Nanostructures and toughening mechanisms in lightly cross-linked all-methacrylate copolymer/functional block copolymer blends

Abstract

Functional triblock copolymers (BCPs), i.e., poly(glycidyl methacrylate/methyl methacrylate)-b-poly(lauryl methacrylate)-b-poly(glycidyl methacrylate/methyl methacrylate) triblock copolymers [(P(GMA/MMA)-b-PLMA-b-P(GMA/MMA)], were investigated as toughening modifiers for all-methacrylate polymer blends. Methyl methacrylate (MMA) was copolymerized with methacrylic acid (MAA) in the presence of the BCPs. Without MAA in the polymethacrylate matrices, the BCP blends formed micron-scale phase structures by polymerization-induced phase separation. In matrices copolymerized with MAA, self-assembled nanostructures, such as curved lamellae, worm-like cylindrical micelles, or spherical micelles were formed. The BCP blends with worm-like cylindrical nano-micelles achieved much higher fracture toughness than those with spherical nano-micelles. The toughening mechanisms were elucidated by transmission electron microscopy. Cavitation was initiated in worm-like cylindrical nano-micelles, and the aligned cavitation formed craze-like deformation with increased loads. This relieves hydrostatic tensile stress in front of the crack tip, forming a large shear yield zone within the craze-like deformation region, contributing to high toughness.

Keywords

• block copolymer
• morphology
• polymer alloys
• nanoblends
• compatibilization