Brush Grafting Density Research Articles

XPS Depth-Profiling Studies of Chlorophyll Binding to Poly(cysteine methacrylate) Scaffolds in Pigment-Polymer Antenna Complexes Using a Gas Cluster Ion Source.

X-ray photoelectron spectroscopy (XPS) depth-profiling with an argon gas cluster ion source (GCIS) was used to characterize the spatial distribution of chlorophyll a (Chl) within a poly(cysteine methacrylate) (PCysMA) brush grown by surface-initiated atom-transfer radical polymerization (ATRP) from a planar surface. The organization of Chl is controlled by adjusting the brush grafting density and polymerization time. For dense brushes, the C, N, S elemental composition remains constant throughout the 36 nm brush layer until the underlying gold substrate is approached. However, for either reduced density brushes (mean thickness ∼20 nm) or mushrooms grown with reduced grafting densities (mean thickness 6-9 nm), elemental intensities decrease continuously throughout the brush layer, because photoelectrons are less strongly attenuated for such systems. For all brushes, the fraction of positively charged nitrogen atoms (N+/N0) decreases with increasing depth. Chl binding causes a marked reduction in N+/N0 within the brushes and produces a new feature at 398.1 eV in the N1s core-line spectrum assigned to tetrapyrrole ring nitrogen atoms coordinated to Zn2+. For all grafting densities, the N/S atomic ratio remains approximately constant as a function of brush depth, which indicates a uniform distribution of Chl throughout the brush layer. However, a larger fraction of repeat units bound to Chl is observed at lower grafting densities, reflecting a progressive reduction in steric congestion that enables more uniform distribution of the bulky Chl units throughout the brush layer. In summary, XPS depth-profiling using a GCIS is a powerful tool for characterization of these complex materials.

Hybrid Bonding Bottlebrush Polymers Grafted from a Supramolecular Polymer Backbone.

Bottlebrush polymers, macromolecules consisting of dense polymer side chains grafted from a central polymer backbone, have unique properties resulting from this well-defined molecular architecture. With the advent of controlled radical polymerization techniques, access to these architectures has become more readily available. However, synthetic challenges remain, including the need for intermediate purification, the use of toxic solvents, and challenges with achieving long bottlebrush architectures due to backbone entanglements. Herein, we report hybrid bonding bottlebrush polymers (systems integrating covalent and noncovalent bonding of structural units) consisting of poly(sodium 4-styrenesulfonate) (p(NaSS)) brushes grafted from a peptide amphiphile (PA) supramolecular polymer backbone. This was achieved using photoinitiated electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization in water. The structure of the hybrid bonding bottlebrush architecture was characterized using cryogenic transmission electron microscopy, and its properties were probed using rheological measurements. We observed that hybrid bonding bottlebrush polymers were able to organize into block architectures containing domains with high brush grafting density and others with no observable brushes. This finding is possibly a result of dynamic behavior unique to supramolecular polymer backbones, enabling molecular exchange or translational diffusion of monomers along the length of the assemblies. The hybrid bottlebrush polymers exhibited higher solution viscosity at moderate shear, protected supramolecular polymer backbones from disassembly at high shear, and supported self-healing capabilities, depending on grafting densities. Our results demonstrate an opportunity for novel properties in easily synthesized bottlebrush polymer architectures built with supramolecular polymers that might be useful in biomedical applications or for aqueous lubrication.

Surface-Initiated Polymerization with an Initiator Gradient: A Monte Carlo Simulation.

Due to the difficulty of accurately characterizing properties such as the molecular weight (Mn) and grafting density (σ) of gradient brushes (GBs), these properties are traditionally assumed to be uniform in space to simplify analysis. Applying a stochastic reaction model (SRM) developed for heterogeneous polymerizations, we explored surface-initiated polymerizations (SIPs) with initiator gradients in lattice Monte Carlo simulations to examine this assumption. An initial exploration of SIPs with 'homogeneously' distributed initiators revealed that increasing σ slows down the polymerization process, resulting in polymers with lower molecular weight and larger dispersity (Đ) for a given reaction time. In SIPs with an initiator gradient, we observed that the properties of the polymers are position-dependent, with lower Mn and larger Đ in regions of higher σ, indicating the non-uniform properties of polymers in GBs. The results reveal a significant deviation in the scaling behavior of brush height with σ compared to experimental data and theoretical predictions, and this deviation is attributed to the non-uniform Mn and Đ.

