High molecular weight polyvinyl acetate (PVAc) with Pn of 1.5×104～2.0×104 and polyvinyl alcohol(PVA) with Pn of 4.1×103～6.6×103 were prepared by mini-emulsion polymerization of vinyl acetate with 2

2′-azobis(2

4_dimethyl valeronitrile) (ADMVN) as initiator

and sodium dodecyl sulfate (SDS)/cetyl alcohol (CA) as surfactant/cosurfactant.PVAc with Pn of 1.5×104～2.0×104 and PVA with Pn of 2.1×103～4.4×103 were also obtained by mini-emulsion with 2

2-azobis(2-amidinopropane)(dihydrochloride） (AAPH) as initiator.The effects of the initiator concentration

temperature and VAc/H2O ratio on molecular weight and conversion were investigated

and the dependence of SDS/CA(mol/mol) ratio on the particle diameter distribution of polyvinyl acetate microspheres and nucleation mechanism was discussed.The stablest mini-emulsion system was obtained at cCA∶cSDS=3∶1. Nucleation occured mostly in monomer droplets regardless of using ADMVN or AAPH as initiator

and the particle diameter distribution of PVAc microspheres with ADMVN as initiator was narrower than the particle diameter distribution with AAPH as initiator.