Multitechnique characterization of thin films of immiscible polymer systems: PS–b‐PMMA diblock copolymers and PS–PMMA symmetric blends

Immiscible polymer systems are known to form various kinds of phase‐separated structures capable of producing self‐assembled patterns at the surface. In this study, different surface characterization methods were utilized to study the surface morphology and composition produced after annealing thin polymer films. Two different SIMS techniques—static time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) and dynamic nano‐SIMS—were used, complemented by x‐ray photoelectron spectrometry (XPS) and atomic force microscopy (AFM). Thin films (spin‐coated onto silicon wafers) of polystyrene (PS)–poly(methyl methacrylate) (PMMA) symmetric blends and diblock copolymers of similar molecular weight were investigated. Surface enrichment by PS was found on all as‐cast samples. The samples were annealed at 160 °C for different time periods, after which the blend and the copolymer films exhibited opposite behaviour as seen by ToF‐SIMS and XPS. The annealed blend surface presented an increase in the PMMA concentration whereas that of copolymers showed a decrease in PMMA concentration compared with the as‐cast sample. For blends, the nano‐SIMS as well as AFM images revealed the formation of phase‐separated domains at the surface. The composition information obtained from ToF‐SIMS and XPS, as well as the surface mapping by nano‐SIMS and AFM, allowed us to conclude that PS formed phase separated droplet‐like domains on a thin PMMA matrix on annealing. The three‐dimensional nano‐SIMS images showed that the PS droplets were supported inside a rim of PMMA and that these droplets continued from the surface like columnar rods into the film until the substrate interface. In the case of annealed copolymer samples, the AFM images revealed topographical features resembling droplet‐like domains on the surface but there was no phase difference between the domains and the matrix. In the case of copolymers, owing to the covalent bonding between the blocks, complete phase separation was not possible. The three‐dimensional nano‐SIMS images showed domain structures in the form of striations inside the film, which were not continuous until the substrate interface. Information from the different techniques was required to gain an accurate view of the surface composition and topographical changes that have occurred under the annealing conditions. Copyright © 2005 John Wiley & Sons, Ltd.     

Catenated PS–PMMA Block Copolymers via Supramolecularly Templated ATRP Initiator Approach

A novel route to synthesize catenated macrocyclic PS–PMMA block copolymers is demonstrated via combination of supramolecular chemistry and controlled radical polymerization (CRP). Polymerization of styrene with bromopropionate ester initiator coupled with phenanthroline Cu(I) complex affords a four arm PS macroinitiator, which upon further chain extension by polymerization of MMA generates a four arm PS–PMMA block copolymer. Intramolecular coupling of PS–PMMA–Br arms via low temperature styrene‐assisted atom transfer radical coupling (ATRC) leads to the formation of PS–PMMA catenand, which generates the metal‐free catenated macrocyclic PS–PMMA block copolymer after removal of Cu metal. The interlocked structures of catenated block copolymers are confirmed by GPC, NMR, and AFM image analysis.     

Mesoscopic simulation of metastable microphases in the order–order transition from gyroid-to-lamellar states of PS–PI diblock copolymer

The formation of metastable microphases during the order–order transition (OOT) from gyroid-to-lamellar states of a poly(styrene)–poly(isoprene) (PS–PI) copolymer has been investigated on a mesoscopic level using dissipative particle dynamics simulations. The formation of the gyroid microphase was obtained via an order–disorder transition process (ODT). The microphase was then subjected to thermal heating cycles. A thermodynamic instability of poly(styrene) microdomains due to temperature effects induces anisotropic composition fluctuations in the gyroid structure and a microphase transformation from gyroid-to-lamellar takes place via an OOT. Two metastable microphases (hexagonal perforated layers and cylinders) were detected during the thermal process. Results are consistent with experimental and theoretical studies.     

The crystallization of polymer–diluent mixtures

A theory pertinent to the nucleation of polymer-diluent systems for molecules of finite molecular weight has been developed. These results have been applied to the crystallization from polyethylene-α-chloronaphthalene mixtures using molecular weight fractions of polyethylene ranging from 4,000 to 250,000. This analysis is carried out over the composition range extending from pure polymer to a polymer fraction of 0.30. According to this theory, the interfacial basal free energy decreases as either the molecular weight or diluent concentration decreases.     

