Abstract: Suspension polymers ofa) from 80 to 100% by weight of methyl methacrylate andb) from 0 to 20% by weight of further monomers capable of undergoing free radical polymerization,are obtainable by polymerization at a temperature of from 100.degree. to 140.degree. C. which is virtually constant over the major part of the polymerization time by means of an initiator system consisting of two or more peroxide initiators I having different decomposition temperatures T at which in each case half of the initiator has decomposed after 1 hour, whereinthe initiator I.sub.min having the lowest decomposition temperature has a decomposition temperature T.sub.min of from 60.degree. to 100.degree. C.,the initiator I.sub.max having the highest decomposition temperature has a decomposition temperature T.sub.max of from 100.degree. to 140.degree. C., the difference between T.sub.max and T.sub.min is greater than 10.degree. C. and I.sub.max is a perketal of the general formula (1) ##STR1## where R.sup.1 and R.sup.

Abstract: Emulsion graft copolymers composed ofa) 2-10% by weight of a core composed of80-99.99% by weight of methyl methacrylate (I),0.01-5% by weight of allyl methacrylate (II),0-19.99% by weight of other monofunctional comonomers (III) and0-3% by weight of other di- or polyfunctional comonomers (IV),b) 15-50% by weight of a first shell composed of60-89.99% by weight of a C.sub.1 -C.sub.20 -alkyl acrylate (V),10-39.99% by weight of a vinylaromatic monomer (VI),0.01-5% by weight of II,0-10% by weight of I and/or III,0-3% by weight of IV,c) 5-20% by weight of a second shell with a composition as indicated under (a),d) 15-50% by weight of a third shell with a composition as indicated under (b),e) 15-30% by weight of a fourth shell composed of80-99.95% by weight of I,0.05-2% by weight of a regulator (VII) and0-19.95% by weight of III,are suitable as additives to increase the impact strength of thermoplastic compositions.