Application of thermal methods in the characterisation of poly(urethane‐urea)s formed by reaction injection moulding

Abstract Differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) have been used in conjunction with tensile testing and transmission electron microscopy (TEM) to characterise novel segmented poly(urethane‐urea) (PUU) network materials formed by reaction injection moulding (RIM). Materials were based on a modified liquid 4,4′‐diphenylmethane diisocyanate and a polyether triol in admixture with one of three hindered aromatic diamines: 3,5‐diethyltoluene diamine (DETDA); methylene‐bis‐2,6‐diisopropylaniline (MMIPA); methylene‐bis‐(2‐methyl‐6‐isopropylaniline) (MMIPA). The materials ranged from tough translucent elastomers to opaque brittle plastics depending on the chemical nature and weight fraction of the hard segments (HS). DSC and DMTA studies showed the PUU materials to be phase‐separated; this was confirmed by TEM and tensile testing. The soft‐segment glass transition temperatures (DSC and DMTA) were independent of composition but varied with diamine structure. Hard‐segment glass transition temperatures could only be evaluated by DMTA and no evidence of crystallinity was found by thermal methods or by wide angle x‐ray diffraction. Heat capacity measurements and DMTA suggested that some degree of phase mixing had occurred, to a greater extent in the DETDA and MDIPA systems. Phase inversion was observed by DMTA and confirmed at ∼55% hard‐segment content for DETDA systems by tensile testing.