Trimethylbenzoyl-diphenylphosphine Oxide Research Articles

Experimental Composite Resin with Myristyltrimethylammonium Bromide (MYTAB) and Alpha-Tricalcium Phosphate (α-TCP): Antibacterial and Remineralizing Effect.

The aim of this study was to develop an experimental composite resin with the addition of myristyltrimethylammonium bromide (MYTAB) and α -tricalcium phosphate (α-TCP) as an antibacterial and remineralizing material. Experimental composite resins composed of 75 wt% Bisphenol A-Glycidyl Methacrylate (BisGMA) and 25 wt% Triethylene Glycol Dimethacrylate (TEGDMA) were produced. Some 1 mol% Trimethyl benzoyl-diphenylphosphine oxide (TPO) was used as a photoinitiator, and butylated hydroxytoluene (BTH) was added as a polymerization inhibitor. Silica (1.5 wt%) and barium glass (65 wt%) particles were added as inorganic fillers. For remineralizing and antibacterial effect, α-TCP (10 wt%) and MYTAB (5 wt%) were incorporated into the resin matrix (α-TCP/MYTAB group). A group without the addition of α-TCP/MYTAB was used as a control. Resins were evaluated for their degree of conversion (n = 3) by Fourier Transform Infrared Spectroscopy (FTIR). The flexural strength (n = 5) was assessed based on ISO 4049:2019 requirements. Microhardness was assessed to calculate softening in solvent (n = 3) after ethanol immersion. The mineral deposition (n = 3) was evaluated after immersion in SBF, while cytotoxicity was tested with HaCaT cells (n = 5). Antimicrobial activity (n = 3) was analyzed against S. mutans. The degree of conversion was not influenced by the antibacterial and remineralizing compounds, and all groups reached values > 60%. The α-TCP/MYTAB addition promoted increased softening of polymers after immersion in ethanol and reduced their flexural strength and the viability of cells in vitro. A reduction in S. mutans viability was observed for the α-TCP/MYTAB group in biofilm formation and planktonic bacteria, with an antibacterial effect > 3log10 for the developed materials. Higher intensity of phosphate compounds on the sample's surface was detected in the α-TCP/MYTAB group. The addition of α-TCP and MYTAB promoted remineralizing and antibacterial effects on the developed resins and may be a strategy for bioactive composites.

Effects of photoinitiators on dental composite resins: a narrative review

In recent years, the components of dental composites have changed in an attempt to improve their biomechanical and chemical properties. Therefore, dentistry contains many different photoinitiator systems, the most common being the binary camphorquinone and tertiary amine system, and most dental light curing agents are designed to suit the camphorquinone (CQ) absorption range. The alternation of the photoinitiator can cause changes in the values of biomechanical properties, such as degree of conversion, hardness, and biocompatibility. This review contains a comparison of the biomechanical properties of dental composites including different photosensitizers, among others: camphorquinone, phenanthrenequinone, benzophenone, and 1-phenyl-1,2 propanedione, trimethyl benzoyl-diphenylphosphine oxide, benzoyl peroxide. The literature reviews used and the observation of randomized studies were from the Bireme, PubMed, SciElo, and LILACS databases from 2008 to February 2021. Objective: To present the action of light-curing agents in composite resin and their mechanical characteristics concluded that the market is constantly evolving related to photoinitiators.

Influence of Photo-initiator concentration on photoactivation of composites prepared with LTCC and silver powders for DLP based 3D printing and their characterization

