Block copolymerizations of vinyl acetate by combination of conventional and atom transfer radical polymerization

Four different methods of block copolymerization, combining atom transfer radical polymerization (ATRP) and conventional radical polymerization, were studied. The first two methods employed azo compounds containing activated halogen atoms. 2,2'-Azobis[2-methyl-N-(2-(4-chloromethybenzoyloxy)-ethyl)propionamide] (AMBEP) was used to initiate the polymerization of vinyl acetate (VAc) at 90 degrees C. The resulting pVAc with a Cl terminal group (M-n = 47 900; Mw/Mn = 2.21) was subsequently used as a macroinitiator for styrene (St) to yield pVAc-b-pSt (M-n = 91 600; M-w/M-n= 1.80). In the second method, 2,2'-azobis[2-methyl-N-(2-(2-bromoisobutyryloxy)ethyl)propionamide] (AMBEP) was first used tb polymerize n-butyl acrylate (BA) at 30 degrees C in the presence of CuBr/tris[2-(dimethylamino)ethyl]amine (Me-6-TREN). The pBA (M-n = 7500; M-w/M-n = 1.15) with the preserved central azo unit was dissolved in VAc and extended to a block copolymer (M-n = 41 800; M-w/M-n = 3.56). Alternatively, ATRP has been combined with a redox initiated system. VAc was polymerized in the presence of CCl4/Fe(OAc)(2)/N,N,N',N ",N "-pentamethyldiethylenetriamine (PMDETA) to yield pVAc with trichloromethyl end groups (M-n = 3600; M-w/M-n = 1.81). The polymer obtained was dissolved in styrene and block copolymerized by ATRP to form pVAc-b-pSt (M-n = 24 300; M-w/M-n = 1.42). In the last method, pBA with a bromine end group (M-n = 2460; M-w/M-n = 1.32) as prepared by ATRP was dissolved in VAc together with CuBr/1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (Me-4-cyclam) to initiate VAc polymerization. A block copolymer with M-n = 4450 and M-w/M-n= 2.58 was prepared. In the presence of 20 mol % of CuBr2 the polydispersity was further reduced to 1.73.