Vinyl methyl ether, stereoregular

Since coordination of the ether oxygen is involved in the stereoregulating step, any factor which weakens this will decrease stereospecificity. This explains why the more hindered, higher alkyl vinyl ethers give less stereoregular polymerization than vinyl methyl ether. 

Stereoregular Polymerization. Chemists at GAF Corporation were first to suggest that stereoregularity or the lack thereof is responsible for both nontacky and crystalline or tacky and amorphous polymers generated from IBVE with BF2 0(C2H )2, depending on the reaction conditions (22,23). In addition, it was shown that the crystalline polymer is actually isotactic (24). Subsequentiy, the reaction conditions necessary to form such polymers have not only been demonstrated, but the stereoregular polymerization has been extended to other monomers, such as methyl vinyl ether (25,26). 

Investigations were made on the I. R. spectra of poly-[(S)-l-methyl-propylj-vinyl-ether and poly-[(S)-2-methyl-butyl]-vinyl-ether (65) a band at 911 cm-1 related to stereoregularity was detected in the spectrum of the former while a crystallinity band at 827 cm-1 was found in the latter. The spectra of polymers obtained from an optically active or a racemic monomer did not reveal any remarkable difference. 

Table 12. Physical properties of the most stereoregular fraction of the polymers of the optically active and racemic (1-methyl-propyl)-vinyl-ether and (2-methyl-butyl)-vinyl-ether obtained using the Al(i-OCaH1)g-HtSOi catalytic system (65)...

On the contrary, in the case of the poly-[(S)-2-methyl-butyl]-vinyl-ether, where the asymmetric carbon atom is in the y position with respect to the principal chain, no remarkable dependence of optical activity on stereoregularity has been observed at 589 m/r however a slight dependence has been noticed at lower wavelengths (113a, b). 

In agreement with the data on poly-a-olefins and poly-vinyl-ethers having the side chain asymmetric carbon atoms in the y-position with respect to the main chain, stereoregularity does not exert a remarkable influence on the rotatory power of poly-acrylates and poly-methacrylates. In fact, according to the quantitative data reported by H. Sobue, K. Matsuzaki, S. Nakano (135), and to the qualitative indications given by Liu, Szuty and Ullmann (64), concerning respectively poly-menthyl-meth-acrylate and poly-(l-methyl-benzyl)-methaciylate, the specific optical activity of the polymers does not vary by more than 30% when varying, within a wide interval, the isotactic triads content of the polymers (Table 18). 

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