Photoinduced optical anisotropy in azobenzene containing block copolymer–homopolymer blends. Influence of microstructure and molecular weight

Microstructure in two diblock methacrylic azo polymers and in some of their blends with PMMA of different molecular weights as well as their photoinduced anisotropy have been investigated. The block copolymers have similar structure but different azo content and degree of polymerization. A synthetic strategy based on a controlled radical polymerization (ATRP) of polymeric blocks and their coupling by click chemistry has been applied to obtain an azo block copolymer of high molecular weight. Microphase segregation has been observed in the block copolymers and in most of the blends. In blends of the block copolymer with lower degree of polymerization (Block 1) azo microdomains change from lamellar to spherical morphology when the azo content decreases from 24 to 3 wt.%. In the block copolymer with higher degree of polymerization (Block 2) and its blends, down to 3 wt.% azo content, spherical azo microdomains have been found. A decrease of the order parameter (η) and the photoinduced birefringence normalized to the azo content (|Δn|_norm) has been found in blends of Block 1 when the azo content decreases. However, |Δn|_norm and η values similar to those in the azo homopolymer have been observed in Block 2 and its blends. These blends can be used to lower the azo content while keeping a photoinduced response similar to that in the azo homopolymer.     

Role of the molecular weight and the composition on the hydrolysis kinetics of monolayers of poly(α-hydroxy acid)s

The hydrolysis kinetics of spread insoluble monolayers of poly(α-hydroxy acid)s with various molecular weights and lactic acid–glycolic acid molar ratios was followed by measuring simultaneously the decrease in the surface area at constant surface pressure and the evolution of the surface potential. The interfacial hydrolysis at alkaline pH leads to the progressive fragmentation of the polymer molecules and the appearance of charged insoluble products (detected by measuring the surface potential) and small soluble fragments (detected by measuring the decrease in the surface area). The data obtained by both approaches were interpreted in the framework of the random scission model. The rates of hydrolysis are larger for polymers with smaller initial polymerization numbers and increase with the decrease in the molar ratio of lactic acid units. Received: 7 December 1998 Accepted in revised form: 8 March 1999     

Polymerization of p -triethylstannyl-α-methylstyrene

Summary Polymerization of p-triethylstannyl--methylstyrene was studied under 6000 atm pressure in the presence of various initiators. Polymers were isolated and their elemental composition and properties were determined.     

Thermal Decomposition of Poly-α-methylstyrene

Kinetic studies on the decomposition of poly-α-methylstyrene samples with molecular weights ranging from 3.7 × 10³ to to 2.0 × 10⁵ have been carried out with the differential thermo-gravimetric technique. Changes in molecular weight distributions with decomposition, at different temperatures, have been studied by gel-permeation chromatography. A depolymeriza-tion mechanism was shown to be responsible for the decomposition phenomenon. The order of reaction for this depolymerization reaction was found to be one. The values of the activation energy for samples of different molecular weights showed no specific trends; however, it would appear that polymers with relatively higher molecular weights have lower activation energies of decomposition. The proportions of the three steric forms, viz., isotactic, heterotactic, and syndiotactic, in the polymer before and after thermal treatments did not change, suggesting that stereoregularity has no apparent effect on the decomposition of poly-α-methylstyrene.     

MALDI-TOF/TOF CID study of poly(α-methylstyrene) fragmentation reactions

MALDI-TOF/TOF CID experiments are reported for hydroxylated poly(α-methylstyrene) precursor ions (PAMS: m/z 1,445.9 (n = 10), 2,036.3 (n = 15), 2,626.7 (n = 20), 3,217.1 (n = 25), and 3,807.5 (n = 30), where the number of repeat units n corresponds to the oligomer mass numbers). The influences of structure, molecular weight, and kinetic energy on degradation mechanisms were examined to test the generality of our multi-chain fragmentation model developed for polystyrene. Our results indicate that poly(α-methylstyrene) free radicals are formed initially through multiple chain breaks and subsequently undergo a variety of depolymerization reactions to yield predominantly monomer and dimer species; the intensity of each species depends on the effective kinetic energy selected for the CID process. Each depolymerization mechanism is presented in detail with experimental and computational data to justify/rationalize the process and its kinetic energy dependence. These processes show the complex interrelationships between the various pathways along with preferred production of tertiary radicals, which suppresses the appearance of primary radicals. Additionally, Py-GC/MS experimental data are presented to allow a comparison of the multimolecular free radical reactions in pyrolysis with the unimolecular fragmentation reactions of MS/MS. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Structure-propery relationship of low molecular weight ‘liquid’ polymers in blends of sulfur cured SSBR-rich compounds

