Femtosecond laser writing of PPV‐doped three‐dimensional polymeric microstructures

Poly(para‐phenylene vinylene) (PPV) is a key material for optoelectronics because it combines the potential of both polymers and semiconductors. PPV has been synthesized via solution‐processable precursor route, in which the precursor polymer poly(xylene tetrahydrothiophenium chloride) (PTHT) is thermally converted to PPV throughout the sample as a whole. Much effort has been devoted to fulfill spatial selectivity of PPV conversion. However, none of the methods proposed stand for PPV conversion three dimensionally, which would be appealing for the design of microdevices. Here, we demonstrate the potential of fs‐laser direct writing via two‐photon polymerization (2PP) to fabricate PPV‐doped 3D microstructures. PTHT is incorporated into the polymeric material and it is subsequently converted to PPV through a thermal treatment. Optical measurements, taken prior and after thermal conversion, confirm the PTHT to PPV conversion. Fs‐laser direct writing via 2PP can be exploited to fabricate a variety of 3D microdevices, thus opening new avenues in polymer‐based optoelectronics. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 479–483     

The thermal conversion of the tetrahydrothiophene‐precursor polymer to poly(p‐phenylene vinylene)

This paper reports the thermal conversion of the tetrahydrothiophene (THT)‐precursor to poly(p‐phenylene vinylene) (PPV). Detailed investigations of the conversion process show that the leaving groups THT and HCl do not eliminate simultaneously. Moderate temperatures (≤125 °C) are sufficient to eliminate the THT while a higher temperature of ≈150 °C is necessary for the leaving group HCl. Furthermore, the THT groups split off at two characteristic temperatures. Our investigations have shown that a consistent picture of the reaction mechanism can only be obtained if the configuration of the polymer chain is considered. For the total reaction of the THT‐precursor to PPV a reaction mechanism is suggested that consists of at least four steps. Copyright © 1999 John Wiley & Sons, Ltd.     

Synthesis and characterization of naphthyl‐substituted poly(p‐phenylenevinylene)s with few structural defects for polymer light‐emitting diodes

A series of naphthyl‐substituted poly(p‐phenylenevinylene)s (2N‐PPV, 4N‐PPV, and NAP‐PPV) has been synthesized and characterized by Fourier transform IR, ¹H NMR, and elemental analysis. The polymers possess excellent solubility, high molecular weights, good thermal stability, and high photoluminescence efficiencies. Thermogravimetric analysis reveals the onset of degradation to be 347, 301, and 306 °C for 2N‐PPV, 4N‐PPV, and NAP‐PPV, respectively. The differential scanning calorimetry investigation gives the respective glass‐transition temperature values of 118, 135, and 141 °C. The UV and photoluminescence spectra measurements reveal that the polymers exhibit similar optical properties, indicating that side‐chain substitution has little effect on the optical properties of this series of polymers. Proton NMR measurement of the signal due to tolane–bisbenzyl defects at around 2.7 ppm indicates that all the polymers have negligible amounts of tolane–bisbenzyl defects along the polymer main chain as a result of the steric bulk imposed by the naphthalene side chain. The highest occupied and lowest unoccupied molecular orbital energy levels of the polymers are investigated through cyclic voltammetry. Polymer light‐emitting diodes utilizing the polymers as the emissive layer with a configuration of indium tin oxide/poly(3,4‐ethylenedioxythiophene)/polymer/Ba/Al are fabricated and evaluated. The diodes emit blue‐green to yellow‐green light with maximum peaks at 518, 542, and 486 nm for 2N‐PPV, 4N‐PPV, and NAP‐PPV, respectively. The respective turn‐on electric fields of the diodes are 0.84, 0.69, and 0.83 MV/cm and the respective maximum external quantum efficiencies are 0.08, 0.54, and 0.02%. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1647–1657, 2004     

Influence from Thermal Elimination Temperature of Precursor Polymer and Film‐forming Methods on the Photophysics of the Poly(2,5‐didodecyloxy‐p‐phenylenevinylene)

