A Highly Efficient Polyurethane‐Type Polymeric Photoinitiator Containing In‐chain Benzophenone and Coinitiator Amine for Photopolymerization of PU Prepolymers

Abstract

Summary: A novel polyurethane‐type polymeric photoinitiator (PUIOA) was synthesized through polycondensation of a novel diamine AAPBP, TDI and MDEA. The BP and coinitiator amine structures were successfully introduced into the backbones of PUIOA. A polymeric photoinitiator without the coinitiator amine in the polymer chain (PUIO) was also synthesized for comparison. FT‐IR, 1H NMR and GPC analyses confirmed the structures of polymeric photoinitiators. The UV‐vis spectra of PUIOA and PUIO are similar to the parent AAPBP, and both exhibit high red‐shifted maximal absorption as compared with BP. ESR spectra indicate that PUIOA can generate free radicals most efficiently. Photopolymerization of the Polyurethane prepolymer, initiated by PUIOA, PUIO/MDEA, AAPBP/MDEA and BP/MDEA, was studied by photo‐DSC. The results show that PUIOA is the most efficient photoinitiator for PU prepolymer.Synthesis routes for polymeric photoinitiators.magnified imageSynthesis routes for polymeric photoinitiators.

Effect of the Structure of Photosensitive Groups Contained in Novel PU‐Type Polymeric Benzophenone Photoinitiators on Photopolymerization

“…Their maximum absorption ( λ max ) and the values of the molar extinction coefficient at λ max ( ε ) are summarized in Table 1. According to our previous work, the main benzenoid π ‐ π *‐type transition of the bare BP is usually at 254 nm 24. From Figure 1 and Table 1, the maximal absorption of PUSBA‐c is 250 nm, which is slightly lower than that of the bare BP.…”

“…As shown in Figure 2(a), ESR signals have six‐line hyperfine splitting when amine radicals are trapped, which is usually explained by a triplet with α ‐nitrogen, and a further split into a doublet with a β ‐proton 21. From the literature and our previous work,22–24, 49 the methenyl radicals marked in Figure 2(a) have been confirmed as the main radicals for photopolymerization.…”

“…Firstly, due to the more efficient proton transfer in PUSBA‐s than in PUSBA‐o and PUSBA‐c, the hydrogen‐abstraction reaction between the excited state of the BP moieties and the BDEA moieties may more readily take place and form a high concentration of free radicals, as discussed in the ESR analysis. Secondly, the photolysis reaction of the CS bond can generate four types of free radicals,22–24 which would be favorable for the polymerization of TMPTA. Finally, compared with PUSBA‐o and PUSBA‐c, the relatively‐longer‐wavelength absorption maximum of PUSBA‐s would certainly account for its increased photoefficiency.…”

“…The research of photoinitiators plays a very important role in the development of UV‐curing technology 5, 6. Polymeric photoinitiators that contain side‐chain or in‐chain photosensitive chromophores have drawn remarkable interest recently 7–26. Compared with low‐molecular‐weight analogues, polymeric photoinitiators have been justified by various advantages, such as non‐yellowing, low‐odor, compatibility improvement with formulation components as well as of lower contaminant release 27–36.…”

A Highly Efficient Polymerizable Photoinitiator Comprising Benzophenone, Thio Moieties, and N‐Arylmaleimide

“…[21,31] Moreover, the polarity of the microenvironment of BP moieties will increase in the presence of imide group (nitrogen atom), and the increasing polarity may increase its maximum of absorption. [25] The polarity of the microenvironment of BP moieties in MTBP, due to the maleimide group directly links to BP moieties, will increase relatively higher than that of the indirectly one, MTPBP. Therefore, MTBP possesses a slightly higher p-p à absorption than MTPBP.…”