A broadly applicable cross-linker for aliphatic polymers containing C–H bonds

Abstract

Addition of molecular cross-links to polymers increases mechanical strength and improves corrosion resistance. However, it remains challenging to install cross-links in low-functionality macromolecules in a well-controlled manner. Typically, high-energy processes are required to generate highly reactive radicals in situ, allowing only limited control over the degree and type of cross-link. We rationally designed a bis-diazirine molecule whose decomposition into carbenes under mild and controllable conditions enables the cross-linking of essentially any organic polymer through double C–H activation. The utility of this molecule as a cross-linker was demonstrated for several diverse polymer substrates (including polypropylene, a low-functionality polymer of long-standing challenge to the field) and in applications including adhesion of low–surface-energy materials and the strengthening of polyethylene fabric.

Covalent Functionalization of Melt-Blown Polypropylene Filters with Diazirine–Photosensitizer Conjugates Producing Visible Light Driven Virus Inactivating Materials.

“…The surface of the MBPP was then covalently functionalized with 3 using a modified procedure from Lepage et al 30 To facilitate this, the reactivity of the diazirines in 3 was first analyzed by differential scanning calorimetry (DSC). These data revealed an onset temperature of 108 °C (determined by extrapolation of the tangent of the upward slope to the fitted baseline of the plot) and a peak temperature of °C (Fig.…”

“…The diazirine functionality is not limited to C-H bond activation and can also be used to functionalized more reactive O-H and N-H bonds in polyalcohols and polyamides which could be used for post-processing functionalization of different materials that would benefit from self-sterilization in healthcare settings. 30 Future testing will focus on the development of this technology to understand the performance limitations of the material with respect to repeated sequential virus inactivation, potential photobleaching, light intensity-dependent performance, response to washing and detergents, and performance against different types of pathogens. The optimization of inactivation materials should be focused on developing technology that is broadly applicable, robust, and possesses broad spectrum activity without the potential for developing resistance.…”

“…One of our research groups recently described a family of bis-diazirine reagents that can be used to crosslink simple aliphatic polymers like polyethylene and polypropylene. 30,31 The reagents work by expelling nitrogen gas (N2) from the tethered diazirine groups upon thermal or photochemical stimulation, to afford high-energy carbenes can then undergo rapid and nearly barrierless insertion any available C-H bonds. In principle, such a technique can also be used to add functionality to base polymeric materials: the desired functional group can simply be tethered to one or more diazirine units, and the resulting conjugate can then be irreversibly linked to the surface of any polymeric material through appropriate activation of the diazirine function.…”

Structure–Activity Relationships of Voltaglue Organic Blends

“…Diazirine doubles as the electron acceptor (forming the diazirinyl radical) and covalent crosslinker (via carbene insertion). [ 11,12 ] This dual function is initially advantageous, but as electrocuring progresses, the decay of diazirine lowers the electron mobility brought upon by the Dz – /Fc + pair. Ferrocene (grafted) serves as an ideal electron donor, as it is stable under ambient conditions and readily oxidized at 0.6 V (vs Ag/AgCl).…”

Flexible polyfluorinated bis-diazirines as molecular adhesives

“…1b ) that can be used as a universal crosslinker for aliphatic polymers. 9 Compound 1 works by releasing N 2 upon thermal or photochemical activation to afford reactive carbene species that are capable of undergoing efficient C–H insertion with a wide range of polymer materials. Because bis-diazirine 1 can react twice, it is able to form new connections between polymer strands, resulting in outcomes characteristic of polymer crosslinking: increased average molecular weight, loss of solubility, increased glass transition temperature, loss of melting transition, etc.…”