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In this paper, a series of novel trans‐1, 4‐polyisoprene/isotactic polybutene (TPI/iPB) in‐reactor blends were synthesized by isoprene and butene sequential two‐stage polymerization technology with spherical TiCl4/MgCl2 type Ziegler‐Natta catalyst. The components, structures, and properties of the as‐obtained TPI/iPB reactor blends were characterized by gel permeation chromatography, Fourier transform Infrared spectroscopy, and differential scanning calorimetry. The active trans‐1, 4‐polyisoprene (TPI) particles obtained in the initial isoprene polymerization by the Z‐N catalyst can be acted as microreactors to initiate butene polymerization subsequently. The TPI/iPB reactor blends with varied components were in situ synthesized within the reactor. The preparative‐temperature rising elution fractionation (p‐TREF) technique was used to fractionate the TPI/iPB reactor blends based on the elution temperature ranged from −40°C to 90°C. The weight distribution and microstructure of each fraction were investigated. The reactor blends are composed of crystallizable high trans‐1, 4‐uint polyisoprene obtained from the first‐stage isoprene polymerization, high isotactic polybutene obtained from the second‐stage butene polymerization and TPI‐b‐iPB block copolymer with different sequence structure obtained from the initial time of the second stage. This work is expected to propose the possible polymerizations of a‐olefins and conjugated dienes by using heterogeneous Ziegler‐Natta catalyst and provide a kind of novel rubber/plastic reactor blend materials. Highlights: The first synthesis of the trans‐1, 4‐polyisoprene/isotactic polybutene reactor blends.p‐TREF technique was used to analyze the composition of TPI/iPB reactor blends.Detailed structure characterization of the fractions including GPC and NMRTPI‐b‐iPB block copolymer can be obtained through the sequential polymerization.Rubber/plastic reactor blend materials were fabricated by the Z‐N catalyst. [ABSTRACT FROM AUTHOR]

Natural rubber （NR）/trans-1,4-polyisoprene （TPI） composites with shape memory effect were prepared, and the effect of carbon nanotubes （CNTs） amount on the properties of the composites was studied. The results showed that with the increase of CNTS, the scorch time and curing time of the composites were shortened, and the curing rate and crosslinking density were slightly increased, and the tensile strength, modulus and hardness all showed an obvious upward trend, while the elongation at break did not change significantly, indicating that CNTs played a reinforcing role. However, the shape fixation rate decreased from 91.83% to 86.64%, and the shape recovery rate dropped from 95.43% to 90.76% in the shape memory properties. When the amount of CNTs was 6 phr（mass） and the DC voltage was above 80 V, the composites exhibited good electrical stimulation shape memory behavior.

A series of well-defined iminopyridine-titanium complexes were prepared and characterized by nuclear magnetic resonance spectroscopy, X-ray diffraction analysis and elemental analysis. Isoprene polymerization was carried out by using those complexes as main catalyst and dried methylaluminoxane as cocatalyst.The results showed that the iminopyridine-titanium complexes with strong electron-donating group possessed high activity （up to 6.3×104 g/（mol·h））, high cis-1,4 -unit selectivity (up to 74%) and excellent thermo-stability（up to 90 ℃）. The increased steric hindrance of substituent groups would significantly reduce the catalytic acti-vity, molecular weight and cis-1,4-unit selectivity. These results indicated that the ligand structure had more effects on activity than stereo-selectivity.

Background: Natural rubber is an economically important material. Currently the Pará rubber tree, Hevea brasiliensis is the main commercial source. Little is known about rubber biosynthesis at the molecular level. Next-generation sequencing (NGS) technologies brought draft genomes of three rubber cultivars and a variety of RNA sequencing (RNA-seq) data. However, no current genome or transcriptome databases (DB) are organized by gene. Results: A gene-oriented database is a valuable support for rubber research. Based on our original draft genome sequence of H. brasiliensis RRIM600, we constructed a rubber tree genome and transcriptome DB. Our DB provides genome information including gene functional annotations and multi-transcriptome data of RNA-seq, full-length cDNAs including PacBio Isoform sequencing (Iso-Seq), ESTs and genome wide transcription start sites (TSSs) derived from CAGE technology. Using our original and publically available RNA-seq data, we calculated co-expressed genes for identifying functionally related gene sets and/or genes regulated by the same transcription factor (TF). Users can access multi-transcriptome data through both a gene-oriented web page and a genome browser. For the gene searching system, we provide keyword search, sequence homology search and gene expression search; users can also select their expression threshold easily. Conclusion: The rubber genome and transcriptome DB provides rubber tree genome sequence and multi-transcriptomics data. This DB is useful for comprehensive understanding of the rubber transcriptome. This will assist both industrial and academic researchers for rubber and economically important close relatives such as R. communis, M. esculenta and J. curcas. The Rubber Transcriptome DB release 2017.03 is accessible at http://matsui-lab.riken.jp/rubber/. [ABSTRACT FROM AUTHOR]

