Patent Document ID: 9733564
Application ID: 13879737
Patent Flag: 1

Claim One:
1. A method for producing a polymer by copolymerization of at least two monomers α 1 to α n having different copolymerization reactivities to obtain a polymer (P) comprising at least two monomer units α′ 1 to α′ n in a target composition having a content ratio of the monomer units α′ 1 to α′ n of (P) according to α′ 1 :α′ 2 :. .. :α′ n ; the method comprising: first feeding dropwise to a polymerization reactor at least one solution Sa comprising the at least two monomers α 1 to α n in a first composition ratio such that a proportion of a monomer having the lowest copolymerization reaction rate among the at least two monomers α 1 to α n is greater than in the target composition; adding to the reactor dropwise a polymerization initiator either after the addition of the at least one solution Sa or simultaneous with the addition of Sa, feeding to the reactor at least one solution Tb comprising the at least two monomers α 1 to α n in a second composition ratio equal to the target composition either simultaneous with the start of the solution Sa or after the addition of Sa wherein the addition of Sa is complete before the addition of Tb; and after completion of the addition of solution Tb, feeding at least one solution Uc comprising the at least two monomers α 1 to α n monomers in a third composition such that a proportion of the monomer having the lowest copolymerization reaction rate is smaller than in the target composition, wherein when a period of time between the start and completion of dropwise addition of the solution Uc is defined as a later dropping time; a value obtained by dividing the total feed amount of monomers in the later step by the later dropping time is defined as an average feed rate, 50 to 95% of the monomers of U c are fed in a higher rate than the average feed rate during a high rate feed period of time between 0% to k % of the later dropping time wherein k is 5 to 95%; wherein n is an integer of at least 2, when a standard time is defined as a time elapsed from the start of the addition of the polymerization initiator to completion of the addition of Tb, the polymerization initiator is added at such rate that 30 to 90% of the total feed of the polymerization initiator is added during the initial 5 to 20% of the standard time, and a total amount of the monomers in the at least one solution Uc is from 0.1 to 10 mass % of a total feed amount of the monomers.