Concentrations Of PMMA Research Articles

Photophysical Analysis of Aggregation-Induced Emission (AIE) Luminogens Based on Triphenylamine and Thiophene: Insights into Emission Behavior in Solution and PMMA Films.

Aggregation-Induced Emission (AIE) luminogens have garnered significant interest due to their distinctive applications in different applications. Among the diverse molecular architectures, those based on triphenylamine and thiophene hold prominence. However, a comprehensive understanding of the deactivation mechanism both in solution and films remains lacking. In this study, we synthesized and characterized spectroscopically two AIE luminogens: 5-(4-(bis(4-methoxyphenyl)amino)phenyl)thiophene-2-carbaldehyde (TTY) and 5'-(4-(bis(4-methoxyphenyl)amino)phenyl)-[2,2'-bithiophene]-5-carbaldehyde (TTO). Photophysical and theoretical analyses were conducted in both solution and PMMA films to understand the deactivation mechanism of TTY and TTO. In diluted solutions, the emission behavior of TTY and TTO is influenced by the solvent, and the deactivation of the excited state can occur via locally excited (LE) or twisted intramolecular charge transfer (TICT) state. In PMMA films, rotational and translational movements are constrained, necessitating emission solely from the LE state. Nevertheless, in the PMMA film, excimers-like structures form, resulting in the emergence of a longer wavelength band and a reduction in emission intensity. The zenith of emission intensity occurs when molecules are dispersed at higher concentrations within PMMA, effectively diminishing the likelihood of excimer-like formations. Luminescent Solar Concentrators (LSC) were fabricated to validate these findings, and the optical efficiency was studied at varying concentrations of luminogen and PMMA.

In vitro assessment of inflammatory skin potential of poly(methyl methacrylate) at non-cytotoxic concentrations.

Poly(methyl methacrylate) (PMMA) is considered an attractive substrate material for fabricating wearable skin sensors such as fitness bands and microfluidic devices. Despite its widespread use, inflammatory and allergic responses have been attributed to the use of this material. Therefore, the main objective of this study was to obtain a comprehensive understanding of potential biological effects triggered by PMMA at non-cytotoxic concentrations using in vitro models of NIH3T3 fibroblasts and reconstructed human epidermis (RhE). It was hypothesized that concentrations that do not reduce cell viability are sufficient to activate pathways of inflammatory processes in the skin. The study included cytotoxicity, cell metabolism, cytokine quantification, histopathological, and gene expression analyses. The NIH3T3 cell line was used as a testbed for screening cell toxicity levels associated with the concentration of PMMA with different molecular weights (MWs) (i.e., MW ~5,000 and ~15,000 g/mol). The lower MW of PMMA had a half-maximal inhibitory concentration (IC50 ) value of 5.7 mg/cm2 , indicating greater detrimental effects than the higher MW (IC50 = 14.0 mg/cm2 ). Non-cytotoxic concentrations of 3.0 mg/cm2 for MW ~15,000 g/mol and 0.9 mg/cm2 for MW ~5,000 g/mol) induced negative metabolic changes in NIH3T3 cells. Cell viability was severely reduced to 7% after the exposure to degradation by-products generated after thermal and photodegradation degradation of PMMA. PMMA at non-cytotoxic concentrations still induced overexpression of pro-inflammatory cytokines, chemokines, and growth factors (IL1B, CXCL10, CCL5, IL1R1, IL7, IL17A, VEGFA, FGF2, IFNG, IL15) on the RhE model. The inflammatory response was also supported by histopathological and gene expression analyses of PMMA-treated RhE, indicating tissue damage and gene overexpression. Results suggested that non-cytotoxic concentrations of PMMA (3.0 to 5.6 mg/cm2 for MW ~15,000 g/mol and 0.9 to 2.1 mg/cm2 for MW ~5,000 g/mol) were sufficient to negatively alter NIH3T3 cells metabolism and activate inflammatory events in the RhE skin.

A hybrid approach of surface and direct absorption of solar radiation on parabolic solar collector.

