Spatial scale-dependent tracer diffusion in bulk polycarbonate studied by holographic relaxation

The diffusion of a photochromic dye tracer in polycarbonate was studied by a holographic relaxation technique (forced Rayleigh scattering) at temperatures close to the glass transition temperature. By varying the holographic grating period the results could be interpreted via the spatial scale dependence of apparent diffusion coefficients within a two-state diffusion model. This indicates inhomogeneities on the scale of a few micrometers in the polymer glass.     

Synthesis and study of photochromic properties of copolymers based on functionalized chromenes

Chromenes functionalized with methacryl groups were synthesized and involved into the radical polymerization to obtain copolymers with ethyl acrylate. Comparison of spectral kinetic characteristics of poly(methyl methacrylate) glasses containing chromenes and photochromic copolymers as additives led to a conclusion that incorporation of a photochromic compound as a part of a copolymer into the polymeric glass increases efficiency of photocoloration of photochromic compounds in the polymeric layer.     

Flame retardancy of polycarbonate enhanced by adding fly ash

We have developed a flame‐retardant polycarbonate resin whose flame retardancy is greatly enhanced by adding fly ash (a by‐product from thermal power plants). Fly ash with comparatively small average particle sizes (<10 µm) raised the flame retardancy of polycarbonate because of the hydrogen bond that forms between the polycarbonate and the hydroxy group on the fly ash surface. This bond primarily improves the heat resistance of the polycarbonate and also isomerizes the polycarbonate to promote carbonization. The polycarbonate with 25 wt% of the fly ash showed good other main characteristics, such as mechanical properties and moldability, comparable to those of a flame retardant polycarbonate reinforced with glass fiber, used for electronic products such as desktop computers, etc. Applying the fly ash eliminates the need to use current retardants such as organic halogen compounds and thus promotes the perceived environmental safety of flame‐ retardant polycarbonate. In addition, being able to use less raw resin by adding the fly ash means that less energy is required to manufacture flame‐retardant polycarbonate. Copyright © 2007 John Wiley & Sons, Ltd.     

Electrochromism of indolinobenzospirans dissolved in rigid amorphous polymer matrices

The effect of a static electric field on the position of absorption bands of colored stereoisomers of two photochromic compounds of the indolinobenzospiropiran group dissolved in matrices of poly(methyl methacrylate), poly(n-butyl methacrylate), polystyrene, and polycarbonate at room temperature was studied. In the case of matrices with the polymethacrylates the effects observed show that applied electric field produces a shift of thermal equilibrium towards stablization of stereoisomers of larger dipole moment. On the basis of kinetic measurements of attainment of thermal equilibrium on switching the electric field off, the rate constants of their interconversion have been determined. In the case of matrices with polystyrene and polycarbonate, a small red shift only was observed.     

Carbon tetrachloride-induced crack healing in polycarbonate

Crack healing induced by carbon tetrachloride in polycarbonate has been studied at temperatures in the range of 40–60°C. The carbon tetrachloride treatment reduces the glass transition temperature of polycarbonate. Crack healing is observed because the effective glass transition temperature in polycarbonate is reduced to below the test temperature by the carbon tetrachloride treatment. Two distinctive stages of crack healing are divided based on the recovery of mechanical strength and fractograph. The first stage corresponds to the progressive healing due to the convolution of wetting and self-diffusion, which has a constant crack closure rate. Immediately following the first stage, the second stage, corresponding to the self-diffusion of polymer chain, enhances the quality of healing behavior. The transport of carbon tetrachloride in polycarbonate consists of case I (concentration gradient controlled) and case II (relaxation controlled) behaviors. The direction of case II is opposite to that of case I. The solubility decreases with increasing temperature, but diffusivity and velocity for mass transfer, crack closure rate, and diffusion coefficient for the diffusion front have the opposite trend. The first stage of crack healing is controlled by case II transport. The transport of carbon tetrachloride changes the fracture behavior of polycarbonate from ductile to brittle. A comparison of crack healing in polycarbonate and poly (methyl methacrylate) is made. © 1994 John Wiley & Sons, Inc.     

