Grafted PMMA Chains Research Articles

Development of Water-Resistant Autohesive Strength of Polyethylene Plates with Photografting of Alkyl (Meth)Acrylates

This study aims to confer autohesive strength to polyethylene (PE) plates by swelling the grafted layers, which were formed on the PE plates grafted with alkyl (meth)acrylate monomers, with 1,4-dioxane, and subsequently heat-pressing them. For the methyl methacrylate (MMA)-grafted PE (PE-g-PMMA) plates, the location of grafting was restricted to the outer surface region and the grafted layer with higher densities of grafted PMMA chains was composed. When the grafted PE plates were immersed in 1,4-dioxane, and then heat-pressed while applying the load, autohesion was developed. The substrate failure was observed for the PE-g-PMMA plates and the grafted amount at which the substrate failure was observed decreased with the procedures that decreased the methanol concentration of the solvent, the MMA concentration, the grafting temperature, and the heat-press temperature, and/or increased the load. The lowest grafted amount of 45 μmol/cm2 for the substrate failure was obtained under the conditions where the PE-g-PMMA plate prepared at 0.75 M and 60 °C in a 70 vol% aqueous methanol solution was heat-pressed at 60 °C while applying the load of 2.0 kg/cm2. The swelling of the grafted layers with 1,4-dioxane considerably contributed to the development of autohesion, bringing the inter-diffusion of grafted PMMA chains and coincident entanglement of grafted PMMA chains during the heat-pressing. The fact that the substrate failure occurred indicates that an autohesive strength higher than the ultimate strength of the used PE plate was obtained. Our approach provides a novel procedure to develop the water-resistant autohesion of PE plates.

Adhesion Behavior of Ti\u2013PMMA\u2013Ti Sandwiches for Biomedical Applications

The “stress-shielding” problem, common with metallic implants, may be solved by using biocompatible sandwiches with a polymeric core between two metallic skin sheets. To achieve such sandwiches, a process route has been developed, beginning with the grafting of poly-(methyl-methacrylate) (PMMA) on titanium (Ti) sheets via the “grafting from” technique. Grafting resulted in variable thicknesses of PMMA on the Ti sheets. Hot-pressing was used to prepare semi-finished Ti–PMMA–Ti sandwiches. The adhesion was achieved by the interpenetration between PMMA sheet and the grafted PMMA chains. Investigation was carried out to understand the influence of the grafted PMMA thickness on the adhesion strength. Similar adhesion strengths were found for the sandwiches despite variable grafted PMMA thicknesses, indicating a successful grafting of PMMA on large-scale Ti sheets. The adhesion followed the autohesion theory, where a time-dependent increase in adhesion strength was found for the sandwiches.

Polymer Spherulitic Growth Kinetics Mediated by Nanoparticle Assemblies

We systematically examine the role of the self-assembly state of polymer-grafted silica nanoparticles (GNPs) on the spherulitic growth kinetics of a poly(ethylene oxide) (PEO) matrix. The nanoparticles (NPs) are functionalized with either unimodal or bimodal polymer brushes to systematically control their self-assembly within the semicrystalline polymer matrix. In the former case, we employ a poly(methyl methacrylate) (PMMA) brush (miscible with PEO), while the latter has a short dense polystyrene (PS carpet) brush, which is immiscible with the PEO matrix, and a long, sparse PMMA brush. The unimodal GNPs always yield well-dispersed NPs possibly because both the silica NP surface and the PMMA interact favorably with the PEO. The addition of the short PS carpet makes the interaction between the surface and the matrix PEO unfavorable. However, since the NPs also have grafted PMMA chains, they act akin to surfactants and provide access to a range of self-assembled structures. In all cases, the addition of NPs decreases the PEO spherulitic growth rates. Surprisingly, we find that the spatial dispersion of NPs does not change the secondary nucleation activation energy barrier of the PEO crystallization, such that the temperature dependence of spherulite growth kinetics is relatively unaffected by the NPs. Instead, the main effect of the NPs on spherulitic growth kinetics arises from variations of the melt’s viscosity. Two apparently “universal” trends are found—bare NPs and large assemblies of GNPs appear to approximately follow the same dependence for the role of additives on polymer viscosity. On the other hand, all self-assembled NP structures which have at least one nanoscale dimension (well-dispersed NPs, one-dimensional strings or two-dimensional sheets) follow another general behavior, but one where the viscosity is much larger. Such unusual viscosity increases have been previously observed in the pioneering experiments of Composto and Winey, but there is currently no available theoretical description that can capture these changes and their effects on polymer crystallization.

