Grafting-from Method Research Articles

Nonconjugated amylopectin-grafted copolymers with dual fluorescence/low-temperature phosphorescence emission and superior processability

Nonconjugated fluorescent polymers devoid of large π–π conjugated structures have received considerable attention due to their significant academic importance and broad application potentials in various fields. Herein, we report an effective strategy to fabricate multifunctional fluorescent amylopectin derivatives and reveal their unique aspects of aggregation-induced emission (AIE), cryogenic long-persistent phosphorescence (~6 s) and excellent processabilities characteristics, which are extremely different from traditional luminogens. These amylopectin-graft-poly(n-butyl acrylate-co-1-vinylimidazole) copolymers (Amylopectin-BVs) prepared by the grafting-from method employing RAFT and experienced subsequently with metal-ligand cross-linking. Specifically, clustering-triggered fluorescent emission or cryogenic long-persistent phosphorescence of amylopectin could be achieved by the aggregation of oxygen and nitrogen atoms along with conformation rigidification, which shows great promise in optoelectronic and biological applications.

Thermally responsive porous membranes with both switching wettability and permeability prepared via grafting-to and grafting-from methods

Pre-synthesized amino-functional poly(N-isopropylacrylamide) (PNIPAm, grafting-to) and monomer (NIPAm, grafting-from) were grafted on with polydopamine pre-functionalized porous polyvinylidene difluoride (PVDF) membrane to fabricate thermally responsive membranes. Scanning electron microscopy revealed irregular particles and more homogeneous spherical particles on the surface of membranes fabricated by grafting-to and grafting-from, respectively. Grafting yield and chemical analyses further indicated higher grafting density for membranes prepared by grafting-from method. The lower grafting density of PNIPAm obtained by grafting-to method resulted in poor switching wettability and permeability; water contact angle and water permeance of the membrane increased from 41° to 49° and from 270 to 440 L m−2h−1bar−1 when temperature. was enhanced from 25 to 45 °C and thereby passed through the lower critical solution temperature (33 °C) of PNIPAm. The membrane obtained by grafting-from method showed a switching wettability between superhydrophilic and hydrophobic properties (0° at 25 °C to 117° at 45 °C) with a higher thermal responsive factor in water permeance (200 L m−2h−1bar−1 at 25 °C and 480 L m−2h−1bar−1 at 45 °C). From the results it can be concluded that the grafting-from approach is better suitable to fabricate thermally responsive membranes, and the membranes can be further tuned and applied to separate mixtures containing particles of various sizes while maintaining good antifouling and thermally induced cleaning properties.

A Comparative Study of "Grafting to" and "Grafting from" Conjugation Methods for the Preparation of Antibody-Temperature-Responsive Polymer Conjugates.

Early diagnosis of infectious diseases is still challenging particularly in a nonlaboratory environment or limited resources areas. Thus, sensitive, inexpensive, and easily handled diagnostic approaches are required. The lateral flow immunoassay (LFIA) is commonly used in the screening of infectious diseases despite its poor sensitivity, especially with low pathogenic loads (early stages of infection). This article introduces a novel polymeric material that might help in the enrichment and concentration of pathogens to overcome the LFIA misdiagnosis. To achieve this, we evaluated the efficiency of introducing poly(N-isopropylacrylamide) (PNIPAAm) into immunoglobulin G (IgG) as a model antibody using two different conjugation methods: grafting to (GT) and grafting from (GF). The IgG-PNIPAAm conjugates were characterized using SDS-PAGE, DLS, and temperature-responsive phase transition behavior. SDS-PAGE analysis revealed that the GF method was more efficient in introducing the polymer than the GT method, with calculated polymer introduction ratios of 61% and 34%, respectively. The GF method proved to be less susceptible to steric hindrance and more efficient in introducing high-molecular-weight polymers into proteins. These results are consistent with previous studies comparing the GT and GF methods in similar systems. This study represents an important step toward understanding how the choice of polymer incorporation method affects the properties of IgG-PNIPAAm conjugates. The synthesized polymer allowed binding and enrichment of mouse IgG that was used as a model antigen with a clear LFIA band. On the basis of our findings, this system might help in improving the sensitivity of simple diagnostics.

Antimicrobial Functionalization of Silicone-graft-poly(N-vinylimidazole) Catheters.