This paper presents a novel approach of utilizing a spectrally selective coating inside the absorber tube of a solar parabolic collector for enhanced photothermal conversion. The photothermal performance of a hybrid system that incorporates an internal coating and nanofluid is analyzed in the present work. The internal coating developed is a composite of PMMA/CuO/Epoxy and as applied using the simple dip-coating technique. The maximum weighted solar absorptance of the internal coating was found to be 57.51%. The significance and interactions of the coating process variables, like concentrations of PMMA and CuO and the number of dips, were analyzed using the central composite design (CCD) of response surface methodology (RSM). An optimized coating (Concentration of PMMA and CuO: 4997.7 and 170.8 mg/30 ml, Number of Dips: 4) was arrived at based on the desirability function. Prior to the introduction of internal coating on the parabolic solar collector, a lab-scale photothermal conversion study was carried out using the optimized internal coating. The results revealed the superior performance of the internal coating when compared with that of pure surface absorption and direct absorption. Finally, the optimized internal coating was incorporated in a parabolic collector, with CuO nanofluid as a working fluid. Maximum efficiency of 62.80% was obtained for the hybrid system the internal coating and CuO nanofluid, compared to 31.6% for a direct absorption solar collector.

Synthesis and Characterisation of Polytetrafluoroethylene Composite for Electrical Insulation and Dielectrics

This work provides an experimental study to measure the electrical properties of Polytetrafluoroethylene polymer and how it improves through the process of mixing with different volume rates of Poly (methyl methacrylate) PMMA. The relationship of the actual dielectric constant with frequency for pure and dopped models with different concentrations of PMMA (5%, 7%, 10%) and for a range of frequencies ranging between 1-1000 KHz, at the room temperature was investigated. The results show an increase in the dielectric constant of the composites compared to the pure models for all concentrations, which indicates that the polymers interaction gives support to the polytetrafluoroethylene infrastructure. The mixing process, also, leads to an increase in the values the imaginary part of the dielectric constant compared to the pure model, and this is due the significant increase in the number of dipoles resulting from the addition process which in turn led to increase the amount of energy lost due to rotation or friction of the dipoles with each other. This increase, in turn, led to a corresponding rise in the values of the loss tangent tanδ and the AC conductivity of the models. The experimental results show a 90 % increase in the dielectric constant of the composite at 500 KHz compared to the pure Polytetrafluoroethylene, which provide a good electrical insulation material for electronic circuits.

Poly(methylmethacrylate) coating on quantum dot surfaces via photo-chemical reaction for defect passivation

An effective poly(methylmethacrylate) (PMMA) coating process via photo-chemical reaction for quantum dots (QDs) was investigated. Various concentrations of PMMA were tested and the optimal concentration was confirmed to be 0.1 mM. The quantum yield (QY%) of the 0.1 mM PMMA-coated sample showed a 27% increase in efficiency relative to the as-synthesized CdSe/ZnS QDs due to the passivation of defect states on the surface. The QY% enhanced by PMMA was further increased by light irradiation because of the strong interactions and bonding between the surface atoms and functional groups of PMMA (acrylic groups). The excitation and formation of electron-hole pairs generated by light irradiation lead to strong interactions and chemical bonding on the surface; this is applicable to other cadmium QDs. When the QDs were passivated by a photo-chemical method, the QY% increased by approximately 20% for CdSe, CdSe/ZnS, and CdSe/ZnSe QDs. In order to evaluate the long-term stability depending on the PMMA coating, the QDs were stored for 12 months. The efficiency of as-synthesized bare QDs, initially 90%, drastically decreased to 17% after 12 months, but the PMMA-coated QDs with our coating method maintained a high efficiency of over 75%.

An All-Organic Composite System for Resistive Change Memory via the Self-Assembly of Plastic-Crystalline Molecules.

An all-organic composite system was introduced as an active component for organic resistive memory applications. The active layer was prepared by mixing a highly polar plastic-crystalline organic molecule (succinonitrile, SN) into an insulating polymer (poly(methyl methacrylate), PMMA). As increasing concentrations of SN from 0 to 3.0 wt % were added to solutions of different concentrations of PMMA, we observed distinguishable microscopic surface structures on blended films of SN and PMMA at certain concentrations after the spin-casting process. The structures were organic dormant volcanos composed of micron-scale PMMA craters and disk type SN lava. Atomic force microscopy (AFM), cross-sectional transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive X-ray spectrometer (EDX) analysis showed that these structures were located in the middle of the film. Self-assembly of the plastic-crystalline molecules resulted in the phase separation of the SN:PMMA mixture during solvent evaporation. The organic craters remained at the surface after the spin-casting process, indicative of the formation of an all-organic composite film. Because one organic crater contains one SN disk, our system has a coplanar monolayer disk composite system, indicative of the simplest composite type of organic memory system. Current-voltage (I-V) characteristics of the composite films with organic craters revealed that our all-organic composite system showed unipolar type resistive switching behavior. From logarithmic I-V characteristics, we found that the current flow was governed by space charge limited current (SCLC). From these results, we believe that a plastic-crystalline molecule-polymer composite system is one of the most reliable ways to develop organic composite systems as potential candidates for the active components of organic resistive memory applications.

