Abstract
A systematic study of the asymmetric cyclocopolymerization of bis(4-vinylbenzoate)s, derived from chiral diols, with styrene has been made from the viewpoint of synthesizing the main-chain chiral polymer. On the basis of using over 30 chiral diols as templates, we summarize the relationship between the structure of the chiral template and the chiroptical properties of the template-free polymer. For simple chiral diols, the chirality induction efficiency increased in the order 1,2-diol < 1,4-diol < 1,3-diol. Chiral diols with two chiral centers exhibited higher chirality induction efficiency than those having one chiral center only. The chirality induction efficiency for cyclic 1,2-diols increased with the ring size in the order 5- < 6- < 7- < 8-membered rings, and that for acyclic 1,2-diols increased with the bulkiness of the substituent at the chiral center. In addition, a chirality induction mechanism has been proposed on the basis of model radical cyclization experiments and computational studies. Chirality induction could be caused by the inhibition of the formation of one racemo unit among the four stereoisomers due to the strong dependence of the stereoselectivity in intermolecular additions on the absolute configuration of the cyclized radical. The mechanism was examined using the Lewis-acid and monomer-concentration effects.
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