Dispersion polymerization of MMA in supercritical CO2 in the presence of poly(poly(ethylene glycol) methacrylate-co-1H,1H,2H,2H-perfluorooctylmethacrylate)

Various random copolymers of poly(poly(ethylene glycol) methacrylate-co-1H,1H,2H,2H-perfluorooctylmethacrylate) (p(PEGMA-co-FOMA)) with different poly(ethylene glycol) (PEG) chain length (M_n = 300, 475, and 1100) and different FOMA content have been synthesized in supercritical carbon dioxide (scCO₂) via free-radical polymerization. The copolymers containing above 50 wt% FOMA could be used as a stabilizer for the polymerization of methyl methacrylate (MMA) in scCO₂. For PEGMA (300) and PEGMA (475) copolymers, the copolymeric stabilizer with 67–69 wt% FOMA content was shown to be optimal to produce micrometer-size spherical PMMA powder. The size of pendant PEG group and the composition of copolymer as well as the concentration of MMA affected on the size of PMMA particles and the stability of PMMA latexes in CO₂.     

Kinetic study of atom transfer radical homo- and copolymerization of styrene and methyl methacrylate initiated with trichloromethyl-terminated poly(vinyl acetate) macroinitiator

Atom transfer radical bulk copolymerization of styrene (St) and methyl methacrylate (MMA) was performed in the presence of CuCl/PMDETA as a catalyst system and trichloromethyl-terminated poly(vinyl acetate) telomer as a macroinitiator at 90 °C. The overall monomer conversion was followed gravimetrically and the cumulative average copolymer composition at moderate to high conversion was determined by ¹H NMR spectroscopy. Reactivity ratios of St and MMA were calculated by the extended Kelen–Tudos (KT) and Mao–Huglin (MH) methods to be r_St = 0.605 ± 0.058, r_MMA = 0.429 ± 0.042 and r_St = 0.602 ± 0.043, r_MMA = 0.430 ± 0.032, respectively, which are in good agreement with those reported for the conventional free-radical copolymerization of St and MMA. The 95% joint confidence limit was used to evaluate accuracy of the estimated reactivity ratios. Results showed that in the controlled/living radical polymerization systems such as ATRP, more reliable reactivity ratios are obtained when copolymer composition at moderate to high conversion is used. Good agreement between the theoretical and experimental composition drifts in the comonomer mixture and copolymer as a function of the overall monomer conversion was observed, indicating the accuracy of reactivity ratios calculated by copolymer composition at the moderate to high conversion. Instantaneous copolymer composition curve and number-average sequence length of comonomers in the copolymer indicated that the copolymerization system tends to produce a random copolymer.     

Enhanced nonlinear optical and optical limiting properties of graphene/ZnO hybrid organic glasses

Graphene/ZnO (G/ZnO) composites were synthesized for the first time by a wet chemical method. X-ray diffraction and transmission electron microscopy analyses demonstrated that ZnO nanoparticles with an average diameter of about 5 nm uniformly covered the graphene surfaces. G/ZnO composites were dispersed in methyl methacrylate (MMA), polymerized at 75 °C for 30–35 min, and finally, dried at 45 °C for 10 h, to afford G/ZnO/PMMA organic glasses. UV–visible spectra showed that the band gaps of the G/ZnO/PMMA organic glasses were about 3.54 eV, larger than that of bulk ZnO because of the small size effect of ZnO nanoparticles. The nonlinear optical (NLO) and optical limiting (OL) properties of the G/ZnO/PMMA organic glasses were investigated by a modified Z-scan technique. The total NLO coefficient α₂ of the G/ZnO/PMMA organic glass was as high as 1530 cm/GW, which was approximately 5.6 and 7.8 times larger than those of G/PMMA and ZnO/PMMA organic glasses. The enhanced NLO properties of the G/ZnO/PMMA organic glasses led to excellent OL performance, which was attributed to the positive synergistic effects between graphene and ZnO.     

