Process for producing high molecular weight monovinylidene aromatic polymers

A process for producing a monovinylidene aromatic polymer having molecular weight (Mw) greater than 275,000 which comprises polymerizing a monomer mixture comprising a monovinylidene aromatic monomer in the presence of: A) from 10 to 2000 ppm by weight of at least one free radical generating, branching polymerization initiator; and B) from 10 to 2000 ppm of one or more organic gel reduction agent selected from the group consisting of: 1) mercaptans, terpenes, halocarbons and halohydrocarbons, such agent having up to 20 carbons, 2) distillate recovered from the reaction devolatilization process (recycle), and 3) mixtures of 1) and 2).