Thermoreversible covalent crosslinking of maleated ethylene/propylene copolymers with diols

Abstract

The objective of this study is the thermoreversible crosslinking of maleated ethylene/propylene copolymer (MAn‐g‐EPM) using the equilibrium reaction with diols. Covalent hemi‐ester crosslinks are formed via the reaction of anhydrides with alcohols, while an equilibrium shift at elevated temperatures may result in their removal. High conversions to hemi‐ester are obtained at low temperatures in the presence of p‐toluenesulfonic acid, whereas conversions are low at high temperatures. The presence of microphase‐separated aggregates acting as physical crosslinks was demonstrated for MAn‐g‐EPM and all crosslinked materials. The covalent crosslinks were only formed within the aggregates, resulting in stronger aggregates that persisted to higher temperatures. The tensile strength and elasticity were significantly improved upon increasing level of crosslinking, whereas the type of diol has less influence. The covalently crosslinked MAn‐g‐EPM was reprocessable via compression molding at temperatures above 175 °C. Irreversible diester formation occurred for the longer diols, but did not prevent reprocessing, while short diols evaporated. Both effects lowered the level of crosslinking, resulting in significantly changed mechanical properties. The reprocessability does not originate from an equilibrium shift, but from a dynamic exchange between crosslinked and non‐crosslinked functional groups, which allows crosslinks to disconnect and the corresponding chain segments to diffuse between aggregates. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1810–1825, 2008

Thermoreversible cross-linking of maleated ethylene/propylene copolymers with diamines and amino-alcohols

“…No significant differences were observed in the FTIR spectra of (many) different samples taken from the reaction product, which suggests that the gelation does not result in non-homogeneous materials. The reaction of the cyclic anhydride groups with the alcohol functionalities does not occur in solution even in the presence of a catalyst [24], so no gelation occurs in solution for the 1 eOH, 2 eOH, OHeOH and 3 eOH crosslinkers. Cross-linking only occurs after solvent evaporation and is catalyzed by a suitable catalyst ( p-toluenesulfonic acid) for the diol (OHeOH cross-linker) [24] or by the amine groups [19] for the reactions with the 1 eOH, 2 eOH and 3…”

“…MAn-g-EPM was partially (around 50%) or fully hydrolyzed via exposure to water from air for prolonged time at room temperature prior to the modification reactions with cross-linkers containing one or two 3 amine groups, respectively. For the modification with the OHeOH cross-linker, 5 mol% of p-toluenesulfonic acid, based on the molar amount of anhydride groups, was added to the solution as a catalyst [24]. Next, 0.5 mol of (di-functional) cross-linker per mol of grafted anhydride, was added to the solution, which was stirred for at least 30 min.…”

“…This paper discusses our continuing work on the thermoreversible cross-linking of the same MAn-g-EPM, now using diamines and amino-alcohols, with the main aim to improve the thermoreversibility compared to cross-linking with diols [24]. As discussed above, the reaction of the anhydride groups of MAn-g-EPM with amines is also thermoreversible.…”

“…During previous work in our group, the thermoreversible covalent cross-linking of maleated ethylene/propylene copolymer (MAn-g-EPM) with diols [24] was studied, while ionic interactions with metal cations [25] and hydrogen bonds combined with ionic interactions [26] were explored as well. MAn-g-EPM cross-linked with diols (Scheme 1A) was repeatedly processable via compression molding, indicating that the cross-links are indeed thermoreversible.…”

Development of materials and technologies for control of polymer recycling

“…More than 99% of azomethine bonds were hydrated in o10 min at ambient temperature. Mee et al 76 reported thermoreversible covalent crosslinking of maleated ethylene/propylene copolymers with diols (Scheme 21). Covalent hemi-ester crosslinks were formed via the reaction of anhydride side chains and diol linkers.…”