Detection of Nanometer-Scale Mixing In Phosphate-Glass/Polyamide-6 Hybrids by H-1-P-31 NMR

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Polymers and High Performance Materials


The size of phosphate-glass (Pglass) particles dispersed in a polyamide-6 (PA6) matrix by melt blending has been characterized by H-1-P-31 solid-state nuclear magnetic resonance (NMR). H-1 spin diffusion from similar to 75% of the H-1 in the glass to the polyamide is observed within 50 ms, indicating proximity on a 30 nm scale. Fast dephasing of a quarter of the P-31 magnetization by dipolar couplings to polyamide protons in P-31{H-1} heteronuclear recoupling with dephasing by strong homonuclear interactions of protons (HARDSHIP) NMR shows that similar to 25% of the Pglass is within 0.5 nm from the polyamide. This is confirmed by H-1-P-31 heteronuclear correlation NMR spectra with inverse T-2,T-H filtering, which document relatively fast (1 ms) cross polarization from PA6 protons, identified by their upfield chemical shift and short transverse relaxation time T-2,T-H, to a significant fraction of P-31 in the glass. The P-31 spectrum associated with the polyamide H-1 reveals that the phosphate sites near the polyamide matrix are chemically altered but differently than previously observed in Pglass-polyethylene hybrids, where no such contact was proven. As expected, the P-31 sites that cross-polarize from the polyamide protons also exhibit pronounced dephasing in P-31{H-1} HARDSHIP experiments. HARDSHIP experiments after cross polarization and P-31 spin diffusion experiments indicate that the similar to 25% of phosphate that is within 0.5 nm from the polyamide is not dispersed in the polymer but on the surface of similar to 10 nm diameter Pglass particles. This study represents the first conclusive evidence of intimate mixing of the hybrid components. Further, it suggests that this is an excellent model system for exploring new routes for driving organic polymers and inorganic glass to self-assemble into useful organic/inorganic hybrid materials.

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Chemistry of Materials





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