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Development of new side-chain liquid crystalline copolymers exhibiting chiral mesophases

Three new acrylate monomers, two of which containing a chiral carbon atom within the flexible spacer linking the ester functionality to the mesogenic side-groups, were synthesised and characterised by differential scanning calorimetry, polarised optical microscopy, X-ray diffractometry, optical activity measurement, etc. The chiral monomers exhibit highly ordered S*I or S*H phases. Homo- and copolymers were produced by radical polymerisation, as well as by UV irradiation in the form of oriented films, using the three new monomers plus a fourth achiral acrylate, that had already been described in the literature. The polymeric films produced by photopolymerisation were found to retain the original orientation of the monomeric films.
The homopolymers produced from the chiral acrylates exhibit two S*F and S*C phases, as determined by POM and X-ray diffraction. Three series of copolymers were produced, in the whole composition range, using couples of chiral and achiral monomers. All the copolymers, but one, display at least two S*C modifications and a S*F phase, whose layer spacing is similar to those of the corresponding chiral homopolymers more than it is to that of the achiral one.
All the chiral copolymers, but one, exhibit low pyroelectric and piezoelectric activity. One of them, however, containing 50 mole% of chiral units, shows considerable piezoelectric response in the glassy S*F phase (d31 = 4 nC/N), as well as marked pyroelectric response (PS = 6 nC/cm2, at 75°C) in the lower temperature S*C modification. Both S*F and S*C phases of this copolymer are characterised by larger molecular tilt angle and lower intralayer ordering than the other copolymers of similar composition.
It is hoped that a prosecution of the studies carried out within the project may lead to the development of new copolymers with properties granting their possible application as ferroelectric materials.

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Università degli Studi di Pisa
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