Foldable Bottlebrush Polymers

1. Non-Technical Summary

A bottlebrush polymer consists of a long linear backbone densely grafted with many relatively short linear side chains. Recent advances have shown that mechanical, physical, and biochemical features can be independently encoded into the molecular architecture of bottlebrush polymers. Nevertheless, as for any polymers, it is of foundational importance to understand the molecular structure of bottlebrush polymers.

A widely accepted view is that strong steric repulsion among highly overlapped side chains pre-strains the bottlebrush backbone. However, recent breakthroughs suggest that for a bottlebrush polymer with highly incompatible backbone and side chains, the backbone does not have to be pre-strained; instead, it can fold into a cylindrical core with all grafting sites on its surface, thereby reducing interfacial free energy.

This so-called foldable bottlebrush polymer provides a new building block for the development of polymer-based soft (bio)materials. This project seeks to establish the deterministic relationships between molecular architecture, mesoscopic conformation, and macroscopic properties of foldable bottlebrush polymers and networks, as well as to demonstrate the application of foldable bottlebrush polymers as a new class of resins for multi-material additive manufacturing.

The resulting knowledge, materials, methods, and tools will positively impact polymer science and engineering, drug delivery, tissue engineering, soft robotics, and advanced manufacturing. By providing opportunities for interdisciplinary research and organizing local scientific activities, this program will train students from diverse backgrounds to be next-generation scientific leaders in polymers and soft materials.

Through outreach interactions with local high schools, the PI will leverage additive manufacturing demonstrations to attract students to STEM fields. 2. Technical Summary

The research goal of this project is to establish the foundational science of foldable bottlebrush polymers and networks. Guided by a new molecular theory, foldable bottlebrush polymers with prescribed molecular architecture parameters will be designed, synthesized, and characterized to elucidate their deterministic molecular architecture-mesoscopic structure-nonlinear mechanical property relationships.

Based on the understanding of individual foldable bottlebrush polymers, a constitutive law will be developed to describe the remarkable nonlinear stress-strain behavior of foldable bottlebrush polymer networks. Finally, the foldable bottlebrush concept will be exploited to develop photocurable resins of dramatically different mechanical properties but crosslinked by the same chemistry.

Using a customized additive manufacturing platform, these resins will be transformed into functional multi-material three-dimensional structures. These research activities will develop new knowledge for designing, methods for creating, and technologies for processing foldable bottlebrush polymers and networks.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.