Macromolecular Architectures

Summary

There is always a degree of uncertainty surrounding measurements of polymeric materials, especially complex mixtures of with varying distributions in chemistry, sequence, and architecture among polymer chains. The ability to accurately characterize complex polymers and quantify structure-property relationships has always been convoluted by the innate heterogeneity of the material, the limitations of the chosen measurement method, and any applied external stimuli.  Model materials, with limited heterogeneity, and systematically varied chemistries and chain topologies can validate where the uncertainty lies within measurement methods and be used to develop new measurements to target existing areas where measurements are qualitative or inconclusive. This research involves design of model materials and methods that minimize heterogeneity and permit investigations of solution and bulk properties with systematic changes in material composition. 

 

This project covers four main research thrusts: model polymers for systematic investigation of material properties, characterization of ocean plastics, model bottle brushes and bottle brush networks for ultra-soft materials, and immobilized peptides for surface sensing platforms

 

 

 

 

 

 

Description

This project focuses on the design, synthesis, and characterization of model thermoplastics,  thermoplastic elastomers (TPEs), polymer brushes, bottle brushes, and networks with systematic variation of polymer sequence, chemistry, and architectures to generate libraries of quantitative structure-property-performance relationships, validated by multiple measurement methods. These coupled materials and measurements aim to develop next-generation reference materials and methods to improve characterization of complex, heterogeneous real-world plastics

 

Design and Measurements of Families of Model Polymers

Designing a family of model materials using controlled synthetic methods enables probing the solution and bulk phase properties of polymers to elucidate the impact of local chain composition on material properties. Current efforts in the project focus on the effects of short-chain branching in dilute solution properties of polyethylenes, as well as investigating the impact of sequence control and sequence defects on solution and processable properties of polyolefins for improved separation and compatibilization.  These polyolefin families also have potential as next generation molar mass standards.

 

This research, published in Macromolecules in 2020, highlights the systematic decrease in intrinsic viscosity, [h], with increasing short chain branch length

 

The project is currently looking at these structure-property relationships in a number of areas and applications in bulk materials as well.  This has been demonstrated in model bottle brush networks to quantify the effects of mechanical properties, thickness, conformal contact, and adhesion of model bottlebrush networks in solvent-free cleaning of cultural heritage.

The systematic study of solvent-free bottlebrush networks by varying macromonomer (MM) to crosslinker (XL) ratio finds that a decrease in shear modulus improves conformal contact and, as a result, improves cleaning of simulated grime from a surface.

 

Likewise, the incorporation of selective deuterium labeling has permitted small-angle neutron scattering on bulk phase bottle brushes, demonstrating through modeling of experimental data and simultaneous molecular dynamics simulations, that bottlebrushes have similar backbone correlation lengths to solution polyelectrolytes.  In addition to the synthesis and measurement of these materials, molecular dynamics simulations have been used to validate experimental structure-property data with theory.

Synthesis, small-angle neutron scattering, and modeling indicate that  backbone correlation length of bottle brush polymers in the melt resemble those of polyelectrolytes in solution

 

Sequence control and selective tethering of amino acid peptides, as well as accurate characterization of the grafting density and adsorption of these bio-polymer brushes is also being investigated as ways to overcome challenges in protein sequencing, where low abundance, non-static composition of sequences makes proteome quantification challenging.

 

Polymer Degradation Metrology

This project also has research collaborations regarding characterization of catalytically and environmentally degraded materials to determine the changes in chemistry, molar mass distribution, and chain architecture as plastics decompose, which are necessary to generate accurate models of degradation kinetics and material half-life. The research area aims to develop methodologies to quantitatively identify recovered materials and characterize molar mass, branching content, and chemical composition of degraded of plastics from ocean debris and laboratory-controlled degradation experiments. This has applications in studying failure of ballistic fibers, development of catalysts for chemical recycling, and environmental aging metrics. 

 

Coupling of chemical, macromolecular, and thermal characterization methods give a more complete picture of environmental degradation of plastics, especially when coupled with sampling into the z-direction of a recovered material

 

 

 

Major Accomplishments

a. Publications:

i. Orski, S. V.; Kassekert, L. A.; Farrell, W. S.; Kenlaw, G. A.; Hillmyer, M. A.; Beers, K. L. Design and Characterization of Model Linear Low-Density Polyethylenes (LLDPEs) by Multi-Detector Size Exclusion Chromatography. Macromolecules 2020, 53, 7, 2344-2353.

ii. Hsueh,  H-C.; Kim, J. H. Orski, S.; Fairbrother, A.; Jacobs, D.; Perry, L.; Hunston, D.; White, C.; Sung, L. Micro and Macroscopic Mechanical Behaviors of High-Density Polyethylene Under UV Irradiation and Temperature. Polym. Degrad. Stab. 2020, 174, 109098.

iii. Duncan, T. T.; Chan, E. P, Beers, K .L. Maximizing Contact of Supersoft Bottlebrush Networks with Rough Surfaces To Promote Particulate Removal. ACS Appl. Mater. Interfaces 2019, 11, 48, 45310–45318.

iv. J. Sarapas, T. Martin, A. Chremos, J. Douglas, K. Beers. Bottlebrush polymers in the melt and polyelectrolytes in solution share common structural features. Proc. Nat. Acad. Sci. 2020, 117 (10) 5168-5175

v. Farrell, W. S.; Orski, S. V.; Kotula, A. P.; Baugh III, D. W.; Snyder, C. R.; Beers, K. L. Precision, Tunable Deuterated Polyethylene via Polyhomologation. Macromolecules. 2019, 52, 15, 5741-5749.

vi. Jung, M. R.; Horgen, F. D.; Orski, S. V.; Rodriguez C., V.; Beers, K. L.; Balazs, G. H.; Jones, T. T.; Work, T. M.; Brignac, K. C.; Royer, S.-J.; et al. Validation of ATR FT-IR to Identify Polymers of Plastic Marine Debris, Including Those Ingested by Marine Organisms. Mar. Pollut. Bull. 2018, 127, 704–716.

Associated Product(s)

a. This project is also responsible for testing and answering questions on NIST’s polyethylene and polystyrene molar mass reference materials and SRMs.