Backbone Dynamics of Poly(isopropyl Acrylate) in Chloroform

Alternative Title

A deuterium NMR study


The backbone dynamics of poly(isopropyl acrylate) (PIPA) in chloroform have been studied over a wide composition and temperature range using deuterium NMR. The polymer was specifically labeled with deuterium in the methine position so that only one resonance would be seen. The results of T1 and T2 measurements were used to test the log χ2, VJGM, Bendler-Yaris (BY), and Skolnick-Yaris (SY) models of polymer reorientation. It was found that, even though all the models could mimic the data, they did not always fit the data in a physically realistic way. The log χ2 model yielded results which were not physically realistic even in dilute solution. The results from the VJGM, BY, and SY models were roughly indistinguishable despite their different formulations. All three models contain two parameters, each of which are dominated by either fast or slow motions. Further, it was seen that in dilute solution, the fast motion has an energy of activation of about 5 kcal/mol which is independent of concentration. In more concentrated solutions the energies of activation for the slow-motion parameters are concentration dependent and range from 12 to 30 kcal/mol. In concentrated solutions, it was found that T1 and T2 cannot be represented by a single model but the T2 measurements can be used to define a division between semidilute and concentrated solution when [η]Cc ≅ 30 for PIPA-CHCl3. It was also found that the T2 values for the concentrated solutions could be fit by using a free volume approach. The free volume parameters were calculated and judged to be reasonable when compared to the other systems. © 1984 American Chemical Society.



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© 1984 American Chemical Society (ACS), All rights reserved.

Publication Date

01 Jan 1984