Styrene copolymers, polystyrene compositions, and injection-molded articles

A polystyrene resin composition which comprises a styrene copolymer and at least one additive, wherein the styrene copolymer has a weight average molecular weight of about 200,000 to 2,000,000;

• has 1 to 20 branching points in Z-average molecular weight;
• has no methyl ethyl ketone/methanol mixture-insoluble matter;
• has a methanol-soluble matter content of not more than 5% by weight;
• and has a melt flow rate (MFR:
• g/10 min.) not lower than the value A defined by the following equation:
• A=(13.2-0.11.times.VSP)/(2.5.times.10.sup.-4 .times.Mw.sup.0.7 -1.2)
• where VSP denotes the Vicat softening point (.degree.C.) and Mw denotes the weight average molecular weight of the styrene copolymer;
• and
• wherein said styrene copolymer is (i) a copolymer of a styrene compound and a compound having a plurality of vinyl groups or (ii) a copolymer of a styrene compound, a compound having a plurality of vinyl groups and a compound copolymerizable with the styrene compound;
• wherein said compound having a plurality of vinyl groups is included in an amount of about 100 to 1200 ppm by weight relative to said styrene copolymer.

A styrene copolymer having a weight average molecular weight of about 200,000 to 2,000,000;

• having 2 to 20 branching points in Z-average molecular weight;
• having no methyl ethyl ketone/methanol mixture-insoluble matter;
• having a methanol-soluble matter content of not more than 5% by weight;
• and having a melt flow rate (MIR:
• g/10 min.) not lower than the value A defined by the following equation:
• A=(13.2-0.11.times.VSP)/(2.5.times.10.sup.-4 .times.Mw.sup.0.7 -1.2)
• where VSP denotes the Vicat softening point (.degree.C.) and Mw denotes the weight average molecular weight of the styrene copolymer;
• and
• wherein said styrene copolymer is (i) a copolymer of a styrene compound and a compound having a plurality of vinyl groups or (ii) a copolymer of a styrene compound, a compound having plurality of vinyl groups and a compound copolymerizable with the styrene compound;
• wherein said compound having a plurality of vinyl groups is included in an amount of about 100 to 1200 ppm by weight relative to said styrene copolymer.

An injection-molded article prepared by injection-molding a polystyrene resin composition which comprises a styrene-copolymer and at least one additive, wherein the styrene copolymer has a weight average molecular weight of about 200,000 to 2,000,000;

• has 2 to 20 branching points in Z-average molecular weight;
• bas no methyl ethyl ketone/methanol mixture-insoluble matter;
• has a methanol-soluble matter content of not more than 5% by weight;
• and has a melt flow rate (MFR:
• g/10 min.) not lower than the value A defined by the following equation:
• A=(13.2-0.11.times.VSP)/(2.5.times.10.sup.-4 .times.Mw.sup.0.7 -1.2)
• where VSP denotes the Vicat softening point (.degree.C.) and Mw denotes the weight average molecular weight of the styrene copolymer;
• and
• wherein said styrene copolymer is (i) a copolymer of a styrene compound and a compound having a plurality of vinyl groups or (ii) a copolymer of a styrene compound, a compound having a plurality of vinyl groups and a compound copolymerizable with the styrene compound;
• wherein said compound having a plurality of vinyl groups is included in an amount of about 100 to 1200 ppm by weight relative to said styrene copolymer.