کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
1397068 984213 2005 9 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Influence of molecular weight and chemical structure of soft segment in reaction kinetics of polycarbonate diols with 4,4′-diphenylmethane diisocyanate
موضوعات مرتبط
مهندسی و علوم پایه شیمی شیمی آلی
پیش نمایش صفحه اول مقاله
Influence of molecular weight and chemical structure of soft segment in reaction kinetics of polycarbonate diols with 4,4′-diphenylmethane diisocyanate
چکیده انگلیسی

This third paper in this series regarding the mechanism and kinetics of urethane systems presents the results obtained in the study of the influence of molecular weight and chemical structure of several polycarbonate diols on the polycondensation reaction with 4,4′-diphenylmethane diisocyanate (MDI), comparing them with those obtained previously for condensation reaction with p-tolyl isocyanate (p-TI). The substitution effect induced in the second isocyanate group by the reaction of the first isocyanate group of a symmetric diisocyanate likes MDI has been studied by size exclusion chromatography (SEC) using a model monoalcohol. The condensation reaction kinetics is adequately described by an autocatalyzed third order rate equation. The values obtained for rate constants, using a Runge–Kutta mathematical model, suggest association phenomena by hydrogen bonding implying hydroxyl groups but also urethane groups. In bulk and in stoichiometric conditions, the association phenomena observed increase proportionally on one hand, to the decrease of molecular weight of macrodiol and on the other hand, to the tendency to form intramolecular hydrogen bonds. The activation energies were obtained from the evaluation of kinetic data at different temperatures in the range 45–65 °C. As association phenomena increase, activation energies decrease. The slightly higher activation energies obtained for polycondensation compared to condensation are explained because of the rapid increase of viscosity of the medium.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: European Polymer Journal - Volume 41, Issue 12, December 2005, Pages 3051–3059
نویسندگان
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