TY - JOUR
T1 - Semiflexible liquid-crystalline polyesters based on twin bis(P-oxybenzoyl) units
T2 - Part 2.-effect of molar mass on mesomorphic behaviour
AU - Laus, Michele
AU - Angeloni, Annino Sante
AU - Spagna, Alessandro
AU - Galli, Giancarlo
AU - Chiellini, Emo
PY - 1994
Y1 - 1994
N2 - The effect of the molar mass (Mn) and molar mass distribution (Mw/Mn) on liquid-crystalline phase-transition behaviour was investigated for four polymers of the general class CmCm which were based on two mesogenic bis(p-oxybenzoyl) units and two linear alkylene spacer segments containing m (m = 5 or 7) and n (n = 5, 7 or 10) methylene groups, respectively. Each polymer exhibited smectic and nematic mesophases. The polymers were fractionated into various samples having different Mn and Mw/Mπ values. The liquid-crystalline phase-transition parameters of samples C7C7 and C7C10 increased with Mn until a limiting value of Mn≈6000-8000 g mol-1, and then remained constant. In complete contrast, for samples C5C5 and C5C7 the stability of the smectic mesophase increased, whereas that of the nematic mesophase decreased with increasing Mn. In particular, for the former samples the nematic mesophase turned from enantiotropic to monotropic with increasing Mn, and then disappeared in correspondence to a critical value of Mn≈7000 g mol-1. In addition, wide Mw/Mn values were found to increase the stability of the nematic mesophase.
AB - The effect of the molar mass (Mn) and molar mass distribution (Mw/Mn) on liquid-crystalline phase-transition behaviour was investigated for four polymers of the general class CmCm which were based on two mesogenic bis(p-oxybenzoyl) units and two linear alkylene spacer segments containing m (m = 5 or 7) and n (n = 5, 7 or 10) methylene groups, respectively. Each polymer exhibited smectic and nematic mesophases. The polymers were fractionated into various samples having different Mn and Mw/Mπ values. The liquid-crystalline phase-transition parameters of samples C7C7 and C7C10 increased with Mn until a limiting value of Mn≈6000-8000 g mol-1, and then remained constant. In complete contrast, for samples C5C5 and C5C7 the stability of the smectic mesophase increased, whereas that of the nematic mesophase decreased with increasing Mn. In particular, for the former samples the nematic mesophase turned from enantiotropic to monotropic with increasing Mn, and then disappeared in correspondence to a critical value of Mn≈7000 g mol-1. In addition, wide Mw/Mn values were found to increase the stability of the nematic mesophase.
UR - http://www.scopus.com/inward/record.url?scp=0006271741&partnerID=8YFLogxK
U2 - 10.1039/JM9940400437
DO - 10.1039/JM9940400437
M3 - Article
SN - 0959-9428
VL - 4
SP - 437
EP - 443
JO - Journal of Materials Chemistry
JF - Journal of Materials Chemistry
IS - 3
ER -