Synthesis of main chain chiral polymer via asymmetric radical cyclocopolymerization using a chiral diol as a template

The cyclocopolymerization of bis(4-vinylbenzoate) (1) of a chiral diol with styrene has been studied in order to clarify the relationship between chir al template structure and its chirality inductivity. The polymerization was carried out using AIBN as an initiator in dry toluene ([1+styrene](0) = 0. 1 mol L-1) at 60 degrees C. After removal of the chiral template from the r esulting polymer 2, the template-free polymer, i.e., poly[(methyl 4-vinylbe nzoate)-co-styrene] (3), showed optical activity, which significantly depen ded on the chiral template used. When the optically active polymer 3 was ob tained, the specific rotations ([alpha](435)) Of the polymer increased with a decrease in the mole fraction of methyl 4-vinylbenzoate unit in the poly mer, indicating that the optical activity was attributable to the isolated benzoate diad. According to the exciton chirality method, the CD spectra of polymers 3 indicated that the dextrorotatory polymer 3 had a higher conten t of (S, S)-racemo benzoate diad over (R, R)-racemo one and the levorotator y polymer 3 was in the reverse situation. The stereoselection was also obse rved in the radical cyclization using an organotin compounds as a chain tra nsfer reagent. In addition, the skereoisomer distribution of the resulting cyclized unimers indicated that the chiral template inhibited the formation of the unfavorable raceme diad in four possible diads. The calculated heat of formation of cyclized radical by means of semiempirical MO calculation supported the experimental results and gave a model for chirality induction .