Phase polyurethane elastomers

Elastic Modulus, Network Structure, and Ultimate Tensile Properties of Single-Phase Polyurethane Elastomers... 

Studies have been made of the elastic (time-independent) properties of single-phase polyurethane elastomers, including those prepared from a diisocyanate, a triol, and a diol, such as dihydroxy-terminated poly (propylene oxide) (1,2), and also from dihydroxy-terminated polymers and a triisocyanate (3,4,5). In this paper, equilibrium stress-strain data for three polyurethane elastomers, carefully prepared and studied some years ago (6), are presented along with their shear moduli. For two of these elastomers, primarily, consideration is given to the contributions to the modulus of elastically active chains and topological interactions between such chains. Toward this end, the concentration of active chains, vc, is calculated from the sol fraction and the initial formulation which consisted of a diisocyanate, a triol, a dihydroxy-terminated polyether, and a small amount of monohydroxy polyether. As all active junctions are trifunctional, their concentration always... 

Phase II. In this phase, polyurethane elastomers were prepared using only one prepolymer, B-625, and several catalysts and concentrations in order to determine the optimum properties possible with HER... 

TENSILE DEFORMATION BEHAVIOUR OF THE POLYMER PHASE OF FLEXIBLE POLYURETHANE FOAMS AND POLYURETHANE ELASTOMERS... 

Atomic force microscopy and attenuated total reflection infrared spectroscopy were used to study the changes occurring in the micromorphology of a single strut of flexible polyurethane foam. A mathematical model of the deformation and orientation in the rubbery phase, but which takes account of the harder domains, is presented which may be successfully used to predict the shapes of the stress-strain curves for solid polyurethane elastomers with different hard phase contents. It may also be used for low density polyethylene at different temperatures. Yield and rubber crosslink density are given as explanations of departure from ideal elastic behaviour. 17 refs. 

Thermoplastic elastomers, e.g., polyurethane elastomers, have an entirely different structure that is heterogenic. They have an elastomeric matrix and phase-separated hard blocks, which act as embedded physical crosslinking sites. The hard blocks can be softened at elevated temperatures to obtain a single-phase melt that is easily processed. Upon cooling, the two-phase nature is recovered and the material becomes a solid again. 

Several studies have been published in recent years on the properties of RIM polyurethanes and polyurethane-ureas (1-7). Unlike most studies, however, we have restricted our attention to simplified linear systems in order to establish the effect of reaction rates and mold temperatures on the phase separation and molecular weight of segmented polyurethane elastomers produced by RIM(6). 

Through this work we have demonstrated the following points concerning phase separation and properties 1n bulk RIM polymerized polyurethane elastomers ... 

In this work, we describe an automated differential scanning calorimetric (DSC) technique that can be used to measure polymerization kinetics for formation of urethane block polymers. The same technique is also used to measure phase separation during formation of polyurethane elastomers and the effect that separation has on the polymerization. The elastomer formulations consisted of modified liquid p,p -diphenyImethyl diisocyanate (MDI), 1,4-butanediol and an (oxypropylene-oxyethylene) macroglycol for the soft segment. 

Polyurethane elastomers derive their elastomeric properties from phase separation of the hard and soft copolymer segments, such that the hard (urethane) segment domains serve as crosslinks between the amorphous soft segment domains, which are usually polyesters or polyethers. We are interested in the systems in which the hard segments are prepared from diphenyl-methane 4,4 -diisocyanate (MDI) with a linear diol as the chain extender ... 

Phase I. In this phase of the study, the feasibility of chain extending polyurethane elastomers with HER was determined. A variety of elastomers were prepared by chain extending the following prepolymers with HER (see Table I for their chemical descriptions) ... 

Phase I The properties of the phase I elastomers are shown in Tables I and II. The mechanical properties of all the elastomers, both polyether based (Table III) and polyester based (Table IV) were, in general, comparable with conventionally chain extended MDI-based polyurethane elastomers (3). 

In the absence of a blowing agent and with conditions favoring the formation of linear chains, thermoplastic polyurethane elastomers can be formed. Materials with different properties can be obtained by altering the ratio of hard to soft blocks, and it is also observed that, in many cases, the hard segments can crystallize. This can give rise to phase-separated structures, shown schematieally in Figure 2.6, which behave as thermoplastic elastomers (see also Section 15.6). 

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