In recent years, many patents have been published that are claiming the use of low molecular weight ‘liquid’ polymers in tire tread applications. Herein, tire producers generally introduce improved balances of the tire performances such as wet grip, abrasion resistance and rolling resistance. To understand the influence of the low molecular weight ‘liquid’ polymers in detail, an investigation was carried out to create more clarity about the influence of the structure of these polymers on in-rubber properties and about their interaction with the base polymers and fillers. One basic formulation was selected: A silica filled compound with styrene butadiene copolymer (SSBR), polybutadiene (BR) and natural rubber (NR) that is representing a winter tire tread formulation. Different structures of the low molecular weight ‘liquid’ polymer were added to this compound and compared. Results are discussed for the curing torques and crosslink densities to evaluate the influence on the crosslinking. Payne effect and bound rubber content was measured to evaluate the filler-filler interactions and filler-polymer interactions, respectively. The mechanical properties and dynamic mechanical analysis results deliver finally indications for the expected tire performance.     

Influence of chlorosulfonated polyethylene network structure on poly(acrylonitrile-styrene-acrylate)/poly(α-methylstyrene-acrylonitrile) blends: Mechanical properties,morphologies, glass transition behavior and heat resistance

Acrylonitrile-styrene-acrylate terpolymer and poly(α-methylstyrene-acrylonitrile) (ASA/α-MSAN, 25/75) with different loadings of chlorosulfonated polyethylene (CSM) were prepared via melt blending, with goals of toughening modification of ASA/α-MSAN blends and maintaining the heat resistance simultaneously. The results revealed CSM had excellent toughening effect at room temperature. At 0 °C, impact strength increased linearly with CSM content. However, toughening effect of CSM was undesirable at −30 °C. The temperature-dependent toughening efficiency of CSM was significantly related to its glass transition behavior. Scanning electron microscope analysis on cryo-fractured surfaces revealed the toughening mechanism was the formation of CSM toughening network in matrix, which was further confirmed by selective extraction tests. The formation of CSM network could lead to increased glass transition temperature of the blends at the low temperature region according to dynamic mechanical thermal analysis. Different from other toughening agents, CSM network uncompromised the heat resistance of ASA/α-MSAN blends.     

Effects of molecular structure and equivalent weight on facilitated transport of alkenes in Ag(I)–PFSI membranes

Fluxes and separation factors are reported for the facilitated transport of a variety of C₆ alkenes and dienes through two Ag(I)-exchanged polyfluorosulfonate ionomer membranes. For acyclic dienes, the largest separation factors are observed between those compounds with the greatest difference in spacing of the double bonds, and those with completely external versus internal double bonds. For cases where the spacing of the double bonds is the same, the compound with at least one terminal double bond exhibited a higher flux. The trends in fluxes for cyclic dienes is quite different; 1,4-cyclohexadiene is transported more slowly than cyclohexene while 1,3-cyclohexadiene is transported almost eight times more rapidly than cyclohexene. Methyl-substituents on the carbons comprising double bonds have minor effects on the transport properties. As anticipated, PFSI materials that contain more ion-exchange sites and absorb greater quantities of water exhibit slightly greater fluxes and separation factors for most alkene separations.     

The effects of the molecular weight and structure of poly(acrylic acid) on the formation of “blue silver”

Using UV-spectroscopy and transmittance electron microscopy it was shown that the structure of macromolecules and molecular weight of poly(acrylic acid) can significantly affect the synthesis and stabilization of so-called “blue silver.”     