The memory effect of metastable β form crystals of trans-1,4-polyisoprene (TPI) is investigated with its thermodynamically stable α-TPI as reference. Unexpectedly, β-TPI exhibits a stronger memory effect over α-TPI. The memory temperature of β-TPI can be 20 °C higher than its equilibrium melting point (78 °C), while α-TPI has lost memory below the equilibrium melting point (87 °C). Moreover, the ordered structures in β-TPI memorized melt accelerate spherulite growth, and the growth rate depends on melting time, similar to previous mesomorphic isotactic polypropylene studies, implying metastable phase may have universal memory effects: wide memory temperature range, crystal nucleation and growth accelerating. The higher memory temperature of metastable phase may be from weak entropic difference with isotropic melt, which cannot overcome the barrier from entanglements as thermodynamically stable phase, leading to slow relaxation. This discovery can regulate crystalline morphologies of polymers by controlling the locations of different form crystals. [ABSTRACT FROM AUTHOR]

MicroRNAs (miRNAs), a group of endogenous small non-coding RNAs, play important roles in plant growth, development, and stress response processes. Eucommia ulmoides Oliver (hardy rubber tree) is one of the few woody plants capable of producing trans-1, 4-polyisoprene (TPI), also known as Eu-rubber, which has been utilized as an industrial raw material and is extensively cultivated in China. However, the mechanism of TPI biosynthesis has not been identified in E. ulmoides. To characterize small RNAs and their targets with potential biological roles involved in the TPI biosynthesis in E. ulmoides, in the present study, eight small RNA libraries were constructed and sequenced from young and mature leaves and fruits of E. ulmoides. Further analysis identified 34 conserved miRNAs belonging to 20 families (two unclassified families), and 115 novel miRNAs seemed to be specific to E. ulmoides. Among these miRNAs, fourteen conserved miRNAs and 49 novel miRNAs were significantly differentially expressed and identified as Eu-rubber accumulation related miRNAs. Based on the E. ulmoides genomic data, 202 and 306 potential target genes were predicted for 33 conserved and 92 novel miRNAs, respectively; the predicted targets are mostly transcription factors and functional genes, which were enriched in metabolic pathways and biosynthesis of secondary metabolites. Noticeably, based on the expression patterns of miRNAs and their target genes in combination with the Eu-rubber accumulation, the negative correlation of expression of six miRNAs (Eu-miR14, Eu-miR91, miR162a, miR166a, miR172c, and miR396a) and their predicted targets serving as potential regulators in Eu-rubber accumulation. This study is the first to detect conserved and novel miRNAs and their potential targets in E. ulmoides and identify several candidate genes potentially controlling rubber accumulation, and thus provide molecular evidence for understanding the roles of miRNAs in regulating the TPI biosynthesis in E. ulmoides. [ABSTRACT FROM AUTHOR]

Synthesis of a cyclodextrin (CD) polyrotaxane is achieved for the first time by simultaneous free radical polymerization of isoprene, threading by CD, and stoppering by copolymerization of styrene. This reaction is performed in an eco-friendly manner in an aqueous medium similar to classical emulsion polymerization. Threaded CD rings of the polyrotaxane are cross-linked by hexamethylene diisocyanate, leading to highly elastic slide-ring gels. [ABSTRACT FROM AUTHOR]

In dentistry, pure gutta-percha (trans-1,4-polyisoprene (TPI)) is widely used as a main component of root canal filling materials. TPI has an interesting shape memory formed through cross-linking, and this characteristic is expected to be very effective for development of novel dental treatments; in particular, modification of the shape recovery temperature to the intraoral temperature (37 °C) will enhance the applicability of the shape-memory effect of TPI in root canal filling. In this study, trial test specimens consisting of varying proportions of TPI, cis-polyisoprene, zinc oxide, stearic acid, sulfur and dicumyl peroxide were prepared and the temperature dependence of their shape recovery, recovery stress and relaxation modulus were measured. Additionally, their sealing abilities were tested using glass tubing and a bovine incisor. As the ratio of cross-linking agent in the specimens increased, a decrease in recovery temperature and an increase in recovery stress and recovery speed were observed. In addition, the test specimen containing the highest concentration of cross-linking agent showed superior sealing ability under a thermal stimulus of 37 °C in both sealing ability tests. [ABSTRACT FROM AUTHOR]

