High Grafting Density Research Articles

Enhanced foamability of isotactic polypropylene/polypropylene‐grafted‐nanosilica nanocomposites in supercritical carbon dioxide

AbstractPolypropylene‐grafted nanosilica (PP‐g‐SiO2) was prepared by us as a new modified nanosilica with long polymer chains and high grafting density. It was found that the addition of PP‐g‐SiO2 resulted in remarkable strain‐hardening behavior of PP. Herein, the foaming behavior of isotactic polypropylene (iPP)/PP‐g‐SiO2 nanocomposites was investigated by using supercritical carbon dioxide (scCO2) as a blowing agent. The results demonstrated that the incorporation of PP‐g‐SiO2 could obviously enhance the foamability of iPP. In particular, the uniform cell distribution and smaller cell size could be obtained by 1 wt% particle loading, and 5 wt% particle content showed a wider foaming temperature range and higher cell density. The noticeable enhancement in the foamability of iPP was attributed to the reinforced melt strength, high melt elasticity and the increased heterogeneous nucleation caused by well dispersed and long polypropylene chains grafted SiO2. These findings provide new insights to improve the foaming ability of iPP with incorporation of modified nanoparticles.

Free energy for inclusion of nanoparticles in solvated polymer brushes from molecular dynamics simulations.

The inclusion of nanoparticles (NPs) into solvated polymer brushes (PBs) provides a path for designing novel nanocomposites and a multifunctional surface for wide applications. Despite intensive study over the years, the correlation between the structural properties of NPs (or PBs) and the NP-PB interactions is still to be well unveiled. Here, we present molecular dynamics simulations with the umbrella sampling method to systematically investigate the interaction between NPs and PBs, via calculating the free energy cost (Uins, associated with the inclusion of NPs into PBs) as a function of a series of factors, such as brush grafting density (ρg), grafted polymer chain architecture, NPs' size, NPs' surface properties, and NPs' shape and surface structure, as well as the solvent quality. Our results show that at a fixed NP size, the inclusion free energy approximately scales with the osmotic pressure (Π) of PBs under good solvent conditions [Uins∼Π(ρg)∼ρg 3/2], regardless of the NPs' shape and surface properties. Once the radius of the NP (RNP) is varied, a scaling law, Uins∼RNP 3, can be obtained for NPs deeply inserted in swollen PBs with a high grafting density. While for shallow inclusions, a surface tension correction of the form ∼RNP 2 plays a role. Further studies reveal that Θ and poor solvents will weaken the osmotic pressure effects of PBs and reversely enhance the surface tension effects due to the increased NP-brush repulsion. Our simulation results verify previous theoretical perspectives that the Uins can be approximated by the sum of the volume and surface contributions from the osmotic pressure Π and surface tension γ (Uins∼ΠRNP 3+γRNP 2). Our work not only helps us to understand the applicability of previous theories on the NP-PB system but also reveals the key factors that impact the NP-PB interaction in a series of probable conditions, which may provide valuable guidelines for designing and engineering novel nanomaterials based on functional NPs and PBs.

Polystyrene-attached graphene oxide with different graft densities via reversible addition-fragmentation chain transfer polymerization and grafting through approach

Graphene oxide (GO) modified with double bond was utilized in grafting polystyrene chains to its surface through reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene. For this purpose, 3-(((2-aminoethyl)amino)dimethylsilyl)propyl methacrylate (OD) including double bond and amine groups was prepared and used for modification of GO in different grafting densities by a ring-opening nucleophilic reaction. Then, polystyrene-grafted GO was obtained by “grafting through” RAFT polymerization of styrene. Successful using of RAFT polymerization, efficiency of the grafting reaction, different characteristics of the graphene-attached and free polystyrene chains were investigated. Proton nuclear magnetic resonance spectroscopy confirmed successful synthesis of OD. Its grafting on GO was also confirmed by using X-ray photoelectron spectroscopy. The neat and modified GO layers were also investigated by Fourier transform infrared and Raman spectroscopies. Size exclusion chromatography was used to study molecular weight and polydispersity index of the attached polystyrene chains. Thermogravimetric analysis provides degradation temperature, char content, and grafting ratio of the modifier and polystyrene chains. Grafting ratio of OD was 10.3 and 4.4% for the modified GO layers with high and low grafting densities, respectively. Layers morphology was visually studied by scanning and transmission electron microscopies. Flat and smooth graphite platelets were changed to wrinkled layers after oxidation, and converted to opaque layers after grafting with polystyrene chains. High length of small molecule modifier in this study resulted in highly efficient grafting reaction.

