PMMA人工晶状体表面的CF4/O2等离子体修饰

为了改善聚甲基丙烯酸甲酯(PMMA)人工晶状体的生物相容性和透光性, 采用CF4/O2等离子体技术修饰其表面. 通过衰减全反射红外光谱(ATR-FTIR)、X射线光电子能谱(XPS)、静态接触角(CA)测定、扫描电子显微镜(SEM)、紫外-可见近红外光谱(UV-Vis)等方法进行表征, 结果表明, 经CF4/O2等离子体处理后, PMMA表面的含氟和含氧基团增加, 其表面的亲水性增强, 生物相容性改善, 紫外光的隔离效率增大. 因此, 通过CF4/O2等离子体修饰能够有效地改善PMMA人工晶状体的性质.     

Wavelength effect on the photoinduced reaction of polymethylmethacrylate

Polymethylmethacrylate (PMMA) containing benzophenone (BP) was photo-irradiated with monochromatic radiation of wavelength 260–360 nm using the Okazaki Large Spec-trograph (OLS). On irradiation of PMMA films containing BP in air, the sensitized main-chain scission and photocrosslinking of PMMA took place simultaneously. These reactions are dependent on irradiation wavelength. The threshold wavelength for both reactions is found to be ca. 380 nm. The number of main-chain scission and amount of gel increased with the increase of BP concentration in PMMA. Photosensitized main-chain scission favors the irradiation of radiation at ca. 280 nm and photocrosslinking takes place efficiently with the exposure of 340 nm radiation. A possible mechanism for photosensitized reaction is proposed. © 1995 John Wiley & Sons, Inc.     

Nanohole structure prepared by a polystyrene-block-poly(methyl methacrylate)/poly(methyl methacrylate) mixture film

Cylindrical nanoporous structures were prepared by using a mixture film of polystyrene-block-poly(methyl methacrylate) copolymer (PS-b-PMMA) and PMMA homopolymer (hPMMA), and they were analyzed by transmission electron microtomography (TEMT), X-ray reflectivity (XR), and grazing incidence small-angle X-ray scattering. For this purpose, the mixture film was spin-coated onto a silicon wafer modified by a neutral brush for PS and PMMA blocks, which generates PMMA cylindrical microdomains oriented normal to the substrate. Two methods were employed to prepare nanoporous structures: (1) all of the PMMA phase (PMMA block and PMMA homopolymer) in the film was removed by UV irradiation, followed by rinsing with a selective solvent (acetic acid) to PMMA and (2) only PMMA homopolymer was removed by selective solvent etching without UV irradiation. We found via TEMT and XR that the nanoporous structure in the film prepared by UV irradiation exhibited almost perfect cylindrical shape throughout the entire film thickness. However, when the film was rinsed with a selective solvent, nanoporous structures were not straight cylinders but had a funnel shape in which the diameter of nanopores located near the top of the film was larger than that located near the bottom of the film.     

Photochemical fabrication of a well-defined diblock copolymer nanotemplate using 172-nm vacuum ultraviolet light

Well-ordered nanopore arrays were successfully prepared from polystyrene (PS) and poly(methyl methacrylate) (PMMA) diblock copolymer (DBC) film based on a photochemical approach using 172-nm vacuum ultraviolet (VUV) light. Since the etching selectivity between the PS and PMMA domains against activated oxygen species generated by the VUV irradiation of atmospheric oxygen molecules was markedly different, PMMA was preferentially decomposed, resulting in the formation of PS nanopore arrays. Both the photoetching rate and final morphology depended greatly on the atmospheric pressure during VUV irradiation. Since at 10 Pa the PS domains degraded less due to the shortage of oxygen molecules in the atmosphere, the residual matrix kept its fine nanostructures up to 40 min of irradiation. The matrix could be eliminated completely when irradiation was extended to 60 min at this pressure. On the other hand, at 10(3) Pa the DBC film was removed completely from the substrate within 10 min of irradiation. However, at 10(3) Pa, not only the decomposition of the PMMA domains, but also the photoetching rate of the PS domains accelerated significantly resulting in marked distortion of the generated nanostructures. By selecting an appropriate atmospheric pressure and time for VUV irradiation, we were able to control both nanoarray formation and elimination without the use of any physical and/or chemical treatment.     

