Synthesis and properties of liquid crystalline polyacetylenes with different spacer lengths and bridge orientations

A group of mesomorphic polyacetylenes with different lengths of alkyl space r -{HC=C[(CH2)(m)-OCO-Biph-OC7H15]}(n)-[1(m), m = 2, 3, 4, 9] and orientati ons of ester bridge - {HC= C[(CH2)(3)-CO2-Biph-OC7H15]}(n)-[2(3)] are synth esized, and the effects of the structural variables on the properties of th e polymers are investigated. The liquid crystalline acetylene monomers n-{[ (4'-heptoxy-4-biphenylyl)carbonyl]oxy}-1-alkynes 3(m) and 5-{[(4'-heptoxy-4 -biphenylyl)carbonyl]oxy}-1-pentyne 4(3) are prepared by consecutive etheri fication and esterification reactions. The T-m and T-i values of 3(m) decre ase with an increase in the spacer length (m). While 3(3) shows a monotropi c SmA phase, its counterpart with a different eater orientation 4(3) exhibi ts an enantiotropic SmB phase. The monomers are polymerized by transition-m etal halides and carbonyls, and the polymerizations catalyzed by WCl6Ph4Sn under optimal conditions produce polymers with high molecular weights (up t o 1.2 x 10(5)) in high yields (up to 92%). The structures and properties of the polymers are characterized and evaluated by IR, UV, TCA, DSC, POM, and XRD analyses. With the increase in the spacer length, the thermal stabilit y of the polymers increases, their T-g and T-i decrease, and the packing ar rangements in their mesophases change from mixed mono- and bilayer structur es to a homogeneous monolayer structure. Compared to 1(3), 2(3) shows a blu e-shifted absorption spectrum (Delta lambda(max) > 30 nm), a higher T-g and T-i(Delta T similar to 40 degrees C), and a better packed SmA(d) structure .