Copper-mediated Living Radical Polymerization Research Articles

Hydrophilic Nonwoven Nanofiber Membranes as Nanostructured Supports for Enzyme Immobilization.

The high porosity, interconnected pore structure, and high surface area-to-volume ratio make the hydrophilic nonwoven nanofiber membranes (NV-NF-Ms) promising nanostructured supports for enzyme immobilization in different biotechnological applications. In this work, NV-NF-Ms with excellent mechanical and chemical properties were designed and fabricated by electrospinning in one step without using additives or complicated crosslinking processes after electrospinning. To do so, two types of ultrahigh-molecular-weight linear copolymers with very different mechanical properties were used. Methyl methacrylate-co-hydroxyethyl methacrylate (p(MMA)-co-p(HEMA)) and methyl acrylate-co-hydroxyethyl acrylate (p(MA)-co-p(HEA)) were designed and synthesized by reverse atom transfer radical polymerization (reverse-ATRP) and copper-mediated living radical polymerization (Cu0-MC-LRP), respectively. The copolymers were characterized by nuclear magnetic resonance (1H-NMR) spectroscopy and by triple detection gel permeation chromatography (GPC). The polarity, topology, and molecular weight of the copolymers were perfectly adjusted. The polymeric blend formed by (MMA)1002-co-(HEMA)1002 (Mw = 230,855 ± 7418 Da; Mn = 115,748 ± 35,567 Da; PDI = 2.00) and (MA)11709-co-(HEA)7806 (Mw = 1.972 × 106 ± 33,729 Da; Mn = 1.395 × 106 ± 35,019 Da; PDI = 1.41) was used to manufacture (without additives or chemical crosslinking processes) hydroxylated nonwoven nanofiber membranes (NV-NF-Ms-OH; 300 nm in fiber diameter) with excellent mechanical and chemical properties. The morphology of NV-NF-Ms-OH was studied by scanning electron microscopy (SEM). The suitability for enzyme binding was proven by designing a palette of different surface functionalization to enable both reversible and irreversible enzyme immobilization. NV-NF-Ms-OH were successfully functionalized with vinyl sulfone (281 ± 20 μmol/g), carboxyl (560 ± 50 μmol/g), and amine groups (281 ± 20 μmol/g) and applied for the immobilization of two enzymes of biotechnological interest. Galactose oxidase was immobilized on vinyl sulfone-activated materials and carboxyl-activated materials, while laccase was immobilized onto amine-activated materials. These preliminary results are a promising basis for the application of nonwoven membranes in enzyme technology.

Coating Titania Nanoparticles with Epoxy-Containing Catechol Polymers via Cu(0)-Living Radical Polymerization as Intelligent Enzyme Carriers.

Immobilization of enzyme could offer the biocatalyst with increased stability and important recoverability, which plays a vital role in the enzyme's industrial applications. In this study, we present a new strategy to build an intelligent enzyme carrier by coating titania nanoparticles with thermoresponsive epoxy-functionalized polymers. Zero-valent copper-mediated living radical polymerization (Cu(0)-LRP) was utilized herein to copolymerize N-isopropylacrylamide (NIPAM) and glycidyl acrylate (GA) directly from an unprotected dopamine-functionalized initiator to obtain an epoxy-containing polymer with terminal anchor for the "grafting to" or "one-pot" modification of titania nanoparticles. A rhodamine B-labeled laccase has been subsequently used as a model enzyme for successful immobilization to yield an intelligent titania/laccase hybrid bifunctional catalyst. The immobilized laccase has shown excellent thermal stability under ambient or even relatively high temperature above the lower critical solution temperature (LCST) at which temperature the hybrid particles could be facilely recovered for reuse. The enzyme activity could be maintained during the repeated use after recovery and enzymatic degradation of bisphenol A was proven to be efficient. The photocatalytic ability of titania was also investigated by fast degradation of rhodamine B under the excitation of simulated sunlight. Therefore, this study has provided a facile strategy for the immobilization of metal oxide catalysts with enzymes, which constructs a novel bifunctional catalyst that will be promising for the "one-pot" degradation of different organic pollutants.

Synthesis and Assembly of Laccase-Polymer Giant Amphiphiles by Self-Catalyzed CuAAC Click Chemistry.

