusions

Table 1. Characteristics of the prepared polymers

Figure 2. TGA (A) and DTG (B) traces for the

(co)polymers prepared. heating rate = 10°C/min

Figure 4. Activation energy as a function of

conversion for each (co)polymer analyzed

Figure 3. Characteristic curves of the KAS

isoconversional method for PNIPAM

Acknowledgements :

This work was supported by a grant of the Ministry of National Education, CNCS – UEFISCDI, project number PN-II-ID-PCE-2012-4-0082. GT acknowledges the �nancial support of the Sectoral Operational Programme Human Resources Development, �nanced from the European

Social Fund and by the Romanian Government under the contract number POSDRU/156/1.2/G/135764 "Improvement and implementation of universitary master programs in the �eld of Applied Chemistry and Materials Science - ChimMaster".

The copolymers show a lower thermostability compared with the PNIPAM / PBMDO homopoly-mers, the higher the BMDO procentage the lower the stability.

a- determined by 1H NMR b - determined by GPCc- determined by DSC

In order to use KAS isoconversional method, the degradation of each material was studied at multi-ple heating rates. The activation energy of global degradation process decreases with the BMDO content. The variation of E as a function of conver-sion is suggesting that the degradation process involves multi step reactions.

Sample Monomer

X, %

(NIPAM/BMDO)copolymera

mol/mol

Mn b PDI b Tg

c

°C

PNIPAM 90 100/0 6300 1.39 127

PNB1 65 49/51 3180 1.95 51

PNB2 60 23/77 2860 1.91 25

PBMDO 36 0/100 3600 2.65 17

PRIOCHEM

CNCS CNFIS