Organocatalyzed Copolymerization of CO, Se, and Oxetane: O/Se Exchange Reaction Determining Chain Structure

The incorporation of selenium (Se) atoms into polymers has garnered significant interest. However, methods to introduce selenium atoms into polymers remain limited, particularly for approaches that directly utilize elemental selenium. This work presents a novel copolymerization of gaseous carbon monoxide (CO), solid Se powder, and liquid oxetane (OX) to synthesize Se-containing polymers with tunable structure, using commercially available alkyl borane and organic bases as the binary metal-free catalyst system. The polymerization process includes two steps: the reduction of CO and Se to form COSe and alternating copolymerization of COSe with OX. The O/Se exchange reaction (O/Se ER) was discovered during the polymerization, which can alter the polymer structure. The O/Se ER could be significantly suppressed by the binary organocatalyst system at 60 °C, affording well-defined poly(selenocarbonate) in a fast and selective manner. The poly(selenocarbonate) is semi-crystalline exhibiting a melting temperature of 116 °C, a number-average molecular weight of 39 kDa, a tensile strength of 5.0 ± 0.4 MPa, and an elongation of 5.5 ± 0.5%. Interestingly, the poly(selenocarbonate) could be completely converted into the poly(selenoether) by utilizing the O/Se ER, i.e., decarboxylation in the presence of organic bases at high temperatures. This work provides an efficient synthetic method for synthesizing Se-containing polymers from readily available monomers.