Dual-nodal PMMA-supported Eu3 +-containing metallopolymer with high color-purity red luminescence

Based on chemical grafting of the complex monomer [Eu(TTA)₃(4-vinyl-Py)₂] (HTTA = 2-thenoyltrifluoroacetylacetate, 4-vinyl-Py = 4-vinyl-pyridine) with two active vinyl groups and MMA (methyl methacrylate), the dual-nodal PMMA-supported metallopolymers with high color-purity Eu^3 +-based luminescence are obtained. The physical properties show that their luminescent properties (τ_obs = 494–552 μs and Ф_Eu^L = 50–55%) are distinctively enhanced from copolymerization in comparison with those (τ_obs = 470 μs and Ф_Eu^L = 44%) of the complex monomer besides the improvement of thermal-stabilities.     

First example of PMMA-supported and highly luminous color-purity red-light metallopolymer based on a tris-β-diketonate Zn2 +-Eu3 +-complex

Through the copolymerization of a complex monomer [Zn(L)(4-vinyl-Py)Eu(TTA)₃] (2; H₂L = N,N′-bis(salicylidene)cyclohexane-1.2-diamine; 4-vinyl-Py = 4-vinyl-pyridine and HTTA = 2-thenoyltrifluoroacetonate) with MMA (methyl methacrylate), the first example of PMMA-supported and highly luminous (Ф_Eu^L = 63.1%) color-purity red-light metallopolymer poly(MMA-co-2) based on a tris-β-diketonate Zn^2 +-Eu^3 +-complex is obtained.     

Coatings and surface modification by methane plasma polymerization

Polymers formed from plasma-polymerized methane were employed to modify the surface properties of silicone rubber membrane. Polymers were evaluated based on the energy input parameter W/FM, where W is the discharge power, F is the monomer flow rate, and M is the molecular weight of the monomer. Dealing with the characteristics of plasma polymerization and the deposited polymer film, the effect of pumping rate on deposition rate and the coating thickness, surface energy, and gas permeabilities of methane-plasma-polymer-coated silicone rubber membrane were investigated in three plasma regions. Because more reactive species are expelled at high pumping rates, the monomer-deficient region is reached at lower W/FM in the high pumping rate system than that in the low pumping rate system. The composite parameter W/FM had a strong influence on coating thickness, gas permeability, surface energy, and the polar component of the surface energy but little effect on its dispersion component. Examination of gas permeabilities indicated that coating thickness was another important controlling factor on the properties of plasma polymer.     

NIR luminescence comparison of Zn-Nd Schiff-base complex doped or single-nodal grafted into PMMA

Through doping or grafting of a new ZnNd Schiff-base complex monomer [Zn(L)(4-vinyl-Py)Nd(NO₃)₃] (2; H₂L = N,N′-bis(3-methoxy-salicylidene)phenylene-1,2-diamine; 4-vinyl-Py = 4-vinyl-pyridine) into PMMA (poly(methyl methacrylate)), two kinds of hybrid materials 2@PMMA and Poly(2-co-MMA) with significantly improved physical properties including good Nd^3 +-centered near-infrared (NIR) luminescence were obtained. Especially the single-nodal ZnNd-grafted Poly(2-co-MMA) soluble in organic solvents exhibits the high sensitization efficiency (η_sens = Φ_Nd^L/Φ_Nd^Nd = 81%) even at a high feed molar ratio up to 1:50.     

Effect of methyl methacrylate monomer on bond strength of denture base resin to acrylic teeth

Bond failures at the acrylic teeth and denture base resin interface are still a common clinical problem in prosthodontics. The effect of methyl methacrylate (MMA) monomer on the bond strength of three types of denture base resins (Acron MC, Lucitone 550 and QC-20) to two types of acrylic teeth (Biotone and Trilux) was evaluated. Twenty specimens were produced for each denture base resin/acrylic tooth combination and were randomly divided into control (acrylic teeth received no surface treatment) and experimental groups (MMA was applied to the surface of the acrylic teeth for 180 s) and were submitted to shear tests (1 mm/min). Data (MPa) were analyzed using three-way ANOVA/Student's test (α=0.05). MMA increased the bond strength of Lucitone denture base resins and decreased the bond strength of QC-20. No difference was detected for the bond strength of Acron MC base resin after treatment with MMA.     

