Effect of Reaction Conditions on Synthesis and Properties of MultiArm Star-Branched Polyisobutylenes ROBSON F. STOREY, KELLY A. SHOEMAKE * The University of Southern Mississippi, Department of Polymer Science, Box 10076, Hattiesburg, Mississippi 39406 Received 21 February 1997; accepted 13 August 1997 ABSTRACT: A series of multiarm star-branched polyisobutylenes was synthesized from narrow polydispersity arms with molecular weights ranging from 12,000 to 60,000 g/mol, via living carbocationic polymerization using the cumyl chloride/TiCl 4 /pyridine initiating system and divinylbenzene (DVB) as core-forming comonomer. The effect on star develop- ment of arm molecular weight, temperature, solvent composition, and DVB concentration was studied. The rate of star formation and the weight-average number of arms per star polymer, N V w , were found to scale inversely with arm molecular weight; N V w Å 60 was attained for 13,100 g/mol arms, but N V w Å 2.5 for 60,000 g/mol arms. It was established that star formation was much faster at 0807C compared to 237C, regardless of solvent composition. For hexane : methyl chloride (MeCl) solvent compositions containing from 40 to 60 vol % MeCl, star–star coupling was observed at 0807C, but not at 237C, even after 312 h; for the most polar 40 : 60 hexane : MeCl composition, star–star coupling was so extensive at 0807C that gelation was observed after only 44 h. The rate of star formation was found to be substantially higher in 60 : 40 hexane : MeCl compared to 60 : 40 hexane : methylene chloride (MeCl 2 ). Some reactions containing MeCl were immediately warmed to 237C after DVB addition, and the MeCl thus volatilized was replaced with either MeCl 2 or hexane for the duration of the star-forming reaction. Slightly higher rates were consistently observed when MeCl 2 was the replacement solvent. The strong influence of initial MeCl content on rate of star formation was found to persist throughout the star- forming reaction, even when the solvent was immediately converted to 100% hexane. The fraction of arms that remained unlinked into stars was found to be higher at the higher temperature and at lower solvent polarity. Regardless of solvent or temperature, the residual arm fraction was approximately the same at a given stage of star development as measured by the average number of arms per star. One star sample was produced with the UV-transparent 2-chloro-2,4,4-trimethylpentane initiator; analysis showed that the residual arm fraction had approximately the same UV absorbance as the star fraction, indicating efficient crossover to DVB and the potential for approximately quantitative arm incorporation given sufficient time. q 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 471–483, 1998 Keywords: Multiarm star-branched polyisobutylenes; reaction conditions; synthesis INTRODUCTION from a central branching point. These polymers have been synthesized, in most cases by living Star-branched polymers consist of multiple, lin- anionic chain polymerization, 1,2 using one of three ear polymer chains ( arms ) radiating outwardly basic procedures, namely, ( 1 ) linking of mono- functional living chains using a multifunctional * Current address: Georgia Pacific, 2883 Miller Rd., Deca- linking (terminating) agent; (2) use of a multi- tur, GA 30035 functional initiator ; and ( 3 ) sequential addition Correspondence to: R. F. Storey of a difunctional vinyl monomer, such as divinyl- Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 36, 471–483 (1998) q 1998 John Wiley & Sons, Inc. CCC 0887-624X/98 / 030471-13 benzene ( DVB ) , to monofunctional living chains. 471 8g66 97033t / 8g66$$033T 12-19-97 15:09:30 polca W: Poly Chem