Photodegradation of polymer materials containing flame-cut agents

Photodegradation of incombustible materials [polystyrene (PSt) and polypropyrene (PP) containing 2 wt% of decabromodiphenyl oxide (DBDE) or tetrabromobisphenol-A (TBA) as a flame-cut agent] were studied using Okazaki Large Spectrograph (OLS). Samples were irradiated in air at 23°C with monochromatic light of wavelengths at 260, 280, 300, 320, 340, and 360 nm, UV-visible spectra and FTIR spectra were measured to identify the chemical structural changes of the polymers. Number of chain scissions, which is a measure of the polymer degradation, was estimated from the results of GPC measurements. It was found that the photostability of PP and PSt was reduced by the addition of DBDE or TBA. Photodegradation of these polymers took place by the irradiation of the light of wavelengths lower than 320 and 360 nm for the polymers containing TBA and DBDE, respectively. The most effective irradiation wavelengths for main chain scission are found to be 260–280 and 300 nm for PP or PSt–TBA samples and PP or PSt–DBDE samples, respectively. © 1993 John Wiley & Sons, Inc.     

Photooxidative degradation of polyethylene containing flame retardants by monochromatic light

Photodegradation of incombustible polymer materials [high-density (HD) and low-density (LD) polyethylene (PE) containing 0.5 to 2.0 phr of decabromodiphenyl ether (DBDE) or tetrabromobisphenol A (TBA) as a flame retardant] were studied using an Okazaki Large Spectrograph (OLS). Samples were irradiated in air at 23°C with monochromatic light of wavelengths at 260, 280, 300, 320, 340, and 360 nm. Ultraviolet and Fourier transform infrared (FTIR) spectra were taken to estimate the chemical changes caused by photoirradiation. Molecular weight change was followed by gel permeation chromatography (GPC) measurements. It was found that the photostability of PE samples was reduced by the addition of flame retardants. The threshold wavelengths of photodegradation are 320 nm and 360 nm for PE–TBA samples and PE–DBDE samples, respectively. Main-chain scission is favored when the irradiation was carried out with the light of wavelength 300 nm for HDPE–DBDE and HDPE–TBA samples. The most effective irradiation wavelengths for crosslinking are found to be 300 nm and 280 nm for LDPE–DBDE and LDPE–TBA samples, respectively. 1995 John Wiley & Sons, Inc.     

Photodegradable polymers. II. Preparation of styrene copolymers with alkyl and phenyl β-styryl ketones and their photodegradability

Photodegradable polymers having pendent carbonyl groups attached directly to the polymer chain were prepared by copolymerization of styrene (St) with alkyl and phenyl β-styryl ketones (RCOCH?CHC₆H₅), where R = CH₃, C₂H₅, n-C₅H₁₁, n-C₁₁H₂₃, t-C₄H₉, cyclo-C₆H₁₁, and C₆H₅. The photodegradability of these copolymers was traced by viscometric and IR spectroscopic measurements. The degradability of St–benzalacetophenone (BAPh) copolymer is greater than that of St–alkyl styryl ketone copolymers under the irradiation of a high-pressure Hg lamp. The photodecomposition behavior St–BAPh copolymer was investigated in detail by a spectoirradiation technique. The changes in molecular weight and its distribution by photodegradation were measured by gel permeation chromatography, and the quantum yield for bond scission along the main chains of the copolymer was estimated to be about 5 × 10^?3 by 328 nm irradiation in a benzene solution. Examination of the effect of wavelength of the radiation on the bond scission showed that 328-nm light is most effective. The photochemical degradation process was shown to occur chiefly via triplet state of carbonyl groups by the quenching technique using 1,3-cyclohexadiene as a triplet quencher. The quantum yield of decarbonylation process was also estimated to be about 4.2 × 10 ^?2 in benzene.     

