Photocuring of multifunctional monomers initiated by camphorquinone/amine systems for application in dental restorative resins

University dissertation from Stockholm : Karolinska Institutet, -

Abstract: This thesis deals with the photopolymerization of mono-, di- and trifunctional monomers initiated by carnphorquinone (CQ) alone and/or with different amines (AMH) as coinitiators in air as well in nitrogen. The kinetics of photopolymerization was measured by photoisothermal calorimetry (photo-DSC), which allowed the measurement of the rate of polymerization (Rp), maximum rate of polymerization (Rpmax), time of inhibition (tinh), time at which Rpmax was obtained (tmax), double bond conversion (p) and maximum double bond conversion (pmax). The monomers that have been employed in this work are: tris[2-(acryloyloxy)ethyl] isocyanurate (TAEI), Poly(melamine-co-formaldehyde)acrylate monomer (PMFA), hydroxyethyl. acrylate (BEA), glycidyl. methacrylate (GMA), triethylene glycol dimethacrylate (TEGDM), polyethylene glycol diacrylate (PEGDA). Effectiveness of polymerization of different monomers (W depends on their chemical structure, functionalities, purities and also on their physical properties. Acrylate monomers are more reactive than methacrylates. Reactivities of monomers increase when their functionalities are increased. The most reactive is tri-functional tris[2(acryloyloxy)ethyl] isocyanurate. Oxygen present in ambient air generally inhibits photopolymerization and an increase in the tinh, because it reacts with the free amine radicals and monomer propagation radicals giving peroxy radicals. Oxygen also quenches the triplet state of CQ (3CQ'). The studies of the mechanism of photocuring of monomers indicated that photocuring reaction can be carried out in the presence of CQ alone; in this case monomers act as hydrogen-atom donors; addition of amines (AMH) clearly accelerate the polymerization reaction, for each monomer, there is an optimal CQ and AMH concentration The type of monomers and AMIH, as well as the concentration of CQ and AMH all affect the polymerization kinetics. Double bond conversions (p), however, which occur during polymerization differ depending on the type of monomer and photoinitiation system used (CQ-AMH). Monomer conversions (pm) for many monomers and their mixtures are very high reaching 80-90 %. Some other factors such as temperature, addition of inorganic fillers and presence of saliva, influence in different ways the kinetics of polymerization, double bonds and monomer conversions. The hardness of photocured samples and/or polymerization shrinkage depend on the monomer systems, CQ and AMH concentration, filler contents, reaction temperature and saliva contents.

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