Controlling phase separated domains in UV-curable formulations with OH-functionalized prepolymers

Abstract

Modification of photocurable radical systems with high molecular weight prepolymers enables access to a wide array of polymer structures and properties. Chemical structure design of these prepolymers may lead to photopolymerization-induced phase separation in such in which the domain size and distribution as well as the interactions between prepolymers and the polymer network may be controlled. In this work, we use a controlled radical polymerization technique to synthesize prepolymers composed of butyl acrylate (BA) and hydroxyethyl acrylate in order to create hydroxyl (OH) pendant groups either at the ends or randomly distributed along the predominantly BA chain. Modulating the OH group placement and prepolymer molecular weight has a significant impact on polymer structure and properties of cross-linked acrylate systems. Specifically, photopolymerization of tetraethylene glycol diacrylate (TTGDA) with prepolymers leads to a variety of distinct phase-separated morphologies and phase distributions. These morphological changes along with the incorporation of linear low T_g prepolymers within the glassy acrylate network increase polymer elongation at break up to 9-fold while slightly reducing the Young's modulus. Consequently, these systems demonstrate a significant increase in tensile toughness at different temperatures due to formation of multiple domains. Additionally, incorporation of prepolymers into a 3D printing model acrylate formulation leads to objects with more than 500% increase in impact strength. This study shows that placement of OH groups at the ends or throughout the BA backbone enables various phase-separated morphologies for photocurable radical systems, generating polymers with enhanced elongation at break, tensile toughness, and impact strength.