Macromolecular Postpolymerization of Siloxane Exchange to Assemble Multiple Siloxane Linkages

Copolymerization greatly enriches the variety of polymers and provides flexibility to tailor polymer properties. However, copolymerization is a more challenging research topic than homopolymerization because it requires comprehensive consideration of the relative polymerization activity of the monomers, monomer feeding ratios, and dosing methods, and the distribution of monomers (random, block, or alternating) in the polymer chain. Here, we demonstrate that the macromolecular postpolymerization via siloxane exchange mechanism is a robust strategy for assembling multiple siloxane linkages into the chain directly from commercially available cyclosiloxane monomers, independent of copolymerization constraints. Specifically, we used the assembly of D4Ph2 and D3F monomers into the polysiloxane chain as a model system, which to our knowledge has not been reported in published work for the successful direct copolymerization of those two monomers by ring-opening polymerization. The corresponding structures were confirmed by 1H NMR, 29Si NMR, DOSY–1H NMR, DSC, and MALDI-TOF MS. Experimental studies and density functional theory (DFT) calculations suggest that siloxane exchange is a thermodynamically favorable process (ΔG < 0). Additionally, the mechanical properties of the assembled elastomers (elongation at break >450% and tensile strength >7 MPa) are comparable to those of commercial polysiloxane elastomers. Altogether, this work presents an approach toward the siloxane equilibrium mechanisms in macromolecular postpolymerization assembly of multiple siloxane linkages to circumvent copolymerization challenges.