US 5,312,575 AGranted

Microagglomeration of impact modifiers

AssigneeRohm and Haas Company

InventorMorris C. Wills

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Abstract

Core/shell impact modifiers, useful in toughening poly(vinyl chloride) and other thermoplastics, are prepared at small particle sizes by an emulsion polymerization process, agglomerated by a novel technique which has little effect on emulsion solids, are further encapsulated by a final shell, and are isolated by spray-drying or coagulation. The isolated particles are readily re-dispersed to their original particle size in the matrix polymer.

Claims16

Dependent claims

A process for preparing a core/shell impact modifier which comprises:

a) forming by emulsion polymerization a latex of rubbery polymer particles having a glass transition temperature below about -20 degrees C. and a particle size below about 100 nm diameter, the rubbery polymer particle being formed from at least 75 weight percent of units derived from butadiene, C.sub.2 -C.sub.8 lower alkyl esters of acrylic acid, or mixtures thereof;
b) forming by sequential emulsion polymerization in the presence of the latex of rubbery polymer particle, under conditions wherein essentially no new polymer particles are formed, a latex of first core/intermediate shell polymer particles, the intermediate polymer shell having a glass transition temperature above about -20 degrees C., the intermediate shell being formed predominately from units derived from methyl methacrylate, and the intermediate shell being from about 5% to about 20% by weight of the first core/intermediate shell polymer particles;
c) agglomerating the latex of first core/intermediate shell polymer particles to form a latex of agglomerated particles of at least 150 nm diameter, the solids content of the latex of first core/intermediate shell polymer particles being no higher than about 40 percent, and the solids content of the latex of agglomerated particles being no higher than about 30%.
d) forming an encapsulating shell of hard polymer having a glass transition temperature at least 60 degrees C. in a final core/shell polymer by sequential emulsion polymerization onto the agglomerated particles, under conditions wherein essentially no new polymer particles are formed, the encapsulating shell being formed predominately from units derived from methyl methacrylate, the encapsulating shell comprising from about 5 to about 20% by weight of the final core/shell polymers, the total shell content being now lower than about 14% by weight of the final core/shell polymer, the sequential emulsion polymerization being conducted in the latex of the agglomerated particles, and the final core/shell polymer remaining in latex form;
and, if desired,
e) isolating the final core/shell polymer.

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Dependencies are inferred from the claim text.

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Abstract

A process for preparing a core/shell impact modifier which comprises:

a) forming by emulsion polymerization a latex of rubbery polymer particles having a glass transition temperature below about -20 degrees C. and a particle size below about 100 nm diameter, the rubbery polymer particle being formed from at least 75 weight percent of units derived from butadiene, C.sub.2 -C.sub.8 lower alkyl esters of acrylic acid, or mixtures thereof;
b) forming by sequential emulsion polymerization in the presence of the latex of rubbery polymer particle, under conditions wherein essentially no new polymer particles are formed, a latex of first core/intermediate shell polymer particles, the intermediate polymer shell having a glass transition temperature above about -20 degrees C., the intermediate shell being formed predominately from units derived from methyl methacrylate, and the intermediate shell being from about 5% to about 20% by weight of the first core/intermediate shell polymer particles;
c) agglomerating the latex of first core/intermediate shell polymer particles to form a latex of agglomerated particles of at least 150 nm diameter, the solids content of the latex of first core/intermediate shell polymer particles being no higher than about 40 percent, and the solids content of the latex of agglomerated particles being no higher than about 30%.
d) forming an encapsulating shell of hard polymer having a glass transition temperature at least 60 degrees C. in a final core/shell polymer by sequential emulsion polymerization onto the agglomerated particles, under conditions wherein essentially no new polymer particles are formed, the encapsulating shell being formed predominately from units derived from methyl methacrylate, the encapsulating shell comprising from about 5 to about 20% by weight of the final core/shell polymers, the total shell content being now lower than about 14% by weight of the final core/shell polymer, the sequential emulsion polymerization being conducted in the latex of the agglomerated particles, and the final core/shell polymer remaining in latex form;
and, if desired,
e) isolating the final core/shell polymer.

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