A series of poly(p‐phenylenevinylene)s (PPVs) with good solubility were synthesized from thermal elimination of precursor poly(2,5‐didodecyloxy‐p‐phenylenevinylene) at different temperature via Wessling method. The polymer photophysics were influenced by the thermal elimination condition, which was consistent with NMR and IR characterizations. The additional absorption peak at longer wavelength and the red‐shifted emission maximum both in solution and in film, for PPVs obtained at high elimination temperature, indicated the existence of longer conjugated blocks in these systems. The emission maximum for drop‐cast film (436 nm) for PPV obtained under 200°C (PPV200) was 16 nm blue shifted to the spin‐coated films (452 nm) or 29 nm to the solution (465 nm). The SEM study showed drop‐cast film had the morphology of isolated conjugated particles in the matrix while blurry linear structure was found for spin‐coated film, which was consistent with the photophysics. The discussion about this difference was carried out based on the consideration of the flexibility of the polymer chains and different conjugated length of PPV in different states.     

Synthesis and electro‐optical properties of light‐emitting polymers containing oxadiazole derivatives for light‐emitting diodes applications

Two PPV‐based bipolar polymers containing 1,3,4‐oxadiazole pendant groups were synthesized via the Gilch polymerization reaction for use in light‐emitting diodes (LEDs). The resulting polymers were characterized using ¹H and ¹³C NMR, elemental analysis, DSC, and TGA. These polymers were found to be soluble in common organic solvents and are easily spin‐coated onto glass substrates, producing high optical quality thin films without defects. The electro‐optical properties of ITO/PEDOT/polymer/Al devices based on these polymers were investigated using UV‐visible, PL, and EL spectroscopy. The turn‐on voltages of the OC₁Oxa‐PPV and OC₁₀Oxa‐PPV devices were found to be 8.0 V. The maximum brightness and luminescence efficiency of the OC₁Oxa‐PPV device were found to be 544 cd/m² at 19 V and 0.15 cd/A, respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1098–1110, 2008     

Palladium‐catalyzed three‐component coupling polycondensation of aromatic diiodide,aromatic bis(boronic acid propanediol ester), and norbornadiene: A new route for poly(p‐phenylene vinylene)

A novel synthetic method for soluble precursor polymers of poly(p‐phenylene vinylene) (PPV) derivatives by the palladium‐catalyzed three‐component coupling polycondensation of aromatic diiodides, aromatic bis(boronic acid) derivatives, and norbornadiene is described. For example, the polymerization of 1,4‐diiodo‐2,5‐dioctyloxybenzene, benzene‐1,4‐bis(boronic acid propanediol ester), and norbornadiene at 100 °C for 3 days provided a polymer consisting of the three monomer units in a 97% yield (number‐average molecular weight = 3100, weight‐average molecular weight/number‐average molecular weight = 1.37). A derivative of PPV was produced smoothly by the retro Diels–Alder reaction of the polymer both in a dodecyloxybenzene solution and in a film at 200 °C in vacuo. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3403–3410, 2005     

Photochemical stability of dicyano‐substituted poly(phenylenevinylenes) with different side chains

The photodegradation mechanism study has been conducted on poly(2,5‐dioctyl‐1,4‐phenylene‐1,2‐dicyanovinylene) (C8‐diCN‐PPV) and poly[2,5‐bis(decyloxy)?1,4‐phenylene‐1,2‐dicyanovinylene] (ROdiCN‐PPV) to understand the reason behind the faster photodegradation of C8‐diCN‐PPV which has a lower LUMO. In both polymers, radical superoxide anion mechanism, which is responsible for electron‐rich RO‐PPVs, is found to be energetically unfavorable for both diCN‐PPVs due to diCN substitution. The IR analysis results confirm this and suggest that singlet oxygen (O₂) is the main culprit for photodegradation of both polymers, which cleaves the C?C bonds into carboxylic acids. The rates of MW reduction (by GPC) and increase in carbonyl IR absorption intensity are in excellent agreement for both polymers. Phosphorescence study indicates that the faster photodegradation of C8‐diCN‐PPV is due to intersystem crossing, which helps generate singlet O₂ upon photoexcitation. No phosphorescence was detected in RO‐diCN‐PPV, suggesting that inefficient intersystem crossing makes RO‐diCN‐PPV photochemically more stable. This work shows that a small difference in side chain structure can lead to a significant difference in photochemical stability. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2820–2828     

