Polymer networks remain an essential class of soft materials. Despite their use in everyday materials, connecting the molecular structure of the network to its macroscopic properties remains an active area of research. Much current research is enabled by advances in modern polymer chemistry providing an unprecedented level of control over macromolecular structure. At the same time, renewed interest in self-healing, dynamic, and/or adaptable materials continues to drive substantial interest in polymer network design. As part of a special issue focused on research performed in the Polymer Science and Engineering Department at the University of Massachusetts, Amherst, this review highlights connections between macromolecular structure of networks and observed mechanical properties as investigated by the Tew research group.

Synthetic polymer scaffolds can encapsulate transition metal catalysts (TMCs) to provide bioorthogonal nanocatalysts. These 'polyzymes' catalyze the generation of therapeutic agents without disrupting native biological processes. The design and modification of polymer scaffolds in these polyzymes can enhance the catalytic performance of TMCs in biological environments. In this study, we explore the hydrophobic design space of an oxanorborneneimide-based polymer by varying the length of its carbon side chain to engineer bioorthogonal polyzymes. Activity studies indicate that modulating the hydrophobicity of the polymer scaffold can be used to enhance the catalyst loading efficacy, catalytic activity, and serum stability of polyzymes. These findings provide insight into the structural elements contributing to improving polymeric nanocatalysts for a variety of applications.

Posterior capsule opacification (PCO) is the most common complication of cataract surgery, and intraocular lens (IOL) implantation is the standard of care for cataract patients. Induction of post-operative epithelial-mesenchymal transition (EMT) in residual lens epithelial cells (LEC) is the main mechanism by which PCO forms. Previous studies have shown that IOLs made with different materials have varying incidence of PCO. The aim of this paper was to study the interactions between human (h)LEC and polymer substrates. Polymers and copolymers of 2-hydroxyethyl methacrylate (HEMA) and 3-methacryloxypropyl tris (trimethylsiloxy) silane (TRIS) were synthesized and evaluated due to the clinical use of these materials as ocular biomaterials and implants. The chemical properties of the polymer surfaces were evaluated by contact angle, and polymer stiffness and roughness were measured using atomic force microscopy. studies showed the effect of polymer mechanical properties on the behavior of hLECs. Stiffer polymers increased α-smooth muscle actin expression and induced cell elongation. Hydrophobic and rough polymer surfaces increased cell attachment. These results demonstrate that attachment of hLECs on different surfaces is affected by surface properties , and evaluating these properties may be useful for investigating prevention of PCO.

Poly(ethylene glycol) (PEG) is a highly biocompatible and water-soluble polymer that is widely utilized for biomedical applications. Unfortunately, the immunogenicity and antigenicity of PEG severely restrict the biomedical efficacy of pegylated therapeutics. As emerging PEG alternatives, biodegradable zwitterionic polymers (ZPs) have attracted significant interest in recent years. Biodegradable ZPs generally are not only water-soluble and immunologically inert, but also possess a range of favorable biomedically relevant properties, without causing long-term side effects for biomedical applications. This review presents a systematic overview of recent studies on biodegradable ZPs. Their structural designs and synthetic strategies by integrating biodegradable base polymers with zwitterions are addressed. Their applications in the delivery of small molecule drugs (as mono-drugs or multi-drugs) and proteins are highlighted.

Organocatalyzed atom transfer radical polymerization (O-ATRP) is a method of producing polymers with precise structures under mild conditions using organic photoredox catalysts (PCs). Due to the unknown toxicity of PCs and their propensity to introduce color in polymers synthesized by this method, removal of the PC from the polymer product can be important for certain applications of polymers produced using O-ATRP. Current purification methods largely rely on precipitation to remove the PC from the polymer, but a more effective and efficient purification method is needed. In this work, an alternative purification method relying on oxidation of the PC to PC followed by filtration through a plug to remove PC from the polymer and removal of the volatiles was developed. A range of chemical oxidants and stationary phases were tested for their ability to remove PCs from polymers, revealing chemical oxidation by -bromosuccinimide followed by a filtration through a silica plug can remove up to 99% of the PC from poly(methyl methacrylate). Characterization of the polymer before and after purification demonstrated that polymer molecular weight, dispersity, and chain-end fidelity are not signficantly impacted by this purification method. Finally, this purification method was tested on a range of dihydrophenazine, phenoxazine, dihydroacridines, and phenothiazine PCs, revealing the strength of the chemical oxidant must match the oxidation potential of the PC for effective purification.

