Photochemical Polymerization Research Articles

High Performance Quantification of Complex High Resolution Polymer Mass Spectra.

Modern soft ionization mass spectrometry provides chemical information on various polymers with unparalleled resolution and sensitivity. However, the interpretation of the resulting highly complex mass spectra is hampered by the sheer amount of contributing macromolecular species. For example, state-of-the-art reversible deactivation radical polymerization techniques, which are generally considered to be highly controlled, can still generate tens or even hundreds of species in a narrow mass window. Moreover, the multitude of species typically leads to partially overlapping isotopic patterns, further complicating the data evaluation. Herein, a rapid and powerful three-step methodical approach is introduced that enables the successful identification and quantification of the contributing species. The approach is subsequently implemented in "pyMacroMS", a high performance algorithm that allows for ultrafast processing of high resolution polymer mass spectra with varying complexities. The power of our algorithm is demonstrated on the example of a photochemical atom transfer radical polymerization (photoATRP) of three monomers, ultimately leading to 908 identified species. pyMacroMS is available free of charge under a GNU General Public License v3.0.

Photochemical, Thermal Free Radical, and Cationic Polymerizations Promoted by Charge Transfer Complexes: Simple Strategy for the Fabrication of Thick Composites

A novel strategy for the preparation of extremely thick composites by photochemical and/or thermal free radical polymerization (FRP) and/or cationic polymerization (CP) under low-energy consumption visible light emitted diodes (LEDs) is described. The approach is based on the use of charge transfer complexes (CTCs) formed between N-aromatic amines (donors) and iodonium salts (Iod, acceptors). Remarkably, it is demonstrated for the first time that these CTCs can be used as thermal initiators for free radical polymerization (FRP) initiation with performances comparable to dibenzoyl peroxide-based systems. The decomposition temperature of these CTC thermal initiators can be modulated through the selection of the amine, providing much safer conditions for synthesis, storage, and handling than that of the classical thermal initiators. A good stability in resin is also noted.

Full Quantification of the Light-Mediated Gilch Polymerization

Alkoxy-substituted poly(p-phenylenevinylenes) (PPVs) continue to be major workhorse materials in optoelectronics, ranging from thin film electronics to bioimaging. An attractive synthetic route toward PPVs is the Gilch polymerization. Nevertheless, obtaining control over molecular weight and chain constitution is challenging due to the free-radical nature of this reaction. In this work we quantitatively show with in situ UV-irradiation NMR spectroscopy how control over the Gilch polymerization can be enhanced by irradiation with UV-light. The potential of this method has been demonstrated but never interpreted within a quantitative framework, resulting in a lack of mechanistic and kinetic insight. We account for this not only by in situ analyzing and modeling the photochemical Gilch polymerization but also by characterizing the photolysis of the starting material. The latter shows that the solvent THF likely acts as radical transfer agent in the Gilch pathway and similar precursor-based biradical routes. ...

Photochemistry for Well-Defined Polymers in Aqueous Media: From Fundamentals to Polymer Nanoparticles to Bioconjugates.

This review article highlights recent developments in the field of photochemistry and photochemical reversible deactivation radical polymerization applied to aqueous polymerizations. Photochemistry is a topic of significant interest in the fields of organic, polymer, and materials chemistry because it allows challenging reactions to be performed under mild conditions. Aqueous polymerization is of significant interest because water is an environmentally benign solvent, and the use of water enables complex polymer self-assembly and bioconjugation processes to occur. This review focuses on powerful new developments in photochemical aqueous polymerization reactions and their applications to the synthesis of well-defined polymer nano-objects and bioconjugates. It is anticipated that these aqueous photopolymerizations will enable the next generation of self-assembled structures and biohybrid materials to be developed under mild and environmentally friendly conditions.

Preparation of Graphene Oxide/Poly(1-vinylimidazole) Composites for Resistive Switching Memory.

In this study, a photochemical polymerization using graphene oxide (GO) as an initiator generated a new composite film with poly(1-vinylimidazole) (PVI) covered the GO sheets. Atomic force microscopy and infrared spectroscopy revealed the uniform layering of the PVI on the sheets. An ITO/GO-PVI/Cu device was fabricated from this synthesized film, and it exhibited a write-once-read-many-times (WORM) memory functionality with resistance switching under an applied voltage of -3.2 V. The ON/OFF current ratio of the device reached 106. An analysis of the current-voltage characteristics of the device indicated that the ON-state charge transport followed Ohmic conduction with metallic behavior, while the OFF-state charge transport was dominated by a trap-limited space charge limited conduction.

