Generation of One-Dimensional Fibrous Polyethylene Nanocrystals in Epoxy Thermosets

Abstract

The one-dimensional (1D) polyethylene (PE) nanocrystals were generated in epoxy thermosets via crystallization-driven self-assembly. Toward this end, an ABA triblock copolymer composed of PE midblock and poly(ε-caprolactone) (PCL) endblocks was synthesized via the ring opening metathesis polymerization followed by hydrogenation approach. The nanostructured thermosets were obtained via a two-step curing approach, i.e., the samples were cured first at 80 °C and then at 150 °C. Under this condition, the one-dimensional (1D) fibrous PE microdomains with the lengths up to a couple of micrometers were created in epoxy thermosets. In contrast, only the spherical PE microdomains were generated while the thermosets were cured via a one-step curing at 150 °C. By the use of the triblock copolymer, the generation of 1D fibrous PE nanocrystals is attributable to crystallization-driven self-assembly mechanism whereas that of the spherical PE microdomains follows traditional self-assembly mechanism. Compared to the thermosets containing the spherical PE microdomains, the thermosets containing the 1D fibrous PE nanocrystals displayed quite different thermal and mechanical properties. More importantly, the nanostructured thermosets containing the 1D fibrous PE nanocrystals displayed the fracture toughness much higher than those only containing the spherical PE nanocrystals; the KIC value was even three times as that of control epoxy.

Controlling block copolymer one-dimensional self-assembly in polymeric matrices

“…Analogously, polystyrene- b -polycaprolactone (PS- b -PCL) with 2 : 1 ratio between blocks (1.8 : 1 strictly) forms crystalline PCL nanoribbons in a polystyrene matrix. 3 In this case, a miscible block with almost twice the volume of the immiscible block managed to stabilize the developed crystalline micelles. There are more examples in the literature showing different stability ratios according to the employed formulation.…”

“…1 Particularly, 1D nanostructures formed by a semicrystalline polymeric phase are a promising choice, as they possess a range of remarkable properties related to their crystalline nature and high aspect ratio. 2,3 In this context, it was already demonstrated that it is possible to access to 1D semicrystalline nanostructures in a polymer matrix through the self-assembly of an amphiphilic block copolymer (BCP) in the reaction precursors [3][4][5][6] or by its reaction-induced microphase separation (RIMPS). 7,8 In the latter approach, both blocks of the BCP are initially soluble in the reactive solvent, but one of them becomes insoluble during matrix polymerization generating self-assembled nanophases (micelles).…”