Copolymerizable blocked isocyanate diols are prepared by reacting a blocking agent with an isocyanate group of an organic diisocyanate under controlled conditions, thereby forming a blocked isocyanate group, and reacting the second isocyanate group in a subsequent step with the amine portion of a selected amine diol under anhydrous conditions. The resultant products are used to prepare self-crosslinkable, linear polyurethanes of high molecular weight.