High-density zwitterionic polymer brushes exhibit robust lubrication properties and high antithrombotic efficacy in blood-contacting medical devices

High-performance catheters are essential for interventional surgeries, requiring reliable anti-adhesive and lubricated surfaces. This article develops a strategy for constructing high-density sulfobetaine zwitterionic polymer brushes on the surface of catheters, utilizing dopamine and sodium alginate as the primary intermediate layers, where dopamine provides mussel-protein-like adhesion to anchor the polymer brushes to the catheter surface. Hydroxyl-rich sodium alginate increases the number of grafting sites and improves the grafting mass by more than 4 times. The developed high-density zwitterionic polymer brushes achieve long-lasting and effective lubricity (μ<0.0078) and are implanted in rabbits for four hours without bio-adhesion and thrombosis in the absence of anticoagulants such as heparin. Experiments and molecular dynamics simulations demonstrate that graft mass plays a decisive role in the lubricity and anti-adhesion of polymer brushes, and it is proposed to predict the anti-adhesion of polymer brushes by their lubricity to avoid costly and time-consuming bioassays during the development of amphoteric polymer brushes. A quantitative influence of hydration in the anti-adhesion properties of amphiphilic polymer brushes is also revealed. Thus, this study provides a new approach to safe, long-lasting lubrication and anticoagulant surface modification for medical devices in contact with blood. Statement of significanceHigh friction and bioadhesion on medical device surfaces can pose a significant risk to patients. In response, we have developed a safer, simpler, and more application-specific surface modification strategy that addresses both the lubrication and anti-bioadhesion needs of medical device surfaces. We used dopamine and sodium alginate as intermediate layers to drastically increase the grafting density of the zwitterionic brushes and enabled the modified surfaces to have an extremely low coefficient of friction (μ = 0.0078) and to remain non-bioadhesive for 4 hours in vivo. Furthermore, we used molecular dynamics simulations to gain insight into the mechanisms behind the superior anti-adhesion properties of the high-density polymer brushes. Our work contributes to the development and application of surface-modified coatings.

Surface-Initiated PET-RAFT via the Z-Group Approach.

Surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) is a user-friendly and versatile approach for polymer brush engineering. For SI-RAFT, synthetic strategies follow either surface-anchoring of radical initiators (e.g., azo compounds) or anchoring RAFT chain transfer agents (CTAs) onto a substrate. The latter can be performed via the R-group or Z-group of the CTA, with the previous scientific focus in literature skewed heavily toward work on the R-group approach. This contribution investigates the alternative: a Z-group approach toward light-mediated SI photoinduced electron transfer RAFT (SI-PET-RAFT) polymerization. An appropriate RAFT CTA is synthesized, immobilized onto SiO2, and its ability to control the growth (and chain extension) of polymer brushes in both organic and aqueous environments is investigated with different acrylamide and methacrylate monomers. O2 tolerance allows Z-group SI-PET-RAFT to be performed under ambient conditions, and patterning surfaces through photolithography is illustrated. Polymer brushes are characterized via X-ray photoelectron spectroscopy (XPS), ellipsometry, and water contact angle measurements. An examination of polymer brush grafting density showed variation from 0.01 to 0.16 chains nm-2. Notably, in contrast to the R-group SI-RAFT approach, this chemical approach allows the growth of intermittent layers of polymer brushes underneath the top layer without changing the properties of the outermost surface.

Explaining Giant Apparent pK_{a} Shifts in Weak Polyelectrolyte Brushes.

Recent experiments on weak polyelectrolyte brushes found marked shifts in the effective pK_{a} that are linear in the logarithm of the salt concentration. Comparing explicit-particle simulations with mean-field calculations we show that for high grafting densities the salt concentration effect can be explained using the ideal Donnan theory, but for low grafting densities the full shift is due to a combination of the Donnan effect and the polyelectrolyte effect. The latter originates from electrostatic correlations that are neglected in the Donnan picture and that are only approximately included in the mean-field theory. Moreover, we demonstrate that the magnitude of the polyelectrolyte effect is almost invariant with respect to salt concentration but depends on the grafting density of the brush. This invariance is due to a complex cancellation of multiple effects. Based on our results, we show how the experimentally determined pK_{a} shifts may be used to infer the grafting density of brushes, a parameter that is difficult to measure directly.

Sticky Architecture: Encoding Pressure Sensitive Adhesion in Polymer Networks.