Synthesis and characterization of polyaniline/NiO nanocomposite

Spherical nickel oxide (NiO) nanoparticles were prepared by using nickel chloride as precursor in the ethylene glycol as solvent and urea as precipitant. The X‐ray diffraction study showed that NiO has single‐phase cubic structure with average crystallite size of 35 nm. The prepared NiO nanoparticles were incorporated into polyaniline (PANI) matrix during in situ chemical oxidative polymerization of aniline with different molar ratios of aniline: NiO (12 : 1, 6 : 1, and 3 : 1) at 5°C using (NH₄)₂S₂O₈ as oxidant in aqueous solution of sodium dodecylbenzene sulfonic acid, as surfactant and dopant under N₂ atmosphere. The synthesized composites have been characterized by means of X‐ray diffraction (XRD), thermogravimetric analysis, Fourier transform infrared (FTIR), scanning electron microscopy, TEM, and vibrating sample magnetometer for its structural, thermal, morphological, and magnetic investigation. The XRD and FTIR studies show that the NiO particles are in the composite. The room temperature conductivities of the synthesized PANI, PANI/NiO (12 : 1), (6 : 1), and (3 : 1) composites were found to be 3.26 × 10^?4, 1.88 × 10^?4, 1.5 × 10^?4, and 4.61 × 10^?4 S/cm, respectively. The coercivity (H_c) and remnant magnetization (M_r) of NiO, PANI/NiO NCs (12 : 1), (6 : 1), and (3 : 1) at 5 K was found to be 8.22 × 10^?2, 6.31 × 10^?2, 6.42 × 10^?2, 6.27 × 10^?2 T, and 6.64 × 10^?3, 1.83 × 10^?4, 3.07 × 10^?4, and 3.98 × 10^?4 emu/g, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The effect of side chains on the reactive rate and surface wettability of pentablock copolymers by ATRP

The reactive rate and surface wettability of three pentablock copolymers PDMS‐b‐(PMMA‐b‐PR)₂ (R = 3FMA, 12FMA, and MPS) obtained via ATRP for coatings are discussed. Poly(dimethylsiloxane) (PDMS) is used as difunctional macroinitiator, poly(methyl methacrylate) (PMMA) as the middle block, while poly(trifluoroethyl methacrylate) (P3FMA), poly(dodecafluoroheptyl methacrylate) (P12FMA) and poly(3‐(trimethoxysilyl)propyl methacrylate) (PMPS) as the end block, respectively. Their reactive rates obtained by gas chromatography (GC) analysis indicate that 3FMA gains 8.053 × 10^?5 s^?1 reactive rate and 75% conversion, higher than 12FMA (4.417 × 10^?5 s^?1, 35%), but MPS has 1.9389 × 10^?4 s^?1 reactive rate and 96% conversion. The wettability of pentablock copolymer films is characterized by water contact angles (WCA) and hexadecane contact angles (HCA). The PDMS‐b‐(PMMA‐b‐P12FMA)₂ film behaves much higher advancing and receding WAC (120° and 116°) and HCA (60° and 56°) than PDMS‐b‐(PMMA‐b‐P3FMA)₂ film (110° and 106° for WAC, 38° and 32° for HAC) because of its fluorine‐rich surface (20.9 wt % F). However, PDMS‐b‐(PMMA‐b‐PMPS)₂ film obtains 8° hysteretic contact angle in WAC (114°–106°) and HAC (32°–24°) due to its higher surface roughness (138 nm). Therefore, the fluorine‐rich and higher roughness surface could produce the lower water and oil wettability, but silicon‐rich surface will produce lower water wettability. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40209.     

Effect of hydrophilic chain length on the aqueous solution behavior of block amphiphilic copolymers PMMA‐b‐PDMAEMA

A series of amphiphilic block copolymers, polymethyl methacrylate (PMMA)‐b‐poly[2‐(dimethylamino)ethyl methacrylate] (PDMAEMA), were synthesized by atom transfer radical polymerization (ATRP) method. Surface tension, dynamic light scattering (DLS), transmission electron microscope (TEM), and atomic force microscopy (AFM) studies were performed to investigate the aqueous micellar behavior of these block amphiphiles. At a fixed degree of polymerization (DP) of PMMA block (DP = 55), the PDMAEMA block length was found to have a significant influence on the critical micelle concentration (cmc) values and hydrodynamic size of aggregates. An increase in the DP of PDMAEMA from 11 to 337, resulted in a decrease in the cmc from 1.44 × 10^?5 to 5.81 × 10^?7 M (a factor of almost 24.8), and a decrease in the Z (2R_h) from 85.5 to 15.5 nm (pH = 4), respectively. TEM and AFM results indicated that by changing the soluble block lengths, spherical, short rod, crew‐cut, vesicles or large aggregates can be observed in the solution. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Melt viscosity and flow birefringence of polycarbonate

