The dependence of the photoinitiator concentration on the degree of conversion, mechanical properties and colour appearance of dental materials was studied. Alterations due to changes in the concentration of the photoinitiator were-undertaken. Test samples prepared by photopolymerizing BisGMA and TEGDMA in the presence of the photoinitiator camphorquinone (CQ) were prepared and submitted to mechanical analyses, i.e., compressive and diametral tensile strength and Barcol hardness tests and CIELAB colour analysis. The hardness and compressive tests showed a levelling off at concentrations around 0.5% and remained at those values up to 1.0%, whereas the DTS didn´t show any variation over that range of concentrations. The colour experiments showed dependence with the concentration of CQ in the photopolymerizing system due to its intense absorption in the yellow region. The results indicate that photopolymerization systems containing CQ/EDB as photoinitiator at concentrations between 0.5 and 1.0% present similar mechanical properties.

Silver (AgNPs) and gold (AuNPs) nanoparticles in aqueous solution were generated and stabilized using the 10-oxo-10H-dibenzene thiopyran-3-4-dicarboximide chitosan (TXICh) macrophotoinitiator. The photoinitiator and the nanoparticles in aqueous solution were characterized by UV-Vis spectroscopy and transmission electron microscopy (TEM). Pure TXICh in aqueous solution forms self-assembled particles with diameter around 30 nm. AgNPs were prepared using TXICh in the presence and absence of triethanolamine (TEOH). During irradiation, a broad band in the range of 410-415 nm was observed, corresponding to the plasmon absorption, indicating the AgNPs formation. TEM images revealed that the AgNPs had spherical shape in the absence and presence of TEOH. The synthesis of AgNPs in the presence of TEOH occurred rapidly (maximum conversion reached after 15 min), whereas in its absence 4 hours were required. The AgNPs prepared with TXICh/TEOH presented smaller and more uniform nanoparticles size. AuNPs were also prepared using TXICh as photoinitiator/stabilizer system. These nanoparticles showed an intense surface plasmon band at 530 nm and the TEM images revealed spherical particles of around 4 nm. These studies indicate that TXICh can act not only as a photoinitiator, but also as a stabilizer in the AgNPs and AuNPs formation.

A synthesis method was developed capable of obtaining pristine gold nanoparticles (AuNPs) using the lowest possible amount of auxiliary compounds. An aqueous solution of HAuCl4.3H2O was irradiated, in the absence of any stabilizing species, with the 532-nm radiation of a Nd:YAG laser. Spherical shaped AuNPs were produced by this method with sizes below 10 nm. The crystalline structures were stable for up to 28 days. A mechanism for this process is also proposed based on the initial cleavage of water molecules by the laser irradiation followed by the formation of hydrogen peroxide that reduces the gold species AuIII. The resulting species of these reactions (H2 and O2) were identified by mass spectrometry. This new method suggests that laser irradiation is a feasible alternative to produce ready-to-use AuNPs, for drug delivery, diagnostics or bio-imaging.

This paper describes the activities in the area of Photochemistry in Brazil, from its origins at the beginning of the last Century until now. The original Research Groups (formed until 1980) in this area, as well as those created afterwards are indicated. Different orientations and specialties in photochemistry, and their extensions and uses in other fundamental and applied areas are mentioned. The number of indexed scientific papers published by photochemists based in Brazil increased from 30 to 130 during the 2000-2016 period.