Radiation induced effects on the microhardness measurements of poly(methyl methacrylate): poly (vinylidene fluoride) polyblends

Solution-mixed poly(methyl methacrylate) (PMMA): poly(vinylidene fluoride) (PVDF) polyblends with different weight percentage ratios were irradiated with various doses of gamma irradiation (1–100 Mrad). The effect of irradiation on the strength of blend specimens was studied by measuring the surface microhardness using a Vickers microhardness tester attached to a Carl Zeiss NU-2 Universal research microscope. The irradiation was found to produce hardening in the blend specimens; however, the degree of hardening depends upon the dose level, testing conditions and also on the miscibility of PMMA and PVDF in the blend specimens. The increase and decrease in microhardness has been explained on the basis of crosslinking and scissioning. The two limits of irradiation dose were 1 and 75 Mrad where significant changes in mechanical strength were observed.     

Mechanistical studies on the electron-induced degradation of polymethylmethacrylate and Kapton

Mechanisms for the electron-induced degradation of poly(methyl methacrylate) (PMMA) and Kapton polyimide (PMDA-ODA), both of which are commonly used in aerospace applications, were examined over a temperature range of 10 K to 300 K under ultra high vacuum (～10(-11) Torr). The experiments were designed to simulate the interaction between the polymer materials and secondary electrons produced by interaction with galactic cosmic ray particles in the near-Earth space environment. Chemical alterations of the samples were monitored on line and in situ by Fourier-transform infrared spectroscopy and mass spectrometry during irradiation with 5 keV electrons and also prior and after the irradiation exposure via UV-vis. The irradiation-induced degradation of PMMA resulted in the formation and unimolecular decomposition of methyl carboxylate radicals (CH(3)OCO) forming carbon monoxide (k = 4.60 × 10(-3) s(-1)) and carbon dioxide (k = 1.29 × 10(-3) s(-1)). Temperature dependent gas-phase abundances for carbon monoxide, carbon dioxide, and molecular hydrogen were also obtained for the PMMA and Kapton samples. The lower gas yields detected for irradiated Kapton were typically one or two orders of magnitude less than PMMA suggesting a higher degradation resistance to energetic electrons. In addition, UV-vis spectroscopy revealed the propagation of conjugated bonds induced by the irradiation of PMMA and indicated a decrease in the optical band gap by an increase in absorbance above 500 nm in irradiated Kapton.     

Controlled release in hard to access places by poly(methyl methacrylate) microcapsules triggered by gamma irradiation

Gamma irradiation was investigated as a triggering stimulus for the activation of poly(methyl methacrylate) (PMMA) microcapsules. PMMA was exposed to varying doses of irradiation and analyzed by differential scanning calorimetry, size‐exclusion chromatography, and nuclear magnetic resonance. It was found that the glass transition temperature (T_g) of the polymer decreases at low irradiation doses. Additionally, T_g can be physically adjusted by adding a plasticizer, and both kinds of microcapsules were successfully prepared with non‐plasticized and plasticized PMMA shell. Finally, impermeable microcapsules were shown to become permeable after irradiation and release an encapsulated cross‐linker, which enables the remotely controlled formation of polydimethylsiloxanes in traditionally unavailable places. Therefore, the activation method has significant implications for industrial application. Copyright © 2015 John Wiley & Sons, Ltd.     

Microwave-Assisted Coating of PMMA beads by silver nanoparticles

Microwave (MW) irradiation was found to be a new technique for coating silver nanoparticles with an average size of approximately 31 nm onto the surface of poly(methyl methacrylate) PMMA beads (3 mm diameter). The microwave polyol reduction was carried out under an argon atmosphere. Silver nanoparticles were obtained by the MW irradiation of a solution mixture containing silver nitrate (or silver acetate), poly(ethylene glycol), ethanol, water, and 24 wt % aqueous ammonia for 5 min in the presence of PMMA beads, yielding a PMMA-nanosilver composite. By controlling the atmosphere and reaction conditions, we could achieve the deposition of silver nanoparticles onto the surface of poly(methyl methacrylate) and vary the amount of the silver anchored to the surface. The resulting silver-deposited PMMA samples were characterized using X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray analysis, high-resolution scanning electron microscopy, X-ray photoelectron spectroscopy, and volumetric titration with potassium thiocyanate (KSCN) according to the Folgard method.     