DLP (Digital Light Processing) based 3D (three dimensional) printing had been a widely used additive manufacturing technique with its broad aspects in rapid prototyping, packaging, biomedical applications, PCB etc due to its high resolution and reliability. Since, drive for miniaturization in electronic industry had been increasing; the need of additive manufacturing becomes better and reliable solution for fabrication of electronic device. In this study, we attempt to adopt LTCC (Low Temperature co-fired ceramic) technology with DLP based additive manufacturing machine to reduce lead time, running cost and investment cost while increasing production volume to levels suited for SMEs. This work reports our 3D Printing trials with composites using LTCC/dielectric and silver powder. Initial trials using the commercially available resins showed residue after firing the package which indicates its unsuitability for electronic packaging applications. Hence, the new resin was formulated by varying the Photo-initiator 2,4,6 -trimethyl benzoyl diphenyl phosphine oxide (TPO) Concentration. Photoresist was prepared by mixing the Photo-initiator (1 to 3wt %), Surfactant (2.5wt %) and diacrylate based monomer (96.5 -94.5wt%) in planetary mixer and the composition was optimised. Curing parameters for the unloaded resin such as exposure time, Intensity etc were varied accordingly and optimised. The photoresist and the printed samples were analysed for their viscosity, optical inspection, NMR, FTIR. Printing trials were done by preparing composites with Dielectric (LTCC) and conducting material (Silver) using above prepared photopolymer in 50:50 ratio. Effect of variation in the exposure time and intensity on the loading of functional material for curing has also been studied. Printed patterns were then sintered at about 875°C with standard LTCC firing cycle. No residue was observed after the sintering cycle. Trials using composites with different material were also tried. Characterisation of these composites and printed packages are reported. For 50% loading of functional material shrinkage of about 29% was observed. Effect of solid loading on shrinkage of sintered sample were also studied and reported.

Influence of Monowave and Polywave LED Unites on G-Aenial Resin Composites’ Polymerization: An In Vitro Study

Objectives: Trimethylbenzoyldiphenylphosphine oxide and phenylpropanedione photoinitiator components in resin composites have been used widely due to their white color. However, it seems that there are some limitations in the required polymerization initiator wavelength. This study aimed to evaluate the polywave and monowave light-activating devices (LEDs) on polymerization and shrinkage strain of two dental composites with different photoinitiator systems. Methods: In this experimental study, 24 samples were prepared in two groups, including G-Aenial A2 and bleach composites. Each group was divided into two subgroups: one cured by monowave LED unit and the other by polywave device. Then shrinkage strain of samples was evaluated using bonded disk technique. Results: Results showed the shrinkage strain of A2 and bleach composites using PW device was significantly greater than MW device. In addition, the A2 composite shrinkage action polymerized with MW device was significantly lower than shrinkage action of A2 and bleach composite using PW machine. Conclusion: The findings of this study revealed that polywave LEDs were more beneficial for the polymerization of resin composites.

The Photoinitiators Used in Resin Based Dental Composite-A Review and Future Perspectives.

The presented paper concerns current knowledge of commercial and alternative photoinitiator systems used in dentistry. It discusses alternative and commercial photoinitiators and focuses on mechanisms of polymerization process, in vitro measurement methods and factors influencing the degree of conversion and hardness of dental resins. PubMed, Academia.edu, Google Scholar, Elsevier, ResearchGate and Mendeley, analysis from 1985 to 2020 were searched electronically with appropriate keywords. Over 60 articles were chosen based on relevance to this review. Dental light-cured composites are the most common filling used in dentistry, but every photoinitiator system requires proper light-curing system with suitable spectrum of light. Alternation of photoinitiator might cause changing the values of biomechanical properties such as: degree of conversion, hardness, biocompatibility. This review contains comparison of biomechanical properties of dental composites including different photosensitizers among other: camphorquinone, phenanthrenequinone, benzophenone and 1-phenyl-1,2 propanedione, trimethylbenzoyl-diphenylphosphine oxide, benzoyl peroxide. The major aim of this article was to point out alternative photoinitiators which would compensate the disadvantages of camphorquinone such as: yellow staining or poor biocompatibility and also would have mechanical properties as satisfactory as camphorquinone. Research showed there is not an adequate photoinitiator which can be as sufficient as camphorquinone (CQ), but alternative photosensitizers like: benzoyl germanium or novel acylphosphine oxide photoinitiators used synergistically with CQ are able to improve aesthetic properties and degree of conversion of dental resin.