Introduction Pure gutta-percha (trans-1, 4-polyisoprene [TPI]) has been used extensively as a main component of gutta-percha for root canal filling. TPI has the interesting shape memory property by cross-linking, and this polymer was commercialized under the product name of SMP-2 (Kuraray Corp, Kashima, Japan). Therefore, the purpose of this study was to examine the thermal properties and the mechanism of the shape memory function of cross-linked SMP-2. Methods The crystalline of the TPI was observed by x-ray diffraction. The effects of temperature on shape recovery, recovery stress, and relaxation modulus (Er[5]) were measured in cross-linked cylindrical specimens of SMP-2. Differential scanning calorimetry was used to monitor thermal events. Results On heating, a pronounced increase in recovery stress, a marked decrease in Er(5), and endothermic DSC peaks were observed over the same temperature range (38°–51°C) with shape recovery. On the other hand, on cooling, a pronounced decrease in recovery stress, a marked increase in Er(5), and an exothermic DSC peak were observed over the same temperature range (27°–33°C). Conclusions The shape memory property of TPI is derived from its crystallinity and cross-linking ability. Fixing the deformed shape and shape recovery from the deformed shape to the original shape is relatively easy to achieve by changing the temperature of SMP-2. The shape memory function of the cross-linked SMP-2 was expected to be very useful as a root canal filling material by the modification of its some thermal properties. [ABSTRACT FROM AUTHOR]

Basal media including Murashige and Skoog (MS), Woody Plant Medium (WPM), and Driver and Kuniyuki (DKW) media were compared for use in guayule regeneration and propagation. Explants grown on MS basal medium showed large size calli with multiple shoots, but the calli produced on DKW medium were of higher quality, and longer true shoots were produced. Adventitious root formation was best in WPM basal medium. A comparison of macro and micro nutrient levels in MS, DKW, and WPM media revealed significant differences in the calcium levels. Under controlled conditions, guayule plants in vitro incorporated calcium into plant tissues in proportion to the amount available. Moreover, the addition of calcium nitrate tetrahydrate at moderate levels into MS medium significantly improved the emergence of single, elongated true shoots, suggesting a requirement for calcium in guayule tissue culture. We have further explored selection agent (antibiotic) concentration for the identification of transgenic plants using a spectinomycin resistance gene (aadA). Based on the results, we have improved tissue culture protocols for guayule including spectinomycin as the selection agent. [ABSTRACT FROM AUTHOR]

The strain-induced crystallization (SIC) behaviors of crosslinked blends based on natural rubber (NR) and trans-1,4-polyisoprene (TPI) with different content of TPI were probed explored by using synchrotron two-dimensional wide angle X-ray diffraction and dynamic mechanical analysis. The results showed that when TPI content is less than 70% no reflection peak of TPI but NR crystallite diffractions can be observed and the diffractions of TPI βform appear when TPI content is 70 wt % in the cocured blend. SIC of cocured blends started at smaller strain ratio than the pure NR. By calculating Δ S, it is found that the drop in entropy upon strain decreased when TPI is incorporated into NR due to the reduction of molecular mobility of NR. The degree of SIC and crystallization rate index in crosslinked blends monotonously decreased with the increase of TPI content. The apparent crystallite size exhibited some surprising variations. L and L decreased with the increase of TPI content in the cocured blends. These observations were usually caused by two factors: (i) Less number of polymer chains could involve in crystal growth due to the lower mobility of polymer chains in the cocured blends which is proved by dynamic mechanical analysis results; (ii) The mean distance between nuclei decreases, which was caused by the fluctuation of crosslink density in NR phase derived from the heterogeneous distribution of curatives in two phases supported by the varying tendency of curing degree and crosslink density. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 [ABSTRACT FROM AUTHOR]

