The use of LEDs as novel and efficient light sources for the photopolymerization of various monomers (acylate, epoxy), interpenetrating polymer networks and thiols–ene, leads to the development of novel photoinitiating systems adapted for the LED emission.
International audienceThree copper complexes (E1, G1, and G2) with different ligands in combination with an iodonium salt (and optionally another additive) were used to generate radicals upon soft visible light exposure (e.g., polychromatic visible light from a halogen lamp, laser diodes at 405 and 457 nm, LEDs at 405 and 455 nm). This approach can be worthwhile and versatile to initiate free radical photopolymerization, ring-opening cationic photopolymerization, and the synthesis of interpenetrating polymer networks. The photochemical mechanisms for the production of initiating radicals are studied using cyclic voltammetry, electron spin resonance spin trapping, steady state photolysis, and laser flash photolysis techniques. The photoinitiation ability of the copper complexes based photoinitiating systems are evaluated using real-time Fourier transform infrared spectroscopy. G1 and G2 are better than the well-known camphorquinone (CQ)-based systems (i.e., TMPTA conversion = 18%, 35%, 48%, and 39% with CQ/iodonium salt, CQ/amine, G1/iodonium salt, and G2/iodonium salt, respectively; halogen lamp exposure). Interestingly, some of these systems are also better than the well-known type I phosphine oxide photoinitiator (BAPO) clearly showing their high performance. These copper complexes can be used as highly efficient catalysts in photoredox catalysis
Commercial or clinical
tissue adhesives are currently limited due
to their weak bonding strength on wet biological tissue surface, low
biological compatibility, and slow adhesion formation. Although catechol-modified
hyaluronic acid (HA) adhesives are developed, they suffer from limitations:
insufficient adhesiveness and overfast degradation, attributed to
low substitution of catechol groups. In this study, we demonstrate
a simple and efficient strategy to prepare mussel-inspired HA hydrogel
adhesives with improved degree of substitution of catechol groups.
Because of the significantly increased grafting ratio of catechol
groups, dopamine-conjugated dialdehyde–HA (DAHA) hydrogels
exhibit excellent tissue adhesion performance (i.e., adhesive strength
of 90.0 ± 6.7 kPa), which are significantly higher than those
found in dopamine-conjugated HA hydrogels (∼10 kPa), photo-cross-linkable
HA hydrogels (∼13 kPa), or commercially available fibrin glues
(2–40 kPa). At the same time, their maximum adhesion energy
is 384.6 ± 26.0 J m–2, which also is 40–400-fold,
2–40-fold, and ∼8-fold higher than those of the mussel-based
adhesive, cyanoacrylate, and fibrin glues, respectively. Moreover,
the hydrogels can gel rapidly within 60 s and have a tunable degradation
suitable for tissue regeneration. Together with their cytocompatibility
and good cell adhesion, they are promising materials as new biological
adhesives.
Seven
naphthalimide derivatives (NDP1–NDP7) with different substituents
have been designed as versatile photoinitiators (PIs), and some of
them when combined with an iodonium salt (and optionally N-vinylcarbazole) or an amine (and optionally chlorotriazine) are
expected to exhibit an enhanced efficiency to initiate the cationic
polymerization of epoxides and the free radical polymerization of
acrylates under different irradiation sources (i.e., the LED at 385,
395, 405, 455, or 470 nm or the polychromatic visible light from the
halogen lamp). Remarkably, some studied naphthalimide derivative based
photoinitiating systems (PIS) are even more efficient than the commercial
type I photoinitiator bisacylphosphine oxide and the well-known camphorquinone-based
systems for cationic or radical photopolymerization. A good efficiency
upon a LED projector at 405 nm used in 3D printers is also found:
a 3D object can be easily created through an additive process where
the final object is constructed by coating down successive layers
of material. As another example of their broad potential, a NDP compound
enveloped in a cyclodextrin (CD) cavity, leads to a NDP–CD
complex which appears as a very efficient water-soluble photoinitiator
when combined with methyldiethanol amine to form a hydrogel. The high
interest of the present photoinitiator (NDP2) is its very high reactivity,
allowing synthesis in water upon LED irradiation as a green way for
polymer synthesis.The structure/reactivity/efficiency relationships
as well as the photochemical mechanisms associated with the generation
of the active species (radicals or cations) are studied by different
techniques including steady state photolysis, fluorescence, cyclic
voltammetry, laser flash photolysis, and electron spin resonance spin-trapping
methods.
International audienceThe abilities of two naphthalimide derivatives with a methacryloyl group to initiate, when incorporated in multi-component systems, a ring-opening polymerization of epoxides and a radical polymerization of acrylates under different irradiation sources (e.g. very soft halogen lamp irradiation, laser diode at 457 nm, laser diode at 405 nm and blue LED bulb at 462 nm) have been investigated. One of them is particularly efficient for the cationic and radical photopolymerization of an epoxide/acrylate blend in a one-step hybrid cure and leads to the formation of an interpenetrated polymer network IPN (30 s for getting tack free coatings). The migration stability of one of these naphthalimide derivatives is found to be excellent in the cured polyacrylates and IPNs. The photochemical mechanisms are studied by steady state photolysis, fluorescence, cyclic voltammetry, electron spin resonance spin trapping and laser flash photolysis techniques
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