Tertiary amine and tooth mineral hydroxyapatite facilely trigger self-cure of 10-MDP based adhesives

The present work aims to investigate if a novel self-cure system, mediated by tertiary amine ethyl 4-(dimethylamino)-benzoate (4E) and tooth mineral hydroxyapatite (HAp), would trigger polymerization of model adhesives based on a popular self-etch monomer, 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP). The effect of 4E and HAp contents on degree of conversion (DC), polymerization rate (Rp), and induction period (IP) was investigated. The occurrence of such self-cure phenomenon in adhesives that underwent prior inadequate light cure was also evaluated. Model self-etch adhesives were prepared by using a monomer mixture of 10-MDP with 2-hydroxyethyl methacrylate at1:1 wt ratio. 4E (0.3–1.3 wt%), and HAp (0.5–2 wt%) were added to the mixture. Benzoylperoxide and N,N-dihydroxyethyl-p-toluidine were used as conventional chemical-cure system, and trimethylbenzoyl-diphenylphosphine oxide as light-curing photoinitiator. The polymerization processes and mechanical properties of model adhesives were evaluated by real time ATR/FT-IR and nanoindentation, respectively. The 4E-HAp system successfully triggered self-cure of 10-MDP based model adhesives. DC, Rp and IP were apparently affected by both 4E and HAp contents. DC of self-cure of the model adhesives was much higher than that of the conventional chemical-cure system. 4E-HAp initiated self-cure further boosted DC to ∼100% regardless of prior light exposure, and significantly improved elastic modulus and hardness, thus provided a novel polymerization method to effectively salvage curing of the adhesives after inadequate light-cure.

IN-VITRO RELEASE STUDY AND ANTIMICROBIAL PROPERTY EVALUATION OF OFLOXACIN LOADED POLY (2-HYDROXYETHYL METHACRYLATE) / POLY (CAPROLACTONE) / POLY (ETHYLENE GLYCOL) HYDROGEL SYSTEM FOR BURN WOUND MANAGEMENT

Monomer 2-hydroxy ethyl methacrylate containing small amounts of poly(caprolactone) and poly(ethylene glycol) incorporated with an antibiotic ofloxacin was polymerized by photopolymerization technique using 2,4,6 trimethyl benzoyl diphenyl phosphine oxide (TPO) as photoinitiator. Encapsulation efficiency and in vitro drug release was studied using UV-visible spectroscopy. Swelling analysis was resorted to compare fluid uptake ability of hydrogel containing the drug with bare polymer. Zone of inhibition assay showed hydrogel containing 1% Ofloxacin to possess strong antimicrobial property Hemolysis assay demonstrated the hydrogel system to be non-hemolytic. Non-cytotoxic character of the hydrogel was confirmed using fibroblast cells. Cell adhesion studies showed non-attachment of fibroblasts to the polymer and improved cell proliferation simultaneously. Key words: Ofloxacin, Encapsulation efficiency, Hydrogel, Antimicrobial

Light-Cured Self-Etch Adhesives Undergo Hydroxyapatite-Triggered Self-Cure

Light cure is a popular mode of curing for dental adhesives. However, it suffers from inadequate light delivery when the restoration site is less accessible, in which case a self-cure mechanism is desirable to salvage any compromised polymerization. We previously reported a novel self-cure system mediated by ethyl 4-(dimethylamino)-benzoate (4E) and hydroxyapatite (HAp). The present work aims to investigate if such self-cure phenomenon takes place in adhesives that underwent prior inadequate light cure and to elucidate if HAp released from the dental etching process is sufficient to trigger it. Model self-etch adhesives were formulated with various components, including bis[2-methacryloyloxy)ethyl]-phosphate (2MP) as acidic monomer and trimethylbenzoyl-diphenylphosphine oxide (TPO) as photoinitiator. In vitro evolution of degree of conversion (DC) of HAp-incorporated adhesives was monitored by infrared spectroscopy during light irradiation and dark storage. Selected adhesives were allowed to etch and extract HAp from enamel, light-cured in situ, and stored in the dark, after which Raman line mapping was used to obtain spatially resolved DC across the enamel-resin interface. Results showed that TPO+4E adhesives reached DC similar to TPO-only counterparts upon completion of light irradiation but underwent another round of initiation that boosted DC to ~100% regardless of HAp level or prior light exposure. When applied to enamel, TPO-only adhesives had ~80% DC in resin, which gradually descended to ~50% in enamel, whereas TPO+4E adhesives consistently scored ~80% DC across the enamel-resin interface. These observations suggest that polymerization of adhesives that underwent insufficient light cure is salvaged by the novel self-cure mechanism, and such salvaging effect can be triggered by HAp released from dental substrate during the etching process.