Novel Dopant for Conductive Polymers: Spherical Polyelectrolyte Brushes

Conductive polymers with special structure and excellent physical and chemical properties, have become a research focus in materials science since the first discovery in 1977. While a growing body of work in recent years has concentrated on the improvement of the electrical conductivity of conductive polymers by using doping technique. The spherical polyelectrolyte brushes (SPB) consisting of polyelectrolyte chains grafted densely to the surface of the core particles, have shown great promise of novel dopant for conductive polymers due to its spherical structure, high charge density and high grafting density. After summarizing the researches of the general dopant for conductive polymers, this review mainly emphasizes on the preparation, doping mechanism and advance prospect of conductive polymers doped with spherical polyelectrolyte brushes.

Coronal or Sagittal Incisions: A Mathematical Approach to the Problem

Introduction: The debate on using sagittal (parallel) or coronal (perpendicular) incisions is ongoing. However, it is our belief that coronal incisions reduce injury to the subdermal vasculature while allowing for higher graft density. In this article, we will use mathematics to support our stance that coronal incisions cause less injury to the recipient area. Objective: To mathematically prove why coronal incisions cause less trauma to the recipient area and to quantify the exact percentage of graft density increase. Method: The trigonometric theory was applied to find an equation that correlates the size of both sagittal and coronal incisions with the size of a square-end blade at any given angle. Results: Using sagittal incisions with a square-end blade directed at an acute angle results in a wound that is significantly greater in length than the size of the blade. However, using coronal incisions, the blade creates the same size wound independently of the entry angle. Conclusion: Coronal incisions minimize injury to the skin while maximizing graft density, potentially allowing for better results.

Facile Fabrication of Bio- and Dual-Functional Poly(2-oxazoline) Bottle-Brush Brush Surfaces.

Poly(2‐oxazoline)s (POx) bottle‐brush brushes have excellent biocompatible and lubricious properties, which are promising for the functionalization of surfaces for biomedical devices. Herein, a facile synthesis of POx is reported which is based bottle‐brush brushes (BBBs) on solid substrates. Initially, backbone brushes of poly(2‐isopropenyl‐2‐oxazoline) (PIPOx) were fabricated via surface initiated Cu0 plate‐mediated controlled radical polymerization (SI‐Cu0CRP). Poly(2‐methyl‐2‐oxazoline) (PMeOx) side chains were subsequently grafted from the PIPOx backbone via living cationic ring opening polymerization (LCROP), which result in ≈100 % increase in brush thickness (from 58 to 110 nm). The resultant BBBs shows tunable thickness up to 300 nm and high grafting density (σ) with 0.42 chains nm−2. The synthetic procedure of POx BBBs can be further simplified by using SI‐Cu0CRP with POx molecular brush as macromonomer (M n=536 g mol−1, PDI=1.10), which results in BBBs surface up to 60 nm with well‐defined molecular structure. Both procedures are significantly superior to the state‐of‐art approaches for the synthesis of POx BBBs, which are promising to design bio‐functional surfaces.

Synthesis of temperature and light sensitive mixed polymer brushes via combination of surface-initiated PET–ATRP and interface-mediated RAFT polymerization for cell sheet application

In this study, a series of temperature and light sensitive mixed polymer brushes consisting of poly(2-(2-methoxyethoxy) ethyl methacrylate) [poly(MEO2MA)] and poly(N-[4-[(4-nitrophenyl) azo] phenyl] acrylamide) [poly(NPAPAA)] units were grown on silicon wafer via the combination of surface-initiated photoinduced electron transfer-atom transfer radical polymerization (PET-ATRP) and interface-mediated reversible addition-fragmentation chain transfer (RAFT) polymerization. This process was realized in five consecutive steps: (i) coupling of previously synthesized (3-aminopropyl) triethoxysilane-2-bromoisobutyryl bromide (APTES-BIBB) and (3-aminopropyl) triethoxysilane-t-butoxycarbonyl (APTES-t-BOC) mixtures to the Si-OH surface under self-assembly monolayer conditions (ii) synthesis of poly(MEO2MA) units via surface-initiated PET-ATRP (iii) replacement of terminal-Br atoms at poly(MEO2MA) units with biocompatible maleimide molecules (iv) removal of the t-BOC group from APTES-t-BOC and bonding of the RAFT agent to the APTES, and (v) synthesis of poly(NPAPAA) units via the interface-mediated RAFT polymerization. The surface compositions of APTES-BIBB and APTES-t-BOC molecules were determined by the water contact angle data analyzed with the Israelachvili-Gee model and by the X-ray photoelectron spectroscopy measurements. The grafting density (σ, chains nm−2) and the average distance between grafting points (D, nm) of the mixed polymer brushes are about 0.56 chains nm−2 and 1.52 nm, respectively, indicating high grafting density. The lower critical solution temperatures (LCSTs), trans-cis and cis-trans transition times were in the range of 24.6–29.2 °C, 10–25 min and 8–20 min, respectively, depending on the surface composition of the polymer brushes. Cell culture studies revealed successful cell detachment either via the temperature reduction or UV irradiation methods. The cell recovery ratios were recorded as 99.05 ± 0.45% and 83.95% ± 0.58%, respectively. These experimental findings provided basic information at the molecular level in the preparation of temperature and light- sensitive bioactive surfaces for cell sheet preparation and detachment state.

