Preparation of polymers of vinylaromatic compounds under superatmospheric pressure in the presence of volatile hydrocarbons

A process for preparing a polymer of vinylaromatic compounds at from 0 to 150° C. in the presence of a metallocene complex as catalyst, wherein the metallocene catalyst is a metallocene complex of formula II

• wherein
• R7 to R11 are hydrogen, C1-C10-alkyl, 5- to 7-membered cycloalkyl which in turn may bear C1-C6-alkyl groups as substituents, C6-C15 -aryl or aralkyl or two adjacent radicals may also together form a cyclic group having from 4 to 15 carbon atoms, or Si (R12)3, where R12 i s C1-C10-alkyl, C6-C15-aryl or C3-C10- cycloalkyl,
• M is a metal of transition groups Ill to VI of the Periodic Table of the Elements or a lanthanide metal,
• Z1 to Z5 are hydrogen, halogen, C1-C10-alkyl, C6-C15-aryl, C1-C10-alkoxy or C1-C50-aryloxy, and
• z1 to z5 are 0, 1, 2, 3, 4 or 5, where the SUM z1+z2+z3+z4+z5 corresponds to the valence of M minus 1,
• which is in a supported form, the support being selected from the group consisting of silica gels, finely divided polyolefins, polyethylene glycol, polybutylene terephthalate, polyethylene terephthalate, polyvinyl alcohol, polystyrene, polybutadiene, polycarbonates and copolymers thereof,
• and the polymerization is carried out at a pressure of from 5 to 300 bar in the presence of an aliphatic C1-C4-hydrocarbon and, as cocatalyst, a coordination complex selected from the group consisting of
• i) a strong uncharged Lewis acid of the formula III
• M1X1X2X3 (III)
• wherein
• M1 is an element of main group III of the Periodic Table, and
• X1, X2 and X3 are hydrogen, C1-C10-alkyl, C6--C15-aryl, alkylaryl, arylalkyl, haloalkyl, or haloaryl each having from 1to 10 carbon atoms in the alkyl radical and from 6 to 20 carbon atoms in the aryl radical, or fluorine, chlorine, bromine or iodine, and
• ii) an ionic compound having a Lewis acid cation of the formula IV
• [(Aa−)Q1Q2. . . Qz]d− (IV)
• wherein
• A is an element of main groups I to VI or transition groups I to VIII of the Periodic Table,
• Q1 to Qz are radicals bearing a single negative charge selected from the group consisting of C1-C28-alkyl, C6-C15-aryl, C1-C28-alkyl-C6-C20-aryl, C6-C20-aryl-C1-C28-alkyl, C1-C28-haloalkyl, C6-C20-haloaryl, halogen, C1-C28-alkoxy, C6-C15-aryloxy, silyl, rnercaptyl, C1-C10-cy-C1-C10-cycloalkyl and C1-C10-cycloalkyl which is substituted by C1-C10-alkyl,
• a is an integer from 1 to 6,
• z is an integer from 0 to 5, and
• d corresponds to the difference a-z, but d is greater than or equal to 1 with the proviso that the metallocene complex cannot be Ag[B(C6H5)4].