ma9b02506_si_001.pdf (270.98 kB)
Kinetic Investigation on the Cationic Polymerization of o‑Phthalaldehyde: Understanding Ring-Expansion Polymerization
journal contribution
posted on 2020-02-21, 16:04 authored by Anthony Engler, Paul A. KohlDepolymerizable polymers are of interest
for engineering applications,
especially when their decomposition products can be recycled back
into high-value monomers. Polyphthalaldehyde and its derivatives form
cyclic polymer products which can depolymerize rapidly from the solid
state. To facilitate the development of these materials into technologies,
the polymerization kinetics of this system was investigated. A microflow
reactor was used to examine the cationic polymerization of o-phthalaldehyde with boron trifluoride diethyl etherate
as the polymerization catalyst. By utilizing a microflow reactor,
mass and heat resistances could be minimized to probe the kinetics
of the reaction. High molecular weight polymer, >270 kDa, was formed
in 10 s. Kinetic and molecular weight data indicate that two polymerization
regimes exist. The first regime is characterized by controlled growth
rates to moderate molecular weight polymers. The second regime occurs
above a threshold concentration, where intermolecular chain transfer
dominates the polymerization kinetics, resulting in an exponential
growth of the polymer molecular weight via fusion of adjacent polymer
chains. A ring-expansion polymerization model is proposed to explain
these polymerization results. These findings enable greater synthetic
control to achieve targeted polymer properties for poly(aldehydes)
and identifies kinetic methods that can be employed to assess the
activity of other polymerization catalysts.