Interfacial Compatibilization in Ternary Polymer Nanocomposites: Comparing Theory and Experiments

In this work, we examine binary and ternary nanocomposites of poly(methyl methacrylate) grafted silica nanoparticles (PMMA-NP), in poly(styrene-ran-acrylonitrile) (SAN), and poly(methyl methacrylate) matrices as a platform to directly probe governing parameters guiding phase behavior and nanoparticle assembly in composite materials. Through the addition of PMMA matrix chains similar in molecular weight to the grafted PMMA chains and significantly smaller than the SAN matrix chains, we observe increased nanoparticle miscibility in off-critical compositions due to interfacial segregation of PMMA matrix chains. A simple interfacial model provides a general guideline for predicting the extent of compatibilization. Further insights on compatibilization behavior are provided by polymer particle pair correlation functions and structure factors obtained using polymer reference interaction site model theory calculations as well as polymer concentration profiles from molecular dynamics simulations. This study serves as a guideline to facilitate PNC processing and design of materials for a broad range of technological applications.

Qualitative Effect of the Polymerization Rate on the Nanoparticle Dispersion in Poly(methyl methacrylate)/Silica Nanocomposite Films

In this study, we investigate the effect of the polymerization rate, mainly mediated by the initiator concentration, on the nanoparticle dispersion in the nanocomposite films formed by poly(methyl methacrylate) (PMMA) and [3-(methacryloyloxy)propyl]trimethoxysilane-modified silica nanoparticles (M-SiO2) via free radical polymerization of the precursory solution, that is, 15.5 wt % M-SiO2 nanoparticles dispersed in the methyl methacrylate (MMA) monomer, in which the tethered silanes at the particle surface bearing the reactive vinyl groups were capable of polymerizing with the MMA monomer. At slower polymerization, the nanoparticles self-organized to form a large-length scale network structure with the mass fractal of average dimension of 2.7; contrarily, the nanoparticles exhibited better dispersion when the polymerization proceeded at a faster rate. According to the scenario of perturbed polymerization kinetics in the presence of nanoparticles, we propose a possible mechanism through which the MMA monomers at a lower polymerization rate may constitute longer “multiple grafted PMMA chains” along particle surfaces by an optimal balance between the polymerization of the monomer and the grafting reaction of the monomer onto the particle surface, forming the M-SiO2-rich clusters by interparticle bridging; the multiple grafting reaction also occurred in between any two neighboring M-SiO2 nanoparticles situated respectively at the two adjoining clusters to induce the intercluster bridging, thereby leading to a hierarchical fractal network. However, both the polymerization and the grafting reaction of MMA monomers at a higher polymerization rate formed the shorter free and grafted PMMA chains, providing steric stabilization to retain better dispersity of nanoparticles.

Selective location and migration of poly(methyl methacrylate)- grafted clay nanosheets with low grafting density in poly(methyl methacrylate)/poly(styrene-co-acrylonitrile) blends

The location and migration of poly (methyl methacrylate)-grafted clay (clay-g-PMMA) nanosheets with low grafting density in a phase-separated polymer blend of poly (methyl methacrylate)/poly (styrene-co-acrylonitrile) (PMMA/SAN) was investigated. The grafting density and molecular weight for grafted PMMA chains on the surface of clay nanosheets was about 0.04 chains/nm2 and 7.8 × 104, respectively, indicating that the grafted chains might exhibit the mushroom-like distribution. With phase separation of PMMA/SAN blend matrix, the well-dispersed clay-g-PMMA nanosheets in the blend matrix were first located in the SAN-rich phase and then gradually migrated to the interface between PMMA and SAN. The first abnormal location of modified clay in the blend matrix might be attributed to the favorable interaction between clay-g-PMMA and SAN induced by the miscibility of grafted PMMA/surrounding SAN chains and the unfavorable interaction between clay-g-PMMA and PMMA without any interpenetration of grafted and matrix chains. The enhanced miscibility between grafted PMMA and surrounding SAN just began to be destroyed after being annealed for a long time, resulting in the final migration of clay-g-PMMA to the interface of PMMA/SAN (thermodynamic equilibrium state).

Nanocomposites comprised of homogeneously dispersed magnetic iron-oxide nanoparticles and poly(methyl methacrylate).

