reagents on proportionate basis but additionally 1 mol 56 1 g of diphenyl ether dpe which acts an end capping agent was added along with msa before addition of ppba thus a fraction of end capping agent required was added right at the onset of polymerization stage polymerization was continued as in example 5 and after 12 h another 56 1 g of dpe was added to complete the end capping the second stage of end capping was continued for additional 12 h the batch was then worked up as in example 10 with msa as the diluent and a product with inherent viscosity of 1 12 dl g was obtained the polymer was melt stable at 380 u00b0 c and exhibited very good mechanical properties as listed in the table below thus even by adding end capping agent from the beginning in the polymerization stage a product with good molecular weight excellent mechanical properties and thermal stability could be obtained by the above method the examples below demonstrate the effectiveness of other end capping agents to thermal stability of the polymer the polymerization was conducted as mentioned in example 10 except only half the amount of phosphorus pentoxide was used the reaction was terminated when desired viscosity was obtained the polymer was then worked up as mentioned in example 10 except for the fact that reaction mass was diluted with edc instead of msa 200 g of the polymer so obtained was re dissolved in.