In this work, we present the modification of a medical-grade silicone catheter with the N-vinylimidazole monomer using the grafting-from method at room temperature and induced by gamma rays. The catheters were modified by varying the monomer concentration (20-100 vol%) and the irradiation dose (20-100 kGy). Unlike the pristine material, the grafted poly(N-vinylimidazole) chains provided the catheter with hydrophilicity and pH response. This change allowed for the functionalization of the catheters to endow it with antimicrobial features. Thus, the quaternization of amines with iodomethane and bromoethane was performed, as well as the immobilization of silver and ampicillin. The inhibitory capacity of these materials, functionalized with antimicrobial agents, was challenged against Escherichia coli and Staphylococcus aureus strains, showing variable results, where loaded ampicillin was amply better at eliminating bacteria.

A stable amphiphilic hybrid nanoparticle compatibilizer constructed from polyhedral oligomeric silsesquioxane (POSS) for immiscible thermoplastic polyurethane/methyl vinyl silicone elastomer (TPU/MVQ) blends

A series of amphiphilic hybrid POSS particles grafted with PDMS chains and PU analogue chains (PUA-POSS-PDMS) were prepared by a grafting-from method, and can be used as compatibilizers for TPU/MVQ blends.

Thiol-selective native grafting from polymerization for the generation of protein-polymer conjugates.

Protein-polymer conjugates combine properties of biopolymers and synthetic polymers, such as specific bioactivity and increased stability, with great benefits for various applications from catalysis to biomedicine. Furthermore, polymer conjugation can mimic important posttranslational modifications of proteins such as glycosylation. There are typically two approaches to create protein-polymer conjugates: the protein is functionalized in advance with an initiator for a grafting-from method or a previously produced polymer is conjugated to the protein via a grafting-to method. In this study, we present a new approach that uses native proteins and allows for direct grafting-from using a thiol-induced, light-activated controlled radical polymerization (TIRP) that is initiated at thiols from specific cysteine residues of the protein. This straightforward method is employed to introduce polymers onto proteins and enzymes without any prior protein modifications, it works in aqueous buffer and maintains the protein's native structure and activity. The resulting protein-polymer conjugates exhibit high molar masses and low dispersities. We demonstrate the versatility of this approach by introducing different types of polymers such as hydrophilic poly(2-hydroxyethyl acrylate) (pHEAA), temperature-responsive poly(N-isopropylacrylamide) (pNIPAM) as well as glycopolymers mimicking the natural protein glycosylation and enabling selective interactions. We present successful combinations of the protein and polymer functions e.g., temperature-induced aggregation leading to an increase in enzyme activity and the introduction of artificial glycosylation inducing specific protein-protein cluster formation and giving straightforward access to glycosurfaces. Based on this straightforward, potentially scalable yet highly controlled synthesis of protein-polymer conjugates, various areas of applications are envisioned ranging from biomedicine to material sciences.

Multibranched polymethacrylates by anionic grafting-from method via desilylation of poly(4-trimethylsilylmethylstyrene)

Abstract A benzyltrimethylsilane (BnTMS)/potassium tert-butoxide (t-BuOK) initiator system for anionic polymerization was applied to poly(4-trimethylsilylmethylstyrene) (PTMSMS) in the presence of 1,1-diphenylethylene (DPE) to construct polyanion macroinitiators and polymerize methacrylate monomers therefrom. Using this method, desilylation of PTMSMS was quantitatively processed and methacrylate monomers were polymerized from the macroinitiator. The obtained multibranched polymers had narrow molecular weight distributions, indicating the well-controlled polymerization of the monomers from the macroinitiator. Therefore, it was demonstrated that PTMSMS can be a suitable precursor for the preparation of multibranched polymers. Additionally, a sequential addition of methacrylate monomers to the polyanion macroinitiator lead to a core-shell multibranched polymer with a narrow molecular weight distribution.

Surfaces Coated with Polymer Brushes Work as Carriers for Histidine Ammonia Lyase.

The immobilization of enzymes on solid supports is an important challenge in biotechnology and biomedicine. In contrast to other methods, enzyme deposition in polymer brushes offers the benefit of high protein loading that preserves enzymatic activity in part due to the hydrated 3D environment that is available within the brush structure. The authors equipped planar and colloidal silica surfaces with poly(2-(diethylamino)ethyl methacrylate)-based brushes to immobilize Thermoplasma acidophilum histidine ammonia lyase, and analyzed the amount and activity of the immobilized enzyme. The poly(2-(diethylamino)ethyl methacrylate) brushes are attached to the solid silica supports either via a "grafting-to" or a "grafting-from" method. It is found that the grafting-from method results in higher amounts of deposited polymer and, consequently, higher amounts of Thermoplasma acidophilum histidine ammonia lyase. All polymer brush-modified surfaces show preserved catalytic activity of the deposited Thermoplasma acidophilum histidine ammonia lyase. However, immobilizing the enzyme in polymer brushes using the grafting-from method resulted in twice the enzymatic activity from the grafting-to approach, illustrating a successful enzyme deposition on a solid support.

