Molecular Weight Poly Methyl Methacrylate Research Articles

Are Metal-Free Monolithic Crowns the Present of Prosthesis? Study of Mechanical Behaviour.

Purpose: To analyze in vitro the mechanical behavior of five types of complete coverage crowns fabricated from different materials. Materials and methods: Seventy-five full coverage crowns were divided into five groups according to material: Group I, metal core with feldspathic ceramic covering (MC- control group); Group II, zirconia core with feldspathic ceramic covering (CZ); Group III, tetragonal monolithic zirconia (TMZ); Group IV, cubic monolithic zirconia (CMZ); Group V, high molecular weight polymethyl methacrylate (PMMAG) doped with graphene nanoparticles. All crowns underwent in vitro fatiguing by dynamic loading in wet conditions to simulate the masticatory forces to which prosthodontic materials are subject in the oral medium. Lastly, fracture resistance was evaluated by static compression testing. Results: The fracture resistance values obtained were as follows: Group MC, 2443.6 ± 238.6 N; Group CZ, 2095.4 ± 329.2 N; Group TMZ, 2494.6 ± 236.6 N; Group CMZ, 1523.6 ± 325.2 N; and Group PMMAG, 1708.9 ± 386.6 N. Group MC presented higher strength with statistically significant differences in comparison with Groups CZ (P = 0.002), CMZ (P < 0.001), and PMMAG (P < 0.001). Weibull distribution showed less probability of cumulative biomechanical failure in Groups MC and TMZ. Conclusions: Metal-ceramic and tetragonal zirconia showed high fracture resistance, while cubic zirconia and PMMA doped with graphene nanoparticles obtained lower values.

The Influence of Molecular Weight on the Orientation and Properties of Polymethyl Methacrylate Sheets

The influence of molecular weight on the process of orientation stretching and the combination of physicomechanical characteristics of specimens of polymethyl methacrylate (PMMA) is examined. Orientation stretching and increase in the molecular weight of PMMA from 0.52 to 4.6 × 106 g/mol lead to a considerable increase in strength and elastic modulus (σt by a factor of 2.6, E by a factor of 2.5). It is established that the deformation characteristics of oriented PMMA specimens increase by a factor of 10 when the molecular weight is increased from 0.52 to 4.6 × 106 g/mol, which opens up new possibilities in the processing of sheets and films of PMMA.

Morphological study of polymethyl methacrylate microcapsules filled with self-healing agents

Polymethyl methacrylate (PMMA) microcapsules filled with epoxy prepolymer, 3-aminomethyl-3,5,5-trimethylcyclohexylamine, and pentaerythritol tetrakis (3-mercaptopropionate) as healing agents have been prepared separately through internal phase separation method for self-healing purposes. PMMA with two different molecular weights (M¯1=36,000g/mol and M¯2=550,000g/mol) were used with two types of different emulsifiers (ionic and polymeric) to prepare microcapsules. The morphology of healing agent microcapsules was investigated using field emission scanning electron microscopy (FESEM). It was found that PMMA microcapsules separately filled with epoxy and amine had core-shell morphologies with smooth surfaces. The mercaptan/PMMA particles exhibited core-shell and acorn-shape morphologies. The surface morphology of mercaptan microcapsules changed from holed to plain in different emulsion systems. The spreading coefficient (S) of phases in the prepared emulsion systems were calculated from interfacial tension (σ) and contact angle (θ) measurements. The theoretical equilibrium morphology of PMMA microcapsules was predicted according to spreading coefficient values of phases in emulsion systems. It was also found that the surface morphology of PMMA microcapsules depended strongly on the nature of the core, molecular weight of PMMA, type and concentration of emulsifier.

Variation of periodic crazing based on polymer blends of an ultra‐high and a low molecular weight poly(methyl methacrylate)

ABSTRACTPeriodic crazes are caused in a polymer film by the unique mechanical method using bending. Generation of a craze depends on entanglements of the molecular chains of a polymer. Therefore, control of composite morphology of periodic crazes was attempted by varying the entanglements of molecular chains. An effective entanglement network became sparse by polymer blends of an ultra‐high molecular weight polymethylmethacrylate (PMMA) and a low molecular weight PMMA. Consequently, the composite morphology of periodic crazes caused in the blend film varied. In other words, the periodic craze can be used for the evaluation of the effective entanglements. In addition, it was figured out that PMMA of which the number‐average molecular weight (Mn) is less than twice of the effective entanglement molecular weight (Me*) works as a plasticizer in the blend film. And also, it was revealed that the mechanical properties of the blend film decreased dramatically at Mn ≒ 6Me*. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44332.

