Simultaneous control over the molecular weight and tacticity of poly(vinyl acetate) using a low-temperature photoinitiated RAFT process in fluoroalcohols So-Hee Shim, a Min-kyoung Ham, a June Huh, b Young-Ku Kwon c and Young-Je Kwark * a A photoinitiated RAFT process in fluoroalcohols (FAs) was successfully applied to the preparation of poly(vinyl acetate) and its hydrolyzed polymer, poly(vinyl alcohol), permitting the simultaneous control over the molecular weight (MW) and tacticity. The polymerization reaction displayed living polymerization characteristics, evidenced with linear relationships between ln([M] 0 /[M]) and time, and between the MW and the conversion. Polymers of higher syndiotacticity could be prepared by using the FA solvent, achieving a 62.4% racemic diad at 20  C. The syndiotacticity of the polymer increased with increasing concentrations of FAs or with decreasing polymerization temperatures, and the dependence was stronger than the one observed in conventional radical polymerization reactions due to the slower RAFT process. Furthermore, by performing a sequential polymerization reaction involving the high- temperature reaction in the bulk state and the low-temperature reaction in the FAs, stereoblock copolymers of poly(vinyl alcohol) could be obtained. Introduction Control over tacticity in polymer chemistry is important because it affects the properties of the resulting polymers; however, tacticity is very difficult to control in the context of radical polymerization reactions because the energy difference between two enantiomers of an active radical species is small and the energy barrier between the enantiomers is low compared to the thermal energy at the polymerization temper- ature. Several general strategies have been proposed to effec- tively increase these energy differences. Bulky substituents can be used to introduce steric hindrance effects that increase the energy difference. Monomers with bulky substituents 1–4 and cyclic monomers 5–7 fall into this category and yield stereospe- cic radical polymerization. The use of protic solvents or additives, such as uoroalcohols (FAs) 8–11 or Lewis acids, 12–16 can also improve the stereospecicity of a radical polymerization reaction involving carbonyl-containing monomers. Additives that can form strong hydrogen bonds or coordination bonds with the carbonyl groups in a monomer can increase the effective size of side groups as a means for introducing steric hindrance. In addition to increasing the substituent size in a monomer, lower temperatures can be effective at improving the stereospecicity of a reaction. At lower temperatures, the rate at which enantiomers interconvert is reduced, yielding higher levels of the preferred enantiomeric conguration in the nal product. On the other hand, the molecular weight (MW) and its distribution (MWD) in a radical polymerization may be controlled by selecting an appropriate polymerization tech- nique. 17,18 The reversible addition and fragmentation chain transfer (RAFT) process is a controlled radical polymerization technique that has been widely used due to the diversity of monomers to which it may be applied. 19,20 In recent years, several attempts have been made to simul- taneously control both the MW and the tacticity of vinyl poly- mers prepared by a RAFT process. 21–24 Wan et al. reported that syndiotactic poly(N-vinyl pyrrolidinone) with a controlled MW could be obtained by a RAFT process in FAs. 25 The same group also reported the use of triple hydrogen bonding between acrylamide derivatives and a cyclic imide mediator to increase the syndiotacticity of the prepared polymers. 26 The isotacticity may also be improved using Lewis acids in RAFT processes involving acrylamide. 27–30 It is generally difficult to apply a RAFT process at low temperatures because conventional RAFT processes use a thermal initiator, such as AIBN or BPO, and polymerization usually proceeds at elevated temperatures. High temperatures unfortunately disfavor the preparation of highly stereospecic polymers. Poly(vinyl acetate) (PVAc) is oen used as a precursor of poly(vinyl alcohol) (PVA). Because the properties of PVA depend on its MW and tacticity, polymerization techniques that enable a Department of Organic Materials and Fiber Engineering, Soongsil University, Seoul 156-743, Republic of Korea. E-mail: ykwark@ssu.ac.kr b Department of Materials Science and Engineering, Yonsei University, Seoul 120-740, Republic of Korea c Department of Nano-Systems Engineering, Inha University, Incheon 402-751, Republic of Korea Cite this: Polym. Chem., 2013, 4, 5449 Received 7th February 2013 Accepted 1st July 2013 DOI: 10.1039/c3py00203a www.rsc.org/polymers This journal is ª The Royal Society of Chemistry 2013 Polym. Chem., 2013, 4, 5449–5455 | 5449 Polymer Chemistry PAPER