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This article was downloaded by: [Eindhoven Technical University] On: 16 November 2014, At: 03:57 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK International Journal of Polymer Analysis and Characterization Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/gpac20 Chain Flexibility Characterization of Poly(oxymethylene) Zhongde Xu a , Chengwei Su a , Dun Li a , Yi Huang a & J. W. Mays b a Institute of Polymer Science and Engineering, East China University of Science and Technology , Shanghai, 200237, People's Republic of China b Department of Chemistry , University of Alabama at Birmingham , Birmingham, AL, 35294, USA Published online: 24 Sep 2006. To cite this article: Zhongde Xu , Chengwei Su , Dun Li , Yi Huang & J. W. Mays (1998) Chain Flexibility Characterization of Poly(oxymethylene), International Journal of Polymer Analysis and Characterization, 4:5, 471-477, DOI: 10.1080/10236669808009729 To link to this article: http://dx.doi.org/10.1080/10236669808009729 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the

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Page 1: Chain Flexibility Characterization of Poly(oxymethylene)

This article was downloaded by: [Eindhoven Technical University]On: 16 November 2014, At: 03:57Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH,UK

International Journalof Polymer Analysis andCharacterizationPublication details, including instructions forauthors and subscription information:http://www.tandfonline.com/loi/gpac20

Chain FlexibilityCharacterization ofPoly(oxymethylene)Zhongde Xu a , Chengwei Su a , Dun Li a , Yi Huang a

& J. W. Mays ba Institute of Polymer Science and Engineering,East China University of Science and Technology ,Shanghai, 200237, People's Republic of Chinab Department of Chemistry , University of Alabamaat Birmingham , Birmingham, AL, 35294, USAPublished online: 24 Sep 2006.

To cite this article: Zhongde Xu , Chengwei Su , Dun Li , Yi Huang & J.W. Mays (1998) Chain Flexibility Characterization of Poly(oxymethylene),International Journal of Polymer Analysis and Characterization, 4:5, 471-477, DOI:10.1080/10236669808009729

To link to this article: http://dx.doi.org/10.1080/10236669808009729

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all theinformation (the “Content”) contained in the publications on our platform.However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness,or suitability for any purpose of the Content. Any opinions and viewsexpressed in this publication are the opinions and views of the authors, andare not the views of or endorsed by Taylor & Francis. The accuracy of the

Page 2: Chain Flexibility Characterization of Poly(oxymethylene)

Content should not be relied upon and should be independently verified withprimary sources of information. Taylor and Francis shall not be liable for anylosses, actions, claims, proceedings, demands, costs, expenses, damages,and other liabilities whatsoever or howsoever caused arising directly orindirectly in connection with, in relation to or arising out of the use of theContent.

This article may be used for research, teaching, and private study purposes.Any substantial or systematic reproduction, redistribution, reselling, loan,sub-licensing, systematic supply, or distribution in any form to anyone isexpressly forbidden. Terms & Conditions of access and use can be found athttp://www.tandfonline.com/page/terms-and-conditions

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Page 3: Chain Flexibility Characterization of Poly(oxymethylene)

Inr. J . Polym. Anal. Characr., 1998 Vol. 4, pp. 471-477 Reprints available directly from the publisher Photocopying permitted by license only

0 1998 OPA (Overseas Publishers Association) N.V Published by license under

the Gordon and Breach Science Publishers imprint.

Printed in India.

