Star-block polymers of multiple polystyrene-b-polyisobutylene arms radiating from a polydivinylbenzene core

The synthesis together with mechanical property and rheological characteriz ation of novel star-block copolymers comprising multiple polystyrene (PSt)- b-polyisobutylene (PIB) arms emanating from polydivinylbenzene (PDVE) cores are described. The synthesis strategy involved the preparation of PSt-b-PI B-Cl-t (i.e., diblocks fitted with a tert-chlorine terminus at the PIB end) by sequential living block polymerization of St and IB, ionizing the -Cl-t terminus by TiCl4, at room temperature, and linking the PSt-b-PIBcircle pl us prearms by DVB. Molecular characterization was effected mainly by triple detector GPC including refractive index (RI)-, UV-, and laser light scatte ring (LLS)-GPC traces. Evidence for intra- and intermolecular reactions bet ween individual star-blocks is presented and a comprehensive mechanism to t he final product is proposed. The stress-strain behavior of star-blocks has been studied and is compared with those of linear triblocks (i.e., two-arm stars) of similar arm molecular weights and composition in the 25-70 degre es C range. The mechanical properties of star-blocks are invariably superio r to those of the triblocks over the entire temperature range. The rheologi cal behavior of star-blocks and linear triblocks has been compared in terms of dynamic viscosity at various frequencies. Star-blocks exhibit significa ntly lower melt viscosities than their linear counterparts, which signals i mproved processing behavior. We have also compared select rheological prope rties of the commercially available PSt-b-(hydrogenated-1,4-polybutadiene)- b-PSt thermoplastic elastomer (Kraton G 1650) with those of PIB-based linea r triblocks and multiarm star-blocks of similar glassy/rubbery compositions . The melt viscosities of PIB-based triblocks and star-blocks were signific antly lower than that of Kraton G over the entire frequency range investiga ted. (C) 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2235-22 43, 1999.