Energy Elasticity of Tie Molecules in Semicrystalline Polymers

Elastic response of the disordered phase between crystal lamellae in semicrystalline polymers is modelled on the assumption that the stress is transferred by bridging (tie) molecules. The deformation characteristics of short poly(methylene) (PM) bridges were computed by using two methods: (a) the single‐molecule loading by molecular mechanics (MM) calculations and (b) the chain‐ensemble averaging by lattice simulations. The energy elastic functions ensuing from both methods differ considerably. In MM the loading of chains containing numerous gauche defects by an external force F yields the sawtooth‐like profile of the force (F)–length (R) functions brought about by the stress‐induced gauche–trans conformational transitions. The Young's moduli E of PM chains containing several gauche defects can be less than 1% of the all‐trans value E_T; by elimination of the defects the moduli steeply increase. In contrast, the ensemble‐averaging approach gives a smooth increase of the (positive) elastic force f with chain length R and a decrease of the (negative) energy component of the elastic force f_U with R. Both energy deformation mechanisms, single‐chain loading (by F) and statistical (by f_U), are complementary and can simultaneously be operative in the interlamellar (IL) phase. Their proportion in the stretching process should depend on the chain mobility and structural homogeneity (history) of the sample, particularly on the presence of the so‐called rigid amorphous fraction in the IL phase.     

Energetics of Stretching of Conformational Defects in Extended Poly(methylene) Chains

The deformation energetics of highly extended poly(methylene) segments with conformational defects of the kink and jog types, is investigated by molecular mechanics calculations. The deformation potential displays abrupt discontinuities as a result of sudden gauche‐to‐trans conformational transitions accompanied by a release of the elastic energy stored in all valence parameters. By stretching, the chain defects are sequentially annihilated, with the weakest elements interconverting first. Due to sudden drops in force the calculated force–length curves F(R) display a sawtooth‐like profile. The force jumps define a maximum load F_c that defect chains can bear prior to conformational “yielding”. The F_c in the range about 0.7–1.1 nN is found in highly extended multikink chains. The results suggest that the sawtooth‐like profile can be a common feature of mechanochemistry of bridging polymers with the restricted number of available conformations. A similar pattern of F(R) curves were previously observed at stretching and sequential unfolding of compact structural domains in biomacromolecules. Further, the calculations predict a distinct reduction of the longitudinal Young's modulus E with increasing concentration of kinks in molecules.     

Dielectric relaxation analysis of starch oligomers and polymers with respect to their chain length

Starch belongs to the polyglucan group. This type of polysaccharide shows a broad β-relaxation process in dielectric spectra at low temperatures, which has its molecular origin in orientational motions of sugar rings via glucosidic linkages. This chain dynamic was investigated for α(1,4)-linked starch oligomers with well-defined chain lengths of 2, 3, 4, 6, and 7 anhydroglucose units (AGUs) and for α(1,4)-polyglucans with average degrees of polymerization of 5, 10, 56, 70, and so forth (up to 3000; calculated from the mean molecular weight). The activation energy (E_a) of the segmental chain motion was lowest for dimeric maltose (E_a = 49.4 ± 1.3 kJ/mol), and this was followed by passage through a maximum at a degree of polymerization of 6 (E_a = 60.8 ± 1.8 kJ/mol). Subsequently, E_a leveled off at a value of about 52 ± 1.5 kJ/mol for chains containing more than 100 repeating units. The results were compared with the values of cellulose-like oligomers and polymers bearing a β(1,4)-linkage. Interestingly, the shape of the E_a dependency on the chain length of the molecules was qualitatively the same for both systems, whereas quantitatively the starch-like substances generally showed higher E_a values. Additionally, and for comparison, three cyclodextrins were measured by dielectric relaxation spectroscopy. The ringlike molecules, with 6, 7, and 8 α(1,4)-linked AGUs, showed moderately different types of dielectric spectra. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 188–197, 2004     