Chain Flexibility Characterization of Pol y (oxymet hylene) ZHONGDE XU a,*, CHENGWEI SU a, DUN LI a, YI HUANG a

and J.W MAYS

a Institute of Polymer Science and Engineering, East China University of Science and Technology, Shanghai20023Z People's Republic of China; Department of Chemistry, University of Alabama at Birmingham, Birmingham, AL 35294, USA

(Received 12 December 7997; Revised28 February 1998)

Flory's characteristic ratio C, for poly(oxymethy1ene) (POM) has been measured by Stockmayer from viscosity measurements in hexafluoroacetone sesquihydrate. The value of C, determined was 10.5, almost the same as that for polystyrene. This C, value was suspected of being higher than the real C, value of POM because of the strong solvation power of hexafluoroacetone hydrate and its specific interaction with POM. In this paper, the C , of POM were determined in m-cresol at 100°C and p-chlorophenol at 60°C via intrinsic viscosity measurements. Characteristic ratios of 6.72 and 6.97 were found at 60°C and 10o"C, respectively. The results show that the POM chain is more flexible than polystyrene and is similar in flexibility to polyethylene chain. The positive temperature coefficient of chain dimensions indicates that more compact chain conformations have lower energies. The Mark-Houwink-Sakurada equations for POM in rn-cresol (100°C) and p-chlorophenol(6o"C) have been evaluated simultaneously.

Keywords: Poly(oxymethy1ene); Characteristic ratio C,; Chain flexibility; Dilute solution viscosity; MHS equation

INTRODUCTION

Flory's characteristic ratio, C,, is the most common parameter for characterization of polymer chain flexibility,"] which is defined as:

* Corresponding author.

47 1

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Page 4: Chain Flexibility Characterization of Poly(oxymethylene)

472 ZHONGDE XU et a1

where ( Y ~ ) ~ is the unperturbed (theta condition) mean-square end-to- end distance, and N is the number of main chain bonds of length I . For a freely jointed chain, which has neither rotational hindrances nor bond angle restrictions, ( Y ~ ) ~ is equal to N12. Thus, the value of C, is equal to 1 for a freely jointed chain, and larger C, values indicate the departure from freely jointed behavior, that is, diminished flexibility due to fixed bond angles and rotational hindrances. Therefore, the value of C, is a quantitative measure of polymer chain flexibility.

C, for poly(oxymethy1ene) (POM) has been estimated by Stockmayer and Chad2] from viscosity measurements in hexafluoro- acetone sesquihydrate. The value of ~ O / M " ~ was 1200 f 80 x low4 nm and C, was 10.5, almost the same as that of polystyrene.[31 We suspect that this C, value of 10.5 is higher than the real C, value of POM because of the strong solvation power of hydrogen bonds between the hexafluoroacetone hydrate and POM chain. The possible form of solvation was suggested as follows:[21

In this paper we report the C, values of POM obtained by the combined measurements of weight-average molecular weights and intrinsic viscosities in m-cresol (lOOOC) and in p-chlorophenol (60°C). The C, values of 6.97 in m-cresol ( 100°C) and 6.72 in p-chlorophenol (60°C) are quite different from the C, value of 10.5 and is comparable to the values C,=7.4-8.4[41 found for other more flexible polymer chains, such as polyethylene. The temperature coefficient of unper- turbed chain dimensions for POM and the Mark-Houwink-Sakurada (MHS) equations, both in the POM m-cresol system (IOOOC) and in

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CHAIN FLEXIBILITY OF POM 473

the POM p-chlorophenol system (60°C) have been evaluated and dis- cussed below.

EXPERIMENTAL SECTION

The POM samples were POM copolymers (with 5 wt% 1,3-dioxolane) from Shanghai Solvent Company, and thus contain 3% oxyethylene units. This should have a negligible influence on the measurements of ( Y ~ ) ~ and C,, nevertheless, the POM copolymer is more stable than POM homopolymer for solution measurements at higher temperature.

The solvent hexafluoroacetone (Shanghai Institute of Organo- Fluorine Materials) was distilled before use. The solvents rn-cresol and p-chlorophenol were analytical reagent grade and purified by distil- lation under reduced pressure.

The weight-average molecular weights (M,) of the POM samples were determined with a Brookhaven 200SM laser light scattering pho- tometer. This instrument was equipped with a Spectra-Physics 200 argon laser source and at a wavelength of 514.5 nm. Hexafluoro ace- tone hydrate was used as the solvent at a temperature of 25 f 0.01"C. The dn/dc of POM hexafluoroacetone hydrate system (25°C) at 514.5 nm is 0.129 mL/g. The weight-average molecular weights were obtained by Zimm plots.