Relative photon absorption determination and the influence of photoinitiator system and water content on C=C conversion, water sorption/solubility of experimental self-etch adhesives

The present study aimed to determine the influence of photoinitiator/co-initiator system and the water content on polymerization efficiency, water sorption and solubility of experimental self-etch adhesives; as well as to understand the relation between photoinitiators and the curing unit on the resultant properties. Experimental adhesive formulations were formulated by mixing bis-2-methacyloyloxy-ethyl phosphate (2MP, Sigma Aldrich, USA) and 2-hydroxyethylmethacrylate (HEMA, Esstech Inc., USA) in equal parts by weight. Four photoinitiators were used: camphorquinone (CQ), phenantrequinone (PQ), trimethylbenzoyl-diphenyl-phosphine oxide (TPO) and bisacyl-phosphine oxide (BAPO). The tertiary amine ethyl-4-dimethylaminobenzoate (EDMAB) and the salt diphenyliodonium hexafluorphosphate (DPI) were tested as co-initiators. The following groups were tested: CQ+EDMAB, CQ+EDMAB+DEPI, PQ, PQ+EDMAB, PQ+DPI, PQ+EDMAB+DPI, TPO TPO+DPI, BAPO and BAPO+DPI. Materials were tested both without and with the addition of 10wt% of deuterium water (D2O). Photoinitiator absorption and the light-curing emission spectra were determined with a spectrophotometer to calculate the relative photons absorption (RPabs). Degree of conversion was obtained with Fourier-transformed infrared spectroscopy (FTIR/ATR). Water sorption and solubility were determined after successive weighting procedures. Results were analyzed by two-way analysis of variance (ANOVA) followed by Tukey׳s post-hoc test (α=0.05). PQ exhibited the highest RPabs values (334.9), followed by CQ (52.8), BAPO (33.7) and TPO (8.4). TPO-based material presented the highest DC in the neat state. Considering the formulations with water addition, TPO- and BAPO-based materials presented the highest values, whereas CQ- and PQ-based ones produced conversion values below 4.6. TPO- and BAPO-based materials presented superior performance than CQ- and PQ-based ones for water sorption and solubility. It was possible to conclude that self-etch adhesives ability to polymerize was not only dependent on the relation between light and photoinitiators spectra, but also individual characteristics of free radicals development and that groups formulated with TPO and BAPO presented superior properties as those formulated with CQ and PQ.

Photo-polymerization efficiency of self-etch dental adhesives composed of camphorquinone or trimethylbenzoyl-diphenyl-phosphine oxide

Unique design of self-etch adhesive monomers combines acidic functional group and double bond into a single molecule, which presents complexity as using the environmentally-sensitive photoinitiators in such a system. The objective of this study was to evaluate the kinetics of polymerization for self-etch adhesives cured with two different photoinitiators camphorquinone (CQ) and trimethylbenzoyl-diphenyl-phosphine oxide (TPO). Model self-etch adhesives contained bis[2-(methacryloyloxy)ethyl] phosphate (2MP) and 2-hydroxyethyl methacrylate (HEMA) (mass ratio of 2MP:HEMA=1:1). Different contents of water from 0wt% to 60wt%, or NaOH from 0.2wt% to 2wt% were incorporated to the system. The adhesives were cured using quartz–tungsten–halogen (QTH) or light-emitting diode (LED) light curing units. The degree of conversion (DC) and polymerization rate (PR) of the model self-etch adhesives were determined using ATR/FT-IR with a time-based spectrum analysis. TPO generally outperformed CQ/4E to initiate the self-etch adhesives when using the QTH curing unit. In addition, the DC of the TPO-initiated adhesives displayed increasing trend with water content, in contrast to a decreasing trend for the CQ/4E-initiated system. Furthermore, polymerization of the TPO-initiated system was independent of pH of the self-etch adhesives, whereas the DC and PR of the CQ/4E-initiated system were strongly influenced by the pH. As the LED curing unit was used, polymerization of both TPO and CQ/4E-initiated adhesives was greatly depressed. However, the DC and PR of the CQ/4E initiated adhesives could be improved by increasing pH of the system. In summary, the TPO-initiated system exhibits superior polymerization performance to the CQ/4E system as well as water-favorable and pH-independent features as using QTH curing unit.

