Inspired by the unique and efficient wound healing processes in biological systems, several approaches to develop synthetic polymers that can repair themselves with complete, or nearly complete, autonomy have recently been developed. This review aims to survey the rapidly expanding field of self-healing polymers by reviewing the major successful autonomic repairing mechanisms developed over the last decade. Additionally, we discuss several issues related to transferring these self-healing technologies from the laboratory to real applications, such as virgin polymer property changes as a result of the added healing functionality, healing in thin films v. bulk polymers, and healing in the presence of structural reinforcements.

While original epoxy resin-based self-healing systems used the commercially available endo-isomer of dicyclopentadiene (DCPD), the exo-stereoisomer is known to have much faster olefin metathesis reaction rates with first-generation Grubbs' catalyst. Here, we measure the energy to failure of healed specimens as a function of healing time and compare the kinetics of damage repair for endo- and exo-DCPD, and mixtures of the two isomers. Using catalyst loading levels previously reported to be effective for endo-DCPD, exo-DCPD was found to heal approximately 20 times faster than the endo-isomer, but with a lower healing efficiency. The fracture toughness of the repaired specimens decreased when the exo content of the blends was greater than 40% and, for the pure exo-DCPD, when the catalyst loadings were below 1%. Possible causes of the reduced healing efficiencies of the exo-DCPD healing agent are discussed.

A new isosorbide-based polyphosphate was synthesized and applied as a flame-retardant for polylactic acid (PLA). The storage modulus and glass transition temperature of PLA/polyphosphonate blends was unaffected by the inclusion of polyphosphonate, but moderate depressions of PLA's tensile strength (16%, 28%, and 45% reduction from PLA at a polyphosphonate mass percentage of 5%, 10%, and 15%, respectively) and strain-at-break (0%, 17%, and 30% reduction from PLA at a polyphosphonate mass percentage of 5%, 10%, and 15%, respectively) were observed. Modified UL-94 flammability testing indicated that isosorbide-based polyphosphonates are effective flame retardants for PLA and are able to self-extinguish flames in less than 2 s to achieve V2 and V0 ratings at polyphosphonate mass percentage of 5% and 15%, respectively. Fire test data indicates a gas phase mechanism that can quench the flame when no external radiant heat flux is present (e.g., in modified UL-94 testing) but does not affect the material's heat release rate in forced combustion (e.g., in cone calorimetry). Use of the biobased flame retardants described herein yields flame retardant PLA containing up to 97% by mass of bio-derived content.

A method to recover fracture toughness after failure and increase thermal properties of polylactic acid (PLA) for use within durable goods applications is presented. Microcapsules were incorporated into PLA to form a composite material in which the microcapsules served the dual purpose of (1) releasing self-healing additives to fracture regions and (2) serving as nucleating agents to improve the PLA composite's thermal tolerance. Self-healing was achieved though embedment of dicyclopentadiene-filled microcapsules and Grubbs' first generation ruthenium metathesis catalyst, the former being autonomically released into damage volumes and undergoing polymerization in the presence of the catalyst. This approach led to up to 84% recovery of the polymer composite's initial fracture toughness. Additionally, PLA's degree of crystallinity and heat deflection temperature were improved by ∼ 11% and ∼ 21 °C, respectively, relative to nonfilled virgin PLA, owing to microcapsule-induced nucleation. The self-healing system developed here overcomes many property limitations of PLA that can potentially lead to its incorporation into various durable goods.

A commercial norbornyl-functionalized linseed oil, blended with a bicyclic norbornene-based crosslinking agent (at loadings ranging from 0 to 50 wt %) undergoes ring-opening metathesis polymerization with the 1st generation Grubbs' catalyst to form a biorenewable polymer network. Comonomers are characterized, the thermal and mechanical properties of the cured systems are investigated by dynamic mechanical analysis, and thermal decomposition is evaluated by thermogravimetric analysis. The resin is shown to consist of a modified linseed oil and small oligomers of cyclopentadiene. Broad tan d peaks suggest inhomogeneous phase morphologies, which result in complex crosslinking behaviors. The thermal stability of the polymers increases with increasing crosslinker content. V V C 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6851-6860, 2008