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

Citation
Jwy. Lam et al., Synthesis and properties of liquid crystalline polyacetylenes with different spacer lengths and bridge orientations, MACROMOLEC, 33(14), 2000, pp. 5027-5040
Citations number
104
Language
INGLESE
art.tipo
Review
Categorie Soggetti
Organic Chemistry/Polymer Science
Journal title
MACROMOLECULES
ISSN journal
0024-9297 → ACNP
Volume
33
Issue
14
Year of publication
2000
Pages
5027 - 5040
Database
ISI
SICI code
0024-9297(20000711)33:14<5027:SAPOLC>2.0.ZU;2-R
Abstract
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 .