The Synthesis Of Several Chiral ATRP Initiators And Their Helix-sense-selective Initiating Function For ATRP

Inspired by its potential applications in materials science, such as ferroelectricliquid crystals (LCs), nonlinear optical materials, the separation of enantiomers andasymmetric catalysis, helical polymers has attracted increasing attention since lateyears. In the preparation of helical polymers, anionic polymerization and coordinationpolymerization are generally used to control the isotactic configuration of the polymer.In recent years, with the development of living radical polymerization, the controlability to the stereo configuration of polymers in radical polymerization is greatlyenhanced. However, there is few report of using atom transfer radicalpolymerization(ATRP) to synthesize helical polymers. For the first time, wesynthesized several chiral bromocarboxylates initiator and used them as the initiatorsof atom transfer radical polymerization(ATRP) and anticipated this ATRP would behelical-sense-selective.Firstly, six chiral initiators containing bulky chiral groups were synthesized.Among them, N-menthyl α-bromophenylacetamide,(3β,5α)-cholestan-3-yl α-bromophenylacetate and (R)-2-bromomethyl-2’-trifluoromethanesulfonyloxy-1,1’-binaphthyl are new compounds. Their structure was determined by13C NMR,1H NMR and elemental analysis.Then, these six ATRP chiral initiators were used as chiral atom transfer radicalpolymerization initiator for the helically selective polymerization of1-Phenyldibenzosuberyl methacrylate (PDBSMA). Excepting (S)-2-bromomethyl-2’-trifluoromethane-sulfonyloxy-1,1’-binaphthyl, other Five ATRP chiral initiatorshave helix-sense-selective ability in initiating the ATRP of bulky monomer PDBSMA.In particular,(S)-2,2’-Bis(bromomethyl)-1,1’-binaphthyl, α-bromobenzeneacetic acidmenthyl ester and (S)-2-bromomethyl-2’-methyl-1,1’-binaphthyl have very goodhelix-sense-selective ability. The helix-sense selectivity depended on thepolymerization temperature, and the ceiling temperature is60oC. The circulardichroism (CD) of polymer indicated that the poly(PDBSMA) initiated by the ATRPchiral initiators could form one-handed-helix-sense excess polymer.These five ATRP chiral initiators were also used as chiral atom transfer radicalpolymerization initiator for the helically selective polymerization of4,4-dimethyl-1-penten-3-one. Experiments showed that4,4-dimethyl-1-penten-3-onecould not form polymer by ATRP in the presence of these chiral initiators. Finally, the combinations of (-)-Sparteine or (+)-sparteine with these five ATRPchiral initiators were used for the helically selective polymerization of PDBSMA.However, moderate yield, low specific rotation, decrescent molecular weight andwidening molecular weight distribution, all of this, showed that the combinations ofsparteine combined with our five chiral initiators gave a bad answer for the thehelically selective ATRP of PDBSMA.