Macromolecular reaction and interdiffusion in a compatible polymer blend

A theory describing slow macromolecular reaction and interdiffuion in a compatible polymer blend is suggested based on the linear non-equilibrium thermodynamic principles. A simple model system is considered. In a blend consisting initially of homopolymers A and B, the transformation A → B proceeds with the B units accelerating the reaction. A system of diffusive-reaction equations for relevant macroscopic variables is derived. The randomness of the reacting chains' structure gives rise to a new interdiffusion mode in addition to the reacting polymer-homopolymer B interdiffusion. Numerical calculations reveal that the diffusive intermixing of reacting chains of different composition may significantly affect the reaction rate and the local compositional heterogeneity as well. It is possible to discriminate the fast- and the slow-mode theories of interdiffusion using reaction kinetics data. Under certain conditions, the reaction may proceed in a non-trivial autowave-like regime.     

Birefringence control by hydrogen bonding on compatible polymer pair composed of hydrogenated ring‐opening polymer and modified polystyrene

A new polymer blend composed of a hydrogenated ring‐opening polymer (HROP) with an ester group and hydroxyl functionalized polystyrene (HFP) produced the excellent transparent materials which enabled a precise birefringence control in keeping with the other physical properties for optical film use. The blend with a composition from 0.28 to 0.35 for the HFP weight fraction showed an extraordinary wavelength dispersion, transmitting through a zero birefringence point at the critical fraction of 0.45, while each polymer showed an ordinary wavelength dispersion. The observed excellent transparency even above those of the glass transition temperature was attributed to a depressed phase separation that resulted from strong hydrogen bond between the ester and hydroxyl groups. An IR analysis of the film demonstrated a remarkable red‐shift in the carbonyl peak with an increase of the hydroxylated polystyrene content, indicating a strong hydrogen bond between those groups. This new polymer blend provides a useful design to achieve practical demands for film use, both optical and mechanical under the fabrication conditions using the melt extrusion technique. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3132–3143     

4H‐1‐Benzopyrans by a tandem SN2‐SNAr reaction

Treatment of 2‐fluoro‐5‐nitrobenzyl bromide with active methylene compounds in the presence of excess potassium carbonate in acetone leads to the formation of highly functionalized 4H‐1‐benzopyrans by a tandem S_N2‐S_NAr reaction sequence. The reaction works well with β‐keto esters, β‐keto sulfones, β‐keto phosphine oxides, β‐keto phosphonates and β‐keto nitriles. The reaction is simple to perform and affords products in 50‐92% yields.     

Monte Carlo simulation of a polymer-analogous reaction in a polymer blend

The autocatalytic polymer-analogous reaction A → B in a blend composed of two contacting layers of compatible homopolymers A and B is studied by numerical simulation using the dynamic continuum Monte Carlo method. The evolution of the numerical density of units A and units initially belonged to the chains of homopolymer A is investigated in the course of the reaction and interdiffusion. Local characteristics of the distribution of the homopolymer with respect to its composition and blocks A and B with respect to their length are calculated at different times. The dispersions of the above distributions are appreciably higher than the corresponding dispersion of the Bernoullian copolymer of the same average composition, despite the random character of the reaction. This effect can be provided by changes in the composition of the blend on the scale of the reacting chain as well as by the diffusive mixing of the above chains. For the products of the polymer-analogous reaction, the broadening of the compositional distribution is predicted also by the theoretical model, which describes interdiffusion in the reacting system on scales that are markedly greater than the size of a polymer chain.     

