Vinyl chloride/diallyl phthalate(VC/DAP) suspension copolymerizations were carried out in a 5L autoclave and 200ml stainless steel reactors at temperature of 45℃.The apparent reactivity ratios of VC and DAP were calculated as rVC =0.769

rDAP =0.374.The existence of the gel point of the VC/DAP copolymerization system was ascertained and the critical initial concentration of DAP ( fcr ) at which gel began to form was in range of 0 .466～0. 493mmol/mol VC.The degree of polymerization(DP) and indexs of distribution of molecular weight (MWD)of copolymer increased as the initial concentration of DAP (f20) increased when f20 was less than fcr

and DP also increased with increase of conversion.When f20 was larger than fcr

DP and indexs of MWDof sol fraction decreased as f20 increased

but the gel content increased

the gel content also increased as conbersion increased.