Equilibrium Anionic Polymerization of p-lsopropyl-α-methylstyrene in Tetrahydrofuran

The equilibrium anionic polymerization of p-isopropyl-α-methylstyrene in tetrahydrofuran with potassium and sodium-naphthalene complex as initiators has been investigated in the temperature range of -20 to +20° C by use of high-vacuum techniques. The comparison of these results with those obtained previously for the equilibrium polymerization of α-methyl-styrene revealed that, because of the p- substituted bulkier isopropyl group in the monomer, the values of δG_c, the free-energy change upon the polymerization of 1 mole of liquid monomer to 1 base-mole of liquid amorphous polymer of infinite chain length, are slightly higher in the present studies. The values of ΔH_c and ΔS ^ccomputed from the plots of ΔG_c /RT versus 1/T yielded values which are lower than that for the α-methylstyrene-THF system. The effect of p-substitution is also observed in the higher values of the monomer equilibrium concentration [M] and lower values of β[β = x_ms-x_sp (V_m/V_s)].

where x_ms and x are monomer-solvent and solvent-polymer interaction parameters, respectively, and V_m /V_s is molar volume ratio of monomer to solvent. The values of x_ms for the p-isopropyl-α-methylstyrene-THF system increase regularly with increasing temperature, whereas in α-methylstyrene-THF system the increase in x^ms was not that marked     

Influence of γ-radiation on iodine-doped poly (3-pentylthiophene)

The influence of -radiation on iodinedoped poly (3-pentylthiophene) has been studied. Doping accompanied by -radiation brings about a decrease of iodine release rate. An increased dopant concentration in the poly (3-pentylthiophene) leads to an increased conductivity, which may be accounted for by the formation of bipolarons in the irradiated and doped samples.     

Photoreactions of trans-poly(vinyl cinnamate) and low molecular weight model compounds—Part I

Various cinnamates serving as model compounds for poly(vinyl cinnamate), trans-ethyl (trans-ECi), trans-methyl (trans-MCi), cisethyl (cis-ECi) and trans,trans-1,3-trimethylene dicinnamate (trans,-trans-TMCi) were irradiated at concentrations of 1–5 × 10⁻⁵ mol litre⁻¹ in chlorine-containing solvents (CH₂Cl₂, CCl₄, 1,1,2-trifluorotrichloroethane) and chlorine-free solvents (per-fluoro-2-(n-butyl)-tetrahydrofurane, 1-ethoxy-2-acetoxy-ethane, PMMA). For trans-ECi the quantum yield φ (trans → cis) is higher in chlorine-free solvents (0·40–0·45) than in chlorine-containing solvents (c. 0·26). Fluorescence spectra, recorded with trans-ECi and trans, trans-TMCi possess two peaks at 325 nm and at 375 nm in chlorine-containing solvents and only one peak at 325 nm in chlorine-free solvents. The fluorescence lifetime (slow mode) at 325 nm is 15±5 ns and at 375 nm 25±5 ns. Flash photolysis experiments revealed S₁ → S_n absorption spectra (lifetime 15±5 ns) in all solvents and with all solutes. In chlorine-containing solvents an additional long-lived absorption (lifetime 5–10 μs) was observed.From the results it is concluded that singlet-excited cinnamates form exciplexes of C-T character with the chlorine-containing solvents used in this work. Moreover, the results revealed—in accord with earlier findings—that upon direct excitation, cinnamates undergo chemical changes exclusively via electronically excited singlet states.     

New data on the molecular compounds of stereoisomeric ditertiary glycols of the series 1,4-di-(α-hydroxy-sec-alkyl)-cyclohexanes

Summary 1¹,4¹-Dihydroxy-1¹,4¹-diethyl-1,4-dipropylcyclohexanes, like the previously described 1¹,4¹-dihydroxy-1¹,4¹-dimethyl-1,4-diethylcyclohexanes, give a molecular compound of three molecules of cis- and one molecule of trans-form.     