Use of a Photocleavable Initiator to Characterize Polymer Chains Grafted onto a Metal Plate with the Grafting-from Method.

The thorough characterization of polymer chains grafted through a "grafting-from" process onto substrates based on the determination of number (Mn) and weight (Mw) average molar masses, as well as dispersity (Ɖ), is quite challenging. It requires the cleavage of grafted chains selectively at the polymer-substrate bond without polymer degradation to allow their analysis in solution with steric exclusion chromatography, in particular. The study herein describes a technique for the selective cleavage of PMMA grafted onto titanium substrate (Ti-PMMA) using an anchoring molecule that combines an atom transfer radical polymerization (ATRP) initiator and a UV-cleavable moiety. This technique allows the demonstration of the efficiency of the ATRP of PMMA on titanium substrates and verification that the chains were grown homogeneously.

Grafting-To and From for Multiplexed Chemical-Warfare-Agent Responsive Polymer Brushes

Surface-tethered polymers have important applications in functional polymer coatings, particularly for the development of chemically responsive surfaces. Here, we combined the traditional grafting-to and grafting-from methods to create a new surface grafting strategy, termed grafting-to and from, using surface-initiated ring-opening metathesis polymerization (SI-ROMP). In this method, poly(pentafluorophenyl methacrylate) is grafted to an amine terminated surface. Surplus reactive esters after reaction with surface amines render this polymer a connecting or tie layer that can be further reacted to provide dense ROMP initiation sites. This amplification of grafting sites results in thick and environmentally stable polymer brushes upon SI-ROMP. With the goal of developing polymer-grafted breathable membranes that autonomously react to multiple chemical warfare agents (CWAs), we demonstrate the benefit of this method by employing amine reactive monomers in the grafting-from step. This enables diverse postsynthetic functionalization for the facile screening of chemical motifs to enhance response capabilities to mustard blister agents. Surface-tethered triarylmethanol-containing polymers with four distinct functional groups are prepared and challenged with the vapor of 2-chloroethyl ethyl sulfide (CEES), a simulant of mustard agent, in humid air. Importantly, hydroxyl groups effectively improve CWA response and the resulting polymer brushes show chain collapse after both CEES and diethylchlorophosphate (DCP) treatment. Our results illustrate that the grafting-to and from method can be used to grow functional and robust polymer coatings for various applications.

Grafting density and antifouling properties of poly[N-(2-hydroxypropyl) methacrylamide] brushes prepared by “grafting to” and “grafting from”

Poly(HPMA) brushes prepared by a grafting-from method suppress fouling from blood plasma by an order of magnitude better than the polymer brushes of the same molecular weight prepared by a grafting-to method.

Preparation of nanoparticles of shellac and shellac-oligomer conjugates

Shellac is a natural biodegradable oligoester produced by lac insects, containing reactive functional groups such as hydroxyl, carboxylic acid, ester, aldehyde, and alkene groups, which can be used for chemical functionalization. Herein, shellac is functionalized with poly(ethylene glycol) (PEG) or poly(N-isopropylacrylamide) (PNIPAM) via grafting-to and grafting-from methods. The functional polymer conjugates are then processed as nanoparticles by the miniemulsion-solvent evaporation process. Shellac-PEG nanoparticles are enriched with apolipoprotein AI after incubation in fetal bovine serum at 37 °C. Moreover, shellac-PNIPAM nanoparticles adsorb specifically prothrombin at 37 °C (T > volume phase transition temperature, VPTT).

Combining ‘grafting to’ and ‘grafting from’ to synthesize comb-like NCC-g-PLA as a macromolecular modifying agent of PLA

The surface modification of nano particles is very important in nanotechnology. Grafting from (GF) and grafting to (GT) are two main methods to prepare surface modified nanoparticles like nanocellulose crystalline (NCC) grafted with polylactic acid (PLA) chains. In the GF method, the NCC can get high grafting degree but short side chains to improve its compatibility with the polymer matrix. The GT method can help obtain long side chains to increase the chain entanglements but owns low grafting density. To take the advantage of both methods, a mixed modification method combining GT and GF methods was put forward to synthesize comb-like NCC-g-PLA (NP) as a macromolecular modifying agent of PLA. Firstly, GT Method was used to obtain long side-chain NP to improve chain entanglement. Secondly, the GF method was applied to obtain NP-g-PLA (NPL) and NP-g-PDLA (NPD) with additional short side chains to improve its dispersion and compatibility in the PLA matrix. The products showed an enhanced nucleation effect, the degree of crystallinity (Xc ) of PLA composites increased almost four times with only 1 wt% NPD or NPL. What’s more, the storage modulus and loss modulus of the composite melts also increased with 1 wt% NPL or NPD. The NPD/PLA shows a higher effect than NPL/PLA owning to stronger interaction originated from the stereocomplex (SC) network of PLA matrix with PDLA short chains in NPD.