Nanocomposites with a high, uniform loading of magnetic nanoparticles are very desirable for applications such as electromagnetic shielding and cancer treatment based on magnetically induced hyperthermia. In this study, a simple and scalable route for preparing nanocomposites with a high, uniform loading of magnetic nanoparticles is presented. The magnetic iron-oxide nanoparticles were functionalized with a methacrylate-based monomer that copolymerized in a toluene solution with the methyl methacrylate (MMA) monomer. The resulting suspension of magnetic nanoparticles decorated with poly(methyl methacrylate) (PMMA) chains in toluene were colloidal, even in the presence of a magnetic field gradient. Nanocomposites were precipitated from these suspensions. The transmission electron microscopy investigation of the prepared nanocomposites revealed that the magnetic nanoparticles were homogeneously dispersed in the PMMA matrix, even in amounts up to 53 wt %. The uniform dispersion of the nanoparticles in the PMMA matrix was attributed to the good solvation of the grafted PMMA chains from the magnetic nanoparticles by the PMMA chains of the matrix. The nanocomposites were superparamagnetic and exhibited large values for the saturation magnetization of up to 36 emu/g. Moreover, the nanocomposite with the largest amount of incorporated nanoparticles exhibited relatively large values for the specific power loss when subjected to alternating magnetic fields, giving this material great potential for the magnetically induced hyperthermia-based treatment of cancer.

Effect of grafted graphene nanosheets on morphology evolution and conductive behavior of poly(methyl methacrylate)/poly(styrene-co-acrylonitrile) blends during isothermal annealing.

A facile method was developed for directly grafting poly(methyl methacrylate) (PMMA) to graphene oxide (GO) without surface modification, with the resultant insulating PMMA-g-GO nanosheets further reduced in situ to give conductive grafted reduced graphene oxide (RGO) nanosheets. The effect of PMMA-g-RGO nanosheets on the morphological evolution and conductive behavior of partially miscible blends of poly(methyl methacrylate)/poly (styrene-co-acrylonitrile) (PMMA/SAN) upon annealing above their phase-separation temperature was investigated using phase-contrast microscopy (PCM) with a real-time online digital picoammeter. With phase separation of the blend matrix, the well-dispersed PMMA-g-RGO nanosheets in the homogeneous matrix preferentially migrated to the SAN-rich phase and showed remarkably little aggregation. Surface grafting of PMMA-g-RGO might inhibit the aggregation of nanosheets in the blend matrix and weaken the retardation effect of nanosheets on the morphology evolution of the blend matrix. Furthermore, the percolation behavior of dynamic resistivity for ternary nanocomposites was attributed to the formation of a PMMA-g-RGO conductive network in the SAN-rich phase. The activation energy of conductive pathway formation was closer to the activation energy of flow for PMMA than that of SAN.

Reactive Compatibilization: Formation of Double-Grafted Copolymers by In Situ Binary Grafting and Their Compatibilization Effect.

Reactive compatibilizers are usually used to enhance the compatibility of immiscible polymer blends. However, reactive linear compatibilizers containing reactive groups on the main chains form graft copolymers during reactive blending, and such graft copolymers with an asymmetric molecular structure are often "pulled in" or "pulled out" under mechanical shear. Double-grafted compatibilizers have a symmetric structure, and they usually exhibit higher compatibilizing efficiency. In this work, we propose a binary grafting strategy during melt blending to form compatibilizers located at the interface of an immiscible polymer blend. Specifically, poly(methyl methacrylate) (PMMA) oligomer with carboxylic end groups (PMMA-COOH) and poly(styrene-co-glycidyl methacrylate) (SG) copolymer were simultaneously incorporated into immiscible poly(vinylidene fluoride)/poly(l-lactic acid) (PVDF/PLLA) blends. The carboxylic acid groups of both the PMMA oligomer and PLLA can react with the epoxide groups on the SG main chains. Therefore, novel compatibilizing polymers with both PMMA and PLLA chains grafted onto the SG main chains form in situ. The grafted PMMA chains can entangle with PVDF, and the grafted PLLA chains are embedded in the PLLA phase, so the double-grafted copolymers act as effective compatibilizers for the PVDF/PLLA blends. Moreover, the effects of the PMMA molecular weight and PMMA loading (number of grafted PMMA side chains) on the compatibilization efficiency were investigated. The compatibilizing efficiency increases with increasing molecular weight and number of side chains in the ranges considered in this study. This one-pot synthesis of double-grafted compatibilizers by in situ grafting provides a new and simple method to prepare double-comb compatibilizers, and it offers the possibility of high-efficiency compatibilization.