AGET ATRP of methyl methacrylate catalyzed by FeCl3/iminodiacetic acid in the presence of air

The recently developed living free-radical polymerization system, atom transfer radical polymerization using activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP), was used for methyl methacrylate (MMA) polymerization in the presence of a limited amount of air, using a novel catalyst system based on iron (FeCl₃) complexes with iminodiacetic acid (IDA) and using ascorbic acid (VC) as a reducing agent. The kinetics of AGET ATRPs of MMA with different amounts of VC in the presence of air was investigated. The results of the polymerizations demonstrated the features of “living”/controlled free-radical polymerization such as the number-average molecular weights increasing linearly with monomer conversion and narrow molecular weight distributions (M_w/M_n = 1.31–1.44).     

Quality of diamond wafers grown by microwave plasma CVD: effects of gas flow rate

We found a strong impact of gas flow rate on diamond growth process in a 5 kW microwave plasma chemical vapour deposition reactor operated on CH₄-H₂ gas mixtures. Diamond films of 0.1–1.2 mm thickness and 2.25 in. in diameter were produced at H₂ flow rates varied systematically from 60 sccm to 1000 sccm at 2.5% CH₄. The highest growth rate, 5 μm h⁻¹, was observed at intermediate F values (≈300 sccm). Carbon conversion coefficient (the number of C atoms going from gas to diamond) increases monotonically up to 57% with flow rate decrease, however, this is accompanied with a degradation of diamond quality revealed from Raman spectra, thermal properties and surface morphology. High flow rates were necessary to produce uniform films with thermal conductivity >18 W cm⁻¹ K⁻¹. Diamond disks with very low optical absorption (loss tangent tgδ<10⁻⁵) in millimetre wave range (170 GHz) have been grown at optimized deposition conditions for use as windows for high-power gyrotrons.     

Fabrication and characterization of reaction-bonded silicon carbide with poly(methyl methacrylate) as pore-forming agent

Reaction-bonded silicon carbide (RBSC) ceramics were prepared by liquid silicon infiltration at 1600 °C using a carbon biscuit. The green body was made by slip casting a stabilized carbon powder slurry, followed by pyrolysis in a vacuum furnace at 1000 °C for 2 h; the density of the biscuit (ρ_b) was controlled using poly(methyl methacrylate) (PMMA) powder as pore former in mass proportion from 30% to 50% in 5 percentage point intervals. The particle size of the PMMA had significant effects on the microstructure, distribution of residual silicon, and the mechanical properties of the ceramic. For 40 mass% PMMA with d₅₀=1.17 μm and d₅₀=0.51 μm, ρ_b was 0.81 and 0.82 g/mL, with corresponding biscuit porosities of 51% and 50%, which gave peak values of both RBSC ceramic density of 3.07 and 3.10 g/mL, and flexural strength of 741 and 794 MPa, respectively. XRD analysis showed that the main phase was β-SiC, with a small quantity of α-SiC. Using PMMA with d₅₀=0.51 μm, a small quantity of residual Si was well dispersed with grain size <1 μm. “Black core” residual carbon in the RBSC was successfully avoided when ρ_b≤0.82 g/mL (mass proportion PMMA≥35%). PMMA as pore former favored the elimination of the detrimental black core and the preparation of dense RBSC with good mechanical properties.     

Very hard ZrC thin films grown by pulsed laser deposition

Thin ZrC films were grown on (1 0 0) Si substrates at temperatures from 30 to 500 °C by the pulsed laser deposition technique. Auger electron spectroscopy investigations found that films contained oxygen concentration below 2.0 at%, while X-ray photoelectron spectroscopy investigations showed that oxygen is bonded in an oxy-carbide type of compound. The films’ mass densities, estimated from X-ray reflectivity curve simulations, and crystallinity improved with the increase of the substrate temperature. Williamson–Hall plots and residual-stress measurements using the modified sin² ψ method for grazing incidence X-ray diffraction showed that the deposited films are nanostructured, with crystallite sizes from 6 to 20 nm, under high micro-stress and compressive residual stress. Nanoindentation investigations found hardness values above 40 GPa for the ZrC films deposited at substrate temperatures higher than 300 °C. The high density of the deposited films and the nm-size crystallites are the key factors for achieving such high hardness values.     

