Chemiluminescence and transfer of energy in polymers

Russian Chemical Bulletin -     

The direct fluorination of hydrocarbon polymers

A new technique for direct fluorination has been used to prepare several new fluorocarbon polymers. The direct fluorination of poly-p-xylylene, polyisobutylene, Novolac and a highly crosslinked phenolic resin has produced fluorocarbon polymers which bear a strong structural resemblance to their hydrocarbon polymer precursors, though some crosslinking may occur. The thermal properties of these polymers have been investigated by DSC and TGA techniques.     

Radiation-induced dielectric loss in hydrocarbon polymers

The dielectric loss of several cables insulated with hydrocarbon polymers has been measured over the frequency range of 10^?3–10⁴ Hz at 50° after being subjected to neutron doeses of up to 65 Mrad. The loss data show that a new loss process appears upon irradiation and that the frequencies associated with this loss are not those that are characteristic of those found for the unirradiated polymaric relaxations, ruling out main-chain motions. This loss seems to be related to dose and is probably due to local dipoles that are formed by the irradiation. It is also shown that the dominant behavior is not due to simple ionic conductivity. © 1993 John Wiley & Sons, Inc.     

Control of organoclay structure in hydrocarbon polymers

Two different kinds of organoclays were prepared by mixing a pristine montmorillonite and a double‐chain ammonium salt in many different thermoplastic or elastomeric polymers. Independently of the chemical nature of the considered polymers, the obtained organoclays presented a basal spacing of 4 or 6 nm, when the mixing occurred in the absence or in the presence of a small amount of stearic acid (SA), respectively. X‐ray diffraction and Fourier transform infrared measurements support the hypothesis that these two kinds of organoclays correspond to paraffin‐type tilted and perpendicular bi‐layer intercalates, respectively. The co‐intercalation of SA molecules with the double‐chain amphiphile is suggested, to explain the observed expansion of the clay interlayer distance. The obtained results suggest an easy way to control the organoclay structure in polymer composites. Moreover, the authors on the basis of these results propose a criticism to the extensive literature that systematically explains most d basal spacing increase observed for clays in polymer with the penetration of apolar polymer chains in the clay interlayer space. Copyright © 2010 John Wiley & Sons, Ltd.     

Photorearrangements of hydrocarbon polymers with pendant double bonds

A study was made of the microstructural changes that occur in ultraviolet irradiation under vacuum of thin films of 1,2-poly(cis-1,4-hexadiene) (CHD), 1,2-poly(trans-1,4-hexadiene) (THD), 1,2-poly(trans-1,3-pentadiene) (TPD), equibinary (1,2,-1,4) polybutadiene (EB), and equibinary (3,4-1,4) polyisoprene (EI). These polymers—all containing pendant double bonds—undergo important photoinduced loss of unsaturation, presumably through cyclization of the double bonds, by analogy to the previously reported photocyclization of 1,2-polybutadiene (VB) and 3,4-polyisoprene (VI)films. For the equibinary polymers, which contain internal as well as external (or pendant) double bonds, the loss of unsaturation is considered to involve photocyclization of 1,2-1,4 and 1,2-1,2 dyads in EB and of 3,4-1,4 and 3,4-3,4 dyads in EI. Accompanying thecyclization process in CHD, THD, and TPD is a direct photochemical cis-trans isomerization of ? CH?CH? double bonds analogous to that originally noted for 1,4-polybutadiene. The photorearrangements in the above polymers with pendant double bonds were compared to the corresponding thermally induced rearrangements reported previoulsy;for VB and VI, in particular, the thermal, photo-and radiation-induced cycli-zations were found to be very similar, possibly having a common nonradical, nonionic mechanism involving excited double bonds.     

On the spin gaps of conjugated hydrocarbon polymers

Many of the (ideal) infinite conjugated hydrocarbon polymers do not present a gap at the Fermi level in tight-binding calculations. However, due to the bielectronic interaction the excitation energy from the ground state to the lowest triplet state may be nonzero for some lattices (called spin gapped), while other lattices will keep a singlet-triplet degeneracy (spin-gapless lattices). This difference results in qualitative differences in their magnetic properties. Making use of the relevance of Heisenberg Hamiltonians for the study of the lowest states of conjugated hydrocarbons, this paper presents some qualitative arguments to predict the spin-gap character of various classes of such polymers. The arguments are based on real space renormalization group procedures, which considers fragments of the polymers as effective spins. Numerical evaluations, based on a renormalized excitonic method, confirm the qualitative predictions.     

