Isoprene Content Research Articles

A sensitive coumarin fluorescence sensor designed for isoprene detection and imaging research in plants

The release of isoprene by plants is considered to be an adaptation to the environment. Herein, a highly selective coumarin fluorescent probe (DMIC) was designed for detecting isoprene. When isoprene came into contact with the maleimide of DMIC, an electrophilic addition process took place. The powerful push-pull effect of DMIC was disrupted. Simultaneously, intramolecular charge transfer was initiated. This enabled DMIC to achieve rapid detection of isoprene within 5 min. Furthermore, excellent linearity was observed in the concentration range of 1–560 ppm (R2 = 0.996). A limit of detection is 1.6 ppm. DMIC was applied to in vitro studies of plant release of liberated isoprene. By monitoring the release of isoprene from different tree species throughout the day, the dynamics of isoprene release from plants throughout the day have been successfully revealed. In addition, the release of isoprene varied considerably among different tree species. In particular, the biocompatibility of DMIC allowed for the in vivo detection of isoprene using fluorescence imaging. The results successfully revealed the dynamics of isoprene release in plants under stress. The amount of isoprene that a plant produced increased with the severity of the stress it experienced. This suggested that the level of isoprene content in plants could be used as a preliminary indicator of the physiological health status of plants. This research demonstrates great potential for clarifying signal transduction in biological systems. It provided ideas for further understanding the biology of isoprene.

Copolymerization of ethylene and isoprene via silicon bridge metallocene [rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2] catalyst: A new way to control the composition and microstructure of copolymers

The copolymerization of ethylene (E) with isoprene (Ip) was performed catalyzed by a symmetrical catalyst exhibiting a silicon bridge [rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2 with the combination of borate/TIBA activator. The effect of cocatalyst, Ip concentration, and polymerization temperature on the activity, molecular weight (Mw), distribution (MWD), comonomer composition, chain structure (regio- and stereoselectivity), and resulting side reactions were logically addressed. Gel-permeation chromatography (GPC) was used to characterize the Mw and polydispersity, while nuclear magnetic resonance (NMR) was employed for the chain structure of the polymers. The catalytic activity was significantly lower by increasing the Ip concentration in the feed, and the isoprene content in resulting polymers was lower under the reaction condition, leading to higher activity. Insertion of isoprene units in polymer structure demonstrates the higher regioselectivity for the 3,4 connections than the 1,4 connections and is expected to be a high-resistance polymer against acids. The MWD presented monomodal even with a higher concentration (1.44 mol/L) and did not appear as low Mw peaks of Ip. The Mw was higher with a broader MWD when purely TIBA was used as a cocatalyst, and it significantly reduced and presented a narrowed MWD with TEA in the cocatalyst. The higher efficiency of the catalyst for the higher insertion of Ip (C=C double bond) effectively modifies the polymer backbone. It is expected to be a promising candidate for easily degradable and favorable solutions for solving environmental problems caused by PE. wastes.

Nanoscale simulation of the thylakoid membrane response to extreme temperatures.

The thylakoid membrane is in a temperature-sensitive equilibrium that shifts repeatedly during the life cycle in response to ambient temperature or solar irradiance. Plants respond to seasonal temperature variation by changing their thylakoid lipid composition, while a more rapid mechanism for short-term heat exposure is required. The emission of the small organic molecule isoprene has been postulated as one such possible rapid mechanism. The protective mechanism of isoprene is unknown, but some plants emit isoprene at high temperature. We investigate the dynamics and structure for lipids within a thylakoid membrane across temperatures and varied isoprene content using classical molecular dynamics simulations. The results are compared with experimental findings for temperature-dependent changes in the lipid composition and shape of thylakoids. The surface area, volume, and flexibility of the membrane, as well as the lipid diffusion, increase with temperature, while the membrane thickness decreases. Saturated thylakoid 34:3 glycolipids derived from eukaryotic synthesis pathways exhibit altered dynamics relative to lipids from prokaryotic synthesis paths, which could explain the upregulation of specific lipid synthesis pathways at different temperatures. Increasing isoprene concentration was not observed to have a significant thermoprotective effect on the thylakoid membranes, and that isoprene readily permeated the membrane models tested.

