Vinylene Units Research Articles

Butadiene polymerization with various half-titanocenes

The polymerizations of butadiene were performed with various half-titanocenes in combination with either modified methylalumoxane (MMAO) or (C 6H 5) 3CB(C 6F 5) 4/trialkylaluminum and the latter activator showed higher catalyst activities. The substitution of an alkyloxy group for a Cl atom in CpTiCl 3 decreased activity and did not change the microstructure of polymers. CpTiBr 3 and half-titanocenes with substituents on a Cp ring exhibited lower activities, but the microstructure of higher vinyl unit contents. The results of activity suggest cationic active species of Ti(+4).

Excitons in Segmented Polymers for High Photo- and Electro-Luminesence Efficiency

ABSTRACTThe photoluminesence (PL) quantum efficiency of poly(p-phenylene vinylene) (PPV) varies with preparation and processing. We report the achievement of nearly 100% PL quantum efficiency through design and synthesis of alternating rigid conjugated segments of dimethoxy -PV (three dimethoxy -phenyl and two vinyl units) and flexible nonconjugated segments along the polymer backbone. There is enhanced solubility in desired solvents and increased interchain separation through the incorporation of the methoxy sidegroups, forming poly [1,6-hexanedioxy -2,6-dimethoxy-1,4-phenylene]-1,2-ethenylene-[3,6-dimethoxy-1,4-phenylene]-1,2-ethenylene-[3,5-dimethoxy-1,4-phenylene], or GDBBC. The nearly temperature-independence of the PL decay at different emission wavelengths of the alternating block co-polymer (ABC) shows that the excitons are highly localized due to the blocking by non-conjugated segments as well as due to increased interchain separation due to the methoxy sidegroups. The contrasting temperature- and time- dependent results for the corresponding PV oligomer and PPV, supports the role of reduced exciton migration in achieving high quantum efficiency. The results are compared to the exciton confinement at the interface of light emitting electron and hole transporting polymers, forming an exciplex, for which the luminescence decay is also temperature independent. Electroluminescent devices using GDBBC as the lightemitting layer and incorporating poly[1-phenyl-2-(p-n-carbazolylphenyl) acetylene], (PDPA-Cz), as hole transporting layer, in the structure ITO/PDPACz/GDBBC/Alq/MgAg have ~1% external quantum efficiency with green emission from the GDBBC. EL devices based on exciplex emission are also discussed.

Reactive polymers incorporating silyl enol ether groups, 3. Incorporation ofα,β-bis(siloxy)vinylene units into the backbone of vinyl polymers by free-radical (co)polymerization of 2,3-bis(trialkylsiloxy)butadienes

2,3-Bis(trimethylsiloxy)butadiene (1) and 2,3-bis(tert-butyldimethylsiloxy)butadiene (2) have been homopolymerized and copolymerized with styrene (St) and methyl methacrylate (MMA) under free-radical conditions. Comparison of initial rates and molecular weights with polymerizations conducted under identical experimental conditions on monosubstituted analogs, 2-trimethysiloxybutadiene (3) and 2-(tert-butyldimethylsiloxy)butadiene (4), demonstrated that the second substituent does not decrease the polymerizability significantly despite the additional steric hindrance introduced in the monomer. Extensive H-1 and C-13 NMR characterization of the polymers demonstrated that the main incorporation mode is of the 1,4-type, allowing more than 95% of the butadienyl subunit to be incorporated in the main chain as an alpha,beta-bis(trialkylsiloxy)vinylene functional group. Monomer reactivity ratios r(1) and r(2) at 60 degrees C were determined from copolymer composition curves obtained at low conversions and are compared with values obtained for other 1,2-butadienyl systems.

Reactive polymers incorporating silyl enol ether groups, 3. Incorporation of α,β-bis(siloxy)vinylene units into the backbone of vinyl polymers by free-radical (co)polymerization of 2,3-bis(trialkylsiloxy)butadienes

Reactive polymers incorporating silyl enol ether groups, 3. Incorporation of α,β-bis(siloxy)vinylene units into the backbone of vinyl polymers by free-radical (co)polymerization of 2,3-bis(trialkylsiloxy)butadienes

Approaches to the controlled formation of network polymers: 1. Synthesis and evaluation of monomers with vinyl differentiation

The synthesis of novel crosslinking agents N-acryloyl, N-methacryloyl methylenediamine ( 1) and N-acryloyl, N′-methacryloyl ethylenediamine ( 2) with non-identical vinyl functionalities is described. When incorporated into crosslinked networks, the resultant polymers exhibit a higher degree of porosity than the more conventional systems where the vinyl functionalities are identical, as evidenced by protein mobility studies using electrophoresis and water permeability experiments. This may be attributed to the formation of a bimodal pore size distribution arising from a crosslinking mechanism which is dictated by the relative reactivities of the differentiated vinyl units within the novel monomers.