Synthesis and characterization of new sulfone‐derivatized phenylenevinylene‐based conjugated copolymers with evolving energy levels and gaps

A new series of stable, processable, and chain end functionalizable sulfone‐derivatized phenylenevinylene‐based conjugated polymers (SFPVs) containing different donor type comonomers have been synthesized and characterized. The polymer main chains are consisted of a sulfone‐phenylene electron accepting unit coupled with an electron donating unit which is derived from one of the dialdehyde comonomers based on benzene, thiophene, and pyrrole (with or without alkoxy side chains). The optical energy gaps (E_g) of the new polymers (in solvent) are in a range of 1.9–2.3 eV, with the lowest energy gap obtained from the polymer containing pyrrole as the donor unit. By using a combination of strong donor unit (such as pyrrole) and a relatively weak but stable acceptor unit (sulfone‐substituted benzene), E_g of the conjugated polymers can be tailored to below 2 eV, while the vinylene bonds on the polymer main chain are still chemically stable to survive strong basic conditions as compared with the S,S‐dioxo‐thiophene‐based PTV polymers developed earlier for potential supra‐molecular block copolymer systems. The lowest energy gap P(Pyrrole‐SFPV) exhibited 10 times better photoelectric power conversion efficiency than P(TV‐SFPV). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

4‐Styrylquinolines from cyclocondensation reactions between (2‐aminophenyl)chalcones and 1,3‐diketones: crystal structures and regiochemistry

Structures are reported for two matched sets of substituted 4‐styrylquinolines which were prepared by the formation of the heterocyclic ring in cyclocondensation reactions between 1‐(2‐aminophenyl)‐3‐arylprop‐2‐en‐1‐ones with 1,3‐dicarbonyl compounds. (E)‐3‐Acetyl‐4‐[2‐(4‐methoxyphenyl)ethenyl]‐2‐methylquinoline, C₂₁H₁₉NO₂, (I), (E)‐3‐acetyl‐4‐[2‐(4‐bromophenyl)ethenyl]‐2‐methylquinoline, C₂₀H₁₆BrNO, (II), and (E)‐3‐acetyl‐2‐methyl‐4‐{2‐[4‐(trifluoromethyl)phenyl]ethenyl}quinoline, C₂₁H₁₆F₃NO, (III), are isomorphous and in each structure the molecules are linked by a single C—H…O hydrogen bond to form C(6) chains. In (I), but not in (II) or (III), this is augmented by a C—H…π(arene) hydrogen bond to form a chain of rings; hence, (I)–(III) are not strictly isostructural. By contrast with (I)–(III), no two of ethyl (E)‐4‐[2‐(4‐methoxyphenyl)ethenyl]‐2‐methylquinoline‐3‐carboxylate, C₂₂H₂₁NO₃, (IV), ethyl (E)‐4‐[2‐(4‐bromophenyl)ethenyl]‐2‐methylquinoline‐3‐carboxylate, C₂₁H₁₈BrNO₂, (V), and ethyl (E)‐2‐methyl‐4‐{2‐[4‐(trifluoromethyl)phenyl]ethenyl}quinoline‐3‐carboxylate, C₂₂H₁₈F₃NO₂, (VI), are isomorphous. The molecules of (IV) are linked by a single C—H…O hydrogen bond to form C(13) chains, but cyclic centrosymmetric dimers are formed in both (V) and (VI). The dimer in (V) contains a C—H…π(pyridyl) hydrogen bond, while that in (VI) contains two independent C—H…O hydrogen bonds. Comparisons are made with some related structures, and both the regiochemistry and the mechanism of the heterocyclic ring formation are discussed.     

