Lewis acids with RAFT

Lewis acids (dicthylaluminum chloride, ethyl aluminum scsquichloridc) have been used in conjunction with ATRP to provide greater alternating tendency in S-MMA copolytnerization.519 However, poor control was obtained because of interaction between the catalyst (CuCI/dNbpy) and the Lewis acid. Better results were obtained by RAFT polymerization/10 Copper catalysts, in particular Cu(lI)Br/PMDETA, have been shown to coordinate monomer but this has negligible influence on the outcome of copolymerization/6 ... 

For MMA polymerization, the addition of a Lewis acid, specifically scandium triflate [Sc(OTf)3], is known to increase the fraction of isotactic triads and enhance the rate of polymerization. Similar stereocontrol was observed for RAFT polymerization with cumyl dithiobenzoate and Sc(OTf)3. However, these RAFT polymerizations gave only poor control over molecular weight and polydispersity. Our NMR analyses confirm that the poor... 

A special case of control over the structure of copolymers may include the first stereoblock copolymers made by CRP. By applying either RAFT or ATRP to polymerization of acrylamides in the presence of rare-earth triflates such as Y(OTf)3 and Yb(OTf)3, it was possible to enhance isotacticity of A(A/-dmiethylacrylamide (DMA) from 50% meso to 90% meso dyads (170). At the same time control of molecular weights and polydispersity was preserved. Similar results were obtained for RAFT of A(-ispropylacrylamide (171). The ATRP and RAFT of DMA was applied to the first one-pot stereoblock synthesis by radical mechanism. RAFT or ATRP of DMA were started without Lewis acid to produce the first atactic block. Subsequently, the complexing agent was added at the desired conversion to continue the chain growth with the preferential isotactic placement (170). 

Poly(N,N-dimethylacrylamide) with controlled MW, low values for M /Mn, and a high proportion of meso dyads (approx. 85%) was prepared using ATRP (methyl 2-chloropro-pionate/CuCl/MeeTREN) and RAFT (with cumyl dithiobenzoate transfer agent) in the presence of Y(OTf)3. These systems were used for the first one-pot synthesis of stereoblock copolymers by RP. Well-defined stereoblock copolymers, atactic-l -isotactic poly(N,N-dimethylacrylamides), were obtained by adding Y(OTf)3 to either an ongoing RAFT or ATRP polymerization, started in the absence of the Lewis acid. "... 

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