Preparation and Characterization of Silicone Liquid Core/Polymer Shell Microcapsules via Internal Phase Separation

Microcapsules with a silicone liquid core surrounded by a polymeric shell were synthesised through the controlled phase separation. The dispersed silicone phase consisted of the shell polymer PMMA, a good solvent for the PMMA (dichloromethane, DCM) and a poor solvent (methylhydrosiloxane dimethylsiloxane) for the PMMA. The morphology of the PMMA microcapsules was investigated by ATR‐FTIR and by optical microscopy. Microcapsules were prepared with different emulsifiers and different concentrations of acetone and PMMA in the oil phase. The thermal stability of the PMMA microcapsule and the content of the silicone oil core were assessed by TGA. 1H‐NMR spectroscopy and an extraction method were also used to determine the content of the silicone liquid core in the microcapsules.

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Castor oil was modified by transesterification with pentaerithritol. In a parallel step, starch was divided into monosaccharide units by glycosylation in order to obtain products with high hydroxyl content. The values of hydroxyl index were measured according to the content of pentaerithritol and starch used in the synthesis. Novel simultaneous interpenetrating polymer networks (SINs) of polyurethane (PU) and poly(methyl methacrylate) (PMMA) in different weight ratios of 100/0, 90/10, 80/20, 70/30, 60/40 and 50/50 were prepared based on polyol-glucosides. The polyurethane network was created by reacting the poliol-glucosides with isophorone diisocyanate maintaining a molar ratio NCO/OH = 1. The PMMA network was synthesized using benzoyl peroxide as initiator and ethylene glycol dimethacrylate as the crosslinker. The SINs were characterized in their mechanical properties, such as Shore A hardness, tensile strength and elongation at break. Thermal stability of SINs was measured using thermogravimetric analysis (TGA). Surface morphology measured using scanning electron microscope (SEM) showed two-phase morphology for all the SINs. SINs based on polyurethane from castor oil modified and poly(methyl methacrylate) show limited compatibility at low concentrations of PMMA, but are totally incompatible at higher concentrations of PMMA.

Effect of the Tacticity of PMMA Adsorbed on Alumina and Silica on the Specific Entropy Change of Polymer by Inverse GC

Inverse gas chromatography (IGC) at infinite dilution is a powerful technique to characterize the superficial and interfacial properties of solid substrates as oxides, polymers or polymers adsorbed on oxides. It can also be used to determine the physicochemical properties and the transition phenomena of polymers. In this paper, IGC was used to determine the changes, as a function of temperature, of the specific free enthalpy ΔG and deduce the specific entropy ΔS of poly (methyl methacrylate) (PMMA) adsorbed on alumina or on silica for different tacticities of PMMA. The study of the surface properties of PMMA/SiO2 and PMMA/Al2O3, revealed an important difference in the physicochemical behaviour of oxides covered by various concentrations of PMMA. This study also highlighted an important effect of the tacticity of the polymer on the specific entropy of PMMA adsorbed on oxides.

Electrospinning of cyclodextrin functionalized poly(methyl methacrylate) (PMMA) nanofibers

Cyclodextrin functionalized PMMA nanofibers (PMMA/CD) were successfully produced by electrospinning technique with the goal to develop functional nanowebs. Bead-free uniform electrospun PMMA/CD nanofibers were obtained from a homogeneous solution of CDs and PMMA in dimethylformamide (DMF) using three different types of CDs, α-CD, β-CD and γ-CD. The electrospinning conditions were optimized in order to form bead-free PMMA/CD nanofibers by varying the concentrations of PMMA and CDs in the solutions. The concentration of CDs was varied from 5% up to 50% w/w, with respect to the PMMA matrix. We find that the presence of the CDs in the PMMA solutions facilitates the electrospinning of bead-free nanofibers from the lower polymer concentrations and this behavior is attributed to the high conductivity and viscosity of the PMMA/CD solutions. The X-ray diffraction (XRD) spectra of PMMA/CD nanowebs did not show any significant diffraction peaks indicating that the CD molecules are homogeneously distributed within the PMMA matrix and does not form any phase separated crystalline aggregates. Furthermore, attenuated total reflection Fourier transform infrared (ATR-FTIR) studies elucidate that some CD molecules are located on the surface of the nanowebs. This suggests that these CD functionalized nanowebs may have the potential to be used as molecular filters and/or nanofilters for waste treatment purposes.