Abstract: Guayule (Parthenium argentatum Gray) is now a commercial crop for the production of high-quality, hypoallergenic natural rubber latex. Because guayule is relatively resistant to both insect and disease pests, its cultivation requires little chemical input. It has been postulated that guayule''s chemical defense system is based on terpene derivatives such as guayulins A and B. The goals of this research were to: (1) describe the distribution of guayulins A and B throughout the plant, (2) determine whether guayulins can be used as a predictor of rubber content/yield (is guayulin content related to rubber content), and (3) determine whether the guayulin content/distribution has been changed through plant breeding. Two plants each of three different lines (11591, AZ-1, and AZ-3) and two ages (1 and 2 years old) were harvested at the soil line in the fall of 2002 and spring of 2003. Plants were separated into eight parts: brown leaves, green leaves, stem tips, stems less than 5mm in diameter, stems between 5 and 10mm, stems greater than 10mm, green stems, and flower parts. Samples were analyzed for guayulins A and B and rubber content. Guayulins A and B and rubber were found in all plant parts, but were most prevalent in stems larger than 10mm in diameter, and were significantly correlated with each other in these stems. Guayulin A was found in greater concentrations than guayulin B. There were no significant differences between plant ages for rubber, or guayulin content at the time of harvest, or guayulins for harvest season. Rubber percent was higher in spring, which agrees with numerous other investigations. Guayulin A in the stems is correlated with the total rubber in the plant, suggesting it as a potential selection tool. However, rubber in the same plant parts has a higher correlation with total plant rubber and remains a better and easier selection criterion than guayulin A. The extent to which guayulin contents differed between older, relatively unimproved lines and newer improved lines was evaluated. Variety 11591 had a higher concentration of guayulin A than guayulin B, so that the ratio of A to B was much higher than in the two improved lines (AZ-1 and AZ-3). It appears that the ratio of guayulin A to guayulin B has been changed in the two newer selections, but it is unclear whether this will affect pest resistance. [Copyright &y& Elsevier]

Polarized IR spectra for two conformations of trans-1,4-polyisoprene (α-and β-gutta-percha) were calculated. The IR dichroism of the absorption bands was calculated for both conformations. The computed results for polarized IR spectra and IR dichroism agree reasonably well with the respective experiment data. [ABSTRACT FROM AUTHOR]

The thermodynamics based on the interaction of small molecules on a polymer melt surface has been studied by molecular simulations. The melt surface structure of cis-1,4-polyisoprene was constructed using a molecular dynamics simulation technique. The system contained 20 polymer chains and a total of 30,000 carbon atoms. The excess chemical potential and enthalpy terms (average interaction energy between the gas and the polymer) were obtained using a test-particle-insertion method with excluded volume map sampling as a function of the position from the inside to the surface. The thickness of the surface estimated by the density change was 1.3 nm at 373 K. The excess chemical potential showed a minimum and a negative value only at the surface just beyond the position with half of the inside density. These results show the intrinsic properties of the polymer surface which accommodates gas molecules due to adsorption. [ABSTRACT FROM AUTHOR]

Abstract: A comparative study on biodegradation of di-cumyl peroxide (DCP) crosslinked and uncrosslinked natural rubber by Pseudomonas sp. was carried out. Decrease in organic carbon content along with the changes in tensile strength of the treated rubber, both DCP crosslinked and uncrosslinked natural rubber, indicated rubber hydrocarbon utilization by the Pseudomonas sp. A decrease in 60.88% MPa and 41.66% MPa was observed after five month’s old treated uncrosslinked natural rubber and DCP crosslinked rubber, respectively. Biodegradation was more pronounced in natural uncrosslinked rubber, which was further confirmed by the formation of aldehydic compounds with decrease in CH2 stretching frequencies. [Copyright &y& Elsevier]

Abstract: A comparative study on natural rubber (NR) biodegradation through solid-state fermentation (SSF) and submerged fermentation (SmF) has been carried out for both bacterial as well as fungal species. Changes in the organic carbon content along with the average molecular weight of the treated rubber samples indicated rubber hydrocarbon utilization and its degradation. Proportion of sol and gel content of the treated rubber also varied with the SmF and SSF treatment. Further, presence of aldehyde groups in the treated rubber indicated rubber biodegradation. The comparative results showed SSF to be a better treatment method for rubber biodegradation. [Copyright &y& Elsevier]