Interplay of electrostatic repulsion and surface grafting density on surface-mediated DNA hybridization

Single-molecule Förster Resonance Energy Transfer was used to observe the adsorption of fluorescently-labeled “target” DNA oligonucleotides and their association and hybridization with complementary DNA “probes” tethered to the surface as a function of surface grafting density. Ionic strength was varied systematically to disentangle the potentially competing effects of probe accessibility and electrostatic repulsion. At high ionic strength, when the Debye length was ~1 nm, the adsorption of target DNA was not significantly inhibited by the presence of tethered probe DNA, even at high grafting density, and the fraction of adsorbed target strands undergoing hybridization increased systematically with grafting density, leading to a dramatic increase in the net hybridization rate at high grafting density. However, at lower ionic strength, when the Debye length was ≥3 nm, the adsorption rate of target DNA decreased and the fraction of adsorbed target strands undergoing hybridization saturated at high probe grafting density (≥7,000 strands/µm2), presumably due to electrostatic repulsion. As a result, the net rate of hybridization exhibited a maximum as a function of grafting density. This has important consequences for the design of systems that optimize surface-mediated DNA hybridization under low-salt high-stringency conditions.

Improving permeability and antifouling performance of poly (ether ether ketone) membranes by photo-induced graft polymerization

Poly (ether ether ketone) (PEEK) ultrafiltration membrane was modified with 2-hydroxylethyl acrylate (HEA) as a hydrophilic monomer through light-initiated grafting polymerization to improve its permeability and antifouling property. The effects of monomer concentration and irradiation time on the surface’s chemical structure and morphology, degree of grafting (DG), surface hydrophilicity and pore volume of the membranes were systematically investigated; meanwhile, the antifouling property were characterized and analyzed using bovine serum albumin (BSA) as a model foulant. The results indicate that the DG and hydrophilicity of the membrane surface are enhanced with the increase of either monomer concentration or irradiation time. The water flux of modified membrane using 0.3 mol/L HEA and 20 min irradiation time is 1.52 times that of unmodified membrane, and the irreversible fouling decreases from 51 % to 10.9 %. In this work, the graft chain length and graft density are considered to be controlled by the factors of monomer concentration and irradiation time, respectively. Compared with increasing the graft density, the increase of the graft chain length is more easily to lead to a decrease in membrane permeability. Meanwhile, the long chain length is more important than the high graft density to achieve excellent antifouling performance.

Hybrid Mesoporous Silica Nanoparticles Grafted with 2-(tert-butylamino)ethyl Methacrylate-b-poly(ethylene Glycol) Methyl Ether Methacrylate Diblock Brushes as Drug Nanocarrier.

This paper introduces the synthesis of well-defined 2-(tert-butylamino)ethyl methacrylate-b-poly(ethylene glycol) methyl ether methacrylate diblock copolymer, which has been grafted onto mesoporous silica nanoparticles (PTBAEMA-b-PEGMEMA-MSNs) via atom transfer radical polymerization (ATRP). The ATRP initiators were first attached to the MSN surfaces, followed by the ATRP of 2-(tert-butylamino)ethyl methacrylate (PTBAEMA). CuBr2/bipy and ascorbic acid were employed as the catalyst and reducing agent, respectively, to grow a second polymer, poly(ethylene glycol) methyl ether methacrylate (PEGMEMA). The surface structures of these fabricated nanomaterials were then analyzed using Fourier Transform Infrared (FTIR) spectroscopy. The results of Thermogravimetric Analysis (TGA) show that ATRP could provide a high surface grafting density for polymers. Dynamic Light Scattering (DLS) was conducted to investigate the pH-responsive behavior of the diblock copolymer chains on the nanoparticle surface. In addition, multifunctional pH-sensitive PTBAEMA-b-PEGMEMA-MSNs were loaded with doxycycline (Doxy) to study their capacities and long-circulation time.

