Spatial and temporal evolution of the photoinitiation rate for thick polymer systems illuminated by polychromatic light: selection of efficient photoinitiators for LED or mercury lamps

BACKGROUND: Four common free radical photoinitiators were evaluated for use in thick photopolymerizations illuminated with a medium‐pressure 200 W mercury–xenon arc lamp and a high‐intensity 400 nm light‐emitting diode (LED) lamp. For each photoinitiator/lamp combination, the spatial and temporal evolution of the photoinitiation rate profile was analyzed by solving the set of differential equations that govern the light intensity gradient and initiator concentration gradient for polychromatic illumination. RESULTS: The simulation results revealed that two of the four photoinitiators evaluated were ineffective for photoinitiating thick polymer systems. The photoinitiator bis(2,4,6‐trimethylbenzoyl)‐phenylphosphine oxide, in combination with the 400 nm LED lamp, was shown to be the most efficient photoinitiator/light source combination for photoinitiation of thick systems. CONCLUSION: The results show that some photoinitiators commonly used for photopolymerization of thin coatings are ineffective for curing thick systems. LED light sources provide advantages over traditional mercury lamps, and may have tremendous potential in the effective photoinitiation of thick polymer systems. Copyright © 2008 Society of Chemical Industry     

Prospects in the application of a frontally curable epoxy resin for cured-in-place-pipe rehabilitation

Photocurable acrylates and vinyl esters are among the most commonly used resins in cured-in-place-pipe (CIPP) rehabilitation technology, as they impart excellent thermomechanical properties in composite pipes. In the quest for achieving a higher energy efficiency of the photo-curing process in CIPP, the frontal polymerization technique is a viable alternative that requires a lower irradiation dosage coupled with exceptionally high curing speeds and depths. Herein, for the first time, we report the application of frontal polymerization in the rehabilitation of underground pipes using a newly developed frontally curable epoxy-based resin (Trelleborg Self-Curing*). The neat resin is characterized for degree of cure, glass transition temperature, and mechanical properties via FTIR, DMA, and tensile tests, respectively. In a comprehensive way, the properties are benchmarked against commercially available acrylate (Trelleborg Light Cure*) and vinyl ester (Trelleborg Rapid Cure*) resins to evaluate their applicability for CIPP. The results show a higher glass transition temperature and final monomer conversion for the frontally cured resin, which cures significantly faster than the reference resins under the same irradiation conditions. In proof-of-concept trials, the newly developed resin successfully cures polymeric liners in a PVC host pipe with 100% water tightness and without losing its structural integrity. Results from ring stiffness tests for cured composite pipes additionally show that liners cured with Trelleborg Self-Curing* resin pass the minimum required Young's modulus for non-pressure drainage pipes as per ASTM F1216. Thus, frontally curable epoxy-based resins are a promising and competitive alternative to acrylates and vinyl esters in CIPP.     

Design of polymer nanofiber systems for the immobilization of homogeneous catalysts - Preparation and leaching studies

In this paper a novel general concept for the immobilization of catalysts is presented. It will be shown that catalysts covalently bound to low-molecular weight polystyrene (M_n > 4000 g/mol) can be immobilized into high molecular weight polystyrene nanofibers using the electrospinning process. The immobilized catalyst-oligostyrene conjugates are well dispersed within the fibers as shown by DSC and X-ray studies. In DMSO, the oligostyrene tails of the catalysts suppress the leaching of the catalysts out of the fibers into the solution for thermodynamic reasons. Leaching studies are conducted using naphthalene-conjugated oligostyrenes using fluorescence spectroscopy. The naphthalene-polystyrene conjugates with defined molecular weight are readily prepared using nitroxide-mediated radical polymerization (NMP). As a model catalyst system, proline-polystyrene conjugates are synthesized by NMP to study catalyst leaching out of the polystyrene nanofibers used as a catalyst matrix.     

