The precipitated polymeric powder was collected by filtration, washed with distilled water, treated with 5% sodium hydrocarbonate aqueous solution, kept overnight, washed thoroughly with water till neutral reaction and dried in air. Then, soluble part of polymer was extracted by DMF and precipitated by water. The polymers obtained were dried in vacuo (323 K/2 kPa)
and were stored in a desiccator over phosphorus pentoxide