Covalent coupling of hydrophobic polymers to the exterior of hydrophilic proteins would mediate unique macroscopic assembly of bioconjugates to generate amphiphilic superstructures as novel nanoreactors or biocompatible drug delivery systems. The main objective of this study was to develop a novel strategy for the synthesis of protein-polymer giant amphiphiles by the combination of copper-mediated living radical polymerization and azide-alkyne cycloaddition reaction (CuAAC). Azide-functionalized succinimidyl ester was first synthesized for the facile introduction of azide groups to proteins such as albumin from bovine serum (BSA) and laccase from Trametes versicolor. Alkyne-terminal polymers with varied hydrophobicity were synthesized by using commercial copper wire as the activators from a trimethylsilyl protected alkyne-functionalized initiator in DMSO under ambient temperature. The conjugation of alkyne-functionalized polymers to the azide-functionalized laccase could be conducted even without additional copper catalyst, which indicated a successful self-catalyzed CuAAC reaction. The synthesized amphiphiles were found to aggregate into spherical nanoparticles in water and showed strong relevance to the hydrophobicity of coupled polymers. The giant amphiphiles showed decreased enzyme activity yet better stability during storage after chemical modification and self-assembly. These findings will deepen our understanding on protein folding, macroscopic self-assembly, and support potential applications in bionanoreactor, enzyme immobilization, and water purification.

Copper-Mediated Living Radical Polymerization (Atom Transfer Radical Polymerization and Copper(0) Mediated Polymerization): From Fundamentals to Bioapplications.

Copper-Mediated Living Radical Polymerization (Atom Transfer Radical Polymerization and Copper(0) Mediated Polymerization): From Fundamentals to Bioapplications.

Dendritic Cell Lectin-Targeting Sentinel-like Unimolecular Glycoconjugates To Release an Anti-HIV Drug

A series of cyclodextrin-based glycoconjugates, including glycoclusters and star glycopolymers, were synthesized via combination of CuAAC Huisgen coupling and copper-mediated living radical polymerization. These glycoconjugates showed high affinity binding to the human transmembrane lectin DC-SIGN and act as inhibitors to prevent the binding of HIV envelope protein gp120 to DC-SIGN at nanomolar concentrations. The star block glycopolymers showed high loading capacity of hydrophobic anticancer and anti-HIV drugs, indicating promising applications in HIV-therapeutic and smart drug delivery.

Copper-mediated living radical polymerization (SET-LRP) of lipophilic monomers from multi-functional initiators: reducing star–star coupling at high molecular weights and high monomer conversions

The SET-LRP of lipophilic monomers (n-butyl and lauryl acrylate) from a lactose based octa-functional initiator is described. A range of highly defined lipophilic poly(acrylate) stars are prepared to relatively high molecular weights (Mn,target > 100 000 g mol−1 in some cases) and high monomer conversions (≥99%) with excellent control retained over molecular weight distributions (PDI values as low as 1.03). Phase separation of star polymers from the reaction media during polymerization is seen to occur which is advantageous in reducing star–star coupling in certain cases, without limiting the attainment of near quantitative conversions. A comparison is made between heterogeneous and homogeneous polymerization protocols to illustrate this finding.

High-affinity glycopolymer binding to human DC-SIGN and disruption of DC-SIGN interactions with HIV envelope glycoprotein.

Noncovalent interactions between complex carbohydrates and proteins drive many fundamental processes within biological systems, including human immunity. In this report we aimed to investigate the potential of mannose-containing glycopolymers to interact with human DC-SIGN and the ability of these glycopolymers to inhibit the interactions between DC-SIGN and the HIV envelope glycoprotein gp120. We used a library of glycopolymers that are prepared via combination of copper-mediated living radical polymerization and azide−alkyne [3+2] Huisgen cycloaddition reaction. We demonstrate that a relatively simple glycopolymer can effectively prevent the interactions between a human dendritic cell associated lectin (DC-SIGN) and the viral envelope glycoprotein gp120. This approach may give rise to novel insights into the mechanisms of HIV infection and provide potential new therapeutics.

Multi-End-Functionalized Polymers: Additives to Modify Polymer Properties at Surfaces and Interfaces

An ongoing challenge in polymer science is the preparation of materials with specific surface properties which differ from that of the bulk, for example, hydrophobicity, wettability, chemical resistance, adhesion, or biocompatibility, while retaining the advantageous mechanical properties of the bulk polymer. We have explored the use of multi-end-functionalized polymer additives which undergo rapid adsorption to a surface or interface as an efficient method of modifying surface properties. Aryl ether moieties bearing up to four C8F17 groups have been used as initiators in the copper-mediated living radical polymerization of both styrene and methyl methacrylate, and the resulting polymers have been used as additives to render the surfaces of the corresponding bulk polymers hydrophobic and oleophobic. When such an additive consisting of a polystyrene chain with a molecular weight of ~10 000 g mol-1 end-capped with four C8F17 groups is present (in a matrix of polystyrene) at levels between 5 and 10 wt %, near PTFE-like surface properties result.