Effective carbon sequestration in Italian agricultural soils by in situ polymerization of soil organic matter under biomimetic photocatalysis

AbstractFacing an exploding population growth with consequent increase of agriculture intensification, new chemical technologies are being sought to limit organic matter losses and reduce land degradation. Here, we report that an effective organic carbon sequestration in different cropped soils of Italy is obtained by an in situ photo‐oxidative coupling among soil humic molecules, when catalyzed under solar irradiation by a water‐soluble biomimetic iron‐porphyrin catalyst amended to field soils. A 3‐year long field study showed that the catalyst‐assisted in situ photochemical polymerization of humic matter enabled a yearly sequestration of soil organic carbon that ranged from 2.2 to 3.9 t ha−1 y−1, despite the periodical soil disturbance due to a conventional tillage management. This significant stabilization of organic matter was observed not only in bulk soils but also in water‐stable aggregates, whose loss of organic carbon during separation was limited in catalyst‐treated soils. Although crop yields were the same in treated and control soils, measurements of phospholipids fatty acids and soil enzyme activities indicated that the catalyzed in situ photo‐oxidative coupling of humic molecules did not alter the structure and activity of microbial communities and the biological functions of soils. This innovative and ecologically safe catalytic technology may be developed as a useful soil management practice to stabilize organic matter in situ in arable soils, while concomitantly ensuring soil functions and sustainability of crop production.

Room temperature synthesis and binding studies of solution-processable histamine-imprinted microspheres.

Accurate quantification of histamine levels in food and in biological samples is important for monitoring the quality of food products and for the detection of pathophysiological conditions. In this study, solution processable histamine-imprinted microspheres were synthesized at 30°C via dilute free radical phototochemical polymerization technique using ethylene glycol dimethacrylate (EGDMA) as the crosslinker and methacrylic acid (MAA) as the monomer. The processability of the resulting polymer is dictated by the monomer feed concentration (eg, 4 wt% 80:20 EGDMA:MAA formulation) and solvent (acetonitrile). Whereas, the particle size is influenced by the monomer feed concentration, the presence of template molecule, and independent of the crosslinker content. Evaluation of the binding performance of the photochemically imprinted polymers (PCP) with different crosslinker content (80 and 90 wt%) indicated that the selective binding capacity was notably higher in PCP-80 (N= 16.0 μmol/g) compared to PCP-90 (N= 10.1 μmol/g) when analyzed via frontal analysis capillary electrophoresis (FACE) using Freundlich isotherm. In addition, PCP-80 microspheres are more selective toward histamine than conventional thermal polymers (CTP-80) prepared at 60°C in the presence of structural analogs such as histidine, imidazole, and tryptamine under cross-rebinding and competitive conditions. These results demonstrated that histamine-selective imprinted polymers can be obtained readily using room temperature photochemical polymerization where these materials can be subsequently used as recognition element for optical-based histamine sensing.

Effects of photoinitiator on electro-optical properties of polymerization-induced phase separation blue-phase liquid crystals.

We have reported polymer-dispersed blue-phase (PDBP) liquid-crystal films via polymerization-induced phase separation. PDBP films are prepared by photochemical polymerization of curable crosslinking agent, monomer and blue-phase liquid crystal under an ultraviolet (UV) light. The influences of photoinitiator and weight ratio between monomer/crosslinking agent and blue phase on the electro-optical properties of PDBP liquid-crystal samples are investigated. The electro-optical (E-O) properties of PDBP films are determined in the top-down electro-optical cell. PDBP liquid-crystal films show good E-O properties with high contrast ratio and fast response time.

One-Dimensional Coordination Polymers of Bis(3-pyridyl-acrylamido)ethane: Influence of Anions and Metal Ions on Their Solid State [2 + 2] Photochemical Polymerization and Dimerization Reactions

The coordination polymers (CPs) of bis(3-pyridyl-acrylamido)ethane (L) with nitrate, acetate, and perchlorate salts of Cu(II), Cd(II), and Zn(II) were synthesized, and their crystal structures have been analyzed with respect to the influence of anions, hydrogen bonding, and their solid state [2 + 2] photochemical reactivity. Four out of the six CPs (1–4) containing NO3– and AcO– ions were found to form one-dimensional chains and exhibit solid state [2 + 2] reactivity. Two CPs (5–6) containing ClO4– ions were found to form ML2 discrete complexes which are photostable. The CPs 1 and 4 were found to form single [2 + 2] dimers, while 2 and 3 resulted in the formation of polymers via solid state [2 + 2] polymerization upon irradiation. The photoproducts are characterized by 1H NMR, electrospray ionization mass spectrometry, and matrix-assisted laser desorption/ionization–time of flight (MALDI-TOF) spectra. The dimer was charecterized by single crystal X-ray structure determination. The MALDI-TOF analyses of po...

