Fourier Transform IR (FTIR) Studies of the Degradation of

Jun 1, 1983 - M. M. COLEMAN and G. T. SIVY. Pennsylvania State University, Materials Science and Engineering Department, Polymer Science Section, ...
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32 Fourier Transform IR (FTIR) Studies of the Degradation of Polyacrylonitrile Copolymers Downloaded by UNIV OF CALIFORNIA SAN DIEGO on October 17, 2013 | http://pubs.acs.org Publication Date: June 1, 1983 | doi: 10.1021/ba-1983-0203.ch032

M. M. COLEMAN and G. T. SIVY Pennsylvania State University, Materials Science and Engineering Department, Polymer Science Section, University Park, PA 16802 Fourier transform IR spectroscopy (FTIR) offers consid­ erable potential for studying the complex reactions oc­ curring in the degradation of polyacrylonitrile (PAN) copolymers. Results obtained from studies of PAN co­ polymers containing methacrylic acid, acrylamide, and vinyl acetate are reviewed and results of a terpolymer of PAN containing vinyl acetate and itaconic acid are presented.

FOURIER TRANSFORM

I R ( F T I R ) results on the degradation of polyac­ rylonitrile ( P A N ) and its α-deuterated analogue were presented pre­ viously (I, 2). F r o m the results of these studies we c o n c l u d e d that the mechanism of the degradation of P A N under r e d u c e d pressure at 200 °C i n v o l v e d cyclization to y i e l d an i m i n e f o l l o w e d by tautomerism to the enamine. T h e enamine is subsequently o x i d i z e d to y i e l d a final pyridone structure. T h e c h e m i c a l structure of the c y c l i c p y r i d o n e has several implications c o n c e r n i n g the formation of carbon fibers from P A N precursors. T h e ladder structure imparts rigidity along the c h a i n i n the form of sequences of c y c l i z e d groups. A d d i t i o n a l l y , we believe that extensive interchain hydrogen b o n d i n g b e t w e e n the p o l y m e r chains through the C = 0 and Ν—H groups w i l l have a major role i n maintaining the structure of the degraded material as it is p y r o l i z e d finally to carbon fibers. I f the n u m b e r of c y c l i z e d sequences i n the initial stages of degradation can be m a x i m i z e d and the n u m b e r of oxidative side reactions m i n i m i z e d , superior high-performance car­ b o n fibers c o u l d be obtained. T h e degradation of P A N at 200 °C u n d e r reduced pressure is a relatively slow process; presumably, i n i t i a t i o n is by anionic impurities or i n i t i a l degradation products. H o w e v e r , i n c l u ­ sion of specific comonomers into the P A N c h a i n , such as v i n y l acetate (VAc), methaerylic a c i d ( M A A ) , acrylamide ( A M ) , acrylic acid (AA), 0065-2393/83/0203-0559$06.00/0 © 1983 American Chemical Society In Polymer Characterization; Craver, C.; Advances in Chemistry; American Chemical Society: Washington, DC, 1983.

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on October 17, 2013 | http://pubs.acs.org Publication Date: June 1, 1983 | doi: 10.1021/ba-1983-0203.ch032

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POLYMER CHARACTERIZATION

and itaconic acid (IA), markedly affects the rate of degradation. T h e pyrolysis of P A N copolymers containing the comonomers A A , V A c M A A , I A , a n d A M separately has b e e n studied u s i n g primarily therm a l analysis techniques (3, 4). H e a t i n g rates i n a l l cases were 10 °C/min and temperatures to 500 °C were considered. H o w e v e r , we are concerned primarily w i t h the initial reactions occurring i n the degradation of P A N copolymers at temperatures b e l o w the onset of the major exothermic reaction (i.e.,