Low haze transparent compositions and processes for preparing them

Low haze impact-resistant transparent compositions which comprise:

• (a) 40-99% by weight of a thermoplastic resin based on homopolymers and/or copolymers of alkyl esters of methacrylic acid with alkyl esters of acrylic acid, wherein the alkyl group contains from 1 to 8 carbon atoms;
• and
• (b) 60-1% by weight of polymeric particles having multilayer structure, diameters in the range from 100 to 300 nm, and coefficient of variation, relative to the average value of particle diameters, less than 0.1, constituted by 8-30% by weight of a central core, comprising:
• a central core based on a cross-linked elastomer intimately blended with an acrylic resin as defined in (a) wherein the amount of elastomer is within the range of from to 0.3 to 7% by weight of the entire particle;
• optionally a first layer of said acrylic resin grafted on said central core;
• a second layer of cross-linked elastomer grafted on said first resin layer;
• and
• a third layer of resin grafted on said second layer of cross-linked elastomer;
• said core being made by the following steps:
• (i) preparing a seed of elastomer in aqueous emulsion by feeding and polymerizing monomers selected from the alkyl or alkoxylalkyl esters of acrylic acid, wherein the alkyl group contains from 1 to 8 carbon atoms, and those containing a double ethylenic unsaturation, optionally in mixture with amounts of vinylic monomer of up to 30% by weight, and containing from 0.5 to 2% by weight of grafting monomers;
• (ii) swelling of the above seed, by absorption of one or more monomers selected from the alkyl esters of methacrylic acid, wherein the alkyl group contains from 1 to 8 carbon atoms, optionally in admixture with minor amounts of C.sub.1 -C.sub.8 alkyl or alkoxy-alkyl esters of acrylic acid, and containing 0.05-2% by weight of grafting monomers, said swelling being carried out to such an extent to obtain final particles with the above-mentioned coefficient of variation of diameters;
• and
• (iii) polymerizing said alkyl esters absorbed in the elastomeric seed, to yield the central core.