Dynamic heterogeneity and nanophase separation in rubber-toughened amine-cured highly cross-linked polymer networks. (August 2022)

• Record Type: Journal Article
• Authors: Alam, Todd M.; Ahn, Juhong; Lee, Sangwoo; Leguizamon, Samuel C.; Jones, Brad H.
• Is Part Of: Polymer testing. Volume 112(2022)
• Publication Date: 2022-08
• Subjects: Polymerization-induced phase separation -- Glass transition -- Microstructure -- Dynamic heterogeneity -- Spin diffusion; Polymers -- Testing -- Periodicals; Polymères -- Tests -- Périodiques; 620.1920287
• DOI: 10.1016/j.polymertesting.2022.107616
• Languages: English
• ISSNs: 0142-9418

Abstract

Abstract: Solid state nuclear magnetic resonance (NMR) spectroscopy and small-to wide-angle X-ray scattering (SWAXS) methods were used to characterize the heterogeneous dynamics and polymer domain structure in rubber modified thermoset materials containing the diglycidyl ether of bisphenol A (DGEBA) epoxy resin and a mixture of Jeffamine reactive rubber and 4, 4-diaminodicyclohexylmethane (PACM) amine curing agent. The polymer chain dynamics and morphologies as a function of the PACM/Jeffamine ratio were determined. Using dipolar-filtered NMR experiments, the resulting networks are shown to be composed of mobile and rigid regions that are separated on nanometer length scales, along with a dynamically immobilized interface region. Proton NMR spin diffusion experiments measured the dimensions of the mobile phase to range between 9 and 66 nm and varied with the relative PACM concentration. Solid state 13 C magic angle spinning NMR experiments show that the highly mobile phase is composed entirely of the dynamically flexible polyether chains of the Jeffamine rubber, the immobilized interface region is a mixture of DGEBA, PACM, and the Jeffamine rubber, with the PACM cross-linked to DGEBA predominantly residing in the rigid phase. The SWAXS results showed compositional nanophase separation spanning the 11–77 nm range. These measurements of the nanoscale compositional and dynamic heterogeneity provide molecular level insight into the very broad and controllable glass transition temperature distributions observed for these highly cross-linked polymer networks. Highlights: Phase-separated, rubber-toughened epoxy networks were investigated. Solid state NMR and X-ray scattering characterization indicate nanodomains. Magic angle spinning experiments used to identify domain composition. Spin diffusion experiments used to estimate domain size. Broad glass transitions are associated with large distributions in domain size.