Pressure sensitive adhesives (PSAs) are ubiquitous materials within a spectrum that span from office supplies to biomedical devices. Currently, the ability of PSAs to meet the needs of these diverse applications relies on trial-and-error mixing of assorted chemicals and polymers, which inherently entails property imprecision and variance over time due to component migration and leaching. Herein, we develop a precise additive-free PSA design platform that predictably leverages polymer network architecture to empower comprehensive control over adhesive performance. Utilizing the chemical universality of brush-like elastomers, we encode work of adhesion ranging 5 orders of magnitude with a single polymer chemistry by coordinating brush architectural parameters-side chain length and grafting density. Lessons from this design-by-architecture approach are essential for future implementation of AI machinery in molecular engineering of both cured and thermoplastic PSAs incorporated into everyday use.

Surface Coassembly of Binary Mixed Polymer Brushes and Linear Block Copolymer Chains.

Binary mixed polymer brushes (BMPBs) are two different homopolymer chains that are covalently anchored to the solid surfaces at high grafting densities. One feature of the BMPBs is the unique ability to make surface phase separation under external stimuli. In this research, we demonstrate that different surface nanostructures can be fabricated by surface coassembly of BMPBs and free block copolymer (BCP) chains. Polystyrene/poly(2-(dimethylamino)ethyl methacrylate) (PS/PDMAEMA) BMPBs on silica particles (PS-PDMAEMA-SiO2) are synthesized by a two-step "grafting to" approach. PDMAEMA-b-PS block copolymer (BCP) chains and PS-PDMAEMA-SiO2 make surface self-assembly and a variety of surface nanostructures are formed in methanol. The grafting densities of PS and PDMAEMA brushes, solvent, and the BCP structures all exert significant influences on the surface morphology. With an increase in PDMAEMA grafting density, the surface structures change from perforated layers, to rods, and to spherical surface micelles (s-micelles). The PS grafting density also exerts an effect on the formation of the surface nanostructures. At low PS grafting density, sparsely distributed s-micelles are produced, and at high density, densely distributed s-micelles are observed. Based on transmission electron microscopy and scanning electron microscopy results, a surface phase diagram is constructed, which provides a guide to the surface morphology control.

Semi-heterogeneous asymmetric organocatalysis: Covalent immobilization of BINOL-derived chiral phosphoric acid (TRIP) to polystyrene brush grafted on SiO2 nanoparticles

Reduced mass transfer and tedious immobilization of expensive chiral organocatalyst are two bottlenecks for the large-scale synthesis of optically active molecules in heterogeneous asymmetric organocatalysis. Here, a quasi-homogeneous organocatalysis is achieved by anchoring BINOL-derived phosphoric acid (TRIP) to polystyrene (PS) brush grafted on SiO2 nanoparticles via one-pot, effectively improving mass transfer due to the open stretching of TRIP-anchored PS brush in toluene. The PS brush enables TRIP to catalyze asymmetric allylation in significantly higher yields and enantioselectivities than PS-supported TRIP, and inslightly higher yields than homogeneous TRIP. The sparser grafting density of PS brush is more conducive to the swelling of PS brush, leading to the faster mass transfer of reactants from the top to end of PS brush. Overall,the one-pot anchoring of TRIP to PS brush combines the advantages of homogeneous and heterogeneous organocatalysis, providing an ideal strategy for solving the two bottlenecks in heterogeneous asymmetric organocatalysis.

Facile optimization of grafted chain length on antifouling properties based on hyperbranched polyglycerol

Surface-grafted polymer brushes for enhancing biofouling resistance are determined by both the grafting density and chain length of brush on the antifouling membrane surfaces. However, the relations and internal regularities between the arrangement of polymer brush and the permeability and antifouling properties remain unsolved. The accurate effect of chain length is lost on the biofouling resistance behaviors. Herein, antifouling membrane surfaces of hyperbranched polyglycerol (HPG) brushes are obtained via tuning the chain lengths of HPG brush. The wettability and proteins' static adsorption are dramatically improved with the increase of HPG chain lengths. The parameter of chain volume overlap is preliminarily involved to describe the spatial distribution of HPG brushes. Unexpectedly, we demonstrate that the chain length of HPG is critical and a medium-length HPG brush displays an emerging permeability by a dense enough chain volume overlap (Dv) of the HPG architecture. The biofouling resistance behaviors are optimized using the response surface methodology. As the HPG brush grafting density increased, a higher flux recovery regardless of the chain lengths is observed. Qualitative and quantitative assays of E. coli and S. aureus attachment further reveal the low fouling characteristics of hyperbranched membrane surfaces. A deeper understanding of how the chain length of polymer brushes impacts permeability and the anti-biofouling property provides general guidance on the effectiveness of grafted polymer brushes.