Charge distribution in PVDF/PMMA blends under DC field

The charge distribution in poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blends under direct current (DC) electrical field was measured by the pulsed electro-acoustic method (PEA). It was found that the field distribution tended to be uniform and the amount of charges were much smaller than the values estimated by the ordinary additive rule in the PVDF/PMMA blends. Differential scanning calorimeter (DSC), wide-angle X-ray diffraction (WAXD), dynamic mechanical thermal analysis (DMA) and scanning electron microscopy (SEM) were employed to investigate the miscibility and phase structures of PVDF/PMMA blends. The results show that the amorphous regions in the blends comprised amorphous PVDF regions and the miscible PVDF/PMMA regions. At low concentrations of PMMA, the miscible domains were separated and could not transport charges effectively. When the PMMA concentration increased, more and more miscible domains became a continuous phase, and charges could be transported easily and effectively through the miscible phase because polar groups of PMMA could act as hopping sites for charge transportation. Therefore, the decrease in charge amount could be attributed to changes of phase structure and excellent miscibility of the blends.

Influence of aggregation on the phosphorescence of iridium complex in poly(methyl methacrylate) matrix

AbstractIn this study, novel phosphorescent compound of iridium(III)bis(2,3‐diphenylquinoxaline)2‐(benzoimidazol‐2‐yl)pyridine (IrQB) was prepared and the emission study suggests the solid form of IrQB has less phosphorescence intensity than its solution in tetrahydrofuran (THF). To avoid the potential aggregation of IrQB in the concentrated state, poly(methyl methacrylate) (PMMA) was intentionally added as isolator to make solutions of different concentrations in THF and then solid films of IrQB/PMMA of different compositions after THF removal. Films of IrQB/PMMA prepared from dilute solutions exhibit two emission bands centered at 540 and 640 nm, respectively, which is in contrast to the sole 640‐nm emission band observed for films prepared from semidilute solutions. The 540‐ and 640‐nm bands show progressive variations of the intensity with temperature. Emission band at 540 nm is derived from the polarized optical microscope and is attributed to the IrQB aggregates, whose life‐time indicates it is phosphorescent in nature. This aggregate formation is strongly affected by the applied concentrations of IrQB and PMMA in the preparative solution state. Model to postulate the mechanism of aggregate formation in the solution and the derived film states is thereby presented in this study. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 631–639, 2008

Effect of Talc and Synthetic Sodium Aluminum Silicate (SSAS) on the Properties of PC/PMMA Blend

The advent of plastics and the wide range of fillers that are available have made modifications as precise as the tailored resins themselves. To modify the properties of polymer either by using fillers or by preparation of polymer blends gives rise to new materials with tailored properties. More complex, three-component systems, obtained by the addition of inorganic filler to an immiscible blend may be of interest. Blends of polycarbonate (PC) with poly(methyl methacrylate) (PMMA) exhibit improved toughness characteristics via a two-phase structure. In this investigation the effect of talc and synthetic sodium aluminum silicate (SSAS) as fillers on properties of PC/PMMA blends has been examined. The neat blends of PC at different concentrations of PMMA were studied for their mechanical, electrical, and rheological properties. It was observed that 75/25 PC/PMMA blend showed more improved properties than that of individual polymers and hence was used to study the effect of filler loading on mechanical, electrical, and rheological properties.

Engineering properties of Novolac resin‐PMMA{poly(methyl methacrylate)} IPN system

AbstractFull and semi interpenetrating polymer networks (IPNs) based on phenol‐formaldehyde resin (Novolac) and poly(methyl methacrylate) have been made by in situ sequential technique of IPN formation. These systems of different compositions were characterized with respect to their mechanical properties, such as, ultimate tensile strength (UTS), percentage elongation at break, modulus, and toughness. Thermal properties were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Extent of phase mixing of the two polymers was envisaged from the micrographs obtained by polarizing light microscopy (PLM). The effects of variation of the blend ratios on the above‐mentioned properties were examined. There was a decreasing trend of modulus and UTS with consequent increases in elongation at break and toughness for both types of IPNs with increase in proportions of PMMA. Lowering of glass transition temperatures (with respect to pure crosslinked Novolac resin) of the IPNs with increasing proportions of PMMA was observed, indicating a plasticizing influence of PMMA on the rigid and brittle matrix of phenolic resin. The TGA thermograms exhibit lowering in thermal stability of the IPNs with respect to pure phenolic resin in the regions of higher temperatures. With increase in proportion of PMMA the onset of degradation of the IPNs is shifted towards lower temperature zone. The surface morphology as revealed by PLM indicates distribution of discrete domains of PMMA in the phenolic resin matrix. The two phase interfaces are quite sharp at higher concentrations of PMMA. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2764–2774, 2004

