CAREER: Dynamics and structure of comb polymer elastomers

NON-TECHNICAL SUMMARY: Polymer networks consisting of branch polymer architectures (polymers with sidechains attached to linear backbones) can be used to independently tune material stiffness and elasticity. Supersoft and hyper-elastic solvent-free materials offer potentially transformative opportunities for emerging applications in stretchable electronics and biomaterials. Controlling network properties, however, remains a significant challenge due to synthetic limitations associated with the underlying branch polymer architecture. This research project will directly investigate the relationship between network structure, mechanics, and branch polymer architecture by developing synthetic methods to precisely control branch length, spacing between branches, and the chemistry that links branches together. Light scattering and rheological characterization techniques will be used to measure network properties under varying solutions and bulk conditions. The insights gained from this research will address a critical knowledge gap in understanding the mechanical properties of topologically complex polymer networks, including those that depend on deformation history. The results from this project are expected to inform design of tunable materials with enhanced processing efficiency and predictable mechanical properties for applications that use films, fibers, and foams. Outreach efforts will be developed to increase intellectual breadth and the number of scientists in soft matter research by creating innovative symposia focused on community college teachers and students and on cross-sector collaboration between academia, industry, and national laboratories. TECHNICAL SUMMARY: The molecular design of branch polymer elastomers offers a potentially transformative route towards synthetic networks with gel-like softness, high elasticity, and enhanced strain-adaptive stiffening for applications ranging from stretchable electronics to biomimetic tissues. The efficacy of these materials is dependent on the underlying polymer topology (i.e., linear, comb, and bottlebrush polymers) of the cross-linked network. For example, comb and bottlebrush elastomers have unprecedented mechanical properties because stiffness and elasticity can be decoupled by varying sidechain length, sidechain spacing, and cross-link spacing. Due to synthetic limitations, however, the cross-link and sidechain uniformity and spacing are challenging to control precisely and characterize experimentally. Thus, there remains a critical need for an experimental platform with precise control of cross-link and sidechain spacing to elucidate structure-function relationships in branch polymer elastomers. This CAREER project will address these outstanding challenges through investigation of model comb polymers with precise topological parameters to develop a fundamental understanding of the effects of cross-link and sidechain uniformity on elastomer formation, mechanical properties, and structure, thus establishing a new paradigm in elastomer design. Expertise in polymer synthesis, X-ray/neutron scattering, solution dynamics, and STEM outreach will be integrated to address three research aims and one educational aim: (1) determine the role of comb polymer topology on elastomer formation and dynamics, (2) understand the effects of comb polymer topology on elastomer mechanics, (3) characterize the effects of comb polymer topology on elastomer structure, and (4) establish new symposia and research opportunities for undergraduates to increase intellectual breadth and support scientists in soft matter research. 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.