Synthesis and aqueous solution properties of stimuli-responsive triblock copolymers

Two series of poly(di(methylamino)ethyl methacrylate)--poly(di(ethylene glycol)methyl ether methacrylate)--poly(di(methylamino)ethyl methacrylate), pDMAEMA--pDEGMEMA--pDMAEMA, and poly(di(ethylamino)ethyl methacrylate)--poly(di(ethylene glycol)methyl ether methacrylate)--poly(di(ethylamino)ethyl methacrylate), pDEAEMA--pDEGMEMA--pDEAEMA, triblock copolymers have been synthesized using copper-mediated living radical polymerization. Kinetic studies showed that the polymerizations were controlled yielding copolymers with MWt similar to predicted values with narrow polydispersities. UV/Vis experiments in aqueous solution indicate that the incorporation of pDMAEMA hydrophilic segments into the pDEGMEMA polymeric chains causes an increase in the lower critical solution temperature (LCST). Conversely, the incorporation of pDEAEMA hydrophobic segments has the reverse effect. It has been demonstrated that the cloud points of the copolymers increase when blocks pDMAEMA and pDEAEMA are protonated. At acidic pH and above 35-40 °C, the pDEGMEMA inner blocks become insoluble and, consequently, upon contact with water they form micellar aggregates constituted of a pDEGMEMA hydrophobic core with a pDMAEMA or pDEAEMA hydrophilic shell. At pH = 8.3 and 25 °C, the pDMAEMA--pDEGMEMA--pDMAEMA triblock copolymers form ordered aggregates of larger size. In addition under these conditions, in aqueous solution the pDEGMEMA form aggregates of smaller size than those found in the case of copolymers with pDMAEMA. Surface-tension measurements suggest that homopolymers, as well as copolymers, are surface active. The pDEGMEMA polymers present low values of the critical aggregation concentration (cac), due to their amphiphilic properties. The combination of pDEGMEMA thermosensitive segments with pDMAEMA and pDEAEMA blocks sensitive to pH and temperature has given rise to the formation of intelligent materials with responses to both stimuli. Their behavior depends on the MWt and the composition of the copolymers.

Amide Functional Initiators for Transition-Metal-Mediated Living Radical Polymerization

Amide initiators were used successfully for copper-mediated living radical polymerization (often called ATRP) of a range of methacrylates to narrow molecular weight homopoymers and block copolymers from initiator species containing a bromo-2-methylpropionamide. The polymerization of methyl methacrylate (MMA) occurs efficiently with a copper chloride (Cu(I)Cl)/N-n-octyl-2-pyridylmethanimine catalyst by maintaining a relatively low temperature for initiation and slowly increasing to the reaction temperature. By keeping the reaction at 25 °C for 30 min before heating to 90 °C, a number-average molecular weight (Mn) of 12 900 g mol-1 and a polydispersity of (PDI) = 1.24 at 70% conversion (where [MMA]/[initiator] = 100) were obtained. The polymers produced showed molecular weights in good agreement with the theoretical and polydispersities of 1.20. Where the reaction was heated to 90 °C, immediately high mass was obtained (26 600 g mol-1) in low yield (33%). When copper bromide (Cu(I)Br) was used in place of Cu(I)Cl, the obtained mass was much higher than the theoretical values. Polymerization from an initiator based on l-alanine under these conditions gave poly(methyl methacrylate) (PMMA) with Mn = 8100 g mol-1 (PDI = 1.23) as compared to the theoretical value of 5900 at this conversion (58% after 7 h). Polymerization of a other methacrylates including butyl methacrylate (Mn = 8700 (PDI = 1.27), Mn,theo = 7000), benzyl methacrylate (Mn = 11 400 (PDI = 1.25), Mn,theo = 9700), dimethylaminoethyl methacrylate (DMAEMA) (Mn = 10 900 (PDI = 1.24), Mn,theo = 8100), and also poly(ethylene glycol) methacrylate (Mn = 8100 (PDI = 1.24), Mn,theo = 6500) were also polymerized. The successful polymerization of styrene using bromo-2-methylpropionamide initiators is also reported with optimum conditions needing 110 °C in the presence of Cu(I)Br and N-n-octyl-2-pyridylmethanimine yield polymer with Mn = 5800 (PDI = 1.27). Poly(methyl methacrylate) was also used as macroinitiator with DMAEMA to form an AB block copolymer, confirming the living nature of the polymers (Mn = 34 700 (PDI = 1.25)). A triblock polymer of methyl methacrylate and poly(dimethylsiloxane) (PDMS) was also prepared from a difunctional bromo-2-methylpropionamide poly(dimethylsiloxane) initiator (Mn = 29 600 (PDI = 1.27)).

