Process for preparing high tear-strength polydiene polyurethane

A process for preparing a polydiene polyurethane having high tear strength, which process comprises reacting

• a. a polydiene glycol prepared with use of dilithio compound as a catalyst, and having a functionality of from 1.8 to 2.1, a number average molecular weight of from 1,000 to 5,000 and a residual lithium content of less than 30 ppm after treatment with mineral acid other than sulfuric acid;
• b. a diisocyanate compound, and
• c. a chain extending agent selected from diamine and diol compounds by the prepolymer method, and compounding 10 to 50 parts by weight of carbon black per 100 parts by weight of the total amount of said polydiene glycol, said diisocyanate compound and said chain-extending agent before curing, the equivalent ratio of the isocyanate groups in said polydiene glycol being 1.5 to 3.0, the equivalent ratio of active hydrogens in said chain-extending agent to the isocyanate groups in said prepolymer being 0.8 to 1.1, and the curing temperature being 50.degree. to 140.degree. C., the ratio of chain length between physical cross-links in the corresponding non-loaded polyurethane to the particle size of said carbon black being established within the range of from 2.4 to 15, and the chemical crosslink density of said corresponding non-loaded polydiene polyurethane being 4 .times. 10.sup.-5 mole/cc or less.