Advisor:Prof. R.A. Register
Undergraduate Institution: MIT
M.S.E. Thesis Research:
Dynamic Differential Scanning Calorimetry (DDSC) has been applied to study the processes of melting and recrystallization in ethylene-methacrylic acid, E/MAA, ionomers in order to obtain the initial crystal thickness distribution produced by a variety of annealing histories. The heat flow response to a modulated temperature profile is analyzed using Fourier transformation to assess the extent of recrystallization which occurs during the DSC scan. Nichols' model was used to approximate the melting temperatures of the crystals which form during recrystallization. Ionomers with low neutralization levels and annealed for long times at room temperature showed little or no recrystallization, while ionomers with high neutralization levels and short periods of annealing showed moderate levels of recrystallization. The double melting endotherm of E/MAA ionomers arises from a true bimodal crystal thickness distribution, and is not the result of concurrent melting and recrystallization. The thicker crystals in the distribution, 35 - 60 angstroms, form quickly during primary crystallization, while crystals approximately 25 angstroms thick form during room-temperature annealing.