Cationic starch graft copolymers and novel process for the preparation of cationic starch graft copolymers

1. Cationic starch graft polymer composed of the monomers a) to d)

a) 20- 80% by weight of acrylamide, methacrylamide or mixtures thereof,

b) 3- 20% by weight of at least one basic or cationic vinyl monomer,

c) 0.005- 1.5% by weight of at least one bifunctional or higher-functional crosslinking agent,

d) 0- 10% by weight of at least one nonionic or anionic vinyl monomer which differs from the monomers mentioned under a) to c)

and a grafting base e)

e) 15- 70% by weight of at least one starch whose molecular weight has been reduced by partial degradation,

the sum of a) to e) being 100% by weight; wherein the cationic starch graft polymer can form a 5 to 25 percent by weight solution in water at 23° C.; and

wherein the cationic starch graft polymer is a product of a process comprising

a first step comprising free radical polymerization of grafting base e) in water with at least 30% by weight of the total amount of component b) to form a reaction mixture, and

a second step comprising free radical polymerization of components a), c), d), and any remaining amount of component b) in the presence of the reaction mixture.

2. Cationic starch graft polymer according to claim 1 , wherein component a) is acrylamide.

3. Cationic starch graft polymer according to claim 1 , wherein component b) is a vinyl compound which has a double bond capable of free radical polymerization and which contains either a permanently cationic charge or a basic group which is present in completely or partly protonated form under weakly acidic conditions.

4. Cationic starch graft polymer according to claim 1 , wherein monomer c) is a water-soluble (i.e.>3 g/l at 23° C.) divinyl compound.

5. Cationic starch graft polymer according to claim 1 , wherein the starch is additionally derivatized.

6. Cationic starch graft polymer according to claim 1 , wherein the starch is a cationic starch.