Chain Transfer Rate Research Articles

The advancement of EVA polymerization kinetics and development of high-performance EVOH polymerization process

Ethylene-vinyl alcohol copolymer (EVOH) is a material with excellent barrier properties, produced via the radical copolymerization of ethylene and vinyl acetate in solution, followed by alcoholysis in methanol with NaOH as a catalyst. It is widely used in packaging and medical materials. However, balancing the barrier properties and processability remains challenging. Currently, multi-scale research methods using density functional theory (DFT) to explore polymerization mechanisms and obtain kinetic data, combined with process simulation methods to develop high-performance EVOH polymerization process, are gaining attention. Therefore, this study employs DFT and transition state theory (TST) methods to study the kinetics of chain growth and chain transfer reactions of radicals at first, yielding the average chain growth and chain transfer rate constants for copolymerization reactions. Then, based on these rate constants, process simulations were used to model the ethylene–vinyl acetate solution copolymerization reactor, developing polymerization process for EVOH with high barrier properties as well as EVOH with both high barrier properties and good processability. These findings provide suggestions and guidance for EVOH production and application.

Possibilities For Using Ionic Liquids In The Polymerization Process

Abstract The paper investigates the polymerization of various methacrylate esters in different ionic liquids (ILs) and compares the results with those obtained in traditional organic solvents, particularly benzene. The study highlights the influence of ILs on the polymerization process, focusing on factors such as polymer yield, average molecular weight, and thermal stability. The results indicate a relatively higher degree of polymerization in ILs compared to benzene under identical conditions. Additionally, polymers synthesized in ILs exhibit higher average molecular weights and thermal stability. The observed differences are attributed to the unique properties of ILs, such as low chain transfer rate constants and the ability to stabilize active radicals during polymerization. The findings underscore the potential of ILs as promising reaction media for polymer synthesis, offering improved efficiency and polymer properties compared to conventional organic solvents.

Using temperature to modify the reaction conditions and outcomes of polymers formed using transfer-dominated branching radical telomerisation (TBRT).

Transfer-dominated Branching Radical Telomerisation (TBRT) enables the production of branched polymers with step-growth backbones using radical telomerisation chemistry. By conducting identical TBRTs over a broad temperature range, the role of temperature in telomer formation and branching has been evaluated. Elevated temperature limits telomer length, thereby allowing a >10% reduction in the amount of telogen required to produce near identical high molecular weight branched polymers.

АКРИЛОВІ МОНОМЕРИ НА ОСНОВІ РОСЛИННИХ ОЛІЙ ІЗ ВИСОКИМ ВМІСТОМ ЕСТЕРІВ ОЛЕЇНОВОЇ КИСЛОТИ

New acrylic monomers were obtained via transesterification of olive, canola, and high-oleic soybean oils by N-hydroxyethylacrylamide. The kinetic features of homopolymerization of these monomers were studied and the influence of linoleic (C18: 2) and linolenic (C18: 3) acid esters on the polymerization rate and the molecular weight of homopolymers were compared. It was found that the chain transfer and propagation rate constants increase in monomer’s range: olive (CM = 0.016) <high-oleic soybean (CM = 0.018) <canola (CM = 0.025). Features of homopolymerization are associated with varying degrees of unsaturation of fatty acid fragments.

Kinetic and thermal study of ethylene-propylene copolymerization catalyzed by ansa-zirconocene activated with Alkylaluminium/borate: Effects of linear and branched alkylaluminium compounds as cocatalyst

Ethylene-propylene (EP) copolymerizations was carried out with two ansa-metallocene: rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2 (Mt-I) and rac-Et(Ind)2ZrCl2 (Mt-II) combined with borates activators like ([Me2NPh][B(C6F5)4] (Borate-I), [Ph3C][B(C6F5)4] (Borate-II). Different structures of alkylaluminum( triethylaluminium (TEA), triisobutylaluminium (TIBA) and TEA/TIBA mixture of 25/75, 50/50, 75/25 mol ratios were used as cocatalysts. The choice of ligand structure and, more importantly, the nature of the cocatalyst significantly impact these systems' activity and the polymeric materials' properties. Borate-II has been shown as giving higher activities than Borate-I with both ansa-metallocene, attending 5.6 × 106 g/mol Zr*h. Mt-I gives higher activities and molecular weight but produced copolymers with low ethylene content, melting points, and crystallinity than Mt-II. The activities were very close to each other with 100% TIBA. Still, Mt-I became more active than Mt-II when TEA was more than 25% in the cocatalyst system. The effects of alkylaluminiums catalysts cocatalyst on EP copolymer molecular weight (Mw) and molecular weight distribution (MWD) were much more complicated. The MWD curve changed from broad to narrow with Mt-I when TIBA was replaced by a different mole ratio of TEA/TIBA ratio. The technique used for the assessment of active centers [C*]/[Zr] fraction in the ansa-metallocene catalyst was quenched label by using 2-thiophenecarbonyl chloride (TPCC) to determine the effects of alkylaluminiums catalysts structure on the propagation rate constants (kP) of EP copolymers. The [C*]/[Zr] value of Mt-I/Borate-I/TIBA is lower than those of the Mt-I/Borate-I/TEA and Mt-I/Borate-I/TEA/TIBA system. The main differences appear between catalysts containing pure TIBA and those containing TEA, possibly due to the faster rate of chain transfer with Al—Et than with bulky Al—iBu. Adding TEA in metallocene/borate/alkylaluminiums catalysts catalysts can be applied as an effective method to regulate the molecular weight of EP copolymer with a high degree of activity

Solvent Effects on Thiol–Ene Kinetics and Reactivity of Carbon and Sulfur Radicals