This paper reports the effect of the SWy-1 montmorillonite content on the kinetic thermal degradation of poly(2-hydroxyethyl methacrylate) (PHEMA)/SWy-1 nanocomposites prepared by in situ photopolymerization, using thermogravimetry analysis (TGA). 2-Hydroxyethyl methacrylate was photopolymerized in the presence of SWy-1 clay mineral using 2-hydroxy-3- (3,4-dimethyl-9-oxo-9H-thioxanthen-2-yloxy)-N,N,N-trimethyl-1-propanium chloride (QTX) and triethanolamine as the photoinitiating system. X-Ray diffraction analysis indicates that the PHEMA/SWy-1 nanocomposites present an intercalated structure. The isoconversional Flynn-Wall-Ozawa method was used to estimate activation energies and pre-exponential factors for the thermal decomposition. All nanocomposites exhibited improvement in their thermal stability, mainly due to the large interaction between the PHEMA intercalated in the SWy-1 structure. The activation energies for PHEMA/SWy-1 nanocomposites increased when increasing the clay content. The SWy-1 clay mineral acts as a better insulator, mass transport barrier and as a "crosslinking agent", increasing the activation energies for the decomposition of the polymer present in the nanocomposites.

O comportamento fotofísico do corante pseudoisocianina (PIC) foi estudado em solução macromolecular (alginato de sódio) e hidrotrópica (toluenossulfonato e estirenossulfonato de sódio). A localização do corante nestes meios modifica as propriedades espectroscópicas e os tempos de vida dos estados excitados. Os efeitos são atribuídos à interação do corante com as macromoléculas ou sua localização nos agregados hidrotrópicos, que induzem a formação de agregados J ou constringem suas movimentações internas reduzindo a velocidade da conversão interna. Os tempos de vida do estado triplete do corante em alginato foram de 20-30 ns em soluções recém preparadas, enquanto que, deixando a solução repousar por algumas horas o decaimento vira biexponencial com a formação de uma nova espécie com tempo de vida ao redor de 150 ns. Esta última é atribuída às moléculas do corante localizadas no ambiente do alginato.

The photophysical behaviour of the dye pseudoisocyanine (PIC) was studied in macromolecular (sodium alginate) and hydrotropic (sodium toluenesulphonate and sodium styrenesulphonate) solutions. It was found that the placement of the dye in these media affected the spectroscopic properties and the lifetimes of its excited states. The effects are traced down to the interactions of the dye molecules with the macromolecules or their placement in the hydrotropic aggregates, inducing the formation of J-aggregates of the dye or constraining its internal movements reducing the rate of internal conversion. The lifetimes of the triplet state of the dye in alginate were of the order of 20-30 ns in freshly prepared solutions, whereas when leaving the solution to rest for some hours the decay became biexponential with the growing of a species with lifetime around 150 ns. The latter is assigned to dye molecules placed in the alginate network.

O objetivo deste trabalho é correlacionar o grau de conversão de copolímeros de 2,2-bis[4-(2-hidróxi-3-metacriloiloxipropóxi) fenil]propano (BisGMA) e dimetacrilato de trietilenoglicol (TEGDMA) (copolímeros TB) obtidos por fotopolimerização, usando o sistema fotoiniciador canforquinona/etil 4-dimetilaminobenzoato (CQ/EDB), com a eluição de monômeros e a absorção de água. A eluição de monômeros foi avaliada a partir da imersão dos polímeros em etanol/água e análise por CLAE (cromatografia líquida de alto rendimento). A absorção de água de saliva artificial foi determinada gravimetricamente. Os resultados mostram que a composição dos copolímeros TB influencia a cinética de polimerização, a quantidade de monômeros eluídos, o grau de conversão e a quantidade de água adsorvida. Uma boa correlação foi encontrada entre estas propriedades.

The aim of this work was to correlate the degree of conversion with residual monomer release and water absorption of 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy) phenyl]propane (BisGMA) and triethyleneglycol dimethacrylate (TEGDMA) (TB copolymers) obtained by photopolymerization, using canforquinone/ethyl 4-dimethylaminobenzoate (CQ/EDB) photoinitiator. The monomer release from the copolymers was evaluated by immersion in ethanol/water and HPLC (high performance liquid chromatography) analysis. Water absorption from artificial saliva was determined by mass variation. The results show that the composition of the TB copolymers influences the polymerization kinetics, the amount of the released monomers, the degree of conversion and the amount of adsorbed water. A clear correlation can be found between these properties.

