Epoxybutane polymer structure

CHR—CO—), polyoxy acids (—O—CHR—CO—), poly-l-alkylbuta-dienes (—CH=CH—CHR—CH2—). To the same class iKlong the polymers with two asymmetric atoms for every monomer unit, such as polysoibates (—CH=CH—CHA—CHB—, 32 and 33) where both eiythio- and thieo-diisotactic forms are chiral, or polyhexadiene (—CH=CH—CHA—CHA—) and poly-2,3-epoxybutane (—O— CHA-CHA-), 39, where only the thieo-diisotactic structures are chiral, and the polymers of some bicyclic monomers such as those shown in 41 and 42. Other examples are the polymers obtained by hydrogen transfer fk m substituted benzalacetone (79, Scheme 17) (266, 267). 

Crystalline Polymers of the 2,3-Epoxybutanes-Structure and Mechanism Aspects. J. Amcr. chem. Soc. 83, 3538 (1961). 

Some Mechanism Aspects of Epoxide Polymerisation. Stereochemical Structure of the Crystalline Polymers from the 2,3-Epoxybutanes. J. Polymer Sci. B 2, 1085 (1964). 

Some mechanism aspects of epoxide polymerization. Stereochemical structure of the crystalline polyethers from the 2,3-epoxybutanes. J. Polymer Sci.B2,1085 (1964). 

The polymerization of 2,3-epoxybutane with the same initiator as used with propylene oxide shows that the oxygen/substituted-carbon atom bond can be cleaved and, hence, a mechanism can be logically proposed to account for the head-to-head, tail-to-tail structures identified by Price and Vandenberg. With 2,3-epoxybutane, it was found that amorphous polymer could also be as pure disyndiotactic as the crystalline forms. Amorphous polymer could arise from short sequences of stereoregularity that were too short to form crystallizable segments. These could arise when coordination of monomer temporarily displaced alkoxide, interrupting chain growth, which, when resumed, could be selective for the antipode monomer. 

At low temperatures, about -78°C, in triisobutylaluminum/ water-initiated polymerization, which is presumed to be a cationic initiation, an amorphous (elastomeric) polymer is obtained from cis-2,3-epoxybutane, and a crystalline polymer, melting point 100°C, is obtained from the trans-isomer. In a copolymerization of the two isomers, the cis-oxide enters the copolymer at about twice the rate of the trans-isomer. Further, the low-temperature, cationic poly(trans-2,3-epoxybutane) with a crystalline melting point of 100°C was found to consist of diad units with a mesodiisotactic structure, while the crystalline polymer formed by coordinate polymerization of the cis-monomer, melting point 162°C, had diad units that were racemic diisotactic. These results make apparent the importance of the monomer coordination step in polymer chain growth in coordinate polymerizations. 

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