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.
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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.,
