Synthesis and characterization of well-defined poly(alpha-methylstyrene)-b-poly(dimethylsiloxane) block copolymers

The anionic synthesis is reported for AB and ABA narrow distribution block copolymers of poly(alpha -methylstyrene) (PAMS, A) and poly(dimethylsiloxan e) (PDMS, B) with molecular weights ranging between 8.2 x 10(3) and 1.9 x 1 0(5). 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 degreesC followed by the sequential addition of styre ne, 2-3 equiv of 2,2,5,5-tetramethyl-2,5-disila-1-oxacyclopentane (EDS) at -20 degreesC, and hexamethylcyclotrisiloxane (D-3) at 25 degreesC. A more c onvenient synthesis without the use of styrene is the direct end-capping of living PAMSLi with EDS at -10 "C followed by the polymerization of DQ at 2 5 degreesC. The living block copolymers were then end-capped with Me3SiCl o r coupled with Me2SiCl2 to give matching AB and ABA narrow distribution blo ck copolymers. The glass transition temperatures of the PAMS blocks were at least 10 degreesC higher than that of the PAMS-PS blocks.