Photopolymerization of a novel tetraoxaspiroundecane and silicon‐containing oxiranes

New multifunctional silorane‐based systems were investigated, with respect to their photoreactivity, as potential matrix resins for low‐shrinkage/stress dental composites. The objective of this investigation was to synthesize and evaluate the reactivity of a silicon‐analogue oxaspirocyclic monomer with silorane‐based matrix resin systems during visible‐light polymerization. The experimental formulations contained (1) a silicon‐containing 1,5,7,11‐tetraoxaspiro[5.5]undecane (TOSU– IV ), (2) a phenylmethylsilane containing two cyclohexyloxiranyl groups, (3) a cyclotetrasiloxane containing four cyclohexyloxiranyl groups, and (4) a photocationic initiator system. Three main aspects were studied: (1) the photoreactivity of the tetraoxaspiroundecane (TOSU)/silorane reactant mixtures with differential scanning photocalorimetry, (2) oxirane ring‐opening reactions of siloranes during binary photopolymerization with Fourier transform infrared (FTIR), and (3) oxaspirocyclic ring‐opening reactions of the TOSU reactant during homophotopolymerization and binary photopolymerization with FTIR and NMR. A diallyl ether precursor of TOSU– IV was also included in selected studies. The main findings were as follows: (1) a feasible route for the successful synthesis of a silicon analogue (TOSU– IV ) was developed; (2) TOSU– IV was compatible and photoreactive, making possible the reduction of polymerization stress in silorane‐based matrix resins; and (3) spectroscopic evidence for both oxirane and oxaspirocyclic ring opening during the visible‐light photopolymerization of the test formulations was found. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 336–344, 2007     

Effect of polymerization conditions on o‐phenylenediamine and o‐phenetidine oxidative copolymers

A series of new o‐phenylenediamine (OPD)/o‐phenetidine (PHT) copolymers with partly phenazine‐like structures has been successfully synthesized at three polymerization temperatures by chemically oxidative polymerization in four different polymerization media. The molecular structures and properties of the resulting OPD/PHT polymers were investigated by IR, UV–vis and high‐resolution ¹H NMR spectroscopies, and DSC, in order to ascertain the effect of reaction temperature, comonomer ratio and acid medium. The copolymerization mechanism of OPD with PHT monomers has been proposed. It is found that the statistical OPD/PHT copolymer obtained at a temperature of 118 °C has a higher degree of polymerization than that obtained at 12–17 °C. The OPD content in the copolymers calculated from NMR spectroscopic analysis is higher than that in the feed OPD content, whereas the OPD content calculated from element analysis is slightly lower than the feed OPD content. It can be predicted that denitrogenation takes place in the OPD units during the polymerization process at OPD/PHT molar ratios of 90/10 and 100/0. These OPD/PHT copolymers exhibit a much better solubility than the OPD homopolymer, hence suggesting an incorporation of PHT units into the phenazine structure of the homopolymer. The thermal behavior of the copolymers was also studied. Copyright © 2004 Society of Chemical Industry     

Evaluation of Difunctional Vinylcyclopropanes as Reactive Diluents for the Development of Low‐Shrinkage Composites

Polymerization shrinkage of dental composites remains a major concern. Free‐radically polymerizable cyclic monomers can be a conceivable alternative to methacrylates for the development of low‐shrinkage composites. In this study, the one‐step synthesis of the novel low viscosity difunctional vinylcyclopropanes 1 – 4 is described. Photopolymerization kinetics of these monomers are investigated by photo‐differential scanning calorimeter, using bis(4‐methoxybenzoyl)diethylgermane as photoinitiator. Real‐time near‐infrared photorheology measurements are performed to evaluate rheological behavior (i.e., time of gelation, polymerization‐induced shrinkage force) and chemical conversion (i.e., double bond conversion at the gel point, final double bond conversion) of the vinylcyclopropanes in situ. The potential of these monomers as reactive diluents in dental restorative materials is evaluated. Composites based on vinycyclopropanes 1 – 4 show good mechanical properties and exhibit significantly lower volumetric shrinkage and shrinkage stress than corresponding dimethacrylate‐based materials. The results indicate that such monomers are promising candidates for the replacement of commonly used low viscosity dimethacrylates such as triethylene glycol dimethacrylate in dental composites.