Chemically activated 1,1-dimethylcyclopropane from photolysis of isobutene–neopentane–diazomethane–oxygen mixtures

A study of the structural isomerization rate of chemically activated 1,1-dimethylcyclopropane from singlet methylene addition to the double bond of isobutene is reported. Singlet methylenes were produced from the 4358- and 3660-Å photolysis of diazomethane in the presence of added oxygen. Theoretical rates calculated via RRKM theory are in excellent agreement with experiment for calculations utilizing activated complex structures and critical energies consistent with known thermal Arrhenius parameters, and excitation energies consistent with previous determinations of ΔH(CH₂) + E*(CH₂) = 116.1 and 112.6 kcal/mole for diazomethane photolyses at 3660 and 4358 Å, respectively.     

The analysis of mixtures II–Pattern separation III–Pattern separnration

The work previously described has been extended and amplified. Product moment correlation coefficients are shown to be useful in separation of component spectra. The 'ab initio' analysis of a four component mixture is described.     

Experimental and kinetic study of shock initiated ignition in homogeneous methane–hydrogen–air mixtures at engine‐relevant conditions

The ignition delay time of two stoichiometric methane/hydrogen/air mixtures has been measured in a shock tube facility at pressures from 16 to 40 atm and temperatures from 1000 to 1300 K. Overall, the observed reduction in ignition delay with some methane replaced by hydrogen is relatively small given the large concentration of hydrogen involved in the current study. With a high hydrogen mole fraction (35% of the total fuel), a reduction of the ignition‐promoting effect was observed with reduced temperature. A detailed chemical kinetic mechanism was used to simulate ignitions of test mixtures behind reflected shocks. An analysis of the mechanism indicates that at higher temperatures, the rapid decomposition of hydrogen molecules leads to a quick formation of H radical pools, which promote the chain branching through H + O₂ ? O + OH. At lower temperatures, the branching efficiency of hydrogen is low; a weak effect of hydrogen on methane ignition could be result from the reaction between H₂ and methylperoxy CH₃O₂, which contributes extra H radicals to the reaction system. The effects of hydrogen also decrease with increasing pressure; this is related to the negative pressure dependence of hydrogen at the second ignition limit. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 221–233, 2006     

Mechanical behavior and tensile fractography of compatible vinylchloride–vinylacetate–maleic acid terpolymer and nitrocellulose blends

Vinylchloride–vinylacetate–maleic acid terpolymer (VMCH) and nitrocellulose (NC) were blended at 10% (W/V) concentration is cyclohexanone at different weight fractions. Compatible blends were obtained at all weight fractions. This paper reports the mechanical behavior of solvent cast blend films of VMCH and NC. The films were prepared by solution blending and subsequent casting on a mercury surface. Depending on the composition, the tensile behavior ranged from brittle to ductile. The effect of the blend ratio on the properties shows that within the Hookeian region the modulus and strength have a positive deviation from linearity, whereas the elongation has a negative deviation. The effect of the blend ratio on the ultimate properties of the materials shows a positive deviation in strength up to 63 wt% VMCH composition and a negative deviation in elongation and toughness. The tensile fractography of the pure VMCH and VMCH/NC blends shows the presence of peaks, foldings of fibrils along with cavities or voids, which indicate a ductile mode of failure with craze-initiated fracture. Fractography of the pure NC Indicates a brittle mode of failure wit h craze-initiated fracturing.     

Templated nanostructured PS‐b‐PEO nanotubes

With anodic aluminum oxide (AAO) membranes as wetting templates, nanotubes of the cylinder‐forming polystyrene‐block‐poly(ethylene oxide) (PS‐b‐PEO) copolymer were generated. The PS‐b‐PEO solution was introduced into the cylindrical nanopores of an AAO membrane by capillary force and polymeric nanotubes formed after solvent evaporation. Because of the water solubility of the cylindrical PEO microdomains and the orientation of the cylindrical PEO microdomains with respect to the nanotube walls, the nanotubes were permeable to aqueous media. PS‐b‐PEO nanotubes were also prepared on the interior walls of amorphous carbon nanotubes (a‐CNTs). Because of the unique water permeability of the PEO microdomains, an avenue for functionalizing the interior of the a‐CNTs is enabled. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2912–2917, 2007     