Grafting and properties of a porous poly(methyl methacrylate) film on a silicon surface by a one‐step dipping method

ABSTRACTIn this study, we prepared a porous poly(methyl methacrylate) (PMMA) film on an Si surface with a novel dipping method. We conducted the process by directly dipping the Si substrate into acidic aqueous media in a simple flask at 10 °C. First, 4‐nitrobenzene diazonium tetrafluoroborate (NBD) was spontaneously reduced at the Si surface. Then, the aryl radicals during the reduction of NBD were directly grafted onto the Si surface. Meanwhile, the aryl radicals initiated the polymerization of methyl methacrylate (MMA) monomers, and the radical‐terminated PMMA chains formed in the solution were grafted onto the Si surface. Because water was a poor solvent for MMA, the grafted PMMA chains easily aggregated together, and this resulted in a porous polymer film. The porosity of the film depended on the grafting time and the MMA concentration. Furthermore, the permittivity of the porous PMMA film was relatively low, and its dielectric dissipation factor was extremely small. Therefore, its excellent dielectric properties should allow the porous film to have many applications in industry. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44930.

Electromagnetic interference shielding properties of polymer-grafted carbon nanotube composites with high electrical resistance

Poly(methyl methacrylate) (PMMA)-grafted multiwalled CNTs were prepared, and then dispersed into additional PMMA matrix, yielding highly insulated PMMA–CNT composites. The volume resistivity of PMMA–CNT was as high as 1.3×1015Ωcm even at 7.3wt% of the CNT. The individual CNTs electrically-isolated by the grafted PMMA chains in PMMA–CNT transmitted electromagnetic (EM) waves in the frequency range of 0.001–1GHz, whereas the percolated CNTs in a conventional composite prepared by blending PMMA with the pristine CNTs strongly shielded the EM waves. This result suggests that the intrinsic conductivity of the CNT itself in PMMA–CNT does not contribute to the EM interference (EMI) shielding in the frequency range of 0.001–1GHz. On the other hand, PMMA–CNT exhibited EMI shielding at the higher frequency range than 1GHz because the dielectric loss of the CNT itself was rapidly increased over 1GHz. At 110GHz, PMMA–CNT with 7.3wt% of the CNT had EMI SE of as high as 29dB (0.57mm thickness), though is slightly lower than that of the percolated conventional composite (35dB). Thus, it is demonstrated that the highly insulated PMMA–CNT has the good EMI shielding at extremely high frequency range (30–300GHz).

Reinforcement and plasticization of PMMA grafted MWCNTs for PVDF composites

Poly (methyl methacrylate) (PMMA) grafted carboxyl-modified multiwalled carbon nanotubes (MWCNTs–COOH), synthesized through emulsion polymerization, were introduced into polyvinylidene fluoride (PVDF) by solution blending. MWCNTs–COOH aggregated easily in PVDF matrix and the reinforcing effect for the matrix became notable only when the MWCNTs–COOH network structure was formed. However, the grafted PMMA chains on the surface of MWCNTs–COOH reduced the inter-tube interactions and greatly improved the dispersion of MWCNTs in the PVDF matrix. In this case, low grafting degree of PMMA was beneficial to the formation of MWCNTs–COOH network, while high grafting degree of PMMA led to that the contact between MWCNTs became less possible and the network structure of MWCNTs was hard to form. The grafted PMMA chains at high grafting degree showed a plasticization effect in the melt state.

Synthesis and Solution Properties of Loose Polymer Brushes Having Polyimide Backbone and Methylmethacrylate Side Chains

AbstractSummary: Graft‐copolymers with polyimide backbone and PMMA side chains are synthesized by ATRP of methylmethacrylate on the polyimide macroinitiator. The obtained copolymers, macroinitiator, and cleaved side chains are investigated by 1H NMR, SEC, static and dynamic light scattering, sedimentation, and viscosimetry in solutions. The synthesized copolymer is relatively loose polymer brushes: the average distance between grafted PMMA chains is ∼11 nm (4 repeat units of the backbone). The hydrodynamic and conformational characteristics of graft‐copolymers change on passage from ethylacetate to chloroform due to difference in the thermodynamic quality of the solvents with respect to the copolymer components. The backbone is characterized more extended conformation than individual polyimide macromolecule.

Surface modification of silica nanoparticles by UV-induced graft polymerization of methyl methacrylate

In this study we modified the surface of silica nanoparticles with methyl methacrylate by UV-induced graft polymerization. It is a surface-initiated polymerization reaction induced by ultraviolet irradiation. The resulting organic–inorganic nanocomposites were near-monodisperse and fabricated without homopolymerization of the monomer. Substantial increase in mean particle size was observed by SEM image analysis after UV-induced grafting of methyl methacrylate onto pure silica particles. FT-Raman spectroscopy and X-ray photoelectron spectroscopy studies of these materials revealed the successful grafting of methyl methacrylate onto the silica surface. The formation of a covalent bond between the grafted PMMA chains and silica surface was indicated by FT-Raman spectra. Thermogravimetric analysis of the PMMA-grafted silica particles indicated the polymer contents in good agreement with SEM photographs.