Pseudo-interpenetrating polymer networks based on tetrafunctional epoxy resins and poly(methyl methacrylate)

Pseudo-interpenetrating polymer networks (p-IPNs) of an epoxy resin and poly(methyl methacrylate) (PMMA) were synthesized simultaneously. Methyl methacrylate (MMA) was polymerized with benzoyl peroxide in the presence of an oligomeric epoxy resin, which contained stoichiometric amounts of either a tetrafunctional [i.e., ethylenediamine (EDA)] or hexafunctional [i.e., triethylenetetramine (TETA)] crosslinking agent. The resulting materials would be useful for aerospace, automotive, medical, and dental applications. The structure of the epoxy resin (i.e., tetraglycidyl 4,4′-diamine diphenyl methane) was confirmed by elemental analysis and IR and NMR spectroscopies. The thermal, mechanical, and kinetic behaviors of the polymeric networks produced from this oligomeric epoxy resin and the p-IPNs of this crosslinked epoxy with linear PMMA were compared. Time-resolved IR spectroscopy of the cyclic ether group in the epoxy at 906 cm−1 revealed kinetic information between 40 and 80°C for a complex reaction scheme. In the absence of MMA, the asymptotic final conversion of epoxide groups was achieved after (1) 60 min of chemical crosslinking at 50°C and (2) 30 min of crosslinking at 80°C with tetrafunctional EDA. In the presence of 10 wt % MMA, asymptotic final conversions of the epoxide group were achieved after (1) 150 min at 40°C, (2) 80 min at 50°C, and (3) 30 min at 80°C. In agreement with other kinetic studies based on the same epoxy resin but different crosslinking agents, these solvent-free polymerizations were diffusion-controlled during the later stages of chemical crosslinking because the apparent reaction order was very close to unity, via an unsteady state batch reactor model with lumped-parameter kinetics. The thermal expansion coefficients of the crosslinked epoxy resin increased at higher concentrations of PMMA, but hexafunctional TETA produced a higher crosslink density and reduced the thermal expansion relative to the same networks and p-IPNs prepared with tetrafunctional EDA. Elastic modulus, fracture stress, and toughness increased synergistically when the epoxy resin was crosslinked with EDA at 40°C in the presence of 10 wt % MMA. This p-IPN exhibited minimal shrinkage, on the order of 0.15%, during the actual polymerization. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1858–1868, 2003

Study of the transition temperatures and acid–base properties of poly (methyl methacrylate) adsorbed on alumina and silica, by using inverse gas chromatography technique

The study of phenomena transitions in polymers is of vital importance in material sciences and more particularly when polymers are adsorbed on oxides. In a previous study, we determined the glass transition temperatures of poly (methyl methacrylate) (PMMA) adsorbed on alumina, by using the inverse gas chromatography (IGC) at infinite dilution. This technique proved to be an excellent technique to determine not only the glass transitions, but also β-transition and liquid–liquid transitions of polymers adsorbed on solid substrates. In this paper, we also used the IGC technique to determine the second order transitions of the systems PMMA/SiO 2 and PMMA/Al 2O 3, at various covered surface fractions and for various tacticities of the polymer (atactic, isotactic and syndiotactic). The maxima of the dispersive component of the surface energy γ s d of our two systems, obtained by IGC at infinite dilution, indicated clearly the presence of transition temperatures (glass or local transitions). In general, we observed with PMMA, three principal maxima that reflect the changes in motions leading to reorganisation and rearrangement of the various groups or chain segments of the polymer. The change in the retention mechanism of the probes at the transition temperatures is attributed to an increased molecular mobility of the polymer segments, allowing for the penetration of the probes into the polymer layer. The study of the chemical physical properties of PMMA/SiO 2 and PMMA/Al 2O 3, revealed an important difference in the acidic and basic behaviour, in Lewis terms, of oxide covered by various concentrations of PMMA. This study also highlighted an important effect of the tacticity of the polymer on the acidic basic character of PMMA adsorbed on oxides.

