Heterotelechelic silicones: Facile synthesis and functionalization using silane-based initiators

The synthetic utility of heterotelechelic polydimethylsiloxane (PDMS) derivatives is limited due to challenges in preparing materials with high chain-end fidelity. In this study, anionic ring-opening polymerization (AROP) of hexamethylcyclotrisiloxane (D3) monomer using a specifically designed silyl hydride (Si–H)-based initiator provides a versatile approach towards a library of heterotelechelic PDMS polymers. A novel initiator, where the Si–H terminal group is connected to a C atom (H–Si–C) and not an O atom (H–Si–O) as in traditional systems, suppresses intermolecular transfer of the Si–H group, leading to heterotelechelic PDMS derivatives with a high degree of control over chain-ends. In-situ termination of the D3 propagating chain end with commercially available chlorosilanes (alkyl chlorides, methacrylates, and norbornenes) yields an array of chain-end functionalized PDMS derivatives. This diversity can be further increased by hydrosilylation with functionalized alkenes (alcohols, esters, and epoxides) to generate a library of heterotelechelic PDMS polymers. Due to the living nature of ring opening polymerization and efficient initiation, narrow-dispersity (Đ < 1.2) polymers spanning a wide range of molar masses (2 – 11 kg mol−1) were synthesized. With facile access to α-Si–H and ω-norbornene functionalized PDMS macromonomers (H–PDMS–Nb), the synthesis of well-defined super-soft (Gʹ = 30 kPa) PDMS bottlebrush networks, which are difficult to prepare using established strategies, was demonstrated.