The polydispersiiy (M,IM,) of the POM samples was estimated by Waters 150C size exclusion chromatography with a p-Styragel column set from 500 to 106A. Purified fresh rn-cresol (with 2% a-pinene as antioxidant) was the carrier solvent at a flow rate of lmL/min. The temperature was 100°C.

The dilute solution viscosities of POM samples in rn-cresol at 100 f 0.05"C and p-chlorophenol at 60 f 0.05"C were measured in Ubbelohde viscometers having negligible kinetic energy corrections. Two percent a-pinene was added to the solvents to avoid degradation of POM. The values of intrinsic viscosities were obtained by conventional extrapolation to infinite dilution of the vsp/c and In q,/c vs c plots.

RESULTS AND DISCUSSION

The evaluation of C , is most conveniently accomplished by the com- bined measurements of weight-average molecular weights and intrinsic

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414 ZHONGDE XU et al.

viscosities [q] (assuming Flory’s hydrodynamic parameter CJ is known). [q] can be measured either in thermodynamically good solvents or in an ideal solvent, that is, under theta conditions. Measurements in good solvents require the application of extrapolation to infinitely low molecular weights as shown by the procedures of Burchard[’] and Stockmayer and Fixman?”

[ v ] / M ’ / ~ = KO + 0.51CJ.oBM’/2, (2)

in which a plot of [v]/M”~ vs value of KO, ( Y ~ ) ~ / M can be determined from the relationship

yields KO as the intercept. From the

[qle = (a.o((r2)0)3/2/M = K0M’12, (3)

KO = @0((r2 )0 /M)3 /2 , (4)

where ( r2)o represents the mean-square unperturbed end-to-end distance in cm’, [v] is intrinsic viscosity in cm3/g, and @O is the Flory constant which has been found experimentally to have the value of

Flory’s characteristic ratio, C,, can then be calculated from the 2.5 (*o.i) x

following:

where N is the number of bonds in the chain and N‘ denotes the number of backbone chain bonds per repeat unit, I is the mean-square average bond length, and M0 is the mass per repeat unit. For POM chain, N’ is 2 per repeat unit, I is taken as 0.143 nm, and Mo is 30.

The dilute solution characterization results of POM samples, includ- ing M,, M,/Mn, [q] and Huggins coefficient k’ are listed in Table I. From the [q] and M , data in Table I, a plot of ln[q] vs In M,, yields the following relationships for POM:

[q] = 3.70 x lop2 M:705 (m-cresol, 100°C, mLg-I), (6)

[77] = 1.91 x 10-2M:792 (p-chlorophenol, 60°C, mLg-I). (7)

Because polydisperse POM samples (M,/Mn = 1.58-2.68) were used, the correction for polydispersity effects must be considered.

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CHAIN FLEXIBILITY OF POM 475

TABLE I Characteristics of POM samples

Sample M ,

POM- 1 POM-2 POM-7 POM- 10 POM-9 POM-3 POM-4 POM-8 POM-6

10.8

I 9.70

7.50 7.38 6.50 5.69 5.29 5.29

2.12 130.0 1.58 123.9 2.65 102.2 2.68 99.0 2.00 97.5 1.84 I 1.73 82.1

79.9 79.7 1.63

I

kl [?I2 W g - ' )

0.39 I 0.38 169.2 0.41 136.3 0.36 139.7 0.40 135.5

124.0 108.0 0.28

0.35 106.7 0.34 105.0

I

k;

I 0.35 0.33 0.37 0.32 0.43 0.32 0.32 0.41

~

Subscript 1 m-cresol (lOO"C), 2. p-chlorophenol(6o"C)

The correction method employed was suggested by Xu et dt8] Using Weslau's distribution function to describe the molecular weight distri- bution of the samples, we get the following equation:

where K, is the coefficient of MHS equation from polymer samples with broad distribution, Km is the coefficient of the MHS equation from monodisperse polymer samples, and cr is the exponent of the MHS equation.

