Water absorbing and urine stable step-wise grafted starch-polyacrylonitrile copolymers

An alkali metal carboxylate salt of a starch polyacrylonitrile graft copolymer said salt being produced by saponifying a starch-polyacrylonitrile graft copolymer, said copolymer having a starch to acrylonitrile mole ratio of at least 1:6 and being produced from a thinned starch by step-wise grafting.

A process of preparing a starch polyacrylonitrile graft copolymer, said process comprising:

• reacting starch with a portion of a predetermined amount of acrylonitrile, in the presence of a free radical initiator to provide a grafted copolymer, and thereafter, reacting said grafted copolymer with the remaining portion of said predetermined amount of acrylonitrile in the presence of additional amounts of free radical initiator to provide a more highly grafted copolymer, the mole ratio of said starch to acrylonitrile in said more highly grafted copolymer being at least 1:6.

A process of preparing a starch acrylonitrile graft copolymer which comprises grafting starch with a portion of a predetermined amount of acrylonitrile in the presence of a free radical initiator, holding said grafting reaction mixture until the reaction is no longer exothermic and the temperature remains substantially constant, increasing the temperature to within the range of from 50.degree. to 70.degree. C. and holding at said temperature range until said grafting reaction is substantially complete;

• and thereafter, grafting copolymer prepared as above specified with the remaining portion of said predetermined amount of acrylonitrile, in the presence of a free radical initiator, holding said grafting reaction mixture until the reaction is no longer exothermic and the temperature is substantially constant, increasing the temperature within the range of 50.degree. to 70.degree. C and holding until the grafting reaction is substantially completed, the mole ratio of starch to acrylonitrile in the final product being at least 1:6.