     

Studies on the dielectric properties of poly(o‐toluidine) and poly(o‐toluidine‐aniline) copolymer

Poly(o‐toluidine) (PoT) and poly(o‐toluidine co aniline) were prepared by using ammonium persulfate initiator, in the presence of 1M HCl. It was dried under different conditions: room temperature drying (48 h), oven drying (at 50°C for 12 h), or vacuum drying (under vacuum, at room temperature for 16 h). The dielectric properties, such as dielectric loss, conductivity, dielectric constant, dielectric heating coefficient, loss tangent, etc., were studied at microwave frequencies. A cavity perturbation technique was used for the study. The dielectric properties were found to be related to the frequency and drying conditions. Also, the copolymer showed better properties compared to PoT alone. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 592–598, 2004     

Photopolymerization of methyl methacrylate by 2,2′‐dithiodiethanol: Effect of reaction conditions

The photopolymerization of methyl methacrylate (MMA) through the use of a novel disulphide, 2,2′‐dithiodiethanol (DDE), was studied. This photoinitiator is of special interest because of its possible use in the synthesis of polyurethane macrophotoinitiator. The photopolymerization was carried out in the Heber multilamp photochemical reactor (COMPACT‐LP‐MP88) at 254 nm. The effects of reaction conditions on the polymerization of MMA were studied. It was observed that the percentage conversion and molecular weight increased with the increases of monomer concentration and reaction time. However, for the initiator to monomer molar ratio, there was a critical molar ratio for maximum conversion. The results suggested the living radical nature of the photoinitiator, which was further investigated by the preparation of block copolymer with acrylonitrile. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1601–1606, 2006     

Using aluminium triflate as a co‐catalyst for the polymerization of o‐phenylenediamine and its derivatives

Aromatic diamine monomers, including o‐phenylenediamine (oPD), 4‐methyl‐o‐phenylenediamine (4Me‐oPD), 4,5‐dimethyl‐o‐phenylenediamine (dMe‐oPD) and 4‐(tert‐butyl)‐o‐phenylenediamine (tBu‐oPD), were polymerized by chemical oxidation using ammonium persulfate as an oxidant. Aluminium triflate (Al(OTf)₃) was also used for the first time as a co‐catalyst under various reaction conditions for the polymerization of oPD derivatives. The polymerization yield was improved when Al(OTf)₃ was introduced to the polymerization reaction for most polymers. The solubility of poly(4‐methyl‐o‐phenylenediamine) (P(4Me‐oPD)), poly(4,5‐dimethyl‐o‐phenylenediamine) (P(dMe‐oPD)) and poly(4‐(tert‐butyl)‐o‐phenylenediamine) (P(tBu‐oPD)) polymers was improved compared with the poly(o‐phenylenediamine) (P(oPD)) polymers in most common solvents. The homopolymers obtained were characterized by Fourier transform IR spectroscopy, UV?visible spectroscopy, ¹H and ¹³C NMR, wide‐angle X‐ray diffraction, DSC and TGA. The results showed that the yield, solubility and structure of the polymers are significantly dependent on the polymerization conditions. DSC measurements indicated that the polymers exhibited melting and crystallization transitions. The polymers also showed good thermal stability and decompose above 400 °C in nitrogen. © 2013 Society of Chemical Industry     

Photopolymerization kinetics of dimethacrylate‐based light‐cured dental resins

The influence of certain factors [structure and concentration of tertiary amines as coinitiators, monomer composition, presence of inorganic pigments, and incident light intensity (I₀)] on the polymerization rates (R_p), polymerization quantum yields, and conversions of bisphenol A–bis(glycidyl methacrylate) (Bis‐GMA)/triethylene glycol dimethacrylate based resins was studied. The initial rate of bulk polymerization increased and the final conversion decreased with the content of Bis‐GMA in the mixture. In contrast, it was established that, for all monomer compositions, the R_p grew when increasing the I₀, the R_p being directly proportional to the square root of I₀. Such behavior is in agreement with the well‐known kinetic expression for the ideal radical photoinitiated polymerization in solution of monofunctional monomers, in spite of the complexity of the dimethacrylate mixtures that were studied. Both the structure and the concentration of reducing amine affected the efficiency of the initiator system and therefore the kinetic behavior of polymerization of these formulations under irradiation. The rate of polymerization increased with the increase of coinitiator concentration over the interval of 0–1%, but later it diminished when increasing the amine content, suggesting that the excess coinitiator retards the polymerization process. The study of the photoreduction of camphorquinone in the presence of different amines showed that the efficiency of the coinitiator depends not only on its ability to photoreduce camphorquinone, forming amine‐derived radicals, but also on the reactivity of these radicals toward the initiation of acrylic monomer polymerization. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1016–1023, 2005     