Structure of a Planar Brush of Grafted Polyelectrolyte Stars

For planar brushes made of grafted polyelectrolyte stars, an analytical theory based on a stepwise approximation of the brush density profile is developed. Particular attention is paid to the effect of formation of a layered structure with the division of stars into two populations and the influence of arm charge and salt concentration on this phenomenon. It is shown that an increase in the number of stars with an extremely stretched arm by which the star is grafted to the surface is facilitated by an increase in the grafting density, the number of arms, or the degree of ionization of the arms. In the latter case, the average brush density decreases, while in the former two cases it increases. It is demonstrated that the theory based on the three-step approximation of the density profile describes well the results of self-consistent field modeling and the best agreement is achieved at a high degree of ionization, a large number of arms, and a high grafting density.

Self-limiting covalent modification of carbon surfaces: diazonium chemistry with a twist.

The chemistry of carbon surfaces has regained traction in recent years in view of its applicability towards covalent modification of a variety of (2D) materials. A general requisite is the formation of a dense and well-defined monolayer of aryl groups covalently bound to the surface. Given the use of reactive chemistries however, it is often not easy to achieve precise control over the monolayer growth while maintaining high grafting densities. Here we present a straightforward experimental protocol for the fabrication of well-defined covalent monolayers onto the surface of graphite. Using a combination of surface analytical tools, we demonstrate that the ascorbic acid mediated dediazoniation of aryldiazonium salts leads to self-limiting growth of monolayers with high grafting densities. The aryl radicals preferentially attach to the basal plane of the substrate and once the surface is covered with a covalent monolayer, the surface reaction does not proceed further to an appreciable extent. The layer thickness of the covalent films was measured using atomic force microscopy whereas the grafting efficiencies were assessed using Raman spectroscopy. The chemical composition of the grafted films was studied using X-ray photoelectron spectroscopy whereas scanning tunneling microscopy provided nanometer scale insight into the structure of the covalent films. Mechanistic aspects of the process are also discussed. The self-terminating chemistry described here is a new addition to the synthetic armory for covalent modification of materials and sets a strong foundation for achieving precise nanoscale control over the covalent functionalization process.

PEGylated gold nanoparticles promoted rapid macromolecular chain-end transformation and formation of injectable hydrogels.

Azide-alkyne click cycloaddition and Michael addition reactions are useful for the synthesis and modification of biologically relevant macromolecules. Acceleration of these reactions at the macromolecular chain-ends and backbone has been achieved by gold [Au-(PEG-SH)n] nanoparticles (NPs) stabilized with multi-thiol-functional poly(ethylene glycol) containing tertiary amine groups in its backbone. The Au NPs successfully activate electron rich alkyne and acrylate functionalities of macromolecules at low substrate concentration leading to the enhancement of the reaction rate. The Au NPs successfully accelerate the gelation rate of reactive prepolymers leading to the rapid formation of injectable hydrogels. The Au nanocomposite hydrogels exhibited higher ultimate modulus and porosity than those of the pristine hydrogels. The grafting density (chains per nm2) of the stabilizer onto the Au NP surface plays a crucial role towards the activity of the NPs. The conversion of the chain-end functionality and gelation rate increase with decreasing grafting density onto the NP surface. A high grafting density lowers the activity of the Au NPs through blocking the active metal surface. The developed Au NPs may be a potential agent for the rapid preparation of biologically relevant macromolecular entities.

Biomimetic Asymmetric Polymer Brush Coatings Bearing Fencelike Conformation Exhibit Superior Protection and Antifouling Performance.

