RAPID COMMUNICATION Synthesis of an Exact Graft Copolymer of Isoprene and Styrene with Two Branches STELLA PARASKEVA, NIKOS HADJICHRISTIDIS Department of Chemistry, University of Athens, Panepistimiopolis, Zografou, 15771 Athens, Greece Received 4 October 1999; accepted 19 December 1999 Keywords: exact graft copolymer; anionic polymerization; living linking agent; 1,4-bis(phenylethenyl)benzene INTRODUCTION The ultimate synthetic goal for comb-shaped polymers is the control of all architectural parameters related to the comb structure (exact comb). These parameters are the molecular weight of the backbone, the molecular weight (same or different) of the branches, and the number and position of the branches along the back- bone chain. Although the control of the molecular weight of the backbone, the molecular weight of the branch, and the number of identical branches has al- ready been achieved (e.g., see ref. 1), controlling the position of the branches (of the same or different mo- lecular weight) is a challenging problem of polymer chemistry. Until now, only exact comb-shaped polymers with one branch have been prepared by anionic polymeriza- tion and controlled chlorosilane chemistry 2,3 or living linking procedures. 4,5 Comb homopolymers (H-shaped) and copolymers (-shaped) with two equal branches have also been prepared 6 with difunctional living chains and controlled chlorosilane chemistry, but the two junction points are equidistant from the chain ends. Recently, 7 multigraft copolymers with regularly spaced junction points were prepared by step-growth polymerization of ,-dilithium chains with dichloro- methylsilyl end-capped chains. This method does not allow different distances between the junction points along the backbone. In this communication, we report the synthesis of an exact graft copolymer (EGC) of isoprene and styrene with two branches (Scheme 3). The synthesis is based on a method developed by Quirk et al. 8 for the synthesis of an EGC of styrene and butadiene with one branch and proposed for the synthesis of an EGC with two branches. The difference is that we used 1,4-bis(phen- ylethenyl)benzene (PEB) instead of the meta compound (mPEB) used by Quirk et al. EXPERIMENTAL Methyllithium (Aldrich), methyltriphenylphospho- nium iodide (Aldrich), and 1,4-dibenzoylbenzene (Al- drich) were used for the preparation of the linking agent PEB by the Wittig reaction according to litera- ture procedures. 9 PEB was purified by column chroma- tography with activated silica gel 60 (Merck; 230 – 400 mesh) as the support and a mixture of hexane/methyl- ene chloride (5/1 v/v) as the eluent. The chromato- graphic process was monitored by thin-layer chroma- tography (silica gel 60, fluorescent indicator; Ma- cherey–Nagel). The sample showing only one spot, in a shortwave UV light, was collected, and the mixture of solvents was removed by distillation under reduced pressure. The white crystalline product (mp 136.8°C) was kept in a dry box to prevent oxidation of the double bonds. PEB was diluted with benzene via high-vacuum Correspondence to: N. Hadjichristidis (E-mail: nhadjich@ atlas.uoa.gr) Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 38, 931–935 (2000) © 2000 John Wiley & Sons, Inc. 931