Low molar mass polybutadiene made crosslinkable by silane moities introduced via addition of thiol to double bond: 3. Synthesis and kinetic study

Low molar mass polybutadiene was made crosslinkable under moisture by the addition of mercapto propyl triethoxy silane to double bonds. The reaction was carried out at 75°C in the presence of AIBN as initiator. AIBN concentration and time showed that triethoxy silane groups were introduced quantitatively in the range of 1.05 to 7.9 per chain. A 1H n.m.r. study showed clearly that only vinylic units reacted at low modification rates. Volumetric titration of the remaining thiol was used to follow the reaction. A new mechanism is proposed here to lead to a kinetic relation, similar to the one already used by several authors, but kinetically provable. Moreover, it has been pointed out that there is probably an evolution of kinetic constants with the progress of the reaction due to, among other reasons, a local steric hindrance at the level of vinyl sequences and/or a variation in chain conformation.

Miscibility behaviour in blends of copolymers of vinyl alcohol with poly(ethyloxazoline)

Miscibility of poly(ethyloxazoline) (PEOX) with poly(ethylene-co-vinyl alcohol) (EVAL copolymers) containing 78, 68, 56 and 25 mol-% of vinyl alcohol units has been investigated and compared with the results obtained for the mixtures of PEOX with poly(vinyl acetate-co-vinyl alcohol) (ACAL copolymers). Differential Scanning Calorimetry (DSC) results indicate that PEOX is immiscible with EVAL25. The miscibility behaviour of the blends of EVAL78, EVAL68 and EVAL56 with PEOX was determined by dilute solution viscometry; the results show that EVAL78 and EVAL68 are miscible with the tertiary polyamide PEOX for all compositions. EVAL56/PEOX blends are immiscible in certain compositions. Infrared spectroscopy studies of miscible and immiscible blends reveal the existence of specific interactions via hydrogen bonding between the hydroxyl groups in vinyl alcohol units of the copolymers and the carbonyl group in the tertiary amide. According to these results, infrared spectroscopy is not apt to reveal miscibility within the system studied.

Miscibility behaviour in blends of copolymers of vinyl alcohol with poly(ethyloxazoline)

Miscibility of poly(ethyloxazoline) (PEOX) with poly(ethylene-co-vinyl alcohol) (EVAL copolymers) containing 78, 68, 56 and 25 mol-% of vinyl alcohol units has been investigated and compared with the results obtained for the mixtures of PEOX with poly(vinyl acetate-co-vinyl alcohol) (ACAL copolymers). Differential Scanning Calorimetry (DSC) results indicate that PEOX is immiscible with EVAL25. The miscibility behaviour of the blends of EVAL78, EVAL68 and EVAL56 with PEOX was determined by dilute solution viscometry; the results show that EVAL78 and EVAL68 are miscible with the tertiary polyamide PEOX for all compositions. EVAL56/PEOX blends are immiscible in certain compositions. Infrared spectroscopy studies of miscible and immiscible blends reveal the existence of specific interactions via hydrogen bonding between the hydroxyl groups in vinyl alcohol units of the copolymers and the carbonyl group in the tertiary amide. According to these results, infrared spectroscopy is not apt to reveal miscibility within the system studied.

Acid catalysed reactions of 5-formyluracils with enamines. A facile synthesis of 5-acylvinyluracils

5-Formyl-1,3-dimethyluracil ( 1) reacts with secondary amine derived enamines of ketones and aldehydes to provide 5-(acyvinyl)uracil derivatives. The presence of a CH 3 group at C-6 of 1 induces a competitive annulation reaction. Depending on the bulk of substituents 5-(acylvinyl)-uracils acquire cis -diene and E or Z configurations on the vinyl unit. Enamines derived from 1,3-cyclohexanedione and ethyl acetoacetate react with 1 in 1 : 2 stoichiometric manner to provide 5-(9-xanthenyl)uracil and 5-(6-cycohexadienyl)uracil (X-ray) derivatives.

