Polymeric particles and their preparation
AssigneeTioxide Group Limited
InventorsGerald K. Chip, Alfred Rudin
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Abstract
Swollen core/sheath polymeric particles are disclosed having one or more voids in the core formed by reaction with a base such as sodium hydroxide. The sheath contains styrene or similar monomer polymerized in an amount greater than 25 mole percent and the polymer is free of acid groups. The core contains acid groups. Swelling is effected at an elevated temperature and in the absence of an organic solvent. The swollen particles on drying in a paint or other composition have air in the voids and act then as opacifying agents.
Claims14
A process for the preparation of core/sheath polymer particles which comprises establishing a monomer system of at least one ethylenically unsaturated monomer with acid functionality, polymerising said system in the form of an aqueous emulsion to form core particles, establishing an aqueous dispersion of said core particles and a nonionic monoethylenically aromatic substituted monomer or a mixture of monomers containing more than 25 mole per cent of said nonionic monomer and said nonionic monomer or mixture of monomers being free of polymerisable acid groups and effecting polymerisation of said nonionic monomer or monomer mixture to deposit on said core particles a hard sheath free of acid groups, mixing said core/sheath particles so formed with a non-volatile fixed or permanent base in the absence of organic solvent to swell said cores to generate therein one or more voids.
Dependencies are inferred from the claim text.