(643f) Kinetic Investigation on the Cationic Polymerization of Cyclic Poly(phthalaldehyde)

Polyphthalaldehyde and its copolymers are metastable polymers that have been shown to rapidly depolymerize from the solid state back into its constituent monomers due to their subambient ceiling temperatures. This depolymerization upon triggering makes these materials well suited as a chemically recyclable polymers, sacrificial materials for semiconductor manufacturing, or fabricating stimuli-responsive devices. Although interest in phthalaldehyde-based polymers has increased in the past decade, there has not been a thorough investigation of the cationic polymerization kinetics since its discovery in 1967. In this work, a continuous microflow reactor was utilized to probe the kinetics of this rapid, cationic polymerization in dichloromethane using boron trifluoride diethyl etherate as the Lewis acid catalyst. Under proper catalyst loadings, polymer nominal molecular weights exceed 250 kDa in 10 seconds of reaction time at -78 °C. Molecular weight and time–conversion data supports a theory for two polymerization regimes, which has not been observed before in batch polymerizations of this polymer. The initial chain growth regime involves the creation of many polymer chains of moderate molecular weight. At higher conversions a kinetic transition is observed as the polymer chains fuse together at higher rates, causing the observed molecular weight to roughly double in the last 20% conversion. These findings provide fundamental kinetic and molecular weight understanding that enable higher synthetic control of an emerging class of depolymerizable polymers.