Synthesis,crystal structures and anti‐inflammatory activity of four 3,5‐bis(arylidene)‐N‐benzenesulfonyl‐4‐piperidone derivatives

3,5‐Bis(arylidene)‐4‐piperidone (BAP) derivatives display good antitumour and anti‐inflammatory activities because of their double α,β‐unsaturated ketone structural characteristics. If N‐benzenesulfonyl substituents are introduced into BAPs, the configuration of the BAPs would change significantly and their anti‐inflammatory activities should improve. Four N‐benzenesulfonyl BAPs, namely (3E,5E)‐1‐(4‐methylbenzenesulfonyl)‐3,5‐bis[4‐(trifluoromethyl)benzylidene]piperidin‐4‐one dichloromethane monosolvate, C₂₈H₂₁F₆NO₃S·CH₂Cl₂, ( 4 ), (3E,5E)‐1‐(4‐fluorobenzenesulfonyl)‐3,5‐bis[4‐(trifluoromethyl)benzylidene]piperidin‐4‐one, C₂₇H₁₈F₇NO₃S, ( 5 ), (3E,5E)‐1‐(4‐nitrobenzenesulfonyl)‐3,5‐bis[4‐(trifluoromethyl)benzylidene]piperidin‐4‐one, C₂₇H₁₈F₆N₂O₅S, ( 6 ), and (3E,5E)‐1‐(4‐cyanobenzenesulfonyl)‐3,5‐bis[4‐(trifluoromethyl)benzylidene]piperidin‐4‐one dichloromethane monosolvate, C₂₈H₁₈F₆N₂O₃S·CH₂Cl₂, ( 7 ), were prepared by Claisen–Schmidt condensation and N‐sulfonylation. They were characterized by NMR, FT–IR and HRMS (high resolution mass spectrometry). Single‐crystal structure analysis reveals that the two 4‐(trifluoromethyl)phenyl rings on both sides of the piperidone ring in ( 4 )–( 7 ) adopt an E stereochemistry of the olefinic double bonds. Molecules of both ( 4 ) and ( 6 ) are connected by hydrogen bonds into one‐dimensional chains. In ( 5 ) and ( 7 ), pairs of adjacent molecules embrace through intermolecular hydrogen bonds to form a bimolecular combination, which are further extended into a two‐dimensional sheet. The anti‐inflammatory activity data reveal that ( 4 )–( 7 ) significantly inhibit LPS‐induced interleukin (IL‐6) and tumour necrosis factor (TNF‐α) secretion. Most importantly, ( 6 ) and ( 7 ), with strong electron‐withdrawing substituents, display more potential inhibitory effects than ( 4 ) and ( 5 ).     

Magnitude and origin of the attraction and directionality of the halogen bonds of the complexes of C6F5X and C6H5X (X = I, Br, Cl and F) with pyridine

The geometries and interaction energies of complexes of pyridine with C₆F₅X, C₆H₅X (X=I, Br, Cl, F and H) and R_FI (R_F=CF₃, C₂F₅ and C₃F₇) have been studied by ab initio molecular orbital calculations. The CCSD(T) interaction energies (E_int) for the C₆F₅X–pyridine (X=I, Br, Cl, F and H) complexes at the basis set limit were estimated to be ?5.59, ?4.06, ?2.78, ?0.19 and ?4.37 kcal mol^?1, respectively, whereas the E_int values for the C₆H₅X–pyridine (X=I, Br, Cl and H) complexes were estimated to be ?3.27, ?2.17, ?1.23 and ?1.78 kcal mol^?1, respectively. Electrostatic interactions are the cause of the halogen dependence of the interaction energies and the enhancement of the attraction by the fluorine atoms in C₆F₅X. The values of E_int estimated for the R_FI–pyridine (R_F=CF₃, C₂F₅ and C₃F₇) complexes (?5.14, ?5.38 and ?5.44 kcal mol^?1, respectively) are close to that for the C₆F₅I–pyridine complex. Electrostatic interactions are the major source of the attraction in the strong halogen bond although induction and dispersion interactions also contribute to the attraction. Short‐range (charge‐transfer) interactions do not contribute significantly to the attraction. The magnitude of the directionality of the halogen bond correlates with the magnitude of the attraction. Electrostatic interactions are mainly responsible for the directionality of the halogen bond. The directionality of halogen bonds involving iodine and bromine is high, whereas that of chlorine is low and that of fluorine is negligible. The directionality of the halogen bonds in the C₆F₅I– and C₂F₅I–pyridine complexes is higher than that in the hydrogen bonds in the water dimer and water–formaldehyde complex. The calculations suggest that the C? I and C? Br halogen bonds play an important role in controlling the structures of molecular assemblies, that the C? Cl bonds play a less important role and that C? F bonds have a negligible impact.     