Chemically activated 3-methyl-l-butene and 2-methyl-l-butene from photolysis of diazomethane–isobutene–neopentane–oxygen mixtures

An experimental study of the decomposition kinetics of chemically activated 2-methyl-l-butene and 3-methyl-l-butene produced from photolysis of diazomethane-isobutene-neopentane-oxygen mixtures is reported. The experimental rate constants for 3-methyl-l-butene decomposition were 1.74 ± 0.44 × 10⁸ sec^?1 and 1.01 ± 0.25 × 10⁸ sec^?1 at 3660 and 4358 Å, respectively. 2-Methyl-l-butene experimental decomposition rate constants were found to be 5.94 ± 0.59 × 10⁷ sec^?1 at 3660 Å and 3.42 ± 0.34 × 10⁷ sec^?1 at 4358 Å. Activated complex structures giving Arrhenius A-factors calculated from absolute rate theory of 10^{16.6 ± 0.5} sec^?1 for 3-methyl-l-butene and 10^{16.2 ± 0.4} sec^?1 for 2-methyl-l-butene, both calculated at 1000°K, were required to fit RRKM theory calculated rate constants to the experimental rate constants at reasonable E₀ and E* values. Corrected calculations (adjusted E₀ values) on previous results for 2-pentene decomposition gave an Arrhenius A-factor of 10^{16.45 ± 0.35} sec^?1 at 1000°K. The predicted A-factors for these three alkene decompositions giving resonance-stabilized methylully radicals are in good internal agreement. The fact that these A-factors are only slightly less than those for related alkane decompositions indicates that methylallylic resonance in the decomposition products leads to only a small amount of tightening in the corresponding activated complexes. This tightening is a significantly smaller factor than the large reduction in the critical energy due to resonance stabilization.     

Electrogenerated Chemiluminescence of Donor–Acceptor Molecules with Thermally Activated Delayed Fluorescence

The electrochemistry and electrogenerated chemiluminescence (ECL) of four kinds of electron donor–acceptor molecules exhibiting thermally activated delayed fluorescence (TADF) is presented. TADF molecules can harvest light energy from the lowest triplet state by spin up‐conversion to the lowest singlet state because of small energy gap between these states. Intense green to red ECL is emitted from the TADF molecules by applying a square‐wave voltage. Remarkably, it is shown that the efficiency of ECL from one of the TADF molecule could reach about 50 %, which is comparable to its photoluminescence quantum yield.     

Velocity‐correlation analysis in polymer–solvent mixtures

The subject of this article is the combined interpretation of intradiffusion and mutual‐diffusion data for polymer–solvent mixtures in terms of integrals over velocity self‐correlation functions and velocity cross‐correlation functions. The combination of mutual‐diffusion, intradiffusion, and activity data allows the evaluation of velocity‐correlation coefficients (VCCs) and distinct‐diffusion coefficients in systems containing one monodisperse solute. This study is the first attempt to extend these approaches to polymers that are polydisperse solutes. Because of the polydispersity, this correlation analysis may become critical for polymers. Its application to polydisperse samples requires the reduction of intradiffusion and mutual‐diffusion coefficients to the same average. After such a reduction, the VCCs and distinct‐diffusion coefficients are evaluated for a homologous series of poly(ethylene glycol)s (PEGs). Attractive PEG–PEG interactions depend on the chain length and concentration of PEG. In this analysis, network formation in PEG–water systems appears to be a smooth process. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 43–51, 2002     

Phase behavior of polylactides in solvent–nonsolvent mixtures

Isothermal phase diagrams for the semicrystalline poly-L-lactide (PLLA) and the amorphous poly-DL-lactide (PDLLA) in combination with several solvent–nonsolvent combinations (dioxane/water, dioxane/methanol, chloroform/methanol, and NMP/water) have been determined. The locations of the liquid–liquid miscibility gap, the solid–liquid miscibility gap and the vitrification boundary in the isothermal phase diagrams at 25°C were identified. The liquid–liquid miscibility gap for the systems with PLLA was located in the same composition range as the corresponding systems with PDLLA. For the systems containing PLLA solid–liquid demixing was thermodynamically preferred over liquid–liquid demixing. Attempts were made to correlate the experimental findings with predictions on the basis of the Flory-Huggins theory for ternary solutions using interaction parameters derived from independent experiments. Qualitative agreement was found between the theoretical predictions and the experimentally obtained liquid–liquid miscibility gap. No good agreement was found for the solid–liquid miscibility gap. © 1996 John Wiley & Sons, Inc.     