H‐bonding and stacking interactions between chloroquine and temozolomide

The interactions between temozolomide and chloroquine were examined via Dispersion‐Corrected Density Functional Theory and MP2 methods. Chloroquine was considered in both its lowest energy structure and in a local minimum where its aromatic system and secondary amine group are free to interact directly with temozolomide. The accessibility of these two components to intermolecular interaction makes the lowest energy dimer of this local monomer minimum competitive in total energy with that involving chloroquine's most stable monomer geometry. In either case, the most stable heterodimer places the aromatic ring systems of the two molecules parallel and directly above one another in a stacked geometry. Most of the local minima are also characterized by a stacked geometry as well. Comparison between B3LYP and B3LYP‐D binding energies confirms dispersion is a primary factor in stabilizing these structures. © 2016 Wiley Periodicals, Inc.     

Relaxation of liquid‐crystalline polymer fibers in polycarbonate–liquid‐crystalline polymer blend system

The relaxation of liquid‐crystalline polymer (LCP) fibers in the polycarbonate (PC)/LCP blend was examined under various conditions on a hot‐stage microscope. LC5000 is a thermotropic LCP consisting of 80/20 hydroxybenzoic acid and poly(terephthalate). The geometry of the fibers is not an important factor in the relaxation process. Fibers of different aspect ratios and lengths relaxed at the same rate and exhibited identical onset times. Increasing the temperature caused the fibers to relax faster, especially near the nematic‐transition temperature. The fibers relaxed almost immediately when subjected to a temperature of 285 °C. At 280 °C the fibers were stable for 43 min, whereas at 270 °C no noticeable relaxation was evident. Addition of compatibilizer stabilized the fibers by enhancing the interfacial adhesion between the fibers and the PC matrix. Consequently, LCP fibers in the compatibilized system relaxed at a much higher temperature (294 °C) as compared with the uncompatibilized system (275–280 °C). © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2307–2312, 2003     

An H‐shaped polymer bonding β‐cyclodextrin at branch points: Synthesis and influences of attached β‐cyclodextrins on physical properties

We report on the synthesis of an H‐shaped polymer bonding β‐cyclodextrin (β‐CD) at branch points and influences of attached β‐CD on physical properties. First, a poly(ethylene glycol)(PEG)‐based functional macroinitiator bearing two azidos and four chlorines at chain‐ends (PEG‐2N₃(‐4Cl)) was prepared via terminal modification reactions. Then, PEG‐2N₃(‐4Cl) was applied to initiate the atom transfer radical polymerization of N‐isopropylacrylamide, leading to the synthesis of an H‐shaped block polymer with PEG as the central chain and poly(N‐isopropylacrylamide) (PNIPAM) as side‐arms (PEG‐2N₃(‐4PNIPAM)). Azido groups were at the branch points of the polymer. Finally, the click reaction between PEG‐2N₃(‐4PNIPAM) and alkynyl monosubstituted β‐cyclodextrin (β‐CD) afforded another H‐shaped polymer with two β‐CDs bonding at the polymer branch points (PEG‐2CD(‐4PNIPAM)). The glass transition temperature (T_g) and lower critical solution temperature (LCST) of the H‐shaped polymer increased after the attachment of β‐CD. The self‐assembly and thermal responsive behaviors, as well as the encapsulation behaviors of PEG‐2CD(‐4PNIPAM) were also altered. When temperature was below the LCSTs, PEG‐2N₃(‐2PNIPAM) dissolved in water molecularly, whereas PEG‐2CD(‐4PNIPAM) could self‐assemble into nano‐sized micelles. After the LCST transitions, PEG‐2N₃(‐4PNIPAM) aggregated into micron‐sized unstable particles, whereas PEG‐2CD(‐4PNIPAM) transformed into PNIPAM‐cored nanomicelles. Besides, PEG‐2CD(‐4PNIPAM) can encapsulate doxorubicin below its LCST due to the formation of micelles. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Quantification issues in ToF‐SSIMS and AFM co‐analysis in two‐phase systems,exampled by a polymer blend

