Differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy (DRS) demonstrate that highly concentrated solutions of poly(n-butyl methacrylate) (PBMA; M, = 450 OOO, Mw/Mn = 1.06) in 2-propanol (2-POH) solidify upon cooling in two clearly distinguishable steps. With this endothermal system, for which the 8 temperature (24 "C) is almost identical with the glass transition temperature of the pure polymer (22 "C), the solutions gel thermoreversibly some 60-40 O C before they become glassy. The gelation is interpreted in terms of noncrystalline physical cross-links, which result from the preference of the energetically highly favored polymer/ polymer contacts over polymer/solvent contacts; the resulting intersegmental clusters amplify a partial freezing-in of the mobility of the macromolecules that can already be observed in the absence of solvent by means of DRS measurements. Qualitatively the glass transition temperature of the pure PBMA is changed by the addition of 2-POH in the usual way. The low solvent quality, however, causes extra effects, which favor the vitrification. A so far only empirical equation is proposed to describe these thermodynamic contributions. IntroductionIn liquid mixtures, the molecular mobility of the
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.