Alternatives for multiobjective optimization of a polymerization process

The optimal control policies for a polymerization process, particularly for batch free‐radical polymerization of methyl methacrylate, were determined using a multiobjective optimization technique. The process objectives considered in the optimization include monomer conversion, polydispersity index, polymerization degree, and total reaction time, weighted and combined in a scalar objective function. The decision variables were the initial concentration of the initiator and the temperature represented by isothermal steps. For solving the optimization problem, several methods based on sequential quadratic programming and a genetic algorithm were used and compared. Combining them into a hybrid method (the genetic algorithm provided the initial values for the traditional iterative method) led to the best results. The aims of this study were to develop an approach for optimizing the polymerization process and to describe alternatives for formulating and solving this problem, emphasizing the importance of user decision in choosing solutions based on technological criteria. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3680–3695, 2006     

Effect of the addition of inert or TEMPO‐capped prepolymer on polymerization rate and molecular weight development in the nitroxide‐mediated radical polymerization of styrene

The importance of diffusion‐controlled (DC) effects on controlled radical polymerization (CRP) processes has been rather controversial and usually considered only if there is some mismatch between experimental data and model predictions of polymerization rate and molecular weight averages. Results from an experimental study designed to create conditions in which DC effects may be present from the outset for the bimolecular nitroxide‐mediated radical polymerization (NMRP) of styrene in the presence of 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) and dibenzoyl peroxide (BPO), are presented herein. The experiments consisted of adding size exclusion chromatography (SEC) polystyrene (PS) standards or nitroxyl‐capped PS (of different molecular weights, in several proportions), to a conventional recipe of bimolecular NMRP of styrene, and studying the effect of their presence on polymerization rate and molecular weight development. A previously developed kinetic model for NMRP of styrene was modified to take into account the presence of prepolymer as an inert “solvent,” or as a monomolecular “controller” of high molecular weight. The effects of DC reactions (propagation, termination, activation, and deactivation of polymer radicals) were modeled using conventional free‐volume theory. Reasonably, good agreement between experimental data and model predictions with either modeling approach was obtained. It was concluded that DC effects are weak in the NMRP of styrene, even in the presence of prepolymer. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Photopolymerization of N-vinylcarbazole in dichloromethane in the presence and absence of free radical photoinitiators

The photopolymerization of N-vinylcarbazole in dichloromethane was investigated, both in the presence and absence of free radical photoinitiators. The steric microstructure of the poly(N-vinylcarbazole) (PVK) samples produced was monitored as a function of temperature qualitatively, using ¹H n.m.r. and quantitatively, using glass transition temperature measurements. The activation enthalpy and entropy differences between isotactic propagation when the previous diad was syndiotactic and syndiotactic propagation when the previous diad was isotactic (ΔH³_s/i-ΔH³_i/s) and (ΔS³_s/j-ΔS³_i/s) respectively were obtained from plots of log X_i/X_sversus 1/T for the free radically and cationically polymerized components of the PVK samples. Values for (ΔH³_s/i-ΔH³_i/s) and (ΔS³_s/i-ΔS³_i/s) of ?2.65 kJ mol^?1 and ?11.7 J mol^?1 grad^?1 respectively were found for free radically polymerized fractions and +260 J mol^?1 and ?0.3 J mol^?1 grad^?1 for cationically polymerized fractions.     

紫外光引发AM—DMC自由基共聚研究

采用光敏引发聚合的方法,以丙烯酰胺（AM）和甲基丙烯酰氧乙基三甲基氯化铵（DMC）为单体,通过水溶液自由基共聚法制备了阳离子聚丙烯酰胺（CPAM）,讨论了单体浓度、阳离子单体比例、引发温度、引发剂浓度、光照强度对产品性能的影响,最终确定了最佳反应条件：单体质量分数30％,阳离子单体质量分数5％,引发温度22℃,引发剂质量分数0．35％,光照强度0．798mW／cm^2。通过红外光谱对产品进行了表征。     

Behavior of UV‐cured print inks on LDPE and PBAT/TPS blend substrates during curing,postcuring, and accelerated degradation

During radiation curing, a reactive formulation is converted into a highly crosslinked coating film by means of polymerization reactions. This three‐dimensional (3D) network is resistant to external degrading factors as it cannot be undone by any physical–chemical means. In this study, various ultraviolet (UV)‐curable ink formulations with different pigments were developed. The behavior of the UV‐curable inks was evaluated during UV curing in a photocalorimeter or in a UV tunnel. Inks were exposed to accelerated aging in an accelerated weathering chamber and their physical–chemical properties were investigated. The presence of residual fractions of unreacted species trapped in the 3D network formed during UV curing interferes with the degradation of the main structure during exposure in the weathering chamber. The ink formulations that did not easily absorb UV light increased in gloss and hardness, indicating that residual crosslinking is taking place at the same time that degradation is occurring. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41116.     

