High impact polystyrene having high modulus and resistance to environmental stress cracking

A composition comprising:

• a rubber-modified monovinyl aromatic polymer
• i) including about 90 weight percent or more of a monovinyl aromatic polymer matrix, based on the total weight of the rubber-modified monovinyl aromatic polymer;
• and
• ii) from about 2 to about 7.5 weight percent of one or more elastomeric polymers, based on the total weight of the composition;
• and having a volume average diameter of 5 μm to 30 μm;
• and
• greater than 2 weight percent to 7 weight percent mineral oil, based on the total weight of the compositions;
• wherein the monovinyl aromatic polymer matrix is derived from one or more monovinyl aromatic monomers, and the monovinyl aromatic polymer matrix has a sufficiently high molecular weight so that the retention in the elongation at break after 10 days in corn oil at 1% strain is about 15% or more;
• the monovinyl aromatic polymer matrix is sufficiently rigid so that the composition has a tensile modulus of about 1500 MPa or more as measured according to ISO 527-2;
• and
• the molecular weight of the monovinyl aromatic polymer matrix is characterized by a weight average molecular weight of 200,000 to about 280,000 g/mol and a polydispersity index of 2.7 or more.

A composition consisting of:

• a rubber-modified monovinyl aromatic polymer consisting of
• i) about 90 weight percent or more of a monovinyl aromatic polymer matrix, based on the total weight of the rubber-modified monovinyl aromatic polymer;
• and
• ii) from about 2 to about 7.5 weight percent of one or more elastomeric polymers, based on the total weight of the composition;
• and having a volume average diameter of 5 μm to 30 μm;
• and
• greater than 2 weight percent to 7 weight percent mineral oil, based on the total weight of the compositions;
• wherein the monovinyl aromatic polymer matrix is derived from one or more monovinyl aromatic monomers, and the monovinyl aromatic polymer matrix has a sufficiently high molecular weight so that the retention in the elongation at break after 10 days in corn oil at 1% strain is about 15% or more;
• the monovinyl aromatic polymer matrix is sufficiently rigid so that the composition has a flexural modulus of about 1500 MPa or more as measured according to ISO 178;
• and
• the molecular weight of the monovinyl aromatic polymer matrix is characterized by a weight average molecular weight of 200,000 to about 280,000 g/mol and a polydispersity index of 2.7 or more.

A method of forming a composition comprising the steps of:

• i) polymerizing one or more monovinyl aromatic monomers in the presence of one or more elastomeric polymers to form a rubber-modified monovinyl aromatic polymer including a monovinyl aromatic polymer matrix characterized by a weight average molecular weight of 200,000 to about 280,000 g/mol and a polydispersity index of 2.7 or more;
• and
• ii) preparing a polymeric composition by blending at least the rubber-modified monovinyl aromatic polymers and 2 weight percent to 7 weight percent of mineral oil;
• wherein the the rubber-modified monovinyl aromatic polymer includes:
• i) about 90 weight percent or more of the monovinyl aromatic polymer matrix, based on the total weight of the polymeric composition;
• and
• ii) from about 2 to about 7.5 weight percent of the one or more elastomeric polymers, based on the total weight of the rubber-modified monovinyl aromatic polymer;
• wherein the one or more elastomeric polymers has a volume average diameter of 5 μm to 30 μm;
• the monovinyl aromatic polymer matrix has a sufficiently high molecular weight so that the retention in the elongation at break after 10 days in corn oil at 1% strain is about 15% or more;
• and
• the monovinyl aromatic polymer matrix is sufficiently rigid so that the composition has a tensile modulus of about 1500 MPa or more as measured according to 527-2.