Synthesis and investigation of monomodal hydroxy-functionalized PEG methacrylate based copolymers with high polymerization degrees. Modification by “grafting from”

The synthesis of monomodal copolymers with poly(ethylene glycol) (PEG) side chains from commercial poly(ethylene glycol) methacrylates (PEGMA) by atom transfer radical polymerization (ATRP) is verified. Two hydroxy-functionalized PEGMA macromonomers (520 g/mol and 360 g/mol) were copolymerized with methyl methacrylate (MMA) using various initial feed (1.5/98.5–50/50 mol.%). The copolymers P(MMA-co-PEGMA) with high degree of polymerization, e.g. 100–275 of repeating units in the backbone including 7–56 PEG side chains, were obtained. The relative reactivity ratios of PEGMA and MMA determined by the Jaacks method indicated slightly faster incorporation of macromonomer into polymeric chain than MMA (r_MMA = 0.79; r_PEGMA = 1.27). The polymers containing at least 17 mol.% of PEGMA units were water-soluble and exhibited clouding point at temperature in a broad range of 39–70 °C. The temperature-sensitive effect makes these polymers as a potential carriers in drug delivery systems. In the case of copolymers insoluble in water, a three-step procedure, including esterification to ATRP multifunctional macroinitiators, ATRP of tert-butyl methacrylate (tBMA) by grafting from, deprotection of carboxylic groups by removing tert-butyl groups, was applied to extend PEG grafts and expand the content of hydrophilic fraction (32–94 mol.%), what efficiently developed polymer solubility in polar solvents giving possibility for the future biomedical applications.     

Kinetic studies of semibatch emulsion copolymerization of methyl methacrylate and styrene in the presence of high intensity ultrasound and initiator

The present work deals with kinetic studies of copolymerization of methyl methacrylate and styrene using ultrasound assisted semibatch emulsion copolymerization in the presence of sodium dodecyl sulfate (emulsifier) and potassium persulfate (external initiator). The effect of temperature, acoustic intensity, initiator loading, surfactant concentration and monomer concentration on the extent of conversion has been investigated. The extent of polymerization was observed to increase with an increase in the temperature, and concentrations of initiator, monomer and surfactant. Further, the initial polymerization rate increased with an increase in the acoustic intensity from 11.2 to 23.1 W cm⁻² and then it was found to decrease with a further increase to 33.80 W cm⁻². The novelty of this work lies in the fact that there have been only limited kinetic studies for the approach of ultrasound assisted emulsion copolymerization. It has been also established in the present work that the formation of fine and stable monomer droplets, due to the cavitational activity at/near the interface of immiscible monomer phase and subsequent disruption by micro jets, leads to the smaller final polymer particle size and under optimized conditions, it was found to be about 40 nm.     

Thermal analysis of submicron nanocrystalline diamond films

The thermal properties of sub-μm nanocrystalline diamond films in the range of 0.37–1.1 μm grown by hot filament CVD, initiated by bias enhanced nucleation on a nm-thin Si-nucleation layer on various substrates, have been characterized by scanning thermal microscopy. After coalescence, the films have been outgrown with a columnar grain structure. The results indicate that even in the sub-μm range, the average thermal conductivity of these NCD films approaches 400 W m^− 1 K^− 1. By patterning the films into membranes and step-like mesas, the lateral component and the vertical component of the thermal conductivity, k_lateral and k_vertical, have been isolated showing an anisotropy between vertical conduction along the columns, with k_vertical ≈ 1000 W m^− 1 K^− 1, and a weaker lateral conduction across the columns, with k_lateral ≈ 300 W m^− 1 K^− 1.     

Optical scattering of nanocrystalline Pb(ZrxTi1−x)O3 films

Optical characterization methods, like spectrophotometry at UV–vis-NIR wavelengths and prism-coupler method, were applied to polycrystalline Pb(Zr_xTi_1?x)O₃ thin films at various thicknesses. Thin films were deposited at room temperature by pulsed laser deposition on MgO (1 0 0) substrates and post-annealed at different temperatures. X-ray diffraction and atomic force microscopy were used to characterize the crystal structure and surface morphology of the thin films, respectively.Well oscillating transmission with a sharp fall near the absorption edge was found in films with high orientation and low surface roughness. Changes in the surface morphology and crystal orientation were found to modulate optical interference maxima and minima of the transmittance spectra and to increase the width of the TE₀ mode (Δβ ≈ 0.06) indicating an increase in the scattering losses of the films. Single-phase oriented films had sharpest coupling values (Δβ ≈ 0.005) of the TE₀ mode.     

