Linear polyurethanes, having high molecular weight, were prepared by interfacial polycondensation from halogen substituted aromatic bischloroformates and aliphatic diamines, piperazines, and aromatic diamines. Examples of specific intermediates are hexamethylenediamine, piperazine, homopiperazine (see formula), m-phenylendiamine, and the bischloroformates of 2,2-bis (4-hy-droxy-3,5-dichlorophenyl) propane, 2,2-bis(4-hydroxy-3,5-dibromophenyl) propane, and 2,2-bis(4-hydroxyphenyl) hexafluoropropane:

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In comparison with corresponding unhalogenated polyurethanes, the polymers from this study, particularly those based on piperazines, had high glass transition and softening temperatures. Polyurethanes in this class, like most ring-containing polyurethanes, do not have sufficient thermal stability at their high melting points for easy melt for easy melt forming. They were more soluble in a variety of common solvents and had excellent resistance to ultraviolet light. Surprisingly, the irregularity introduced into the polymer chain by the use of such intermediates as homopiperazine (formula above) or 2-methylpiperazine did not inhibit crystallization. On the other hand the symmetry provided by trans-2,5-dimethylpiperazine greatly reduced solubility in many solvents. Several polyamides and a polyurea from homopiperazine are included.