Aggregation States and Segmental Dynamics of Poly(methyl methacrylate) in Nanofiber Mats

Nanofiber mats composed of polymers,having a large surface-to-volumeratio and high porosity, have been widely applied in the environmentaland biomedical fields but fundamental knowledge on the polymer chainsin the mats seems to be limited. We here report the aggregation statesand segmental dynamics of poly-(methyl methacrylate)-s (PMMAs) withdifferent stereoregularities in electrospun nanofiber mats. Attenuatedtotal reflectance Fourier transform infrared (ATR/FTIR) spectroscopyrevealed that, in the case of atactic PMMA (at-PMMA),the population of the trans-trans conformation of the main chain part, which allows carbonyl groupsof the side group to interact affirmatively with each other, increasedin the electrospun nanofiber mat. On the other hand, in the case ofisotactic PMMA (it-PMMA), the skeletal conformationwas unchanged even in the nanofiber mat. As a result of the aggregationstates of PMMA chains, the glass-transition temperature (T (g)) of the electrospun nanofiber mats increased and remainedunchanged from the corresponding bulk value for at- and it-PMMA, respectively. These findings shouldbe useful for designing materials and devices composed of electrospunnanofibers.