ANIONIC-POLYMERIZATION OF ACRYLIC-MONOMERS .21. ANIONIC SEQUENTIAL POLYMERIZATION OF 2-ETHYLHEXYL ACRYLATE AND METHYL-METHACRYLATE

A mixed complex of a polydentate lithium alkoxide, i.e., lithium 2-(2-methoxyethoxy) ethoxide (LiOEEM), and of a mono- or bisfunctional organolithium initiator, i.e., (diphenylmethyl)lithium (DPMLi) or lithium naphthalene/diphenylethylene, has been used to synthesize well-controlled AB (BA), ABA, and BAB block copolymers of methylmethacrylate (MMA) (A) and 2-ethylhexyl acrylate (2EtHA) (B), irrespective of the monomer addition order. Although the 2EtHA block copolymerization initiated with monofunctional living PMMA macroanions at -78 degrees C in a 75/25 toluene/THF mixture gives rise to a precisely-tailored PMMA-b-P2EtHA diblock polymer, the reverse sequence, i.e.,from P2EtHA anions to the MMA type monomer, always results in contamination by homo-P2EtHA. This has been interpreted in terms of the short shelf lifetime of P2EtHA anions present. Nevertheless, a pure P2EtHA-b-PMMA type diblock copolymer can be produced at -100 degrees C, while keeping other conditions unchanged. More importantly, a well-controlled PMMA-b-P2EtHA-b-PMMA triblock copolymer has been prepared through a three-stage process with a monofunctional initiator, actually providing a potential pathway toward the direct synthesis of a novel type of fully acrylic thermoplastic elastomer, instead of the more complicated hydrolysis/transalcoholysis process previously demonstrated by us.