Magnetic and spin effects in the photoinitiation of polymerization

Application of a moderate external magnetic field increases the efficiency of triplet photoinitiators of polymerization. The reasons for this observation are briefly outlined. Such well-documented magnetic and spin effects as the magnetic isotope effect (MIE) and chemically induced dynamic nuclear and electron polarization (CIDNP and CIDEP) have been observed under the photolysis of photoinitiators. CIDEP results are emphasized. The study of CIDEP under the photolysis of initiators allows the detection and identification of free radicals of initiators and the spin multiplicity of the reacting photoinitiator (triplet or singlet). The transfer of the spin polarization of the initiator free radical to monomers is a promising technique for following radical reaction pathways. The results of a CIDEP study of the sensitized decomposition of phosphine oxide photoinitiators are presented

Photoinitiation of Acrylate Polymerization By 2-Methyl-1- [4-(Methylthio)Phenyl]-2-Morpholino-Propan-1-one - some Effects of the Morpholino Substituent

N-Isopropylmorpholine (IPM) was used as a model to investigate the properties of the morpholino substituent present in 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one (1). It was shown by real time IR (RTIR) spectroscopy, photocalorimetry, bulk polymerization studies and the curing of thin films that IPM acts as a physical quencher for the triplet state of 1 and that it is a very poor hydrogen donor. Thus any interaction of the ground state of 1 with its triplet state is likely to lead to physical quenching, thereby reducing the initiating efficiency of 1. Evidence is also presented that the use of high concentrations of N-methyldiethanolamine can lead to reduction of the triplet state of 1, thereby enhancing the initiating efficiency of 1. It was confirmed that thioxanthones can sensitize the alpha cleavage of 1

Critical Exponents of Photoinitiated Gelation at Different Light Intensities

A photo-differential scanning calorimetric (Photo-DSC) technique was used to study the photoinitiated radical polymerization of a 75% epoxy diacrylate (EA) and 25% tripropyleneglycoldiacrylate (TPGDA) mixture with 2-mercaptothioxanthone (TX-SH) as photoinitiator by, using different light intensities. Photopolymerization reactions were carried out under identical conditions of temperature and initiator concentration. It was observed that all conversion curves during gelation at various Might intensities present good sigmoidal behavior as predicted by the percolation model. Observations around the critical time, called the glass transition point (t(g)), taken for polymerization to reach the maximum rate (R-pmax) show that the gel fraction exponents beta obeyed the universal percolation picture. On the other hand, R-pmax, t(g), and final conversion values were found to be dependent on the UV light intensity

Spontaneously designed, self-assembled and oriented ZnO nanorods by photoinduced polymerization of epoxydiacrylate formulation in the presence of 2-mercapto-thioxanthone

Here we report an environmentally friendly, fast, efficient and low cost method for in-situ preparation of ZnO nanorods in polymer matrix which is obtained using epoxydiacrylate formulation by UV irradiation. Compared to our previous study, the shape of the ZnO nanoparticles even with the same photoinitiator was found to mainly depend on the polymer matrix, but another important finding that was seen from the SEM images is that the type of photoinitiator helped for spontaneous self-assembly and orientation of ZnO nanoparticles. This very important issue arose when the one component Type II photoinitiator, namely, 2-mercapto thioxanthone was used in formulation. Self-assembly and orientation of ZnO nanorods in polymer were not the case either with Thioxanthone and Thiophenol or in the presence of Type I photoinitiator. All these experimental results for synthesis of ZnO nanoparticles in hydrophilic and hydrophobic polymer matrices may help to understand the effect of photoinitiator and polymer

The effect of heavy metals on the anthracene-Me-beta-cyclodextrin host-guest inclusion complexes

Anthracene was used to form an inclusion complex with methylated--cyclodextrin (Me-beta-CD) in water. In aqueous Me--CD solution, typical fluorescence emission of anthracene was observed. Benesi-Hildebrand's method was used to obtain the stoichiometry of the anthracene-Me--CD complex. The Stern-Volmer quenching constants, K-sv, and fluorescence quantum yields were calculated according to changes in the fluorescence emission intensity of anthracene-Me-beta-CD inclusion complexes by adding various amounts of Pb2+ and Cd2+ salts in water. The K-sv values and fluorescence quantum yields indicate that Pb2+ salts quench the anthracene-Me-beta-CD inclusion complexes more efficiently than Cd2+ salts