Dielectric absorption in hydrocarbon polymers with non-polar additives

Polypropylene films containing various non-polar additives including CCl₄, tetramethylsilane and CS₂ (99.9 or 99.8%) exhibit weak dielectric absorption at the temperatures where molecular tumbling motions are expected on the relevant timescale. The absorption possibly corresponds to rotational jumps of up to 90° between inequivalent orientations of the additive molecules as has been suggested for ammonium in alums.     

Mechanism of alternating copolymerization of polar and hydrocarbon polymers

Radical copolymerization of butyl methacrylate with 2,3-dimethylbutadiene in the presence of Al(C₂H₅)₂Cl or ZnCl₂ results in alternating copolymers. The nature of active centers and the mechanism of polymerization in these systems have been studied by means of ESR measurements in combination with calorimetry at low temperatures. The active centers are monoradicals propagating by alternative addition of single monomer molecules; thus the reaction can be described in terms of a conventional kinetic scheme of radical additional polymerization. Participation of binary donor—acceptor complexes of the monomers in the reaction has not been confirmed. Similar conclusions have been drawn for the other alternating system studied, maleic anhydride–2,3-dimethylbutadiene. The feasibility of formation of alternating copolymers in the studied systems by the conventional mechanism of binary radical copolymerization has been confirmed by qualitative quantum-chemical treatment of the propagation reactions with due account to the donor–acceptor interactions in the transition state.     

Synthesis of polymers having alternating siloxane and hydrocarbon units

Summary The hydrolysis of dichloro compounds in which the chlorine atoms were attached to terminal silicon atoms in chain compounds gave both liquid and solid organosilicon polymers in which hydrocarbon or sila-hydrocarbon units alternated with siloxane units.     

Application of tandem analyser to SIMS studies of hydrocarbon polymers

The fragmentation of ions sputtered from the surface of low-density poly(ethylene) (LDPE) has been investigated by studying their collisionally activated dissociation (CAD) when incident upon a variety of target gases in the collision cell of a triple quadrupole SIMS instrument. It was found that heavier targets resulted in more extensive CAD than was observed with lighter targets but that sulphur hexafluoride is inefficient target because of the amount opf energy that is transferred to its vibrational modes of motion (rather than being available to induce fragmentation in the parent ion.) The behaviour observed for an oxygen target was quite different to that observed for other targets (at higher pressures). In general oxygen induced markedly greater fragmentation for the small parent ions but xenon was the preferred target for the larger parent ions. Fragmentation patterns could readily be assembled for all of the parent ions observed in the SIMS spectrum of LDPE using the CAD data. There are good indications that the data obtained may assist in indentification of ion structures and in elucidation of general rules governing the fragmentation of organic materials during SIMS. For example, LDPE fragment ions were found to obey quite strictly the Even Electron Rule, a well-known rule in mass spectrometry.     

Formation of clay intercalates with organic bilayers in hydrocarbon polymers

The formation of clay intercalates with three different kinds of organic ammonium salts, when mixed in the presence of synthetic or natural polyisoprene rubber, has been investigated. X‐ray diffraction and transmission electron microscopy (TEM) experiments have shown that intercalates with organic bilayers, rather than with interdigitated organic monolayers, are obtained only for the ammonium salts presenting two long alkyl chains and only in the presence of the natural rubber (NR). These results have been qualitatively rationalized on the basis of suitable interlayer densities. Both monolayer and bilayer clay intercalates remain stable for short‐term heating procedures at temperatures lower than 250°C. For treatments at higher temperatures, where the decomposition of the organic ammonium salt occurs, both kinds of clay intercalates maintain intralayer crystalline order. However, the decomposition of the organic modifier leads to the formation of pristine and exfoliated clay for the intercalates with organic monolayers and bilayers, respectively. Copyright © 2008 John Wiley & Sons, Ltd.     

Analysis of hydrocarbon polymers by matrix-assisted laser desorption / ionization-fourier transform mass spectrometry

A quick and effective sample preparation is demonstrated for matrix-assisted laser desorption/ionization (MALDI) analysis of nonpolar polymers. Polyisoprene, polystyrene, and polybutadiene polymers were investigated by using as matrix a 2,5-dihydroxybenzoic acid and silver nitrate combination. Silver cationized oligomers produce useful spectra that can be signal averaged to characterize polymer distributions extending up to 6000 u by using a 3-T Fourier transform mass spectrometer. Because an electrostatic ion deceleration protocol was used to extend the mass range, trapping discrimination is shown to exist for molecular weight distributions broader than about 2500 u. However, an integral procedure can be used to reconstruct the true polymer profiles through co-addition of signal transients obtained by using various gated deceleration times. For polymers with narrower mass distributions, silver cationization along with signal averaging provides rapid and accurate polymer characterization for nonpolar polymer systems by using standard MALDI Fourier transform mass spectrometry instrumentation.     