Effects of the o‐aromatic ring in the molecular chain on the properties of polyester polyols

A series of liquid polyester polyols from adipic acid (AA), phthalic anhydride (PA), ethylene glycol, propanediol‐1,2, and trihydroxymethylpropane, varying in the molar ratio of PA to AA, were prepared. The effects of the o‐aromatic ring in the molecular chain, which came from PA, on the viscosity, glass‐transition temperature, and thermal degradation temperature of the polyester polyols were studied with viscometry, differential scanning calorimetry, and thermogravimetry. The intrinsic viscosity and glass‐transition temperature increased with the concentration of the o‐aromatic ring increasing. The temperature of the maximum thermal degradation rate for aliphatic polyester polyols was 434.20°C. Two steps of thermal degradation were found when there were o‐aromatic rings in the molecular chain. One thermal degradation temperature was 358.36–360.48°C, and the other was 412.85–427.18°C. Polyester polyols with o‐aromatic rings had higher stability at lower temperatures (<240.00°C). However, aliphatic polyester polyols had higher stability at higher temperatures (300.00–480.00°C). The activation energy and order of degradation were calculated from thermogravimetric curves. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1617–1624, 2002     

In‐situ curing analysis of photoreplicated objective lenses using Raman and IR spectroscopy

Optical pick‐up lenses are used in optical storage devices such as CD, DVD, and Blu‐Ray Disc. The production of such lenses is based on UV‐induced polymerization of a mixture of a dimethacrylate monomer and an initiator on a spherical glass substrate. The shape of the polymer layer is defined with an aspherical transparent mold. This means that the coating is completely surrounded by glassy materials during processing. Raman spectroscopy is applied in situ to monitor the polymerization reaction under conditions that closely resemble the actual production process. As a result improvements can be made to the reaction conditions if necessary. Data are compared to results obtained with IR spectroscopy in an off‐line approach. The value of the in situ characterization using Raman spectroscopy is illustrated by the observation that contrary to expectation, the local rate of polymerization is not influenced by shrinkage effects caused by local variations in volume relaxation in the wedge‐shaped sample volume. Instead, even quartz glass mold plates with a thickness of 30 times that of liquid monomer were deformed to accommodate for thermodynamically required volume shrinkage. The assumption of isochoric polymerization in a confined volume turned out to be incorrect. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1287–1295, 2006     

Synthesis and characterization of poly(o‐toluidine) doped with organic sulfonic acid by solid‐state polymerization

Poly (o‐toluidine) (POT) salts doped with organic sulfonic acids (β‐naphthalene sulfonic acid, camphor sulfonic acid, and p‐toluene sulfonic acid) were directly synthesized by using a new solid‐state polymerization method. The FTIR spectra, ultraviolet visibility (UV–vis) absorption spectra, and X‐ray diffraction patterns were used to characterize the molecular structures of the POT salts. Voltammetric study was done to investigate the electrochemical behaviors of all these POT salts. The FTIR and UV–vis absorption spectra revealed that the POT salts were composed of mixed oxidation state phases. All POT salts contained the conducting emeraldine salt (half‐oxidized and protonated form) phase; the pernigraniline (fully oxidized form) phase is predominant in POT doped with β‐naphthalene sulfonic acid, and POT doped with p‐toluene sulfonic acid had the highest doping level. The X‐ray diffraction patterns showed that the obtained POT doped with organic sulfonic acids were lower at crystallinity. The conductivity of the POT salts were found to be of the order 10^?3‐10^?4 S/cm. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1630–1634, 2005     

Preparation and anticoagulant property of phosphorylcholine‐terminated o‐benzoylchitosan derivative

To improve the solubility in organic solvent of chitosan, o‐benzoylchitosan was synthesized by acylation with benzoyl chloride and then used in the reaction with 2‐chloro‐1,3,2‐dioxaphosphospholane (COP) to prepare phosphorylcholine‐terminated o‐benzoylchitosan (PC‐BCS). PC‐BCS had a structure with a phospholipid polar group characterized by FTIR and ¹H NMR. PC‐BCS had been polysubstituted by a PC group, which made PC‐BCS viscous liquid. The anticoagulant properties of PC‐BCS were evaluated by means of blood‐clotting and platelet adhesion assay. The blood‐clotting assay indicated that PC‐BCS could prolong the blood‐clotting process. Platelet adhesion assay showed that PC‐BCS could effectively inhibit the platelet adhesion and activation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 489–493, 2003     