Melt viscosity and flow birefringence of bisphenol A-type polycarbonate were measured and analyzed by the application of rubber-like photoelastic theory. The melt viscosity in the Newtonian flow region increased with the molecular weight to the power of 3.4. In polycarbonate, the shear stress of the Newtonian flow region was to 10⁶ dyn/cm², whereas in PMMA it was at most 3 = 10⁵ dyn/cm². The flow birefringence δn has a linear relation with shear stress S, that is δn = 5.7 × 10^?10 S. The principal polarization difference of flow unit α₁ – α₂ was 1.62 × 10^?23 cm³, which was obtained by the application of the rubber-like elastic theory. In PMMA, it was 3.9 = 10^?25 cm³; about 1/40 of that was polycarbonate. The anisotropy of polarizability of the flow unit of polycarbonate was also about 40 times larger than that of PMMA. So the anisotropy reflected the large flow birefringence of the polycarbonate.     

Degradation of benzene,toluene ethylbenzene and p‐xylene (BTEX) in aqueous solutions using UV/H2O2 system

The homogeneous degradation of benzene (B), toluene (T), ethylbenzene (E) and p‐xylene (X) (BTEX) was studied in aqueous solutions, at pH 3.0, of hydrogen peroxide (5.8 mM ) under UV irradiation in a photoreactor equipped with a 300 nm lamp of light intensity 3.5 × 10^?5 Ein L^?1 min^?1. BTEX was substantially degraded by the H₂O₂/UV system, with >90% disappearing in 10 min of irradiation. The decomposition of BTEX was studied either as single or as multi‐component systems. The effects of irradiation time, amounts of H₂O₂ in molar ratios, rate of degradation and competition between components were thoroughly examined. It can be stated that the rate of BTEX degradation in mixture was higher than those for the individual components due to external effects of the absorption of UV light by the mixture, and their effects on enhancing the formation of OH^? radicals. The appropriate figure of merit, the electrical energy per mass (EE/M), was estimated at various molar ratios and it was confirmed that the best value was the one depicted for p‐xylene (0.065 kWh kg^?1). A theoretical model for the degradation pathway was proposed. Copyright © 2004 Society of Chemical Industry     

Preparation of a polymer containing indole groups by RAFT polymerization and one‐phase synthesis of AuNPs‐polymer nanocomposites

A one‐phase synthesis of AuNPs‐polymer nanocomposites using HAuCl₄ as the precursor is reported in this article. A flexible polymer, poly(2‐(4‐(di(1H‐indol‐3‐yl)methyl)phenoxy) ethyl methacrylate) (PMPEM), containing indole groups on the side chain was utilized as both a reducing reagent and soft template in the system. The PMPEM‐Au nanocomposites with three different sizes of AuNPs (25–50, 2, and 5 nm) were obtained just through choosing different solvents such as toluene, tetrahydrofuran (THF), and N,N‐dimethylformamide, respectively. Nanocomposites including the size of 25–50 and 2 nm AuNPs showed strong NLO absorption and refraction behaviors. The nonlinear refractive index n₂ of PMPEM‐Au nanocomposites prepared in toluene and THF were 9.35 × 10^?11 and 1.85 × 10^?10 m²/W, third‐order susceptibility χ⁽³⁾ were 2.55 × 10^?11 and 4.26 × 10^?11 esu, respectively. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Light‐scattering study of poly(hydroxy ester ether) in N,N‐dimethylacetamide solution

Static and dynamic light‐scattering techniques were used to study biodegradable thermoplastic poly(hydroxy ester ether) in N,N‐dimethylacetamide (DMAc). A weight‐average molecular weight M_W = 6.4 × 10⁴ g/mol, radius of gyration R_G = 9.4 nm, second‐virial coefficient A₂ = 1.05 × 10^?3 mol mL/g², translational diffusion coefficient D = 1.34 × 10^?7 cm²/s, and hydrodynamic radius R_H = 8.3 nm are reported. In addition, the effect of H₂O on the polymer chain's conformation and architecture in a DMAc/H₂O solution is evaluated. Results suggest that H₂O makes the mixed solvent poorer as well as promotes polymer chain branching via intramolecular transesterification. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1737–1745, 2001     

