Synthesis, morphology, and mechanical properties of poly(methyl methacrylate)-b-poly(n-butyl acrylate)-b-poly(methyl methacrylate) triblocks. Ligatedanionic polymerization vs atom transfer radical polymerization

Poly(methyl methacrylate)-b-poly(n-butyl acrylate)-b-poly(methyl methacryla te) triblock copolymers have been prepared by ligated anionic polymerizatio n (LAP; 8K-50K-8K) and atom transfer radical polymerization (ATRP; 9K-51K-9 K). Size exclusion chromatography, nuclear magnetic resonance, and differen tial scanning calorimetry have confirmed that the molecular structure of th e two triblock copolymers is essentially identical. However, important diff erences are found in dynamic mechanical properties, viscoelastic properties , and stress-strain behavior. Indeed, the ATRP copolymer has low storage mo dulus, high complex viscosity, high order-disorder transition temperature, and poor ultimate tensile strength and elongation at break, compared to tho se of the LAP analogue. Marked differences also observed by tapping mode at omic force microscopy in the microscopic morphology of thin films of these copolymers. All these observations can be explained by the slow initiation of MMA by the poly(n-butyl acrylate) macroinitiator used in ATRP in contras t to what happens when MMA is added to living poly(tert-butyl acrylate) ani ons. As a result, the polydispersity of the short poly(methyl methacrylate) (PMMA) outer blocks is much broader in the ATRP copolymer, although the po lydispersity index of the triblock is only 1.15. This heterogeneous structu re of the ATRP triblock is also supported by the comparison of homo-PMMAs p repared by LAP and ATRP.