Degree of conversion and microhardness of TPO-containing resin-based composites cured by polywave and monowave LED units

ObjectivesTo determine the degree of conversion (DC) and Knoop microhardness (KHN) of resin-based composites (RBCs) containing trimethylbenzoyl-diphenylphosphine oxide (TPO) cured by polywave or monowave LED light-curing units (LCUs). MethodsThree groups (each n=5) of Tetric EvoCeram (Ivoclar Vivadent), Vit-l-escence (Ultradent) and Herculite XRV Ultra (Kerr) were prepared in Teflon moulds (5mm in diameter and 2mm thick) and cured with polywave Bluephase® G2 (Ivoclar Vivadent), polywave Valo (Ultradent) or monowave Bluephase® (Ivoclar Vivadent; control) resulting in 9 groups. DC and KHN were determined using micro-Raman spectroscopy and Knoop microhardness, respectively. High-performance liquid chromatography and nuclear magnetic resonance spectroscopy were used to confirm the presence or absence of TPO in the three uncured materials. Data were statistically analysed using two-way and one-way ANOVA and DC and KHN were correlated using Pearson's correlation (α=0.05). ResultsTPO was confirmed in Tetric EvoCeram and Vit-l-escence but not in Herculite XRV Ultra. All three LCUs produced comparable KHN for Tetric EvoCeram and Herculite XRV Ultra (p>0.05). Both polywave LCUs resulted in significantly higher KHN for Vit-l-escence and higher DC in Tetric EvoCeram and Vit-l-escence than the monowave Bluephase® (p<0.05). Conversely, Bluephase® showed higher DC than the two polywave LCUs in Herculite XRV Ultra (p<0.05). Pearson's correlation coefficient was r=0.818. ConclusionsPolywave LED LCUs improved monomer to polymer conversion and KHN in the two TPO-containing RBCs, but not in Herculite XRV Ultra. DC and KHN were linearly correlated in all three RBCs. Vit-l-escence showed the highest DC and KHN of the three materials tested. Clinical significanceThe use of polywave LEDs significantly improves both the DC and KHN of materials which contain TPO. This should be taken into account when curing bleached shades of RBCs even if the manufacturers do not indicate the presence of TPO in their materials.

Curing efficiency of dental resin composites formulated with camphorquinone or trimethylbenzoyl-diphenyl-phosphine oxide

ObjectivesSince photoinitiator systems for dental resins based on camphorquinone (CQ) present color disadvantages, trimethylbenzoyl-diphenyl-phosphine oxide (TPO) has been proposed as an alternative. However, there are remaining considerations about its curing efficiency. The aims of the present investigation were: to characterize the relationship between the photoinitiator absorption spectra and the light spectrum emitted from a QTH light (absorbed power density, PDabs); to evaluate the kinetics of polymerization, and the depth of cure for filled dimethacrylate resins formulated with different photoinitiator systems. MethodsCQ+EDMAB (control); TPO and TPO+EDMAB were used in 50:50 Bis-GMA/TEGDMA resins. Photoinitiator absorption and QTH-light emission were evaluated using a spectrophotometer and kinetics of polymerization with differential scanning calorimetry (DSC) (n=3). Depth of cure was analyzed by the scraping method (n=5), as recommended by ISO4049. One-way ANOVA/Tukey's (p<0.05) was used to analyze the results. ResultsCQ presented higher PDabs than TPO (364 and 223mW/cm3, respectively). The DSC revealed that TPO and TPO+EDMAB produced a faster reaction than CQ+EDMAB. Composite formulated with CQ+EDMAB produced higher depth of cure (6.3±0.4mm) than those with TPO (4.3±0.1) or TPO+EDMAB (4.2±0.3). SignificanceAlthough CQ presented higher PDabs than TPO, formulations containing TPO exhibited higher reactivity than that with CQ. On the other hand, materials formulated with TPO demonstrated lower depth of cure than that with CQ. Therefore, its use as an alternative photoinitiator requires further investigation, with higher concentrations.

