Chirality Induction in Cyclopolymerization. 3. Template Effect of Chiral Acyclic 1,3-Glycols on the Cyclocopolymerizations of (S)-1,3-Butanediyl and (2S,4S)-2,4-Pentanediyl Bis(4-vinylbenzoate)s with Styrene

Abstract

The copolymerizations of (S)-1,3-butanediyl and (2S,4S)-2,4-pentanediyl bis(4-vinylbenzoate)s (1a and 1b) (M 1 ) with styrene (M 2 ) were carried out using AIBN in toluene at 60 °C. The obtained copolymers (2) consisted essentially of the cyclic repeating and styrene units, because the characteristic absorption due to the vinyl protons disappeared in the 1 H-NMR spectra. The copolymerization reactivities of 1a and 1b were higher than that of styrene, resulting in the mole fraction of the M 1 unit in the copolymer 2 being higher than that of the M 2 unit for every monomer feed. The monomer reactivity ratio, which was calculated by the Kelen-Tudos method, was r 1 = 4.39 and r 2 = 0.20 for 1a and r 1 = 3.81 and r 2 = 0.28 for 1b. The specific rotation ([α] 435 , c 1.0 in CHCl 3 ) changed from +283° to +182° for 2a and from +434° to +319° for 2b. After removing the chiral templates from 2a and 2b, poly[(methyl 4-vinylbenzoate)co-styrene]s (3a and 3b) were obtained. The specific rotation ([α] 435 , c 1.0 in CHCl 3 ) varied from -0.5° to -24.0° for 3a and from -0.4° to -46.3° for 3b, which indicated that the (2S,4S)-2,4-pentanediyl template approximately doubled in effect for the asymmetric induction by comparison with the (S)-1,3-butanediyl one. A split Cotton effect with a negative Cotton effect and a positive one was observed for the CD spectrum of 1 and the reversed one for 3. According to the CD exciton chirality method, the clockwise twist of the two 4-vinylbenzoates of 1 transmitted their chirality to 3 in which two 4-vinylbenzoyl groups twisted counterclockwise, i.e., an (R,R)-configuration of vicinal (methyl 4-vinylbenzoate) units in the main chain.