10.1021/acs.macromol.7b00622.s001
P. Garra
P.
Garra
F. Dumur
F.
Dumur
D. Gigmes
D.
Gigmes
A. Al Mousawi
A.
Al Mousawi
F. Morlet-Savary
F.
Morlet-Savary
C. Dietlin
C.
Dietlin
J. P. Fouassier
J. P.
Fouassier
J. Lalevée
J.
Lalevée
Copper (Photo)redox Catalyst for Radical Photopolymerization
in Shadowed Areas and Access to Thick and Filled Samples
American Chemical Society
2017
ROOH
viscosity methacrylate blends
polymerization
mW
LED
Cu
sample
conversion
1.4 mm
2017-05-09 17:38:37
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Copper_Photo_redox_Catalyst_for_Radical_Photopolymerization_in_Shadowed_Areas_and_Access_to_Thick_and_Filled_Samples/4988837
The
free radical polymerization of low viscosity methacrylate blends
upon a LED irradiation at 405 nm under air is carried out using Cu(I)/iodonium
salt/tin(II) organic derivative as photoinitiating systems. The system
exhibits a high reactivity; where tin derivative plays a crucial role.
It operates through a catalytic cycle in which Cu(I) is regenerated
and can be used at low concentrations (0.1–0.3 wt %). Remarkable
performances are achieved. At first, a final methacrylate conversion
of 82% after 40 s in 1.4 mm thick samples is obtained for an irradiance
of 35 mW/cm<sup>2</sup> whereas such a conversion is only reached
only when using a Cu(I)/iodonium salt system under a 200 mW/cm<sup>2</sup> light exposure. Second, a 55% conversion is still obtained
after 150 s under a very low irradiance (2.5 mW/cm<sup>2</sup>). Third,
almost tack-free thick samples (1.4 mm) under air are produced upon
sunlight exposure (65% of conversion for the 1.4 mm thick sample after
90 s of irradiation). Fourth, the photocuring of clear samples as
thick as 9 cm (and presumably even more) with an impressive homogeneity
through the entire polymerizable medium is feasible; the photopolymerization
of 8.5 cm thick filled samples is also realized. Fifth and last, a
lateral polymerization beyond the irradiated area is demonstrated
with unprecedented extensions of 8 mm (tin(II) = 1.3%) and 28 mm (tin(II)
= 8%), which allows polymerization reactions to occur in shadowed
areas. The chemical mechanisms are studied by steady state photolysis
and ESR-spin trapping experiments. The subsequent role of the hydroperoxides
(ROOH) formed during the polymerization reaction is a key point i.e.
for the polymerization in shadowed areas (thick and filled samples),
these latent species (ROOH) will be generated from the oxygen inhibition
and can diffuse for a full curing of the samples through a ROOH/Cu(I)
redox initiation.