Metathesis Degradation Research Articles

Metathesis of butadiene rubber for the sustainable production of polyesters and polyols

Synthetic rubbers and elastomers are used extensively in different industries today, and more than 11.8 million tons are consumed annually. Butadiene rubber (BR) is the second most important synthetic rubber, with a worldwide consumption of about 3.44 million tons annually. In response to the high demand, production, and waste of BR and other industrial rubbers, a global effort has been made to reduce elastomeric, plastic, and microplastic pollution by studying various mechanisms of polymer degradation, including thermal degradation, mechanical treatment, UV exposure, and chemical processes.This work reported the synthesis of polyesters and polyols via metathesis degradation reaction from BR using the fatty acid methyl 10-undecenoate and the fatty alcohol 10-undecen-1-ol as chain transfer agents (CTA), using mild reaction conditions and a Ru catalyst. Polyesters and polyols were successfully produced with 94-97% yield. The formation of polyol, polyester, and by-products was assessed by FT-IR, NMR, GC/MS, and TGA. The molecular weights (Mn, Mw, Mz, and PDI) before and after degradation of BR and the products obtained were characterized by GPC. Different mole ratios BR:CTA were used to control the molecular weights; the Mw obtained ranged from 395 to 3963 Da.The proposed metathesis route may contribute to the reuse and recycling of BR to obtain sustainable products with added value for the synthesis of new materials.

Selective synthesis of α-vinyl-ω-vinylidene-oligoisoprene as a macromonomer via ethenolysis of polyisoprene

Oligoisoprene macromonomer, which bears a terminal vinyl group, was prepared by the metathesis degradation of high-molecular-weight polyisoprene with ethylene for coordination polymerization. The ethenolysis of polyisoprene using the 2nd-generation Grubbs catalyst (G2) at ambient pressure gave heterotelechelic (α-vinyl-ω-vinylidene) oligoisoprene, keeping the stereoregularity in high yield, whereas the 1st generation Grubbs catalyst was immediately deactivated. In such metathesis degradation, an intramolecular side reaction giving cyclic oligomers may be competitive, but ethenolysis proceeded with high selectivity, probably because of the least steric effect of ethylene. The ethenolysis is also applicable for the degradation of natural rubber-derived polyisoprene, although the catalytic activity decreased. The prepared oligoisoprene macromonomer was successfully copolymerized with ethylene using a phenoxyimine-ligated titanium catalyst, and the reactivity of the macromonomer was almost the same as that of 1-hexadecene. The oligoisoprene-grafted polyethylene showed a typical stress‒strain curve, of which the tensile modulus and yielding stress are comparable to those of linear low-density polyethylene.

Synthesis of Biobased Hydroxyl-Terminated Oligomers by Metathesis Degradation of Industrial Rubbers SBS and PB: Tailor-Made Unsaturated Diols and Polyols.

Biobased hydroxyl-terminated polybutadiene (HTPB) was successfully synthesized in a one-pot reaction via metathesis degradation of industrial rubbers. Thus, polybutadiene (PB) and poly(styrene-butadiene-styrene) (SBS) were degraded via metathesis with high yields (>94%), using the fatty alcohol 10-undecen-1-ol as a chain transfer agent (CTA) and the second-generation Grubbs-Hoveyda catalyst. The identification of the hydroxyl groups (-OH) and the formation of biobased HTPB were verified by FT-IR and NMR. Likewise, the molecular weight and properties of the HTPB were controlled by changing the molar ratio of rubber to CTA ([C=C]/CTA) from 1:1 to 100:1, considering a constant molar ratio of the catalyst ([C=C]/Ru = 500:1). The number average molecular weight (Mn) ranged between 583 and 6580 g/mol and the decomposition temperatures between 134 and 220 °C. Moreover, the catalyst optimization study showed that at catalyst loadings as low as [C=C]/Ru = 5000:1, the theoretical molecular weight is in good agreement with the experimental molecular weight and the expected diols and polyols are formed. At higher ratios than those, the difference between theoretical and experimental molecular weight is wide, and there is no control over HTPB. Therefore, the rubber/CTA molar ratio and the amount of catalyst play an important role in PB degradation and HTPB synthesis. Biobased HTPB can be used to synthesize engineering design polymers, intermediates, fine chemicals, and in the polyurethane industry, and contribute to the development of environmentally friendly raw materials.

Fluorinated nitrile-butadiene rubber (F-NBR) via metathesis degradation: Closed system or open system?

