Biomacromolecular Engineering: Design, Synthesis and Characterization. One-pot Synthesis of Block Copolymers of Arborescent Polyisobutylene and Polystyrene

Novel arborescent block copolymers comprising of an arborescent rubbery polyisobutylene (PIB) midsegment and glassy polystyrene (PSt) end blocks were prepared by sequential addition of monomers. Synthesis was conducted by the use of 4-(2-methoxyisopropyl) styrene as an inimer-type initiator in conjunction with titanium tetrachloride (TiCl4) in 60:40 (v/v) methylcyclohexane/methyl chloride solvent mixture. Isobutylene was polymerized for 1–2 hr and then prechilled styrene in the same solvent mixture was sequentially added with select additives to the reaction flask. The recovered block copolymers were purified and then characterized by 1H-NMR, size exclusion chromatograph (SEC), tensile test, atomic force Microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Samples with 16.4–32.8 wt% PSt and Mn = 47,600–125,900 g/mol (Mw/Mn = 2.02–4.45) displayed thermoplastic elastomeric properties with 5–9.2 MPa tensile strength and 490–920% elongation. The arborescent block copolymers showed surface morphologies ranging from spherical to cylindrical/lamellar nanometer-sized discreet PSt phases dispersed in a continuous PIB matrix, with a 10 nm PIB layer on the surface. Drug release profiles of paclitaxel from two arborescent blocks were found to be similar to that measured from Translute®. Copyright © 2006 John Wiley & Sons, Ltd