Use Of Random Copolymer Research Articles

Supra-biological performance of immobilized enzymes enabled by chaperone-like specific non-covalent interactions

Designing complex synthetic materials for enzyme immobilization could unlock the utility of biocatalysis in extreme environments. Inspired by biology, we investigate the use of random copolymer brushes as dynamic immobilization supports that enable supra-biological catalytic performance of immobilized enzymes. This is demonstrated by immobilizing Bacillus subtilis Lipase A on brushes doped with aromatic moieties, which can interact with the lipase through multiple non-covalent interactions. Incorporation of aromatic groups leads to a 50 °C increase in the optimal temperature of lipase, as well as a 50-fold enhancement in enzyme activity. Single-molecule FRET studies reveal that these supports act as biomimetic chaperones by promoting enzyme refolding and stabilizing the enzyme’s folded and catalytically active state. This effect is diminished when aromatic residues are mutated out, suggesting the importance of π-stacking and π-cation interactions for stabilization. Our results underscore how unexplored enzyme-support interactions may enable uncharted opportunities for using enzymes in industrial biotransformations.

Biodegradation Control of Chitosan Materials by Surface Modification with Copolymers of Glycidyl Methacrylate and Alkyl Methacrylates

Chitosan is a promising polymer from natural polysaccharides, which is an environmentally friendly compound from renewable raw materials. Chitosan has biodegradability, biocompatibility, and antibacterial and other activities. In this article, we report the biodegradation control of chitosan materials by use of random copolymers based on glycidyl methacrylate and (fluoro)alkyl methacrylates as surface modifiers. We show that grafting of copolymers allows increasing the hydrophobicity of chitosan materials with initial contact angles up to 114° from 89° for films and up to 154° from 123° for aerogels. We demonstrate that modified aerogels retain contact angles of more than 150° for a long contact time with water while the initial aerogel fully wets for 30 s. The resulting chitosan aerogels have high porosity with a pore size of 100–200 µm, and the pore walls are 0.6–0.7-µm-thick film formations. Our study of lyophilic properties of modified chitosan substrates showed a change in the hydrophobicity of the materials as a function of length of the hydrocarbon radical in the side groups of the (fluoro)alkyl methacrylates in the copolymers. We demonstrate that the rate of biodegradation of the resulting materials decreases with an increase in the number of hydrophobic groups in the modifier. The obtained chitosan materials with hydrophobic coatings have potential as a protective layer for wound dressings with an extended service life.

Two-Way Reversible Shape Memory Polymers Made of Cross-Linked Cocrystallizable Random Copolymers with Tunable Actuation Temperatures

Two-way reversible shape memory polymers (2W-SMPs) are highly desirable for many applications. We report for the first time the use of random copolymers with cocrystallizable monomeric units for the preparation of such polymer networks. Homopolymers and random copolymers of e-caprolactone and ω-pentadecalactone were designed and made by ring-opening polymerization with Candida antarctica lipase B as catalyst. The melting temperatures of these prepolymers may be adjusted by the use of various molar ratios of the comonomers. Upon thiol–ene cross-linking, the polymer network exhibited two-way reversible shape memory effects under both stress-free and stress conditions. The actuation temperature (TA) of the 2W-SMP under stress-free condition can be tuned in a broad range using a selected mixture of prepolymers followed by photo-cross-linking with a multifunctional cross-linker. Increasing the initial stretching stress amplitude led to an increased absolute strain change under both stress-free and stress condi...

Controlling Block Copolymer–Substrate Interactions by Homopolymer Brushes/Mats

Control over the orientation of cylindrical and lamellar domains is required for pattern transfer in block copolymer lithography. Previous work mainly focuses on the use of random copolymer brushes to control the wetting behaviors of block copolymers (BCPs), but random copolymerization is only limited to a few monomer pairs. Here we demonstrate the use of homopolymer brushes/mats to modify the substrate to form a chemically homogeneous surface. The surface affinity is tuned by changing the monomer substituent, and a variety of wetting behaviors are obtained in BCP films on homopolymer brushes/mats. Three series of hydroxy-terminated or cross-linkable homopolymers, including polymethacrylate, polyacrylate, and polystyrene derivatives, are prepared for controlling the BCP–substrate interaction. Both preferential and nonpreferential wetting behaviors of poly(styrene-b-methyl methacrylate), poly(styrene-b-rac-lactide), and poly(styrene-b-propylene carbonate) films are obtained as the homopolymer structures ch...

Integration of a templated directed self-assembly-based hole shrink in a short loop via chain

The use of directed self-assembly (DSA) of cylinder forming block copolymers (BCP) for contact hole shrink applications has gained increased attention due to the dimensions that can be achieved with this materials. Recent work has focused on engineering the dimensions and surface energy of the templates to obtain straight profiles of the cylinders assembled in them. However, the impact of process optimization on defect formation is measured using scanning electron microscopy before and after transferring the BCP features to a hardmask, which provides limited information about the presence of defects or three-dimensional morphologies in the polymer structures. To identify the presence of single defects in arrays of various densities and sizes, we use Kelvin and chain structures available in the IMEC 28-nm node via chain electrical test vehicle, Everest, in combination with templated DSA. We tuned the surface energy and dimensions of the templates with the use of random copolymers and through the exposure conditions, respectively. Finally, the contact holes obtained with templated DSA of BCP were subsequently transferred into a relevant stack to apply advanced metallization processes and, ultimately, validated electrically.

