The production of copolymers from N-vinyl lactams and hydrophobic comonomers by free radical polymerization is known. The production of such copolymers is carried out in an organic solvent such as an alcohol or a mixture of water and an organic solvent having a high solvent content. Generally, the polymerization is carried out under reflux of a solvent. The more volatile hydrophobic monomer compared to N-vinyl lactam enters the gas phase and condensate in this manner.
For many applications, it is desirable to dissolve in water to give a clear solution, ie a solution having a concentration of 5% by weight of a copolymer having a FNU value of <20. However, there is a problem in that different reactivity and different polarities of the monomers may result in an increase in the concentration of the hydrophobic monomer, which results in the formation of a homopolymer which is not water-soluble from the hydrophobic monomer. Even at a small amount of 500 to 1000 ppm, such a homopolymer causes turbidity in the aqueous solution of the copolymer. The increase in the concentration of hydrophobic monomers is particularly likely to occur in the gas phase and in the condensate, and may also occur on the walls of the reactor and on the surface of the polymerization medium.
Suitable water-soluble vinyl lactams are N-vinylpyrrolidone, 3-methyl-N-vinylpyrrolidone, 4-methyl-N-vinylpyrrolidone, 5-methyl-N-vinylpyrrolidone, N- Vinylpyridone, N-vinylpiperidone, N-vinylcaprolactam, preferably N-vinylpyrrolidone. The vinyllactam is used in an amount of from 30 to 90% by weight, preferably from 50 to 90% by weight.
It is suitable for the production of water-soluble polymers in which the hydrophobic monomer content is from 10 to 70% by weight, preferably from 10 to 50% by weight, based on the monomer mixture. Suitable hydrophobic monomers are those having a solubility in water of from 1 to 100 g/l. Suitable hydrophobic monomers are, for example, vinyl acetate, vinyl propionate, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, t-butyl acrylate, methyl methacrylate, N-vinylcaprolactam, Ethyl acrylate, acrylonitrile or methacrylonitrile. The hydrophobic monomers are especially those which have a boiling temperature range of from 60 to 130 ° C at atmospheric pressure, so that they can be evaporated under polymerization conditions. Even at a boiling point slightly lower than the polymerization temperature, the hydrophobic monomer can enter the gas phase with the solvent in the case of having sufficient miscibility with the solvent and boiling of the solvent. A preferred hydrophobic monomer is vinyl acetate.