Living radical graft polymerization of methyl methacrylate to polyethylene film with typical and reverse atom transfer radical polymerization

AbstractNickel‐mediated atom transfer radical polymerization (ATRP) and iron‐mediated reverse ATRP were applied to the living radical graft polymerization of methyl methacrylate onto solid high‐density polyethylene (HDPE) films modified with 2,2,2‐tribromoethanol and benzophenone, respectively. The number‐average molecular weight (Mn) of the free poly(methyl methacrylate) (PMMA) produced simultaneously during grafting grew with the monomer conversion. The weight‐average molecular weight/number‐average molecular weight ratio (Mw/Mn) was small (<1.4), indicating a controlled polymerization. The grafting ratio showed a linear relation with Mn of the free PMMA for both reaction systems. With the same characteristics assumed for both free and graft PMMA, the grafting was controlled, and the increase in grafting ratio was ascribed to the growing chain length of the graft PMMA. In fact, Mn and Mw/Mn of the grafted PMMA chains cleaved from the polyethylene substrate were only slightly larger than those of the free PMMA chains, and this was confirmed in the system of nickel‐mediated ATRP. An appropriate period of UV preirradiation controlled the amount of initiation groups introduced to the HDPE film modified with benzophenone. The grafting ratio increased linearly with the preirradiation time. The graft polymerizations for both reaction systems proceeded in a controlled fashion. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3350–3359, 2002

Radiation effect on polyesters

Poly(3-hydroxybutyrate)(PHB) and its copolymer poly(3-hydroxybutyrate-3-hydroxyvalerate) [P(HB-HV)] were irradiated with γ-rays in air or vacuum. Polymer chain scission occurred and resulted in depression of melting points ( T m), glass-transition temperatures ( T g) and number-average molecular weight ( M n ). Decrease in M n of the sample irradiated in vacuum was smaller than that irradiated in air, implying introduction of crosslinking. The T m and T g of samples irradiated in air were inversely proportional to M n . Their biodegradability was clearly promoted with decreasing M n . Radiation grafting of methyl methacrylate (MMA) or 2-hydroxyethyl methacrylate (HEMA) was carried out by in-source polymerization. Degree of grafting ( X g) increased as irradiation dose increased and leveled off around 5 kGy. The X g of PHB grafted was lower than that of P(HB-HV) because of higher crystallinity of the former. Crosslinking between the grafted PMMA chains was easily formed. Biodegradability of both polymers steeply decreased by introduction of MMA grafting, while that of polymers grafted with HEMA increased at first because of improvement of wettability then steeply decreased with increasing X g of HEMA.

Some aspects of graft copolymerization on holocellulose

AbstractGraft copolymers of acrylonitrile and methyl methacrylate on unmodified holocellulose and holocellulose containing between 0.3 and 4.6% thiol groups were prepared by the use of Ce4 + initiator in aqueous medium at 29°C. It was found that although the extent of graft polymer formation on the holocellulose was appreciably reduced by the presence of thiol groups, thiolation showed little influence on the frequency of grafting. The molecular weight of grafted PMMA chains was higher than for PAN grafts; but the latter were more frequently grafted on the backbone polymer. The observed low frequency of grafting is thought to indicate that radicals formed on the cellulosic substrate may not be very reactive towards graft polymer formation.

Melt rheology of ionomer filled with methyl methacrylate–grafted perlite

The shear viscosity, the shear compliance, and their shear rate dependence were determined by a Weissenberg rheogoniometer, and the effect of the grafted poly(methyl methacrylate) chains on the intensification of the interaction at the interface between the ionomer matrix and the filler was discussed. Results were as follows: (1) The relative viscosity of the ionomer filled with MMA-grafted perlite to the matrix ionomer and the yield stress increased with increase in the volume fraction of perlite, and these behaviors were more remarkable in the case of the perlite with larger quantity of grafted PMMA. (2) The effective thickness of the immobilized matrix layer on the filler surface in the Ziegel equation and the crowding factor in the Mooney equation showed larger values in the case of the filled systems of MMA-grafted perlite than in the case of the unmodified perlite. (3) At the same total volume fraction which was the sum of the quantities of the perlite and the grafted PMMA, the relative viscosity and the crowding factor showed respectively a maximum with the quantity of grafted PMMA. (4) The shear compliance of these filled systems decreased with perlite content. A little effect of the amount of grafted PMMA on the compliance was observed at the same volume fraction of perlite. According to these rheological properties, it could be concluded that the grafted PMMA chains were effective in increasing the interaction between the ionomer matrix and the perlite at their interface, particularly in the lower shear rate region.