Synthesis of Ethylene/Isoprene Copolymers Containing Cyclopentane/Cyclohexane Units as Unique Elastomers by Half-Titanocene Catalysts

Ethylene (E) copolymers with isoprene (IP) possessing higher glass-transition temperatures (Tg values, −7.1 to 29.2 °C) than those prepared by the reported catalysts (Tg below −18 °C) have been prepared in the copolymerization by using half-titanocene catalysts containing phenoxide ligand, Cp′TiCl2(O-2,6-iPr2-4-R-C6H2) [Cp′ = C5Me5 (Cp*), R = H (1), SiEt3 (2)]. Their microstructural analysis by NMR spectra revealed that the copolymers contained cyclopentane (major) and cyclohexane units, formed by cyclization after IP and subsequent ethylene insertions, in addition to 1,4- and 3,4-IP inserted units observed as major units in those prepared by reported catalysts. The 1,2,4-Me3C5H2 analogue (R = H) showed better IP incorporation, but the resulting E/IP copolymers possessed rather low Tg values compared to those prepared by 1,2 due to less cyclopentane unit in the microstructure. The Tg value in the E/IP copolymer increased upon the increase of the IP content, and the degree was dependent upon the catalyst employed. Due to their unique microstructure, the resulting E/IP copolymers prepared by 1,2–MAO catalyst systems exhibit promising tensile and elastic properties. The tensile strength initially decreased with an increase in the IP content along with an increase of the elongation at break (up to 600%, IP 3.3–15.6 mol %) and then increased gradually with further increase in the IP contents (IP 18.1–21.5 mol %); the elongation at break then decreased with preserving the tensile strength along with the observation of the yield stress.

Copolymerization of norbornene and conjugated dienes using anilinonaphthoquinone-ligated nickel complexes

Copolymerization of norbornene (NB) with butadiene (BD) or isoprene (IP) was carried out using anilinonaphthoquinone-ligated nickel complexes with MMAO as a cocatalyst. The copolymerization of NB/BD showed higher activity than that of NB/IP. Increasing the ratio of diene in monomer feed decreased the copolymerization activity. Raising the polymerization temperature increased the activity and the molecular weight of the produced polymer but did not significantly affect the comonomer incorporation. The BD content was varied from 11 to 33 mol% with the number-average molecular weight (Mn) of 15000–60000 and the molecular weight distribution (Mw/Mn) of 1.3–1.6, while the IP content was varied from 15 to 41 mol% with Mn of 34000–83000 and Mw/Mn of 1.3–2.1. The glass transition temperatures of the copolymers determined by differential scanning calorimetry were 101–199 °C for the NB/BD copolymers and 97–205 °C for the NB/IP copolymers according to the diene content.

Peroxide‐initiated chemical modification of poly(isobutylene‐co‐isoprene): H‐atom transfer yields and regioselectivity

ABSTRACTThe yield and regioselectivity of H‐atom abstraction by cumyloxy radicals from poly(isobutylene‐co‐isoprene) (IIR) are quantified and discussed in the context of cross‐linking/degradation outcomes and vinyltriethoxysilane (VTEOS) graft yields. Studies of IIR materials with different isoprene contents show that H‐atom abstraction from the allylic functionality provided by isoprene mers is responsible for the heightened H‐atom transfer reactivity of IIR relative to poly(isobutylene). Differences in the reactivity of allylic and alkyl macroradical intermediates makes high isoprene IIR materials less prone to peroxide‐initiated chain scission, but less responsive to VTEOS grafting formulations. Improved knowledge of H‐atom transfer reactivity is extended to a new approach for IIR cross‐linking involving acrylate‐functionalized nitroxyl chemistry. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3102–3109

Quantitative analysis of isoprene units in natural rubber and synthetic polyisoprene using 1H-NMR spectroscopy with an internal standard

Isoprene units in natural rubber (NR) and its synthetic analogues were quantified by 1H-NMR spectroscopy using polyethylene glycol (PEG) as an internal standard. The effect of PEG and rubber concentrations, molar ratio of rubber/PEG, measuring temperature and scan number on the quantification was investigated to establish the respective working range. Analysis of commercial grades of NR revealed that the differences in 1,4 isoprene content is caused by the production process and feedstock, in which proteins and lipids were found to be the major impurity in NR. Gel fraction of NR has insignificant effect on the measurement of 1,4 isoprene content. Furthermore, the new method was found to produce good results for the quantification of 1,4 and 3,4 units of synthetic polyisoprenes.

