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Effects of Chemical Reactions on the Properties of Copolyesters Made from Poly(ethylene terephthalate) Prepolymer and Liquid Crystalline Polymer
No full textCopolyesters were prepared by melt-phase polycondensation of poly(ethylene terephthalate) (PET) prepolymer and a thermotropic liquid crystalline polymer (LCP), 60 mol% p-hydroxybenzoic acid and 40 mol% poly(ethylene terephthalate) (PHB60/PET40). The copolyesters were characterized using gel permeation chromatography (GPC), nuclear magnetic resonance (NMR), thermal analysis, and wide angle X-ray diffraction measurement. The molecular weights of final copolyesters decreased with the addition of LCP. GPC results indicate that chain scission reaction of LCP occurs accompanied by chain-growing reaction of PET. From NMR analysis, LCP added underwent transesterification resulting in statistical reorganization of chain sequence with producing ether type by-products responsible for limiting the chain growth of copolyesters. It was observed that the crystallization of PET was delayed and melting temperature decreased with increasing LCP content in copolyesters. The resulting thermal properties and structural regularities of copolyester can be modified by exchange reactions during preparation
Effects of chemical reaction on the properties of reactive blends between poly(butylene terephthalate) and liquid crystalline polymer
No full textIn order to understand the effects of chemical reaction on the properties of the reactive blend prepared by the melt-phase reaction of poly(butylene terephthalate) and liquid crystalline polymer (LCP), the crystallization behavior, complex viscosity and the molecular weight of the blends were studied. Because of the hindered crystallization due to the presence of the melt phase LCP, the crystallization temperature of the PBT/LCP blend decreased with increasing LCP content. The trans esterification reaction had no effect on the crystallization behavior and complex viscosity, except for A2 sample (PBT90/LCP10 reactive blend at 260 degrees C for 1 hour) and B2 sample (PBT70/LCP30 reactive blend at 260 degrees C for 1 hour). The reactive blends showed the fast crystallization due to annealing and increased the molecular weight due to the end-to-end reaction
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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