This study concerns the measurement of the surface properties of sensitive materials, exampled by a polymer blend of polyvinyl chloride (PVC) and polycarbonate (PC), by static secondary ion mass spectrometry (SSIMS) and atomic force microscopy (AFM) operated in force modulation microscopy mode. It is shown that SSIMS, although damaging the surface little, causes significant subsurface damage. This changes the material behaviour in the irradiated region and leads to changes in the AFM measurements of both the topography and nanomechanical parameters such as the elastic moduli. Alternatively, if AFM is conducted first, contact with the tip may lead to modification of the surface. In order to minimize damage, soft cantilevers (spring constant ～0.1 N m^?1) are used. It is recommended that analyses be conducted on identifiably equivalent or partially overlapping regions, where any damage effects may be separated. Because, in SSIMS, a flood gun neutralizer must be used that irradiates the whole sample, it is recommended that AFM analysis is conducted prior to SSIMS even if different areas of the same sample are to be studied. The fractional areas identified by atomic species in SSIMS and separately by AFM are both the same and give the consistent ratio PVC/PC = 44 : 56. Both of these analyses are characteristic of the substrate below the top monolayer. The fractional areas determined using molecular species in SSIMS and by G‐SIMS both give PVC/PC = 20 : 80, which is interpreted to show that more than half of the PVC surface is covered by a monolayer of PC. Copyright © 2003 John Wiley & Sons, Ltd.     

The role of a compatibilizer to saturate interfacial tension and to emulsify a polymer blend

A linear drop of the interfacial tension between polyamide 6 (PA6) and poly(propylene) (PP) upon increasing concentration of the reactive compatibilizer and a leveling-off at higher compatibilizer contents were found in this study. The reduction of the interfacial tension is compared with the reduction of the dispersed phase size of the corresponding blends. As a result, the domain size is not directly proportional to the interfacial tension under the condition that other factors are equal.     

The effect of hydrogen bonding on the conformations of 2‐(1H‐indol‐3‐yl)‐2‐oxoacetamide and 2‐(1H‐indol‐3‐yl)‐N,N‐dimethyl‐2‐oxoacetamide

In the title compounds, C₁₀H₈N₂O₂, (I), and C₁₂H₁₂N₂O₂, (II), the two carbonyl groups are oriented with torsion angles of −149.3 (3) and −88.55 (15)°, respectively. The single‐bond distances linking the two carbonyl groups are 1.528 (4) and 1.5298 (17) Å, respectively. In (I), the molecules are linked by an elaborate system of N—H...O hydrogen bonds, which form adjacent R²₂(8) and R⁴₂(8) ring motifs to generate a ladder‐like construct. Adjacent ladders are further linked by N—H...O hydrogen bonds to build a three‐dimensional network. The hydrogen bonding in (II) is far simpler, consisting of helical chains of N—H...O‐linked molecules that follow the 2₁ screw of the b axis. It is the presence of an elaborate hydrogen‐bonding system in the crystal structure of (I) that leads to the different torsion angle for the orientation of the two adjacent carbonyl groups from that in (II).     

Unusual H‐Bond Topology and Bifurcated H‐bonds in the 2‐Fluoroethanol Trimer

By using a combination of rotational spectroscopy and ab initio calculations, an unusual H‐bond topology was revealed for the 2‐fluoroethanol trimer. The trimer exhibits a strong heterochiral preference and adopts an open OH???OH H‐bond topology while utilizing two types of bifurcated H‐bonds involving organic fluorine. This is in stark contrast to the cyclic OH???OH H‐bond topology adopted by trimers of water and other simple alcohols. The strengths of different H‐bonds in the trimer were analyzed by using the quantum theory of atoms in molecules. The study showcases a remarkable example of a chirality‐induced switch in H‐bond topology in a simple transient chiral fluoroalcohol. It provides important insight into the H‐bond topologies of small fluoroalcohol aggregates, which are proposed to play a key role in protein folding and in enantioselective reactions and separations where fluoroalcohols serve as a (co)solvent.     

