Substituted and 1,4-Disubstituted 1,3-Butadienes

The polymerizations of 1-substituted (X) and 1,4-disubstituted (XI) 1,3-butadienes involve several possibilities. 3,4-Polymerization of a 1-substituted 1,3-butadiene proceeds with the 

4-polymerization of a 1-substituted 1,3-butadiene can yield four stereoregular polymer structures. The double bond can have cis or trans configurations, and each of these can be 

The all-trans-all-isotactic and all-trans-all-syndiotactic structures for the 1,4-polymerization of 1,3-pentadiene are shown in Fig. 8-6. In naming polymers with both types of stereoisomerism, that due to cis-trans isomerism is named first unless it is indicated after the prefix poly. Thus, the all-trans-all-isotactic polymer is named as transisotactic l,4-poly(l,3-penta-diene) or isotactic poly( -3-methylbut-l-ene-l,4-diyl). 

The sp3 stereocenter (i.e., C ) in XII is chirotopic, like the case of poly(propylene oxide), since the first couple of atoms of the two chain segments are considerably different. The isotactic structures are optically active while the syndiotactic structures are not optically active. 

4-polymerization of 1,4-disubstituted 1,3-butadienes leads to structure (XIII), which can exhibit tritacticity since the repeating unit contains three sites of steric 

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