Preparation of ribbon-like core-crystalline micelles in epoxy and dimethacrylate matrices for potential applications as barrier membranes

Abstract

Significant progress has been recently achieved in the in-situ preparation of high-aspect-ratio crystalline micelles in polymer matrices. However, very little is known about how these structures affect the diffusion of permeant molecules through the matrix. This is a key factor for the potential use of these materials as barrier membranes in applications such as containers, coatings or packaging. In this work, we prepare ribbon-like core-crystalline micelles in thermosetting matrices and analyze their impact on the barrier properties. The materials were prepared by crystallization-driven self-assembly (CDSA) of poly(ethylene-block-ethylene oxide) (PE-b-PEO) in two different matrices: diglycidyl ether of bisphenol A (DGEBA) and poly(ethylene glycol) dimethacrylate (PEGDMA). DGEBA is a rigid matrix that can be plasticized by the corona-forming PEO block, whereas PEGDMA is a flexible matrix with a glass transition temperature that matches that of PEO. This approach allowed us to analyze the behavior of the micellar structure by distinguishing between the effects of the rigid crystalline core and the flexible corona. From water diffusion and permeability measurements we demonstrated that barrier properties are markedly improved by the crystalline cores, which act as impermeable obstacles generating a tortuous path for the diffusion of permeant molecules through the polymer matrix. Although the corona-forming block can act as a plasticizer of the matrix, the tortuosity introduced by the crystalline core is the rate-controlling factor and, as such, determines the improvement in barrier properties.