Using cobaloxime boron fluoride(COBF)and AIBN as catalyst and initiator respectively

the catalytlc chain transfer bulk polymerization of 2-hydroxyporpyl methacrylate(HPMA)was carried out at 60℃and the low molecular weight polymer with a terminal double bond was prepared．The evolution of the apparent chain transfer constant(Capp)of COBF during the polymerization was determined by the Mayo equation and the CLD(chain length distribution)equation respectively．At the beginning of the reaction

the chain transfor constant showed values of up to about 2000

but with the increasing of the monomer conversion

the chain transfer constant decreases and keeps at a value of about 600 for sometime and then decreased again．The most likely cause for the catalyst deactivation is the stable cobalt-carbon bond formed at the first period of the reaction and then roached equilibrium point．When the polymerization proceeds up to middle and high conversion

the chain transfer polymerization is further manipulated by diffusions of polymeric propagating chain and catalyst molecules

and the apparent chain transfer constant fell to value of below 300．It has been found also

that the data determined by the CLD equation are usually lower than those by the Mayo equation．especially at high conversion stage．It is because that both original equations are available for the instantaneous produced polymer or the case of very lower conversion stage．However

the GPC measurements give molecular weight distributions of the cumulated products rather than the instantaneous produced polymer．The number-average polymerization degrees for the instantaneous produced polymers were obtained from the GPC data

and used in the Mayo equation method together with the modification of the monomer concentration．It was believed that the apparent chain transfer constants from the modified Mayo equation method are more available for the middle and high conversion cases．