A hyper-raman spectroscopy,spectrophotometry, and atomic force microscopy study of photochromism of spirocyclic compounds on nanostructured metal films

The specifics of photochromic transformations of spirocyclic molecules at the nanostructured metal surface were studied by hyper-Raman spectroscopy (HRS) and spectrophotometry. Unique nanostructured systems were prepared, and their surface morphology and optical properties were examined. Enhancement of the photochromic transformations near the nanostructured metal surface was revealed. HRS spectra for various classes of spirocyclic compounds adsorbed on nanostructured systems of different types (granular silver films, AgCl-Ag films) were measured. The bands due to in-plane vibrations have the highest intensity, thereby indicating preferred planar geometry of adsorption of the test molecules.     

Polymer Photochromic Composites and Their Spectral and Kinetic Properties

A method for the synthesis of polymer photochromic composites containing photochromic nitro-substituted spiropyran via mechanical mixing in melt is developed, and dependences of the spectral and kinetic properties of the samples on the nature of chosen thermoplastic polymer matrices (polyolefins, polycarbonate) and their processing temperatures are studied.     

6'-对位取代苯乙烯基吲哚啉螺吡喃的合成

利用2-亚甲基吲哚啉和取代水杨醛缩合得到十三种新的烷基苯乙烯基吲哚啉螺苯并吡喃。在苯并吡喃部分含有硝基的螺吡喃显示出逆光致变色行为，其它的则为普通光致变色化合物。同时，结果表明，化合物异构体的稳定性不仅取决于化合物本身的结构，而且还取决于介质环境的影响。     

6′-对位取代苯乙烯基吲哚啉螺吡喃的合成

利用2-亚甲基吲哚啉和取代水杨醛缩合得到十三种新的烷基苯乙烯基吲哚啉螺苯并吡喃。在苯并吡喃部分含有硝基的螺吡喃显示出逆光致变色行为,其它的则为普通光致变色化合物。同时,结果表明,化合物异构体的稳定性不仅取决于化合物本身的结构,而且还取决于介质环境的影响。     

Keggin结构钼磷酸/聚碳酸酯复合物的制备及光致变色性质研究

近年来，多酸－有机复合材料的研究，受到了人们的广泛关注犤１犦。杂多化合物是一类含有氧桥的多核配合物，作为高质子酸，可以提供质子与有机给体形成多酸－有机复合物，这类质子化状态的复合物具有良好的光敏性，这种特性在光化学、氧化还原催化等方面显示出重要用途。聚碳酸酯是一种综合性能优良的光学材料，研究以其为基材的杂多酸－有机复合材料的基本性能，对聚碳酸酯的改性、增进对这类复合材料的理论研究以及拓宽聚碳酸酯的应用都有重要的实际意义，迄今为止，尚未见这方面的报道。本文以Keggin结构钼磷酸（简写为PMo１２）和聚…     

Mechanism of thermal decolorization of benzospirans in some amorphous polymeric matrices

The photochromic effect has been investigated for three compounds of the benzospiran group dissolved in amorphous polymers: poly(methyl methacrylate), poly(n-butyl methacrylate), poly(vinyl acetate), and poly(vinyl n-butyrate). The kinetics of the thermal bleaching reaction above T_g of the matrix follow a first-order equation due to the averaging of free volume distribution related to the diffusion of segments in viscoelastic state. A more complex mechanism of decolorization below T_g has been considered from the point of view of unequal, discrete distribution of environments in which the photochromic molecules exist in the glassy matrix. A change of the activation energy and the mechanism of color decay on passing through T_g is not a rule (PVB), which shows, that for a polymer having long, flexible chains, secondary glass transition phenomena play a decisive role. In the case of glassy polymers (PMMA), the photochromic effect of benzospirans may be employed to determine T_β. It seems, that in addition to steric restrictions for trans–cis isomerization in the decolorization process one must consider the interactions of photochromic molecules with the matrix as well as their chemical nature.     

