Abstract
A series of samples of a modified poly(ethylene terephthalate) has been characterized by gel permeation chromatography, ultraviolet spectrophotometry, differential thermal analysis, and nuclear magnetic resonance techniques. These samples were prepared in the melt phase by reaction of dimethyl terephthalate, ethylene glycol, 1,4-butanediol, and an ultraviolet absorbing monomer, dimethyl Z. To determine if there were heterogeneity in composition as a function of molecular weight, samples were fractionated by preparative scale gel permeation chromatography, and selected fractions were analyzed by ultraviolet spectrophotometry. The composition was found to be relatively constant over the bulk of the distribution; however, the very low-molecular-weight region is appreciably richer in moiety Z. A portion of one of the samples, of ca. 1000 (polystyrene equivalent molecular weight), was submitted for mass spectral examination and found to be a mixture of cyclic dimers of moiety Z and the glycols. The glass transition temperature of the highest molecular weight fraction from the preparative gel permeation chromatography fractionation had the same value (within experimental error) as that of the bulk polymer. This is interpreted as indicating (1) the cyclic dimer material does not act as a plasticizer lowering the glass transition temperature, (2) there is no dependence of glass transition temperature on molecular weight, and (3) no major variation exists in the glycol composition with molecular weight. Two samples of this polymer were prepared using the same monomer feed ratios, temperature, catalyst, etc. These samples were found to have approximately the same viscosity, and molecular weight distributions; however, their glass transition temperatures differed by ca. 10°. This difference was interpreted as indicating that one sample contained more butanediol than expected from the monomer feed concentration. This postulate was confirmed by nuclear magnetic resonance measurements on the bulk samples.
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