Chain fragmentation under liquid‐state and solid‐state conditions

Abstract

SYNOPSISThermally activated fragmentation of copolycarbonates PC (T,A,-.) of bisphenol A (unit CA) and the heat-sensitive diol 1,1,2,2-tetraethyl-l,2-di-(p-hydroxy )phenylethane (unit CT) was studied in the bulk, i.e., in the pure copolymers and in their blends with the polycarbonates of bisphenol A (PCA) or tetramethyl bisphenol A (TMPC) . Fragmentation proceeds via dissociation followed by disproportionation at the central C -C bond of the unit CT. The reaction has rates that are convenient to study near the glass transition temperature. The "chemical" time constants T for the entire reaction and T~ for the disproportionation step compete with the "physical" time constants 6, for segmental motion and 6, for fragment diffusion. A cage effect is observed below T~ = 6,, and effects of delayed matrix response below T = 6, and 7 = 6,. Owing to the two latter effects, parameters such as the glass transition temperature and the structure factor of concentration fluctuations do not respond primarily to the fragmentation, but rather to subsequent relaxation and diffusion processes in the polymer matrix. Keywords: degradation, thermal, of copolycarbonates and their blends glassy polymers, thermal chain fragmentation in liquid and solid states copolycarbonates, pure and in blends, chain fragmentation in RR R"A diphenylethane unit as shown, with four ethyl substituents, was used in this study. The unit was incorporated into polycarbonate chains, at different mole fractions x:has been studied The time constant 7 1 responds sensitively t o intramolecular strain built up by the substituents about the central C -C bond. 7 1 responds also t o polar and mesomeric effects, so that investigation of the thermal stability of these ethanes has helped in understanding the strength of C -C Another feature of this reaction has attracted less CA CT attention. It results in clean irreversible fragmentation. The radicals react, given the necessary vicinal T h e polycarbonates P C ( T,A1-,) are nearly ideal copolycondensates, with several CT units per chain. The synthesis and particularly t h e thermal fragmentation as measured by gel permeation chromatography ( GPC ) are described in detail in ref. 3.

Chain-fragment diffusion in liquid and glassy polymer blends

“…SANS data measured during chain fragmentation at 160 °C in blends of PC(T,Ai-x) with a matrix of polycarbonate (PCA) rather than TMPC have been presented in ref 11. Figure 3 shows the Zimm diagram of the structure factor S*(t) of a blend PC(TxAi-x)/PCA that is equal to that used in the present study in both x and .…”