Distribution of chain defects and microstructures of melt crystallized polyethylene. II. Influence of defect size and of plastic deformation

Unit cell expansion data for (a) melt-crystallized polyethylene (PE) containing known amounts of methyl, ethyl, and butyl branches and for (b) plastically deformed samples, are examined in the light of a model which takes into account the penetration of constitutional defects (branches) at interstitial crystal sites by means of a generation of 2g1 step chain defects (kink isomers). The present analysis complements previous results obtained for melt-crystallized PE samples with a widely varying number concentration ? of butyl or longer branches. An estimation of the concentration of chain defects incorporated into the crystal lattice is carried out. The results reveal that the fraction χ_c of defects which are accomodated within the lattice depends on both the amount and size of the chain defects and on the mechanical deformation of the sample. For PE chains with methyl and ethyl groups, χ_c ≈ 50%, whereas for butyl and longer branches, χ_c does not exceed 20% of the total concentration of defects. In addition, after cold drawing, PE with low amounts (? < 1%) of butyl or longer chain branching, χ_c turns out to be zero; i.e., during deformation single molecular chain rearrangements leading to a chain segregation of defects into the amorphous phase must occur.     

The side chain effects on TPD-based copolymers: the linear chain leads to a higher jsc

Abstract

Alkyl substituents appended to polymers play the determining role on self-assembly and film-forming properties, and on device performance. In this work, we highlight the effects of the linear and branched flexible chains appended to the acceptor moiety (A) in D-A type copolymers. Two thieno[3,4-c]-pyrrole-4,6-dione (TPD) based copolymers PT1 and PT2 with different alkyl chains, were designed and synthesized. By comparison their UV-vis absorptions, HOMO/LUMO energy levels, as well as the characters in polymer solar cells, the influences of alkyl chains were investigated. Both copolymers showed molecular weights of 21?kDa and similar optical properties with a medium band gap of 1.93?eV, while PT2 with the branched chain exhibited a lower HOMO than that of PT1 (?5.43 vs???5.37?eV). In bulk heterojunction (BHJ) solar cells, PT1 with a linear chain presented a short circuit current (J_sc) of 6.76?mA cm^?2, open circuit voltage (V_oc) of 0.89?V and power conversion efficiency (PCE) of 2.92%. To the contrary, PT2 showed a J_sc of 3.53?mA cm^?2, V_oc of 0.99?V, delivering a relatively lower PCE of 2.05%. The result indicates that appending a linear alkyl chain to the TPD unit could sufficient enhance the J_sc value of the related polymer.     

Conformational study of the complementary peptide to a B-cell epitope of the La/SSB autoantigen

Starting from the 20-mer peptide 289–308, one of the experimentally characterized B-cell epitopes of the La/SSB autoantigen, the complementary peptide cpl(289–308), encoded by the complementary RNA was designed. The conformational properties of the cpl(289–308) were investigated in DMSO solution with the combined use of NMR data (vicinal coupling constants, NOE effects and temperature coefficient values), molecular modelling calculations of energy minimization and molecular dynamics. MD calculations led to a folded structure in which a βI-turn, stabilized by the H₈ amide proton to the F₅ carbonyl hydrogen bond, was found for the F₅P₆S₇H₈ sequence, whereas two γ-turns, centred around the E₁₅ and I₁₈ residues respectively, were found in the C-terminal part of the peptide. In the whole crown folded structure of the peptide, the Y₄, F₅, H₈, F₉ and F₁₀ aromatic side chains are situated on one side with the E₁₃, E₁₅, T₁₇ and C₂₀ side chains on the other. This 3D structure resembles and could mimic the binding site of an antibody.     

