G. Galli et al., SEMIFLEXIBLE LIQUID-CRYSTALLINE POLYESTERS BASED ON TWIN BIS(P-OXYBENZOYL) UNITS .1. EFFECT OF SPACER LENGTH ON MESOMORPHIC BEHAVIOR, Journal of materials chemistry, 4(3), 1994, pp. 429-435
Four new series of thermotropic liquid-crystalline polyesters have bee
n prepared, comprising two mesogenic bis(p-oxybenzoyl) units and two l
inear alkylene spacer segments containing m (m = 7, 8, 9, 11) and n (n
= 5-12) methylene groups. Polymers C8Cn exhibited a nematic mesophase
, whereas a nematic and a smectic mesophase were shown by polymers C7C
n, C9Cn and C11Cn. Within each series, the nematic-isotropic transitio
n temperatures and entropies as well as the smectic-nematic transition
temperatures showed typical odd-even alternations in which homologues
with even number n exhibited higher values than adjacent homologues.
In contrast, a reversed odd-even alternation was observed for the smec
tic-nematic transition entropy, in which members possessing an odd num
ber n of methylene groups presented the higher values. The effect of t
he parity and length of the poly(methylene) spacers on the incidence o
f mesophases and on their thermodynamic parameters is discussed.