Quantitative Polymer Characterizations with NMR Cryoprobes through Spin Echo NMR Pulse Sequences

MQ silicone copolymers (MQ resins) and polyethylenes are very important polymers that are used in our daily lives. The microstructures of these polymers dictate some of their important physical properties and applications. However, it remains a challenge to accurately and quantitatively measure microstructural information by NMR due to an acoustic ringing baseline curvature observed with state-of-the-art high-sensitivity helium-cooled NMR cryoprobes. In this work, we report spin echo 90_180 NMR pulse sequences, with adiabatic and hard 180° pulse versions and different delays before and after the 180° pulse, that attenuate acoustic ringing artefacts and the ²⁹Si strong background signal from cryoprobe construction materials. An appropriate methodology to quantitatively measure M (Me₃SiO_1/2), T(OZ) [Si(OZ)O_3/2], and Q (SiO_4/2) structural information of MQ resins (where Z may be H, Na, or iPr), and quantitatively measure the comonomer content information in polyethylene and polyethylene blends, is presented.