Bond length features of linear carbon chains of finite to infinite size: Visual interpretation from Pauling bond orders

Schemes for Kekulé structure counting of linear carbon chains are suggested. Mathematical formulas, which calculate the Pauling bond order P(k, N) of a chemical bond numbered by k, are given for the carbon chain with N carbon atoms. By use of the least‐squares fitting of a linearity, relationships between Pauling bond orders and bond lengths are obtained, and such correlation of the Pauling bond order–bond length can be qualitatively extended to the excited states. The relative magnitudes of Pauling bond orders in unsaturated carbon chains dominate C–C bond lengths a well as the bond length feature with the chain size increasing. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 144–149, 2003     

On the energy difference between the lP and 3P states of the beryllium isoelectronic sequence

Wave functions of the ¹S (ground state), ³P and ¹P states for the beryllium isoelectronic sequence have been obtained in various approximations. The HF ²p orbitals for the ¹P and ³P states are similar except for Be, where the ²p orbital is quite diffuse for the ¹P state. The difference between the experimental E(¹P) – E(³P) and the HF E(¹P) – E(³P) is 0.62 eV for Be and 1.17 ～ 1.40 eV for B⁺ ～ F⁵⁺. The disagreements are attributed to the correlation effects between the 2s and 2p electrons. This is confirmed by ci calculations. It is shown that a limited basis SCF calculation reproduces the above feature of the HF results if we treat the orbital exponents as the variational parameters. The use of the Slater values for the orbital exponents is shown to be inadequate especially for the Be ¹P state. The conclusions of this paper will be useful for discussing the V–T separations of H₂ and C₂H₄.     

Driven Chain Macromolecule in a Heterogeneous Membrane-Like Medium

Monte Carlo simulations are performed to study the conformational relaxation of a large polymer chain driven into a heterogeneous (membranelike) substrate on a discrete lattice. Chains are created on trails of constrained self-avoiding walks (SAW) on the lattice. Kink–jump, crank–shaft, and reptation moves are used to move segments of chains. Short chains of length L _sc are driven by a field E ₁ toward an impenetrable substrate to design a membrane medium with mobile chain segments. A long chain of length L _lc is then driven by a field E ₂ into the membrane medium and is subsequently allowed to relax in a field E ₃. Radius of gyration R _g and end-to-end distance R _e of the long chain are examined. The relaxation of the conformation of the long chain and its magnitude is found to depend on the initial (predeposition) conformation of the chain, i.e., on E ₂. For a relatively relaxed initial conformation (at E ₂ = 0.1), the longitudinal component of the radius of gyration (R _gz ) is found to decay with the driving field E ₃ with a power law, R _gz E ₃ where 0.1 at low field (E ₃ 0.1) and 1/3 at high field E ₃ 0.1.     

Synthesis and characterization of fluorinated telomers containing vinylidene fluoride and hexafluoropropene from 1,6‐diiodoperfluorohexane