Enhancement of the High-Rate Performance of an Organic Radical Thin-Film Battery by Decreasing the Grafting Density of Polymer Brushes

Enhancement of the High-Rate Performance of an Organic Radical Thin-Film Battery by Decreasing the Grafting Density of Polymer Brushes

Adsorption-active polydisperse brush with tunable molecular mass distribution.

Recently, a novel class of responsive uncharged polymer brushes has been proposed [Klushin et al., J. Chem. Phys. 154(7), 074904 (2021)] where the brush-forming chains have an affinity to the substrate. For sufficiently strong surface interactions, a fraction of chains condenses into a near-surface layer, while the remaining ones form the outer brush with a reduced grafting density. The dense layer and the more tenuous outer brush can be seen as coexisting microphases. The effective grafting density of the outer brush is controlled by the adsorption strength and can be changed reversibly as a response to changes in environmental parameters. In this paper, we use numerical self-consistent field calculations to study this phenomenon in polydisperse brushes. Our results reveal an unexpected effect: Although all chains are chemically identical, shorter chains are adsorbed preferentially. Hence, with the increase in the surface affinity parameter, a reduction in the surface grafting density of the residual brush is accompanied by a change in the shape of its molecular mass distribution (MMD). In particular, an originally bidisperse brush can be effectively transformed into a nearly monodisperse one containing only the longer chain fraction. We introduce a method of assigning different chain conformations to one or the other microphase, based on analyzing tail length distributions. In a polydisperse brush with a uniform MMD, short chains are relegated to the adsorbed phase, leading to a narrower effective MMD in the residual brush. Preferential adsorption is not absolute, and longer chains are also partially involved in adsorption. As a result, not only the width of the distribution decreases but also its shape evolves away from the initial uniform distribution. We believe that the effect of preferential adsorption stems from a fundamental property of a polydisperse brush, which is characterized by a spectrum of chemical potential values for monomers belonging to chains of different lengths. Hence, preferential adsorption is also expected in polyelectrolyte brushes; moreover, brush polydispersity would affect coexistence with any other condensed phase, not necessarily related to adsorption.

Dual-responsive zwitterion-modified nanopores: a mesoscopic simulation study.

In this work, dissipative particle dynamics simulation was carried out to investigate the intelligent switching effect of nanopores grafted by the zwitterionic polymer brushes poly(carboxybetaine) with excellent antifouling properties. The result shows that with different grafting densities and grafting lengths, zwitterionic polymer brushes show typical pH- and salt-responsiveness features. When the grafting density is greater than 0.2 accompanying a grafting length of 40, pH has a significant effect on the structure and pore size of the nanopores, that is, the pore remains open under neutral condition and exhibits a switching effect under acidic condition. Similarly, the size of the nanopore can be tuned by altering the grafting density and polymer chain length under salt-concentration-responsive conditions. Differently, compared with the pH effect, the salt concentration has an obvious impact on the switching effect, i.e., responsiveness emerges with a lower grafting density and length. This work provides molecular level mechanism and theoretical guidance for the design of smart nanopores modified by zwitterionic polymer brushes, as well as plays an important role in the construction of nanopores with antifouling and pH/salt-responsive properties.

Grafting Density-Dependent Phase Transition Mechanism of Thermoresponsive Poly(glycidyl ether) Brushes: A Comprehensive QCM-D Study.

Thermoresponsive coatings that exhibit "switchable" protein- and cell-adhesive properties are frequently used for the fabrication of cell sheets. Among other architectures, polymer brush coatings have shown to be especially viable due to their distinct phase transition behavior, which can be tailored via a manifold of adjustable brush characteristics, such as the (co)monomer composition, polymer chain length, and grafting density. Brush coatings based on poly(glycidyl ether)s (PGEs) have shown to efficiently mediate cell sheet fabrication when tethered to various tissue culture substrates. Herein, we report the phase transition of self-assembled PGE brushes with respect to polymer molecular weight (M: 10 and 22 kDa) and grafting density (0.07-0.5 chains nm-2) on gold model substrates studied by quasi-static QCM-D temperature ramp measurements. The brush grafting density can be tuned via the applied grafting conditions, and all brushes investigated feature broad phase transition regimes (ΔT ∼15°C) with volume phase transition temperatures (VPTTs) close to the cloud point temperatures (CPTs) of the PGEs in solution. We further demonstrate that brush coatings with a low grafting density (0.07-0.12 chains nm-2) exhibit a continuous brush-to-mushroom transition, whereas brushes with medium grafting densities (0.3-0.5 chains nm-2) undergo a brush-to-brush transition comprising vertical phase separation during the phase transition progress. These insights help to understand the transition behavior of thin, thermoresponsive brushes prepared via grafting-to strategies and contribute to their rational design for improved functional surfaces.

