Liquid crystalline side chain polymer based on poly(vinylcyclopropane)s

Abstract

$It\{trans}$-Polypentenamers with thermotropic liquid-crystalline cholesteryl and cyanobiphenyl side chains were prepared by ring-opening polymerization of vinylcyclopropane monomers with proper substituents. The monomers prepared were di-6-(cholest-5-en-3β-yloxy)hexyl-2- vinylcyclopropane-1,1-dicarboxylate, VCP-$DCh_6$ (5a), di-6-(4``-cyano-4-biphenyloxy)hexyl-2-vinylcyclopropane-1,1-dicarboxylate, VCP-$DBC_6$ (5b), 6-(cholest-5-en-3β-yloxy)hexyl-1-cyano-2- vinylcyclopropane-1-carboxylate, VCP-$ChC_6$ (6a) and 6-(4``-cyano-4-biphenyloxy) hexyl-1-cyano-2-vinylcyclopropane-1-carboxylate, VCP-$CBC_6$ (6b). The number-average molecular weights were in the range of 25,000-80,100 and $M_w$/$M_n$ values were 3.35-3.80. The conversions were 60-95% yield. The copolymerization behavior of the poly($CBC_6$-co-$ChC_6$) (10) is similar to the poly($DBC_6$-co-$DCh_6$) (9) but more reactive than the bimesogenic copolymers. The obtained PVCP-$DCh_6$, PVCP-$ChC_6$, PVCP-$CBC_6$ and PVCP-ChC are completely soluble in various organic solvents such as chloroform, methylene chloride, benzene but PVCP-$DBC_6$, PVCP-DCh are dissolved only in strong solvents such as DMF and chlorobenzene. Whereas, monomers VCP-$DCh_6$ (5a) and VCP-$DBC_6$ (5b) present cholesteric and smectic mesomorphism, respectively. On the other hand, polymers PVCP-$DCh_6$ (7a) and PVCP-$DBC_6$ (7b) present only a smectic mesophase. 1-Cyano-1-mesogenic monomer VCP-$ChC_6$ (6a) shows a melting at -20℃ and appear 3 phase transitions at 23, 27, 53℃ owing to smectic mesophases and shows a cholesteric phase in the 53-55℃ temperature range. The polymer PVCP-$ChC_6$ (8a) shows a smectic C phase in the 18-151℃ range. The liquid crystalline texture of the PVCP-$CBC_6$ (8b), having two polar cyano groups onto the backbone and terminal of the mesogen, was not developed well for normal samples. As expected, copolymer poly($DBC_6$-co-$DCh_6$) forms a cholesteric mesophase, the structure of which is retained for all temperat...