CATALYTIC CHAIN TRANSFER FOR MOLECULAR-WEIGHT CONTROL IN THE EMULSIONHOMO-MERIZATION AND COPOLYMERIZATION OF METHYL-METHACRYLATE AND BUTYLMETHACRYLATE

The behavior of catalytic chain transfer in semi-batch emulsion polyme rization has been studied for two monomers, viz, methyl and n-butyl me thacrylate. Two different catalytic chain transfer reagents were used with different water solubilities: cobaloxime boron fluoride (COBF), w hich was found to partition approximately equally between organic and aqueous phases, and tetra-phenyl cobaloxime boron fluoride (COPhBF), w hich was found to reside predominantly in the organic phase. The diffe rence in hydrophilicity between the two transfer agents was found to a ffect the polymerization mechanism. COBF exhibited superior transfer b ehavior in all cases, whereas the restricted mobility of the COPhBF ha d a deleterious effect on the efficiency of the transfer mechanism. Th e best results were achieved under monomer flooded conditions using CO BF. MALDI-TOF mass spectrometry analysis shows catalytic chain transfe r to be the dominant mechanism initiating and stopping chain growth as none of the chains appear to have initiator fragment end groups. Anal ysis of copolymers by MALDI-TOF mass spectrometry reveals both molecul ar weight and composition data. (C) 1997 John Wiley & Sons, Inc.