Micro-Raman spectroscopic analysis of the degree of conversion of composite resins containing different initiators cured by polywave or monowave LED units

Objectives To determine the degree of conversion (DC) over 48 h post-curing of resin mixtures containing trimethylbenzoyl-diphenylphosphine oxide (TPO) initiator cured by a polywave or a monowave LED light-curing unit (LCU). Methods In resin mixtures based on equal weight percent (wt%) of BisGMA and TEGDMA the following initiators were added: 0.2 wt% camphorquinone (CQ) + 0.8 wt% ethyl-4-dimethylaminobenzoate (EDMAB) (Group 1); 1 wt% TPO (Group 2) and 0.1 wt% CQ + 0.4 wt% EDMAB + 0.5 wt% TPO (Group 3). Half of the samples in each group ( n = 5) were cured using a polywave (bluephase ® G2, Ivoclar Vivadent) or a monowave LED LCU (bluephase ®, Ivoclar Vivadent). The DC was measured using micro-Raman spectroscopy within 5 min and then 1, 3, 6, 24 and 48 h post-irradiation. The data were analysed using general linear model and two-way ANOVA for the factors ‘time’, ‘material’, ‘surface’ and ‘LCU’ at α = 0.05. Results The initial DC values obtained upon light curing remained similar over a 48 h period. bluephase ® G2 produced the highest DC in Group 2 followed by Group 3, and Group 1. bluephase ® resulted in the highest DC in Group 1, followed by Group 2 and Group 3 ( p < 0.05). Conclusions Unfilled resin materials containing both TPO– and CQ–amine initiators are effectively cured using bluephase ® G2. Resin mixture with the same wt% of initiators is better cured when TPO is the only initiator, compared to CQ–amine only or combined TPO and CQ–amine system. After initial light cure, no additional conversion of uncured monomers was detected in an unfilled resin material over 48 h at 37 °C.

Initiator Addition to Methyl Methacrylate Studied in Liquid and Supercritical Carbon Dioxide

The photochemistry and radical chemistry of two widely used photoinitiators have been studied in liquid and supercritical carbon dioxide solutions and compared to conventional solvents such as acetonitrile and toluene. A specially modified time-resolved electron paramagnetic resonance (TREPR) apparatus was used to detect free radicals produced from the triplet states of dimethoxyphenylacetophenone (DMPA, 1) and trimethylbenzoyldiphenylphosphine oxide (TMDPO, 2) after excitation of the parent compounds using a 308 nm excimer laser. The photochemistry and photophysics of these molecules in CO2 are similar to those observed in conventional solvents. In the presence of methyl methacrylate (MMA) monomer, both benzoyl (1a) and dimethoxybenzyl (1b) radicals from DMPA react to form adduct radicals 1c and 1d, which are indistinguishable by TREPR. The MMA concentration dependence and time dependence of these spectra are simulated and discussed. From 2, the trimethylbenzoyl radical 2a is much less reactive than the diphenylphosphinyl oxide radical 2b. Measurement of the TREPR line width at a constant delay time as a function of MMA concentration gives the rate of addition, kadd, of 2b to MMA ((5.5 ± 0.5) × 107 M-1 s-1 in liquid CO2; (6.1 ± 0.6) × 107 M-1 s-1 in supercritical CO2). These values are close to those observed in acetonitrile ((8.1 ± 1.6) × 107 M-1 s-1) and toluene ((4.0 ± 0.4) × 107 M-1 s-1).

Synthesis and Characterization of Photosensitive Polyimides for Optical Applications

The objective of this research was to prepare colorless photosensitive polyimides for optical applications. In the first approach to these materials two new photosensitive end-capping agents, i.e., 6-(4-aminophenoxy)hexyl methacrylate and di[2-(methacryloyloxyethyl)] 5-aminoisophthalate, for polyimides were prepared. These agents were used along with 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 2,2‘-bis(trifluoromethyl)-4,4‘-diaminobiphenyl to prepare a series of methacrylate end-capped imide oligomers. However, the oligomers required long exposures to UV radiation to affect cure. To improve their photosensitivity, multifunctional additives and photoinitiators were used. A tetrafunctional end-capped oligomer that contained 10 wt % trimethylolpropane triacrylate and 5 wt % trimethylbenzoyldiphenyl phosphine oxide (TMDPO) was photosensitive and displayed good photopatterning properties. A second approach to the desired materials involved the synthesis of a diamine monomer, i.e., 2,2‘-dimethacryloyloxy-4,4‘-diaminobiphenyl, in which methacrylate moieties were attached to the 2- and 2‘-positions of a biphenyl structure. The monomer was polymerized with commercially available dianhydrides such as 6FDA and 4,4‘-oxydiphthalic anhydride. The polyimides obtained were soluble in common organic solvents such as THF, acetone, and chloroform and could be solution cast into thin, water-white films that were highly transparent in the visible light region. The polymers were photosensitive when combined with 5 wt % TMDPO and displayed good photopatterning properties. The polymers, which afforded line patterns 10−30 μm wide and 5−20 μm thick, did not develop color or shrink during UV exposure and subsequent thermal treatments.

