Polyurethane linear segmented

Figure 1.20 The term polyurethane commonly describes a linear segmented copolymer which comprises hard and soft blocks stemming from the use of a mixture of low and high molecular weight diols in the polymerization formulation. The amount of each block-type in the polymer can be adjusted by altering the relative amount of low molecular weight diol to polyol while preserving the ratio of isocyanate functional groups to alcohol groups of all types.

Camberlin, Y, Pascault, J. P. (1983), Quantitative DSC evaluation of phase segregation in linear segmented polyurethanes and polyurethaneureas, J. Polym. Sci., Polym. Chem., 21,415-23. 

Soft blocks are composed of linear, dihydroxy poly ethers or polyesters with molecular weights between 600 and 3000. In a typical polymerization of a thermoplastic polyurethane elastomer, the macroglycol is end capped with the full amount of aromatic diisocyanate required in the final composition. Subsequently, the end-capped prepolymer and excess diisocyanate mixture reacts further with the required stoichiometric amount of monomeric diol to complete the reaction. The diol links the prepolymer segments together while excess diol and diisocyanate form short hard-block sements, leading to the (AB)n structure illustrated in Figure 1. Block lengths in (AB)n polymers are frequently much shorter than those in anionically synthesized ABA block copolymers. 

Time Dependence of Mechanical Properties and Domain Formation of Linear and Crosslinked Segmented Polyurethanes... 

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