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Polyurethanes (PUs) based on diethylene glycol (DEG) and a new isocyanate of variable geometry, 4,4^'-dibenzyl diisocyanate (DBDI), were synthesized by the standard two-step procedure. A macro-diol, hydroxyl-terminated poly(ethylene adipate) (PEA) M _W = 2000 50 (PEA₂₀₀₀ ) was also used in the PU synthesis. The ability of the two benzene rings in the DBDI unit to rotate in two discrete “sin” and “anti” positions around the —CH₂CH₂— ethylene bridge enables a specific coplanar packing structure of the hard domains dibenzyl-based polymers. Molecular orientation of the DBDI-based hard segments and soft segments was monitored by means of infrared dichroic experiments. The effect of the strain history on the orientation of macromolecular chains was studied under uniaxial extension and in cyclical deformation experiments. The high modulus domains derived from the DBDI unit containing the aromatic urethane blocks served to reinforce the rubbery prepolymer phase. Since the two (soft and hard) phases are interpenetrating, both were deformed by the applied stress. When the load was removed, the soft domains relaxed to a nearly isotropic state, while the rigid phase remained plastically deformed.

26:T458,

Polyurethane networks with enhanced thermal stability and electrical insulation properties were prepared from the reaction of epoxy-terminated urethane prepolymers (EPU) and polyimides containing pendant phenol groups (HPI). EPUs were prepared by the reaction of glycidol with NCO-terminated urethane oligomers. The oligomers were prepared from different molecular weight versions of polycaprolactone polyol (CAPA) and hexamethylene diisocyanate. The progress of the reaction was monitored by differential scanning calorimetric analysis in the presence and absence of suitable catalyst. The onset temperature of exothermic reaction of phenolic groups and epoxy rings was chosen as optimum curing temperature and the reaction duration was optimized by gel content measurement. The starting materials and polymers were characterized by conventional spectroscopic methods, and physical, thermal and electrical properties of the crosslinked networks were determined. The novel poly(urethane-imide)s exhibited considerable improvement in thermal and electrical properties in comparison to common polyurethanes.

27:T495,

Two series of thermally modified thermoplastic polyurethane elastomers (TPU)s based on poly(oxytetramethylene glycol) (PTMG) (PT samples), and poly(oxyethylene glycol) (POE) (PO samples) were synthesized from 4,4'-methylene-bis-(4-phenylisocyanate) (MDI) and an aromatic diacid, bis(p