Optical, morphological and dielectric characterization of MBBA liquid crystal-doped hydrogels

Abstract In this work, MBBA liquid crystal-doped hydrogels are investigated through of Scanning Electron Microscopy (SEM), Polarized Optical Microscopy (POM), Optical Transmittance (OT) and Dielectric Spectroscopy (DS) techniques. For the synthesis of the hydrogels and of their composites a solution (20% water and 80% acetone) of the potassium periodate (KIO 4 ) was prepared. The samples were prepared by radicalar photochemical polymerization of acrylamide monomer (AAm) in the presence of N , N ′-methylene-bis-acrylamide (MBAAm) as a cross-linking agent. Potassium periodate (KIO 4 ) was used as a photopolymerization initiator. In such synthesis, acrylamide monomer (AAm-Aldrich, 14, 866–5) was added with cross-linking agent MBAAm (N, N-methylene-bis-acrylamide) and liquid crystals MBBA (N-(4-methoxybenzilidene)-4(butylaniline)). The acetone was used to solubilize the liquid crystal MBBA in the solution. The resulting solution was placed and sealed between two glass plates coated with transparent and conducting films of tin oxide (SnO 2 ) with spacer of 25 μm. All samples were investigated at 15.0 °C, 23.0 °C and 35.0 °C. The electrical behavior of the samples was characterized by using a Solartron 1260A impedance-gain phase analyzer in the frequency range from 10 mHz to 10 MHz with amplitude of 10 mV. The experimental results from DS technique are discussed by using Davidson–Cole and Havriliak–Negami approaches. As one of main results of this work we noticed that the cavities of the hydrogels synthesized with the use of acetone can be able to confine the free ions of the liquid crystal added to the polymeric matrix.

High-refractive quinolinone-based polymers for ophthalmic devices

Seven novel high refractive index (HRI) acrylic monomers, comprising the quinolinone structural motive, have been synthesized and characterized. Cross-linked homo- as well as copolymers were prepared by photochemical bulk polymerization. The homopolymers show refractive indices at 589 nm (n589) ranging from 1.60 up to 1.68, glass transition temperatures (Tg) from 52 to 76 °C, and Abbe numbers (νAbbe) of 19 to 25. Due to these parameters, the homopolymers are not suitable to be used directly for intraocular lens (IOL) manufacture, but the quinolinone monomers may be used as high refractive index components in copolymers. Potential mixtures were calculated theoretically and one example, a copolymer with PEA and PEGPEA, was prepared and characterized. The experimentally found values were Tg = 24 °C, n589 = 1.593, and νAbbe = 28.3. Interestingly, the quinolinone compound which does not have any spacer between the polymerizable group and the high refractive index group appears to be the most useful one. The lightfastness of the new material fulfills the demands for IOLs. Quinolinone derivatives are promising new comonomers for high refractive index copolymers.

Toward 4D Nanoprinting with Tip-Induced Organic Surface Reactions.

