Ordered Structure of Copolyesters Having Mesogenic Components
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Ordered Structure of Copolyesters Having Mesogenic Components Akihiro Niki,+ Hirokazu Hasegawa and Takeji Hashimoto* Department of Polymer Chemistry, Faculty of Engineering Kyoto University, Kyoto 606 Japan +present address: Advanced Polymer Research Laboratory, Corporate Research Institute, Sekisui Chemical Co., Ltd., Shimamoto, Mishima, Osaka 618, Japan. * to whom correspondence should be addressed. Abstract Ordered structures of the multiblock copolyesters composed of pquarterphenyl (DHQ, rigid segments) and poly(ethylene adipate) (flexible segments) were investigated by means of WAXD and SAXS. It was found that only the DHQ segments crystallize but the poly(ethylene adipate) segments hardly crystallize which make this copolyester a good thermoplastic elastomer. The copolyesters exhibit microphase separation above the melting temperature of the DHQ segments. 1. llntroduction Copolymers composed of rigid and flexible segments are interesting materials because such polymers are recently used as high strength engineering plastics 1 or thermoplastic elastomers. 2 In the former case the rigid segments act as mesogens to give liquid-crystalline nature to the copolymers or in the latter case they work as physical cross-links. The copolyesters we used in this study belong to the latter class and are given by Scheme I. They are multiblock copolyesters consisting of the rigid segments of p-quarterphenyl group (4 linearly linked benzene rings) and the flexible segments of an aliphatic polyester.
'-j
j
-J
OC Hac 0
0
p-quarterphenyl
oC2H4oCC4HC -) 0
0
poly(ethylene adipate)
Scheme I It has been reported that these copolyesters exhibit excellent mechanical properties as a thermoplastic elastomer. 2 However, ordered structures or
Mat. Res. Soc. Symp. Proc. Vol. 248. 01992 Materials Research Society
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morphology of this polymer were not clarified yet. The properties of such a material frequently depend on the ordered structure. The purpose of this study is to clarify the ordered structure of these copolyesters and to shed some lights on the origin of their elasticity. For the experimental approach we used small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) techniques. II.
Experimental Methods
1. Samples. The copolyesters with the mesogenic units used in this study were synthesized2 by melt condensation polymerization of 4,4"'-dihydroxy-pquarterphenyl (DHQ), ethylene glycol and dimethyladipate. The persistence length of the rigid sequences of DHQ is limited to one .monomeric unit as shown by Scheme I because DHQ does not polymerize by itself whereas the flexible sequences of poly(ethylene adipate) can grow much longer. These copolyesters are referred as DHQ copolyesters hereafter in this paper. Polyester of ethylene glycol and dimethyladipate (without DHQ) was also prepared as a reference material and is referred as homopolyester hereafter. The characteristics of the DHQ copolyesters and the homopolyester used in this study are given in Table I. The number average molecular weights (Mn)
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