Vinyl acetate (VAc) and butyl acrylate (BuA) copolymers were prepared by batch and semi-continuous emulsion polymerization．The microstructure of final copolymers．as well as a binary homopolymer blend obtained by mixing homopoly-mar iatexes．was analysed using 13C-NMR．As expected，the homopolymer blend is characterized by the presence of resonance spectra representing VAc and BuA hom-osequences，no heterosequence resonance spectre representing copolymer chains is observed．The semi-continuous (SC) copolymer is characterized by abundant hetero-equence appearance．which indicates that a true copolymer is formed while in the batch copolymers，the presence of homosequences of both monomers are predomina-nt over heterosequences．13C-NMR measurement of batch copolymers withdrawn at different conversions was then carried out．It clearly shows that in this process，a BuA-rich copolymer is firstly formed with very few VAc units

and a quasx-pure PVAc is yielded at end of copolymerization after BuA exhausted．It is found，how-ever，that VAc polymerized with BuA at beginning of polymerization is presented as mono-and dyad homosequences inserted into long BuA chais．This seems disagr-eeing with the popular VAc homogeneous nucleation mechanism in emulsion polym-erization．which assumes that at beginning of reaction VAc is mainly polymerized in aqueOUs phase due to its large water solubility，and thus to form VAc oligomers．The glass transition temperature (Tg) measurement confirms well the 13C-NMR res-ults．Like homopolymer blend，batch copolymer manifests 2 well separated Tg’s，one is close to that of PBuA．but obviously different from it，which is considered as evidence of the presence of BuA-rich copolymer；another appears at nearly the same temperature as PVAc，and observed only on the samples withdrawn after BuA being completely exhausted as regard to semi-continuous copolymers，only one Tg is observed

which is situated between those of homopolymers．