Highly Efficient ROP Polymerization of ε‑Caprolactone Catalyzed by Nanoporous Alumina Membranes. How the Confinement Affects the Progress and Product of ROP Reaction

• Published in: Macromolecules 2018-06, Vol.51 (12), p.4588-4597
• Main Authors: Tarnacka, Magdalena, Dzienia, Andrzej, Maksym, Paulina, Talik, Agnieszka, Zięba, Andrzej, Bielas, Rafał, Kaminski, Kamil, Paluch, Marian
• Format: Article
• Language: English
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.8b00409

Efficient ROP polymerization of ε-caprolactone, resulting in products characterized by high molecular weight of low dispersities, remains a challenging task and is currently an important matter of ongoing research, mostly due to the accompanying side reactions, i.e., hydrolysis and transesterification. Herein, we studied in detail the impact of 2D hard confinement on the progress and product of ring-opening polymerization (ROP) of ε-caprolactone with and without water acting as initiator in comparison to the macroscale conditions, where various forms (powder, sheet) of alumina were used. It turned out that applied aluminum oxide nanotemplates act as both catalyst and initiator (INICAT) of ROP nanopolymerization and seem to operate accordingly to the pseudoliving coordination–insertion mechanism, resulting in nanowires of PCL characterized by M n up to 53.5 kg/mol. Additionally, due to the applied confinement, the side reactions were successfully suppressed, resulting in macromolecules of moderate molecular weight distribution (Đ = 1.27–1.41) and unimodal GPC peaks. It can be related to the extremely short nanopolymerization time (around 40 min), which successfully counteracts side reactions to occur. Moreover, our data clearly indicated that nanoporous membranes favor the growth of polymer chains of similar length, resulting in low dispersity of produced macromolecules. We believe that presented data significantly broaden the current state of knowledge and allow for a better understanding of the processes taking place under confinement, which seem to be crucial in any further nanotechnology development.