Modulating the Depolymerization of Self-Immolative Brush Polymers with Poly(benzyl ether) Backbones

Abstract

We have synthesized a series of stimuli-responsive brush polymers by grafting azide-terminated side chains onto a self-immolative, alkyne-bearing poly(benzyl ether) backbone, which is prepared by anionic polymerization of quinone methide-based monomers. Upon exposure to a decapping reagent (Pd(0) or F−), these brush polymers undergo an irreversible degradation cascade from head to tail to yield individual side chains. It is observed that several factors affect the depolymerization kinetics, including solvent polarity, type of counterion, the rate of the decapping chemistry, and interestingly, the rigidity of the side chains.

Post-polymerization ‘click’ end-capping of polyglyoxylate self-immolative polymers

“…For example, Shabat and co-workers have shown that protecting groups can mask nucleophilic functionalities en route to water soluble poly(benzyl urethanes). 30 Zhang and co-workers have used post-synthetic disulfide metathesis 31 and 'click'-type reactions 32 to prepare SIP bottlebrushes and organogels. Gillies and co-workers have developed PPM strategies for preparing a range of functionalized polyglyoxylate and polyglyoxylamide SIPs via transesterification 33 and amidation reactions, 34 which significantly expand the functional scope of these polymers.…”

Self-Immolative Bottlebrush Polypentenamers and their Macromolecular Metamorphosis

“…While many SIPs have been limited to linear and dendritic based topologies, a few have expanded to more complex architectures, such as grafted polymers. 7,32,38 Recently, the first bottlebrush (BB) SIP was reported by Zhang et al 39 which consists of an poly(benzyl ether) backbone with alkyne pendants and an end group capped with a tert-butyldimethylsiloxy (TBDMS) or allyl chloroformate (ACF). Azide terminated poly(ethylene glycol) (PEG) or polystyrene (PS) side chains ( 2 -4 kg mol -1 ) were "grafted-to" the alkyne backbone pendants to produce the BBs.…”

“…While this work was the first of BB SIPs, full depolymerization of these materials was shown to be hampered by rigid side chains (PS) which are proposed to limit optimal backbone conformation for unzipping. 39 Polycyclopentenes (PCP)s, also termed polypentenamers, are derived from ring opening metathesis polymerization (ROMP) of cyclopentene (CP) and are a unique class of elastomers that can depolymerize through ring-closing metathesis (RCM) to reform their low strain CP monomers. 40 While their ability to depolymerize was first determined in 1972, 41 these materials have remained largely underutilized due to long-standing challenges in synthesizing these polymers.…”

Oligo(thioether‐ester)s Blocks in Polyurethanes for Slowly Releasing Active Payloads

“…Such polymers can display a chemical structure with a low ceiling temperature, display plenty of labile bonds in the main chain, present repeating units that allow a chain‐shattering mechanism, or include self‐immolative units . Self‐immolative polymers and dendrimers display a catastrophic degradation that is triggered with a low amount of molecules, typically one trigger molecule per polymer chain …”