Syndiotactic polybutene

A similar behavior has been recently found also for syndiotactic polybutene (s-PB). In fact, two different crystalline forms have been found, which present chains with s(2/l)2 and s(5/3)2 symmetries (shown in Fig. 3a and 3b, respectively). 

As an example we report in this paper the conformational energy maps of two already cited stereoregular polymers, which have been obtained very recently, syndiotactic polystyrene s-PS and syndiotactic polybutene s-PB (Fig. 4 and 5, respectively). In fact, the energy map calculated for s-PS shows... 

The allyloxo complex Cp Ti(OCH2-CH=CH2)3 has been used as a catalyst precursor for the synthesis of polybutene-1 in the presence of MAO as co-catalyst.968 Mono-Cp trialkoxo complexes with different sterically demanding substituents have been used as pre-catalysts for the preparation of syndiotactic polystyrene in water.969... 

Finally, a few comments about the uniqueness of polymer crystal structures and phase space localization are warranted. Almost all crystallizable polymers exhibit polymorphism, the ability to form different crystal structures as a result of changes in thermodynamic conditions (e.g., temperature or pressure) or process history (e.g., crystallization conditions) [12]. Two or more polymorphs of a given polymer result when their crystal structures are nearly iso-energetic, such that small changes in thermodynamic conditions or kinetic factors cause one or another, or both, to form. Polymorphism may arise as a result of competitive conformations of the chain, as in the case of syndiotactic polystyrene, or as a result of competitive packing modes of molecules with similar conformations, as in the case of isotactic polypropylene. In some instances, the conformational change may be quite subtle isotactic polybutene, for example, exhibits... 

Both isotactic poly(propylene-co-butene) [81, 82] and syndiotactic poly(propylene-co-butene) [83] statistical copolymers exhibit isodimorphic behavior when crystallized. In isotactic poly(propylene-co-butene), the copolymer was found to crystallize over the entire range of butene content. A transition in crystal unit cell structure was observed at about 50 mol% butene, where below this composition, the crystalline phase resembled that for polypropylene and above this composition, the copolymer was essentially polybutene with propylene defect units [81]. The observed isodimorphic behavior can be explained by the similar helical chain structures exhibited by both polypropylene and polybutene in the crystal, which results in a relatively small free energy penalty for co-crystallization [42, 81-83],... 

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