In October 1921, Ostromislensky left Russia and moved to Latvia. There he assumed a position of assistant professor at the department of organic chemistry of University of Latvia in Riga. There he taught two major courses, on chemistry of rubber and on chemotherapeutic drugs. In May 1922, at the invitation of Dr. A. Hopkinson from the US "Rubber Company" Ostromislensky moved to New York. There he continued his work on chemistry and technology of rubber and pharmaceuticals in two companies, United States Rubber Company and Goodyear Tire and Rubber Company. In 1925, he opened his "Ostro Research Laboratory", where he studied the pharmaceutical properties of various compounds based on arsenic and vegetable oils which were used to treat leprosy. He also advocated commercial production of chemotherapeutic drugs pyridium and pyrazolone. In 1928 he received a US patent for production of polystyrene which was used by US Rubber for the first commercial production of polystyrene in the early 1930s. He also patented his early work on the synthesis of polyvinyl chloride in the US.
In 1930, Ostromislensky received U.S. citizenship and was invited to work in the company Union Carbide to develop commercial production of butadiene from ethanol. The production ceased only after the World War II, because it could not compete with butylene-based technologies. In the US, Ostromislensky improved several industrial technologies of synthetic rubber production. He also developed a technology for producing safety glass for the automobile windshields.
In one of developed by him reactions, ethanol is oxidized to acetaldehyde, which reacts with additional ethanol over a tantalum-promoted porous silica catalyst at 325–350 °C to yield butadiene:
:CHCHOH + CHCHO → CH=CH-CH=CH + 2 HO
This process was used in the United States to produce government rubber during World War II, and remains in use today in China and India.