Seiichi Kawahara

Initiation of rubber biosynthesis in Hevea brasiliensis: characterization of initiating species by structural analysis

The initiating molecular species for rubber formation in Hevea brasiliensis has been investigated by structural characterization of the terminal group in the rubber by means of 13C NMR and 1H NMR spectroscopy. The presence of trans-isoprene units in trans-trans linkage was confirmed by the characteristic C-1-methylene-carbon signal of the trans-isoprene unit. The number of trans-isoprene units was estimated to be about two from the relative intensity of this signal, and the degree of polymerization of various fractions from transesterified deproteinized natural rubber. Two methyl-proton signals in the trans-trans sequence were detected by 1H NMR spectroscopy. This spectral evidence shows that the trans-isoprene units are in the trans-trans-cis sequence at the initiating terminal. However, the expected methyl- and olefinic-carbon signals and methyl-proton signal of the dimethylallyl group were not detected in natural rubber from regularly tapped trees and from a Hevea seedling. Thus, the direct initiating species of rubber formation is either a C15 allylic diphosphate consisting of two trans-isoprene unites as in the case of farnesyl diphosphate (FDP), but which is modified at the dimethylallyl group, or FDP, the dimethylallyl group of which is modified after polymerization.

Structure and biosynthesis of trans-polyisoprene from Eucommia ulmoides

Abstract The structure of trans -polyisoprene from both bark and leaves of Eucommia ulmoides was analysed by 1 H NMR and 13 C NMR. Both spectra showed characteristic signals of the dimethylallyl-group, as well as terminal ester and diphosphate groups. The degree of polymerization estimated from the intensity ratio of signals from the internal trans -units and the dimethylallyl-group was in fair agreement with that determined by osmometry. The trans -polyisoprene from E. ulmoides is a high molecular-weight homologue of solanesol, consisting of the dimethylallyl-group, 60–3000 internal trans -units, and a terminal aliphatic fatty acid ester-group or a diphosphate group, aligned in that order.

Initiation of biosynthesis in cis polyisoprenes

Abstract The molecular species initiating rubber biosynthesis in leaves of Solidago altissima and Helianthus annuus and sporophores of Lactarius volemus have been analysed by structural characterization of the polyisoprenes by 13 C NMR spectroscopy. The alignment of trans and cis isoprene units in these cis polyisoprenes has been determined using polyprenol-16 [dimethylallyl-( trans ) 2 -( cis ) 13 -OH] and ficaprenol-11 [dimethylallyl-( trans ) 3 -( cis ) 7 -OH], respectively, as model compounds. The C-1 methylene carbon atoms of the trans isoprene units give rise to two and three signals at δ39.7–39.8 for polyprenol-16 and ficaprenol-11, respectively. These signals were assigned by comparison with the signal splitting pattern in solanesol-9 and spin-lattice relaxation times T 1 of the respective carbon atoms, also. Polyprenol-16 gives rise to a signal reflecting the presence of the trans unit in the trans-trans-trans sequence at about 5%. Similarly, ficaprenol-11 contains about 5% of the trans-trans sequence. Rubbers from S. altissima and H. annuus give rise to trans C-1 carbon signals, indicative of the presence of both two trans and three trans sequences in a ratio of 4:3 and 2:1, respectively. By contrast, only the dimethylallyl-( trans ) 2 -sequence was observed in the low M r cis polyisoprene from sporophores of L. volemus . These findings demonstrate that the initiating species of rubber formation in the leaves are both trans , trans -farnesyl diphosphate (FDP) and trans , trans , trans -geranylgeranyl diphosphate (GGDP). Taking into account the presence of about 5% of the unexpected isomeric terminal sequences in these polyprenols, it is concluded that the primer selectivity of rubber transferase in the leaves is not highly specific with respect to the chain length of the allylic diphosphate initiator.

MISCIBILITY AND PRESSURE-SENSITIVE ADHESIVE PROPERTIES OF POLY(VINYLETHYLENE-CO-1,4-BUTADIENE)/TERPENE RESIN BLENDS

Abstract The pressure-sensitive adhesive properties of miscible blends of poly(vinylethylene- co -1,4-butadiene) (V-BR) with terpene resins were investigated on varying both the random copolymer composition (vinyl content) and the blend composition. The V-BR with 47.4 wt% vinyl content was found to be a remarkable rubber for use as a base polymer for a blend adhesive. In V-BR(47.4)/terpene resin blends, excellent pressure-sensitive adhesive properties were revealed for 50 50 blends. The good results for the adhesive properties were interpreted in terms of the dynamic mechanical behaviour of the blends.

