Poly -liquid-crystalline glass transition temperature

Liquid crystalline sUoxanes are limited with respect to the glass transition in comparison to other backbone systems, such as poly(meth)acrylates. Glass transition temperatures of up to 80 °C can be achieved, but there is a hmit for the variations of the mesogenic groups [39]. Therefore, crosslinking is the preferred method. The presence of at least some polymerizable moieties within the side chain groups is necessary. Typical examples for these groups are epoxides, cinnamates, or methacrylates. 

Differences in tacticity were also reflected by thermal data. While the iso-tropization temperature of (-)-poly-(IV-ll) and ( )-poly-(IV-ll),synthesized using initiator 1, stayed approximately unchanged, the isotropization temperatures for the chiral liquid crystalline polymers shifted to higher values when initiators 2 or 3 were used. The difference was up to 7 °C. If the decreased glass transition temperatures (Tg) for the chiral analogues were taken into account, the temperature range of the liquid crystalline phase was broadened by up to 12 °C. This means that a certain diad must be responsible for this behavior. The authors assumed that the diad cmHT was most suitable one for the formation of stable liquid crystalline phases in poly(norbornene) main chains. 

Liquid crystalline poly(ester-imide)s having high glass transition temperatures and good dimensional stability are made from diphenols like t-butylhyd-roquinones [248],phenylhydroquinone [249] andbisphenol A [250]. 

Some polymers may undergo transitions above the glass transition temperature, which Boyer [224] called intermediate transitions at T > Tg for amorphous polymers and T, < T < T for crystalline amorphous polymers. Gas chromatography has demonstrated such a transition in poly(vinyl chloride) [205] it was attributed, as in liquid crystals, to the existence of a state with nematic order at temperatures between T, and... 

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