Water‐soluble poly(ethylene oxide)‐block‐poly(p‐phenylene vinylene) copolymer: Synthesis and characterization

Water‐soluble and photoluminescent block copolymers [poly(ethylene oxide)‐block‐poly(p‐phenylene vinylene) (PEO‐b‐PPV)] were synthesized, in two steps, by the addition of α‐halo‐α′‐alkylsulfinyl‐p‐xylene from activated poly(ethylene oxide) (PEO) chains in tetrahydrofuran at 25 °C. This copolymerization, which was derived from the Vanderzande poly(p‐phenylene vinylene) (PPV) synthesis, led to partly converted PEO‐b‐PPV block copolymers mixed with unreacted PEO chains. The yield, length, and composition of these added sequences depended on the experimental conditions, namely, the order of reagent addition, the nature of the monomers, and the addition of an extra base. The addition of lithium tert‐butoxide increased the length of the PPV precursor sequence and reduced spontaneous conversion. The conversion into PPV could be achieved in a second step by a thermal treatment. A spectral analysis of the reactive medium and the composition of the resulting polymers revealed new evidence for an anionic mechanism of the copolymerization process under our experimental conditions. Moreover, the photoluminescence yields were strongly dependant on the conjugation length and on the solvent, with a maximum (70%) in tetrahydrofuran and a minimum (<1%) in water. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4337–4350, 2005     

Enzyme‐Catalyzed Oxidation of 5‐Hydroxymethylfurfural to Furan‐2,5‐dicarboxylic Acid

Furan‐2,5‐dicarboxylic acid (FDCA) is a biobased platform chemical for the production of polymers. In the past few years, numerous multistep chemical routes have been reported on the synthesis of FDCA by oxidation of 5‐hydroxymethylfurfural (HMF). Recently we identified an FAD‐dependent enzyme which is active towards HMF and related compounds. This oxidase has the remarkable capability of oxidizing [5‐(hydroxymethyl)furan‐2‐yl]methanol to FDCA, a reaction involving four consecutive oxidations. The oxidase can produce FDCA from HMF with high yield at ambient temperature and pressure. Examination of the underlying mechanism shows that the oxidase acts on alcohol groups only and depends on the hydration of aldehydes for the oxidation reaction required to form FDCA.     

A New Kind of Copolymerization of Styrene and p‐Quinodimethane Intermediates

A new kind of copolymerization between styrene and p‐quinodimethane intermediates was realized by adding styrene to a reaction performed via the typical chlorine precursor route toward the synthesis of poly(p‐phenylene vinylene) (PPV). The composition and structure of the obtained copolymers can be adjusted by the feed rate of the two monomers. The resulting copolymers show improved solubility and blue‐shifted photoluminescence as compared with the corresponding PPV derivative.     