θ-Solvent-Mediated Double-Shell Polyethylene Glycol Brushes on Nanoparticles for Improved Stealth Properties and Delivery Efficiency.

Antifouling polymer brushes are widely used to inhibit the formation of protein corona on nanoparticles (NPs) and subsequent accumulation in the liver and spleen. Herein, we demonstrate a θ-solvent-mediated method for the preparation of gold nanoparticles with a high polyethylene glycol (PEG) grafting density. Reaching the θ-solvent by adding salt (e.g., Na2SO4) can significantly increase the grafting density of the PEG brush to 2.08 chains/nm2. The PEG polymer brush prepared in the θ-solvent possesses a double-shell structure consisting of a concentrated polymer brush (CPB) and a semidilute polymer brush (SDPB), denoted as NP@CPB@SDPB, while those prepared in a good solvent have only a SDPB shell, i.e., NP@SDPB. Compared to the NP@SDPB structure, the NP@CPB@SDPB structure decreases the liver accumulation from 34.0%ID/g to 23.1%ID/g, leading to an increase in tumor accumulation from 8.5%ID/g to 12.8%ID/g. This work provides new insights from the perspective of polymer physical chemistry into the improved stealth properties and delivery efficiency of NPs, which will accelerate the clinical translation of nanomedicine.

Polymer brushes with reversibly tunable grafting density

We propose a novel class of responsive polymer brushes, where the effective grafting density can be controlled by external stimuli. This is achieved by using end-grafted polymer chains that have an affinity to the substrate. For sufficiently strong surface interactions, a fraction of chains condenses into a near-surface layer, while the remaining ones form the outer brush. The dense layer and the more tenuous outer brush can be seen as coexisting microphases. The effective grafting density of the outer brush is controlled by the adsorption strength and can be changed reversibly and in a controlled way as a response to changes in environmental parameters. The effect is demonstrated by numerical self-consistent field calculations and analyzed by scaling arguments. Since the thickness of the denser layer is about a few monomer sizes, its capacity to form a microphase is limited by the product of the brush chain length and the grafting density. We explore the range of chain lengths and grafting densities where the effect is most pronounced. In this range, the SCF studies suggest that individual chains inside the brush show large rapid fluctuations between two states that are separated by only a small free energy barrier. The behavior of the brush as a whole, however, does not reflect these large fluctuations, and the effective grafting density varies smoothly as a function of the control parameters.

Precise positioning of enzymes within hierarchical polymer nanostructures for switchable bioelectrocatalysis

The ability to reversibly switch bioelectrocatalytic sensors is attractive for the design of biomonitoring platforms displaying a complex environmental response, or for the protection of biosensors. However, the retention of reversible biocatalytic properties upon multiple environmental cycles, with broad detection range, low signal-to-noise and limit of detection remains challenging. In this report, we demonstrate the precise positioning of the enzyme glucose oxidase within block-copolymer brush nanostructures, via the re-initiation of N-isopropylacrylamide (NIPAM) polymerisation from enzyme-decorated poly(dimethylaminoethyl methacrylate) (PDMAEMA) blocks. We find that the precise design of polymer brush grafting density, thickness and crosslinking of the PNIPAM block enables the stable positioning of biocatalytic sites close to electrode surfaces. The control of the polymer brush nanostructure, its conformation and the distribution of biocatalytic sites is characterised via a combination of in situ ellipsometry, X-ray photoelectron spectroscopy, grazing angle FTIR and surface plasmon resonance. In turn, cyclic voltammetry and electrochemical impedance spectroscopy demonstrate that such control of the polymeric nanostructures confers a unique combination of low limit of detection (23.9μM), a broad dynamic range of glucose sensing (0.05-12.8mM) and true "OFF" state upon pH or thermal stimulation, whilst retaining excellent performance over repeated switching cycles of the sensor. Therefore, hierarchical biocatalytic polymer brushes display unique properties for the design of responsive biosensors and complex multi-functional gating platforms.