The control of chain-ends is fundamental in modern macromolecular chemistry for directed one-to-one bioconjugation and the synthesis of advanced architectures such as block copolymers or bottlebrush polymers and the preparation of advanced soft materials. Polyphosphazenes are of growing importance as elastomers, biodegradable materials and in biomedical drug delivery due to their synthetic versatility. While controlled polymerization methods have been known for some time, controlling both chain-ends with high fidelity has proven difficult. We demonstrate a robust synthetic route to hetero and homo α,ω-chain-end functionalized polyphosphazenes via end-capping with easily accessible, functionalized triphenylphosphine-based phosphoranimines. A versatile thiol-ene "click"-reaction approach then allows for subsequent conversion of the end-capped polymers with various functional groups. Finally, we demonstrate the utility of this system to prepare gels based on homo α,ω-chain-end functionalized polyphosphazenes. This development will enhance their progress in various applications, particularly in soft materials and as degradable polymers.

Herein it is reported how the overlap concentration () can be used to overcome crosslinking due to diol impurities in commercial PEG, allowing for the synthesize of bottlebrush polymers with good control over molecular weight. Additionally, PEG-based bottlebrush networks are synthesized via ROMP, attaining high conversions with minimal sol fractions (<2%). The crystallinity and mechanical properties of these networks are then further altered by solvent swelling with phosphate buffer solution (PBS) and 1-ethyl-3-methylimidazolium ethyl sulfate/DCM cosolvents. The syntheses reported here highlight the potential of the bottlebrush network architecture for use in the rational design of new materials.

Polymer-nanoparticle hydrogels are a unique class of self-assembled, shear-thinning, yield-stress fluids that have demonstrated potential utility in many impactful applications. Here, we present a thorough analysis of the gelation and yielding behavior of these materials with respect to the polymer and nanoparticle component stoichiometry. Through comprehensive rheological and diffusion studies, we reveal insights into the structural dynamics of the polymer nanoparticle network that identify that stoichiometry plays a key role in gelation and yielding, ultimately enabling the development of hydrogel formulations with unique shear-thinning and yield-stress behaviors. Access to these materials opens new doors for interesting applications in a variety of fields including tissue engineering, drug delivery, and controlled solution viscosity.

A comprehensive understanding of the structure, self-assembly mechanism, and dynamics of one-dimensional supramolecular polymers in water is essential for their application as biomaterials. Although a plethora of techniques are available to study the first two properties, there is a paucity in possibilities to study dynamic exchange of monomers between supramolecular polymers in solution. We recently introduced hydrogen/deuterium exchange mass spectrometry (HDX-MS) to characterize the dynamic nature of synthetic supramolecular polymers with only a minimal perturbation of the chemical structure. To further expand the application of this powerful technique some essential experimental aspects have been reaffirmed and the technique has been applied to a diverse library of assemblies. HDX-MS is widely applicable if there are exchangeable hydrogen atoms protected from direct contact with the solvent and if the monomer concentration is sufficiently high to ensure the presence of supramolecular polymers during dilution. In addition, we demonstrate that the kinetic behavior as probed by HDX-MS is influenced by the internal order within the supramolecular polymers and by the self-assembly mechanism.

Few semiconducting polymers are known that possess more than one semi-crystalline structure. Guidelines for rationalizing or creating polymorphism in these materials do not exist. Two different semi-crystalline polymorphs, and , and an amorphous phase have recently been identified for alternating diketopyrrolopyrrole-quaterthiophene copolymers (PDPP4T). The polymorphs differ structurally by the π-π stacking distance, and electronically by the optical bandgap and charge carrier mobility. Here we investigate the corresponding terthiophene (PDPP3T) derivatives, to study the effect of the relative orientation of adjacent DPP units on the polymorphism. In PDPP3T, the relative orientation of DPP units alternates along the chain, while in PDPP4T it is constant. We show that the two polymorphs, and , can also be generated for a PDPP3T polymer in solution and thin film. Interestingly, compared to PDPP4T, more solvents can induce the two distinct semi-crystalline polymorphs for PDPP3T via a  →  →  polymorphic transition.