Fluorinated nitrile-butadiene rubber (F-NBR) could be designed via the metathesis degradation of nitrile-butadiene rubber (NBR) with perfluoroalkylethyl acrylates as fluorination chain transfer agent (F-CTA). Ethylene was produced during the metathesis degradation. Different from the reported works in the open system in which the ethylene escaped, the reaction in a closed system is greener. Here, the metathesis degradation of NBR was investigated in a closed system for the first time, with 2,2,3,4,4,4-hexafluorobutyl acrylate (F6) or 1H,1H,2H,2H-perfluorooctyl acrylate (F13) as F-CTA, respectively. Compared with the reaction in the open system, the metathesis degradation in the closed system with F6 was suppressed due to the reaction equilibrium, while that with F13 was promoted owing to the ethenolysis reaction, which was caused by the ethylene produced during the metathesis degradation. With the proposed green and efficient approach, the fluorinated liquid nitrile-butadiene rubber (F-LNBR) could be designed for various applications.

Controllable synthesis of fluorinated liquid nitrile-butadiene rubber via facile metathesis degradation strategy

The fluorinated liquid nitrile-butadiene rubber (F-LNBR) was designed via the metathesis degradation of nitrile-butadiene rubber (NBR) with 2,2,3,4,4,4-hexafluorobutyl acrylate (F6) as a model fluorination chain transfer agent. The fluorination degree (defined as the mass ratio of F6 units in the resultant F-LNBR) and relative molecular weight of the products after different reaction times were characterized with the 1H NMR and GPC techniques. Prolonging the reaction time, the fluorination degree increased while the relative molecular weight decreased. Based on the 1H NMR and GPC analysis, the reaction mechanism was proposed: the metathesis degradation of NBR by its intramolecular cross metathesis (CM) was the main reaction in the initial stage, leading a distinct decline in the relative molecular weight, while the fluorination via the CM between the 1,4-butadiene units in the resulted LNBR and F6 was the main reaction in the late stage, increasing the fluorination degree.

Nanoporous Poly(lactide) by Olefin Metathesis Degradation

We describe an approach to ordered nanoporous poly(lactide) that relies on self-assembly of poly(butadiene)-poly(lactide) (PB-PLA) diblock copolymers followed by selective degradation of PB using olefin metathesis. The block copolymers were obtained by a combination of anionic and ring-opening transesterification polymerizations. The molar mass of each block was tailored to target materials with either a lamellar or cylindrical microphase-separated morphology. Orientation of these nanoscale domains was induced in thin films and monolithic samples through solvent annealing and mechanical deformation, respectively. Selective degradation of PB was achieved by immersing the samples in a solution of Grubbs first-generation catalyst in cyclohexane, a nonsolvent for PLA. Successful elimination of PB was confirmed by size-exclusion chromatography and (1)H NMR spectroscopy. Direct imaging of the resulting nanoporous PLA was obtained by scanning electron microscopy.

Effect of Triethylaluminium on the Metathesis Degradation of Butadiene Rubber Skd-Nd under the Influence of a Second-Generation Hoveyda–Grubbs Catalyst

Effect of Triethylaluminium on the Metathesis Degradation of Butadiene Rubber Skd-Nd under the Influence of a Second-Generation Hoveyda–Grubbs Catalyst

Study of the Effect of Styrene on the Process of Metathesis Degradation of Skd-Nd Polybutadiene Rubber

Study of the Effect of Styrene on the Process of Metathesis Degradation of Skd-Nd Polybutadiene Rubber

One-Pot Synthesis of Natural Rubber-Based Telechelic cis-1,4-Polyisoprenes and Their Use To Prepare Block Copolymers by RAFT Polymerization

We investigate the one-pot synthesis of a new α,ω-bistrithiocarbonyl-end functionalized telechelic cis-1,4-polyisoprene (Pip) via metathesis degradation from natural rubber (NR) in the presence of the Grubbs second generation catalyst (GII) and a bistrithiocarbonyl-end functionalized olefin as a chain transfer agent (CTA). When the metathesis degradation of the NR of 2 × 106 g mol−1 molecular weight is performed in toluene at 25 °C using the ratio of [Ip]0/[GII]0/[CTA]0 = 100/1/1 (Ip = isoprene units), a cis-1,4-polyisoprene of 14 000 g mol−1 after 4 h is obtained. The functionality estimated by 1H NMR spectroscopy is equal to 1.5 ± 0.1. The structure of telechelic cis-1,4-polyisoprene was confirmed by combination of 1H NMR, 13C NMR spectroscopy and FTIR. The influence of the CTA concentration was investigated. It was found that using higher concentrations of CTA ([Ip]0/[GII]0/[CTA]0 of 100/1/2 and 100/1/5) lead to form a perfectly telechelic cis-1,4-polyisoprene with a functionality of 2 with no significant difference in Mn values (approximately 6400 g mol−1) and in polydispersity indices (∼1.70). The new well-defined α,ω-bistrithiocarbonyl-end functionalized telechelic cis-1,4-polyisoprenes were used successfully as macromolecular chain transfer agents (macroCTAs) to mediate the RAFT polymerization of t-BA using AIBN as the initiator ([t-BA]0/[macroCTA]0/[AIBN]0 = 500/1/0.4) in toluene at 60 °C leading to well-defined P(t-BA)-b-PIp-b-P(t-BA) triblock copolymers.