Modeling gel effect in branched polymer systems: Free‐radical solution homopolymerization of vinyl acetate

In this work a comprehensive mathematical framework is developed for modeling gel effect in branched polymer systems with application in the solution polymerization of vinyl acetate. This model is based on sound principles such as the free‐volume theory for polymer chains diffusion. The model predictions for monomer conversion and number‐ and weight‐average molecular weights were found to be in good agreement with published data in the literature. Moreover, the joint molecular‐weight distribution–long chain branching distribution is calculated by direct numerical integration of a large system of nonlinear ordinary integral‐differential equations describing the mass conservation of macromolecular species in a batch reactor. This allows studying the effect of process conditions such as initiator and solvent concentration on the product quality. It is believed that this work might contribute to a more rational design of polymerization reactors. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

High performance of the linked visible photoinitiator for free radical polymerization based on erythrosine B derivative

A novel erythrosine B derivative linked with a tertiary amine used as a visible light initiator for free radical polymerization was synthesized and characterized. For comparison, the free hydrophobic erythrosine B derivative was also synthesized and its combination with the tertiary amine was used as the separated two component photoinitiator. The linked initiator exhibited higher photoinitiator efficiency in high viscosity monomer than in low viscosity one, compared with the separated counterpart. Especially, when it was combined with iodonium salt, the further promotion of the photoinitiator efficiency was observed, compared with the separated three component system. It was found that as iodonium salt together with tertiary amine was continuously added to the formula with the linked initiator, the photoinitiator efficiency was dramatically enhanced compared with the same addition to the formula with the separated counterpart, revealing the application potential of the linked initiator. And the continuous addition of either the iodium salt or the tertiary amine to the formula only leaded to the small size increase of the photoinitiator efficiency. These results suggested that there existed an interdependent relationship between iodonium salt and tertiary amine in promoting the photoinitiator efficiency of the dye/amine/iodonium salt system. For these, the corresponding synergistic mechanism was proposed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42361.     

Macromolecular photoinitiators enhance the hydrophilicity and lubricity of natural rubber

A mild and facile strategy to coat natural rubber (NR) with a hydrophilic coating is described that uses light and photoinitiator copolymers. Five high molecular weight photoinitiator copolymers, composed of hydrophilic (e.g., 2‐hydroxyethyl acrylate [HEA], poly(ethylene glycol) [PEG], N‐vinylpyrrolidone [NVP], N‐isopropylacrylamide [NIDAM], and acrylic acid [AA]) and hydrophobic benzophenone (BP) units, are synthesized and evaluated for coating NR on UV irradiation. When the HEA/BP, NVP/BP, and AA/BP macromolecular photoinitiators attach to the NR surface, the latter becomes hydrophilic. The resulting hydrophilic coatings on NR sheets are analyzed via FT‐IR spectroscopy, scanning electron microscopy, atomic force microscopy, contact angle measurements, and transwell cytotoxicity assays using NIH 3T3 fibroblast cells. The addition of high molecular weight hydrophilic polymers (e.g., polyvinylpyrrolidone and poly(2‐methacryloyloxyethyl phosphorylcholine)) to the coating further enhances the coating's hydrophilicity and lubricity. The application of these non‐cytotoxic, hydrophilic, and lubricious coatings on NR expands current applications and usage of NR. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43930.     

