The invention is aimed at providing a synthesis method for poly-N-vinylcaprolactam, so as to solve the problems of long time and toxic
solvent in the present
polymerization process. The method comprises the following steps of: A, reaction: performing reduced pressure
distillation on N-vinylcaprolactam, then adding the N-vinylcaprolactam, an initiator azodiisobutyl imidazoline
hydrochloride and a
solvent in a three-neck flask, charging
nitrogen to protect and starting to stir, and heating to 65-80 DEG C, wherein the
solvent is one of absolute ethyl
alcohol and water, and the usage amount of the initiator is 0.1-0.5 folds of the
mass of the N-vinylcaprolactam; and B, post-treatment:
steaming away the solvent at 50 DEG C and under a reduced pressure of 0.08 MPa to obtain a colourless sticky liquid, adding
tetrahydrofuran to dissolve, and separating out by n-
hexane, standing, removing the supernatant, adding ethyl
ether to precipitate, filtering, and
drying at 30 DEG C to obtain the product poly-N-vinylcaprolactam. The synthesis method provided by the invention eliminates the harm on environment by the utilization of toxic solvent; and the average molecular weight detected by GPC (
gel permeation chromatography) is greater than 10000-30000.