Self‐assembled centimetre‐sized rods obtained in the oxidation of o‐phenylenediamine and aniline

Morphologically well‐defined rods of approximately 1 cm in length are effectively and economically obtained by mixing ortho‐phenylenediamine (30 mmol L^?1) with ammonium persulfate (12.5 mmol L^?1) in an acidic solution (0.37 mol L^?1 HCl) at room temperature with and without the presence of 50 mmol L^?1 aniline. These self‐assembled, morphologically uniform products can be potentially scaled up and used as morphological templates to fabricate well‐defined structures of other materials such as conducting polymers. The products were characterized using Raman, UV‐visible, high‐resolution NMR (¹H and ¹³C) and mass spectroscopies, X‐ray diffraction, scanning electron microscopy and elemental analysis. Apart from certain differences in visual appearance and in X‐ray diffractograms, other analytical data suggest that there are no structural changes upon addition of aniline into the reaction mixture. NMR and mass spectra imply that all syntheses carried out either with or without aniline result in a mixture of two products, attributed to 2,3‐phenazinediamine and 3‐aminophenazin‐2‐ol. A formation mechanism based on hydrogen bonding and π–π stacking has been proposed. © 2015 Society of Chemical Industry     

Electropolymerisation and characterisation of nanosize conducting poly[(o‐chloroaniline)‐co‐(4,4′‐diaminodiphenylsulfone)] on a polyaniline‐modified electrode

An exciting methodology for the electrosynthesis of poly(o‐chloroaniline) is proposed, based on the electrochemical polymerisation of o‐chloroaniline (OCA) on a polyaniline‐modified electrode and copolymerisation of OCA with different compositions of biologically important 4,4′‐diaminodiphenylsulfone (DDS) on the same electrode. The copolymer electrosynthesised from an equimolar feed composition of OCA and DDS behaved the best among the other compositions employed for polymerisation. The UV‐visible and Fourier transform infrared spectral data obtained for this copolymer suggest the incorporation of DDS in the polymer chain. The X‐ray diffraction profile of the copolymer indicates a substantial amorphous nature of the as‐synthesised copolymer. Scanning electron micrographs recorded for the homo‐ and copolymer reveal distinctly different morphologies. The average grain size of the prepared copolymer as approximated from the micrographs is 80 nm. The procedure reported is found to be a very efficient method for electrochemically polymerising pristine OCA and poly(OCA‐co‐DDS) and the adopted strategy is the best so far reported for the electrochemical polymerisation of OCA on any electrode surface. Copyright © 2009 Society of Chemical Industry     

Comparison of poly(o‐anisidine) and poly(o‐anisidine‐co‐aniline) copolymer synthesized by chemical oxidative method

In this study, poly(o‐anisidine) [POA], poly(o‐anisidine‐co‐aniline) [POA‐co‐A], and polyaniline [PANi] were chemically synthesized using a single polymerization process with aniline and o‐anisidine as the respective monomers. During the polymerization process, p‐toluene sulfonic acid monohydrate was used as a dopant while ammonium persulfate was used as an oxidant. N‐methyl‐pyrolidone (NMP) was used as a solvent. We observed that the ATR spectra of POA‐co‐A showed features similar to those of PANi and POA as well as additional ones. POA‐co‐A also achieved broader and more extended UV–vis absorption than POA but less than PANi. The chemical and electronic structure of the product of polymerization was studied using Attenuated Total Reflectance spectroscopy (ATR) and UV–visible spectroscopy (UV–vis). The transition temperature of the homopolymers and copolymers was studied using differential scanning calorimetry and the viscosity average molecular weight was studied by using dilute solution viscometry. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effects of different polymerization protocols on the degree of conversion of two dual‐cured core buildup composites polymerized by light‐emitting diode and halogen light‐curing units

