Side-Chain Liquid-Crystalline Polymers from the Alternating Copolymerization of Maleic Anhydride and 1-Olefins Carrying Biphenyl Mesogens

Abstract

Side-chain liquid-crystalline copolymers (SCLCPs) were synthesized from the alternating copolymerization of maleic anhydride with mesogenic 1-olefins. These SCLCPs showed high glass transition temperatures and highly ordered smectic mesophases. The mesophase width increased with spacer length. The terminal alkyl group length determined the degree of order in the hexatic mesophase that was present just above the glass transition temperature. A terminal methoxy group induced a hexatic smectic B mesophase, intermediate terminal alkyl groups induced a smectic E mesophase, and long terminal alkyl groups induced a crystal smectic B mesophase. If the spacer was shorter than the terminal alkyl group, an interdigitated smectic A mesophase was found in which the terminal alkyl groups overlap. A strong correlation was found between the glass transition temperature and the temperature at which the hexagonal or orthorhombic ordered mesophase disappears. Introduction of an ester linkage between the spacer and biphenyl mesogen or replacing the terminal alkoxy group by a cyano terminal group induced a lowering of transition temperatures and a lower degree of order in the mesophase.

Thermotropic behavior of side-chain liquid-crystalline copolymers from maleic anhydride and mesogen-containing methacrylates

“…Other reagents used for syntheses were commercially available and used without further purification. Monomers 1-m, 2, and 3 13,14) , and polymers 4-x, 5-m, 6, and 7 16) were synthesized according to literature procedures. However, the polymerization time was reduced to 48 h.…”

“…The same strategy may be applied to obtain SCLC polymethacrylates with adhesive properties. Contrary to the copolymerization of MA with 1-alkenes, which yields perfectly alternating copolymers 16,20,21) , copolymerization of MA with methacrylates is not strictly alternating due to the tendency of methacrylates to homopolymerize. MA does not homopolymerize under the applied conditions 20,21) .…”

“…Therefore, the polymers were dried in vacuo prior to characterization. Under these conditions ring closure of maleic acid moieties to anhydride moieties occurs 16) . Thin layer chromatography (TLC) showed that only maleic acid moieties were ring-closed and the ester The molecular weights as determined by GPC, the MA content in the polymers as determined by FTIR, and the yields are listed in Tab.…”

“…In a previous study, it was shown that maleic anhydride (MA) copolymerizes with mesogenic 1-alkenes yielding SCLCPs with adhesive properties 16,17) . On polar substrates, thin films may be obtained from SCLCPs with MA moieties that form lamellar structures upon annealing 18) and show autophobicity 19) .…”

“…The synthesis and phase behavior of copolymers containing methoxybiphenyl mesogens will be described. The mesomorphic properties are compared to those of previously described poly(MA-alt-1-alkene)s 16,17) and those of polymethacrylates containing similar mesogens 8,13) . The influence of spacer length and MA content on transition temperatures is studied.…”