Liquid Crystalline Polymers without Mesogenic Units

LIQUID CRYSTALLINE POLYMERS WITHOUT MESOGENIC UNITS 

A liquid crystalline phase is a phase in which molecules or components of molecules take a parallel alignment with thermal fluctuation and with certain transitional disorder. Thus in principle, most linear polymers and even branched or slightly crosslinked polymers can fit in with a liquid crystalline phase. Taking polyethylene as an example, the lowest energy conformation of this polymer is the extended trans form. Suppose that the extended chains or chain segments of PE align in parallel fashion leaving 

Joining in Bassett, Rastogi et al. (1991) have found that poly(4-methyl-1-pentene), also flexible, forms a nematic liquid crystal either when pressure is changed at a constant temperature, or when temperature is changed at a constant high pressure. The phase transition process is reversible. However, because the density of the crystal phase is unusually lower than the noncrystalline phase, the transition of crystal-to-nematic liquid crystal occurs at a high pressure when temperature is decreased rather than increased. Nevertheless, the nematic phase does exist in this flexible aliphatic polymer. 

Thus we see that such flexible aliphatic polymers as polyethylene and poly(4-methyl-l-pentene) indeed form a liquid crystalline phase. 

Liquid crystals formed through pressure change have been named barotropic. Barotropic behavior is observed not only for flexible polymers, it is also rather popular for conventional thermotropic liquid crystalline compounds and polymers. It has been reported by several research groups (e.g., Herrmann et al, 1983 Chandrasekhar and Shashidhar, 1979 Stevens et al., 1984). As an example, Hsiao et al. (1988) claimed that for the aromatic copolymer of 4-hydroxybenzoic acid (20 mol %), hydroquinone (40 mol %) and 1,3-phthalic acid (40mol %), not only would the temperature range of the liquid crystalline phase formed at normal pressure increase with increasing pressure, it would also form a new liquid crystal phase at high pressure. 

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LIQUID CRYSTALLINE POLYMERS WITHOUT MESOGENIC UNITS... 

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