Facile synthesis of graphene/polypyrrole 3D composite for a high‐sensitivity non‐enzymatic dopamine detection

One kind of nanocomposite consisting of graphene and polypyrrole was synthesized via a facile and mild way with the assistant of microwave irradiation. The synthesis route was embedding the polypyrrole into the graphene flakes to form a 3D structure, to achieve larger active surface and higher electro‐catalysis property. Structures and components of the composite were measured by X‐ray diffraction, field emission scanning electron microscopy, and Fourier transform infrared spectroscopy. A stronger electrochemical response of electrode with modified resultant was observed in the electrochemical test. Dopamine sensor based on the composite showed a sensitivity of 363 μA mM ^?1 cm^?2, a linear range of 1 × 10^?4 M to 1 × 10^?3 M , and a detection limit of 2.3 × 10^?6 M (S/N = 3). © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44840.     

Electrical conduction mechanism in plasma polymerized 2‐(diethylamino)ethyl methacrylate thin films

Thin films of different thicknesses were prepared through glow discharge of 2‐(diethylamino)ethyl methacrylate (DEAEMA) using a capacitively coupled reactor. Current density–voltage (J–V) characteristics for plasma polymerized (PP) DEAEMA thin films of thicknesses 100, 200, 250, and 300 nm in aluminum/PPDEAEMA/aluminum sandwich configuration were studied over the temperature range from 298 to 423 K. J–V curves reveal that in the low‐voltage region, the conduction current obeys Ohm's law while in the high‐voltage region the behavior attributed to be space charge‐limited conduction in PPDEAEMA thin films. The carrier mobility was calculated to be about 6.80 × 10^?19 to 2.38 × 10^?18 m^?2 V^?1s^?1 for various thicknesses. The free carrier density was found to be about 1.78 × 10²³ to 2.04 × 10²³ m^?3, and the trap density was found to be about 6.93 × 10²³ to 15.9 × 10²³ m^?3 for different thicknesses. The activation energies were estimated to be about 0.005–0.016 eV for 2 and 30 V of PPDEAEMA thin films of different thicknesses. The low‐activation energies indicate that the thermally activated hopping conduction is operative in PPDEAEMA thin films. POLYM. ENG. SCI., 55:2729–2734, 2015. © 2015 Society of Plastics Engineers     

Electron irradiation of poly(olefin sulfones). Application to electron beam resists

All the poly(olefin sulfones) examined degraded rapidly under electron irradiation. The dose required to effect a molecular weight distribution completely separated from the original distribution as required for fractional solution development was similar for all polymers, viz., 1–2 × 10^?6 coulomb/cm². This indicates that they all have similar values for G(scission). The film thickness of the exposed area decreased at a rate dependent on olefin structure and temperature. This process, termed vapor development, has been attributed to concurrent chain scission and depolymerization. Factors determining the rate of depropagation are discussed.     

Blue‐light‐emitting poly(arylene ethynylenes) containing alternating sequences of biphenylene or fluorenediyl and p‐phenylene moieties linked through triple bonds

