Depolymerization

Abstract

This article provides an overview of depolymerization from a thermodynamic and kinetic perspective. Depolymerization is characterized by the scission of the main chain backbone. Three types of reactions such as random degradation, depolymerization and weak‐link degradation may occur separately or in conjunction with each other. The kinetic treatment of depolymerization processes has been described in the case of random degradation and chain depolymerization. Depolymerization is characterized as their thermodynamic and energetic features such as heat, entropy, free energy for polymerization, bond‐dissociation energy, and activation energy. Current applications of depolymerization are found in various fields such as biological recycling (biorecycling), chemical recycling, agricultural uses in natural environment, and medical uses.

Coordination-induced polymerization of P═C bonds leads to regular (P─C) n polycarbophosphanes

“…The depolymerization reaction follows first-order kinetics, and Arrhenius plots allow us to determine the activation energy E a to be 32.9 ± 5.3 kJ mol −1 (G # 298K = 104.9 ± 9.3 kJ mol −1 ) and 39.8 ± 7.9 kJ mol −1 (G # 298K = 106.1 ± 14.3 kJ mol −1 ) based on 1 H and 31 P NMR, respectively (G # = Gibbs energy of activation). Note that the E a for the depolymerization of polyolefins is much larger (200 to 300 kJ mol −1 ) (35). Under the irradiation with light of  = 365 nm or simply sunlight, quantitative conversion of P2 and P3 to M2 and M3 is achieved at room temperature within 10 min.…”

Ambient Temperature Carbene-Mediated Depolymerization: Stoichiometric and Catalytic Reactions of N-Heterocyclic- and Cyclic(Alkyl)Amino Carbenes with Poly(N-Methylaminoborane) [MeNH–BH2]n

“…In particular, it was unclear whether NHC initiates depolymerization at a site in the interior of the polymer chain, known as random degradation, or whether this can only occur at the chain ends in a process termed unzipping. 42 This work represents an in-depth study of the reaction of stable carbenes, NHCs, 43−46 and CAACs, 47,48 with poly(Nmethylaminoborane) [MeHN−BH 2 ] n . A range of isolable carbenes, IDipp, ItBu (ItBu = 1,3-di-tert-butylimidazol-2ylidene), and CAAC Me (CAAC Me = 1-(2,6-diisopropyl)phenyl-3,3,5,5-tetramethyl-2-pyrrolidinylidene) (Figure 1), with varying steric and electronic properties, were utilized to gain complementary mechanistic insights into the depolymerization process.…”

Enthalpy-Driven Polyisobutylene Depolymerization

“…While the chemistry involved in polymer formation is the most common focus of synthetic polymer chemistry, polymer depolymerization is also important . This is especially true for synthetic polymers and particularly true for polymers that are formed by reactions that generate carbon–carbon σ bonds from monomers containing reactive π bonds.…”

“…Polyolefin formation including formation of polyisobutylene from isobutylene monomers is thermodynamically favored. However, polymers, in general, including polyisobutylene that have reactive end groups can lose monomer units and undergo depolymerization above a so-called ceiling temperature ( T c ) . At this temperature, the depolymerization process becomes thermodynamically more favorable than polymerization.…”