Dose distribution in electron-irradiated PMMA: effect of dose and geometry

Depth-dose distributions for an electron beam are generally determined with either a stack irradiation geometry or a wedge (generally with an angle of about 50°–60°) made from an electrically-conducting material (such as, aluminium) or a non-conducting material (such as, PMMA). If the non-conducting wedge is thicker than the electron range, the stored charge in the material could influence the measured depth-dose distribution. This effect was investigated for 7-MeV electrons for PMMA with the wedge angle varying from 0° to 60°. The maximum-to-surface dose ratio was used as a characteristic parameter of the shape of the distribution. The depth-dose distribution measured by a dosimetry film placed inside the wedge-pair was similar to the standard shape when the wedge angle was larger than about 55° (dose ratio 1.5). However, as the angle was decreased, this ratio sharply increased almost linearly up to about 15°, and then leveled off at about 3. We also studied the effect of the surface dose on this dose ratio for the wedge angle of 0°, where we found that the ratio increased with the dose. Both of these effects can be explained by the presence of the electrostatic field around the dosimetry film due to stored charge in the non-conducting PMMA.     

Effects of clay‐modifying agents on the morphology and properties of poly(methyl methacrylate)/clay nanocomposites synthesized via γ‐ray irradiation polymerization

Via γ‐ray irradiation polymerization, poly(methyl methacrylate) (PMMA)/clay nanocomposites were successfully prepared with reactive modified clay and nonreactive clay. With reactive modified clay, exfoliated PMMA/clay nanocomposites were obtained, and with nonreactive clay, intercalated PMMA/clay nanocomposites were obtained. Both results were confirmed by X‐ray diffraction and high‐resolution transmission electron microscopy. PMMA extracted from PMMA/clay nanocomposites synthesized by γ‐ray irradiation had higher molecular weights and narrow molecular weight distributions. The enhanced thermal properties of the PMMA/clay nanocomposites were characterized by thermogravimetric analysis and differential scanning calorimetry. The improved mechanical properties of PMMA/clay were characterized by dynamic mechanical analysis. In particular, the enhancement of the thermal properties of the PMMA/clay nanocomposites with reactive modified clay was much more obvious than that of the PMMA/clay nanocomposites with nonreactive clay. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3218–3226, 2003     

Living Ab Initio Emulsion Polymerization of Methyl Methacrylate in Water Using a Water‐Soluble Organotellurium Chain Transfer Agent under Thermal and Photochemical Conditions

Ab initio emulsion polymerization of methyl methacrylate (MMA) using a water‐soluble organotellurium chain transfer agent in the presence of the surfactant Brij 98 in water is reported. Polymerization proceeded under both thermal and visible light‐irradiation conditions, giving poly(methyl methacrylate) (PMMA) with controlled molecular weight and low dispersity (?<1.5). Despite the formation of an opaque latex, the photoactivation of the organotellurium dormant species took place efficiently, as demonstrated by the quantitative monomer conversion and temporal control. Control of polymer particle size (PDI<0.030) was also achieved using a semi‐batch monomer addition process. The PMMA polymer in the particles retained high end‐group fidelity and was successfully used for the synthesis of block copolymers.     