Influence of surface-modifying surfactants on the pharmacokinetic behavior of 14C-poly (methylmethacrylate) nanoparticles in experimental tumor models.

The aim of this study was to investigate the different pharmacokinetic behavior of surface-modified poly(methylmethacrylate) (PMMA) nanoparticles. The particles were 14C-labeled and coated with polysorbate 80, poloxamer 407, and poloxamine 908. Plain particles served as control particles. In vivo studies were performed in three tumor models differing in growth, localization, and origin. Particle suspensions were administered via the tail vein, and at given time animals were killed and organs were dissected for determination of PMMA concentration. For the PMMA nanoparticles coated with poloxamer 407 or poloxamine 908, high and long-lasting concentrations were observed in the melanoma and at a lower level in the breast cancer model. In an intracerebrally growing glioma xenograft, the lowest concentrations that did not differ between the tumor-loaded and tumor-free hemispheres were measured. Organ distribution of the four investigated batches differed significantly. For instance, poloxamer 407- and poloxamine 908-coated particles circulated over a longer period of time in the blood, leading additionally to a higher tumor accumulation. In contrast, plain and polysorbate 80-coated particles accumulated mainly in the liver. The strong expression of vascular endothelial growth factor and Flk-1 in the melanoma correlated with high concentrations of PMMA in this tumor. The degree of accumulation of PMMA nanoparticles in tumors depended on the particle surface properties and the specific growth differences of tumors.

Static and dynamic light scattering from multicomponent polymer mixtures PS/PDMS/PMMA/toluene

AbstractThe static and dynamic scattering properties of multicomponent polymer mixtures are examined starting from the theoretical formalism based on the random phase approximation (RPA) for multicomponent polymer mixtures in the presence of a low molecular weight solvent. The results are compared with the light scattering data reported recently by Strazielle and coworkers [1] for polystyrene/polydimethylsiloxane/polymethylmethacrylate/toluene mixtures. The present paper is an extension of the work published recently by these authors [2] and considers data obtained from several concentrations of PMMA. It also includes a discussion of the dynamic properties which are obtained by quasi‐elastic light scattering.

Phase Separation in Concentrated Solutions of Two Homopolymers and a Diblock Copolymer

The dynamic behavior of polystyrene (PS) (M w =9.0×10 5 ), poly(methyl methacrylate) (PMMA) (M w =1.4×10 6 or 1.0×10 5 ), and styrene-methyl methacrylate diblock copolymer (S-b-MMA) (M w =8.0×10 4 ) mixtures in a solvent isorefractive with PMMA (benzene) was investigated by quasielastic light scattering spectroscopy as a function of temperature and PMMA concentration in the phase separation region. Only two main dynamic modes were present at low PMMA concentrations corresponding to the trace diffusion of PS and S-b-MMA visible probes. In the case of PS homopolymer, the probe diffusion coefficient D s c -2.9 , which is close to the reptation prediction for self-diffusion of flexible polymers at Θ-conditions, D s c -3 . The concentration dependence of D c for the trace diffusion of S-b-MMA also follows a power law but with a smaller exponent (D c c -2.3 ). With concentrations of PMMA increasing above a threshold concentration, the decay time distribution displayed a complex structure with three main separated bands. The very slow broad mode was related to the phase separation in the mixture and originates from aggregates of probe polymers. The phase separation also appeared on heating in some solutions with appropriate concentration. Experiments have shown that the early stage of the phase separation in the mixtures is mostly due to the aggregation of the high-molecule-weight PS and the low-molecular-weight block copolymer mostly remains molecularly dissolved. Thus, possibly only the late stage of the phase separation process could be influenced by the presence of the diblock copolymer

Effect of PMMA addition on the solution crystallization of the alpha and beta phases of poly(vinylidene fluoride) (PVDF)

This study determined the effect of PMMA addition on the crystalline forms ( alpha and beta phases) of PVDF, crystallized from solution. The changes in the content of the two phases due to addition of different concentrations of PMMA at different crystallization temperatures were detected by IR spectroscopy. DSC analysis revealed that the melting temperature for both phases and the crystallization temperature of the alpha -phase decreased slowly with the increase of PMMA concentration. It was also observed that small concentrations of PMMA (10 and 15 wt%) favoured the beta -phase crystallization.