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Reversible addition fragmentation chain transfer (RAFT) polymerization of methyl methacrylate (MMA) can be carried out in the presence of cyanoisopropyl methyl trithiocarbonate CH3SC(S)SC(CH3)2CN and scandium triflate Sc(OTf)3to provide simultaneous RAFT-controlled (reversible addition-fragmentation chain transfer controlled) molecular weight and molecular weight distribution (w/n< 1.3 at >95% conversion), Lewis acid-controlled tacticity (mm:mr:rr12:44:44 for a mole ratio Sc(OTf)3/MMA 1:8.5 at 60 °C) and an enhanced rate of polymerization. The tacticities observed for poly(methyl methacrylate) (PMMA) are similar to those observed with scandium triflate in the absence of the RAFT agent. The stability of dithiobenzoate RAFT agents ZC(S)SR in the presence of scandium triflate is strongly dependent on both the Z and R substituent. 2-(ethoxycarbonyl)prop-2-yl dithiobenzoate PhC(S)SC(CH3)2CO2CH3and the polymeric RAFT agent PhC(S)S−(CH3)(CO2CH3)CH2−PMMA appear relatively stable. However, cumyl PhC(S)SC(CH3)2Ph and cyanoisopropyl dithiobenzoate PhC(S)SC(CH3)2CN are rapidly degraded and are therefore not appropriate for direct use in this application. These RAFT agents may, however, be used to synthesize stereoblock copolymers where the RAFT agent is first transformed to an oligomeric or polymeric RAFT agent in the absence of a Lewis acid. Cyanoisopropyl 1H-pyrrole-1-carbodithioate (C4H4N)C(S)SC(CH3)2CN is stable to Lewis acid-induced decomposition but slowly homolyzes at 60 °C (even in the absence of the Lewis acid) to initiate the RAFT polymerization of MMA. [ABSTRACT FROM AUTHOR]

The removal of thiocarbonylthio groups from polymers synthesized by radical polymerization with reversible addition−fragmentation chain transfer (RAFT) by radical-induced reduction has been studied. The efficiency of reduction is strongly dependent on the H-donor and the polymer. The effectiveness of the H atom donors studied increases in the series toluene 2-propanol < triethylsilane < triphenylsilane tris(trimethylsilyl)silane ∼ N-ethylpiperidine hypophosphite < tributylstannane. The end groups of the (meth)acrylic polymers, e.g., poly(butyl acrylate) and poly(methyl methacrylate), are more readily reduced than those of polystyrene. With poor H-donors such as toluene or 2-propanol radical−radical reaction between propagating radicals competes with reduction even when they are used in vast excess as a solvent for the process. Thiocarbonylthio groups of polymers prepared with dithiobenzoate or trithiocarbonate RAFT agents can be replaced by hydrogen by radical-induced reduction with hypophosphite salts, in particular, N-ethylpiperidine hypophosphite. Their use overcomes issues of reagent toxicity and ease of workup associated with the use of stannane and silane H-donors. [ABSTRACT FROM AUTHOR]