Segmented poly[2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylene vinylene] via xanthate and dithiocarbamate precursors: A comparative study of thermal eliminations

Segmented poly[2‐methoxy‐5‐(2‐ethylhexloxy)‐1,4‐phenylene vinylene] (MEH‐PPV)‐x's, which contain conjugated segments of varying lengths that are interspersed by nonconjugated units along the polymer backbone, were synthesized by selective thermal elimination of precursors containing controlled amounts (x) of a thermally labile group, namely, xanthate or dithiocarbamate (DTC). These precursors were in turn synthesized by competitive nucleophilic substitution of the Wessling polyelectrolyte with varying molar fractions of the respective nucleophiles—potassium ethyl xanthate or sodium diethyl dithiocarbamate. Methanol, used as the reaction medium, also served to introduce the second thermally less labile nucleophilic substituent. This approach for the preparation of segmented MEH‐PPV‐x is superior to the previous approach that used acetate as the thermally labile group, because it offers greater control over the composition despite a simpler synthetic procedure. Detailed studies of the thermal‐elimination kinetics of the three precursors, namely, acetate, xanthate, and DTC, both in solution and in thin films, were carried by in situ monitoring of their ultraviolet–visible spectra. These studies revealed that the rates of elimination followed the order, DTC > xanthate > acetate. The activation energies for the elimination were, however, not widely different (ca. 30 kcal/mol), suggesting that the rates primarily reflected differences in the pre‐exponential factor. After elimination, the segmented MEH‐PPV‐x samples exhibited the expected redshift in their absorption and fluorescence spectra with an increasing molar fraction (x) of eliminated segments, which was accompanied by a drastic reduction in the fluorescence quantum yields. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3929–3940, 2003     

Postmodification of poly(9‐alkyl‐9H‐carbazole‐2,7‐diyl)s as a route to new main‐chain‐functionalized carbazole polymers

The postmodification of poly[9‐(2‐hexyldecyl)‐9H‐carbazole‐2,7‐diyl] ( P1 ) upon its reaction with N‐bromosuccinimide affords exclusive and full bromination of the 3,6‐positions of the carbazole repeat units to yield poly[3,6‐dibromo‐9‐(2‐hexyldecyl)‐9H‐carbazole‐2,7‐diyl] ( P2 ). Brominated polymer P2 can be used as a precursor for further functionalization at the 3,6‐positions with the desired functional group to afford other useful polymers. Polymer P2 has hence been reacted with copper(I) cyanide to afford poly[3,6‐dicyano‐9‐(2‐hexyldecyl)‐9H‐carbazole‐2,7‐diyl] ( P3 ). Full substitution of the bromide groups with nitrile‐functional groups has been achieved. The preparation and structural characterization of polymers P2 and P3 are presented together with studies on their electronic conjugation and photoluminescence properties. Cyclic voltammetry studies on polymer P3 indicate that the new polymer is easier to reduce (n‐dope) but more difficult to oxidize than its unsubstituted counterpart ( P1 ) as a result of the introduction of the electron‐withdrawing nitrile‐functional groups at the 3,6‐positions on the carbazole repeat units on the polymer chains. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3336–3342, 2006     

New Classes of Ferromagnetic Materials with Exclusively End‐on Azido Bridges: From Single‐Molecule Magnets to 2 D Molecule‐Based Magnets

A new, flexible synthetic route, which does not require the co‐presence of any organic chelating/bridging ligand but only the “key” precursor Me₃SiN₃, has been discovered and led to a new class of inorganic materials containing exclusively end‐on azido bridges; the reported 3d‐metal clusters and coordination polymers exhibit ferromagnetic, single‐molecule magnet, and long‐range magnetic ordering properties.     

Photophysical characteristics of soluble oligo(p‐phenylenevinylene)–fullerene dyad

The fact that C₆₀ is a good acceptor has stimulated interest in covalently linked complexes, including polymers and oligomers. Photoinduced charge transfer in these systems has great potential for use in photovoltaic devices. In this study, an alternating conjugated oligomer of alkylated carbazole and dialkoxyl‐substituted phenylene, with pendant C₆₀ moieties, (PPV‐AFCAR) was prepared and characterized. The excited‐state properties of PPV–AFCAR were investigated with steady‐state spectroscopy and lifetime measurements. After photoexcitation, photoinduced energy transfer from the oligomer chain to the pendant moiety occurred in great proportion, but a charge‐separation process did not. Whether the energy‐transfer process was measurable or not depended on the system temperature. At 77 K, a quantum yield of more than 50% for energy transfer was found by the fitting of a linear combination of the excitation spectra of the precursor oligomer, the alternating conjugated oligomer of alkylated carbazole and dialkoxyl‐substituted phenylene PPV–ACAR, and the absorption spectra of C₆₀. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3981–3988, 2001     

