Vinylethers optically active

Optically active poly(alkylvinylethers) have been extensively studied by Pino and coworkers [7, 8] and by Liquori et al [9]. [(5)-l-methylpropyl] -vinylether (111) ( =0), (5)-2-methylbutylvinylether (III) ( =1), and the corresponding racemic monomers have been polymerized with the catalytic system Al(i-C4H9)3—H2SO4 and Al(i-OC3117)3 —H2SO4. The polymers of (III) (n=0) are less stereoregular than those of (111) ( =1) obtained with the same catalyst [7, 8]. 

The former method has been used in the case of poly-a-olefins which, due to their paraffinic structure, can be cleaved only under very drastic conditions. As a result of many experiments with monomers having different starting optical purity and with different conversions to polymer, it was shown that the unreacted monomer has the same optical purity as the starting one [24] (Table III). Analogous results were obtained in the case of vinylethers derived from both primary and secondary optically active alcohols (Table IV)... 

Molar optical rotation of some optically active poly-alkyl-vinylethers having different stereoregularity... 

The enantiomeric purity of the polymer was never higher than 10% and no better results were obtained by changing the structure of metalalkyl or varying conversion [46]. Even lower stereoelectivity has been observed in the case of racemic vinylethers in the presence of catalysts obtained from 100% sulfuric acid and aluminum alkoxides derived from optically active secondary alcohols [47]. 

Fractionation of copolymerization products of racemic 1-methylpropyl-vinylether with optically active vinylethers in the presence of stereospecific... 

Analogous results have been obtained in the case of copolymers of optically active alkyl-vinylethers with benzyl-vinylether obtained by stereospecific cationic catalysts [91]. 

In recent years there has been a great number of studies on optically active polymers especially related to the synthesis of polypeptides and to vinyl polymerization. A large number of studies have been devoted to the synthesis of crystalline polymers with stereoregular arrangement of the type produced by Schildknecht [2] with vinylethers, such as isobutyl and methyl in 1947, and Natta [3] with -olefins, such as propylene and styrene. 

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. 

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. 

---