Provided are polymer particles composed of a terminally branched copolymer represented by the following general formula (1) and having a number average molecular weight of not more than 2.5 × 10 4 , wherein, in the formula, A represents a polyolefin chain； R 1 and R 2 each represent a hydrogen atom or an alkyl group having 1 to 18 carbon atoms, and at least one of R 1 and R 2 is a hydrogen atom； and X 1 and X 2 may be the same or different, and each a linear or branched polyalkylene glycol group.
