Poly(methyl methacrylate)-b-poly (n-butyl acrylate)-b-poly(ε-caprolactone) triblock copolymers as tougheners for PMMA matrices

Poly(methyl methacrylate)-b-poly(butyl acrylate)-b-poly(ε-capro-lactone) (PMMA-PBA-PCL) triblock copolymers of typical number-averaged block molecular weights of 45 to 100 kg/mol for PMMA, 25 kg/mol for PBA and 10 kg/mol for PCL were synthesized by sequential nitroxide-mediated polymerization (NMP) of BA and MMA from a SG1 (N-(tert-butyl)-N-(1-diethylphosphono-2,2-dimethylpropyl)) nitroxide-functionalized PCL macroalkoxyamine initiator. This alkoxy-amine was obtained by transformation of an OH-terminated PCL into acrylate-end capped PCL, followed by 1,2-intermolecular radical addition (IRA) of MAMA-SG1 (so-called BlocBuilder® MA). NMP of BA from the macroalkoxyamine proceeded in a controlled manner. The high living chain ratio of PBA-PCL allowed further initiation of NMP of MMA, leading to triblock copolymers with adjustable PMMA block molecular weights. The samples prepared by solvent casting were found to organize in a lamellar morphology for the pure triblock copolymers, and in a spherical morphology when blended with a PMMA homo-polymer of M_n = 40 kg/mol and polydispersity index of 2.1. Finally, the mechanical properties and the local deformation mechanisms of the pure triblock copolymers and their blends with PMMA were investigated by time-resolved SAXS measurements during tensile testing. The dominant microscopic deformation mode of the triblock copolymer was found to change from crazing to cavitation-induced shear yielding, due to the easy-cavitating PCL block of the copolymer.