Chirality Induction in Cyclopolymerization. 2. Synthesis of Optically Active Poly[(methyl 4-vinylbenzoate)-<i>co</i>-styrene] by Cyclocopolymerization of 1,2:5,6-Di-<i>O</i>-isopropylidene-3,4-bis-<i>O</i>-(4-vinylbenzoyl)-<scp>d</scp>-mannitol and -<scp>d</scp>-glucitol with Styrene

Abstract

1,2:5,6-Di- O -isopropylidene-3,4-bis- O -(4-vinylbenzoyl)- d -mannitol ( 1a ) and - d -glucitol ( 1b ) with styrene (St) were polymerized using AIBN in toluene at 60 °C to yield copolymers ( 2a and 2b, respectively) consisting essentially of the cyclic repeating and styrene units. In order to confirm asymmetric induction in 2, the removal of the template from 2 was carried out using KOH in aqueous MeOH, and then the resulting hydrolyzed copolymer was treated with diazomethane for conversion into poly[(methyl 4-vinylbenzoate)- co -styrene] ( 3 ). Copolymers 2a and 2b showed a negative specific rotation, whereas a positive rotation was observed for 3a and 3b . The CD spectrum of 1a exhibited a negative Cotton effect at 300.0 nm and a positive one at 267.3 nm as well as a negative exciton coupling of 1b . According to the exciton chirality method, 1a and 1b had a negative chirality and its benzoate chromophores, the two 4-vinylbenzoyl groups, were twisted counterclockwise. On the other hand, the CD spectrum of 3a ( 1a /St = 0.30/0.70) and 3b ( 1b /St = 0.27/0.73) showed a split Cotton effect with a positive one at 254.9 nm and a negative one at 237.1 nm for 3a and with a positive Cotton effect at 254.7 nm and a negative one at 232.7 nm for 3b . This result indicated that 3 had a positive chirality in which two 4-vinylbenzoyl groups were twisted clockwise, i.e., the vicinal (methyl 4-vinylbenzoate) groups in the main chain were an ( S, S )-configuration.