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One of the useful methods to improve the toughness of epoxy resin is by mixing the resin with poly(ether-sulfone) (PES). In the present work, two hydroxyl-terminated PESs with molecular weights an = 28600 and 4200 were used for blending with epoxy resin. The curing reaction of diglycidyl ether/bisphenol-A (DGEBA) with 4,4'-diaminodiphenyl sulfone (DDS) in the presence of hydroxyl-terminated PES was studied by means of differential scanning calorimetry (DSC) and gel-permeation chromatography (GPC). For the DGEBA-DDS-PES system with a stoichiometric ratio of epoxy and amino groups the DSC experimental results showed that at a fixed molecular weight of PES the curing reaction rate decreases with increasing PES concentration. At a fixed PES concentration (in the range of between 0 and 20 wt.-Yo of PES), the DGEBA-DDS system modified with hydroxylterminated PES with lower molecular weight had a faster curing reaction rate at low conversion and a slower curing reaction rate at high conversion. The GPC results showed the evidence of etherification between low-molecular-weight PES with epoxy resin. However, very little etherification of high-molecular-weight hydroxyl-terminated PES with epoxy resin was found. Based on the experimental results, a curing reaction mechanism of DGEBA with DDS in the presence of hydroxyl-terminated PES is proposed.

ABSTRACT:Polyester based polyurethanes were synthesized from 4,4'-methylene bis(phenyl isocyanate) (MDI) with 1,4-butanediol as a chain extender and low molecular weight polyester-diol as a soft segment. Four polyesters were used in the synthesis of polyurethanes. Two of the polyesters were synthesized from monomers with even carbon atoms, i.e., adipic acid with 1,6-hexanediol (polyester-6-6) and adipic acid with 1,4-butanediol (polyester-6-4). The other two polyesters were synthesized from monomers with odd carbon atoms, i.e., pimelic acid with 1,5-pentanediol (polyester-7-5) and 1,5-pentanedioic acid with I ,5-pentanediol (polyester-5-5). The effects of compatibility between soft-and hard-segments and the chemical structures of polyesters on the phase segregation of soft-and hard-segments were studied by DSC and FT-IR.KEY WORDS Polyurethane I Differential Scanning Calorimetry I Fourier Transform Infrared Spectroscopy I Phase Segregation IThe polyester based urethanes consist of an aromatic diisocyanate with a glycol chain extender as the hard segment and a low molecular weight polyester as the soft segment. They are considered to be linear segmented block copolymer, made up of alternating hard and soft block segments. It has been reported that soft-and hard-segmental phase segregation of polyurethanes is strongly controlled by the compatibility of these two segments and the chain mobility of hard segments inside the soft domain. 1 • 2 Polyurethane of structure -[(0 = C)NH(CH2)nNH(C=O)O(CH 2 )mOJ-has been shown that when "n" and "m" are even the fit of each hydrogen donor group (NH) to each electron donor group (C=O) should be relatively easy, whereas when "n" or "m" is odd the fit should not be perfect. 3 Thus, in an irregular structure (n or m is odd and fit is poor) not all groups should participate in hydrogen bonding, inter-molecular attractions should be weaker, and the melting point should be lower. It is known that the "zigzag" structure of polyester affects the geometric fit of polymer molecules and thus the crystallization behavior of polyesters.In the present work, we studied the soft-and hardsegment phase segregation behavior of polyester basedpolyurethanes with two of the polyesters were synthesized from monomers with even carbon atoms, i.e., adipic acid with 1,6-hexanediol (polyeester-6-6) and adipic acid with 1,4-butanediol (polyester-6-4) and the other two polyesters were synthesized from monomers with odd carbon atoms, i.e., pimelic acid with 1 ,5-pentanediol (polyester-7-5) and 1,5-pentanoic diacid with 1,5-pentanediol (polyester-5-5). Attempt has been made to correlate the polyurethane morphology with the polyester "zigzag" structures, the crystallinity of polyester soft segments, NH to C = 0 structure geometric fit, and the compatibility between soft-and hardsegments. For polyurethanes with same polyester soft segmental molecular weights, with other things being t To whom correspondence should be addressed.equal, the soft-and hard-segmental compatibility increases with increasing polyester -...

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