Copolymerization of propylene with 1,3‐butadiene using isospecific zirconocene catalysts

AbstractPoly(propylene‐ran‐1,3‐butadiene) was synthesized using isospecific zirconocene catalysts and converted to telechelic isotactic polypropylene by metathesis degradation with ethylene. The copolymers obtained with isospecific C2‐symmetric zirconocene catalysts activated with modified methylaluminoxane (MMAO) had 1,4‐inserted butadiene units (1,4‐BD) and 1,2‐inserted units (1,2‐BD) in the isotactic polypropylene chain. The selectivity of butadiene towards 1,4‐BD incorporation was high up to 95% using rac‐dimethylsilylbis(1‐indenyl)zirconium dichloride (Cat‐A)/MMAO. The molar ratio of propylene to butadiene in the feed regulated the number‐average molecular weight (Mn) and the butadiene contents of the polymer produced. Metathesis degradations of the copolymer with ethylene were conducted with a WCI6/SnMe4/propyl acetate catalyst system. The 1H NMR spectra before and after the degradation indicated that the polymers degraded by ethylene had vinyl groups at both chain ends in high selectivity. The analysis of the chain scission products clarified the chain end structures of the poly(propylene‐ran‐1,3‐butadiene). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5731–5740, 2007

Molecular modeling of metathesis degradation of polyalkenamers: 1. Degradation of polynorbornene via cross-metathesis with linear olefins

The molecular modeling of polynorbornene (PNB) degradation via cross-metathesis with ethylene, 2-butene, and 1,4-dichloro-2-butene as chain-transfer agents (CTAs) at 25 °C using the B3LYP/6-31G(d,p) level of theory reveals that chain–chain equilibrium constants depend on the nature of linear olefins used as CTAs. The cross-metathesis of PNB with trans-1,4-dichloro-2-butene as a CTA proceeds with high selectivity. The yield of bis(allyl chloride) functionalized diene reaches 92 mol%. The results of calculations are in agreement with experimental data obtained for the cross-metathesis of PNB with trans-1,4-dichloro-2-butene using highly active ruthenium-based catalyst, (1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) (PCy 3)CI 2RuCHPh.

Synthesis of Poly(propylene-ran-1,3-butadiene) and Its Metathesis Degradation with Ethylene

Synthesis of Poly(propylene-<i>r</i><i>an</i>-1,3-butadiene) and Its Metathesis Degradation with Ethylene

Computational study of metathesis degradation of rubber. distributions of products for the ethenolysis of 1,4-polyisoprene

The molecular modeling of the product distributions for the ethenolysis of 1,4-polyisoprene at 25 °C using the B3LYP/6-31G(d,p) level of theory reveals that chain–ring and chain–chain equilibria are completely shifted toward the formation of 2-methyl-1,5-hexadiene. The amount of cyclic oligomers at equilibrium with linear molecules is small. The concentration of 2-methyl-1,5-hexadiene at equilibrium with linear isoprene oligomers is of 90 mol%. The value of 1,5-hexadiene at equilibrium with butadiene oligomers for the ethenolysis of 1,4-polybutadiene corresponds to 46 mol%. These results are in agreement with experimental data.

Computational Study of Metathesis Degradation of Rubber, 3. Distribution of Cyclic and Linear Oligomers via Intermolecular Degradation of cis-Poly(butadiene)

The molecular modeling of the product distributions for the intermolecular metathesis degradation of cis-poly(butadiene) (cis-PB) in the presence of ethylene as chain-transfer agent (CTA) at 298.15 K using the B3LYP/6-31G (d, p) level of theory reveals that chain–ring and chain-chain equilibria are shifted toward the formation of 1,5-hexadiene. The amount of cyclic oligomers at equilibrium with linear molecules is negligible. The α,ω-vinyl-terminated butadiene oligomers–1,5-hexadiene equilibrium constant depends on the cis/trans isomer ratio in linear butadiene molecules. While the concentration of 1,5-hexadiene at equilibrium with cis-butadiene oligomers is 86 mol-%, this value for trans-butadiene oligomers corresponds to 50 mol-% of 1,5-hexadiene. The results of calculations are in reasonable agreement with recent experimental data on the intermolecular metathesis of 1,4-cis-PB with ethylene using a well-defined ruthenium alkylidene catalyst. The calculations predict that cis-butene as a CTA is more efficient in the metathesis depolymerization of cis-PB compared with ethylene.

