Systematic Assessment of the Photochemical Stability of Photoinitiator-Derived Macromolecular Chain Termini

High Efficiency and Low Migration Hyperbranched Silicone Contain Macrophotoinitiators for UV-Cured Transparent Coatings

A kind of hyperbranched silicone containing macrophotoinitiators (HBSMIs) were synthesized from 2-hydroxy-2-methyl-1-phenyl propanone (HMPP) and the UV-curing behaviors of HBSMIs were investigated in UV-cured transparent polyurethane-acrylate (PUA) coatings. HBSMIs show higher UV-initiating efficiency than HMPP. The migration of HBSMIs from the UV-cured coatings can be as low as 1.7–6.0 wt%, which is obviously lower than the migration of HMPP. There is a remarkable improvement of the tensile strength of the UV-cured materials initiated by HBSMI in comparison to that of the materials prepared with the same PUA initiated by HMPP. Especially for the UV-cured materials prepared from PUA with 20 wt% 1,1,1-tris(hydroxymethyl)propane (TMP), the tensile strength and the strain at break increased from 6.81 MPa to 12.14 MPa and from 43.0% to 71.9%, respectively. The fraction of improvement for the tensile strength and the strain at break is as high as 78.9% and 67.2%, respectively. The coatings prepared with HBSMI also have better UV resistance ability than those coatings prepared with HMPP because they turn slightly yellow when they are aged by UV for about 15 min while the coating prepared with 4 wt% of HMPP will turn yellow only aged by UV for 2 min. These results suggest that preparation hyperbranched silicone containing macrophotoinitiators will be one of the good strategies to improve the curing efficiency of the UV-curing system, reduce the migration of UV initiator from cured material, improve the mechanical and UV resistance performance of UV-cured materials.

Hyphenation of size-exclusion chromatography to mass spectrometry for precision polymer analysis – a tutorial review

Herein we demonstrate how SEC-ESI-MS can be used to analyze complex polymers, a significant challenge in contemporary polymer chemistry.

Installing lactone chain termini during photoinduced polymerization

We exploit the Thorpe–Ingold effect as a spontaneous end group transformation method during photo-induced polymerization of methacrylates using the functional (2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropio-phenone) species as radical photoinitiator.

Wavelength-Dependent Photochemical Stability of Photoinitiator-Derived Macromolecular Chain Termini

Herein, we report the unique-and first time-wavelength-dependent investigation with strictly monochromatic light of 305-405 nm wavelength into the stability of photoinitiator-derived chain termini of poly(methyl methacrylate) using a tunable laser system fused with pulsed-laser irradiation and size exclusion chromatography hyphenated to high-resolution electrospray mass spectrometry (PLI-SEC-ESI-MS). We assess several substitution patterns of methyl groups on the common benzoyl-type radical fragment. Critically, methyl substitution in the 2- and 6-positions of the benzoyl moiety, i.e., in both ortho-positions, resulted in stable chain ends up to approximately 350 nm. The stability can be attributed to a blue-shift of the n-π* transitions (relevant for the end group reactivity) as predicted by earlier density functional theory (DFT) calculations on model species. In sharp contrast, our experiments show a far reduced stability of the end groups commencing from 400 nm onwards, when the dual ortho-methyl substitution in the benzoyl fragment is missing. Thus, we demonstrate that the substitution pattern on the phenyl ring of the benzoyl group dictates the chain end stability as a function of wavelength in excellent agreement with the quantum chemical predictions. Our study thus provides critical insights into selecting suitable photoinitiation systems for specific wavelength regimes.

Bis(mesitoyl)phosphinic acid: photo-triggered release of metaphosphorous acid in solution

We report a photo-triggered, two-step fragmentation mechanism generating metaphosphorous acid.