Xylanase-polymer conjugates as new catalysts for xylooligosaccharides production from lignocellulose

In the past few years, xylooligosaccharides produced from lignocellulosic biomass have attracted great attention. Enzyme catalysis is widely used because of its mild reaction conditions. In order to solve the shortcomings of poor stability and high cost of enzyme, a carrier-free enzyme immobilization technology was introduced. For this purpose, protein-polymer conjugates, kinds of carrier-free immobilized enzymes, were first established by growing poly (N-isopropylacrylamide) chains on xylanase using a grafting-from method, to obtain reusable and high-value xylanase. SDS-PAGE and circular dichroism spectra showed the successful preparation of xylanase-PNIPAAm conjugates, and the integrity of the protein secondary structure. The remaining activity of the xylanase-PNIPAAm conjugates after heat treatment (90 °C) for 60 min was approximately 20 % higher than that of the free xylanase, and a higher pH stability was obtained in the pH range of 2−8. The remaining activity of xylanase-PNIPAAm conjugates was more than 60 % after recycling 5 times. In addition, the mulberry bark synergistic treated by xylanase-PNIPAAm conjugates and cellulase was studied. More than 99.95 % yield of XOS in the degree of polymerization range of 1–3 was produced from mulberry bark. Overall, the construction of xylanase-PNIPAAm conjugates provides a novel method to produce xylooligosaccharides from waste biomass.

Pyridine-2,6-dicarboxaldehyde-Enabled N-Terminal In Situ Growth of Polymer-Interferon α Conjugates with Significantly Improved Pharmacokinetics and In Vivo Bioactivity.

Polymer-protein conjugates are a class of biohybrids with unique properties that are highly useful in biomedicine ranging from protein therapeutics to biomedical imaging; however, it remains a considerable challenge to conjugate polymers to proteins in a site-specific, mild, and efficient way to form polymer-protein conjugates with uniform structures and properties and optimal functions. Herein we report pyridine-2,6-dicarboxaldehyde (PDA)-enabled N-terminal modification of proteins with polymerization initiators for in situ growth of poly(oligo(ethylene glycol)methyl ether methacrylate) (POEGMA) conjugates uniquely at the N-termini of a range of natural and recombinant proteins in a mild and efficient fashion. The formed POEGMA-protein conjugates showed highly retained in vitro bioactivity as compared with free proteins. Notably, the in vitro bioactivity of a POEGMA-interferon α (IFN) conjugate synthesized by this new chemistry is 8.1-fold higher than that of PEGASYS that is a commercially available and Food and Drug Administration (FDA) approved PEGylated IFN. The circulation half-life of the conjugate is similar to that of PEGASYS but is 46.2 times longer than that of free IFN. Consequently, the conjugate exhibits considerably improved antiviral bioactivity over free IFN and even PEGASYS in a mouse model. These results indicate that the PDA-enabled N-terminal grafting-from method is applicable to a number of proteins whose active sites are far away from the N-terminus for the synthesis of N-terminal polymer-protein conjugates with high yield, well-retained activity, and considerably improved pharmacology for biomedical applications.

Fabrication of 2D Block Copolymer Brushes via a Polymer-Single-Crystal-Assisted-Grafting-to Method.

Block copolymer brushes are of great interest due to their rich phase behavior and value-added properties compared to homopolymer brushes. Traditional synthesis involves grafting-to and grafting-from methods. In this work, a recently developed "polymer-single-crystal-assisted-grafting-to" method is applied for the preparation of block copolymer brushes on flat glass surfaces. Triblock copolymer poly(ethylene oxide)-b-poly(l-lactide)-b-poly(3-(triethoxysilyl)propyl methacrylate) (PEO-b-PLLA-b-PTESPMA) is synthesized with PLLA as the brush morphology-directing component and PTESPMA as the anchoring block. PEO-b-PLLA block copolymer brushes are obtained by chemical grafting of the triblock copolymer single crystals onto a glass surface. The tethering point and overall brush pattern are determined by the single crystal morphology. The grafting density is calculated to be ≈0.36 nm-2 from the atomic force microscopy results and is consistent with the theoretic calculation based on the PLLA crystalline lattice. This work provides a new strategy to synthesize well-defined block copolymer brushes.