Abstract: The production of latex or bulk rubber from guayule has been pursued at various times since guayule rubber ceased being an article of commerce more than 60 years ago. Hypo-allergenic guayule latex has been prepared in 25–50-kg laboratory batches. Dilute latex was first washed from ground shrub and then concentrated by a combination of multi-stage centrifugation and creaming steps. This material was used to fabricate prototype medical products. A total of 8.8t of dry guayule rubber was produced by simultaneous extraction of rubber and resin with a mixed organic solvent, followed by fractionation of the polymer stream. This material was tested in aircraft and light truck tires. At present, those seeking to process guayule must be prepared to meet several challenges: increasing the bulk viscosity of the rubber polymer, reducing the level of entrained resin and assuring oxidative and thermal stability. From this standpoint, latex process development remains in its early stages, whereas processing guayule for bulk rubber has been more thoroughly and successfully evaluated. [Copyright &y& Elsevier]

In order to make up for the defects of trans-1,4-polyisoprene (TPI) shape memory polymer, TPI/high density polyethylene (HDPE) hybrid shape memory matrix was prepared from the perspective of matrix composition. The carbon nanotubes (CNTs) with excellent mechanical properties were introduced into the hybrid shape memory matrix. Due to the difference of the inherent properties and geometry of nano-fillers, the change of the content of nano-fillers directly affects the bonding state within the composites. Therefore, it is very important to choose the appropriate content. In order to give full play to the potential of thermodynamics of nano-filler, the TPI/HDPE/CNTs ternary hybrid shape memory nanocomposites were prepared by mechanical melt blending technology combined with dynamic vulcanization and hot-pressing forming technology. The addition of CNTs promotes the formation of the crystal structure of TPI and HDPE, and facilitates the energy transfer between different interface, which greatly improves the thermal conductivity and mechanical properties of the nanocomposites at the same time. The effect of the changes of filler content on the thermodynamic properties of the composite materials were revealed by series of tests. The results show that the CNTs act as nucleating agents in the crystallization region of TPI and HDPE. However, the excessive addition of CNTs can inhibit the formation of HDPE crystal structure. Meanwhile, the crystallinity of nanocomposites is also an important factor affecting its thermal conductivity. The specimens with the CNTs content of 0.5 wt% have excellent tensile resistance and cyclic recovery ability, and it can improve the shape recovery properties. Therefore, the nanocomposite with the CNTs content of 0.5 wt% has the best thermodynamic and shape memory properties., (© 2021 IOP Publishing Ltd.)

Photodegradation of a diene polymer in solution was investigated in the presence of a radical initiator. The use of azobisisobutylonitryl (AIBN) as a radical initiator led to efficient fission of bonds, under ultraviolet irradiation by a mercury lamp. The degradation reaction led to lower solution viscosity. The decrease in viscosity, along with FT-IR and ¹H NMR of the irradiated polymer, indicates that the degradation of the diene polymer proceeds thought the auto-oxidation mechanism. [ABSTRACT FROM AUTHOR]

MicroRNAs (miRNAs), a group of endogenous small non-coding RNAs, play important roles in plant growth, development, and stress response processes. Eucommia ulmoides Oliver (hardy rubber tree) is one of the few woody plants capable of producing trans-1, 4-polyisoprene (TPI), also known as Eu-rubber, which has been utilized as an industrial raw material and is extensively cultivated in China. However, the mechanism of TPI biosynthesis has not been identified in E. ulmoides . To characterize small RNAs and their targets with potential biological roles involved in the TPI biosynthesis in E. ulmoides , in the present study, eight small RNA libraries were constructed and sequenced from young and mature leaves and fruits of E. ulmoides . Further analysis identified 34 conserved miRNAs belonging to 20 families (two unclassified families), and 115 novel miRNAs seemed to be specific to E. ulmoides . Among these miRNAs, fourteen conserved miRNAs and 49 novel miRNAs were significantly differentially expressed and identified as Eu-rubber accumulation related miRNAs. Based on the E. ulmoides genomic data, 202 and 306 potential target genes were predicted for 33 conserved and 92 novel miRNAs, respectively; the predicted targets are mostly transcription factors and functional genes, which were enriched in metabolic pathways and biosynthesis of secondary metabolites. Noticeably, based on the expression patterns of miRNAs and their target genes in combination with the Eu-rubber accumulation, the negative correlation of expression of six miRNAs (Eu-miR14, Eu-miR91, miR162a, miR166a, miR172c, and miR396a) and their predicted targets serving as potential regulators in Eu-rubber accumulation. This study is the first to detect conserved and novel miRNAs and their potential targets in E. ulmoides and identify several candidate genes potentially controlling rubber accumulation, and thus provide molecular evidence for understanding the roles of miRNAs in regulating the TPI biosynthesis in E. ulmoides .