End Group Characterization of Poly(phthalaldehyde): Surprising Discovery of a Reversible, Cationic Macrocyclization Mechanism

Abstract

End-capped poly(phthalaldehyde) (PPA) synthesized by anionic polymerization has garnered significant interest due to its ease of synthesis and rapid depolymerization. However, alternative ionic polymerizations to produce PPA have been largely unexplored. In this report, we demonstrate that a cationic polymerization of o-phthalaldehyde initiated by boron trifluoride results in cyclic PPA in high yield, with high molecular weight, and with extremely high cyclic purity. The cyclic structure is confirmed by NMR spectroscopy, MALDI-TOF mass spectrometry, and triple-detection GPC. The cyclic polymers are reversibly opened and closed under the polymerization conditions. Owing to PPA's low ceiling temperature, cyclic PPA is capable of chain extension to larger molecular weights, controlled depolymerization to smaller molecular weights, or dynamic intermixing with other polymer chains, both cyclics and end-capped linears. These unusual properties endow the system with great flexibility in the synthesis and isolation of pure cyclic polymers of high molecular weight. Further, we speculate that the absence of end groups enhances the stability of cyclic PPA and makes it an attractive candidate for lithographic applications.

End-capped poly(4,5-dichlorophthalaldehyde): a stable self-immolative poly(aldehyde) for translating specific inputs into amplified outputs, both in solution and the solid state

“…As expected, the response is selective for the polymer end-capped with the responsive Alloc group: i.e., a similar experiment with Ac-PCl 2 PA-OiPr (11) and Pd(0) revealed no significant depolymerization (Fig. 7b).…”

Kinetic Analysis of Mechanochemical Chain Scission of Linear Poly(phthalaldehyde)

“…To explore the kinetics of linear PPA degradation, we prepared linear polymer via phosphazine super base‐mediated polymerization. [4b], We initially investigated the ultrasonic degradation of PPA in N , N ‐dimethylformamide (DMF) using an ultrasound power density of 13.7 W cm −2 and an internally monitored temperature between 10 and 15 °C. As shown in Figure , we observed a gradual decrease in PPA concentration and number‐average molecular weight () as a function of sonication time for 32 kDa PPA (PDI = 1.6).…”

Macrocyclization Reactions: The Importance of Conformational, Configurational, and Template-Induced Preorganization

“…This cyclic polymer, formed exclusively by phthalaldehyde repeat units, can undergo re/depolymerization depending on the conditions. 182,183 Interestingly, they have studied the effect of the flexibility/rigidity of the monomers on the molecular weight distribution of the obtained macrocyclic structures, obtaining narrower distributions for the more rigid ones. 184 Otto and co-workers have reported the synthesis of selfreplicating macrocycles 101a−101e by means of a dynamic combinatorial methodology from the corresponding monomer 100 ( Figure 30).…”