Diffusion of water–acetic acid mixtures in epoxy

The solubility and diffusion of water–acetic acid solutions in epoxy resins has been studied by nuclear magnetic resonance imaging (MRI) and spectroscopy (NMR), Fourier transform infrared (FTIR) spectroscopy, and light microscopy (LM). These techniques revealed the progression of a sharp diffusion front at a rate proportional to the square root of time. Both the swelling and rate of diffusion are dependent on acid dilution. At higher acid concentrations, hydrogen bonds were present, which has been interpreted as formation of acid dimers. The results indicate that molecular interactions play a major role in controlling the solubility and diffusion processes. The observation that voids can be filled up with penetrant strongly support the interpretation that molecular interactions rather than concentration gradient are responsible for these effects. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3328–3336, 1999     

Kinetics of malachite green fading in water–ethanol–2‐propanol ternary mixtures

The rate constant of malachite green (MG⁺) alkaline fading was measured in water–ethanol–2‐propanol ternary mixtures. This reaction was studied under pseudo‐first‐order conditions at 283–303 K. It was observed that the observed reaction rate constants, k_obs, were increased in the presence of different weight percentages of ethanol and 2‐propanol. The fundamental rate constants of MG⁺ fading in these solutions were obtained by using the SESMORTAC model. In each series of experiments, the concentration of one alcohol was kept constant and the concentration of the second one was changed. It was observed that at the constant concentration of one alcohol and variable concentrations of the second one, with an increase in temperature, k₂ values decrease according to the trend of hydroxide ion nucleophilic parameter values and k₁ values increase. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 441–453, 2011     

Methyl methacrylate polymerization initiated by triethylborane–peroxide mixtures

The polymerization of methyl methacrylate initiated by triethylborane or triethylborane–peroxide mixtures was studied. The rate of initiation by a mixture of triethylborane and tert-butyl peroxide was found to be first-order in peroxide. The order in triethylborane changes from one at low triethylborane/peroxide to nearly zero at high triethylborane/peroxide. The possibility of a mechanism involving a fast reaction followed by a slow reaction that would initiate the polymerization is discussed.     

Nanostructured organic–inorganic hybrid films prepared by the sol–gel method from self‐assemblies of PS‐b‐paptes‐b‐PS triblock copolymers

ABA‐based triblock copolymers of styrene as block ends and gelable 3‐acryloxypropyltriethoxysilane (APTES) as the middle block were successfully prepared through nitroxide‐mediated polymerization (NMP). The copolymers were bulk self‐assembled into films and the degree of phase separation between the two blocks was evaluated by differential scanning calorimetry (DSC). Their morphology was examined through small angle X‐ray scattering (SAXS) and transmission electron microscopy (TEM), whereas the mechanical properties of the corresponding cross‐linked self‐assembled nanostructures were characterized by dynamic mechanical analysis (DMA). Acidic treatment of the triblock copolymers favored the hydrolysis and condensation reactions of the APTES‐rich nanophase, and induced a mechanical reinforcement evidenced by the increase of storage modulus values and the shift of the glass transition temperature to higher temperatures due to confinement effects. In addition, the lamellar structure of the hybrid films was retained after the removal of the organic part by calcination. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Free-radical polymerizations initiated by triethylaluminum–cuprous chloride mixtures

Methyl methacrylate was polymerized by triethylaluminum—cuprous chloride catalyst. A study of the polymerization kinetics indicated that the overall rate was represented by the equation, R_p = K[AlEt₃] [CuCl]^½ [M]². The overall activation energy was 16.5 kcal/mole. From ESR measurement and the results of copolymerization of methyl methacrylate with styrene, it was suggested that the catalytic system has the character of a radical initiator. A polymerization scheme was also proposed.