Synthesis and characterization of biaxial nematic side chain polymers with laterally attached mesogenic groups

Abstract

The synthesis and characterization of liquid crystalline side chain polymers with mesogenic groups laterally attached to the polymer main chain are described. By variation of the terminal group, mesogenic moiety or spacer length, a change in the glass transition temperature, the nematic to isotropic transformation temperature and the stability of the nematic phase can be achieved. With increasing length of terminal groups, a distinct odd-even effect of the nematic to isotropic phase transformation temperature and also a strong decrease of the glass transition temperature is observed. Macroscopic homeotropic alignment can be achieved in an electric or magnetic field. Conoscopic investigations show optical biaxial behaviour of the nematic phase. A chiral nematic copolymer is the first example of a thermotropic biaxial cholesteric phase.

Side‐On Nematic Liquid Crystal Dendrimers Based on PAMAM and PPI as Dendritic Scaffolds: Synthesis and Characterization

“…The comparison among the thermal behavior of the dendrimers reported here and the linear side chain polymers (derived polymethacrylate and polysiloxane), synthesized by Finkelmann group is especially relevant. In Table are collected data of the mesomorphic properties of two representative side chain polymers (SCP) bearing laterally attached mesogenic units similar to L1(C4) and L2(C5) .…”

“…On the other hand, we used an approach similar to that employed in side chain liquid crystalline polymers. In these polymeric systems, it has been shown that the introduction of laterally attached mesogenic units makes it difficult for the units to adopt the side‐by‐side molecular arrangement typical of lamellar phases, thus favoring a biaxial nematic order …”

“…Series 2 is based on a poly(propylene imine) scaffold (PPI‐(NH 2 ) n ; n = 4, 8, 16, 32, 64) with attached laterally mesogenic groups consisting in a broad mesogenic unit, with the central aromatic ring derived from 1,4‐dihydroxy‐2‐naphthoic acid ( L2 ) bearing pentoxy terminal chains. The objective is the preparing of biaxial nematic phases using a similar approach that has been used in lateral side chain polymers, with the expectation that as dendrimers have significantly lower viscosity than linear polymers do these materials more attractive for optical applications.…”

Recent Advance in Liquid Crystalline Elastomers

“…LCEs can be prepared via side chain, main chain or combined main chain/side group liquid crystalline polymers27~39) using one step or two steps procedure. One step preparations were carried out by radical copolymerization of [31][32][33].…”

Electrooptical properties of liquid crystalline side chain polymers with laterally attached mesogenic units

“…On the other hand one is forced to conclude on the basis of the sign and the magnitude of the electrooptical response that it is the reorientation of the long axis of the mesogenic unit which contributes predominantly to the electrooptical response. It thus seems that constraints exist in the polymers considered here not only for motions about the long axis [17][18][19]-which gives rise to a biaxial character of the nematic phase-but also for reorientational motions of the long axis itself. These constraints prevent a free rotation of the mesogenic units about the short axis and force the long axis to reorient only along selected paths.…”