Imidazole modified acrylate-containing photocured hydrogels for the efficient removal of malachite green dye from aqueous solutions

In this work, we aimed to prepare a simple and an efficient adsorbent for the removal of toxic, cationic dye; malachite green (MG). We reviewed many previous studies and designed our adsorbent based on the rationale that (1) acidic groups containing monomers which are capable of making hydrogen bonds (or electrostatic interactions) with MG are very effective in adsorption and (2) π-π stacking enhances the adsorption capacity. We first synthesized an imidazole-acrylate adduct and used it for the preparation of photocured hydrogels. The imidazole-acrylate adduct was characterized by H NMR and FTIR spectroscopy. The effect of experimental conditions on the MG adsorption properties of the hydrogels such as the effect of pH, time and MG concentration were also investigated. Under the optimum conditions (pH = 6 and 220 min contact time) at room temperature, the maximum adsorption capacity was found as high as 714.28 mg/g. The results showed that the adsorption process of the optimum hydrogel, which can be used 4 times without a significant loss in its adsorption capacity, fits the Langmuir isotherm model. The hydrogel adsorbent displayed good selectivity and reusability.     

Monomers for Adhesive Polymers, 9–Synthesis,Radical Photopolymerization,and Properties of (Meth)acrylamido Dihydrogen Phosphates

5‐Methacrylamidopentyl ( 3a ), 10‐(N‐methylacrylamido)decyl ( 3b ), or 11‐(N‐methylacrylamido)undecyl dihydrogen phosphate ( 3c ) are synthesized by (meth)acrylation of the corresponding ω‐aminoalkane‐1‐ols with methacrylic anhydrid or acryloyl chloride followed by phosphorylation of the formed ω‐(meth)acrylamidoalkane‐1‐ols. The monomers show a significantly improved hydrolytic stability compared to the corresponding methacrylate‐based dihydrogen phosphates. The photopolymerization of 3a–c with a bis(acrylamide) crosslinker confirms a high reactivity in the free‐radical copolymerization. These monomers enable the mediation of a strong bond between the enamel or dentin surface and a restorative composite under self‐etching conditions.

     

Camphorquinone-amines photoinitating systems for the initiation of free radical polymerization

Results of the camphorquinone/hindered piperidines, visible-light photoinduced polymerization of triethyleneglycol dimethacrylate are presented. The effectiveness of piperidines as a coinitiator is compared with a few aliphatic amines and aromatic amines. The main objective in this research was to study the mechanism of photoinitiation of polymerization. Reactive radicals that initiate the polymerization are formed by a mechanism of hydrogen atom abstraction by the triplet state of camphorquinone, mediated by photoinduced electron transfer. The different efficiencies of the aliphatic amines and of the aromatic amines affecting photopolymerization are explained on the basis of the different quenching reactivities of the excited states of camphorquinone.     

Synthesis of non-collapsed hollow polymeric nanoparticles with shell thickness on the order of polymer gyration radius

The hollow polymeric nanoparticles of poly(styrene-co-divinylbenzene) of ultra-thin shell were synthesized by the interfacial RAFT miniemulsion polymerization with various particle sizes, void fractions and crosslinking degrees. With the void fraction increased, the hollow nanoparticles were more likely to collapse once dried. This collapse could be suppressed by simply increasing the level of crosslinker. The fraction of the collapsed hollow particles decreased nearly linearly with the increasing level of crosslinker. The non-collapsed hollow nanoparticles with a void fraction about 60% and shell thickness of 11.5 nm were fabricated with the crosslinker (divinylbenzene) of 0.67 mass fraction based on monomers. The resulted polymeric shell of the hollow nanoparticles was mesoporous, which had high surface area 514 m²/g, extremely large pore volume 2.74 ml/g and a most probable pore diameter of 9 nm. The structures of the hollow nanoparticles were mechanically stable not only in the solvent but also under harsh conditions like high temperature (200 °C) and strong shear. Additionally, the hollow nanoparticles were able to be fully re-dispersed in the solvent. The average hollow particle diameter was tuned from 70 nm to 199 nm by decreasing the level of the amphiphilic RAFT agent. The shell thickness was tuned from 10.6 nm to 19.3 nm by changing the core/shell ratios.     

