Complex sentence: During WWII, Oppenheim who was captured by the Japanese and held as a POW, fled Singapore for a short time to pursue research in Switzerland at the École Polytechnique Fédérale de Lausanne and at Einstein's alma mater, the ETH.
Split into simpler sentences: During WWII, Oppenheim who was captured by the Japanese and held as a POW, fled Singapore for a short time to pursue. He pursued research in Switzerland at the École Polytechnique Fédérale de Lausanne and at Einstein's alma mater, the ETH.