Antifouling surfaces with optimized conformation and compositional heterogeneities are presented with the goal of improving the efficacy of surface protection. The approach exploits the adhesive group (thiol or catechol chain end) to anchor asymmetric polymer brushes (APBs) bearing amphiphilic side chains with synergistic nonfouling and fouling-release abilities onto the surface. The conformation of the APB surface is close to the fencelike structure, which mimics lubricating protein lubricin, endowing the surface with capacity of enhanced protection and antiadhesivity, even facing the high compression of fouling. By utilizing a poly(Br-acrylate-alkyne) macroagent comprising alkynyl and 2-bromopropionate groups, we prepared a series of APB surfaces based on polyacrylate-g-poly(ethylene oxide)/poly(pentafluorophenyl methacrylate) (PA-g-PEO/PPFMA) APBs to explore the influence of the content of the fluorinated segment and bioinspired topological polymer chemistry on their antifouling performance. The APB surfaces can not only provide compositional heterogeneities of PEO and fluorinated segments in each side chain but also give a high surface coverage because of the characteristic of high grafting density of macromolecular brushes. It was found for the first time, as far as we are aware, the fencelike APB surface shows excellent antifouling performance with less protein adsorption (up to 91% off) and cell adhesion (up to 84% off) in comparison with the controlled substrate under relatively long incubation time.

Swelling of multi-responsive spherical polyelectrolyte brushes across a wide range of grafting densities

Multi-stimulus responsive weak polyelectrolyte brushes were grafted by surface-initiated atom transfer radical polymerization from spherical silica nanoparticles across a wide range of grafting densities approaching the limit of close packing of grafting sites: a regime not previously explored in the brush swelling literature. Brushes consisted of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) homopolymers or poly(2-(dimethylamino)ethyl methacrylate)-r-poly(4-metharyloyloxyazobenzene) random copolymers P (DMAEMA-r-MOAB) and were subjected to pH-, temperature-, and photoisomerization-induced swelling and deswelling. Homopolymer brushes were prepared at grafting densities ranging from 0.12 to 1.4 nm−2 and number average degrees of polymerization ranging from 300 to 1200. Two copolymer brushes with 8 mol% and 13 mol% of the nonionizable, photoresponsive MOAB units were compared with homopolymer brushes prepared at similar grafting densities and degrees of polymerization. Dynamic light scattering was used to measure the hydrodynamic radius of grafted nanoparticles, and thus brush thickness, in water. Brush swelling in response to increased DMAEMA protonation followed a single scaling behavior across the full range of degrees of polymerization and grafting densities. Incorporating azobenzene-containing MOAB comonomers introduced a modest photoresponsive control of brush swelling and decreased the brush thickness relative to the comparable PDMAEMA homopolymer brush, without affecting the scaling with respect to protonation. PDMAEMA brushes exhibited a pH-dependent lower critical solution temperature behavior, resulting in a thermal collapse of up to 50% upon heating. This work demonstrates that scaling behaviors previously tested at low grafting densities hold for extremely high grafting densities and that they are unaffected by moderate nonionizable comonomer content.

Grafting carbon nanotubes densely on carbon fibers by poly(propylene imine) for interfacial enhancement of carbon fiber composites

Due to the weak interfacial bonding caused by the poor wettability and adsorption between carbon fibers (CFs) and matrix, CFs cannot fully exert their excellent mechanical properties in carbon fiber reinforced polymer composites. To settle this problem and bring a significant increase of interfacial strength in the composites, chemical grafting method was applied to fabricate the hierarchical reinforcement structure containing carbon nanotubes (CNTs) and CFs using poly(propylene imine) (PPI) molecules as bridges, which had a giant amount of amino groups at the periphery of molecules. CNTs were grafted on the surface of CF homogeneously and firmly with an extremely high grafting density. The surface free energy increased about 66% compared to the acid-treated carbon fiber, due to the obvious change of surface morphology and the increase of polar functional groups. The interfacial shear strength (IFSS) of the CNTs-grafted CF composite greatly increased by as much as 109% compared with that of CF composite without functionalization. The mechanism of this tremendous enhancement was also illustrated in details.

Influence of Polymer Bidispersity on the Effective Particle–Particle Interactions in Polymer Nanocomposites