Design and Synthesis of N-Maleimido-Functionalized Hydrophilic Polymers via Copper-Mediated Living Radical Polymerization: A Suitable Alternative to PEGylation Chemistry

A series of alpha-functional maleimide polymethacrylates (M(n) = 4.1-35.4 kDa, PDi = 1.06-1.27) have been prepared via copper-catalyzed living radical polymerization (LRP). Two independent synthetic protocols have been successfully developed and the polymers obtained in multigram scale, with an 80-100% content of maleimide reactive chain ends, depending on the method employed. A method for the synthesis of amino-terminated polymers, starting from Boc-protected amino initiators, has also been developed, as these derivatives are key intermediates in one of the two processes studied in the present work. The alternative synthetic pathway involves an initiator containing a maleimide unit "protected" as a Diels-Alder adduct. After the polymerization step, the maleimide functionality has been reintroduced by retro-Diels-Alder reaction, by simply refluxing those polymers in toluene for 7 h. These maleimido-terminated materials, poly(methoxyPEG((475))) methacrylates and poly(glycerol) methacrylates, differ for both the nature and size of the polymer side branches and showed an excellent solubility in water, a property that made them an ideal candidate for the synthesis of new polymer-(poly)peptide biomaterials. These functional polymers have been successfully employed in conjugation reactions in the presence of thiol-containing model substrates, namely, reduced glutathione (gamma-Glu-Cys-Gly) and the carrier protein, bovine serum albumin (BSA), in 100 mM phosphate buffer (pH 6.8-7.4) and ambient temperature.

Copper-Mediated Living Radical Polymerization of 2-Vinyl-4,4-dimethyl-5-oxazolone

The copper-mediated living radical polymerization of 2-vinyl-4,4-dimethyl-5-oxazolone (VDM) was investigated. Ligand nature and concentration were varied in order to reach a controlled radical polymerization of VDM. When linear amines such as N,N,N‘,N‘,N‘ ‘-pentamethyldiethylenetriamine (PMDETA) in a 1 to 1 ratio relative to CuBr catalyst are used, very low conversions were obtained. This was attributed to an inactivation of catalyst by polymer complexation. An excess of PMDETA relative to CuBr catalyst yields to an increase of monomer conversion. The use of 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (Me4Cyclam) as a cyclic amine ligand provided polymers in high yields in a short time but experimental molecular masses were higher than theoritical ones and polydispersities remained high. This is consistent with the presence of irreversible terminations. However, using Me6TREN as ligand led to a successful control of the polymerization: the polymers obtained have molecular mass values close to the theoritical ones and relatively narrow polydispersities. The controlled polymerization of VDM has been extended to statistical and block copolymerizations with styrene and methyl acrylate. Relatively low polydispersities (1.15−1.26) were obtained on statistical copolymers. Well-defined block copolymers were prepared by VDM polymerization from polystyrene and poly(methyl acrylate) starting blocks as well as by styrene and methyl acrylate polymerizations from polyVDM starting blocks.

Preparation of Fluorinated Copolymers by Copper-Mediated Living Radical Polymerization

Copper-mediated living radical polymerization mediated with pyridine imine ligands has been used for the synthesis of poly(methacrylate)s and polystyrene incorporating fluorinated moieties as either initiators or monomers as well as in the presence of fluorinated solvents. It was found that fluorinated organics do not interfere detrimentally in the polymerization mechanism. α-Perfluoroalkyl initiators have been used for the polymerization of MMA initiated by both 2-perfluoroalkyl ethyl 2-bromoisobutyrate (ZONYL BA initiator) and 2-perfluoroalkyl ethyl-co-poly(ethylene glycol) 2-bromoisobutyrate (ZONYL FSO initiator) initiators which occurs at an almost identical rate to that initiated by ethyl 2-bromoisobutyrate (EIBr). The Mn increased linearly with conversion, and the polydispersity indices were low throughout all polymerizations (<1.20). Polymerization of MeOPEG-MA initiated by 2-perfluoroalkyl ethyl 2-bromoisobutyrate (ZONYL BA initiator) at 60 °C results in a water-soluble/dispersible polymer with Mn = 6700 g mol-1 and PDI = 1.07. Perfluoroalkylethyl methacrylate (FEMA) proves difficult to homopolymerize due to solubility problems but has been used to form statistical copolymers with MMA and styrene. Synthesis of AB block copolymers using fluorinated macroinitiators with a methacrylate B block gives both hydrophobic, MMA, and hydrophilic, MeOPEG-MA, polymers with well-defined α-terminal block copolymers and PDI as low as 1.10. Copper-mediated living radical polymerization was found to be an effective method for the synthesis of fluorine-containing synthetic polymers.

13C kinetic isotope effects in the copper(I)-mediated living radical polymerization of methyl methacrylate.

Carbon-13 kinetic isotope effects (KIEs) have been determined for free-radical and copper-mediated living radical polymerizations of methyl methacrylate at 60 degrees C. While free-radical polymerization shows only one primary 13C KIE, on the least-substituted double bond carbon (k12/k13 = 1.045), two significant KIEs are observed, one on each double bond carbon, for copper-mediated polymerization (k12/k13(H2C=) = 1.050, k12/k13(=C <) = 1.010), showing that copper-mediated living radical polymerization does not propagate via a simple free radical process.