Hydrophilic polymeric acylphospine oxide photoinitiators/crosslinkers for in vivo blue-light photopolymerization.

Three vinyl-functionalized phosphine oxide photoinitiating monomers have been synthesized: 4-vinylbenzoyldiphenylphosphine oxide (VBPO), 2,6-dimethyl-4-vinylbenzoyldiphenylphosphine oxide (DMVBPO), and 2,4,6-trimethylbenzoylphenyl-4-vinylphenylphosphine oxide (TMBVPO). VBPO was copolymerized with vinylpyrrolidone or vinyl acetate (PPI-1a) and dimethylacrylamide (PPI-1b). DMVBPO and TMBVPO were both copolymerized with dimethylacrylamide (PPI-2 and PPI-3, respectively). The choice of vinylphosphine oxide and comonomer(s) had a significant influence on the properties of the resulting PPI. PPI-1a was not stable in solution in 2-hydroxyethyl methacrylate (HEMA), whereas the VBPO-dimethylacrylamide (DMA) copolymer (PPI-1b) was stable in HEMA but not stable in aqueous solutions. PPI-2 was both soluble and stable in water up to 22 months. PPI-1a was as effective as trimethylbenzoyldiphenylphosphine oxide (TPO, BASF Lucirin). PPI-2 was more effective in the polymerization of HEMA/water mixtures than PPI-3. PPI-2 and PPI-3 acted as self-cross-linking species, resulting in the formation of hydrogels; PPI 3 was more effective in this. PPI-2 was very effective in forming hydrogels based on poly(ethylene glycol) diacrylate.

Thermally and photochemically induced cationic polymerization using 2-methyl-1-(2-phenyl-2-propenyloxy)-pyridinium salts as initiators

2-Methyl-1-(2-phenyl-2-propenyloxy)-pyridinium hexafluoroantimonate ( III) and hexafluorophosphate ( IV) were synthesized. Their capability to act as initiator or coinitiator for the cationic polymerization of oxiranes and vinyl ethers was examined. Monomers under investigation were cyclohexene oxide (CHO), vinyl cyclohexene dioxide (VCHD), and n-butyl vinyl ether (nBVE). These monomers turned out to be polymerizable in the presence of III or IV provided free radicals are generated thermally at 80°C or photochemically at λ > 360 nm with the aid of appropriate radical sources, e.g. 2,2′-azobisisobutyronitrile, phenylazotriphenylmethane (PAT), and dibenzoyl peroxide (thermal radical sources) and benzoin, PAT and trimethylbenzoyl diphenylphosphine oxide (TMDPO) (photochemical radical sources). The polymerization of CHO is also induced in the absence of a free radical source at λ = 300 nm where III absorbs light and also thermally at 80°C, but here at a low rate. The latter process is very likely to be due to self-initiated free radical generation similar to that known for neat styrene. Regarding sources generating electrophilic free radicals the mode of action of III concerning the promotion of the cationic polymerization seems to be based on the addition-fragmentation mechanism. Accordingly, a free radical adds to the carboncarbon double bond and fragmentation of the adduct radical results in the formation of a reactive onium radical cation. Evidence for the oxidation of nucleophilic radicals such as the triphenylmethyl radical by the onium ion was not obtained in this work. In conclusion, a wide range of radical sources can be employed in conjunction with onium salt III or IV to tune conditions (temperature and wavelength, respectively) for the cationic polymerization of various monomers.