Latex Clearing Protein—an Oxygenase Cleaving Poly( cis -1,4-Isoprene) Rubber at the cis Double Bonds

Gordonia polyisoprenivorans strain VH2, a potent rubber-degrading actinomycete, harbors two latex clearing proteins (Lcps), which are known to be essential for the microbial degradation of rubber. However, biochemical information on the exact role of this protein in the degradation of polyisoprene was lacking. In this study, the gene encoding Lcp1VH2 was heterologously expressed in strains of Escherichia coli, the corresponding protein was purified, and its role in rubber degradation was examined by measurement of oxygen consumption as well as by chromatographic and spectroscopic methods. It turned out that active Lcp1VH2 is a monomer and is responsible for the oxidative cleavage of poly(cis-1,4-isoprene) in synthetic as well as in natural rubber by the addition of oxygen (O2) to the cis double bonds. The resulting oligomers possess repetitive isoprene units with aldehyde (CHO-CH2-) and ketone (-CH2-CO-CH3) functional groups at the termini. Two fractions with average isoprene contents of 18 and 10, respectively, were isolated, thus indicating an endocleavage mechanism. The activity of Lcp1VH2 was determined by applying a polarographic assay. Alkenes, acyclic terpenes, or other rubber-like polymers, such as poly(cis-1,4-butadiene) or poly(trans-1,4-isoprene), are not oxidatively cleaved by Lcp1VH2. The pH and temperature optima of the enzyme are at pH 7 and 30°C, respectively. Furthermore, it was demonstrated that active Lcp1VH2 is a Cu(II)-containing oxygenase that exhibits a conserved domain of unknown function which cannot be detected in any other hitherto-characterized enzyme. The results presented here indicate that this domain might represent a new protein family of oxygenases.

Cationic Tropidinyl Scandium Catalyst: A Perfectly Acceptable Substitute for Cationic Half-Sandwich Scandium Catalysts in cis-1,4-Polymerization of Isoprene and Copolymerization with Norbornene

Different nonmetallocene rare earth metal alkyl complexes such as monotropidinyl (Trop) scandium dialkyl complex (Trop)Sc(CH2SiMe3)2(THF) (1), ditropidinyl yttrium alkyl complex (Trop)2Y(CH2SiMe3)(THF) (3) as well as binuclear lutetium alkyl complex bearing one tetradentate dianionic 6-N-methyl-1,4-cycloheptadienyl (NMCH) ligand [(NMCH)Lu(CH2SiMe3)(THF)]2 (2) have been synthesized in high yields via one-pot acid–base reaction by using of the tris(trimethylsilylmethyl) rare earth metal complexes with the readily available natural product tropidine. The polymerization experiments indicate that the monotropidinyl scandium dialkyl complex 1 displays reactivity akin to that of the analogous monocyclopentadienyl scandium dialkyl complexes. In the presence of activator and a small amount of AlMe3, complex 1 exhibits similar activities (up to 1.6 × 106 g molSc–1 h–1) but higher cis-1,4-selectivities (up to 100%) than (C5H5)Sc(CH2SiMe3)2(THF) (cis-1,4-selectivity as 95%) in the isoprene polymerization, yielding the pure cis-1,4-PIPs with moderate molecular weights (Mn = 0.5–11.2 × 104 g/mol) and bimodal molecular weight distributions (Mw/Mn = 1.48–6.07). Moreover, the complex 1/[Ph3C][B(C6F5)4/AliBu3 ternary system also shows good comonomer incorporation ability in the copolymerization of isoprene and norbornene similar to the [C5Me4(SiMe3)]Sc(η3-CH2CHCH2)2/activator binary system, affording the random isoprene/norbornene copolymers with a wide range of isoprene contents around 57–91 mol % containing cis-1,4 configuration up to 88%.

