Sequential Bulk Anionic Polymerization of Alpha-Methylstyrene and Isoprene to Form Diblock and Triblock Copolymers

alpha-Methylstyrene (AMS) is determined to polymerize anionically by initiation with sec-bultyllithium under bulk conditions with control of molecular weight depending on reaction time. Furthermore, the reactivity between AMS and isoprene in a mixture at a high AMS concentration (90% v/v) indicates a strong inclination for almost sole isoprene polymerization (>97%). The microstructure of the polyisoprene is determined to be predominately 1,4-polyisoprene in the bulk AMS polymerization. These results afford a sequential process for the formation of diblock and triblock copolymers whereby the anionic initiation of AMS in the bulk produces a living poly(alpha-methylstyrene) (PAMS) that upon addition of isoprene results in a living PAMS-b-polyisoprene (PAMS-b-PI). Triblock copolymer can be prepared by adding N,N,N',N'-tetramethylethylenediamine to increase the crossover reaction to reinitiate AMS from the living diblock and form PAMS-b-PI-b-PAMS. Gel permeation chromatography, H-1 NMR spectroscopy, differential scanning calorimetry, and thermal gravimetric analysis are used to characterize the products.