End-Groups of Poly(p-phenylene sulfide) Characterized by DNP NMR Spectroscopy

Abstract

Characterization of the local chemical structure of high-performance engineering plastics is essential for rational polymer blending to achieve outstanding physical properties. The inherent high chemical stability, however, has hampered their detailed characterization using conventional analytical methods. Herein, we demonstrate that dynamic nuclear polarization enhanced solid-state NMR combined with a thermal treatment approach for sample preparation enables characterization of end-groups of poly(p-phenylene sulfide) (PPS). Mildly heating PPS mixed with TEKPol/1,1,2,2tetrachloroethane (TCE) solution resulted in a high sensitivity enhancement from 13 C CPMAS signals of PPS, and further optimization of the conditions using 1-chloronaphthalene (1-CN) as a solvent led to an enhancement factor (ε) as high as ∼43, while a conventional incipient wetness impregnation method with TEKPol/TCE afforded an enhancement factor of only ∼4. Mechanistic studies with electron paramagnetic resonance and scanning electron microscopy analysis demonstrated that thermal treatment at 60 °C promoted the distribution of the PA solution into a surface layer of PPS while suppressing the decomposition of TEKPol. The developed sample preparation approach enabled us to observe 13 C and even 15 N signals assignable to end-groups of PPS in a reasonable measurement time by using a natural abundance sample. According to the observed signals, which were identified by comparing with signals from low-molecular-weight model compounds, sodium carboxylate is present at the chain-end position, suggesting that the termination step of PPS production involves an S N Ar reaction of p-chlorophenyl intermediate with the secondary amine of the ring-opened N-methylpyrrolidone used as a solvent for PPS production.

Supercritical CO2 impregnation process applied to polymer samples preparation for dynamic nuclear polarization solid‐state NMR

“…In other words, investigators should try and adapt the various available protocols to their specific case, and this may prove daunting. This is especially true for polymer materials where careful optimization of sample preparation conditions is typically required to achieve meaningful results, [ 29–36 ] with no guarantee of success in the end. In parallel, supercritical CO 2 (scCO 2 ) impregnation has been used for a long time in the field of polymer materials to impregnate specific components (e.g., additives, active pharmaceutical ingredients, dyes, and organic metallic complexes) in a polymer matrix.…”

Elucidations of Structure and Molecular Dynamics of Complex Polymers by State-of-the-Art Solid-State NMR Spectroscopy

“…Even confronted with those substantial challenges, DNP has well demonstrated its great potentials in addressing challenging problems in polymers. For example, Sato et al proposed a thermal treatment approach for DNP sample preparation, enabling to identify the end-groups of high-performance engineering plastics, poly­( p -phenylene sulfide), whose detailed chemical structures are hard to be analyzed using conventional analytical methods like gel permeation chromatography (GPC) or solution NMR due to its inherent high chemical stability . Besides, DNP can be used for structural elucidation of cross-linked polymers, especially characterizing the small proportion of chemical bonding sites and functionalities. , Moreover, by using DNP, Mollica et al found that 13 C-labeled glycerol forms transient forms prior to crystallization in a frozen dilute solution .…”