# Development of Low Temperature Activatable Aryl Azide Adhesion Promoters as Versatile Surface Modifiers

## TL;DR

This paper introduces new low-temperature adhesion promoters that allow for surface modification of materials using milder conditions than previously possible.

## Contribution

The novel contribution is the design of aryl azide compounds that can be activated below 100 °C, enabling versatile surface modification.

## Key findings

- Substituted aryl azides can be activated at temperatures below 100 °C, as shown by DFT and experiments.
- The o,o-difluoro substituted p-phenoxy azide activates at around 70 °C and enables C–H insertion.
- Monomolecular PVP films were successfully attached to surfaces using the new adhesion promoters.

## Abstract

An innovative approach for the immobilization of polymeric
films
is the use of bifunctional compounds called adhesion promoters, that
create a stable chemical “bridge” between materials,
allowing for versatile and permanent surface modification. To connect
coating materials that lack reactive groups, the “bridge”
forming adhesion promoter needs a highly reactive group that can insert
in otherwise unreactive chemical bonds. Activatable perfluoro-aryl
azides are commonly used to achieve this, with the limitation that
their thermal activation is constrained to elevated temperatures—typically
far above 100 °C—and photolytic activation is often unfeasible
due to geometry or opaque materials. To overcome this limitation,
we designed and synthesized three small organic molecules based on
substituted aryl azides with the aim of lowering the activation temperature
that restricts the use of existing aryl azides. We demonstrate both
computationally via density functional theory (DFT) calculations and
experimentally that the activation temperature of an aryl azide can
be tuned by varying its substituents, giving access to mild activation
temperatures (below 100 °C). The most reactive compound was the
ο,ο-difluoro substituted p-phenoxy azide,
which forms a nitrene and undergoes C–H insertion reactions
at temperature of around 70 °C. This allows functionalization
of surfaces with polymers that have no reactive groups under gentle
conditions. The synthesized molecules were incorporated into a polymeric
backbone to form adhesion promoters allowing covalent attachment of
polymeric films to substrates by thermal activation below 100 °C.
As an example, we successfully generated monomolecular films of polyvinylpyrrolidone
(PVP), a polymer used and approved for medical devices due to its
hydrophilic and lubricious properties. The effectiveness of attachment
was assessed qualitatively and quantitatively using spectroscopic
ellipsometry (ELM) and X-ray photoelectron spectroscopy (XPS).