Liquid–liquid interfacial slip induced layer instability in a thin polymer bilayer

Abstract We investigate the influence of interfacial slip on the layer instability of thin polymer bilayer (polymethylmethacrylate (PMMA)/polystyrene (PS)/solid substrate). In the case of the bilayer system with a high molecular weight (M w ) PMMA upper layer, it is found that the viscosity ratio of the two layers can greatly affect the instability modes of the polymer bilayer and there is a switchover of two different instability modes: (I) the dewetting of the PMMA upper layer on the PS under layer and (II) the dewetting of the PS under layer between the PMMA upper layer and the solid substrate. With the increase in the viscosity ratio between the PMMA upper layer and the PS under layer, the instability mode shifts from the instability mode I to the instability mode II. From our experimental results, it is found that the interfacial slip effect at the PMMA-PS interface is an important reason behind this switchover and the instability of the polymer bilayer system becomes a kinetically controlled one. However, in the case of the bilayer system with a lower M w PMMA upper layer, the viscosity ratio of the two layers does not alter the instability mode of thin polymer bilayer and only the PMMA upper layer dewets on the PS under layers with different M w . The instability of the polymer bilayer system is a thermodynamic controlled one.

Photolithography with polymethyl methacrylate (PMMA)

Polymethyl methacrylate (PMMA) is widely used as an electron beam resist but is not used as a photoresist because of its insensitivity to electromagnetic radiation with wavelengths longer than about 300 nm. In this paper we describe a technique for performing conventional photolithography with high molecular weight PMMA at the widely used 365 nm i-line wavelength. The technique involves photosensitizing PMMA with Irgacure 651—a commercially available photo-initiator that can cause PMMA strands to cross-link. Optimum amount of Irgacure can produce a negative tone photoresist with adequate photosensitivity and plasma etch resistance. We describe this technique in detail with complete processing conditions and discuss the effects of varying Irgacure 651 concentration in PMMA as well as changes in UV exposure dose. We also show example structures patterned with commonly available materials and equipment. Finally, we show that it is possible to carry out gradient lithography with this approach, in order to produce structures in relief in photosensitive PMMA.

Robust graphene wet transfer process through low molecular weight polymethylmethacrylate

Poly (methyl methacrylate) (PMMA) is commonly used during the transfer process of chemical vapor deposited (CVD) graphene. Since PMMA on graphene surfaces is removed by breaking polymerization backbone bonds (de-polymerization), using shorter polymer chains can be a self-solving method for PMMA residue removal. We report on graphene properties transferred with different average molecular weight poly (methyl methacrylate) (PMMA). We obtained enhanced field effect mobility and reduced hole doping without post-annealing for lower average molecular weight PMMA. Also, the graphene surfaces transferred by lower average molecular weight PMMA was free of polymer debris with clean morphology, which was confirmed by carbon 1s X-ray photoemission spectroscopy. This graphene transfer process can be used to avoid additional thermal budget which can cause degradation of device performance.

Use of Gd powder as catalyst for single electron transfer‐living radical polymerization: Applications for synthesis of high molecular weight polymethyl methacrylate

Use of Gd powder as catalyst for single electron transfer‐living radical polymerization: Applications for synthesis of high molecular weight polymethyl methacrylate

Study on Mechanical Properties of Nanocompo-Sites Prepared Using Elastomeric Copolymers and Nano-SiO&lt;sub&gt;2&lt;/sub&gt;

Nanocomposites were obtained by mixing elastomeric copolymer and nanoSiO2 in double-screw extruder at 130-150°C, in which the elastomeric copolymer was prepared by copolymerization of poly (methyl methacrylate (PMMA) macromonomer and butyl acrylate (BA) in benzene using azobisisobutyro-nitrile (AIBN) as initiator. The results indicated that increasing the amount of PMMA, the molecular weight of PMMA and copolymers, nanosilica charged resulted in improving the tensile strength and modulus at 300% elongation of nanocomposites, on the contrary, decreasing ultimate elongation and permanent set decrease. In additions, the tensile strength and the modulus at 300% elongation of nanocomposites reached to a maximum while the mass ratio of nanoSiO2 to copolymer was 3%.

