Synthesis and bulk properties of poly(methyl methacrylate)-b-poly(isooctylacrylate)-b-poly(methyl methacrylate)

A series of well-defined poly(methylmethacrylate) (PMMA)-b-poly(isooctylacr ylate) (PIOA)-b-PMMA triblock copolymers (MIM) has been synthesized by tran salcoholysis of PMMA-b-poly(tert-butylacrylate) (PtBA)-b-PMMA precursors (M TM) by isooctyl alcohol. Phase separation is observed for all the investiga ted triblock copolymers, thus containing PMMA outer blocks in the 3500-50,0 00 molecular weight (MW) range and PIOA inner block with MW in the 100,000- 300,000 range. The ultimate tensile properties of these MIM triblock copoly mers are poor even when PMMA blocks of 50,000 MW are associated with an inn er PIOA block of 300,000 MW. A reasonable explanation should be found in th e molecular weight between chain entanglements (M-e), which has been estima ted at 60,000 for PIOA, much higher than M-e for the traditional polydiene central blocks in the well-known thermoplastic elastomers of the triblock t ype. The tensile behavior of MIM copolymers has been successfully accounted for by a simple elastomer model free from chain entanglements, supporting the view that the lack of entanglements in the central block is very detrim ental to the mechanical properties of the investigated fully (meth)acrylate triblock copolymers. (C) 2000 Elsevier Science Ltd. All rights reserved.