Azo‐Polymer Janus Particles Assembled by Solvent‐Induced Microphase Separation and Their Photoresponsive Behavior

We report the successful fabrication of photoresponsive Janus particles (JPs) composed of an epoxy‐based azo polymer and poly(methyl methacrylate) (PMMA). Two representative azo polymers, of which one polymer (BP‐AZ‐CN) has cyano groups as electron‐withdrawing substituents on the azobenzene moieties and the other polymer (BP‐AZ‐CA) has carboxyl groups as the electron‐withdrawing substituents, were adopted for the investigation. The nanoscaled JPs, with a narrow size distribution and different azo polymer/PMMA ratios, were fabricated through self‐assembly in solution and as dispersions. Upon irradiation with linearly polarized light (λ=488 nm), two types of photoresponsive behavior were observed for JPs in the solid state. For JPs composed of BP‐AZ‐CN and PMMA, the light irradiation caused the azo‐polymer component to be stretched along the light polarization direction. Conversely, for JPs composed of BP‐AZ‐CA and PMMA, the azo‐polymer component became separated from PMMA component under the same irradiation conditions. These observations are valuable for a deeper understanding of the nature of self‐assembly and photoinduced mass‐transport at the nanometer scale.     

Structure induced by irradiation of femtosecond laser pulse in dyed polymeric materials

We investigated the structures induced by an irradiation of a near‐infrared (NIR) femtosecond laser pulse in dye‐doped polymeric materials {poly(methyl methacrylate) (PMMA), thermoplastic epoxy resin (Epoxy), and a block copolymer of methyl methacrylate and ethyl acrylate‐butyl acrylate [p(MMA/EA‐BA) block copolymer]}. Dyes used were classified into two types—type 1 with absorption at 400 nm and type 2 with no absorption at 400 nm. The 400‐nm wavelength corresponds to the two‐photon absorption region by the irradiated NIR laser pulse at 800 nm. Type 1 dye‐doped PMMA and p(MMA/EA‐BA) block copolymer showed a peculiar dye additive effect for the structures induced by the line irradiation of a NIR femtosecond laser pulse. On the contrary, dye‐doped Epoxy did not exhibit a dye additive effect. The different results among PMMA, p(MMA/EA‐BA) block copolymer, and Epoxy matrix polymers are supposed to be related to the difference of electron‐acceptor properties. The mechanism of this type 1 dye‐additive‐effect phenomenon for PMMA and p(MMA/EA‐BA) block copolymer is discussed on the basis of two‐photon absorption of type 1 dye at 400 nm by the irradiation of a femtosecond laser pulse with 800 nm wavelength and the dissipation of the absorbed energy to the polymer matrix among various transition processes. Dyes with a low‐fluorescence quantum yield favored the formation of thicker grating structures. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2800–2806, 2002     

Study on dosimetry of bremsstrahlung radiation processing

The dosimetry in high-power bremsstrahlung irradiation for the industrial processing has been studied. The dosimeter systems used are cylindrical ionization chamber to measure average exposure rate and CTA, clear PMMA and alanine dosimeters for routine dosimetry. The results gave some useful information on the measurement of average exposure rate using the ionization chamber. Clear PMMA and alanine dosimeters showed good characteristics for their usefulness as routine dosimeters for X-ray irradiation in the industrial processing.     

Efficiency of radiation-induced main-chain scission of poly (methyl methacrylate) depends on the irradiation temperature because of coexisting monomer

Effect of irradiation temperature on the main-chain scission of poly (methyl methacrylate) (PMMA) caused by γ-irradiation was studied by means of gel permeation chromatography and ESR spectroscopy. Although no temperature dependency was observed on the scission efficiency for purified PMMA, the efficiency for crude or monomer-doped purified PMMA was decreased by decreasing the temperature below ca. 200 K. Above 200 K the efficiency was constant and did not depend on the purity of PMMA. ESR study of the irradiated PMMA revealed that the suppression of the scission below 200 K is induced by the addition of methyl methacrylate monomer to primary radical species, which otherwise cause the main-chain scission by warming the polymer above 200 K. The primary radical generated above 200 K immediately converts to the scission-type ? CH₂ ? ?(CH₃) COOCH₃ radical through the β-scission of the polymer main chain, so that the efficiency of the scission does not depend on both the impurity and the irradiation temperature. © 1994 John Wiley & Sons, Inc.     

Composition and origin of trace elements in fog water studied by INAA

Characterization of dilute solution of gamma-irradiated polymethyl methacrylate (PMMA) in acetone has been carried out. The polymer sample in form of natural beads was administered a gamma-ray dose of 30 kGy by a cobalt-60 radiationsource. Various types of viscosities, viscosity average molecular weight, shape and size of irradiated PMMA and its two fractions were calculated. The results were compared with those for unirradiated PMMA. Degradation of PMMA as a result of irradiation has been observed.     