Connective CC Double Bond Formation for the Synthesis of Donor- and Acceptor-Substituted Poly(p-phenylenevinylene)s

A carbon−carbon bond formation through cation−anion coupling allows the synthesis of poly(p-phenylenevinylene)s (PPV) 1 and 2a−f, which contain donor and acceptor groups in each vinylene unit. The crucial step in the double bond formation is the quantitative elimination of methanethiol at room temperature. In this work we describe the optimization of the molecular weight of polymers of structure types 1 and 2a−f with regard to (i) solubility of the monomers and polymers and (ii) the reactivity and side reactions of the monomers. The simultaneous donor and acceptor substitution on the central double bond in PPV-analogous structures raises the question of the additivity of dipoles in each repeat unit of a conjugated polymer chain from the viewpoint of potential use in electrooptical applications. The sequence of donor and acceptor groups along the π-conjugated chain can be controlled by the choice of suitable monomers and is crucial for the alignment of the dipole components. The aggregation of polymers 1 a...

Comparative study of the effect of incorporation of vinylene linkages on the electronic structures of heterocyclic polymers

Using theab initioband structure results of double-zeta quality of polythiophene (PTP), polyfuran (PFU) and polyacetylene (PA), the effects of incorporation of varying percentages of vinylene units on the electronic structures and conduction properties of PTP and PFU have been investigated using a negative-factor counting method in the tight-binding approximation. Both periodic and aperiodic distributions of vinylene units have been studied. The results show that the incorporation of vinylene units makes the heterocyclic polymers better conductors of electricity both intrinsically as well as extrinsically and that the effects are more pronounced for the aperiodic distribution than for the periodic distribution.

Coordination of a disubstituted alkene in a chelated d 0-metal-alkyl-alkene complex. Evidence for equilibrium between complexes with coordinated and free alkenes

Addition of (Cp* 2YH) 2 ( 4) to 2-methyl-1,4-pentadiene produced the yttrium-alkyl-alkene chelate complex Cp* 2YCH 2CH 2CH 2C(CH 3)=CH 2 ( 2) in which a disubstituted alkene is complexed to the metal center. Evidence for coordination of the alkene unit of 2 comes from the 1H and 13C NMR chemical shifts of the vinyl units and from observation of nOe effects between Cp* protons and vinyl hydrogens. The disubstituted alkene ligand of 2 is weakly bound, and evidence for an equilibrium with substantial amounts of complex 3 with a free alkene was obtained from variable temperature 1H NMR spectroscopy.

Electronic deactivation and energy transfer in doped oligophenylenevinylene nanoparticles

Suspensions of oligophenylenevinylene (nPV) nanoparticles withn = 2 vinylene units are doped with nPVs of longer chainlengths,n = 3–5. Absorption and fluorescence spectroscopy and steady-state and time-resolved fluorescence anisotropy measurements are used to determine the photo-physical properties of the suspensions. Undoped nanoparticles form highly oriented H-aggregates with low fluorescence quantum yields (ΦF ≈ 0.1). Introduction of bulky substituents into the particle constituting molecules perturbs the intermolecular orientation. Upon doping, efficient energy transfer to the dopants is found, changing the color and leading to enhancement of the fluorescence quantum yields up to ΦF = 0.6. The intermolecular orientation is not changed upon doping.

Miscibility in blends of poly(vinyl acetate-co-vinyl alcohol) with poly(N,N-dimethylacrylamide)

Miscibility of poly(N,N-dimethylacrylamide) (PDMA) with poly(vinyl acetate) (PVAC), poly(vinyl alcohol) (PVAL) and poly(vinyl acetate co-vinyl alcohol) (ACAL copolymers) has been investigated over a wide composition range. Differential scanning calorimetry (DSC) results indicate that PDMA is immiscible with PVAC, but is miscible with PVAL and ACAL copolymers in certain range of compositions. The ACAL/PDMA phase diagram for different copolymer compositions has been determined. The variation of the glass transition temperature with blend composition for miscible systems was found to follow the Kwei equation. Infrared spectroscopy studies of blends reveal the existence of specific interactions via hydrogen bonding between hydroxyl groups in vinyl alcohol units and the carbonyl group in the tertiary amide, which appear to be decisive for miscibility.

Comparison of electroluminescent quantum efficiencies of PPV and a PPV-related alternating block copolymer

A comparison of the electroluminescent properties of poly( p-phenylene vinylene) (PPV) and a conjugated/non-conjugated alternating block copolymer has been made. The chromophoric sequences in the latter contain about 76 mol% of sequences containing three phenylene or dimethoxy phenylene rings interspersed with vinylene units, with the remaining chromophores being a distribution of longer sequences containing additional phenylene vinylene units. Photoluminescent and electroluminescent spectra of PPV and the block copolymer are very similar, but the quantum efficiency of the latter is up to two orders of magnitude greater. This is attributed largely to morphological differences between the two macromolecules; the block copolymer can provide greater excitonic confinement by virtue of a phase-segregated morphology.