Thermal decomposition of diethyl ketone triperoxide in methyl methacrylate: Theoretical and experimental study of the initial solvation state and its influence on the polymerization process

The decomposition rate constant (k_d) of diethyl ketone triperoxide (DEKTP, 3,3,6,6,9,9‐hexaethyl‐1,2,4,5,7,8‐hexaoxacyclononane) in methyl methacrylate (MMA) was determined by the kinetic study of its thermal decomposition at temperatures from 110 to 140°C. The calculated k_d for DEKTP in MMA was 2.4 times lower (at 130°C) compared with that previously determined and reported in styrene (St). Density functional theory (DFT) calculations demonstrated that the decomposition of DEKTP molecule in MMA required higher interaction energy than in St, thus explaining its lower k_d value. Bulk polymerization kinetics of MMA using DEKTP as the initiator revealed the presence of an induction period, in contrast with St polymerization, providing clear evidence of the solvation state influence at early polymerization stages. This work provides mechanistic insights into the interactions among the multi‐functional cyclic peroxide DEKTP and vinyl monomers; St and MMA, and their influence on the polymerization kinetics. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42905.     

Studies on the initiation of a free‐radical condensation hybrid polymerization system

Compositions of hexamethoxymethyl melamine (HMMM)–ether polyol and acrylate can be cured by a hybrid polymerization comprising condensation polymerization and free‐radical polymerization, in the presence of a latent acid catalyst at high temperature. It was found that the initiating free radical was derived from the decomposition of hydroperoxides, which was formed by the oxidation of active methylene groups catalyzed by HMMM. It was also found that strong acid could accelerate the free‐radical polymerization in the hybrid system. To make the formulations more flexible, the activities of different types of methylene groups were investigated and two compounds with more active methylene groups and hydroxyl were synthesized, characterized, and used as crosslinker–initiators in the hybrid polymerization system. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1195–1200, 2001     

Efficient visible photoinitiator with high‐spectrum stability in an acid medium for free‐radical and free‐radical‐promoted cationic photopolymerization based on erythrosine B derivatives

Three dye‐linked photoinitiators with excellent spectral stability in an acid medium were synthesized by the covalent bonding of a coinitiator (tertiary amine) and a benzoyl group or two coinitiators to the phenolic and carboxyl group position of erythrosine B. The combination of the iodonium salt and free tertiary amino used to initiate the free‐radical/cationic visible photopolymerization was investigated to acquire the relationship between the structure and performance. The photoinitiating ability of the derivative with the phenolic position bearing a coinitiator was poorer than of the derivative with the carboxyl group bearing one because of the strong back electron transfer of the former. For the derivative with a linked coinitiator on the carboxyl position, the proximity effect between the sensitizer and the coinitiator moiety resulted in an excellent photoinitiating ability for radical/cationic polymerization; this suggested its potential for application. Although radical/cationic photopolymerization could be initiated by the derivative/coinitiator/iodonium salt, the different component ratios between them had different effects on these two polymerizations; this provided useful information for the design of effective photoinitiators for different polymerizations. On the basis of the fluorescence quenching and photopolymerization results, a corresponding synergistic mechanism was proposed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43035.     

Synthesis and characterization of a polymer/multiwalled carbon nanotube composite and its application in the hydration of ethylene oxide

Multiwalled carbon nanotubes (MWNTs) were incorporated into the crosslinking network of a styrene–divinylbenzene copolymer (PS–DVB) via suspension polymerization. The prepared crosslinking PS–DVB with MWNTs was first treated with chloromethyl methyl ether to introduce chloromethyl groups through Friedel–Craft reaction; then, the chloromethylation product was reacted with trimethyl amine to obtain the target polymer/carbon nanotube composite: PS–DVB/MWNT ion‐exchange resin. The obtained composite was characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, Raman spectroscopy, and X‐ray photoelectron spectroscopy. The results show the successful incorporation of MWNTs into the polymer network. The physical and chemical properties of the PS–DVB/MWNT ion‐exchange resin were nearly the same as those of the controlled sample. With its excellent antiswelling properties, the catalytic behavior of the polymer composite was examined in the hydration of ethylene oxide. Also, it demonstrated excellent stability as a catalyst without a decline in conversion and selectivity in a long‐time run. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010