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Isoprene Units (isoprene + unit)
Selected AbstractsMolecular cloning, expression and characterization of cDNA encoding cis -prenyltransferases from Hevea brasiliensisFEBS JOURNAL, Issue 23 2003A key factor participating in natural rubber biosynthesis Natural rubber from Hevea brasiliensis is a high molecular mass polymer of isoprene units with cis -configuration. The enzyme responsible for the cis -1,4-polymerization of isoprene units has been idengified as a particle-bound rubber transferase, but no gene encoding this enzyme has been cloned from rubber-producing plants. By using sequence information from the conserved regions of cis -prenyl chain elongating enzymes that were cloned recently, we have isolated and characterized cDNAs from H. brasiliensis for a functional factor participating in natural rubber biosynthesis. Sequence analysis revealed that all of the five highly conserved regions among cis -prenyl chain elongating enzymes were found in the protein sequences of the Hevea cis -prenyltransferase. Northern blot analysis indicated that the transcript(s) of the Hevea cis -prenyltransferase were expressed predominantly in the latex as compared with other Hevea tissues examined. In vitro rubber transferase assays using the recombinant gene product overexpressed in Escherichia coli revealed that the enzyme catalyzed the formation of long chain polyprenyl products with approximate sizes of 2 × 103,1 × 104 Da. Moreover, in the presence of washed bottom fraction particles from latex, the rubber transferase activity producing rubber product of high molecular size was increased. These results suggest that the Hevea cis -prenyltransferase might require certain activation factors in the washed bottom fraction particles for the production of high molecular mass rubber. [source] Investigation of thiol-ene addition reaction on poly(isoprene) under UV irradiation: Synthesis of graft copolymers with "V"-shaped side chainsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2010Guowei Wang Abstract Poly(isoprene) (PI) with pendant functional groups was successfully synthesized by thiol-ene addition reaction under 365 nm UV irradiation, and the functionalized PI was further modified and used to prepare graft copolymers with "V"-shaped side chains. First, the pendant SCH2CH(OH)CH2OH groups were introduced to PI by thiol-ene addition reaction between 1-thioglycerol and double bonds, and the results showed that the addition reaction carried out only on double bonds of 1,2-addition isoprene units. After the esterification of hydroxyl groups by 2-bromoisobutyryl bromide, the forming macroinitiator was used to initiate the atom transfer radical polymerization (ATRP) of styrene (St) and tert -butyl acrylate (tBA), and the graft copolymers PI- g -PS2 and PI- g -PtBA2 or PI- g -PAA2 (by hydrolysis of PI- g -PtBA2) were obtained, respectively. It was confirmed that the graft density of side chains on PI main chains could be easily controlled by variation of the contents of modified 1,2-addition isoprene units on PI. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3797,3806, 2010 [source] Butadiene,isoprene copolymerization with V(acac)3 -MAO.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 20074 copolymers, Crystalline, amorphous trans - Abstract Butadiene-isoprene copolymerization with the system V(acac)3 -MAO was examined. Crystalline or amorphous copolymers were obtained depending on isoprene content. Both butadiene and isoprene units exhibit a trans -1,4 structure and are statistically distributed along the polymer chain. Polymer microstructure, comonomer composition, and distribution along the polymer chain were determined by 13C and 1H NMR analysis. The thermal and X-ray behaviors of the copolymers were also investigated and compared with results from solid-state 13C NMR experiments. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4635,4646, 2007 [source] Synthesis and Fourier transform Raman spectroscopic study of diene-terminated polystyrene oligomersJOURNAL OF RAMAN SPECTROSCOPY, Issue 3 2005N. J. Ward Abstract Polystyrene oligomers capped with a known number of butadiene or isoprene units were synthesized by ,living' anionic polymerization in cyclohexane. The FT-Raman spectra of these compounds show small but significant differences in ,(CC) wavenumber position depending on whether just a single unit or several units of the diene are present at the chain end. However, if the butadiene experiments are repeated under polar-modified conditions, so that 1,2- rather than 1,4-addition takes place, the ,(CC) Raman band position is found to be independent of the number of ,out-of-chain' vinyl double bonds which are present. This conclusion is explained in terms of the mass change on diene addition to the polymer chains. Application of the method for the quantitation of polymer chain-end diene termination is proposed. Copyright © 2004 John Wiley & Sons, Ltd. [source] Influence of the Composition on Crystal Phase and Thermal Behavior of trans -1,4-Butadiene/Isoprene CopolymersMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 23 2007Fabio Bertini Abstract Butadiene/isoprene copolymers were prepared using the catalyst system V(acac)3 -MAO. The structure of the comonomers is trans -1,4 and the butadiene and isoprene units are statistically distributed along the polymer chain. The attitude of the butadiene sequences to crystallize in the monoclinic form and to evolve in the hexagonal form is preserved in the copolymer for a certain range of composition. The temperature interval between the two endothermic events is progressively reduced by increasing the isoprene content. The monoclinic/hexagonal transition produces a considerable increase in the lamellar thickness of the polymers. Thermal degradation of the copolymers is influenced by the composition and takes place in two different stages: a series of cyclization and cross-linking reactions occur before the decomposition step. [source] | |||||||||||||