Polietilenoglicol (PEG) foi fotooxidado usando o sistema foto-Fenton e comparando com a reação no escuro. Os produtos foram analisados por GPC e HPLC. As amostras tratadas na ausência de luz necessitaram 490 min para que a <img src="/img/revistas/jbchs/v22n3/a18Mlinha.jpg" align=absmiddle>w decrescesse em 50%, enquanto que sob irradiação UV essa mesma proporção foi obtida em 10 min. O decaimento exponencial de <img src="/img/revistas/jbchs/v22n3/a18Mlinha.jpg" align=absmiddle>w com um concomitante aumento na polidispersividade e o número de quebras de cadeia caracteriza um mecanismo de quebra de cadeia aleatório. Os produtos da degradação de PEG em ambos os casos mostram a presença de produtos de massa molecular menor, incluindo etilenoglicóis menores e o ácido fórmico. O mecanismo da fotodegradação corresponde a processos consecutivos, onde etilenoglicóis de maior massa molar geram outros de menor massa, envolvendo quebras sucessivas das cadeias do polímero. O estudo demonstra que o processo de foto-Fenton com irradiação UV é um bom método para a decomposição de PEG.

Polyethyleneglycol (PEG) was photooxidized in a photo-Fenton system and results compared with the dark reaction. The products were analysed using GPC and HPLC. In the absence of light, PEG samples needed 490 min to reduce their <img src="/img/revistas/jbchs/v22n3/a18Mlinha.jpg" align=absmiddle>w by 50%, whereas under UV irradiation, only 10 min were necessary. The exponential decay of <img src="/img/revistas/jbchs/v22n3/a18Mlinha.jpg" align=absmiddle>w with a concomitant increase in polydispersity and number of average chain scission, characterized a random chain scission mechanism. The degradation products of PEG in both systems showed the presence of lower molecular weight products, including smaller ethyleneglycols and formic acid. The mechanism involves consecutive processes, were the larger ethyleneglycols give rise, successively, to smaller ones. This suggests that the mechanism involves successive scissions of the polymer chain. Irradiated samples decomposed faster than those kept in the dark This study proves that the foto-Fenton method associated with UV-light is a good reactant for PEG photodegradation.

Foi estudada a degradação fotooxidativa de QTX (cloreto de 2-hidroxi-3-(3,4-dimetil-9-oxo-9H-tioxanton-2-iloxi)-N,N,N-trimetil-1-propano) em solução aquosa. Os produtos resultantes foram caracterizados por HPLC/ESI-MS e a fotodegradação do corante foi acompanhada por espectroscopia de absorção. O corante apresenta duas bandas em 273 e 402 nm, que decrescem durante a irradiação, enquanto que aparece uma banda na região de 310-350 nm, típica do QTX oxidado. Novos picos devidos aos fotoprodutos da degradação de QTX foram observados por cromatografia e identificados por espectrometria de massa. Os picos em m/z 388, 420 e 270 correspondem a fotoprodutos, e o de m/z 372 é atribuído ao QTX. O pico de m/z 388 corresponde à formação de um grupo sulfóxido e o de m/z 420 sugere a formação de uma sulfona com uma hidroxila no grupo metila. O pico de m/z 270 sugere que o oxigênio reage com QTX abstraindo um hidrogênio do carbono ligado à hidroxila, simultaneamente à eliminação de um grupo amino.

The photooxidative degradation of QTX (2-hydroxy-3-(3,4-dimethyl-9-oxo-9H-thioxanthen-2-yloxy)-N,N,N-trimethyl-1-propanium chloride) has been investigated and photoproducts from QTX degradation in aqueous solution were characterized using HPLC/ESI-MS. The photooxidation of the dye was monitored by electronic absorption spectroscopy. The spectrum of the dye shows bands at 273 and 402 nm. During irradiation, the intensity of these bands decreases together with the appearance of a band at 310-340 nm, typical of oxidized QTX. The chromatograms show the presence of new peaks due to photoproducts of QTX degradation that were identified by mass spectroscopy. The peaks at m/z 388, 420 and 270 were attributed to photoproducts, whereas the peak at m/z 372 is due to QTX. The peak at m/z 388 corresponds to the formation of a sulfoxide group and that at m/z 420 suggested the formation of a sulfone with a hydroxyl on the methyl group. The peak at m/z 270 suggests that oxygen reacts with QTX abstracting a hydrogen atom from the carbon bonded the hydroxyl, together with the release of the amino group.