Performance of hydrocarbon particles on the drying shrinkage of cement mortar

The inherent volume reduction normally witnessed in hydraulic cement mixes is probably one of the most important threats to its durability as this is often accompanied by deleterious cracks. This paper presents experimental findings on the drying shrinkage of poly(1,4-isoprene) modified-hydraulic cement mortar. Based on mechanical and durability requirements 0–20% (vol.) isoprene/water ratio was employed. Normal and modified mortar specimens were prepared, cured and tested for drying shrinkage. Microstructural details of both normal and modified phases were examined through scanning electron microscopy (SEM). In addition, compressive strengths of the hardened mixes and thermogravimetry analysis (TGA) of the poly(1,4-isoprene) were noted. Results have indicated a continuous decrease in the drying shrinkage of mortar with a corresponding increase in poly(1,4-isoprene) up to 10% (vol.) isoprene/water ratio, beyond which the shrinkage increases with increase in the isoprene content. Thus, inclusion of optimum content of poly(1,4-isoprene) into the normal hydraulic cement mortar minimizes its drying shrinkage, principally due to blocking effects of the isoprene particles against the inter-particle attraction of the mixed-conglomerate during the volume reduction. Indeed, this could inhibit formation and propagation of harmful cracks.

Modification of polyisoprene‐block‐poly(vinyl trimethylsilane) block copolymers via hydrosilylation and hydrogenation, and their gas transport properties

ABSTRACTPolyisoprene‐block‐poly(vinyl trimethylsilane) (PI‐b‐PVTMS) block copolymers having different isoprene contents are successfully chemically modified and characterized by proton nuclear magnetic resonance spectroscopy (1H‐NMR), Fourier transform infrared spectroscopy, gel permeation chromatography, and thermogravimetric analysis. Gas transport properties of the initial block copolymers and their derivatives modified via hydrosilylation and hydrogenation are measured. The modified block copolymers show higher permeabilities for O2 and H2 than the unmodified block copolymers while maintaining similar O2/N2 and H2/N2 selectivities. Hydrosilylation and hydrogenation of block copolymers with a low isoprene content result in a permeability increase for O2 and H2 of 15 to 40%, respectively. Similarly, for block copolymers with high isoprene contents, increases in permeabilities up to 125% are observed compared to initial PI‐b‐PVTMS. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym. Phys. 2013, 51, 1252–1261

Poly(vinyl trimethylsilane) and block copolymers of vinyl trimethylsilane with isoprene: Anionic polymerization, morphology and gas transport properties

Poly(vinyl trimethylsilane) (PVTMS) and block copolymers of vinyl trimethylsilane with isoprene were synthesized by anionic polymerization and characterized. The synthesized pure PVTMS has properties similar to a reference material produced about two decades ago and can be used for thin film composite membrane formation. Even at low isoprene content the block copolymers have improved film forming properties compared to the pure PVTMS. However, the presence of the isoprene units in the block copolymers leads to a decrease of the gas permeability but does not affect the selectivity of the membranes (α(O2/N2)=3.9).

Biogenic volatile organic compounds (BVOC) in ambient air over Hong Kong: analytical methodology and field measurement

In this paper, an analytical method using a simple semi-manual cryo-trap technique coupled to gas chromatograph with flame ionisation detector (GC-FID) was developed for the determination of biogenic volatile organic compounds (BVOC) in ambient air. Five common BVOC species have been tested, including isoprene and 4 monoterpenes, i.e. α-pinene, β-pinene, 3-carene (Δ) and limonene. The detection limits were estimated to be about 20 ppt for isoprene and 10 ppt for monoterpenes, with sample injection volume of 50 mL. Based on vegetation types, field measurement work was conducted over urban and rural sites of Hong Kong during summer and winter of 2007. Canister sampling technique was applied in the field measurement. Isoprene contents in rural ambient air were found to be in the range of 60∼1560 ppt in winter and 260∼3270 ppt in summer, respectively. However, in the measurement of monoterpenes, due to their extremely low concentration in the air samples, only β-pinene and limonene were detected by the developed analytical method.

