Kuraray Co., Ltd.

Kazutoshi Mishima

Kazuhiko Maekawa

Takumi Takayama

Hiroyuki Konishi

Disclosed is a vinyl alcohol-based block copolymer that is a block copolymer composed of a vinyl alcohol-based polymer block (B-b) and a copolymer block (B-c) comprising a vinyl alcohol-based monomer unit and an acrylic acid-based monomer unit, wherein a content (Z) of the acrylic acid-based monomer unit relative to all monomer units is 0.05 to 20.0 mol %, the block copolymer has a saponification degree of 80 to 99.99 mol %, the block copolymer has a number-average molecular weight (Mn) of 20,000 to 440,000, the block copolymer has a molecular weight distribution (Mw/Mn) of 1.05 to 1.95, and a ratio (DP/DP) of a number-average polymerization degree (DP) of the vinyl alcohol-based polymer block (B-b) to the number-average polymerization degree (DP) of the block copolymer is 0.010 to 0.999. The copolymer has a fine balance derived from the copolymer block (B-c) of having a superior solubility in water while being unlikely to undergo thickening or gelation due to pH fluctuation, and also has high mechanic strength derived from the vinyl alcohol-based polymer block (B-b).

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Kurashiki, Japan

Kazutoshi Mishima