Cationic Copolymerization of o-Phthalaldehyde and Functional Aliphatic Aldehydes

Abstract

There has been a resurgence of research related to poly(phthalaldehyde) (PPHA) in the past several years because of the demonstration of long room-temperature lifetime and its low ceiling temperature facilitating the ability to rapidly depolymerize the polymer at ambient conditions. This rapid depolymerization upon triggering of PPHA mixtures makes them well suited for fabricating transient devices or stimuli-responsive materials. The copolymerization of phthalaldehyde (PHA) with other aldehydes provides a route to incorporate chemical or physical functionality into PHA-based polymers while still maintaining the favorable degradation properties. Although the anionic copolymerization of PHA with benzaldehydes has been described, only a limited number of examples have been reported on the cationic copolymerization of PHA with other aldehydes. In this study, the synthesis and reactivity behavior of PHA copolymers is reported. Aliphatic aldehydes were chosen for their prevalence and favorable degradation properties. Dichloromethane solvent and the boron trifluoride diethyl etherate Lewis acid catalyst showed the best monomer conversions and highest polymer molecular weights. It was found that the aliphatic aldehyde reactivity for copolymerization increased with the electron-withdrawing nature of the aldehyde, which correlates with the aldehyde hydration equilibrium constant. The molecular weight and copolymer yield decrease with an increase in the aliphatic aldehyde feed concentration. Results indicate that the polymerization conditions used in this study (ca. −78 °C) are above the ceiling temperature of the aliphatic aldehyde comonomers, but this does not prevent copolymerization of the comonomer with PHA. Postpolymerization modifications were performed to introduce functional groups into the PHA-based copolymer that are incompatible with the polymerization chemistry. PPHA copolymers were cross-linked using a radiation-induced thiol−ene click chemistry to show that the mechanical properties can be improved even though the copolymer has a lower molecular weight.

Stimuli‐Responsive Depolymerization of Poly(Phthalaldehyde) Copolymers and Networks

“…Based on previous work on the copolymerization of phthalaldehydes, the copolymerization of the allylated phthalaldehyde and unfunctionalized phthalaldehyde was investigated. [20,22,47] The allylated monomer was successfully incorporated in the copolymerization in a manner that allows variability in cross-linking density. It was found that a 1:1 equivalence of monomers was optimal for high incorporation rates (2.5:1 PPA:Allyl PPA) of the allylated monomer as well as the best overall yields of the statistical copolymer (Table S1, Supporting Information).…”

Residue analysis of thermally depolymerized phthalaldehyde‐based polymer thin films

“…Several polyaldehyde polymers were synthesized throughout this study to test how different variables affect residue formation after thermolysis. The polymers were synthesized via a cationic polymerization mechanism, which has been shown to produce polymers with long shelf‐life 10,11 . Table 1 shows the properties of the polymers used in this study.…”

“…The depolymerization and volatilization of phthalaldehyde copolymers were investigated to see the effect of volatile comonomers on product removal 10,22 . A propanal copolymer, p(PHA‐PA) sample P1, was compared to pPHA at the previously used thermolysis conditions, 5 min at 300°C.…”

“…Propanal was distilled over calcium hydride under an inert atmosphere before use. Polymers used in this study were synthesized according to previously reported methods 10 . Formulations were prepared by dissolving polymer in diglyme on a roller mixer until homogeneous, and then passed through a 0.2 μm syringe filter into a clean vial.…”

“…At temperatures above T c , the polymer is thermodynamically driven to depolymerize but can exist in a metastable state as long as there are no reactive chain ends. These metastable polymers can undergo thermally induced chain scission to introduce reactive chain ends at temperatures higher than T c , such as >100°C 9,10 . Once a backbone bond is broken above T c and reactive chain ends are formed, the polymer can rapidly depolymerize from the solid state into volatile, low‐molecular‐weight products.…”