Future nanomanufacturing tools will prepare organic materials with complex four-dimensional (4D) structure, where the position (x, y, z) and chemical composition within a volume is controlled with sub-1 μm spatial resolution. Such tools could produce substrates that mimic biological interfaces, like the cell surface or the extracellular matrix, whose topology and chemical complexity combine to direct some of the most sophisticated biological events. The control of organic materials at the nanoscale-level of spatial resolution could revolutionize the assembly of next generation optical and electronic devices or substrates for tissue engineering or enable fundamental biological or material science investigations. Organic chemistry provides the requisite control over the orientation and position of matter within a nanoscale reference frame through the formation of new covalent bonds. Several challenges however preclude the integration of organic chemistry with conventional nanomanufacturing approaches, namely most nanolithography platforms would denature or destroy delicate organic and biologically active matter, confirming covalent bond formation at interfaces remains difficult, and finally, only a small handful of the reactions used to transform molecules in solution have been validated on surfaces. Thus, entirely new approaches, where organic transformations and spatial control are considered equally important contributors, are needed to create 4D organic nanoprinting platforms. This Account describes efforts from our group to reconcile nanolithography, and specifically massively parallel scanning probe lithography (SPL), with organic chemistry to further the goal of 4D organic nanoprinting. Massively parallel SPL involves arrays of elastomeric pyramids mounted onto piezoelectric actuators, and creates patterns with feature diameters below 50 nm by using the pyramidal tips for either the direct deposition of ink or the localized delivery of energy to a surface. While other groups have focused on tip and array architetctures, our efforts have been on exploring their use for localizing organic chemistry on surfaces with nanoscale spatial resolution in 3D. Herein we describe the use of massively parallel SPL to create covalently immobilized patterns of organic materials using thermal, catalytic, photochemical, and force-accelerated reactions. In doing so, we have developed a high-throughput protocol for confirming interfacial bond formation. These efforts have resulted in new opportunities for the preparation of glycan arrays, novel approaches for covalently patterning graphene, and a 3D nanoprinter by combining photochemical brush polymerizations with SPL. Achieving true 4D nanoprinting involves advances in surface chemistry and instrumentation development, and to this end 4D micropatterns were produced in a microfluidic photoreactor that can position polymers composed of different monomers within micrometer proximity. A substantial gap remains, however, between these current technologies and the future's 4D nanomanufacturing tools, but the marriage of SPL with organic chemistry is an important step toward this goal. As this field continues to mature we can expect bottom-up 4D nanomanufacturing to begin supplanting conventional top-down strategies for preparing electronics, bioarrays, and functional substrates. In addition, these new printing technologies may enable the preparation of synthetic targets, such as artificial biological interfaces, with a level of organic sophistication that is entirely unachievable using existing technologies.

A New Versatile Water-Soluble Iniferter Platform for the Preparation of Molecularly Imprinted Nanoparticles by Photopolymerisation in Aqueous Media.

The multi-step synthesis of a new water-soluble dithiocarbamate iniferter platform for the preparation of nanoparticles and -gels in aqueous solvents by photoinduced living-radical polymerisation is described herein. The water solubility of the dithiocarbamate iniferter was achieved by incorporating two unprotected glucose units into the iniferter structure by copper(I)-catalysed azide-alkyne cycloaddition ("click chemistry"). Molecularly imprinted nanoparticles (MIPs) specific for 2,4-dichlorophenoxyacetic acid and the corresponding non-imprinted particles (NIPs) were prepared in pure water by using the prepared iniferter as photoinitiator. Radioligand binding tests confirmed a high imprinting factor, and the living character of the iniferter was demonstrated by re-initiating a second photochemical polymerisation on the NIP nanoparticles in water by using ethylene glycol methacrylate phosphate. Our newly synthesised structure is a promising tool for iniferter-mediated photopolymerisations in aqueous media for the preparation of biocompatible nanomaterials with high potential for biomedical applications in a bottom-up fashion.

Novel Dual‐Cure Initiating System for Cationic Polymerization of Epoxides

Pyrylium salts are found to be effective initiators for both photochemical and thermal cationic polymerization of epoxy resin. The photopolymerization results show that triphenylpyrylium salt derivatives are the most efficient structures. These compounds also exhibit some thermal reactivity at room temperature in the absence of light. However in such case, the gel time of the resin is quite high. Therefore, to speed up the thermal reaction, nucleophilic compounds are added as coinitiators, these compounds being known to yield a fast decomposition of pyrylium salts. This indeed increases the polymerization of epoxy resin at room temperature, opening the way to the development of quite efficient dual‐cure photochemical/thermal initiating system for cationic polymerization. image

Optimization of 4D polymer printing within a massively parallel flow-through photochemical microreactor

Brush polymer patterns, where the position (x,y), height (z), and chemical composition of each feature in an array were controlled independently, were prepared by combining massively parallel tip-based photolithography, microfluidics, and photochemical radical polymerizations.

Novel quaternary ammonium-functionalized diacetylenes: Their synthesis and photopolymerization

In this paper, we report the synthesis of novel diacetylenes bearing trimethylammonium end groups, their photochemical polymerization and the spectroscopic characterization of the polymers by different techniques (UV–vis, fluorescence, FT-IR, Raman). The obtained results shed light on the role of the trimethylammonium head group (and its counterions) in the polymerization process. It is also demonstrated that the presence of an internal, H-bondable amide function in the diacetylene tail favors the photopolymerization process as well as the formation of the polydiacetylene in its blue, highly-conjugated form. Moreover, the corresponding polymer in the less-conjugated red phase, typical of polydiacetylenes in solution, shows significantly enhanced emission properties with respect to its counterparts carrying all-saturated lateral chains.

