Steric bulk prevents the formation of strong bonds between Lewis acids and bases in frustrated Lewis pairs (FLPs), where latent reactivity makes these reagents transformative in small molecule activations and metal-free catalysis. However, their use as a platform for developing materials chemistry is unexplored. Here we report a fully macromolecular FLP, built from linear copolymers that containing either a sterically encumbered Lewis base or Lewis acid as a pendant functional group. The target functional copolymers were prepared by a controlled radical copolymerization of styrene with designer boron or phosphorus containing monomers. Mixtures of the B- and P-functionalized polystyrenes do not react, with the steric bulk of the functional monomers preventing the favorable Lewis acid base interaction. Addition of a small molecule (diethyl azodicarboxylate) promotes rapid network formation, cross-linking the reactive polymer chains. The resulting gel is dynamic, can self-heal, is heat responsive, and can be reshaped by postgelation processing.
Sterically hindered
Lewis acid and base centers are unable to form
Lewis adducts, instead forming frustrated Lewis pairs (FLPs), where
latent reactivity can be utilized for the activation of small molecules.
Applying FLP chemistry into polymeric frameworks transforms this chemistry
into responsive and functional materials. Here, we report a versatile
synthesis strategy for the preparation of macromolecular FLPs and
explore its potential with the ring-opening reactions of cyclic ethers.
Addition of the cyclic substrates triggered polymer network formation,
where the extent of cross-linking, strength of network, and reactivity
are tuned by the steric and electronic properties of the ethers. The
resultant networks behave like covalently cross-linked polymers, demonstrating
the versatility of FLPs to simultaneously tune both small-molecule
capture and mechanical properties of materials.
Frustrated Lewis Pair (FLP) chemistry is a significant and growing field since it offers a novel non-metal catalyst for hydrogenation and small molecule activation. Once it was discovered, different FLPs with varying reactivity towards small molecules have been extensively investigated. Its research has mainly focused on small moleculebased FLPs, however, especially in the aspect of hydrogenation reactions. In the field of polymer chemistry, several examples of conventional Lewis pair adduct containing polymers have been reported but there has yet been no exploration of FLPs incorporated into polymers up to the date of this project. Dynamic crosslinked polymeric networks have attracted more attention in recent years as their shape can be post-modified after polymerisation due to their exchangeable crosslinks. This dynamic crosslinking also makes the material stimuli-responsive and provides self-healing properties. This thesis introduces the synthesis of a polymeric network with combined features of frustrated Lewis pairs and dynamic crosslinking. New monomers containing Lewis acid or Lewis base centres were designed and synthesised successfully. For the pair 4styryl-diphenylborane and 4-styryl-diphenylphosphine, the two monomers were found to be able to bind together at high concentration in toluene so as to form a weak conventional Lewis pair (CLP) adduct. An FLP can be obtained when the phosphine monomer was replaced to its more hindered analogue, 4-styryl-dimesitylphosphine, which is reactive enough to form a complex with diethyl azodicarboxylate (DEAD), where the DEAD bridges the boron and phosphorous centres. The monomers obtained were copolymerised with styrene by RAFT polymerisations. It was also found to be possible to control both the molecular weight and the dispersity. The FLP polymers
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