Thermoplastic modacrylic resin and thermoplastic modacrylic resin composition including same

A thermoplastic modacrylic resin comprising a copolymer, the copolymer containing:

• a polymer (A) formed of a modacrylic resin containing a constituent unit derived from acrylonitrile (a1) and a constituent unit derived from an ethylenically unsaturated monomer (a2) other than the acrylonitrile (a1), and
• a polymer (B) composed of a polymer containing a constituent unit derived from acrylonitrile (b1) and a constituent unit derived from an ethylenically unsaturated monomer (b2) other than the acrylonitrile (b1),
• wherein:
• the polymer (B) has a first terminal and a second terminal, and is bonded to the polymer (A) at the second terminal,
• the polymer (B) contains 70 mol % or more of all constituent units derived from the acrylonitrile (b1) in a terminal region including the first terminal and including half of the number of all constituent units in the polymer (B),
• a content of the constituent unit derived from the acrylonitrile (b1) is 3 mol % or more and 30 mol % or less with respect to all the constituent units in the polymer (B),
• in the thermoplastic modacrylic resin, a content of the constituent unit derived from the acrylonitrile (a1) is 35 mass % or more and 84.5 mass % or less, a content of the constituent unit derived from the ethylenically unsaturated monomer (a2) is 15 mass % or more and 64.5 mass % or less, and a content of the polymer (B) is 0.5 mass % or more and 40 mass % or less.