Characterization of 6PV phenylene vinylene oligomer thin films

Investigations of phenylene vinylene oligomer thin films with 7 phenyl, 6 vinyl units (6PV) have been performed by optical and electrical measurements. The optical characterizations including infrared, Raman and UV-VIS spectroscopies were discussed by comparing the results with those obtained in poly( p-phenylene vinylene) (PPV). The electrical properties of oligomer based diodes were studied by measuring the current-voltage-temperature characteristics and the thermally stimulated currents (TSC). At high fields, tunneling of carriers through the interfacial barrier would occur while at lower fields, two distinct temperature ranges were observed. In the high temperature range (> 250 K), a field assisted mechanism occurs involving localized states in the oligomer bulk whereas in the low temperature range, hopping conduction is probable. The TSC spectrum shows two relaxation peaks at 219 and 261 K which correspond to trap depths of 0.4 and 0.55 eV. The deep traps appeared as a characteristic of phenylenevinylene oligomers.

Miscibility and specific interactions in blends of poly(vinyl acetate‐co‐vinyl alcohol) with poly(ethyloxazoline)

AbstractMiscibility of poly(ethyloxazoline) (PEOX) with poly(vinyl acetate) (PVAC), poly(vinyl alcohol) (PVAL) and poly(vinyl acetate‐co‐vinyl alcohol) (ACAL copolymers) has been investigated over a wide composition range. In some blends, due to the small difference between the glass transition temperatures of the components, the enthalpic relaxation method was used as miscibility criterion. Differential scanning calorimetry (DSC) results indicate that PEOX is immiscible with PVAC and PVAL but is miscible with ACAL copolymers in a certain range of compositions. The ACAL/PEOX phase diagram for different copolymer compositions has been determined. The variation of the glass transition temperature with blend composition for miscible systems was found to follow the Kwei equation. Infrared spectroscopy studies of blends reveal the existence of specific interactions via hydrogen bonding between hydroxyl groups in vinyl alcohol units and the carbonyl group in the tertiary amide, which appear to be decisive for miscibility.

Optical excitations in electroluminescent polymers: the poly( para-phenylenevinylene) family

The components of photoexcited states with large spatial extent in the optical absorption spectra of the electroluminescent conjugated polymers are investigated by using the intermediate-exciton theory. We calculate the ratio of the oscillator strengths due to long-range excitons to the sum of all of the oscillator strengths of the absorption, as a function of the monomer number. The oscillator strengths of the long-range excitons in poly( para-phenylene) are smaller than those for poly( para-phenylenevinylene), and those for poly( para-phenylenedivinylene) are larger than those for poly( para-phenylenevinylene). Such relative variations are explained by the differences of the numbers of vinylene units. The oscillator strengths of long-range excitons in poly(di- para-phenylenevinylene) are much larger than those for the above three polymers, due to the increase of the number of phenyl rings. We also find that the energy positions of the almost localized excitons are is nearly the same in the four polymers.

The benzene ring as modulus: synthesis and supramolecular ordering of novel conjugated polymers

Conjugated polymers possess attractive electronic and optical properties which also qualify them as active components of devices. Many conjugated polymers are made up of benzenoid building blocks. The functionalization of benzene rings is therefore a key step in polymer synthesis. Particularly important are functionalizations leading to direct aryl–aryl coupling and to the incorporation of vinylene and ethynylene units. On the other hand the benzene ring serves as a modular building block for controlling the supramolecular structures of macromolecules. The formation of aggregates or of liquid crystalline phases are typical examples (Dietrich et al. 1993). Herein, we present modular approaches towards the synthesis and supramolecular ordering of: (1) ladder–type poly(para–phenylene) (LPP); (2) donor–acceptor–substituted poly(para–phenylene–vinylene) (D/A-PPV); (3) poly(para–phenylenesulphide–para–phenyleneamine) (PPSA); (4) graphite sheets.

Polymer light-emitting diodes utilizing poly(phenylene vinylene)derivatives

We have successfully synthesized highly luminous poly(phenylene vinylene) derivatives. The polymer having m-phenylene vinylene units showed good electroluminescent properties due to the good balance between the exciton confinement and the charge transporting property. The optimized P-LED, having a multi-layer structure, showed a maximum luminance of about 70,000cd/m 2 and a service life of over 1,000 hours