Toughening Epoxy Thermosets with Block Ionomer Complexes: A Nanostructure–Mechanical Property Correlation

Abstract

Block ionomer complexes based on sulfonated polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SSEBS) and a tertiary amine-terminated poly(ε-caprolactone), denoted as SSEBS-c-PCL, were used to toughen epoxy resin. Well-dispersed spherical microdomains, consisting of a poly(ethylene-ran-butylene) core surrounded by a sulfonated polystyrene shell, were revealed by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) in the cured epoxy blends with 10 wt % SSEBS-c-PCL of various compositions. Structural parameters, core radius (R c), effective hard-sphere radius (R hs), and shell thickness (T s) were obtained by fitting the SAXS data with a core–shell model and, for the first time, correlated with the fracture toughness (critical stress intensity factor K IC and strain energy release rate G IC) of the epoxy blends. K IC and G IC were found to increase with increasing R c and R hs but decrease with T s. The blend containing SSEBS-c-PCL with least PCL, i.e., 2.4 wt %, shows nanostructure of the largest R c and R hs, and smallest T s, displaying highest K IC and G IC. Examination of the fracture surfaces indicates that the increased toughness arises from interfacial debonding of spherical microdomains and plastic expansion of resultant nanovoids, followed by small-scale matrix shear deformation. The correlations between nanostructure parameters and fracture toughness have provided a fundamental understanding of nanostructure toughening of thermosets via an innovative strategy based on block ionomer complexes.

Nanostructured epoxy thermoset templated by an amphiphilic PCL-b -PES-b -PCL triblock copolymer

“…The slight shifts of the scattering maxima could be associated with local rearrangement leading to an enhancement of the long‐range order . These results indeed indicate the formation of nanostructures in the epoxy thermosets containing PCL‐ b ‐PES‐ b ‐PCL triblock copolymer when DDS was used as the curing agents …”

Nanostructured thermosets containing π-conjugated polymer nanophases: Morphology, dielectric and thermal conductive properties

“…The nanophases are not formed until the curing reaction occurs with the sufficiently high conversion of the precursors. In the past decade, there have been a great number of reports on the preparation of the nanostructured thermosets by using a variety of block copolymers via self-assembly or RIMPS approach [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. It is realized that thermosets can be significantly toughened via the formation of the nanostructures; the mechanisms of toughness improvement are attributable to the debonding of micelles (or vesicles) from thermosetting matrix, crack deflection or frictional interlocking in the thermosets displaying the terraced morphology [22].…”

“…The PCL-b-P3HT-b-PCL triblock copolymer was incorporated into epoxy to M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 15 prepare the nanostructured thermosets. The triblock copolymer was easily dispersed into the precursors of epoxy; all the mixtures composed of DGEBA, MOCA and the triblock copolymer were homogeneous and transparent at room and elevated temperature.…”

Flexible Epoxy Resin Formed Upon Blending with a Triblock Copolymer through Reaction-Induced Microphase Separation

“…These amphiphilic block copolymers often contained block segments that are miscible and immiscible with epoxy resin; for example, the poly(ethylene oxide) (PEO) block segment is a miscible block segment that has been used most widely to obtain self-assembled nanostructures within epoxy resins [18]. Intermolecular hydrogen bonding interactions with the epoxy resin are often exploited to improve the miscibility.…”