Study of the Possibility of Functionalization of Graphene Oxide Nanoplatelets with Photochromic Chromene and Spiropyrans in Solutions

Russian Journal of General Chemistry - Spectral and kinetic studies of the interaction of the surface groups of graphene oxide nanoplatelets with the molecules of photochromic compounds from the...     

The photochromic properties of indoline spirooxazine-thermoplastic polymer systems obtained by supercritical fluid impregnation

The impregnation of thermoplastic polymers (polyethylene, polypropylene, polymethyl methacrylate, and polycarbonate) with photochromic compounds from the class of indoline spirooxazines in supercritical carbon dioxide (SC-CO₂) was studied. The concentration of the photochrome and the kinetics of decolorization of its colored form depended strongly on the type of the polymer matrix and the structure of spirooxazine. The introduction of 1,3′,3′-trimethylspiro(indoline-2′,3-3H-anthraceno[2,1-b][1,4]oxazine) (SAO) into polycarbonate caused anomalous stabilization (the prolonged conservation of the excited colored form of SAO in the polymer matrix). In contrast to other photochrome-polymer pairs, after supercritical impregnation into polycarbonate, at least 10% of all SAO molecules were in the colored form, which was highly stable and did not decolorize after 150 days; the rest of the impregnated SAO molecules were localized in the matrix as individual molecules, partially colorized after matrix relaxation, or nanocrystals of characteristic sizes ∼10–20 nm. The mechanisms of the anomalous stabilization of the colored SAO form in the polycarbonate matrix are discussed. Original Russian Text ? N.N. Glagolev, A.B. Solov’eva, A.V. Kotova, V.T. Shashkova, B.I. Zapadinskii, N.L. Zaichenko, L.S. Kol’tsova, A.I. Shienok, P.S. Timashev, V.N. Bagratashvili, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 5, pp. 985–992.     

2-芳氧基-1,8-邻苯二甲酰基萘的合成及光致变色性

合成了3种2-芳氧基-1,8-邻苯二甲酰基萘类光致变色化合物,通过核磁共振谱、红外光谱、质谱和元素分析确定了结构.对产物进行了荧光光谱测定,3种光致变色化合物的荧光强度和Stoke位移都较大.用紫外-可见分光光度计对其在丙酮溶液中的光致变色行为进行了测定,3种光致变色化合物在300-600 nm范围内都具有一定的光致变色性能和较大的吸光系数.     

Modification of polymer surfaces based on polyurethanes with photochromic compounds

Russian Chemical Bulletin - The possibility of covalent fixing of hydroxyl-containing photochromic compounds on the surface of polyurethane films containing excess isocyanate groups was studied. By...     

A new photochromic 8pi-system based on an azaheptatriene-tetrahydroazepinoisoquinoline electrocyclization

A new photochromic family of tetrahydroazepinoisoquinolines (THAI) 4a-i has been prepared. It undergoes light-induced ring opening from spiro compounds 4 to betaines 3 that decolorize in a very fast cyclizing reaction. Depending on substitution of the precursors 1 and 6, the photochromic styryltetrahydroindolizines (THI) 5k-q are formed in a periselective way. The conformation and configuration of the new photochromic THAI 4 and THI 5 were investigated by NMR and the structure of both compounds was proven by X-ray analysis. The photochromic properties were studied by laser flash photolysis, which afforded the lifetime of the colored form 3 and 3' in the micro- or nanosecond range.     

