In recent years emphasis has been given on effective utilisation of naturally available and renewable resources for the development of raw materials for various polymer based products. Cashew Nut Shell Liquid (CNSL) and one of its ingredients cardanol has been successfully exploited for the development of phenolic resins for the manufacture of different industrial products. Since cardanol is phenol with meta substituted aliphatic unsaturated long chain, it can be properly modified to a high molecular weight nucleophilic compound containing flexible as well as rigid molecular chains. Such a nucleophilic high molecular weight compound can react with a diisocyanate which is an electrophile to give polyurethane. Therefore by carefully synthesising the high molecular weight nucleophilic compound with different molecular size, functionality and structure, it is possible to develop polyurethanes having wide range of physico-chemical and mechanical properties as well as high performance characteristics, such as long term stability under ageing conditions.