THERMAL-PROPERTIES OF HYDROPHILIC POLY(ETHYLENE-TEREPHTHALATE) MODIFIED BY GRAFTING WITH POLY(ACRYLIC ACID) FOLLOWED BY SALT FORMATION

Poly(ethylene terephthalate) (PET) was modified by grafting with poly(acrylic acid) (PAA) followed by salt formation with alkali and alkali earth metals, amines, and sodium salts of amino acids. Moisture regains of PAA-grafted (18.9%) PET ranged from 2.0 to 13.3%, and the order was as follows; salts of Na salts of amino acids > Na salt > Ca salt > amine salts > acid form. The number of water molecules adsorbed in monolayer state on each functional group ranged from 0.2 to 1.6, and the adsorption was in the same order as that for moisture regain. On heating the grafted PET, the formation of linear and/or cyclic acid anhydrides by dehydration and of ketones by elimination of carbon dioxide from the anhydrides was suggested by IR spectroscopy. TG analysis showed that the grafted derivatives were less stable than PET. Furthermore, the change in chemical structure described above and the reversible reaction between acid anhydrides and carboxylic acids were confirmed by evaluating the storage moduli of PAA-grafted PET films heated or hydrolyzed under several conditions.