THE EFFECT OF BLOCK SEQUENCE LENGTH ON MECHANICAL PROPERTIES OF POLYETHER-POLYESTER CONDENSATION BLOCK COPOLYMER

Abstract

The present investigation was undertaken to shed light on the effects of the composition of hard and soft component, block length and distribution of sequence length of elastic condensation block copolymer upon fiber properties.The polymer used for this purpose was polyether-polyester block copolymer composed of B type polyester (polyethylene-1, 2-diphenoxyethane-p, p′-dicarboxylate) as hard segment and PEG (polyethyleneglycol) as soft segment.The results are summarized as follows:(1). The effect of composition; The values of tensile strength, Young's modulus and work for extention of melt spun fiber became larger with the increase of B type polyester content, whereas elongation and tensile recovery became lower. When 4000 molecular weight PEG was used, these properties showed minimum or maximum value at the composition of 50:50 (wt).(2). The effect of block sequence length; As the glycol molecular weight was increased, fiber properties varied with a trend toward greater tensile strength, Young's modulus and work for extention, and toward lower elongation and elasticity. These result; could be explained on the basis of crystallinity of PEG block sequence and confirmed by X-ray diffraction diagrams which showed that the crystallinity of PEG segment was enhanced with increment of its component or lengthening of its sequence in block copolymer.(3). The effect of distribution of block sequence length; Though two block copolymers having the same composition and the same block sequence length (one of which was prepared by the method of “two step polycondensation” and the other by “one step polycondensation” had nearly the same intrinsic viscosity numbers, peak widths of heat of fusion of crystalline region in DTA melting thermograms were sharper in the former and especially in the solution properties, Huggin's constants were widely dissimilar from each other.“Two step polycondensation” mentioned above refered to the following polycondensation procedure, that was, block copolymer was prepared by polycondensing polyester oligomer having both terminal OH groups with certain molecular weight polyether derivatives having both terminal ester groups. “One step polycondensation” block copolymer was prepared by copolymerizing polyether having both terminal OH groups with ethyleneglycol and dimethyl carboxylate.It was reasonable to estimate that the properties of these two polymers suggested the difference of distributions of sequence length in these polymers, and then the mechanical properties of the melt-spun fibers of these polymers were compared with each other.It was manifested that no marked differences were observed in tensile strength and elongation between “one step” method copolymer and “two step” one, while higher Young's modulus and larger work for extention were obtained for “two step” procedure.