High-resolution latex-state C-13-NMR spectroscopy for natural rubber vulcanizates

摘要

Crosslinking junctions of natural rubber vulcanizates were characterized by high-resolution latex-state C-13-NMR spectroscopy. Vulcanized natural rubber latex was prepared by two methods: i.e., vulcanization of the rubber latex and cryogenic crushing of a rubber sheet vulcanized on a hot press. High-resolution latex-state C-13-NMR spectroscopy was attained even after vulcanization of the rubber latex, as is evident from no background in spectrum and narrow half width of signals independent of vulcanization time. Small signals at 44 ppm and 57 ppm in the aliphatic carbon region were assigned by measurements of both Distortionless Enhancement by Polarization Transfer (DEPT) and Attached Proton Test (APT) to secondary and tertiary carbons of crosslinking points. The assignment was proved by high-resolution solution-state NMR spectroscopy of vulcanized liquid cis-1,4-polyisoprene as a model, in which DEPT, APT, 2-dimensional H-1-H-1 correlation (H-H COSY), 2-dimensional H-1-C-13 correlation (H-C COSY) and 2-dimensional heteronuclear multiple bond correlation (HMBC) measurements were applied.