Greatly enhanced thermo‐oxidative stability of polybenzoxazine thermoset by incorporation of m‐carborane

Novel polybenzoxazine precursor containing m‐carborane unit in the main‐chain has been firstly synthesized through click reaction of diazidomethyl m‐carborane (DAMC) and diacetylene bisbenzoxazine (DABB). Meanwhlie, the traditional polybenzoxazine precursor was also prepared through click reaction of diazidomethyl p‐benzene (DAPB) and DABB as a control. 1H NMR was used to confirm the structures of the monomers and the resulting polymers. FT‐IR and differential scanning calorimetry (DSC) were used to study the curing behavior of carborane‐containing benzoxazine polymer (CCBP). Dynamic mechanical analysis (DMA) study demonstrated that the cured CCBP had high storage moduli and high Tg. Thermogravimetric analysis (TGA) and ablation test showed that the cured CCBP had outstanding thermo‐oxidative stability. During thermal ablation of cured CCBP, organic material was degraded, and a passivation layer with oxidized m‐carboranes was formed, which prevented the underlying polymer from further degradation. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 973–980     

Investigation of Mizoroki‐Heck coupling polymerization as a catalyst‐transfer condensation polymerization for synthesis of poly(p‐phenylenevinylene)

Mizoroki‐Heck coupling polymerization of 1,4‐bis[(2‐ethylhexyl)oxy]‐2‐iodo‐5‐vinylbenzene ( 1 ) and its bromo counterpart 2 with a Pd initiator for the synthesis of poly(phenylenevinylene) (PPV) was investigated to see whether the polymerization proceeds in a chain‐growth polymerization manner. The polymerization of 1 with ^tBu₃PPd(Tolyl)Br ( 10 ) proceeded even at room temperature when 5.5 equiv of Cy₂NMe (Cy = cyclohexyl) was used as a base, but the molecular weight distribution of PPV was broad. The polymerization of 2 hardly proceeded at room temperature under the same conditions. In the polymerization of 1 , PPV with H at one end and I at the other was formed until the middle stage, and the polymer end groups were converted into tolyl and H in the final stage. The number‐average molecular weight (M_n) did not increase until about 90% monomer conversion and then sharply increased after that, indicating conventional step‐growth polymerization. The occurrence of step‐growth polymerization, not catalyst‐transfer chain‐growth polymerization, may be interpreted in terms of low coordination ability of H‐Pd(II)‐X(^tBu₃P) (X = Br or I), formed in the catalytic cycle of the Mizoroki‐Heck coupling reaction, to π‐electrons of the PPV backbone; reductive elimination of H‐X from this Pd species with base would take place after diffusion into the reaction mixture. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 543–551     

A3‐type star polymers via click chemistry

We report a simple preparation of three‐armed (A₃‐type) star polymers based on the arm‐first technique, using a click‐reaction strategy between a well‐defined azide‐end‐functionalized polystyrene, poly(tert‐butyl acrylate), or poly(ethylene glycol) precursor and a trisalkyne‐functional initiator, 1,1,1‐tris[4‐(2‐propynyloxy)phenyl]ethane. The click‐reaction efficiency for A₃‐type star formation has been investigated with gel permeation chromatography measurements (refractive‐index detector). The gel permeation chromatography curves have been split with the deconvolution method (Gaussian area), and the efficiency of A₃‐type star formation has been found to be 87%. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6458–6465, 2006     

Synthesis and chiroptical properties of poly (p‐phenylenevinylene‐alt‐m‐phenylenevinylene) bearing (−)‐trans‐myrtanoxyl groups on the p‐phenylene rings