Computional Study of Metathesis Degradation of Rubber, 2. Distribution of Cyclic Oligomers via Intramolecular Metathesis Degradation of Natural Rubber

Computional Study of Metathesis Degradation of Rubber, 2. Distribution of Cyclic Oligomers via Intramolecular Metathesis Degradation of Natural Rubber

Computional Study of Metathesis Degradation of Rubber, 2. Distribution of Cyclic Oligomers via Intramolecular Metathesis Degradation of Natural Rubber

The results of molecular modeling of the ring distributions for the intramolecular metathesis degradation of natural rubber (NR) at HF/6-31G(d) level of theory showed that in the ring-ring equilibrium participate cyclic oligomers containing from two to four isopropene units with all-trans cyclic isoprene trimer being the main product. The formation of trans, trans, trans-1,5,9-trimethyl-1,5,9-cyclododecatriene from larger rings is thermodynamically favored. According to the calculations, the ring-ring equilibrium for the intramolcular metathesis degradation of cis-polybutadiene (cis-PB) is completely shifted towards the all-trans cyclic butadiene trimer. These results are in reasonable agreement with recent experimental data.

Computational study of metathesis degradation of rubber, 1. Distribution of cyclic oligomers via intramolecular metathesis degradation ofcis-polybutadiene

The results of the molecular modelling of the intramolecular metathesis degradation of cis-polybutadiene (cis-PB) into cyclic oligomers at PM3 level of theory showed that the chain-ring equilibrium is completely shifted towards the all-trans cyclic isomers. The formation of cyclic products, containing from three to six butadiene units, from larger rings is thermodynamically favoured with cyclic butadiene tetramers and pentamers being the main products. These results are in reasonable agreement with most of the available experimental data. The discrepancy observed in some cases between found and calculated ring distributions for the intramolecular metathesis degradation of cis-PB suggests that the reaction is kinetically controlled under certain conditions.

Formation and degradation of 1,4‐polybutadiene via metathesis: new results concerning cyclic oligomers

AbstractThe ring‐opening metathesis polymerization (ROMP) of cyclic oligomers of butadiene (c,c‐1,5‐cyclooctadiene — COD —, t,t,t‐1,5,9‐cyclododecatriene — CDT —), the acyclic diene metathesis (ADMET) of 1,5‐hexadiene and the intramolecular metathesis degradation of 1,4‐polybutadiene (1,4‐BR) were studied using stable tungsten and molybdenum carbene complexes as well as conventional metathesis catalysts. The determination of cyclic oligomers up to rings containing eight butadiene units shows, compared to the literature, different results regarding the distribution, concentration and cis/trans ratio. Kinetic studies of the ROMP of COD and the intramolecular metathesis of 1,4‐BR allow to explain the discrepancy. The ROMP product spectrum for the cyclobutene system known and accepted until now in the literature as ring‐chain equilibrium is controlled kinetically and far apart from thermodynamic equilibrium according to our results.

Photocrosslinking of 1,4‐polybutadiene with α‐thiocyanatoketones as photoinitiators

AbstractThe photocrosslinking of 1,4‐polybutadiene with various α‐thiocyanatoketones 1 as photoinitiators was examined. An excimer laser (308 nm) was used as light source, the samples were irradiated with an intensity of 6,2 mJ per pulse per cm2 under exclusion of oxygen. As initiators were used: phenacyl thiocyanate (1a), 1‐oxo‐1,2,3,4‐tetrahydro‐2‐naphthyl thiocyanate (1b), 1‐oxo‐2‐indanyl thiocyanate (1c), α‐phenylphenacyl thiocyanate (1d), 2‐naphthoylmethyl thiocyanate (1e) and 3‐phenanthrylcarbonylmethyl thiocyanate (1f). 1,4‐Polybutadiene samples that contained 20 mmol of initiator per 100 g were irradiated with 200 to 1000 pulses. 1a and 1b showed the highest crosslinking efficiency. The photochemistry of 1a in solution (2‐propanol, benzene and (Z,Z)‐1,5‐cyclooctadiene) was investigated. Analysis of the photochemical reaction products by combination of gas chromatography (GC) and mass spectrometry (MS) confirmed that the radical cleavage into benzoylmethyl and thiocyanato radicals is the first step of the reaction. Tetrafunctional crosslinks in allyl position were found in traces by means of metathesis degradation followed by GC/MS.

Synthesis of α,ω‐divinylpolyethylene‐like polymers from cis‐1,4‐polybutadiene using partial hydrogenation and metathesis degradation with ethylene

Synthesis of α,ω‐divinylpolyethylene‐like polymers from cis‐1,4‐polybutadiene using partial hydrogenation and metathesis degradation with ethylene