Urethane dimethacrylate monomer

All reactants
were used as received, and their structures are gathered in Scheme 1. Tetrakis(acetonitrile)copper(I)
tetrafluoroborate (Cu(ACN)₄BF₄), tetrakis(acetonitrile)copper(I)
hexafluorophosphate (Cu(ACN)₄PF₆), tin 2-ethylhexanoate (tin(II)), copper(I) iodide (CuI), and neocuproine
(neo) were purchased from Sigma-Aldrich. (Oxydi-2,1-phenylene)-bis(diphenylphosphine)
(DPEphos) and N-vinylcarbazole (NVK) were purchased from Alfa Aesar. Di-tert-butyldiphenyl iodonium hexafluorophosphate (Iod) was
obtained from Lambson Ltd. Deuterated chloroform was obtained from
Eurisotop.
The efficiency of the different redox systems was
checked in a model methacrylate mixture (see Scheme 2) with a low viscosity of 0.053 Pa·s
containing 33.3 wt % 1,4-butanediol-dimethacrylate, 33.3 wt % hydroxypropylmethacrylate,
and 33.3 wt % urethane-dimethacrylate monomer (Sigma-Aldrich). The
efficiency of the different redox cationic initiating systems was
checked in (3,4-epoxycyclohexane)methyl 3,4-epoxycyclohexylcarboxylate
(EPOX), which was obtained from Allnex (UVacure 1500).

The blend “Mix-MA”, used as
a benchmark monomer, has been prepared with 33.3 wt % of (hydroxypropyl)methacrylate,
33.3 wt % of 1,4-butanediol dimethacrylate, and 33.3 wt % of a urethane
dimethacrylate monomer, obtained from Sigma Aldrich and represented
in Scheme 2. Mix-MA
was already used in previous works.^{3 (link),4 (link)} More particularly,
its viscosity is well adapted for the preparation of formulations.
In addition, interestingly, Mix-MA is not too viscous. Therefore,
oxygen inhibition occurs, and only good-performance systems can polymerize
it. BlocBuilder-MA was obtained from Arkema. tert-Butylbenzene was obtained from Sigma-Aldrich.