Aa. Dembek et al., SYNTHESIS OF SOLUBLE, LIQUID-CRYSTALLINE ARAMIDS VIA TRANSITION-METALPI-COMPLEXATION, Macromolecular symposia, 77, 1994, pp. 303-313
An organo-soluble, liquid crystalline organometallic polymer, (p-pheny
leneterephthalamide)Cr(CO)3 [(PPTA)Cr(CO)3], is prepared by polyconden
sation of (p-phenylenediamine)Cr(CO)3 with terephthaloyl chloride. Pol
arizing optical microscopy of this high molecular weight metallo-arami
d shows a nematic liquid crystalline texture in N,N-dimethylacetamide
(DMAc), demonstrating that metal pi-complexation maintains the lyotrop
ic, rigid-rod character of PPTA. A PPTA copolymer with 50% of the diam
ine rings Cr(CO)3 pi-complexed is also soluble and lyotropic in DMAc.
Tensile properties of films of the 100% Cr(CO)3 complexed aramid are i
sotropic in the plane of the film, while those of the 50% complexed an
alog are highly anisotropic. The organometallic substituent is a site
for polymer functionalization: exchange of a carbonyl for a trimethylp
hosphine ligand, and subsequent polymerization affords the phosphine-f
unctionalized (PPTA)Cr(CO)2P(CH3)3, which has a much higher critical c
oncentration for liquid crystal formation. Oxidative decomplexation of
the Cr(CO)3 group yields the parent PPTA, demonstrating the reversibi
lity of the organometallic modification approach.