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

Randomly branched bisphenol A polycarbonates (PCs) were prepared by interfacial 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 (Mw /arm) values based on the composition variables. The amounts of the monomer, branching agent, and chain terminator must be adjusted such that the weight-average functionality of the phenolic monomers (FOH ) 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 molecular weights measured by gel permeation chromatography-UV and gel permeation chromatography-LS consistent with model calculations. In SCB PCs, the minimum Mw /arm that could be realized without gel formation depended on both composition (molecular weight, terminator type) and process (terminator addition point, coupling catalyst) variables. The minimum Mw /arm achieved in the low molecular weight series studied ranged from 3300 to 1000. The use of long chain alkyl phenol terminators gave branched PCs with lower glass-transition temperatures but a higher gel-free minimum Mw /arm. SCB PCs where Mw /arm was less than Mc spontaneously cracked after compression molding, a result attributed to their lack of polymer chain entanglements.