Study on Mechanical Properties of Nanocompo-Sites Prepared Using Elastomeric Copolymers and Nano-SiO&lt;sub&gt;2&lt;/sub&gt;

Nanocomposites were obtained by mixing elastomeric copolymer and nanoSiO2 in double-screw extruder at 130-150°C, in which the elastomeric copolymer was prepared by copolymerization of poly (methyl methacrylate (PMMA) macromonomer and butyl acrylate (BA) in benzene using azobisisobutyro-nitrile (AIBN) as initiator. The results indicated that increasing the amount of PMMA, the molecular weight of PMMA and copolymers, nanosilica charged resulted in improving the tensile strength and modulus at 300% elongation of nanocomposites, on the contrary, decreasing ultimate elongation and permanent set decrease. In additions, the tensile strength and the modulus at 300% elongation of nanocomposites reached to a maximum while the mass ratio of nanoSiO2 to copolymer was 3%.

二步水解法制备凝胶渗透色谱用聚甲基丙烯酸标样&amp;lt;br&amp;gt;Preparation of Monodispersed PMAA for GPC Calibration Standards by Two-Step Hydrolysis

采用二步水解法水解单分散GPC用聚甲基丙烯酸甲酯标样，核磁共振测得其水解率达99%，制得的聚甲基丙烯酸钠经酸化析出后得到聚甲基丙烯酸标样。该聚甲基丙烯酸标样以磷酸盐缓冲水溶液为流动相，采用PLaquagel-OH mixed-H柱串联测得的GPC色谱峰峰形对称，半峰宽窄，分散系数均小于1.3，具有很好的单分散性。粘度法测得其Mη与通过聚甲基丙烯酸甲酯标样参数计算得到的Mη'平均相对误差小于10%，表明水解对聚甲基丙烯酸甲酯主链的聚合度无明显影响。因此，可以用聚甲基丙烯酸甲酯标样的分子量计算得到相应聚甲基丙烯酸标样的分子量。Hydrolyzed monodisperse polymethyl methacrylate for GPC calibration standards by two-step hydrolysis, the degree of hydrolysis reached 99% measured by nuclear magnetic resonance analysis (NMR).The obtained monodisperse polymethylacrylic acid-Na transformed to polymethylacrylic acid by acidification. The polymethylacrylic acid with phosphate buffer solution as mobile phase, used PL aquagel-OH mixed-H columns in series, GPC figures had symmetrical peak shape, narrow half-peak, dispersity were all less than 1.3. Viscosity average molecular weight (Mη') of polymethylacrylic acid calculated by hydrolysis formula compared to the actual results measured by viscosity meas-uring method (Mη), the average relative error were less than 10%, which indicated the hydrolysis did not effect on the degree of polymerization of the main chain. Therefore, we can calculate molecular weight of polymethylacrylic acid from the corresponding molecular weight of polymethyl methacrylate.

Fabrication of photonic crystal structures on flexible organic light-emitting diodes using nanoimprint

Nanoimprint lithography (NIL) was used to create a film with photonic crystal structures in the organic light-emitting diode (OLED) component. By utilizing various stamps, such as with photonic crystal structures and with grating structures in polymethylmethacrylate (PMMA) were studied. The better formability belongs to a stamp of photonic crystal patterns and molecular weight of PMMA in 350K and 996+15K in double layers. A photonic crystal with nanostructures in a period of 400nm was fabricated as a photonic crystal film and was integrated into an organic light emitting diode (OLED). The experiments show that the OLED without photonic crystal films behaves 2.11cd/m^2 for luminous intensity, 2.336cd/A for lightening efficiency (@hL), and 0.475lm/W for lightening power (@hP), under the driving voltage of 10V and current of 0.009012A; the OLED with the photonic crystal films behaves 250cd/m^2 for luminous intensity and 2.774cd/A for @hL, and 0.871lm/W for @hP, under the same driving voltage and same current, which shows that the latter performs well.

