Menthyl-, copolymer with maleic anhydrid

Matsuzaki and Sugimoto [12] have shown that the specific rotation in the copolymer of 1 -menthyl methacrylate with maleic anhydride or TV-p-tolylmaleimide depends on the 1-menthyl methacrylate content, and that the copolymers obtained become optically inactive after cleavage of the optically active side chain by hydrolysis with sulfuric acid. 

In contrast, it was made clear that the copolymers of 1-menthyl vinylether with maleic anhydride or A p-tolylmaleimide still remain optically active after the cleavage of the optically active side chain this was attributed to the adduction of an asymmetric structure due to the rigidity of the polymer chain. 

A special case of asymmetric enantiomer-differentiating polymerization is the isoselective copolymerization of optically active 3-methyl-1-pentene with racemic 3,7-dimethyl-1-octene by TiCl4 and diisobutylzinc [Ciardelli et al., 1969]. The copolymer is optically active with respect to both comonomer units as the incorporated optically active 3-methyl-l-pentene directs the preferential entry of only one enantiomer of the racemic monomer. The directing effect of a chiral center in one monomer unit on the second monomer, referred to as asymmetric induction, is also observed in radical and ionic copolymerizations. The radical copolymerization of optically active a-methylbenzyl methacrylate with maleic anhydride yields a copolymer that is optically active even after hydrolytic cleavage of the optically active a-methylbenzyl group from the polymer [Kurokawa and Minoura, 1979]. Similar results were obtained in the copolymerizations of mono- and di-/-menthyl fumarate and (—)-3-(P-styryloxy)menthane with styrene [Kurokawa et al., 1982],... 

We have attempted the copolymerization of 1-menthyl vinylether ([a] d = -61.5°) with various monomers (styrene, phenylmaleimide, maleic anhydride, dime thy Imaleic ester, dimethylpimalic ester, vinyl-carbonate, and indene) and submitted them to hydrolysis by HBr in order to verify the asymmetry introducing reaction in these radical copolymerizations [15]. The optical rotation, ORD and CD were measured before and after eliminating the active menthyl group by hydrolysis. The results are shown in Table I. All copolymers, with the exception of those containing styrene, showed optical rotation before and after hydrolysis We believe that the introduction of asymmetry to the main chain is demonstrated by our results. 

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