We investigate the role played by the bidispersity of polymer chains on the local structure and the potential of mean force (PMF) between silica nanoparticles (NPs) in a polystyrene melt. We use the hybrid particle-field molecular dynamics technique which allows to efficiently relax polymer nanocomposites even with high molecular weights.The NPs we investigate are either bare or grafted with polystyrene chains immersed in a melt of free polystyrene chains, whereas the grafted and the free polystyrene chains are either monodisperse or bidisperse. The two-body PMF shows that a bidisperse distribution of free polymer chains increases the strength of attraction between a pair of ungrafted NPs. If the NPs are grafted by polymer chains, the effective interaction crucially depends on bidispersity and grafting density of the polymer chains: for low grafting densities, the bidispersity of both free and grafted chains increases the repulsion between the NPs, whereas for high grafting densities we observe two different effects. An increase of bidispersity in free chains causes the rise of the repulsion between the NPs, while an increase of bidispersity in grafted chains promotes the rise of attraction. Additionally, a proper treatment of multi-body interactions improves the simpler two-body PMF calculations, in both unimodal and bimodal cases. We found that, by properly tuning the bidispersity of both free and grafted chains, we can control the structure of the composite materials, which can be confirmed by experimental observations. As a result, the hybrid particle-field approach is confirmed to be a valid tool for reproducing and predicting microscopic interactions, which determine the stability of the microscopic structure of the composite in a wide range of conditions.

Atomistic simulations on nanoimprinting of copper by aligned carbon nanotube arrays under a high-frequency mechanical vibration

Nanoimprinting behaviors of copper substrates and double-walled carbon nanotubes with interwall sp 3 bonds are investigated using molecular dynamics simulations. A high-frequency mechanical vibration with various amplitudes is applied on the carbon nanotube (CNT) mold and copper substrate in different directions. Results show that exciting mechanical resonances both on the CNT and substrate drastically decrease the maximum imprint force and interfacial friction up to 50% under certain amplitudes. Meanwhile, it is demonstrated that defects occur in the {111} plane in the copper substrate during nanoimprinting. For different CNT array densities, a higher grafting density needs more imprint force to transfer patterns. The maximum imprint force for a large range of CNT array densities can be reduced by vibrational perturbations, while reduction rates depend on the CNT grafting density. This work sheds deep insights into the nanoimprint process at the atomic level, suggesting that vibration perturbation is an effective approach for improving the nanoimprinting accuracy and preventing the fracture of nanopatterns.

Surface Modification of Stöber Silica Nanoparticles with Controlled Moiety Densities Determines Their Cytotoxicity Profiles in Macrophages.

Physicochemical properties of nanomaterials play important roles in determining their toxicological profiles during nano-biointeraction. Among them, surface modification is one of the most effective manners to tune the cytotoxicity induced by nanomaterials. However, currently, there is no consistency in surface modification including moiety types and quantities considering the conflicting toxicological profiles of particles across different studies. In this study, in order to systematically investigate how the moiety density affects cytotoxicity of NPs, we chose three different types of functional groups, that is, -NH2, -COOH, and -PEG, and further controlled their densities on modified Stöber silica nanoparticles (NPs). We demonstrated that densities of functional groups could significantly affect the cytotoxicities of Stöber silica NPs. Regardless of the types of functional groups, high grafting densities could ameliorate the cytotoxicities induced by Stöber silica NPs in macrophages, for example, J774A.1 and N9 cells. When equal amounts of functional groups were present, the cell viability increased in the order of -COOH < -NH2 < -PEG. Furthermore, it was shown that surface modification could significantly affect the quantities of the surface silanol, which is the determining factor that affects their cytotoxicity. These results show that it is critical to control the surface moiety both quantitatively and qualitatively, which can tune the interaction outcomes at the nano-bio interface. The results found in this article provide useful guidance to adjust nanomaterial cytotoxicity for safer biomedical applications.

Uniaxial Deformation and Crazing in Glassy Polymer-Grafted Nanoparticle Ultrathin Films.

The deformation behavior of neat, glassy polymer-grafted nanoparticle (PGN) monolayer films is studied using coarse-grained molecular dynamics simulations and experiments on polystyrene-grafted silica. In both the simulations and experiments, apparent crazing behavior is observed during deformation. The PGN systems show a relatively more uniform, perforated sheet craze structure and significantly higher strain at break than reference homopolymers of the same length. Short chain, unentangled PGN monolayers are also simulated for comparison; these are brittle and break apart without crazing. The entangled PGN simulations are analyzed in detail for systems at both high and moderate graft density. Stress-strain curves show three distinct regions: yielding and strain localization, craze widening, and strain hardening preceding catastrophic failure. The PGN stress-strain behavior appears more similar to that of longer chain, highly entangled homopolymer films than to the reference homopolymer films of the same length as the graft chains, suggesting that the particles effectively add additional entanglement points. The moderate graft density particles have higher strain-to-failure and maximum stress than the high graft density particles. We suggest this increased robustness for lower graft density systems is due to their increased interpenetration of graft chains between neighboring particles, which leads to increased interparticle entanglements per chain.