A comparative study of the silent discharge treatment of saturated and unsaturated hydrocarbon polymers

Dielectric barrier air discharge treatment of polyethylene, polypropylene, polyisobutylene, polystyrene, and polyisoprene substrates has been characterized by x-ray photoelectron spectroscopy (XPS). The relative reactivities of these polymers towards silent discharge oxidation are rationalized in terms of ozone molecules interacting with an excited surface. © 1994 John Wiley & Sons, Inc.     

Synthesis of hydrocarbon polymers containing bulky dibenzobicyclic moiety by ROMP and their characteristic optical properties

The eight‐membered cyclic monomer, prepared by Diels–Alder reaction of 1,5‐cyclooctadiene and anthracene, polymerized via Ru‐catalyzed ring‐opening metathesis to efficiently afford high polymers (M_n up to 631,000). Unsaturated moieties in the main chain of the obtained polymer were hydrogenated with a homogeneous ruthenium catalyst in quantitative conversion, confirmed by ¹H‐NMR measurement. The self‐standing membranes were provided by casting the tetrahydrofuran solutions of both nonhydrogenated and hydrogenated polymers. The obtained membranes showed high transparency in the region of >300 nm with mechanical flexibility. Thermal gravimetric analysis revealed that both nonhydrogenated and hydrogenated polymers decomposed in two stages. The first‐stage decomposition starting at around 230 °C was caused by retro Diels–Alder reaction forming anthracene, proven by pyrolysis gas chromatography mass spectroscopy (GC‐MS) analyses. Mechanical grinding of the polymers induced the formation of anthracene in solid state, which transformed the polymer into blue‐luminescent materials under UV irradiation. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1392–1400     

Synthesis and characterisation of sulfonic acid-containing ion exchange membranes based on hydrocarbon and fluorocarbon polymers

Radiation-induced graft copolymerisation has been used to modify polymers with styrene to prepare pre-cursor copolymers that can be subsequently functionalised to produce ion exchange membranes. This paper describes the processes of simultaneous and pre-irradiation graft copolymerisation of styrene to modify hydrocarbon and fluorine-containing polymers and their sulfonation to produce hydrophilic membranes. The effect of varying the grafting conditions and their characterisation by ion exchange capacity, electrolytic resistivity and equilibrium water content is reported.     

Properties of amorphous and crystallizable hydrocarbon polymers. III. Studies of the hydrogenation of polybutadiene

Three methods for hydrogenating anionically prepared polybutadiene (containing about 8% vinyl double bonds) were investigated: homogeneous catalysis (alkylated transition metal salts), heterogeneous catalysis (nickel on kieselguhr; paladium on calcium carbonate), and stoichiometric reaction with in situ generated diimide. The products were characterized by intrinsic viscosity, gel permeation chromatography, infrared spectroscopy, and melt viscosity. Only the heterogeneous catalysts were found to yield completely hydrogenated products without incorporation of foreign groups and without significant change in the large-scale molecular structure of the chain. The 195°C melt viscosity of linear polybutadiene hydrogenated with heterogeneous catalysts is virtually identical with that of linear polyethylene with the same intrinsic viscosity in trichlorobenzene at 135°C. The solid state properties of hydrogenated polybutadiene, containing about 20 ethyl branches/1000 main chain atoms, closely resemble those of commercial branched polyethylene.     

Properties of amorphous and crystallizable hydrocarbon polymers. II. Rheology of linear and star-branched polybutadiene

Some results are reported on the linear viscoelastic properties of polybutadienes with narrow-molecular-weight distributions. The zero shear viscosity η₀ varies as M^3.4 in the linear samples, and viscosity enhancement is found in star-branched samples with long arms, in good agreement with results reported earlier by Kraus and Gruver. The temperature coefficient of viscosity appears to be slightly larger in stars when the arms become long. The steady state recoverable compliance J is 2.1 × 10 ^?7 cm²/dyn in linear samples of high molecular weight, but it increases to values as much as 10 times larger in the stars. The plateau modulus G, obtained from a composite curve for the linear samples, is 1.32 × 10⁷ dyn/cm². The terminal relaxation spectrum of the stars is too broad to allow an evaluation of plateau modulus.