In 1941 Japan bombed Pearl Harbor, bringing the United States into the agony of World War II. Japan seized control of much of Southeast Asia, overrunning the plantations in the Malay Peninsula and East Indies that supplied America with nearly ninety percent of its heavy demand for rubber. The mass production of synthetic rubber became, hence, a formidable challenge for America's chemical community.
Bell Laboratories was one of the places with the most experience in studying the molecular properties of rubber. Work on synthetic rubbers had begun there in the late 1930s in the hope of making these rubbers suitable for use as insulation for telephone cables. In 1943 William O. Baker (b. 1915) began serious investigation into the relation of two physical states of rubber, sol and gel, to the final rubber product. Sols are rubbers with a normal amount of cross-linkages between molecules; gels have more than their share of cross-links, often in three dimensions, and are very rigid. Baker discovered that the high temperatures used in factory drying of rubber, which made the rubber more workable, were splitting molecular chains and producing more gel. The lack of proper control over the reactions and the drying led to "tight rubber," with too high a gel content and unsatisfactory properties in the final product. Although Baker met initial resistance from manufacturers used to traditional drying methods, he succeeded in getting companies to use his techniques for monitoring and limiting gel content. Baker later played a key role in eliminating much of the variation in the styrene content of rubbers.