Molecular weight distribution of polyisoprene from Lactarius volemus

Abstract The L. volemus rubber showed a unimodal M r distribution (MWD), centered around a M r of 2.4 × 10 4 , with a shoulder in the high M r region and two small peaks in the low M r region. Each M r fraction, except for the highest one, contained a dimethylallyl- trans - trans terminal, and poly- cis isoprene units with a hydroxyl or fatty-acid ester terminal group. The lowest M r fraction showed a MWD corresponding to homologues of polyprenols with peaks from 17-mer to higher than 90-mer, having two centres around 21-mer and 32-mer by HPLC analysis. The distribution of chain-length between 35-mer and 90-mer in the next lowest M r fraction, showed a 5 or 6 periodical repeating isoprene unit. It is postulated that the period observed by HPLC arises from the mechanism controlling M r .

Upper critical solution temperature (UCST) phase behaviour and pressure-sensitive adhesive properties in blends of poly(vinyl ethylene-co-1,4-butadiene) with hydrogenated terpene resin

Abstract Pressure-sensitive adhesive ( PSA ) properties of blends of poly-vinyl ethylene -co-1,4- butdiene ), V-BR , with hydrogenated terpene resin were examined using blend films prepared at 70 and 140°C. Since the blend has an upper critical solution temperature of ∼133°C, significant differences between PSA properties of miscible and immiscible blends were indicated. These differences were explained in terms of the dynamic mechanical behaviour. Cohesive failure of the adhesive layer was also discussed with reference to the surface tensions of the V-BR and the hydrogenated terpene resin, these parameters being estimated according to the Flory equation of state theory.

Solution-grown crystal of cis-1,4 polyisoprene

Abstract Synthetic cis -1,4 polyisoprene prepared by a Ziegler catalyst and naturally occurring cis -1,4 polyisoprenes from Hevea brasiliensis and Lactarius volemus were crystallized at −80 to −45°C from dilute hexane solution. The melting temperature, T m , of these solution-grown crystals in hexane solution was determined by differential scanning calorimetry. The T m value of natural rubber from Hevea brasiliensis was higher than that of low molecular weight rubber from Lactarius volemus and synthetic cis -1,4 polyisoprene, and was not varied by removing proteins, mixed fatty acids and linked fatty acids. For fractionated samples, the T m value of rubber from Lactarius volemus decreased in proportion to the molecular weight, while that of natural rubber was independent of the molecular weight.

Interactions in blends of bisphenol-A polycarbonate and poly(styrene-co-methacrylic acid)

Abstract Interactions in bisphenol-A polycarbonate/poly(styrene- co -methacrylic acid) (PC/P(S-MAA)) blends, which show UCST phase transition and Miscibility Valley phenomena in temperature-copolymer composition plane, were investigated by Fourier transform infrared (FT-IR) spectroscopy. It was found that methacrylic acid (MAA) units in poly(styrene- co -methacrylic acid) (P(S-MAA)) formed associated dimers at low temperature and the dimer dissociated with elevating temperature. Since the temperature dissociating associated dimer of MAA units was corresponding to phase transition temperature in PC/P(S-MAA) blends, the UCST phase behavior would be caused by association–dissociation in MAA units.

Structure of solution-grown trans-1,4-polyisoprene crystals : 4. Effect of concentration on crystal form and melting temperature

Abstract The crystallization of synthetic trans -1,4-polyisoprene (TPI) was carried out in 0.05 to 20.0% (wt/vol) hexane, octane and amyl acetate solutions and the melting temperature, T m , of the resulting crystals was measured by differential scanning calorimetry (d.s.c.). The crystal form and T m of the crystals were independent of the concentration of the solutions. On crystallization at low temperatures, TPI crystals appeared before the TPI solutions reached the desired crystallization temperature, T c , and the T m was independent of the T c . This phenomenon was quantitatively analysed with respect to the conversion temperature and the crystallization conditions. In contrast, at high temperatures, TPI crystals were observed after the TPI solutions reached a given T c , and the T m was dependent on the T c .

Estimation of surface tension of poly(vinylidene fluoride-co-hexafluoro acetone) by corresponding states theory

Abstract The theoretical surface tensions γ T S of poly(vinylidene fluoride- co -hexafluoro acetone) (hexafluoro acetone content: 6.5, 8.3, 10.4 mol%) were calculated according to Prigogines corresponding states theory, as has already been extended to surfaces by Patterson and co-workers. The resulting γ T S was nearly consistent with the experimental surface tension γ C S evaluated by a log(1 + cos ϑ ) versus log( γ L ) plot based on the contact angle method.