Mechanical Properties of Nanocomposites Prepared Using Elastomeric Terpolymer and Nano-SiO2

Nanocomposites were obtained by mixing elastomeric terpolymer and nano-SiO2 in double-screw extruder at 130–150°C, in which elastomeric terpolymer was prepared by terpolymerization of poly(methyl methacrylate (PMMA) macromonomer, butyl acrylate (BA), and acrylic acid (AA) in benzene using azobisisobutyronitrile (AIBN) as initiator. The results indicated that increasing the amount of PMMA, the molecular weight of PMMA and terpolymers as well as the content of carboxylic acid were favorable to increase the mechanical properties of nanocomposites. In addition, the tensile strength and the modulus at 300% elongation of nanocomposites reach to a maximum while the mass ratio of nano-SiO2 to terpolymer is 3%.

Mechanical Properties of Elastomeric Terpolymer Nanocomposites Containing Nano-SiO2

Nanocomposites were obtained by mixing elastomeric terpolymer and nano-SiO2 in double-screw extruder at 130-150 °C, in which elastomeric terpolymer was prepared by terpolymerization of poly(methyl methacrylate (PMMA) macromonomer, butyl acrylate(BA), and acrylic acid(AA) in benzene using azobisisobutyronitrile (AIBN) as initiator. The results indicated that increasing the amount of PMMA, the molecular weight of PMMA and terpolymers as well as the content of carboxylic acid were favorable to increase the mechanical properties of nanocomposites. In addition, the tensile strength and the modulus at 300% elongation of nanocomposites reach to a maximum while the mass ratio of nano-SiO2 to terpolymer is 3%.

Polymerization of Methyl Methacrylate with a Novel Carbon Bridged Cyclopentadienyl Chromium Complex

A new carbon bridged cyclopentadienyl chromium complex of the type [ (C5H4)C(CH3)2 CH2(C5H4N) ]CrCl2 was prepared by treatment of CrCl3•(THF) 3 in THF solution with the lithium salt of ligand with cyclopentadienyl and pyridyl group. The chromium complex was characterized by mass spectra and elemental analysis. Activated by Al(i-Bu) 3, the chromium complex displayed a very high activity for methyl methacrylate (MMA) polymerization. After 18 hours, 85.49 % MMA was converted to polymethyl methacrylate (PMMA) with a viscosity average molecular (Mv) of 328000 at 60 °C at MMA/ Al(i-Bu) 3/chromium complex of 2000:20:1 in MMA bulk. The high conversion of MMA and high molecular weight of PMMA are the cause of the unique stable active site formed by the new chromium complex and cocatalyst.

New ionic liquids with hydrolytically stable anions as alternatives to hexafluorophosphate and tetrafluoroborate salts in the free radical polymerization and preparation of ion-conducting composites

The main objective of this study was to replace the traditionally used hydrolytically unstable PF6 and BF4 ionic solvents with new, stable ionic liquids (ILs) and to investigate the potential of ILs in formulation of the polymers based on methyl methacrylate and acrylonitrile with narrow polydispersities, high yields and molecular weights. Various ILs with four anions, namely, tris(pentafluoroethyl)trifluorophosphate, trifluoromethanesulfonate, trifluoroacetate and tetracyanoborate, were tested. The influence of the IL's characteristics on the free radical polymerization process was found to be significant. Trifluoromethanesulfonate- and trifluoroacetate-based ionic solvents provide the formation of polymers with the highest molecular weight (Mr≈8.8 × 105 for polyacrylonitrile (PAN) and Mw≈18.9 × 105 for polymethylmethacrylate (PMMA)) in quantitative yield (PAN, 96%; PMMA, 92%). Taking into account, the high ionic conductivity and satisfactory electrochemical stability of the tetracyanoborate-based ILs, composite films derived from PAN and B(CN)4 ILs were prepared and their physico–chemical properties were investigated. The nature of the cation strongly influences the properties of the resulting composite films, namely, their flexibility, transparency, surface morphology and ionic conductivity (the maximum conductivity was found to be 1.0 × 10−2 S cm−1 at 25 °C). Ionic Liquids (ILs) are design solvents for free radical polymerization and preparation of composite materials! There is NO general rule for choosing of ionic solvent, but by means of design it is possible to select the best one for a concrete process. CF3SO3 and CF3COO based ILs provide the formation of highest molecular weight polyacrylonitrile (PAN, Mn≈8.8 × 105) and polymethylmethacrylate (PMMA, Mw≈18.9 × 105) in a quantitative yield (PAN – 96%, PMMA – 92%). (CF3CF2)3PF3 ILs promote the formation of high molecular weight PMMA even upon the polymerization under the atmospheric pressure with the presence of air oxygen. Nature of the IL stongly influences the properties of the resulted composites films, namely, their flexibility, transparency and surface morphology. Composite films derived from PAN and B(CN)4 ionic liquids possess ionic conductivity as high as 1.0 × 10−2 S cm−1 at 25°C.