The synthesis of original fluorinated (co)telomers containing vinylidene fluoride (VDF) or VDF and hexafluoropropene (HFP) was achieved by radical telomerizations and (co)telomerizations of VDF (or VDF and HFP) in the presence of 1, 6‐diiodoperfluorohexane via a semisuspension process. tert‐Butyl peroxypivalate (TBPPi) was used as an efficient thermal initiator. The numbers of VDF and VDF/HFP base units in the (co)telomers were determined by ¹⁹F and ¹H NMR spectroscopy. They ranged from 10 to 190 VDF base units. Fluorinated telomers of various molecular weights (1200–12,600 g/mol) were obtained by the alteration of the initial [1,6‐diiodoperfluorohexane]₀/[fluoroalkenes]₀ and [TBPPi]₀/[fluoroalkenes]₀ molar ratios. The thermal properties of these fluorinated (co)telomers, such as the glass‐transition temperature and melting temperature, were examined. As expected, these telomers exhibited good thermal stability. They were stable at least up to 350 °C. The compounds containing more than 30 VDF units were crystalline, whereas all those containing VDF‐co‐HFP were amorphous with elastomeric properties, whatever the number was of the fluorinated base units. The structures of I–(VDF)_n–R_F–(VDF)_m–I and I–(HFP)_x(VDF)_n–R_F–(VDF)_m(HFP)_y–I (co)telomers were obtained, and the defects of the VDF chain and the ? CH₂CF₂I and ? CF₂CH₂I functionalities were studied successfully (where R_F = C₆F₁₂). The functionality in the iodine atoms was modified: the higher the VDF content in the telomers, the lower the normal end functionality (? CH₂CF₂I) and the higher the reversed extremity (? CF₂CH₂I). In addition, the percentage of defects increased when the number of VDF units increased. The molecular weights and molecular weight distributions of different telomers and cotelomers were also studied. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1470–1485, 2006     

Molecular orbital studies of polyethylene deformation

Young's modulus E for polyethylene in the chain direction is calculated with molecular orbital theory applied to n-alkanes C₃H₈ through n-C₁₃H₂₈ and analyzed with the cluster-difference method. Semiempirical CNDO, MNDO, and AM1 models and ab initio HF/STO-3G, HF/6-31G, HF/6-31G*, and MP2/6-31G* models are used. Cluster-difference results, when extrapolated to infinite chain length, give E in good agreement with moduli evaluated with molecular cluster or crystal orbital methods, provided minimal basis sets are employed. E decreases from 495 GPa (CNDO) to 336 GPa (MP2/6-31G*) as the level of theory is improved, consistent with established behaviors of the various models. Our calculations do not reproduce earlier molecular cluster or crystal orbital results, which gave E < 330 GPa. The most rigorous MP2/6-31G* model is known to overestimate force constants by ∼ 11%; the scaled modulus E = 299 GPa is in good accord with E = 306 GPa from recent calculations based on experimental vibration frequencies. © 1996 John Wiley & Sons, Inc.     

Study on the chain conformation of polymers.: II. Conformational characteristics of 1,2-polybutadiene and its characteristic ratio

In this work, improvement was made for conformational analysis of 1,2-polybutadiene by means of the molecular mechanics force field program (MM2). Thus the first and the second order interaction energies obtained are much more reasonable. The characteristic ratio of isotactic 1,2-polybutadiene was emphasized properly, which varied with energy E (E = E_η + E_ω″). In the same time, the characteristic ratios for isotactic chain of polystyrene and so on were noticed, which varied with energy E according to the same way as that for isotactic 1,2-polybutadiene. It is shown that there is a general rule or a common feature for isotactic chains of poly -α-olefine and vinyl polymer.     

Superhydrophobic surfaces with low and high adhesion made from mixed (hydrocarbon and fluorocarbon) 3,4‐propylenedioxythiophene monomers

This work concerns new superhydrophobic surfaces, generated by replacing long fluorocarbon chains, which bioaccumulate, with short chains whilst at the same time retaining oleophobic properties. Here, is described the synthesis of novel 3,4‐propylenedioxythiophene derivatives containing both a short fluorocarbon chain (perfluorobutyl) and a hydrocarbon chain of various lengths (ethyl, butyl and hexyl). Superhydrophobic (θ_water > 150°) surfaces with good oleophobic properties (60° > θ_hexadecane > 80°) have been obtained by electrodeposition using cyclic voltammetry. Surprisingly, the lowest hystereses and sliding angles (Lotus effect) are obtained with the shortest alkyl chains due to the presence of microstructures made of nanofibers on the surfaces, whereas, the longest alkyl chains leads to nanosheets with high adhesion (Petal effect). Such materials are potential candidates for biomedical applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 782–788     