Two new poly(arylene ethynylenes) were synthesized by the reaction of 1,4‐diethynyl‐2.5‐dioctylbenzene either with 4,4′‐diiodo‐3,3′‐dimethyl‐1,1′‐biphenyl or 2,7‐diiodo‐9,9‐dioctylfluorene via the Sonogashira reaction, and their photoluminescence (PL) and electroluminescence (EL) properties were studied. The new poly(arylene ethynylenes) were poly[(3,3′‐dimethyl‐1,1′‐biphenyl‐4,4′‐diyl)‐1,2‐ethynediyl‐(2,5‐dioctyl‐1,4‐phenylene)‐1,2‐ethynediyl] (PPEBE) and poly[(9,9‐dioctylfluorene‐2,7‐diyl)‐1,2‐ethynediyl‐(2,5‐dioctyl‐1,4‐phenylene)‐1,2‐ethynediyl] (PPEFE), both of which were blue‐light emitters. PPEBE not only emitted better blue light than PPEFE, but it also performed better in EL than the latter when the light‐emitting diode devices were constructed with the configuration indium–tin oxide/poly(3,4‐ethylenedioxythiophene) doped with poly(styrenesulfonic acid) (50 nm)/polymer (80 nm)/Ca:Al. The device constructed with PPEBE exhibited an external quantum efficiency of 0.29 cd/A and a maximum brightness of about 560 cd/m², with its EL spectrum showing emitting light maxima at λ = 445 and 472 nm. The device with PPEFE exhibited an efficiency of 0.10 cd/A and a maximum brightness of about 270 cd/m², with its EL spectrum showing an emitting light maximum at λ = 473 nm. Hole mobility (μ_h) and electron mobility (μ_e) of the polymers were determined by the time‐of‐flight method. Both polymers showed faster μ_h values. PPEBE revealed a μ_h of 2.0 × 10^?4 cm²/V·s at an electric field of 1.9 × 10⁵ V/cm and a μ_e of 7.0 × 10^?5 cm²/V·s at an electric field of 1.9 × 10⁵ V/cm. In contrast, the mobilities of the both carriers were slower for PPEFE, and its μ_h (8.0 × 10^?6 cm²/V·s at an electric field of 1.7 × 10⁶ V/cm) was 120 times its μ_e (6.5 × 10^?8 cm²/V·s at an electric field of 8.6 × 10⁵ V/cm). The much better balance in the carriers' mobilities appeared to be the major reason for the better device performance of PPEBE than PPEFE. Their highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels were also a little different from each other. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 299–306, 2006     

Studies of methyl methacrylate-methyl α-chloroacrylate,copolymers and poly(methyl α-chloroactylate) as electron sensitive positive resists

Poly(methyl α-chloroacrylate) (PMCA) and the copolymers of methyl methacrylate and methyl α-chloroacrylate (poly(MMA-co-MCA)) have been reported recently to be more susceptible to radiation degradation than poly(methyl methacrylate) (PMMA). In this paper we report our studies of PMCA and poly(MMA-co-MCA) as electron-sensitive positive resists. It has been found that both PMCA and the copolymers are more sensitive than PMMA. Using mixtures of dimethylformamide and 2-propanol as developers, the sensitivities of PMCA and poly(MMA-co-MCA) (38 mole percent MCA) have been found to be 1 × 10^?5 and 6 × 10^?6 coulomb/cm², respectively. It has also been found that crosslinking predominates in PMCA when the electron dose exceeds 6 × 10^?4 coulomb/cm².     

Facile preparation of conductive paint made with polyaniline/dodecylbenzenesulfonic acid dispersion and poly(methyl methacrylate)

We investigated an easy way to prepare industrially a conductive paint made with polyaniline (PANI)/dodecylbenzenesulfonic acid (DBSA) dispersion and poly(methyl methacrylate) (PMMA) in organic media. First, water‐dispersible PANI doped with DBSA was chemically synthesized with aniline sulfate using ammonium persulfate in water, and the resulting PANI/DBSA was readily extracted from the reaction medium with a mixture of toluene and methyl ethyl ketone (MEK) (toluene:MEK = 1:1 (v/v)), which is useful for industrial applications. The obtained PANI/DBSA organic dispersion was mixed with PMMA organic solution to give the corresponding PANI/DBSA conductive paint containing PMMA. A film prepared with the resulting PANI/DBSA conductive paint was found to possess relatively good conductivity and low surface resistivity for a conductive paint utilized for an electrostatic discharge even at low PANI/DBSA content in the PANI/DBSA–PMMA composite film (the conductivity and the surface resistivity were 9.48 × 10^?4 S cm^?1 and 3.14 × 10⁶ Ω cm^?2, respectively, when the feed ratio of PANI/DBSA:PMMA was 1:39 (w/w)). Furthermore, it was found that the conductivity of the film composed of PANI/DBSA–PMMA composite can be readily and widely controlled by the PANI/DBSA content of the composite or by the amount of DBSA used during the PANI/DBSA synthesis. The highest conductivity of PANI/DBSA–PMMA composite film (7.84 × 10^?1 S cm^?1) was obtained when the feed ratio of PANI/DBSA:PMMA was 1:4 (w/w). Copyright © 2007 Society of Chemical Industry     

