Process for producing hydrophobically associating polyacrylamides

A process for producing hydrophobically associating polyacrylamides by radically polymerizing an aqueous solution comprising water-soluble, monoethylenically unsaturated monomers comprising at least

• water,
• 40 mole % to 99.995 mole % of at least one monomer (A) selected from the group of (meth)acrylamide, N-methyl(meth)acrylamide, N,N′-dimethyl(meth)acrylamide or N-methylol(meth)acrylamide, wherein the amount relates to the total of all ethylenically unsaturated monomers in the aqueous solution, and
• 0.005 mole % to 1 mole % of at least one monoethylenically unsaturated monomer (B) selected from the group of
• H2C═C(R1)—O—(—CH2—CH(R2)—O—)k—R3 (I),
• H2C═C(R1)—(C═O)—O—(—CH2-CH(R2)—O-)k-R3 (II),
• H2C═C(R1)—R4—O—(—CH2—CH(R5)—O—)x—(—CH2—CH(R6)—O—)y—(—CH2—CH2O—)z—R7 (III),
• wherein the amount relates to the total of all ethylenically unsaturated monomers in the aqueous solution, and
• wherein the radicals and indices are defined as follows:
• R1:
• H or methyl;
• R2:
• independently H, methyl or ethyl, with the proviso that at least 70 mol % of the R2 radicals are H,
• R3:
• aliphatic and/or aromatic, linear or branched hydrocarbyl radicals having 8 to 40 carbon atoms,
• R4:
• a single bond or a divalent linking group selected from the group consisting of —(CnH2n)—, —O—(Cn′H2n′)— and —C(O)—O—(Cn″H2n″)—, where n is a natural number from 1 to 6, and n′ and n″ are a natural number from 2 to 6,
• R5:
• independently H, methyl or ethyl, with the proviso that at least 70 mol % of the R5 moieties are H,
• R6:
• independently hydrocarbyl radicals of at least 2 carbon atoms,
• R7:
• H or a hydrocarbyl radical having 1 to 30 carbon atoms,
• k a number from 10 to 80,
• x a number from 10 to 50,
• y a number from 5 to 30, and
• z a number from 0 to 10,
• under adiabatic conditions in the presence of suitable initiators for radical polymerization thereby obtaining an aqueous polyacrylamide gel, wherein
• the concentration of the monomers is from 1 mole/kg to 3.3 mole/kg, relating to the total of all components of the aqueous monomer solution,
• the aqueous monomer solution has a temperature T1 not exceeding 30° C. before the onset of polymerization, and
• the temperature of the aqueous polyacrylamide gel T2 after polymerization is from 45° C. to 80° C.