RIM Urethanes Structure/Property Relationships for Linear Polymers
Reaction Injection Molding (RIM) technology represented the major break-through in the polymer processing development of the seventies. This technology, based on the rapid mixing of co-reactive streams and subsequent feeding of the mixture into the polymerization reactor — the mold, — allows for production of large and intricate parts. The relatively low energy input that is required makes this technology especially attractive for today’s needs.
Polyurethanes are perfectly suited for RIM. The fast and exothermic reaction typical for urethane formation does not generate any low molecular weight byproducts. And by the selection of different intermediates, the properties of the resultant polymer can be broadly varied.
In order to investigate the structure/property development of linear RIM urethanes, a series of polyether-based linear (thermoplastic) polyurethanes (TPU) varying in the hard segment content between 20 and 80 weight percent was prepared. 4,4′-Diphenyl-methane diisocyanate (MDI) and 1,4-butanediol (BDO) were the hard segment intermediates. (Oxypropylene-oxyethylene) diols of M̄n = 1000, 2000, 3000 and 4000 were used as the soft segments. Physical-mechanical, dynamic-mechanical and specific heat (DSC) are used to elucidate the mechanical and morphological behavior of the materials. The polyurethanes varied from soft elastomerics (continuous soft phase) to high-modulus plastics (continuous hard phase) with a possible phase inversion at about 60 percent hard segment.
KeywordsHard Segment Soft Segment Flexural Modulus Soft Phase Thermoplastic Polyurethane
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