Boron-methylated dipyrromethene technology for rapid radical polymerizations using low-intensity green light

Background

Visible light has emerged as a promising stimulus to drive polymerizations for a variety of applications, particularly in the biomedical and advanced manufacturing arenas such as 3D printing. This is due to its inherent spatio­temporal control, high penetration depth, low energy, and discrete absorption, which enable benign and wavelength-selective fabrication of multifunctional soft materials.
The discrete absorption of low-energy photons in the visible to near-infrared spectral region results in deeper light penetration into biological materials (e.g., tissue) and a reduction in phototoxicity relative to higher energy ultraviolet (UV) light. As a result, the development of efficient visible light photoinitiating systems will enable biomaterials fabrication, such as 3D cell encapsulation for tissue engineering applications.
However, a major hurdle limiting the implementation of visible light-driven polymerizations is its low efficiency relative to UV light-driven processes. This arises from a difference in the mechanism to generate initiating species for polymeriza­tion, such as radicals, which has been predominantly restricted to bimolecular processes for long-wavelength light (≥500 nm) (i.e., Type II, photoredox) and unimolecular processes for short-wavelength light (<500 nm) (i.e., Type I, photolysis).
The requirement for cocatalysts such as tertiary amines, iodonium salts, and/or borate salts in Type II processes are intrinsically diffusion-limited, slowing overall photocuring rates, increasing complexity and cost, and potentially decreasing biocompatibility of the concomitant resin formulations. Therefore, long-wavelength (>500 nm) Type I photoinitiators offer a compelling alternative. Existing visible light photoinitiators, like bisacyl­phosphine oxide (BAPO) and titanocene derivatives, have low molar absorptivity in the visible region and often require high light intensities or photoinitiator concentrations, limiting their effectiveness and increasing potential toxicity.

Technology overview

Alkylated boron-methylated dipyrromethene (BODIPY) serves as a highly efficient Type I photoinitiator for rapid radical polymerizations under low-intensity green light (∼530 nm). This photoinitiator operates through a homolytic β-scission mechanism at the boron-carbon bond, generating radicals that initiate polymerization. BODIPY derivatives are synthetically modified to increase their excited-state lifetime via halogenation and boron alkylation, resulting in longer triplet excited-state lifetimes and enhancing the likelihood of β-scission and radical formation.
These photoinitiators exhibit high molar absorptivity in the visible region (500-550 nm) and demonstrate significantly faster polymerization rates compared to current visible light photoinitiators. Additionally, BODIPY photoinitiators are stable under ambient conditions and can be used to create transparent polymer films, making them suitable for advanced manufacturing and biomedical applications.
What differentiates BODIPY technology is its ability to efficiently initiate polymerization with low-intensity green light, a feature that current visible light photoinitiators lack. Boron alkylation is the key result to lowering the bond dissociation enthalpy (BDE) for the boron-carbon bond, facilitating β-scission and radical formation. This leads to faster polymerization rates and higher efficiency in radical generation.
Moreover, the long triplet excited-state lifetimes achieved through halogenation further enhance the photoinitiator's performance. Lastly, BODIPY's high molar absorptivity and stability under ambient conditions make it a versatile and reliable choice for applications requiring rapid and efficient polymerization, such as 3D printing, tissue engineering, and dental composites where low-energy, wavelength-selective light is crucial.

Benefits

  • Highly efficient Type I photoinitiator for rapid radical polymerizations
  • Operates under low-intensity green light (∼530 nm)
  • Generates radicals through a homolytic β-scission mechanism
  • Exhibits high molar absorptivity in the visible region (500-550 nm)
  • Enhanced excited-state lifetime through halogenation and boron methylation
  • Significantly faster polymerization rates compared to current visible light photoinitiators
  • Stable under ambient conditions
  • Suitable for creating transparent polymer films
  • Applications in advanced manufacturing and biomedical fields

Applications

  • 3D printing
  • Coatings
  • Adhesives
  • Biomedical applications
  • Dental composites
  • Rapid polymerization
Patent Information:
Direct Link:
https://canberra-ip.technologypublisher.com/tech/Boron-methylated_dipyrrometh ene_technology_for_rapid_radical_polymerizations_using_low-intensity_green_light
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For Information, Contact:
Andrei Zorilescu
Sr. Licensing Specialist
University of Texas at Austin
andrei.zorilescu@austin.utexas.edu