| 摘要 |
The present invention provides a vinylpyrrolidone (co)polymer excellent in the color tone and the thermal yellowing resistance despite its low molecular weight. The vinylpyrrolidone (co)polymer, according to the present invention, is a vinylpyrrolidone (co)polymer which has a Hazen value of not more than 30 in the form of 5% aqueous solution and a K value of not more than 60 and is obtained by a process including the step of polymerizing a polymerizable monomer component with an azo compound initiator and/or an organic peroxide initiator, wherein the polymerizable monomer component includes N-vinylpyrrolidone, and wherein the azo compound initiator has a chemical structure as shown by -C(CH3)2-N=N-C(CH3)2-, and wherein the organic peroxide initiator is soluble in water or ethyl alcohol of 25° C. in an amount of not smaller than 3 weight %.
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