Effect of parameters of a crosslinked polyacrylic matrix on the impregnation of photoactive compounds in supercritical fluids

The effect of the network density of spatially crosslinked polyacrylic transparent matrices and the conditions of their impregnation with a photochromic compound via the use of supercritical carbon dioxide on the concentration of the introduced photochromic compound of the spiroxazin family is studied. The concentration of impregnated filler in a matrix is shown to increase with increases in the interjunction distance (below a certain level) and network chain flexibility as well as with increases in the temperature and pressure of the impregnation process. Impregnation in rigid networks occurs only in surface layers, whereas, in an elastic network, impregnation occurs in the entire volume of a sample. Matrices based on oligourethanemethacrylates are characterized by a good thermodynamic affinity toward spiroxazin photochromic compounds, a fact that makes it possible to increase the concentration of photochromic compounds in the matrix up to 3 wt % under conditions of supercritical impregnation. The photochromic characteristics of an impregnated compound are shown to be preserved in samples.     

Hydrothermal treatment of nanoparticle thin films for enhanced mechanical durability

The mechanical durability of nanoporous all-nanoparticle and polymer-nanoparticle layer-by-layer (LbL) films (80-150 nm thick) on both glass and polycarbonate substrates has been greatly enhanced by hydrothermal treatment (124-134 degrees C). Polymer-nanoparticle films were more durable than all-nanoparticle films after hydrothermal treatment. The optical properties of nanoporous antireflection (AR) films were exploited in an abrasion test (25-100 kPa normal stress) to quantify the extent of abrasive wear observed qualitatively by scanning electron microscopy (SEM). Marginal damage was observed under optimal reinforcement conditions. Untreated films not only delaminated from the surface completely but also damaged their underlying glass and polycarbonate substrates during testing. The nature of the substrate was found to play an important role in determining abrasion resistance, regardless of the level of particle fusion in the film. The low-temperature process enables in situ mechanical reinforcement of otherwise delicate nanoparticle assemblies on plastic substrates. Tribochemical wear was found to planarize the nanoscale surface texture of these films, similar to what is observed in chemo-mechanical polishing (CMP). This finding is useful for anyone trying to make robust superhydrophobic or superhydrophilic coatings. To our knowledge, this is the first report on hydrothermal reinforcement of LbL films.     

Study of spin–lattice relaxation and local motion in dissolved poly[2,2-propanediylbis(3,5-dimethyl-4, hydroxyphenyl)carbonate]

Proton and carbon-13 spin–lattice relaxation times are reported for 10-wt % solutions of tetramethyl bisphenol-A polycarbonate. The relaxation times for both nuclei were measured at two Larmor frequencies and as a function of temperature. These relaxation times are interpreted in terms of three motions: segmental motion, restricted rotational diffusion, and backbone methyl-group rotation. The Hall–Helfand correlation function is used to describe the segmental motion. Internal rotation is described by the usual Woessner approach and restricted anisotropic rotational diffusion by the Gronski approach. As demonstrated by its higher activation energy, correlated segmental motion appears to be slower than the unsubstituted polycarbonate of BPA. In addition, the single-transition processes seem to be still less important than correlated backbone transitions. Phenylene-group rotation is described in terms of restricted rotational diffusion instead of complete anisotropic rotation. The time scale for backbone methyl-group rotation is comparable to that in BPA, a fact indicative of weaker cooperativity between this motion and the other motions. Rotation of the methyl group attached to the phenylene ring is too fast to significantly contribute to relaxation except by partially averaging the dipole–dipole interactions. The higher activation energies for segmental motion observed in solution for this methyl-substituted polycarbonate relative to the unsubstituted polycarbonate parallel a significant increase in the glass transition temperature observed for the substituted material. The restricted pheylene-group rotation in solution is also parallelled by a large upward shift of the low-temperature loss peak in the glassy polymer.     

Use of photochromic spiropyran as a molecular probe of large strain in polycarbonate

The effect of tensile deformation of polycarbonate on the kinetics of the decoloration reaction of photochromic spiropyran dissolved in the polymer was studied. It was shown that the strain-induced change in the decoloration rate can be used for measurement of the temperature jump appearing during deformation and yielding of the specimen provided that structural and thermodynamic changes in the system are taken into account.