Self-driven near-UV and visible light detection based on ITO/Gd-doped BiFeO3/Au heterostructure

Multiferroic BiFeO₃ materials have driven great interest due to their potential in solar-spectrum energy harvesting, optoelectronic and photodetection devices. Here we report effects of electric-field poling on electronic hybridization and domain structure, and their correlations with photovoltaic responses in the ITO/(Bi_0.93Gd_0.07)FeO₃ ceramic/Au heterostructure under 405 nm and 532 nm irradiations. Photovoltaic conversion, photoresponsivity (R) and specific detectivity (D*) are sensitive to ceramic thickness, photon energy, light intensity and electric-field poling. The photoresponsivity and detectivity in the 1 kV/cm poled photovoltaic cell under low-intensity 405 nm irradiation can respectively reach ～4.5 × 10^?2 A/W and 2.5 × 10¹¹ Jones, which are larger than ～2.8 × 10^?2 A/W and 1.56 × 10¹¹ Jones in the unpoled cell. This study demonstrates fast response times of ～1 × 10^?3 s and ～2 × 10^-2 s respectively under 405 nm and 532 nm irradiations. The improved photoresponse was driven jointly by the p-n junction, the field-modulated Schottky barriers and the network of grain boundaries and domain walls.     

Kinetics of leaching of tunisian phosphate ore particles in dilute phosphoric acid solutions

Van der Sluis et al.'s model was used to determine the rate of the partial dissolution of a Tunisian phosphate rock with dilute phosphoric acid (1.5 mass% P₂O₅). When the temperature rises from 25 to 90°C, for a given particle size, the mass-transfer coefficients, k_L°, vary from 3 × 10^?3 to 8 × 10^?3 m ·s^?1. The corresponding diffusion coefficients, D, lies between 6 × 10^?7 and 27 × 10^?7 m²·s^?1. Activation energy is equal to 14 kJ·mol^?1 and values of k_L°, at 25°C, are in the range of 0.28 × 10^?3 and 4 × 10^?3 m·s^?1 when the agitation speed goes from 220 to 1030 rpm, showing that the leaching process is controlled by diffusion rather than by chemical reaction.     

Spectrophotometric determination of Ce(IV), Fe(III) and U(VI) using desferrioxamine B (desferal)

Two moles of desferrioxamine B (desferal) combines with one ion of cerium(IV), Fe(IV) and U(VI) to form intensely coloured chelates having molar absorptivities of 3.8 × 10⁴, 5.5 × 10⁴ and 1.9 × 10⁴ mol^?1 cm^?1 at 443 nm, 293 nm and 376 nm respectively. The system follows Beer's law up to 1.5 μg ml^?1. The effect of desferal concentration, pH, time and foreign species are studied. The results of analysis of simulated wastes are reported.     

High strain rate compressive behavior of PMMA

Polymethylmethacrylate (PMMA) materials are extensively used for diverse applications e.g., protective vehicular windows to eye protection devices. However, the high strain rate deformation and fracture mechanisms of PMMA are far from well understood. Therefore, controlled split Hopkinson pressure bar (SHPB) experiments that could lead to deformation with and without fracture were conducted on PMMA samples at strain rates of ~4 × 10⁰ to 1.3 × 10³ s^?1. With increase in strain rate, the maximum compressive yield strength of PMMA is enhanced by about 25 %. Absence of global failure characterized the deformation at relatively lower strain rates (e.g., ~4.75 × 10² to 6.75 × 10² s^?1), while its marked presence characterized the same at comparatively higher strain rates (e.g., ~7.69 × 10² to 9.31 × 10² s^?1). Attempts were made to explain these observations by the subtle changes in failure mechanisms as revealed from the fractographic examinations of the PMMA samples deformed with and without failures. The implications of the test-condition induced restrictions on the degrees of freedom locally available to the polymeric chains were discussed in the perspective of the relative strain rate dependencies of the yield behaviors of the present PMMA samples.