Thermal decomposition of glassy poly(di-t-butyl fumarate) as a topochemical reaction

Decomposition of t-butyl carboxylate (TBC) groups in a glassy poly(di-t-butyl fumarate) (PDTBF) at 140–170°C proceeds with a sharp acceleration caused by interchain interaction of TBC and carboxylic groups. According to selective dissolution data, at 70% degree of conversion the reaction system contains both unchanged PDTBF and a final product: poly(fumaric acid). For TBC groups decomposition in di-t-butyl fumarate (DTBF)–styrene copolymers above their T_g an apparent rate constant of autocatalysis increases with the increase of DTBF content in copolymer. Together with previously obtained x-ray data these results lead to conclusions about the topochemical character of the PDTBF decomposition. The mechanism suggested includes thermal decomposition of TBC groups (initiation), autocatalytic growth of spheric clusters up to a critical size (an appearance of primary germs of the new phase), and growth and branching of thread-like germs. A mathematical model based on these assumptions describes quantitatively the kinetic data. © 1993 John Wiley & Sons, Inc.