A comparative study on the properties of Eucommia ulmoides gum and synthetic trans-1,4-polyisoprene

C-13 NMR spectra show that Eucommia ulmoides(EU) gum is all-trans-1,4-polyisoprene molecular structure, while synthetic trans-1,4-polyisoprene (STPI) contains 0.52% cis-1,4units and 0.34% 3,4-units which distribute randomly as monomer, dyad, or triad sequences along its macromolecular chain. This will destroy the regularity of macromolecular chain of STPI which will in turn lower its degree of crystallinity, slow its rate of crystallization and reduce its crystal dimensions. When crystallizing from the molten state at room temperature, EU gum can grow more beta-form than alpha-form crystals, while STPI tends to grow more alpha-form than beta-form crystals, which can be proved by WAXD and DSC. As a result, the stress-strain curve of STPI greatly differs from that of EU gum. (C) 2011 Elsevier Ltd. All rights reserved.