Kinetic Analysis of Mechanochemical Chain Scission of Linear Poly(phthalaldehyde)

Abstract

The kinetics of mechanochemical chain scission of poly(phthalaldehyde) (PPA) are investigated. Ultrasound-induced cavitation is capable of causing chain scission in the PPA backbone that ultimately leads to rapid depolymerization of each resulting polymer fragment when above the polymer's ceiling temperature (Tc ). An interesting feature of the mechanochemical breakdown of PPA is that "half-chain" daughter fragments are not observed, since the depolymerization is rapid following chain scission. These features facilitate the determination of rate constants of activation for multiple molecular weights from a single sonication experiment. Additionally, the degradation kinetics are modified with chain-end trapping agents through variation of the nature and amount of small molecule nucleophile or electrophile.

Kinetics and Thermodynamics of Ultrasound-Assisted Depolymerization of κ-Carrageenan

“…Madras et al [28] studied the kinetics of ultrasoundassisted depolymerization of poly(vinyl acetate) in chlorobenzene, while Chakraborty et al [29] investigated the kinetics of ultrasonic degradation of polybutadiene and isotactic polypropylene in solution at different temperatures and in different solvents. Other studies on chitosan [30], apple pectin [31], sea cucumber fucoidan [32], linear poly(phthalaldehyde) [33], carboxylic curdlan [34], and carrageenan [20,21] have also been reported. Lii et al [20] studied the effect of κ-carrageenan concentration on the kinetics of the reaction.…”

Investigations in Fundamental and Applied Polymer Mechanochemistry

“…By applying an analysis similar to that detailed in Section 2.2 -that is, monitoring the decrease in concentration of a discrete molecular weight in the GPC trace over the course of sonicationan entire suite of rate constants was obtained in a single experiment. [ 25 ] Mechanistic probes of the mechanochemical chain scission, supported by computational results obtained by the Martínez group, indicated a heterolytic scission mechanism was operative. In response to mechanochemical activation, the resulting oxocarbenium and hemiacetalate end groups each initiate depolymerization in respective daughter chain fragments.…”

“…One of the benefits of the complete depolymerization and lack of persistent daughter fragments is the ability to calculate rate constants for mechanochemical activation of a range of molecular weights within a single polymer sample. By applying an analysis similar to that detailed in Section – that is, monitoring the decrease in concentration of a discrete molecular weight in the GPC trace over the course of sonication – an entire suite of rate constants was obtained in a single experiment …”

Photodegradable transient bilayered poly(phthalaldehyde) with improved shelf life

“…PPHA degradation can be triggered by different types of stimuli. These include photochemical (eg, visible light, light emitting diode, and ultraviolet), chemical, thermal, and mechanical stimulus . Visible light stimulus is particularly attractive because of the availability of ambient light.…”

“…These include photochemical (eg, visible light, light emitting diode, and ultraviolet), 5,7-9 chemical, 10,11 thermal, 11,12 and mechanical stimulus. 13,14 Visible light stimulus is particularly attractive because of the availability of ambient light. Phillips et al demonstrated the use of a photo-induced electron transfer (PET) reaction between a fused-aromatic-ring sensitizer and photoacid generator (PAG) to create a strong acid that led to PPHA degradation using visible light.…”