Synthesis and performance of multiband responsive phenothiazinium salt-based polymerizable photoinitiators
LIU Pengcheng
LI Lun
LIU Ren
ZHU Yi
Abstract：Objective Photopolymerization is a widely utilized technique across various fields due to its environmentally friendly and effi-cient characteristics.During the process of photopolymerization,photoinitiators(PIs)are essential in determining the excitation wavelength,polymerization type,polymerization rate,and the final material properties.However,conventional PIs are hin-dered by two photophysical phenomena,the inner filter effect,where PIs and their photodegradation byproducts concentrated at the material's surface absorb most of the incident light,and Rayleigh scattering,where a significant portion of incident light is scattered on the surface of a photopolymerization system.These effects prevent subsurface PIs from receiving sufficient activa-tion energy for photolysis,leading to reduced polymerization efficiency,shallow cure depths,and impaired material perfor-mance.Additionally,the small molecules generated from conventional PIs may migrate within the cured material,potentially leading to toxicity.To address this issue,low-migration,multiband responsive polymerizable PIs have been developed.
Methods A photopolymerizable methacrylate phenacyl phenothiazinium salt(Acry-P-PTh)was synthesized by incorporating acrylic ester groups.Its structure,photophysical properties,photochemical behavior,migration ratio,and thermal stability were investigated using ultraviolet-visible absorption(UV-Vis)spectroscopy,real-time infrared(RT-IR)spectroscopy,and differential scanning calorimetry(DSC).
Results and Discussion UV-Vis analysis revealed that Acry-P-PTh was responsive to ultraviolet(UV),visible,and near-infrared(NIR)light,with the peak absorption wavelength shifting to 520 nm,a 5 nm redshift compared to phenacyl phenothi-azinium salt(P-PTh).Photopolymerization kinetics demonstrated that Acry-P-PTh effectively initiated both free radical and cat-ionic polymerization.Under 365 nm,405 nm,and 850 nm irradiation,Acry-P-PTh generated benzoyl radicals and Br∅nsted superacids through C-S bond homolysis.This dual initiation mechanism enabled the polymerization of both acrylate monomers,trimethylolpropane triacrylate(TMPTA),and cationic monomers,EPOX,achieving excellent initiation performance in hybrid systems compared to single-monomer resin systems.Specifically,under 365 nm light irradiation,the final free radical conver-sion rate exceeded 50％,and the final cationic conversion rate exceeded 40％;under 405 nm light irradiation,the final free radi-cal conversion rate exceeded 45％,and the final cationic conversion rate exceeded 45％.Notably,under 850 nm light,EPOX cationic polymerization achieved a 40％conversion rate within 30 min.Migration studies confirmed that Acry-P-PTh exhibited low migration,with post-curing migration ratios lower than those of P-PTh,measuring 4.9％for the free radical system and 3.5％for the cationic system.Thermal stability analysis further revealed high thermal resistance,with polymerization tempera-tures for free radical and cationic polymerization being 233 ℃ and 78℃,respectively.These properties make Acry-P-PTh a promising material for various applications,such as food packaging and biomedicine manufacturing.
Conclusion The synthesized Acry-P-PTh demonstrates broadband absorption across the ultraviolet-visible-near-infrared(UV-Vis-NIR)spectrum.Compared to P-PTh,Acry-P-PTh shows reduced low migration ratio.When mixed with Acry-P-PTh with TMPTA and EPOX monomers,the photocurable system is able to resist higher thermal polymerization temperatures,demonstrat-ing excellent thermal stability.In conclusion,Acry-P-PTh,as an advanced photoinitiator,holds significant potential for practi-cal applications.
Keywords：photocuringphenothiazinepolymerizable photoinitiatorlow migrationnear-infrared
Publication Date：2025-07-01
Online Publishing Date：2026-05-22(First online date of this platform, not the publication date of the document)
Pages：12( 93-104 )