The aim of study was to investigate the effects of various curing protocols with quartz–tungsten halogen (QTH) or light‐emitting diode (LED) light‐curing units on the degree of conversion (% DC) of two dual‐cured core buildup resin composites. Two dual‐cured core buildup resin composites, Clearfil Dc Core Automix (CLF) and Grandio Core Dc (GR), were selected. Specimens were exposed to the polymerization protocols as follows: there was immediate photoactivation or photoactivation delayed by 2 or 5 min by a QTH or LED source, and one group was allowed to chemically polymerize and served as a control (n = 6). The % DC of the specimens was determined with attenuated total reflectance–Fourier transform infrared spectroscopy. The GR samples polymerized with QTH for the 5‐min‐delayed photoactivation had higher % DC values than those self‐cured, and the Clearfil Dc Core Automix (CLF) samples with immediate or delayed curing protocols with halogen yielded higher % DC values than the samples that were chemically polymerized. The comparison of the two resin composites polymerized with halogen showed a higher % DC for CLF than for GR in the 2‐min‐delayed photoactivation. On the other hand, when they were cured with LED, the % DC values of GR significantly increased after the 2‐min‐delayed photoactivation. In light of the results, it might be stated that CLF polymerized with QTH, could be the better option. GR provided adequate chemical polymerization; therefore, it might be useful in areas in which light curing is not possible. Clinicians should consider the polymerization characteristics of dual‐cured resin composites. The use of different composites may require the modification of the application procedures recommended by the manufacturer. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40560.     

A Simple Method for the Reinforcement of UV‐Cured Coatings via Sol‐Gel Photopolymerization

A difunctional methacrylate oligomer was mixed with a variable amount of a MAPTMS precursor in the presence of both a radical and a cationic photoinitiator. The simultaneous photolysis of both photosensitive molecules upon UV irradiation allowed the single‐step generation of a type‐II polymethacrylate/polysiloxane nanocomposite film. Methacrylate and methoxysilyl conversions during irradiation were efficiently monitored by FTIR spectroscopy. The inorganic structure of the resulting silica‐based hybrid films was characterized using ²⁹Si solid‐state NMR. Finally, the reinforcement ability of the resulting hybrid films was also assessed by using a unique range of characterization techniques: DMA, scratch test, and nanoindentation.

     

3D‐Printing of High‐κ Thiol‐Ene Resins with Spiro‐Orthoesters as Anti‐Shrinkage Additive

Tri(ethylene glycol) divinyl ether and the spiro‐orthoester 2‐((allyloxy)methy)‐1,4,6‐trioxospiro[4.4]nonane can be formulated in different ratios and crosslinked by thiol‐ene reactions. The spiro‐orthoester is used as anti‐shrinkage additive, enabling shrinkage reduction of up to 39%. Addition of a radical photoinitiator for the thiol‐ene reaction and a cationic photoinitiator for the double ring‐opening of the spiro‐orthoester enables dual‐curing for application in 3D‐printing. The formulation free of the spiro‐orthoester shows gelation during the printing process and, correspondingly, low resolution. The formulations containing the spiro‐orthoester exhibit higher resolutions in the range of 50 µm. The resins containing mixtures of tri(ethylene glycol) divinyl ether and the spiro‐orthoester show permittivities as high as 10⁴. The dielectric loss factor of the resins is in the range of 0.5–7.6, and the conductivity in the range of 1.3?10^?11 to 2.0?10^?11 S cm^?1. These high‐κ materials can be 3D‐printed by digital light processing for the next generation of electronic materials.     

Electrosynthesis and characterization of o‐phenylenediamine oligomers

The contribution of electrochemical methods to the development of conducting polymers has been most relevant, although the electropolymerization mechanism has not yet been totally elucidated. The formation of a high‐density oligomeric region in the electrode–solution interface has been clearly established as formed by oligomers with different chain lengths. It has been confirmed that, depending on the variables governing the process (applied potential, electrolysis time, concentration, etc), it is possible to control to some extent the oligomer to be generated. In this present work, the electrosynthesis of oligomers of o‐phenylenediamine is proposed. A saturated solution of the monomer was electrolysed at 0.95 V versus SCE over 1 min, using stainless steel as the working electrode material. Under these conditions, a mixture of the dimer and tetramer, relatively easy to separate by thin layer chromatography, was deposited. The products were characterized by mass spectrometry, UV–vis spectroscopy, elemental analysis and ¹H NMR spectroscopy. This approach allows the synthesis of oligomers in a fast and simple way. In addition, the product is directly obtained on the electrode surface, hence making its separation and purification very straightforward. Copyright © 2004 Society of Chemical Industry