Mechanistic Insights on the Anionic Polymerization of Aliphatic Aldehydes

Abstract

Self-immolative polymers are a class of stimuli-responsive macromolecules that can unzip down to monomer level. Among those, aliphatic polyaldehydes are particularly attractive due to their ability to rapidly depolymerize at ambient temperatures. By virtue of their thermal fragility, their preparation is challenging, and no mechanistic details exist about their synthesis. This study aims at clarifying the mechanism of the anionic polymerization of aliphatic aldehydes. For this purpose, several aliphatic aldehydes were polymerized using a variety of initiators. It was found that irrespective of the nature of the initiating species, the enolate formed between the initiator and the monomer is actually triggering the polymerization. The formation of an enolate is also responsible for a chain-transfer reaction to monomer, which limits the molecular weight of the polymer (ktr/kp = 0.0036). The microstructure of the polymer was determined by solid-state 13C nuclear magnetic resonance spectroscopy. It was found that all anionic polymers are linear, mostly isotactic (mm > 60%), and crystalline. These polymers are prone to depolymerize at room temperature in solution, making them interesting candidates as self-immolative polymers.