Vinyl acetate polymerization with RAFT

Homopolymers and block copolymers of vinyl esters were also synthesized under microwave irradiation by RAFT/macromolecular design via interchange of xanthates polymerization without any significant inhibition or retardation, which is often observed imder conventional heating conditions. Poly(vinyl acetate) (PVAc) with molecular weights of 1000-10,000 g/mol was prepared in less than 15 min under microwave irradiation at an apparent temperature of 70 °C in the presence of the commercially available chain transfer agent ethylxanthogen acetic acid (Roy and Sumerlin, 2011). 

Controlled/ Living radical polymerization (CRP) of vinyl acetate (VAc) via nitroxide-mediated polymerization (NMP), organocobalt-mediated polymerization, iodine degenerative transfer polymerization (DT), reversible radical addition-fragmentation chain transfer polymerization (RAFT), and atom transfer radical polymerization (ATRP) is summarized and compared with the ATRP of VAc catalyzed by copper halide/2,2 6 ,2 -terpyridine. The new copper catalyst provides the first example of ATRP of VAc with clear mechanism and the facile synthesis of poly(vinyl acetate) and its block copolymers. 

In addition to ATRP and NMRP, RAFT has also been used in this transformation. As mentioned previously, block copolymers with desired properties can be prepared by careful selection of the CTA, initiator, and monomers. A novel methodology employing this transformation for the synthesis of well-defined AB diblock and ABA triblock copolymers of poly (vinyl alcohol) (PVA) and PEO was recently reported. For this purpose, mono- or difimctional PEOs with xanthate end group were synthesized by anionic polymerization and employed as CTAs in the RAFT polymerization of vinyl acetate (VAc) to yield well-defined PEO-b-PVAc and PVAc-l -PEO-l7-PVAc. Eventually, direct hydrolysis of acetate groups by sodium hydroxide in methanol solution and... 

Polymerization of vinyl acetate monomer can be effected by bulk, solution, or emulsion techniques. The poly(vinyl acetate) formed is then dissolved in solvent (eg, CH3OH) and alcoholized/hydrolyzed with acidic or basic catalysts. Vinyl acetate can also be polymerized in a controlled fashion via RAFT/MADIX (115). PVA is insoluble in CH3OH and precipitates. It is isolated by filtration, washing, and drying. 

An advantage of initiating an ATRP with an PH as the transferable group, over conducting a standard RAFT polymerization, is that no new chains are formed by added radical initiators and higher MW copolymers can be prepared. A similar process also allowed preparation of copolymers with vinyl acetate. The procedure also provides the possibility to conduct both ATRP and RAFT reactions concurrendy or sequentially with ATRP initiators containing pseudohalide as one of the transferable groups. 

Indeed, it is now possible to extend the range of monomers incorporated into a block copolymer by conducting sequential RAFT and ATRP polymerizations employing a dual functional bromoxanthate iniferter (initiator-transfer agent-terminator). Poly(vinyl acetate)-1 -PS, poly(vinyl acetate)- 7-poly (methyl acrylate), and poly(vinyl acetate)- -PMMA block copolymers with low polydispersity 1.25) were prepared... 

One of the major drawbacks of CRPs is the inability to prepare block copolymers of monomers with widely differing reactivities, such as styrene and vinyl acetate, by sequential monomer addition. Thus, the use of chemistries that permit effective coupling between suitably end-functionalized preformed polymer chains is clearly an attractive alternative. Quemener et al. designed two novel RAFT agents that could be used to polymerize styrene and vinyl acetate independently [36] one RAFT agent installed an azide unit at the end of the polyvinyl... 

The living R-ROP of cyclic ketene acetals was achieved with nitroxy-mediated polymerization (NMP) (29), ATRP (30), and RAFT (31) methods to afford the polyesters with low polydispersities. Recently, it has been reported that the block and random copolymers with vinyl monomers showing low polydispersities could also be obtained by living radical ring-opening copolymerizations (32, 33). 

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