High performance resistive switching memory organic films prepared through PPy growing on graphene oxide substrate

In this study, the photochemical polymerization using graphene oxide (GO) as initiator generates a new composite film with polypyrrole (PPy) covering the GO nanosheets. The specular reflection infrared spectroscopy reveals the continuous upload of the conjugated polymers. Structures of the as-synthesized films are studied by using Raman and X-ray photoelectron spectroscopy with the aim of gaining an insight into the interface. The electronic properties of the composite films are investigated using solid-phase ultraviolet photoelectron spectroscopy. Fabricated from the synthesized film, the ITO/GO–PPy/Al device exhibits a nonvolatile rewritable memory with a reversible bistable resistance switching and the turn on voltage of 1.7 V. The ON/OFF current ratio reaches 105. Analyzing the current–voltage characteristics indicates that the ON-state charge transport follows Ohmic conduction, and the OFF-state charge transport is dominated by trap-limited space charge limited conduction.

Chromatographic efficiency comparison of polyhedral oligomeric silsesquioxanes-containing hybrid monoliths via photo- and thermally-initiated free-radical polymerization in capillary liquid chromatography for small molecules

Monolithic poly(methacrylate epoxy cyclosiloxane-co-polyhedral oligomeric silsesquioxanes) (epoxy-MA–POSS) capillary columns have been prepared via either photo- or thermally-initiated polymerization of the corresponding monomers using a 1-propanol/PEG 400 mixture as porogens. Photochemical polymerization was accomplished by irradiation of the UV-transparent capillary for 10min at room temperature, while thermal polymerization was performed at 55°C, 60°C or 65°C for 18h. The evaluation of chromatographic property for two hybrid epoxy-MA–POSS monoliths was carried out. The results indicate that hybrid monoliths fabricated by photochemical initiation exhibit higher column efficiency (97,000–98,400plates/m) than those synthesized by thermal polymerization (41,100–48,000plates/m) in cLC. The higher efficiency of photo-initiated hybrid monoliths is closely related to lower eddy dispersion (A-term) and mass transfer resistance (C-term).

Microstructure and electrical property of epoxy/graphene/MWCNT hybrid composite films manufactured by UV-curing

UV-cured epoxy hybrid composite films were manufactured by efficient and facile cationic photochemical polymerization of 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylate mixtures including 5.0 wt% carbon nanofillers of different graphene/multi-walled carbon nanotube (MWCNT) compositions of 10/0, 9/1, 7/3, 5/5, 3/7, and 0/10 by weight ratio. TEM images confirmed that the mixed carbon nanofillers of graphene and MWCNT were well dispersed in the UV-cured epoxy matrix, while MWCNT as a single carbon nanofiller component was aggregated in the matrix. The electrical resistivity of the composite films was thus varied with the increment of the relative MWCNT content in 5.0 wt% carbon nanofillers, i.e., ∼160 Ωcm for the epoxy/graphene composite film, 30∼80 Ωcm for the epoxy/graphene/MWCNT composite films, and ∼16,200 Ωcm for the epoxy/MWCNT composite film. The decreased electrical resistivity of the epoxy/graphene/MWCNT composite films was associated with the interconnected network formation of graphene sheets and MWCNTs. Thus the UV-cured epoxy/graphene and epoxy/graphene/MWCNT composite films exhibited excellent electric heating performance in terms of rapid temperature response, stable maximum temperature, and high electric power efficiency. In addition, the UV-cured epoxy hybrid composite films as electric heating materials were found to be thermally stable up to ∼290 °C.

Radical polymerization in holographic grating formation in PQ-PMMA photopolymer part I: Short exposure

Photochemical radical polymerization in phenathrenequinone doped poly(methyl methacrylate) photopolymer are investigated theoretically and experimentally at short exposure. In experiments, the dynamic evolution of diffraction efficiency in grating formation is measured. Based on the rate equations of chemical reactions, the analytical expressions of components evolution are deduced to compare the contributions of several photochemical processes to the grating formation. The percentages of these radical polymerizations, namely the polymerization of one PQ with one matrix molecule, the bimolecular combination of MMA molecules, and the disproportionation of MMA molecules, are extracted quantitatively by nonlinear fitting experimental curves. Furthermore, the kinetics parameters, quantum yield Φ and molar absorption coefficient ε of photosensitizers, are determined to demonstrate the rationality of chemical processes. The theoretical results indicate that the polymerization of PQ with matrix is primary photochemical process which dominated the grating formation at short exposure. The contribution of chain polymerization of MMA molecules on the grating can be neglected. This investigation can provide a significant foundation for improving holographic characteristics by photochemical mechanism.