COMPARATIVE MACROSTRUCTURAL CHARACTERIZATION OF NATURAL RUBBERS FROM TRANSGENIC GUAYULE BY HIGH-RESOLUTION SIZE EXCLUSION CHROMATOGRAPHY

ABSTRACT This paper presents macrostructural analysis of NR from transgenic Parthenium argentatum (guayule) in comparison with commercial Hevea brasiliensis (Hevea) and wild-type guayule by using high-resolution size exclusion chromatography (HR-SEC). Analysis of the soluble fraction of commercial Hevea demonstrated a bimodal distribution in the high molecular weight range, with a compact branched structure, and some oligomer content. By contrast, earlier HR-SEC analysis of samples isolated from enzymatically active washed rubber particles of Hevea that are closest to the in vivo state showed linear conformation in the high molecular weight range, with substantial oligomer content. Thus, branching in Hevea is likely due to processing conditions. Simple drying (evaporation of water) of wild-type guayule latex and coagulation and drying of transgenic guayule lattices did not result in branching in the soluble fraction. Our HR-SEC analysis demonstrated for the first time that transgenic modification of the guayule plants can produce NR with lower weight average molecular weight, eliminating the need to “masticate” NR to reduce the viscosity for compounding before using it for tire building and the production of rubber goods. We also propose a new model of in vivo rubber particles where the interior contains high molecular weight rubber swollen in oligomers.