Synthesis of Thermoplastic Elastomers by Yttrium-Catalyzed IsospecificTrans-1,4-Polymerization of (E)-1,3-Pentadiene

Abstract Regio- and stereoselectivity control in the polymerization of 1,3-conjugated dienes is of much interest and importance. We report herein for the first time the isospecific trans-1,4-selective living polymerization of (E)-1,3-pentadiene (EPD) by a C5H5-ligated yttrium catalyst (C5H5)Y(CH2C6H4-NMe2-o)2/[Ph3C][B(C6F5)4], which afforded crystalline isotactic-trans-1,4-polypentadiene showing good elastic properties without vulcanization (tensile strength up to 7.1 MPa with elongation at break of 2600%). The DFT calculations revealed that the stereoselectivity was mainly due to steric repulsion between the C5H5 ligand in the catalyst and the methyl group in EPD.