A macromonomer is a high molecular weight monomer having a polymerizable functional group. The macromonomer is characterized in that a graft copolymer can be easily synthesized by the copolymerization of the macromonomer with another monomer. When a graft copolymer is synthesized using the macromonomer, resins having different properties can be separately incorporated into a branch component and a trunk component respectively and moreover simply and with good purity. Therefore, various pressure-sensitive adhesive compositions obtained using this type of macromonomer are also proposed in the field of adhesives including pressure-sensitive adhesives.
For example, Patent Literature 1 (Japanese Patent Laid-Open No. 1-203412) discloses, as a resin composition for a pressure-sensitive adhesive having good pressure-sensitive adhesive properties such as tack, adhesive force, and cohesive force, a resin composition for a pressure-sensitive adhesive which comprises a graft copolymer obtained by the radical polymerization of a macromonomer having a number average molecular weight of 1000 to 100000 and a glass transition temperature of −20° C. or less, a radical polymerizable monomer having a hydroxyl group or a carboxyl group, and another monomer and in which the glass transition temperature of a trunk polymer is higher than the glass transition temperature of a branch polymer.
Patent Literature 2 (Japanese Patent Laid-Open No. 8-209095) discloses, as a method for improving durability and removability under high temperature and high humidity conditions, an adhesive obtained using a copolymer (weight average molecular weight 500000 to 2000000) of 0.2 to 3 parts by mass of a (meth)acryloyl group-containing macromonomer having a glass transition temperature of 40° C. or more and a number average molecular weight of 2000 to 20000, 57 to 98.8 parts by mass of an alkyl (meth)acrylate, 1 to 20 parts by mass of a functional group-containing monomer, and 0 to 20 parts by mass of another monomer copolymerizable with at least the alkyl (meth)acrylate.
Patent Literature 3 (Japanese Patent Laid-Open No. 11-158450) discloses, as an optionally pressure-sensitive adhesive composition that can be easily bonded to various adherends, can be cured after bonding to exhibit the same level of adhesive force as an adhesive, and is less likely to cause the overflow of the optionally pressure-sensitive adhesive from cut surfaces and the adhesion of the cut surfaces to each other in cutting processing, a curable optionally pressure-sensitive adhesive composition comprising an acrylic pressure-sensitive adhesive polymer obtained by the copolymerization of an alkyl (meth)acrylate monomer and a macromonomer having a number average molecular weight Mn of 1000 to 200000 and a glass transition point Tg of 30 to 150° C. that accounts for 1 to 30% by mass in all monomer components, a photocationic polymerizable compound, and a photocationic photopolymerization initiator.
Patent Literature 4 (Japanese Patent Laid-Open No. 2011-219582) proposes, as a pressure-sensitive adhesive that has excellent pressure-sensitive adhesiveness even when a high content of a filler is contained in the pressure-sensitive adhesive layer of a pressure-sensitive adhesive tape, and maintains pressure-sensitive adhesiveness even when exposed to high temperature, a pressure-sensitive adhesive containing a (meth)acrylic graft copolymer comprising a (meth)acrylic copolymer as a trunk polymer and comprising a (meth)acrylic macromonomer as a branch polymer, a crosslinking agent, and a filler.