O mecanismo geral para a fotodegradação do polietilenoglicol (PEG) usando o sistema H2O2/UV foi determinado por GPC e HPLC, analisando o comportamento de moléculas modelo, como por exemplo os etilenoglicóis de baixa massa molar (tetra-, tri-, di-, e etilenoglicol). Após 30 min de irradiação, a massa molar ponderal média (Mw) do PEG degradado, analisada por GPC, cai para metade do seu valor inicial com um aumento concomitante na polidispersidade e número médio de quebra de cadeia (S). Essa queda acentuada caracteriza uma quebra de cadeia aleatória, formando oligômeros e etilenoglicóis de menor massa molar. A análise da fotodegradação de etilenoglicóis modelo por HPLC permitiu sugerir um mecanismo que envolve processos consecutivos, em que etilenoglicóis maiores originam menores, sucessivamente. A fotodegradação do etilenoglicol formou ácidos carboxílicos de baixa massa molar, como por exemplo os ácidos glicólico, oxálico e fórmico.

The general mechanism for the photodegradation of polyethyleneglycol (PEG) by H2O2/UV was determined studying the photooxidation of small model molecules, like low molecular weight ethyleneglycols (tetra-, tri-, di-, and ethyleneglycol). After 30 min of irradiation the average molar mass (Mw) of the degradated PEG, analysed by GPC, fall to half of its initial value, with a concomitant increase in polydispersitivity and number of average chain scission (S), characterizing a random chain scission process yielding oligomers and smaller size ethyleneglycols. HPLC analysis of the photodegradation of the model ethyleneglycols proved that the oxidation mechanism involved consecutive reactions, where the larger ethyleneglycols gave rise, successively, to smaller ones. The photodegradation of ethyleneglycol lead to the formation of low molecular weight carboxylic acids, like glycolic, oxalic and formic acids.

Foi realizado um estudo para determinar a eficiência da utilização simultânea dos fotoiniciadores fenilpropanodiona (PPD) e canforquinona (CQ) para a polimerização de polímeros acrílicos e avaliar possíveis mecanismos que levem à sinergia ou antagonismo. Foi encontrado que as eficiências de ambos iniciadores usados individualmente são maiores que a da mistura, indicando que quando os iniciadores são usados simultaneamente há uma transferência de energia do iniciador mais eficiente (CQ) para o menos eficiente (PPD). Também, não foi encontrada nenhuma evidência de reação entre a amina presente na formulação da CQ e o PPD no estado excitado.

A study was performed in order to determine the efficiency of the simultaneous use of the photoinitiators phenylpropanedione (PPD) and camphorquinone (CQ) in the polymerization of acrylic polymers and evaluate possible mechanisms leading to synergism or antagonism. It was found that efficiencies of both initiators taken individually are higher than that of their mixture, indicating that when both dyes are used simultaneously there will be an energy transfer from the more efficient initiator (CQ) to the less efficient one (PPD). Also, there was no proof of any reaction between the amine present in the CQ formulation and the PPD excited state.

Foram estudadas as absorções triplete-triplete (TT) e de transientes de tioxantonas substituídas e não substituídas em diferentes solventes, com a finalidade de avaliar o efeito do solvente, assim como dos substituintes no anel aromático. Os espectros determinados alguns microssegundos depois da excitação mostram absorções de três transientes principais: o estado triplete (600-650 nm), o radical cetila da tioxantona (~450 nm) e uma superposição de ambos (~300 nm). A quantidade de radicais formados em solventes não-hidroxílicos é muito menor do que em álcoois. O máximo da absorção TT mostra uma boa correlação com o parâmetro E T(30) dos solventes.