Polymerization of α-methylstyrene in the solid (frozen) state

Russian Chemical Bulletin -     

Transport property of polyaniline and its molecular weight dependence

Ｔｈｅｅｌｅｃｔｒｉｃａｌｃｏｎｄｕｃｔｉｖｉｔｙ(σ)ｏｆｐｏｌｙａｎｉｌｉｎｅ(ＰＡｎ)ｄｏｐｅｄｗｉｔｈｉｎｏｒｇａｎｉｃｐｒｏｔｏｎｉｃａｃｉｄｓｉｓａｂｏｕｔ10Ｓ/ｃｍａｎｄσ(Ｔ)∝ｅｘｐ[-(Ｔ0/Ｔ)1/2].Ｉｔｍｅａｎｓｔｈａｔσｉｎｃｒｅａｓｅｓｗｉｔｈｉｎｃｒｅａｓｉｎｇｔｅｍｐｅｒａｔｕｒｅａｎｄｔｈｅｔｒａｎｓｐｏｒｔｐｒｏｐｅｒｔｙｉｓｉｎａｃｃｏｒｄａｎｃｅｗｉｔｈｔｈｅｖａｒｉａｂｌｅｒａｎｇｅｈｏｐｐｉｎｇ(ＶＲＨ)ｍｏｄｅｌ[1].Ａｆｔｅｒｓｔｒｅｔｃｈｉｎｇ,ｔｈｅＨＣｌｄｏｐ…     

Polyacrylonitrile molecular weight effect on the structural and magnetic properties of metal–carbon nanomaterial

1. Download high-res image (259KB)
2. Download full-size image

     

Influence of solvent polarity on the separation of leucine enantiomers by β-cyclodextrin: a molecular mechanics and dynamics simulation

The interaction between leucine and β-cyclodextrin with different solvents was studied by molecular mechanics and dynamics simulations. In order to analyse the influence of the solvent polarity on the inclusion complex formation and separation process of leucine enantiomers by β-cyclodextrin, the organic modifiers were characterised by the same value of dielectric constant in the electrostatic contribution to the interaction energy, and a different molecular configuration of amino acids (neutral or zwitterion). The complexes formed in polar solvents were more stable than those in non-polar solvents with the same dielectric constant, because the electrostatic contribution is negative for the former and positive for the latter. The optimized structures obtained for leucine enantiomers and β-cyclodextrin in vacuo are non-inclusion complexes. The solvent polarity contributes to increasing the probability of the presence in an inner position for the guest, whereas the results for non-polar configurations were smaller and distributed in larger areas. The regions where the enantiomers spend more time in the simulation correspond to locations with greater chiral discrimination. d-Leu was the first eluted enantiomer in every case, except for a polar solvent with $\epsilon =26$.     

Influence of γ-radiation on the properties of Langmuir-Blodgett layers of poly (3-hexadecylthiophene)

The influence of -radiation on the structure of Langmuir-Blodgett (LB) layers of poly (3-hexadecylthiophene) in mixtures containing stearic and linolenic acids has been studied. The action of -photons leads to structural changes in the conducting polymer backbone as well as to disrupting oriented LB film structures.     

Study on molecular weight cut-off performance of asymmetric aromatic polyimide membrane “Effect of the additive agents”

Asymmetric polyimide membranes were fabricated from casting solution of 18 wt% polyamic acid and 1.3–20 wt% additive agent in dimethylacetamide at 343 K, with 1 min evaporation time, followed by a cyclization process of thermal treatment in a bath of dioctyl sebacate under N₂ in three steps: 1 h at 373 K, 1 h at 473 K, 1 h at 573 K. The effect of additive agents and their quantity on the molecular weight cut-off (MWCO) performance of the asymmetric aromatic polyimide membrane were examined. By changing a sort of additive agents, the MWCO of the fabricated aromatic polyimide asymmetric membranes can be adjusted in the range of 400–650 daltons. By changing amount of additive agents, MWCO of the fabricated aromatic polyimide asymmetric membranes remain almost constant at the value of approximately 400 daltons for pyrene, and increased from 500–650 daltons for polystyrene.     

Influence of the counteranion on silver(I)–dithioether coordination polymers

In order to rationalize the effect of the size and coordinating ability of counteranions upon the structure of Ag(I)–dithioether coordination polymers, a series of such polymers has been synthesized by the combination of the 1,3-bis(methylthio)propane building block and AgX silver salts (X = ClO₄⁻ (1), BF₄⁻ (2), CF₃SO₃⁻ (3), SbF₆⁻ (4), C₆H₅COO⁻ (5), CF₃COO⁻ (6), CF₃CF₂CF₂COO⁻ (7) and ⁻OOCCF₂CF₂COO⁻ (8)). Except in two cases, all complexes form 1D-coordination polymers.