Patent ID: 8349961

Claim:
A process for the preparation of a high-impact vinylaromatic (co)polymer grafted on an elastomer, which comprises: a) dissolving a first portion (X 1 ) of an elastomer in a liquid phase comprising a vinylaromatic monomer and optionally solvent of polymerization to produce a solution; b) adding to the solution from as a functionalization and polymerization catalytic system comprising a free radical initiator (G), with F functionality, capable of extracting a proton from the elastomer polymeric chain and a stable free radical initiator comprising the group ═N—O or the group ═N—O—R′ (I), with molar ratios (I)G·F from 1 to 3, F being equal to the number of functional groups per initiator molecule which, through decomposition, produce two free radicals, wherein R′ is an (iso)alkyl radical C 1 -C 6 or an aryl alkyl radical C 7 -C 20 , optionally containing heteroatoms; (i) functionalizing the first portion (X 1 ) of elastomer with the catalytic system by heating, while stirring, the mixture from b) at a temperature from 80 to 110° C. to produce a functionalized elastomer; (ii) mixing of the functionalized elastomer from (i) with to second portion (X 2 ) of the elastomer to obtain an elastomeric homogeneous composition; (iii) optionally mixing the elastomeric homogeneous composition from (ii) with additional liquid phase essentially constituted by a vinylaromatic monomer and/or solvent of polymerization, (iv) polymerizing the vinylaromatic monomer, at a temperature higher or equal to 120° C., wherein the weight ratio of the vinylaromatic monomer/solvent is from 60/40 to 100/0 and the weight ratio X 1 +X 2 /vinylaromatic monomer is greater than or equal to 8/92; (v) recovering, at the end of the polymerization, a vinylaromatic (co)polymer grafted on the elastomer, wherein the vinylaromatic (co)polymer grafted on the elastomer comprises a rigid matrix formed by a vinylaromatic (co)polymer and an elastomeric phase dispersed in the matrix in the form of particles with a strictly bimodal diameter distribution, wherein the particles comprise a first class having a volume average dimension of from 0.15 to 0.50 μm and a second class having a volume average dimension of from 1 to 8 μm, with a total absence of particles having dimensions between the volume average dimension of the first and second class of particles.