Synthesis and Characterization of Triblock Copolymer of Poly(tetramethylene Oxide) and Poly(methyl Methacrylate)

Abstract

Abstract Anionic polymerization of methyl methacrylate (MMA) was initiated with the disodium salt of dihydroxy-poly(tetra-methylene oxide) (PTMO) in tetrahydrofuran in the presence and the absence of a crown ether. The resulting block copolymer of poly(methyl methacrylate) (PMMA) and PTMO was characterized by 1H NMR spectroscopy, gel permeation chromatography, and solvent extractions. In the absence of the crown ether, a linear triblock copolymer of PMMA-PTMO-PMMA was predominantly obtained, showing a unimodal and relatively narrow molecular weight distribution. In the presence of the crown ether, a linear triblock copolymer and a PTMO grafted block copolymer due to the transesterification reaction between PTMO and a methoxy group in MMA were produced with an increase in polymer yield. The stereosequence distributions of the PMMA part in the copolymers were essentially atactic and the addition of the crown ether increased the fraction of the rr triad. A-B-A type triblock copolymers have recently received much attention because they contain physically and chemically incompatible segments in one macromolecular chain. A large number of block copolymers have been synthesized by various techniques [1]. Due to the low melting and glass transition temperatures of poly(tetramethylene oxide) (PTMO), it is suitable for the center block. Several attempts have been made to synthesize block copolymers of PTMO and a few monomers [2–10]. Tobolsky and his co-workers prepared a peroxide-terminated PTMO and tried to initiate the radical polymerization of methyl methacrylate (MMA) [5]. However, appreciable amounts of MMA homopolymer and unreacted PTMO existed in the product in addition to the block copolymer of PTMO and poly(methyl methacrylate) (PMMA). They could not isolate the pure block copolymer and could not characterize the resulting copolymer. In previous papers we have studied syntheses of the A-B-A type triblock copolymers of poly(ethylene oxide) (PEO) and PMMA [11, 12] and of PEO and polymethacrylonitrile [13] by using the disodium salt of PEO as an initiator. As an extension of this technique, we have investigated the capability of initiating the polymerization of MMA with the disodium salt of PTMO, which is considered to be inferior to PEO in cation-binding ability. The present paper describes the synthesis and characterization of a triblock copolymer of PTMO and PMMA. The effect of the addition of a crown ether on the polymerization is discussed.