Mechanochemical Degradation of Brush Polymers: Kinetics of Ultrasound-Induced Backbone and Arm Scission

Abstract

The ultrasonic degradation of polynorbornene-g-polylactide and polynorbornene-g-polystyrene brush polymers was explored. First-order rate constants for backbone scission were obtained for brush polymers with varying arm lengths (ranging ca. 3–8 kDa) and backbone degrees of polymerization (ranging ca. 78–361). Master curves, in which the rate constant trends for all polymers converge, could be generated by accounting for the rate enhancement from the polymer being in an extended conformation and the contour length being equivalent to the combined length of two arms and the backbone. Slow scission of arms from the backbone was also observed, with first-order rate constants being dependent on the arm length.

Polymer degradation: a short review

“…On the other hand, the flow-induced degradation is undesirable though present in the SEC (Size Exclusion Chromatography) columns where the cleavage of long linear macromolecules, typically those with MW over two millions, distorts the measured MW distribution of a polymer (Barth & Carlin, 1984;Striegel, 2008). The mid-chain cleavage can be also induced by the ultrasound which imposes periodic conformational changes on macromolecules that cause them to rupture (Peterson et al, 2020).…”

“…(2) was found to be applicable, too, though it obeys the mid-chain scission mode. However, in that case, macromolecules of molar masses up to ca 100,000 g/mol are usually not cleaved and so B ∞ must be determined experimentally (Netopilik et al, 1990;Peterson et al, 2020).…”

Molecular Polymer Brushes Made via Ring‐Opening Metathesis Polymerization from Cleavable RAFT Macromonomers

“…Degradable MPBs have become an emerging topic in literature and are prominent regarding their potential and ways to degrade complex polymer topologies. [ 1a,10 ] Several avenues of brush degradation have been introduced to date, featuring most commonly a degradation of the backbone, [ 10a,11 ] a detachment of the side chains, [ 12 ] a degradation of the side chain, [ 11a,13 ] alterations of previously cross‐linked brush‐based nanoparticles, [ 14 ] or a combination of the aforementioned. [ 15 ] In 2005, the Weck group showed the degradation of ester and acetal based norbornene‐oligoethylene glycol molecules, cleaving norbornene units off the residual ethylene glycol residue.…”

“…[ 15 ] In 2005, the Weck group showed the degradation of ester and acetal based norbornene‐oligoethylene glycol molecules, cleaving norbornene units off the residual ethylene glycol residue. [ 12 d] In a polymer context, Jiang et al. synthesized polymer brushes featuring carbonates as linkage between backbone and side chains by postmodification, ultimately detaching the grafted chains under acidic conditions.…”

“…synthesized polymer brushes featuring carbonates as linkage between backbone and side chains by postmodification, ultimately detaching the grafted chains under acidic conditions. [ 12 b] In the Matyjaszewski group, MPBs consisting of cellulose backbones with polyacrylate side chains were degraded either by cleaving off the grafted chain or degrading the backbone. [ 12 c] In 2015, Yu et al.…”