A study of the mechanism of photocrosslinking polymers by quinones

Photocrosslinking of poly(methyl methacrylate) (PMMA) was studied in the solid state in the presence of various quinones. For the study of photocrosslinking mechanism, a PMMA film containing p-benzoquinone (Q) was irradiated with UV light (λ > 370nm) and then purified by reprecipitation. It was found that the reprecipitated polymer has quinone-type moieties, besides the hydroquinone-type moieties, chemically bound to the polymer chain. The reprecipitated polymer film also crosslinking efficiency was higher than that of PMMA film containing Q. It was concluded that the formation of quinone-type structure during irradiation played an important role in the photocrossing of PMMA containing Q.     

Synthesis of cardanol-based photo-active SET-LRP initiator and its application to preparation of UV-cured resin

A benzophenone-containing SET-LRP initiator based on renewable and abundant cardanol was synthesised in 71 % yield using the selective etherification reaction. Next, methyl methacrylate (MMA) as a monomer was polymerised under SET-LRP conditions using the newly prepared initiator to prepare cardanol-end poly(methyl methacrylate) (PMMA). The kinetic results of the polymerisation indicated that the reaction was controllable when the monomer conversion was lower than approximately 50 %, and the molecular masses of PMMA measured by GPC were higher than the theoretical values while the monomer conversion was more than 50 %. In addition, most of the carbon-carbon double bonds of the side hydrocarbon chain of the end-cardanol group in the PMMA were kept intact from ¹H NMR spectrum characterisation. Accordingly, when the cardanol-end PMMA together with a tertiary amine-containing cardanol derivative was irradiated by UV light, the corresponding UV-cured resin was obtained. The chemical resistance and hardness of the UV-cured film were enhanced with the increasing irradiation time.     

Influence of polymer molecular weight on the chemical modifications induced by UV laser ablation

This paper investigates the influence of polymer molecular weight (M(W)) on the chemical modifications of poly(methyl methacrylate), PMMA, and polystyrene, PS, films doped with iodonaphthalene (NapI) and iodophenanthrene (PhenI), following irradiation at 248 nm (KrF excimer laser, 20 ns fwhm and hybrid excimer-dye laser, 500 fs fwhm) and at 308 nm (XeCl excimer laser, 30 ns fwhm). The changes of intensity and position of the polymer Raman bands upon irradiation provide information on cleavage of the polymer bonds. Degradation of PMMA, which is a weak absorbing system at 248 nm, occurs to a higher extent in the case of a larger M(W), giving rise to the creation of unsaturation centers and to degradation products. For highly absorbing PS, no degradation is observed upon irradiation with a KrF laser. Consistently irradiating doped PS at 308 nm, where the absorption is low, induces degradation of the polymer. Results provide direct support for the bulk photothermal model, according to which ejection requires a critical number of broken bonds. In the case of irradiation of doped PMMA with pulses of 248 nm and 500 fs, neither degradation nor dependence with polymer M(W) are observed, indicating that mechanisms involved in the femtosecond laser ablation differ from those operating in the case of nanosecond laser ablation. Participation of multiphoton/avalanche processes is proposed.     

Silver nanostructures embedding in polymethyl methacrylate patterns fabricated using proton beam writing

Proton beam writing (PBW) on polymethyl methacrylate (PMMA) followed by embedding of biosynthesized silver nanoparticles (AgNPs) was investigated. This is the first demonstration of the use of 3 MV Tandetron accelerator at iThemba LABS for fabricating patterns using PBW technique. The irradiation of PMMA was carried out using 3.0-MeV proton beam focused down to micrometer spot size. The fluence of protons was counted as electrical charge per unit monitored by exposure time, beam current, and irradiated area. As expected, the PMMA behaved as a positive resist because of chain scissioning induced from the interaction with proton beam. Morphological characterization using scanning electron microscope (SEM) revealed fabrication of square-like patterns, and atomic force microscopy (AFM) provided the possibility of observing the presence of AgNPs that stood out of the PMMA matrix.