The mechanical properties of polymers depend strongly on the mobility of the underlying chains. Changes in polymer architecture affect inter and intramolecular interactions, resulting in different chain dynamics and ultimately in different bulk polymer mechanical properties. In this talk, I will present a combined experimental and molecular dynamics study on polymers composed solely of intramolecularly crosslinked chains. By assembling the polymer from intramolecularly crosslinked chains commonly known as single chain polymer nanoparticles (SCPNs), we are able to control chain rigidity without modifying polymer chemistry. However, change in the percent of intramolecular crosslinks also changes the prevalence of intermolecular interactions such as entanglements and van der Waals attractions. Experimentally, I will discuss two different material systems: methyl methacrylate(MMA)-based and butyl methacrylate(BMA)-based. In both cases, linear random copolymers with (2-acetoacetoxy)-ethyl methacrylate are synthesized via RAFT. The linear polymers are covalently crosslinked into SCPNs by the addition of trimethylolpropane triacrylate (TMT) in dilute solution. The SCPN are then solvent cast into specimens for bulk thermo-mechanical characterization. These two polymers different significantly in their glass transition temperature (Tg): the BMA copolymer Tg is approximately 40°C lower than the MMA copolymer. Interestingly, the BMA-based copolymer shows an increase in stiffness and strength with increasing intramolecular crosslink density, whereas the MMA-based polymer shows minimal change in stiffness and a decrease in strength. Molecular dynamics simulations are vital for understanding aspects of the nanostructure, deformation, and inter-SCPN interactions that are difficult to measure experimentally. I will present simulation procedures for creating individual SCPN and bulk-like assemblies that capture the essential features of the synthesis and solvent casting procedures. Then I will present a series of analyses that help to interpret the experimental results including: compression on the individual SCPN, measuring radius of gyration within the bulk, quantifying entanglements, and independently tuning intermolecular non-bonded interactions.

Manipulating bulk polymer properties by tailoring intra and intermolecular interactions: Single chain polymer nanoparticle assemblies

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.