Molecularly imprinted dispersive solid-phase microextraction sorbents for direct and selective drug capture from the undiluted bovine serum

The preparation of well-defined new hydrophilic molecularly imprinted polymer (MIP) microspheres and their use as the dispersive solid-phase microextraction (dSPME) sorbents for direct and selective drug (i.e., propranolol) capture from the undiluted bovine serum are described. These MIPs have surface-grafted dense poly(2-hydroxyethyl methacrylate) (PHEMA) brushes with different molecular weights and grafting densities. They were readily prepared via the facile reversible addition-fragmentation chain transfer (RAFT) coupling chemistry. Both the molecular weights and grafting densities of PHEMA brushes showed significant influence on their complex biological sample-compatibility, and only those MIPs bearing PHEMA brushes with high enough molecular weights and grafting densities could selectively recognize propranolol in the undiluted pure milk and bovine serum. In particular, they have proven to be highly versatile dSPME sorbents for directly and selectively capturing propranolol from the undiluted bovine serum with satisfactory recoveries (85.2–97.4%) and high accuracy (RSD = 2.3–3.7%), even in the presence of one analogue of propranolol. The limit of detection was 0.002 μM with a linear correlation coefficient of 0.9994 in the range of 0.01–100 μM. Excellent precision was verified by both the intraday and interday analytical results. Their good reusability was also confirmed. This work demonstrates the high potential of such hydrophilic MIP-based dSPME sorbents for rapid, accurate, and reliable drug determination in complex biological samples.

Surface-Initiated Photoinduced Iron-Catalyzed Atom Transfer Radical Polymerization with ppm Concentration of FeBr3 under Visible Light.

Reversible deactivation radical polymerizations with reduced amount of organometallic catalyst are currently a field of interest of many applications. One of the very promising techniques is photoinduced atom transfer radical polymerization (photo-ATRP) that is mainly studied for copper catalysts in the solution. Recently, advantageous iron-catalyzed photo-ATRP (photo-Fe-ATRP) compatible with high demanding biological applications was presented. In response to that, we developed surface-initiated photo-Fe-ATRP (SI-photo-Fe-ATRP) that was used for facile synthesis of poly(methyl methacrylate) brushes with the presence of only 200 ppm of FeBr3/tetrabutylammonium bromide catalyst (FeBr3/TBABr) under visible light irradiation (wavelength: 450 nm). The kinetics of both SI-photo-Fe-ATRP and photo-Fe-ATRP in solution were compared and followed by 1H NMR, atomic force microscopy (AFM) and gel permeation chromatography (GPC). Brush grafting densities were determined using two methodologies. The influence of the sacrificial initiator on the kinetics of brush growth was studied. It was found that SI-photo-Fe-ATRP could be effectively controlled even without any sacrificial initiators thanks to in situ production of ATRP initiator in solution as a result of reaction between the monomer and Br radicals generated in photoreduction of FeBr3/TBABr. The optimized and simplified reaction setup allowed synthesis of very thick (up to 110 nm) PMMA brushes at room temperature, under visible light with only 200 ppm of iron-based catalyst. The same reaction conditions, but with the presence of sacrificial initiator, enabled formation of much thinner layers (18 nm).

Enhanced adhesion effect of epoxy resin on carbon fiber-reinforced Poly(etheretherketone) via surface initiated photopolymerization of glycidyl methacrylate

Adhesives for carbon fiber-reinforced poly (etheretherketone) (CFR-PEEK) have attracted the interest of researchers as an effective means for bonding this newly developed lightweight and high-performance composite structures. In this study, we developed a method to overcome the lack of interaction between adherends and adhesives through the modification of glycidyl methacrylate (GMA) brushes via surface-initiated photopolymerization. To achieve a better formation of PGMA brushes, some parameters of the surface-initiated photopolymerization, for example, light intensities (e.g., 2, 4, and 8 mW/cm2) and exposure durations (e.g., 15, 30, 45, 60, 90, 120 min) of ultraviolet (UV) treatment, were optimized. The joints using the adherends with an optimized PGMA layer exhibited more than a two-fold increase in the ultimate lap shear strength compared to that using the bare CFR-PEEK adherends, when a commercially available epoxy film adhesive, FM 309-1, is utilized. The influence of the UV intensities was further revealed via a double cantilever beam test, and the adherends with the modification under 4 mW/cm2 of UV irradiation for 2 h exhibited the best performance, owing to the higher grafting density of the PGMA brushes.