Randomly branched bisphenol A polycarbonates. I. Molecular weight distribution modeling, interfacial synthesis, and characterization

Randomly branched bisphenol A polycarbonates (PCs) were prepared by interfa cial polymerization methods to explore the limits of gel-free compositions available by the adjustment of various composition and process variables. A molecular weight distribution (MWD) model was devised to predict the MWD, G, and weight-average molecular weight per arm (M-w/arm) values based on th e composition variables. The amounts of the monomer, branching agent, and c hain terminator must be adjusted such that the weight-average functionality of the phenolic monomers (F-OH) was less than 2 to preclude gel formation in both the long- and short-chain branched (SCB) PCs. Several series of SCB and long-chain branched PCs were prepared, and those lacking gels showed m olecular weights measured by gel permeation chromatography-UV and gel perme ation chromatography-LS consistent with model calculations. In SCB PCs, the minimum M-w/arm that could be realized without gel formation depended on b oth composition (molecular weight, terminator type) and process (terminator addition point, coupling catalyst) variables. The minimum M-w/arm achieved in the low molecular weight series studied ranged from similar to 3300 to similar to 1000. The use of long chain alkyl phenol terminators gave branch ed PCs with lower glass-transition temperatures but a higher gel-free minim um M-w/arm. SCB PCs where M-w/arm was less than similar to M-c spontaneousl y cracked after compression molding, a result attributed to their lack of p olymer chain entanglements. (C) 2000 John Wiley & Sons, Inc.