From Equations (6) and (7) and the Mw/M,, values for each sample, (Kw/Km) can then be calculated, and the appropriate monodisperse molecular weight Mm for each polydisperse POM sample can be esti- mated by the following equation:

The calculated Kw/Km and M , results are listed in Table 11. After polydispersity corrections, the more reliable MHS equations

for POM in the two systems can be evaluated by ln[q] vs In Mw plots:

[VJ = 3.76 x 10-2M0.710 7 (m-cresol, lOO"C, mL/g), (10)

[7] = 1.93 x iO-2M:.796 (p-chlorophenol, 60°C, mL/g). (11)

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476 ZHONGDE XU ei ni.

TABLE I1 samples

Sample (KvIKnII [711 ~ m l x ( ~ w / ~ m ) z ~712 M m 2 x

I POM- 1 0.925 130.0 9.58 0.940 I

The appropriate monodisperse molecular weights of polydisperse POM

9.19 POM-2 0.954 123.9 9.34 0.963 169.2 POM-7 0.904 102.2 6.59 0.923 136.3 6.63 POM-10 0.903 99.0 6.29 0.922 139.7 6.83 POM-9 0.930 97.5 6.42 0.945 135.5 6.78

0.951 124.0 6.11 0.956 108.0 5.17 5.14 POM-4 0.940 82.1

4.99 POM-6 0.951

I POM-3 0.939 I

POM-8 I 19.9 I I 106.7 I 79.7 4.97 0.961 105.0

Subscript 1 rn-cresol (lOO"C), 2 pchlorophenol(6o"C)

The appropriate monodisperse molecular weights M,, listed in Table 11, were used to calculate KO, (r2)o/M and C, by the BSF extra- polation procedure. The results are as follows:

KO = 0.232, ( ro ) /M' /2 = 975 x lop4 nm,

KO = 0.219, (ro)/M'I2 = 957 x nm, C, = 6.72 (p-chlorophenol, 60°C).

Because of solvent and temperature dependence of unperturbed chain dimension, we obtain two different C, values for POM in the two systems. If we neglect the solvent influence on unperturbed chain dimensions, the temperature coefficient of unperturbed chain dimen- sions of POM, K = d ln(r2)o/dT (in units of reciprocal absolute tem- perature), is calculated as 0.96 x lop3. This value is similar to the K

value of 0.78 x of poly(dimethy1 siloxane).['] The positive tem- perature coefficient indicates that more compact chain postures have lower energies.

From our C , data, we can conclude that the chain flexibility of POM is greater than that of polystyrene and is comparable to that of pol ye thylene .[41

C , = 6.97 (m-cresol, 100°C),

References

[l] Flory, P.J. (1969). Stutistical Mechanics of Chnin Molecules (Interscience, New York). [2] Stockmayer, W.H. and Chan, L.L. (1966). J . Polym. Sci., A-2,4,437.

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CHAIN FLEXIBILITY OF POM 477

[3] Brandrup, J. and Immergut, E.H. (1975). Polymer Handbook. 2nd ed. (Wiley- Interscience. New York).

[4] Xu, Zhongde, Hadjichristidis, N., Fetters, L.J. and Mays, J.W. (1995). Adv. Polym. Sci.. 120. 1. - , ,

[5] Burchard, W. (1960). Makromol. Chem., 50,20. [6] Stockmayer, W.H. and Fixman, M. (1963). J. Polym. Sci. Part C , 1, 137. [7] Zimm, B.H. (1980). Macromolecules, 13, 592. [8] Xu, Zhongde el al. (1987). J . Pet. Chem. Tech., 16,442. [9] Xu, Zhongde, Mays, J.W. and Hadjichristidis, N. (1991). Chain Flexibility of

Polymer - Characterization and Structure Relationships (East China Univ. of Chem. Tech. Press, Shanghai).

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