The broad glass transition of soft-segments (SS) in a series of PUU samples was examined by 1H and 13C solid-state NMR. With time-domain wideline separation experiments, two dynamic SS fractions, rigid-SS and mobile-SS, can be discerned. At increasing temperature, the two fractions exchange population, while their decaying constants remain largely unchanged. There is a much stronger temperature dependence of such a population exchange in phase-mixed samples than in phase-separated ones. These observations can be explained by a model in which a sharp glass transition exists in each microdomain. As the Tg of each microdomain is a function of SS/HS (hard segments) population ratio, and the material has a broad distribution of phase mixing among its microdomains, this results in a broad Tg. Therefore, the broad glass transition in PUU is a superposition of many localized, sharp glass transitions. This model would help to predict the response of phase-mixed polymers when subject to high-strain-rate impact: the rubbery microdomains in the materials would successively undergo glass transition according to their extent of phase mixing, resulting in dynamically induced toughening.

Glass transitions of individual microdomains in phase-mixed poly(urethane urea) elastomers investigated by solid-state NMR

249th National Meeting (2015)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.