Synthesis,characterization, and properties of polysilaethers containing moiety Si?H bonds in the side chain

A synthetic route to polysilaethers containing moiety Si? H bonds in the side chain (PSEMH) is reported that allows access to hitherto inaccessible oxygen‐interrupt polysilanes. By a Wurtz reductive coupling reaction, an equimolar ratio of dichloromethylsilane to alkali metal yields dichlorodisilane. The alcoholysis of Wurtz coupling resultants is in situ performed, and the polycondensation of hydrolysis occurs simultaneously in the presence of a small amount of N,N‐(dimethylamino)pyridine. The linear polymer is monomodal PSEMH with molecular weights as high as 24,900. The ultraviolet absorption at 292 nm is due to the interactions of the σ_{(Si? Si)} orbital electron delocalization and the p_π(O)–σ*_{π(Si? O)} delocalization along the (SiSiO)_n skeleton. It is redshifted in comparison with those of permethyl polysilaethers analogues and blueshifted in comparison with those of poly(dialkylsilane)s. The fluorescence emissions of the polysilaethers containing moiety Si? H bonds in the side chain are in a narrow range of 300–400 nm. Si? H bonds in polysilaethers play an important role in hydrosilylation reactions. The polysilaethers containing moiety Si? H bonds in the side chains can be used as the starting point for further functionalization via hydrosilylation. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2476–2482, 2005     

F‐bridged Anions of Bromine and Gold: Predictions of Unexpected Behavior

The significant similarity between MF₃, MF₄^–, and M₂F₇^– (M = Au, Br) is studied using quantum chemical methods. It is expected that compounds containing Au₃F₁₀^– anions are likely to be stable. A theoretical background for the ongoing attempts of their synthesis is provided by calculations on the stabilities and molecular structures of various bromine and gold anions with the general composition of M_nF_3n+1^– (n = 1, 2, 3, 4). The anions show unexpected differences and peculiarities in their energetically preferable molecular structures. Different chain‐like structures are predicted as the global minima for the hypothetical Au₃F₁₀^– and Br₄F₁₃^– anions.     

Effect of endgroup modification on dynamic viscoelastic relaxation and motion of hyperbranched poly(ether ketone)s

Fluoro‐terminated hyperbranched poly(ether ketone) (FHPEK) was synthesized and its end groups were modified with alkyl compounds of different chain lengths, i.e., hexyloxy (C6), dodecyloxy (C12), and octadecyloxy, (C18), to produce alkyl‐modified HPEKs (HPEK‐C6, HPEK‐C12, and HPEK‐C18, respectively). Master curves were constructed by using the time‐temperature superposition principle. The horizontal shift factors, a_T, used for the construction of the master curves were fit using the William‐Landel‐Ferry (WLF) equation. From the fitting parameters, the apparent activation energy, E_a, was estimated. With increasing alkyl chain length, the E_a values were found to decrease in the order FHPEK > HPEK‐C6 > HPEK‐C12, and then increase for HPEK‐C18. The average relaxation time, τ_HN, was determined by fitting of the dynamic moduli G′(ω) and G″(ω) to the empirical Havriliak‐Negami equation. Similarly, the τ_HN values decreased in the order of FHPEK > HPEK‐C6 > HPEK‐C12, and then increased for HPEK‐C18. This indicates that the endgroup modification with short alkyl chains (C6, C12) increased the molecular mobility due to the internal plasticization effect of these alkyl chains. Modification with the longer alkyl chain (C18) retarded the molecular motion through an antiplasticization effect caused by summation of nonpolar hydrophobic interactions between long hydrocarbon chains. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2079–2089, 2008