Synthesis of 2‐(N‐arylimino)pyrrolide nickel complexes and polymerization of methyl methacrylate

AbstractThe synthesis, characterization and methyl methacrylate polymerization behaviors of 2‐(N‐arylimino)pyrrolide nickel complexes are described. The nickel complex [NN]2Ni (1, [NN] = [2‐C(H)NAr‐5‐tBu‐C4H2N]−, Ar = 2,6‐iPr2C6H3) was prepared in good yield by the reaction of [NN]Li with trans‐[Ni(Cl)(Ph)(PPh3)2] in THF. Reaction of [NN]Li with NiBr2(DME) yielded the nickel bromide [NN]Ni(Br)[NNH] (2). Complexes 1 and 2 were characterized by 1H NMR and IR spectroscopy and elemental analysis, and by X‐ray single crystal analysis. Both complexes, upon activation with methylaluminoxane, are highly active for the polymerization of methyl methacrylate to give high molecular weight polymethylmethacrylate with narrow molecular distributions. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Influence of the Molecular Weight of Polymethyl Methacrylate on the Molecular Mobility and Physicomechanical Properties

Influence of the Molecular Weight of Polymethyl Methacrylate on the Molecular Mobility and Physicomechanical Properties

CO2-laser micromachining of PMMA: the effect of polymer molecular weight

This paper reports an investigation on the effects of laser power and processing speed on the depth, width and surface profiles of microchannels manufactured from polymethyl methacrylate (PMMA) of various molecular weights. The CO2 laser employed has a wavelength of 10.6 µm and a maximum power of 25 W. The power used for channel fabrication varied between 0.275 and 2.5 W and the cutting speed ranged from 7.0 to 64 mm s−1. It is observed that the channel depth varies linearly with an increase in laser power at a particular speed. For a prescribed laser power, the channel depth decreased with an increase in laser speed for all the grades of PMMA. The channel width increased with an increase in laser power but decreased with an increase in speed. There is a decrease in the depth of the microchannels with an increase in the molecular weight of PMMA. Though the width decreases with an increase in molecular weights of PMMA, 96.7 kDa PMMA has a smaller width than 120 kDa PMMA which is due to the formation of bulges on the channel rim. The surface profiles of the microchannels were examined by a scanning electron microscope. It is observed that pore formation increased with an increase in molecular weight.

Stretching DNA in polymer nanochannels fabricated by thermal imprint in PMMA

We present results regarding the fast and inexpensive fabrication of polymer biochips forinvestigating the statics and dynamics of DNA confined in nanochannels. The biochips havebeen fabricated by means of nanoimprint lithography (NIL) in low molecular weightpolymethyl methacrylate (PMMA) using a 4 inch diameter two-level hybrid stamp. Thefluidic structures were sealed using thermal polymer fusion bonding. The stamphas nanometer- and micrometer-sized protrusions defined in a thermally grownSiO2 layer and the sol–gel process derived duromeric hybrid polymer Ormocomp, respectively. Thestamp is compatible with molecular vapor deposition (MVD), used for applying a durablechlorosilane based antistiction coating, and allows for imprint up to a temperature of270 °C. The extension of YOYO-1 stained T4 GT7 bacteriophage DNA inside the PMMAnanochannels has been experimentally investigated using epi-fluorescence microscopy. Themeasured average extension length amounts to 20% of the full contour length with astandard deviation of 4%. These results are in good agreement with results obtained bystretching DNA in conventional fused silica nanochannels.