ChemInform Abstract: Self‐Assembly of Random Copolymers

AbstractReview: 134 refs.

Self-assembly of random copolymers.

Self-assembly of random copolymers has attracted considerable attention recently. In this feature article, we highlight the use of random copolymers to prepare nanostructures with different morphologies and to prepare nanomaterials that are responsive to single or multiple stimuli. The synthesis of single-chain nanoparticles from random copolymers and their potential applications are also discussed in some detail. We aim to draw more attention to these easily accessible copolymers, which are likely to play an important role in translational polymer research.

A Novel Architecture toward Third-Generation Thermoplastic Elastomers by a Grafting Strategy

Thermoplastic elastomers (TPEs) are ever sought using a simple robust synthetic approach. Widely successful first-generation TPEs rely on microphase-separated ABA triblock copolymers (Architecture I). Recent multigraft copolymers represent the second-generation TPEs in which multiple branched rigid segments are dispersed in a rubbery backbone matrix (Architecture II). This paper reports our discovery of the third-generation TPEs that are based on rigid backbone dispersed in a soft grafted matrix. This Architecture III allows the use of random copolymers as side chains to access a wide spectrum of TPEs that cannot be achieved by architecture designs of the first two generations. In this report, random copolymer-grafted cellulose, cellulose-graft-poly(n-butyl acrylate-co-methyl methacrylate) copolymers with only 0.9–3.4 wt % cellulose prepared by activators regenerated by electron transfer for atom transfer radical polymerization (ARGET ATRP), as novel thermoplastic elastomers are investigated.

Generalization of the Use of Random Copolymers To Control the Wetting Behavior of Block Copolymer Films

Random copolymer brushes of poly(styrene-r-methyl methacrylate) (PS-r-PMMA) have previously been used to control the wetting behavior of poly(styrene-b-methyl methacrylate) (PS-b-PMMA) block copolymer. Here we demonstrate that the use of random copolymer may be generalized to other block copolymer systems. A series of poly(styrene-r-2-vinylpyridine-r-hydroxyethyl methacrylate) (PS-r-P2VP-r-PHEMA) random copolymers was synthesized and evaluated as brush layers to control the orientation of domains in thin films of poly(styrene-b-2-vinylpyridine) (PS-b-P2VP) block copolymer. On nonpreferential brushes, thin films of PS-b-P2VP had a mixed orientation of domains consisting of a perpendicular orientation of lamellar domains near the copolymer−substrate interface and a parallel orientation of lamellar domains at free surface because of the lower surface energy of the PS block. The composition window of brushes that induce vertical orientation of domains near the substrate ranges from 47.8% styrene to 57.0% styrene, as determined by SEM and GISAXS measurements of films after removal of the parallel-oriented domains at surfaces (remaining film thickness ≈ 50 nm). When the PS-b-P2VP film was confined between two brushes having compositions within the above range, perpendicular-oriented lamellae that traversed the film thickness were obtained.

A GPC method to determine the composition of two component copolymers

The overall composition of random and block copolymers comprising two kinds of repeat units can be determined as a function of molecular weight by a new dual (e.g., UV and RI) detector GPC technique, if one of the repeat units can be specifically “seen” by one of the detectors. The method is demonstrated by the use of random copolymers of styrene (St) and isobutylene (IB) as the UV “visible” and “invisible” components, respectively. Novel triblock copolymers comprising two polyacenaphtylene (PAc) outer-segments and a polyisobutylene (PIB) mid-segment are also analyzed.

Use of random copolymers to determine the helix-coil stability constants of the naturally occurring amino acids

Abstract Short-range interactions dominate in determining the conformational preferences of the amino acid residues in proteins, and a variety of procedures (based on this concept) have been developed to predict the conformational states of the residues of a protein molecule. This paper is concerned with two such conformational states, helical and non-helical (or coil) states; the relative preferences of each of the twenty naturally occurring amino acids for these two states can be expressed in terms of the Zimm-Bragg parameters s and σ. In principle, these parameters can be determined from experimental studies of the thermally-induced helix-coil transition in homopolymers of amino acids in water. However, since most homopolyamino acids are insoluble in water, or are not helical, or (if helical) do not melt between 0 and 100°C in water, resort is had to the host-guest technique in which a random copolymer of a water-soluble host residue and a small amount of a guest residue is prepared. Using the helix-coil transition curves of such a copolymer, and the values of s and σ for the host homopolymer, it is possible to compute the values of s and σ over the temperature range of 0 – 70°C for the guest residue which is, in turn, each of the twenty naturally occurring amino acids. In most cases, the random copolymers are prepared from their N-carboxyan-hydrides, using suitable blocking groups to protect otherwise-reactive side-chain functional groups. The water-soluble copolymers are checked for the absence of racemization, α → β shifts, etc., and for the required degree of randomness. For example, for methionine as a guest residue, cyanogen bromide cleavage of the polymer chain yields a series of oligopeptides which indicates that the methionine was incorporated randomly in the chain. When the resulting values of s and σ are compared to the frequencies of occurrence of helical and non-helical conformations in proteins, a good correlation is obtained in most cases. In those cases where the correlation breaks down, the discrepancy provides information about the influence of specific long-range (e.g., electrostatic) interactions on the helical preferences of the given amino acid residues. The statistical weights deduced from the one-dimensional short-range interaction model are then incorporated with medium- and long-range interactions into a model to try to predict the three-dimensional structures of globular proteins.