Silyl glyoxylates are proposed here
as a new class of high performance
type I photoinitiators for free radical polymerization under air or
in laminate (e.g., (meth)acrylates) upon exposure to different near-UV
(at 395 nm; at 405 nm) and blue (at 477 nm) LEDs. The new proposed
photoinitiators can also be used in the presence of additives that
can enhance their initiating ability: an iodonium salt and an amine
or a phosphine. The silyl glyoxylate-based photoinitiating systems
exhibit excellent polymerization performances upon blue LED light
(at 477 nm) with exceptional bleaching properties compared to camphorquinone (CQ)-based systems.
This can be highly worthwhile for the preparation of colorless polymers
upon visible light. Real-time Fourier transform infrared spectroscopy
(RT-FTIR) experiments are used to monitor the polymerization profiles.
The involved chemical mechanisms are investigated by fluorescence,
laser flash photolysis, electron spin resonance (ESR), and steady
state photolysis experiments. Molecular orbital calculations are also
carried out. The overall excited state processes and the chemical
mechanisms involved in the initiation step are detailed.
Polyoxazolines with a biocidal quarternary ammonium end-group are potent biocides. Interestingly, the antimicrobial activity of the whole macromolecule is controlled by the nature of the group at the distal end. These nonreactive groups are usually introduced via the initiator. Here we present a study with a series of polymethyloxazolines with varying satellite groups introduced upon termination of the polymerization reaction. This allowed us to introduce a series of functional satellites, including hydroxy, primary amino, and double-bond-containing groups. The resulting telechelic polyoxazolines were explored regarding their antimicrobial activity and toxicity. It was found that the functional satellite groups greatly controlled the minimal inhibitory concentrations against the bacteria Staphylococcus aureus and Escherichia coli in a range of 10 to 2500 ppm. Surprisingly, the satellite groups also controlled the hemotoxicity but in a different way than the antimicrobial efficiency.
Although modern dental repair materials show excellent mechanical and adhesion properties, they still face two major problems: First, any microbes that remain alive below the composite fillings actively decompose dentin and thus, subsequently cause secondary caries. Second, even if those microbes are killed, the extracellular proteases such as MMP, remain active and can still degrade collagenousdental tissue. In order to address both problems, a poly(2-methyloxazoline) with a biocidal quaternary ammonium and a polymerizable methacrylate terminal was explored as additive for a commercial dental adhesive. It could be demonstrated that the adhesive rendered the adhesive contact-active antimicrobial against S. mutans at a concentration of only 2.5 wt% and even constant washing with water for 101 days did not diminish this effect. Increasing the amount of the additive to 5 wt% allowed killing S. mutans cells in the tubuli of bovinedentin upon application of the adhesive. Further, the additive fully inhibited bacterial collagenase at a concentration of 0.5 wt% and reduced human recombinant collagenase MMP-9 to 13% of its original activity at that concentration. Human MMPs naturally bound to dentin were inhibited by more than 96% in a medium containing 5 wt% of the additive. Moreover, no adverse effect on the enamel/dentine shear bond strength was detected in combination with a dental composite.
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