Reliable and equitable access to safe drinking water is a major and growing challenge worldwide. Membrane separations represent one of the most promising strategies for the energy-efficient purification of potential water sources. In particular, porous membranes are used for the ultrafiltration (UF) of water to remove contaminants with nanometric sizes. However, despite exhibiting excellent water permeability and solution processability, existing UF membranes contain a broad distribution of pore sizes that limit their size selectivity. To maximize the potential utility of UF membranes and allow for precise separations, improvements in the size selectivity of these systems must be achieved. Block polymers represent a potentially transformative solution, as these materials self-assemble into well-defined domains of uniform size. Several different strategies have been reported for integrating block polymers into UF membranes, and each strategy has its own set of materials and processing considerations to ensure that uniform and continuous pores are generated. This Review aims to summarize and critically analyze the chemistries, processing techniques, and properties required for the most common methods for producing porous membranes from block polymers, with a particular focus on the fundamental mechanisms underlying block polymer self-assembly and pore formation. Critical structure–property–performance metrics will be analyzed for block polymer UF membranes to understand how these membranes compare to commercial UF membranes and to identify key research areas for continued improvements. This Review is intended to inform readers of the capabilities and current challenges of block polymer UF membranes, while stimulating critical thought on strategies to advance these technologies.

Proteins are a widely available biomass source for synthesizing strong and tough engineering polymers because of their propensity to hydrogen bond, chemically stable amide backbone, and demonstrated efficacy at forming relevant material structures in nature. Because the properties of polypeptides in many ways mimic urethane bonds and hard domains, herein proteins are explored as the reinforcing component in a polyurethane-inspired elastomer. Materials are synthesized using a two-step process: first, protein is methacrylated, and then copolymerized with (meth)acrylate comonomers to link protein domains with rubbery polymer chains. This is demonstrated with water-soluble proteins, whey protein and β-lactoglobulin, and a comonomer, hydroxypropyl acrylate (HPA). The resulting elastomers are amorphous and disordered but have microphase-separated morphologies. Materials with a wide range of stiffnesses have been prepared by varying the fraction of protein macro-cross-linkers in the materials. The protein aggregates function like fillers that strengthen the materials, which are shown to be tougher than both unreinforced homopolymers and unmodified proteins. Materials with low cross-link densities prepared using proteins modified at low methacrylation levels are also stiffer than protein−polymer blends. Above an optimal protein methacrylation level, increasing chemical cross-link densities led to lower extents of protein aggregation and decreased moduli.

2 Bio-sourced macromolecules such as cyanophycin are an attractive source for alternative, sustainable plastics. While the chemical structure and biological function of cyanophycin have been previously investigated, its material properties remain largely unexplored. This study investigates the structural, thermal, mechanical, and solution properties of cyanophycin produced from recombinant Escherichia coli. Unplasticized, it has an elastic compression modulus of about 560 MPa and undergoes brittle failure at 78 MPa. Cyanophycin exhibits thermal stability in air up to 200°C and does not undergo glass transition within its limit of thermal stability. The polypeptide is amorphous and has no long-range ordering in the solid state. In solution, watersoluble cyanophycin is thermoresponsive, exhibiting both upper and lower critical solution temperatures. Because the feasibility of industrial scale cyanophycin production through fermentation has been well studied, an expanded understanding of its materials properties should contribute to the development of new applications for this biopolymer.

The wide use of non-biodegradable, petroleum-based plastics raises important environmental concerns, which urges finding alternatives. In this study, an alternative way to produce polymers from a renewable source—milk proteins—was investigated with the aim of replacing polyethylene. Whey protein can be obtained from whey residual, which is a by-product in the cheese-making process. Two different sources of whey protein were tested: Whey protein isolate (WPI) containing 91% protein concentration and whey protein concentrate (WPC) containing 77% protein concentration. These were methacrylated, followed by free radical polymerization with co-polymer poly(ethylene glycol) methyl ether methacrylate (PEGMA) to obtain polymer sheets. Different protein concentrations in water (11–14 w/v%), at two protein/PEGMA mass-ratios, 20:80 and 30:70, were tested. The polymers made from WPI and WPC at a higher protein/PEGMA ratio of 30:70 had significantly better tensile strength than the one with lower protein content, by about 1–2 MPa (the best 30:70 sample exhibited 3.8 ± 0.2 MPa and the best 20:80 sample exhibited 1.9 ± 0.4 MPa). This indicates that the ratio between the hard (protein) and soft (copolymer PEGMA) domains induce significant changes to the tensile strengths of the polymer sheets. Thermally, the WPI-based polymer samples are stable up to 277.8 ± 6.2 °C and the WPC-based samples are stable up to 273.0 ± 3.4 °C.

Proteins have great potential as biomass-derived feedstocks for material synthesis and can form strong materials due to their highly hydrogen-bonded nature. Elastomers comprised of proteins and a synthetic rubbery polymer were prepared by copolymerizing a methacrylated protein and a vinyl monomer, where proteins function as macro-cross-linkers and reinforcing fillers. Selecting a hydrophobic synthetic polymer block partially mitigates the moisture absorption of protein-based materials while maintaining desirable levels of mechanical properties. The use of a hydrophobic monomer is enabled by the use of surfactants that function as compatibilizers, since proteins are generally insoluble in organic solvents and vinyl monomers. Surfactants also lower the softening temperature of proteins, allowing materials to be fabricated solvent free using thermoplastic processing techniques. The preparation of a polyacrylate network toughened through incorporation of protein cross-linking domains is demonstrated using whey protein, the cationic surfactant benzalkonium chloride, and the hydrophobic monomer n-butyl acrylate. The resulting materials are amorphous and disordered but have microphase-separated protein-rich and polyacrylate-rich domains. All materials soften with increasing relative humidity, but the presence of a hydrophobic polyacrylate decreases the material’s moisture absorption at high humidity levels when compared to pure protein and networks comprised of a hydrophilic polyacrylate.