Time-dependent morphology development in segmented polyetherurea copolymers based on aromatic diisocyanates

Abstract

Time-dependent morphology development in segmented polyureas obtained by the stoichiometric reactions between amine terminated poly(tetramethylene oxide) (PTMO) and aromatic diisocyanates were investigated. Polyureas were prepared by reacting aminopropyl terminated PTMO oligomer (M(n) = 1100 g/mol) and various aromatic diisocyanates, such as 1,4-phenylene diisocyanate (PPDI), 1,3-phenylene diisocyanate (MPDI), diphenylmethane diisocyanate (MDI), and tolylene diisocyanate (TDI). Time-dependent FTIR studies were conducted on thin films cast onto KBr discs, which were annealed at 200 degrees C for 10 min in an air oven. After removing from the oven, samples were placed into the FTIR spectrometer at room temperature, where time-dependent spectra were recorded until equilibrium was reached. Time-dependent peak reorganization in 3500-3100 cm(-1) (N-H region), 1750-1450 cm(-1) (C=O region or amide I and amide II regions), and 1180-1020 cm(-1) (C-O-C) were monitored. Depending on the chemical structure and the symmetry of the diisocyanate, major differences were observed in the time needed to reach an equilibrium morphology in these homologous poly(ether urea) copolymers. Symmetric PPDI-based polyurea reached equilibrium in about I h compared with its asymmetric MPDI-based counterpart, which needed about 150 h. Microphase development of the MPDI urea was also characterized by AFM, which gave similar results.