Copolymerization of ethylene with isoprene promoted by titanium complexes containing a tetradentate [OSSO]‐type bis(phenolato) ligand

AbstractCopolymerization of ethylene with isoprene (IP) catalyzed by 1,4‐dithabutanediyl‐linked bis(phenolato) titanium complexes 1 and 2 and methylaluminoxane (MAO) produced exclusively ethylene‐IP copolymers with good activity. The copolymer microstructure can be varied by changing the ratio between the monomers in the copolymerization feed, affording copolymers with IP content ∼60%. The copolymer microstructure was fully elucidated by 13C‐NMR spectroscopy of the copolymers with various IP content revealing a strong tendency to the alternating microstructure. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4200–4206, 2010

Alternating and Random Copolymerization of Isoprene and Ethylene Catalyzed by Cationic Half-Sandwich Scandium Alkyls

The acid-base reactions between the scandium trialkyl complex Sc(CH(2)SiMe(3))(3)(THF)(2) and 1 equiv of Cp'-H afforded straightforwardly the corresponding mono(cyclopentadienyl)scandium dialkyl complexes Cp'Sc(CH(2)SiMe(3))(2)(THF) (Cp' = C(5)H(5) (1), C(5)MeH(4) (2), C(5)Me(4)H (3), C(5)Me(5) (4), C(5)Me(4)SiMe(3) (5)) in 65-80% isolated yields. The analogous half-sandwich complexes having a heteroatom-containing side arm, (C(5)Me(4)R)Sc(CH(2)SiMe(3))(2) (R = CH(2)CH(2)PPh(2) (6), C(6)H(4)OMe-omicron (7)), were obtained by the one-pot metathetical reactions of ScCl(3)(THF)(3) with 1 equiv of the potassium salts of the ligands and 2 equiv of LiCH(2)SiMe(3). The similar reactions of ScCl(3)(THF)(3) with KC(5)Me(4)(C(6)H(4)NMe(2)-omicron) and LiCH(2)SiMe(3) gave a methylene-bridged binuclear complex [{C(5)Me(4)(omicron-C(6)H(4)N(Me)CH(2)-mu}Sc(CH(2)SiMe(3))](2) (8). Complexes 1-8 were fully characterized by (1)H, (13)C NMR, X-ray, and microelemental analyses. The reactions of 5 and 7 with 1 equiv of [PhMe(2)NH][B(C(6)F(5))(4)] in THF afforded quantitatively the structurally characterizable cationic monoalkyl complexes [(C(5)Me(4)SiMe(3))Sc(CH(2)SiMe(3))(THF)(2)][B(C(6)F(5))(4)] (10) and [(C(5)Me(4)C(6)H(4)OMe-omicron)Sc(CH(2)SiMe(3))(THF)(2)][B(C(6)F(5))(4)] (11), respectively. In the presence of an activator such as [Ph(3)C][B(C(6)F(5))(4)], [PhMe(2)NH][B(C(6)F(5))(4)], or B(C(6)F(5))(3), all of the half-sandwich dialkyl complexes 1-7 were active for isoprene polymerization and isoprene-ethylene copolymerization, with the activity and selectivity being significantly dependent on the substituents at the cyclopentadienyl ligands to yield the corresponding homo- and copolymer materials with different microstructures and compositions. In the homopolymerization of isoprene, the less sterically demanding complexes 1 and 2 showed high cis-1,4 selectivity (up to 95%), whereas the more sterically demanding complexes 3-5 yielded 3,4-polyisoprene (51-65%) as a major product. The ether side arm coordinated complex 7 preferred trans-1,4-polyisoprene formation (60-79%), whereas the phosphine analogue 6 showed high cis-1,4 selectivity (84-90%) under the same conditions. In the copolymerization of isoprene and ethylene, complexes 1 and 2 afforded the random copolymers with high isoprene contents (85-92 mol %) and predominant cis-1,4-microstructures (up to 90%), thus constituting the first example of cis-1,4-selective copolymerization of isoprene with ethylene. In contrast, the copolymerization of isoprene and ethylene by 3, 4, 6, and 7 gave, for the first time, almost perfect alternating isoprene-ethylene copolymers. Possible mechanisms of the polymerization and copolymerization processes were proposed on the basis of the DFT calculations.

