Yy. Cheng et al., CRYSTALLIZATION OF MONOTROPIC LIQUID-CRYSTALLINE POLYCARBONATES BASEDON A METHYL-STILBENE MESOGEN AND A METHYLENE-CONTAINING FLEXIBLE SPACER, Macromolecules, 27(19), 1994, pp. 5440-5448
Crystallization behavior has been studied for a series of recently syn
thesized liquid crystalline polycarbonates1 based on a methyl-substitu
ted stilbene mesogen and a methylene-containing flexible spacer. The s
tability of the nematic phase and its relationship to three-dimensiona
l crystallinity were studied. Development of crystallinity was followe
d by isothermal and nonisothermal crystallization using differential s
canning calorimetry (DSC) and polarizing optical microscopy. A monotro
pic liquid crystal phase is identified for these polycarbonates. The m
ultiple melting endotherms seen in the heating scan are assigned to th
e melting of crystals forming either from the mesophase (melting at hi
gher temperature) or from the isotropic phase (melting at lower temper
ature). The number, n, of -(CH2)- units in the flexible spacer affects
the transition temperatures seen in the cooling and heating scans. On
ly a weak odd-even effect is seen in the upper melting of the heating
scan from n = 5 to 8. In this range of spacer length, the region of st
ability of the liquid crystal phase seen in the cooling scan becomes s
maller. When the length of the spacer becomes greater than that of the
mesogen (n greater-than-or-equal-to 9), all the transition temperatur
es drop.