Chiral poly(p‐phenylenevinylene‐alt‐m‐phenylenevinylene)s bearing (?)‐trans‐myrtanoxyl groups on the p‐phenylene rings were synthesized by Wittig's reaction and Heck's reaction, respectively, namely Myr‐PMPV‐w and Myr‐PMPV‐h correspondingly. The chiroptical properties of the polymers were investigated in chlorobenzene solution by circular dichroism. The results showed that both Myr‐PMPV‐w and Myr‐PMPV‐h showed no Cotton effect due to their irregular molecular structure. By the treatment with I₂, most of the cis‐vinylene linkages in Myr‐PMPV‐w were converted to trans‐vinylenes, consequently, the structure of Myr‐PMPV‐w became much more regular, and the resulting polymer ( iso‐Myr‐PMPV‐w ) showed strong bisignate Cotton effects in the π–π* transition. Compared to its analogous poly(p‐phenylenevinylene) (PPV) ( iso‐Myr‐PPV‐w ), iso‐Myr‐PMPV‐w showed much stronger Cotton effect, its maximum g value was about one order of magnitude higher than that of iso‐Myr‐PPV‐w under the same conditions. With increasing concentration and decreasing temperature, the g_max value of iso‐Myr‐PMPV‐w increased, and the maximum absorption was slightly blue‐shifted, but the shape and range of absorption curves did not changed significantly, and no clear isosbestic point could be observed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3336–3343, 2008     

Degradable multisegmented polymers synthesized by consecutive radical addition‐coupling reaction of α,ω‐macrobiradicals and nitroso compound

A consecutive radical addition‐coupling reaction induced by spin‐trapping agent is applied to produce degradable multisegmented polymer using α,ω‐dibromo polymer as a precursor. The macroradical generated by single electron transfer process catalyzed by Cu/PMDETA from α,ω‐dibromo polymer can be efficiently captured by 2‐methyl‐2‐nitrosopropane (MNP), which results in nitroxide radical. The in situ formed nitroxide radical immediately undergoes cross‐coupling reaction with polymeric radical, generating block polymer bridged with alkoxyamine moiety. The consecutive radical addition‐coupling reaction generates multisegmented polymer via step‐growth mechanism. Different multisegmented polymers have been prepared from α,ω‐dibromo‐PS, PtBA, and PtBA‐PS‐PtBA. The block number of multisegmented polymers can be tailored by varying the feed ratio of α,ω‐dibromo precursor to MNP. The multisegmented polymer can be degraded in the presence of hydrogen atom donor or air, and the molecular weight distribution transformed back into shape of its original precursor as it is conjugated by alkoxyamine moieties. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Density functional crystal orbital study of cyano‐substituted poly(para‐phenylene‐vinylene) and poly(quinoxaline‐vinylene)

We have calculated the optical and electronic properties of several conjugated organic polymers: poly(p‐phenylene‐vinylene) (PPV) and its derivatives. Cyano substitutions on the phenylene ring: poly(2,5‐dicyano‐p‐phenylene‐vinylene) (2,5‐DCN‐PPV) and on the vinylene linkage: poly(p‐phenylene‐7(,8)‐(di)cyano‐vinylene) are considered. In addition, poly(quinoxaline‐vinylene) (PQV) is studied. The infinite isolated quasi‐1D chains are treated with periodic boundary conditions, using atomic basis sets. In a comparative study of PPV, some issues regarding the selection of the functionals and basis sets are discussed and excitation energies derived from time‐dependent and from ordinary methods are compared. It is concluded that for these polymers the calculations are informative at the B3LYP/6‐31G** density functional theory (DFT) level. The absolute values might change with improved methods, but the similarity of the polymers suggests that the relative characterization is adequate. Band structures are communicated along with characteristics of the highest occupied and the lowest unoccupied crystal orbitals (HOCO and LUCO). Electron affinities, ionization potentials, valence and conduction bandwidths, and effective masses at the bandgap are given. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006