Photo-induced copper-mediated (meth)acrylate polymerization towards graphene oxide and reduced graphene oxide modification

The preparation of well-dispersed graphene/polymer nanocomposites is challenging due to the poor miscibility of graphene sheets in a polymer matrix. To enhance the interaction between both phases, graphene sheets can be decorated with polymer chains. Herein, different strategies to graft poly(methyl methacrylate) (PMMA) and poly(di(ethylene glycol) ethyl ether acrylate) (PDEGA) chains at various positions on graphene oxide and reduced graphene oxide (GO/rGO) sheets are compared. Chain attachment was achieved by “grafting-to” and “grafting-from” methods. Grafting-to was performed by classical copper (I)-catalyzed alkyne azide cycloaddition. Using a grafting-from approach, PMMA and PDEGA brushes were grown from GO and rGO sheets via surface-initiated photo-induced copper-mediated polymerization (SI-photoCMP). SI-photoCMP is a robust and efficient method that allows polymerizations to be carried out under mild conditions and with reduced catalyst concentration. Moreover, the successful implementation of SI-photoCMP in a continuous-flow set-up enables easy upscaling of the system and is, therefore, a more efficient and environmentally friendly process for GO/rGO surface modification. By using the grafting-to approach, the grafting density of PMMA (Mn = 2,600 g/mol) was one chain per 990 carbons of graphene. In contrast, longer PMMA chains (Mn = 40,300 g/mol) and higher grafting density were obtained via the grafting-from method (one PMMA chain per 140 carbons of graphene).

Branched polyglycidol and its derivatives grafted-from poly(ethylene terephthalate) and silica as surfaces that reduce protein fouling

Hyperbranched polyglycidol-coated silica or poly(ethylene terephthalate) surfaces were obtained as materials with reduced protein adsorption properties. To perform polymer grafting, the wafers were first functionalized: silica (Si) with 3-[bis(2-hydroxyethyl)amino]propyltriethoxysilane, and plasma treatment was applied for poly(ethylene terephthalate) (PET). The grafting-from method, using initiation of the anionic-ring opening polymerization of glycidol by the deprotonated alkoxide groups located on the wafers, was applied to immobilize the polymer on these two kinds of wafers. The grafting-from reactions carried out in solution allowed high molar masses of the tethered polyglycidol to be obtained. The polymerization was performed in the presence of a “free initiator”; thus, the information about molar mass and the structure of grafted polymers was estimated. The hydroxyl groups of Si-immobilized polyglycidol were modified with hydrophilic poly(ethylene glycol) or hydrophobic ethyl carbamate groups. The affinity of the polymer layers to water was controlled by the grafting density and type of polymer modification applied. All hyperbranched polyglycidol-based surfaces were able to reduce the protein adsorption to a high level.

Synthesis of lipase polymer hybrids with retained or enhanced activity using the grafting-from strategy

We report the synthesis of new polymer-protein conjugates using a grafting-from method employing photoinduced electron transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization. Lipase, an industrially important enzyme, was modified with a reversible addition-fragmentation (RAFT) chain transfer agent (CTA) using activated ester chemistry. To study the effects of polymer composition and molecular weight on the enzyme activity, a hydrophilic and hydrophobic polymer were grafted at three different polymer lengths. We found a significant impact of polymer composition on enzyme activity with hydrophobic polymer substantially increasing enzyme activity.

Grafting-From Proteins Using Metal-Free PET-RAFT Polymerizations under Mild Visible-Light Irradiation.

We report a new strategy toward polymer-protein conjugates using a grafting-from method that employs photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization. Initial screening of reaction conditions showed rapid polymerization of acrylamides under high dilution in water using eosin Y as a photocatalyst in the presence of a tertiary amine. A lysozyme-modified chain transfer agent allowed the same conditions to be utilized for grafting-from polymerizations, and we further demonstrated the broad scope of this technique by polymerizing acrylic and styrenic monomers. Finally, retention of the RAFT end group was suggested by successful chain extension with N-isopropylacrylamide from the polymer-protein conjugates to form block copolymer-protein conjugates. This strategy should expand the capabilities of grafting-from proteins with RAFT polymerization under mild conditions to afford diverse functional materials.