Clay‐supported 2‐phenyl‐1H‐imidazole derivatives for heterogeneous catalysis of Henry reaction

Six derivatives ( 1 , 2 , 3 , 4 , 5 , 6 ) of 2‐phenyl‐1H‐imidazole were tested as catalysts of Henry reaction. Three new ( 4 , 5 , 6 ) 2‐phenyl‐1H‐imidazole derivatives, differently substituted (thio)ureas, were synthesized and determined by ¹H NMR and IR spectroscopy and elemental analysis. Two types of catalysis, homogeneous and heterogeneous, were examined and compared. Clay minerals Ca‐MMT and Cu‐MMT were used as solid supports for heterogeneous catalysis. The best results were obtained using compound 2 under conditions of heterogeneous method D from the point of view of yield and reaction time. J. Heterocyclic Chem., (2011)     

Charge‐assisted hydrogen bonding in salts of 2‐amino‐1H‐benzimidazole with 3‐phenylpropynoic acid and oct‐2‐ynoic acid

The 100 K structures of two salts, namely 2‐amino‐1H‐benzimidazolium 3‐phenylpropynoate, C₇H₈N₃⁺·C₉H₅O₂⁻, (I), and 2‐amino‐1H‐benzimidazolium oct‐2‐ynoate, C₇H₈N₃⁺·C₈H₁₁O₂⁻, (II), both have monoclinic symmetry (space group P2₁/c) and display N—H...O hydrogen bonding. Both structures show packing with corrugated sheets of hydrogen‐bonded molecules lying parallel to the [001] direction. Two hydrogen‐bonded ring motifs can be identified and described with graph sets R²₂(8) and R⁴₄(16), respectively, in both (I) and (II). Computational chemistry calculations performed on both compounds show that the hydrogen‐bonded ion pairs are more energetically favourable in the crystal structure than their hydrogen–bonded neutral molecule counterparts.     

Synthesis and Spectrokinetic Studies of a New Family of Photochromic 2H‐Chromenes (=2H‐1‐Benzopyrans): Dimethyl 6‐Aryl‐2,2‐dimethyl‐2H‐chromene‐7,8‐dicarboxylates

A series of dimethyl 6‐aryl‐2,2‐dimethyl‐2H‐chromene‐7,8‐dicarboxylates were synthesized, and the photochromic properties of this new family of dimethyl‐2H‐chromenes were studied under continuous irradiation. The presence of the methoxycarbonyl groups was shown to stabilize the colored forms. This stabilization depended on the solvent, and in two cases the formation of long‐lived opened forms was observed. Under irradiation with a mercury lamp, this family of 2H‐chromenes showed a strong resistance to photodegradation.     

NH2SO3H–SiO2 as a new water‐compatible,recyclable heterogeneous catalyst for the synthesis of novel (α,β‐unsaturated) β‐amino ketones via aza‐Michael reaction

NH₂SO₃H–SiO₂/water as a novel catalytic system was used for the synthesis of (α,β‐unsaturated) β‐amino ketones via aza‐Michael reaction at reflux conditions. The methodology was of general applicability and the catalyst exhibited activity up to five cycles. The catalyst was characterized for the first time using FT‐IR, X‐ray diffraction and scanning electron microscopic–energy dispersion analytical X‐ray. The stability of the catalyst was evaluated by differential scanning calorimetry and TGA/differential thermal analysis. High efficiency of the catalyst along with its recycling ability and the rather low loading demonstrated in reactions are the merits of the presented protocol. Copyright © 2013 John Wiley & Sons, Ltd.     

N—H⋯π hydrogen bonding in 2‐amino­fluorene

The amino group of the title compound, C₁₃H₁₁N, does not form N—H?N hydrogen bonds, but is engaged only in weaker N—H?Ph and C—H?N interactions. An aromatic ring acts as a double hydrogen‐bond acceptor, leading to an infinite H—N—H?Ph?H—N—H?Ph array.