Crosslink Density Changes during the Hydrolysis of Tridimensional Polyesters

Abstract

is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. The hydrolysis of almost ideal networks based on macrodiols (poly(adipate of ethylene glycol)) of average molar mass about 2 kg/mol, with L=18 ester groups per chain has been studied. Tensile testing was used to evaluate the crosslink density through the statistical theory of rubber elasticity at two temperatures and three values of relative humidity. A kinetic model for ester consumption including an autocatalysis term was proposed and combined with two original approaches for modeling the crosslink density changes. This allowed kinetic parameters of hydrolysis to be determined, and very good predictions were obtained for the variations of crosslink density (or elastic modulus) in the three aging conditions considered.The initial curvature of elastic modulus vs. time was predicted positive for weak autocatalysis and negative for strong autocatalysis. The obtained conversion ratio at degelation was found to decrease sharply with the number of esters per elastically active chain.

Improving the water resistance of epoxy-anhydride matrices by the incorporation of bentonite

“…In epoxy–anhydride systems, water can also induce hydrolytic degradation. Each hydrolysis event implies a chain scission and, as consequence, polymer cross‐linked density decrease as well . As the Tg increases as a function of the cross‐linking density, the decrease on this temperature could be related with either plasticization and/or water degradation by hydrolysis.…”

A statistical theory of polymer network degradation

“…The theory proposed below improves and extends a model published recently [17], which combined chemical kinetics and a statistical approach of network degradation that is valid only at low conversions, much before degelation. Conversion ratios up to degelation are covered here, the number of scission sites per chain may be large, and a dispersion of this number is allowed.…”

Plasticizer effect on network structure and hydrolytic degradation

“…Triacetin hydrolysis would generate acetic acid, which is a powerful catalyst of network hydrolysis [16] and would complexify the mathematical treatment of our results [9]. In order to analyze the hydrolytic stability of triacetin within the timescale investigated, it was exposed directly to 75% RH at 60°C.…”

“…-Modeling of elastically active chains consumption exploring for example the influence of the average number of cleavable bonds hold by elastically active chains on the degelation process [9].…”