Topologically Induced Heterogeneity in Gradient Copolymer Brush Particle Materials

Polymers are lightweight, durable, and easily processed into fabricated parts, features that promoted polymers to become the most relevant class of engineering materials by volume. However, recycling polymers is a challenge that materials scientists have been researching for decades. Copolymers are a special class of polymers that are made up of two different monomers and exhibit self-healing properties. The researchers found that when copolymers were added onto the surface of nanoparticles, new structures were formed that enhanced the polymer’s self-healing properties. This discovery is foundational to improving the recyclability of polymers.

An alternate route toward a more sustainable polymer industry is to increase the service lifetime of polymers. An intriguing new concept is to impart the ability to “self-heal” from structural damage. Michael Bockstaller, professor of materials science and engineering at Carnegie Mellon University Materials Science and Engineering, in collaboration with Krzysztof Matyjaszewski, professor of chemistry, has discovered that the binding of copolymers on the surface of nanoparticles that are already used in industrial manufacturing provides an economic and scalable route toward self-healing polymers with increased strength and toughness. This research was published in Macromolecules.

The properties of the resulting materials can be varied by controlling the interactions between nanoparticle building blocks. This concept opens up new possibilities to vary properties of engineering materials without having to change their chemical composition a feature that is highly beneficial in the context of recyclability. While working to make these particles more amenable to fabrication technologies like additive manufacturing, the authors experimented with putting copolymers at the surface of nanoparticles. The research work illustrates how controlling macromolecular architecture can dramatically enhance properties of various advanced materials.

The authors systematically evaluated the effect of BA/MMA composition in grafted random and gradient-type copolymer ligands on the deformation characteristics and thermomechanical properties of particle brush-based hybrid materials. The authors successfully developed a facile method to control copolymer architecture of brush materials based on the variation of the conversion ratio during surface-initiated atom transfer radical polymerization (SI-ATRP). Subsequently, the thermomechanical properties of random and gradient brush systems were determined and compared with those of the linear copolymer analogues. Depending on the grafting density and composition, gradient polymer architectures exhibited heterogeneous microstructures with distinctively different properties as random copolymer analogues. The results thus highlight the importance of chain architecture as a “control parameter” for the design of functional materials based on copolymer brush particle-based hybrid materials. The authors will continue to explore strategies to maximize strength and toughness of copolymer-based self-healing materials and to make them available to scalable production methods.