The Role of Soft Segment Molecular Weight on Microphase Separation and Dynamics of Bulk Polymerized Polyureas

The influence of poly(tetramethylene oxide) (PTMO) soft segment length on the phase-separated microstructure, state of hydrogen-bonded associations, and molecular dynamics was investigated in polyureas polymerized from the bulk. For higher PTMO molecular weights (1000 and 650 g/mol) hard segments self-assemble into ribbon-like domains, while incorporation of a 250 g/mol soft segment leads to a predominately mixed segment material. The degree of microphase separation of the hard and soft segments, however, is rather incomplete for polymers synthesized from 1000 and 650 g/mol PTMO and decreases with decreasing soft segment molecular weight. Broadband dielectric relaxation spectroscopy reveals two segmental relaxations: a soft segment rich (alpha) and slow segmental (alpha(2)) process. When the molecular weight is reduced from 1000 to 650 g/mol the mobility of these processes is reduced, consistent with findings from differential scanning calorimetry and dynamic mechanical analysis.