Deposition of aromatic polyimide thin films in supercritical carbon dioxide

The deposition of aromatic polyimide (API) thin films was carried out in supercritical carbon dioxide (scCO₂) with 20 mol% of N,N-dimethylformamide (DMF) as a cosolvent, and using 4,4′-diaminodiphenyl ether (ODA) and pyromellitic dianhydride (PMDA) as monomers. A new apparatus based on a flow method that consisted of a cold-wall type reactor and two supply lines for each of the API monomers was used. The effect on the morphology of the films was investigated at feeding monomer concentrations and deposition temperatures ranging from 5 × 10⁻⁴ to 5 × 10⁻⁶ on a mole fraction basis and from 423 to 523 K, respectively. The results showed that increasing the monomer concentration and decreasing the deposition temperature increased the thickness of the films, and a smooth surface of the film was obtained at 423 K. Additionally, FT-IR study and thermogravimetric (TG) analysis of the film deposited at monomer mole fractions of 5 × 10⁻⁵ and at a deposition temperature of 473 K were also carried out. The FT-IR spectrum of the deposited film in scCO₂ with DMF represented imide structures although there was a small peak of amide carbonyl stretching that originated from the polyamic acid and DMF. The TG curve indicated the temperature of 5% weight loss was more than 800 K under an air atmosphere after complete imidization.     

Cu3N films prepared by the low-pressure r.f. supersonic plasma jet reactor: Structure and optical properties

A low-pressure r.f. supersonic plasma jet reactor (RPJ) has been used for deposition of Cu₃N thin films. From a comparison of experimental values of composition weight per cent with the theoretically predicted values, it follows that if the r.f. power absorbed in the reactor does not exceed 75 W, stoichiometric Cu₃N films can be obtained. The typical value of the deposition growth rate was found to be in the order of 16 nm min⁻¹ for r.f. power P_w≈40 W. The optical energy gap, E_g, microhardness, H, and Young's modulus, E, of the deposited Cu₃N thin films increase with decreasing r.f. power. They are E_g=1.24 eV, H=8.8 GPa and E=146 GPa for the sample deposited with a r.f. power of 40 W. Deposition of Cu₃N thin films by means of the modificated RPJ reactor (with a multi-jet system) on to internal walls of cavities, holes and on the surface of complex shapes of hollow substrates can be useful for surface-treatment technology.     

First example of near-infrared (NIR) luminescent Yb4(Salen)4-containing metallopolymer through radical copolymerization with MMA (methyl methacrylate)

Through the radical copolymerization of MMA (methyl methacrylate) with a vinyl-containing complex monomer {[Yb₄(L)₂(HL)₂(μ₃-OH)₂(NO₃)₂]·(NO₃)₂} (1; H₂L = N,N′’-bis-(5-(3′-vinylphenyl)-3-methoxy-salicylidene)cyclohexane-1,2-diamine), the first example of PMMA-supported and Yb₄(Salen)₄-containing metallopolymer Poly(1-co-MMA) exhibits significantly improved physical properties besides relatively higher NIR quantum yields (Φ_Yb^Yb = 1.18% and Φ_L^Yb = 0.86%) than those (Φ_Yb^Yb = 1.02–1.04% and Φ_L^Yb = 0.73–0.75%) of complex monomer 1 in solution and 1@PMMA in solid state.     

Viscoelastic and adhesive properties of PMMA-b-PtBA with tackifier

The study of adhesive behavior of poly(methyl methacrylate)-b-poly(t-butyl acrylate) (PMMA-b-PtBA) diblock copolymers is rare in literature. In this study, we prepared a PMMA-b-PtBA diblock copolymer (B-16) by the anionic polymerization technique and compounded it with various amounts of tackifier (Staybelite Ester 3 synthetic resin of Hercules Inc., a triethylene glycol ester of partially hydrogenated wood rosin). The B-16 contained 10 parts of tackifier per hundred parts of polymer (phr), which has a better storage modulus (G') at 120 °C and 0.1 rad/s than counterpart homopolymer PMMAs of different average molecular weights, containing the same phr of tackifier. Increasing the molecular weight of homopolymer PMMA samples (containing 10 phr of tackifier), the G' value at 120 °C increases toward the optimum region. The peel performance relates rather well to the viscoelastic property.