Abstract: The specification discloses a process for cationic polymerization of vinyl aromatic monomers, adhesive compositions containing polymers made by the process and use of the polymers as processing aids for thermoplastic polymers. In the process, a vinyl aromatic monomer is dissolved in an organic solvent containing a complex comprising an in situ formed ester of an unsaturated carboxylic acid and a Lewis acid to provide a polymer having a softening point above about 125.degree. C. and a polydispersity index above about 2.0. Surprisingly, the Lewis acid/acrylate complex causes the reaction to proceed with reduced exothermicity and enables an increase in the softening point and yield as compared with a polymer made without the complex or using other complexes.