Synthesis and Characterization of Well-Defined Poly(α-methylstyrene)-b-poly(dimethylsiloxane) Block Copolymers

Abstract

The anionic synthesis is reported for AB and ABA narrow distribution block copolymers of poly(α-methylstyrene) (PAMS, A) and poly(dimethylsiloxane) (PDMS, B) with molecular weights ranging between 8.2 × 103 and 1.9 × 105. In one approach living PAMS end-capped with a short polystyrene block (PAMS−PSLi) was obtained by the tert-butyllithium initiated polymerization of AMS in THF at −78 °C followed by the sequential addition of styrene, 2−3 equiv of 2,2,5,5-tetramethyl-2,5-disila-1-oxacyclopentane (EDS) at −20 °C, and hexamethylcyclotrisiloxane (D3) at 25 °C. A more convenient synthesis without the use of styrene is the direct end-capping of living PAMSLi with EDS at −10 °C followed by the polymerization of D3 at 25 °C. The living block copolymers were then end-capped with Me3SiCl or coupled with Me2SiCl2 to give matching AB and ABA narrow distribution block copolymers. The glass transition temperatures of the PAMS blocks were at least 10 °C higher than that of the PAMS−PS blocks.