This thesis was a study of the effect of the variation of cross-linkage on the mechanical properties of a polyurethane elastomer prepared from 33’ Bitolyene 44’ diisocyanate and the polyester of adipic acid and ethylene glycol. The investigation consisted of the preparation of polyurethane elastomer, solvent absorption and swelling tests, tensile properties test and hardness test. Three groups of polymer material were prepared. In the first group the R value was varied from 1.0 to 4.5, (the ratio of 33’ Bitolyene 44’ diisocyanate to polyester) and fixed amounts of excess diisocyanate were used. Ethylene glycol was used as the cross-linking agent. In the second and third groups the R value was fixed at 1.65 and 2.5, and the amount of excess diisocyanate after chain extension was varied. The preparation of the elastomer was accomplished by a method based on the literature and preliminary experiments carried out for the purpose of determining optimum conditions for the specific polymer under investigation. All mechanical tests were accomplished by conventional and standard methods. All tests were conducted at 75° F. In addition to these tests the hardness test was carried out at 300° F. The preparation of polyurethane elastomer by bulk polymerization was conducted at atmospheric pressure and 130° C with the reaction requiring a period of 30 minutes for completion. For the molding process, casting, cold molding, hot molding and curing were used. The various degrees of cross-linkage could be obtained by using different ratios of 33’ Bitolylene 44’diisocyanate to polyester and by varying the amount of cross-linked agent, ethylene glycol. The properties associated with cross-linking varied in such a way as to indicate an increase in cross-linking as the R value increased. The solvent absorption and swelling properties decreased with an increase of the R value. The mechanical properties improved with an increased R value. Also the hardness increased with an increase of the R value. / Master of Science