Utilizing self-assembly and polymerization-induced phase separation of photopolymerizable blends to control polymer structure and thermomechanical properties
Creators: name: Grover, Tanner L
Publisher: name: University of Iowa
Year: 2024
Subjects: subject: public abstract
subject: Chemical Engineering
subject: FOS: Chemical engineering

description: Over the past century, the ability to control polymer structure on the submicron scale has gained considerable attention in the material science community. Motivation behind such increased interest is the unique macroscopic properties accessible by regulating polymer structure in this range. Specifically, developing control over structure in photopolymerizable systems is important for coupling this efficient polymerization technique with advanced material properties. However, the current understanding of the relationships between prepolymer composition, reaction kinetics, polymer structure and material properties is limited. In this work, we use prepolymer chemistry and multi-phase formation to manipulate the structure of photopolymerized blends for enhanced material performance.
description: To regulate phase separated structure and mechanical properties of photocured composites, photopolymerization of orthogonal radical/cationic systems (e.g., methacrylates and cyclic ethers) were examined. Considerable differences in reaction kinetics between the radical and cationic polymerizations manifested in polymerization-induced phase separation. Manipulating differences in network polymerization rate through slight modifications to comonomer composition enabled control over phase separation on the submicron level. This control over phase separated morphology provided tailorable polymer mechanical properties. For example, larger phase separated size scales exhibited increased elongation whereas reducing phase separation displayed greater tensile strength. Although composite tensile strength and elongation were adjustable, tensile toughness was maintained regardless of phase separated structure and substantially improved relative to the component materials.
description: Alternatively, utilizing the highly controllable architecture of prepolymerized block copolymers (BCPs) can provide control over phase morphology in photocurable blends. Photoiniferter polymerization was employed to precisely regulate functional group placement, molecular weight (MW), and polydispersity of reactive amphiphilic BCPs. Synthesized BCPs were subsequently used as nanoscale phase separation directors in photopolymerizable epoxy resins. When these blended systems were photopolymerized, the amphiphilic BCPs induced controllable dual phase formation. Intriguingly, diblock BCPs organized the resin matrix through self-assembly with retained ordered through photopolymerization. The imparted individual phases contained significantly different mechanical properties with one phase containing a chemically cross-linked network and the adjacent phase consisting of physical BCP segment entanglements. The dual phase morphologies changed mechanical properties substantially relative to isotropic controls. For example, increasing BCP MW resulted in larger phase separation size scales and increased toughness of the photocured blend.
description: Finally, the chemical composition of BCPs was altered by using different monomers for BCP synthesis. Chemical manipulation of BCP architecture enabled control over individual phase properties and polymer structure enabling further improvements in photopolymer blend mechanical performance. The aim of this work has been to provide guiding principles for controlling polymer structure through self-assembly and phase separation processes. These principles were derived specifically from photoinitiated systems but may be applied to alternative forms of initiation such as thermal polymerization thus extending the impact of this research. The demonstrated outcome is that regulated structure on these length scales facilitates substantially improved polymer toughness and controllable thermomechanical properties.