Depolymerization of Bottlebrush Polypentenamers and Their Macromolecular Metamorphosis

Abstract

The depolymerization of bottlebrush (BB) polymers with varying lengths of polycyclopentene (PCP) backbone and polystyrene (PS) grafts is investigated. In all cases, ring closing metathesis (RCM) depolymerization of the PCP BB backbone appears to occur through an end-to-end depolymerization mechanism as evidenced by size exclusion chromatography. Investigation on the RCM depolymerization of linear PCP reveals a more random chain degradation process. Quantitative depolymerization occurs under thermodynamic conditions (higher temperature and dilution) that drives RCM into cyclopentenes (CPs), each bearing one of the original PS grafts from the BB. Catalyst screening reveals Grubbs’ third (G3) and second (G2) generation catalyst depolymerize BBs significantly faster than Grubbs’ first generation (G1) and Hoveyda–Grubbs’ second generation (HG2) catalyst under identical conditions while solvent (toluene versus CHCl3) plays a less significant role. The length of the BB backbone and PS side chains also play a minor role in depolymerization kinetics, which is discussed. The ability to completely deconstruct these BB architectures into linear grafts provides definitive insights toward the ATRP “grafting-from” mechanism originally used to construct the BBs. Core–shell BB block copolymers (BBCPs) are shown to quantitatively depolymerize into linear diblock polymer grafts. Finally, the complete depolymerization of BBs into α-cyclopentenyl-PS allows further transformation to other architectures, such as 3-arm stars, through thiol–ene coupling onto the CP end group. These unique materials open the door to stimuli-responsive reassembly of BBs and BBCPs into new morphologies driven by macromolecular metamorphosis.

“Close-to-Release”: Spontaneous Bioorthogonal Uncaging Resulting from Ring-Closing Metathesis

“…8 As Ru-based catalysts tolerate water and oxygen, a number of biocompatible protocols have been reported. 9 Davis used olefin metathesis for bioorthogonal ligation via cross-metathesis. Schultz performed cross-metathesis of olefin-bearing proteins using the Hoveyda–Grubbs catalyst (HG-II).…”

Selectively Depolymerizable Polyurethanes from Unsaturated Polyols Cleavable by Olefin Metathesis

“…[ 48,57,64 ] The further realization that cyclopentene, functionalized cyclopentenes, and other five‐membered alkene rings can be ring‐opened through judicious selection of reaction conditions has spawned recent development of polypentenamer elastomers and related materials, including networks with continuous recyclability through sequential ring‐opening and ring‐closing metathesis. [ 65–72 ] Inspired by this general motif, we report here a series of novel PUs derived from carefully designed, unsaturated polyols, enabling facile depolymerization of the PUs by olefin metathesis.…”

“…recently reported the re‐polymerization of depolymerized polypentenamers through thiol‐ene chemistry performed on cyclopentene chain ends. [ 71 ] Here, as a similar initial example, we used metathesis to depolymerize the crosslinked PU poly(HBID‐ co ‐DEDO5) in THF. Thereafter, either trimethylolpropane tris(3‐mercaptopropionate) (TMP) was added at stoichiometric equivalence ([SH]/[CC] = 1) or azobisisobutyronitrile (AIBN) was added at 1% relative to the initial weight of poly(HBID‐ co ‐DEDO5).…”

Kinetic comparison of isomeric oligo(ethylene oxide) (meth)acrylates: Aqueous polymerization of oligo(ethylene oxide) methyl ether methacrylate and methyl 2‐(oligo(ethylene oxide) methyl ether)acrylate macromonomers

“…the "grafting-from" approach, 15,[31][32][33][34][35] coupling chains onto a functionalized backbone via the "grafting-onto" approach, 36,37 and by the polymerization of macromonomers in the "grafting-through" approach. [38][39][40][41][42][43] Synthesis of molecular bottlebrushes by grafting-through of vinyl macromonomers using reversible deactivation radical polymerization (RDRP) provides densely grafted bottlebrushes with side chains on every other carbon along the backbone. However, grafting-through RDRP of macromonomers via RDRP is challenging due to the low concentration of polymerizable vinyl groups, steric hindrance of long chain substituents and high viscosity.…”