The triplet-triplet (TT) and transient absorptions of non-substituted and substituted thioxanthones has been studied in different solvents in order to ascertain the effect of the solvent, as well as the substituents on the aromatic ring. Spectra taken after a couple of ms after the flash show three main transient absorptions due to the triplet state (600-650 nm), the thioxanthone ketyl radical (~450 nm) and an overlap of both (~300 nm). The amount of radicals formed in non hydroxylic solvents is much lower than in alcohols. The maxima of the TT absorption peaks show a good correlation with the E T(30) solvent parameter.

O interesse na Fotoquímica de Polímeros tem crescido nas últimas décadas devido não somente ao grande número de novas aplicações como também à repercussão do ponto de vista econômico, técnico e ecológico. A fotopolimerização/fotocura tem recebido a atenção especial devido às incontáveis aplicações e a sua importância na área de Materiais. A cinética destes processos necessita de métodos analíticos precisos e rápidos para ser avaliada. Entre os métodos analíticos convencionais, os mais usados são a gravimetria e a medida de propriedades macroscópicas, como resistência à tração, à deformação e dureza. Entretanto, para determinações mais analíticas é conveniente usar métodos que permitam estudar a cinética de fotopolimerização em tempo real. Neste sentido têm sido usadas técnicas como dilatometria, espectroscopia Raman, calorimetria, e espectroscopia de infravermelho por transformada de Fourier em tempo real. A atividade no campo da polimerização continua a se expandir em muitas áreas e, recentemente, o interesse nos sistemas do fotoiniciação envolvendo a polimerização via radicais livres, iniciada por luz visível, tem recebido atenção especial. Recentemente, estudos sobre fotopolimerização catiônica induzida pela luz visível começaram a ser pesquisados novamente devido à grande variedade de monômeros que são polimerizáveis por via catiônica mas não por via radicar, como, por exemplo, oxiranas e éteres vinílicos.

The interest for Polymer Photochemistry has been growing in the last decades as a consequence not only of the great number of new applications as well as due to the repercussion of economical, technical and ecological characters. The photopolymerization - photocuring processes have received special attention due to the countless and important applications in the area of Materials. The kinetics of these processes needs fast and precise analytic methods to be evaluated. Among the conventional analytic methods, the most used are gravimetry and the determination of macroscopic properties, as resistance to traction, deformation and hardness. However, for a better insight in the reactions it is convenient to use more advanced analytic methods, in order to study the photopolymerization kinetics in real time. Dilatometry, Raman spectroscopy, calorimetry, and real time Fourier transform infrared spectroscopy are some of the techniques that have been used. Activity in the field of photopolymerization continues to expand in many areas and recently, the interest in photoinitiation systems involving the initiation of free-radical polymerization with visible light irradiation has been retaken. Additionally, studies on cationic photopolymerization induced by visible light started again to be studied because of the large variety of monomers that can be photopolymerized by via cation initiation, but not by free radicals, such as oxiranes and vinyl ethers.

A fotopolimerização de THF foi estudada na presença de sal de trifenilsulfônio e perileno. O mecanismo envolve uma transferência de elétron do estado singlete excitado do perileno para os íons trifenilsulfônio, levando à formação de cátions radicais, que reagem com o tetrahidrofurano. O rendimento aparente de cátions radicais calculado do mecanismo proposto tem o mesmo comportamento geral que as velocidades de polimerização medidas experimentalmente.

The photopolymerization of THF was studied in the presence of a triphenylsulphonium salt and perylene. The mechanism involves an electron transfer from the excited singlet state of perylene to triphenylsulphonium ions, resulting in perylene cation radicals that react with tetrahydrofuran. The calculated apparent yield of cation radicals follows the same general trend than the measured polymerization rates.

An historical overview is provided of the origins, growth and development of the field of photochemistry in Brazil, with special emphasis on the last three decades.