Steroid furostanol glycosides: A new class of natural adaptogenes (Review)

The present review summarizes experimental data revealed while studying the mechanism of the adaptogenic effect of furostanol glycosides (FG) extracted from Dioscorea deltoidea Wall cell culture under the conditions of biotic stress in tomato plants Lycopersicon esculenium Mill. induced by the gall nematode Meloidogyne incognita Kofoid et White. Comparison of changes in isoprene content (phytosterines, tomatin, and carotenoids) and in the rate of oxidative processes in the leaves and roots of intact and treated plants evidence that FG cause nonspecific defense reactions resulting in the formation of systemic acquired resistance. This formation is presented by the enhancement in photosynthetic apparatus pigment fund, pigments of the violaxanthin cycle in particular, by activation of processes related to POL, and by increase in peroxidase activity-enzyme of antioxidant protection.

Feedstock recycling of synthetic and natural rubber by pyrolysis in a fluidized bed

An indirect heated fluidized bed process has been used for the pyrolysis of synthetic and natural rubber. The throughput capacity for the continuously running plant was 500–3000 g/h. The results are compared to a pilot plant for the pyrolysis of whole tires. Beside the recovery of oil and carbon black it was another goal of the study to investigate how much monomer material such as isoprene and isobutene can be obtained from synthetic and natural rubber. The pyrolysis parameters were optimized such as pyrolysis temperature, kind of fluidizing gas, and residence time of the gas in the pyrolysis reactor. Main products of the pyrolysis of tires are an aromatic-rich oil and carbon black, which can be reused. While it was possible to obtain only 2–4 wt% of isobutene, the isoprene content reached 22 wt% from natural rubber.

Cationic Scandium Allyl Complexes Bearing Mono(cyclopentadienyl) Ligands: Synthesis, Novel Structural Variety, and Olefin‐Polymerization Catalysis

The one-pot salt-metathesis reaction of ScCl(3), cyclopentadienyl lithium salts, and allylmagnesium chlorides afforded with ease the corresponding base-free half-sandwich scandium di(eta(3)-allyl) complexes [(C(5)Me(4)SiMe(3))Sc(C(3)H(5))(2)] (1 a), [(C(5)Me(5))Sc(C(3)H(5))(2)] (1 b), and [(C(5)Me(5))Sc(2-MeC(3)H(4))(2)] (1 c) in high yields. Reaction of 1 a with 1 equivalent of [PhNMe(2)H][B(C(6)F(5))(4)] in toluene gave rapidly the N,N-dimethylaniline-coordinated cationic mono(eta(3)-allyl) complex [(C(5)Me(4)SiMe(3))Sc(eta(3)-C(3)H(5))(eta(6)-PhNMe(2))][B(C(6)F(5))(4)] (2). The similar reaction of 1 a with [Ph(3)C][B(C(6)F(5))(4)] yielded the analogous toluene-separated ion pair [(C(5)Me(4)SiMe(3))Sc(eta(3)-C(3)H(5))(eta(6)-PhMe)][B(C(6)F(5))(4)] (3). When [PhNMe(2)H][BPh(4)] was treated with 1 a, the contact ion pair [(C(5)Me(4)SiMe(3))Sc(eta(3)-C(3)H(5))( mu,eta(6)-Ph)BPh(3)] (4) was obtained. Recrystallization of 2, 3, and 4 in THF yielded the corresponding thf-separated ion pair complexes [(C(5)Me(4)SiMe(3))Sc(eta(3)-C(3)H(5))(thf)(2)][B(C(6)F(5))(4)] (5) and [(C(5)Me(4)SiMe(3))Sc(eta(3)-C(3)H(5))(thf)(2)][BPh(4)] (6). The N,N-dimethylaniline-coordinated cationic scandium allyl complex 2 and the toluene-coordinated analogue 3 showed high activity (activity: 3>2) toward the polymerization and copolymerization of isoprene and norbornene to afford random copolymers with a broad range of isoprene content (33-86 mol %). The tight ion pair 4 and the thf-coordinated complexes 5 and 6 showed no activity under the same conditions. These results offer unprecedented insight into the structure-activity relationship of a cationic metal polymerization-catalyst system.

Influence of the Composition on Crystal Phase and Thermal Behavior oftrans-1,4-Butadiene/Isoprene Copolymers

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.

Butadiene–isoprene copolymerization with V(acac)3‐MAO. Crystalline and amorphous trans‐1,4 copolymers

AbstractButadiene‐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