Supramolecular motifs in elastomeric biomaterials facilitate the modular incorporation of additives with corresponding motifs. The influence of the elastomeric supramolecular base polymer on the presentation of additives has been sparsely examined, limiting the knowledge of transferability of effective functionalization between polymers. Here it was investigated if the polymer backbone and the additive influence biomaterial modification in two different types of hydrogen bonding supramolecular systems, that is, based on ureido-pyrimidinone or bis-urea units. Two different cell-adhesive additives, that is, catechol or cyclic RGD, were incorporated into different elastomeric polymers, that is, polycaprolactone, priplast or polycarbonate. The additive effectiveness was evaluated with three different cell types. AFM measurements showed modest alterations on nano-scale assembly in ureido-pyrimidinone materials modified with additives. On the contrary, additive addition was highly intrusive in bis-urea materials. Detailed cell adhesive studies revealed additive effectiveness varied between base polymers and the supramolecular platform, with bis-urea materials more potently affecting cell behavior. This research highlights that additive transposition might not always be as evident. Therefore, additive effectiveness requires re-evaluation in supramolecular biomaterials when altering the polymer backbone to suit the biomaterial application.

Per- and polyfluoroalkyl substances (PFAS) have rapidly accumulated in the environment due to their widespread use prior to commercial discussion in the early 21st century, and their slow degradation has magnified concerns of their potential toxicity. Monitoring their distribution is, therefore, necessary to evaluate and control their impact on the health of exposed populations. This investigation evaluates the capability of a simple polymeric detection scheme for PFAS based on crosslinked, thermoresponsive poly(-isopropylacrylamide) (PNIPAM) hydrogels. Surveying swelling perturbations induced by several hydrotropes and comparable hydrocarbon analogs, tetraethylammonium perfluorooctane sulfonate (TPFOS) showed a significantly higher swelling ratio on a mass basis (65.5 ± 8.8 at 15°C) than any of the other analytes tested. Combining swelling with the fluorimetric response of a solvachromatic dye, nile red, revealed the fluorosurfactant to initiate observable aggregation (i.e., its critical aggregation concentration) at 0.05 mM and reach saturation (i.e., its charge neutralization concentration) at 0.5 mM. The fluorosurfactant was found to homogeneously distribute throughout the polymer matrix with energy dispersive X-ray spectroscopy, marking the swelling response as a peculiar nexus of fluorinated interfacial positioning and delocalized electrostatic repulsion. Results from the current study hold promise for exploiting the physiochemical response of PNIPAM to assess TPFOS's concentration.

Cobaltocenium-containing polyelectrolyte block copolymer nanoparticles were prepared via polymerization-induced self-assembly (PISA) using aqueous dispersion RAFT polymerization. The cationic steric stabilizer was a macromolecular chain-transfer agent (macro-CTA) based on poly (2-cobaltocenium amidoethyl methacrylate chloride) (PCoAEMACl), and the core-forming block was poly(2-hydroxypropyl methacrylate) (PHPMA). Stable cationic spherical nanoparticles were formed in aqueous solution with low dispersity without adding any salts. The chain extension of macro-CTA with HPMA was efficient and fast. The effects of block copolymer compositions, solid content, charge density, and addition of salts were studied. It was found that the degree of polymerization of both the stabilizer PCoAEMACl and the core-forming PHPMA had a strong influence on the size of nanoparticles.

Small-angle scattering measurements of complex macromolecules in solution are used to establish relationships between chemical structure and conformational properties. Interpretation of the scattering data requires an inverse approach where a model is chosen and the simulated scattering intensity from that model is iterated to match the experimental scattering intensity. This raises challenges in the case where the model is an imperfect approximation of the underlying structure, or where there are significant correlations between model parameters. We examine three bottlebrush polymers (consisting of polynorbornene backbone and polystyrene side chains) in a good solvent using a model commonly applied to this class of polymers: the flexible cylinder model. Applying a series of constrained Monte-Carlo Markov Chain analyses demonstrates the severity of the correlations between key parameters and the presence of multiple close minima in the goodness of fit space. We demonstrate that a shape-agnostic model can fit the scattering with significantly reduced parameter correlations and less potential for complex, multimodal parameter spaces. We provide recommendations to improve the analysis of complex macromolecules in solution, highlighting the value of Bayesian methods. This approach provides richer information for understanding parameter sensitivity compared to methods which produce a single, best fit.