The thiol-ene reaction is one of the fundamental reactions in biochemistry and synthetic organic chemistry. In this study, the effect of polar media on the reaction kinetics is taken into account by using the transition state theory; the reactivities of the carbon and sulfur radicals have also been rationalized by using conceptual DFT. The results have shown that the solvents have more impact on hydrogen atom transfer reactions and the chain transfer rate constant, kCT, can be increased by using nonpolar solvents, while propagation reactions are less sensitive to media. Similarly, the kP/kCT ratio can be manipulated by changing the environment in order to obtain tailor-made polymers. Regarding the DFT descriptors, the local and global electrophilicity indices are well correlated with the propagation rate constant kP, whereas the global electrophilicity index is associated with the chain transfer rate constant kCT. Overall, electrophilicity indices can be used with confidence to predict the kinetics of thiol-ene reactions.

Geometrically Constrained Polymerization of Styrene Over Heterogeneous Catalyst Layer in Silica Nanotube Reactors

Styrene has been polymerized to syndiotactic polystyrene (sPS) over a layer of heterogeneous Cp*Ti(OCH3)3/MAO catalyst immobilized onto the surfaces of silica nanotube reactor (SNTR) arrays of 60–200 nm in diameter. The polymer produced in the SNTR arrays has been found to have the molecular weights much larger than the polymers synthesized by a liquid slurry polymerization over silica‐supported catalysts. A dynamic reactor model that consists of diffusion and reaction terms has been derived and solved to quantify the kinetics of styrene polymerization in a single nanotube reactor. The two‐site kinetic model applied to the silica nanotube reactor model shows that the experimentally observed high polymer molecular weight can be fitted if the chain transfer rate constants for monomer and β‐hydride elimination are reduced significantly. The simulation results suggest that the presence of dense crystalline sPS nanofibrils filling the nanotubes constrain the molecular movements of polymer chain ends in the proximity of catalyst sites to limit the chain transfer reactions. POLYM. ENG. SCI., 60:700–709, 2020. © 2020 Society of Plastics Engineers

Influence of Unusual Co-substrates on the Biosynthesis of Medium-Chain-Length Polyhydroxyalkanoates Produced in Multistage Chemostat.

A two-stage chemostat cultivation was used to investigate the biosynthesis of functionalized medium-chain-length polyhydroxyalkanoate (mcl-PHA) in the β-oxidation weakened strain of Pseudomonas putida KTQQ20. Chemostats were linked in sequence and allowed separation of biomass production in the first stage from the PHA synthesis in the second stage. Four parallel reactors in the second stage provided identical growth conditions and ensured that the only variable was the ratio of decanoic acid (C10) to an unusual PHA monomer precursor, such as 10-undecenoic acid (C11:1) or phenylvaleric acid (PhVA). Obtained PHA content was in the range of 10 to 25 wt%. When different ratios of C10 and C11:1 were fed to P. putida, the produced PHA had a slightly higher molar ratio in favor of C11:1-based 3-hydroxy-10-undecenoate. However, in case of PhVA a significantly lower incorporation of 3-hydroxy-5-phenylvalerate over 3-hydroxydecanoate took place when compared to the ratio of their precursors in the feed medium. A result that is explained by a less efficient uptake of PhVA compared to C10 and a 24% lower yield of polymer from the aromatic fatty acid ( = 0.25). In addition, PHA isolated from cultivations with PhVA resulted in the number average molecular weight two times lower than the PHA produced from C10 alone. Detection of products from PhVA metabolism in the culture supernatant showed that uptaken PhVA was not entirely converted into PHA, thus explaining the difference in the yield polymer from substrate. It was concluded that PhVA or its related metabolites increased the chain transfer rate during PHA biosynthesis in P. putida KTQQ20, resulting in a reduction of the polymer molecular weight.

Kinetics of Radical Chain Polymerization: 1. Time-Dependent Distributions of Macroradicals and Oligomers

Numerical and analytical solutions of kinetic equations and the relevant equations for the moments of distribution of macroradicals and oligomers during radical chain polymerization are presented. It has been shown that the initial chain growth occurs in the ballistic mode involving first-generation primary radicals. The chain transfer in which a macroradical, reacting with a solvent, forms an oligomer and the primary radical of the next generation, causes a transition from the ballistic to the diffusion mode in which distributions of chains of different generations are mixed. Time-dependent distributions have been found for chain propagation and transfer rate constants independent of chain length.

Employing Heterocyclic Hypervalent Iodine Compounds with ICl Bonds as Initiators and Chain Transfer Agents in the Synthesis of Branched Polymers

AbstractHeterocyclic hypervalent (HV) iodine(III) compounds with ICl bonds and various substituents at the N atom are synthesized and found to be very efficient chain transfer agents in the polymerization of styrene with transfer coefficients exceeding that of CCl4 by 2–3 orders of magnitude, depending on the structure. The chain transfer rate coefficients are also determined. Due to the presence of thermally labile HV bonds, the compounds degrade homolytically upon heating and can initiate radical polymerization. For instance, 1‐chloro‐2‐hexyl‐1,2‐benziodazol‐3(2H)‐one, is used in the polymerization of styrene, which yields low molecular weight polymers with alkyl chloride groups at the α‐ (initiation) and the ω‐chain ends (transfer). Chain‐end functionalization reactions with azide and chain extension under low‐catalyst‐concentration atom transfer radical polymerization (ATRP) conditions of the prepared telechelic polymers are carried out. The same initiator/chain transfer agent is successfully employed in the synthesis of highly branched polymers with multiple alkyl chloride‐type chain ends when added to mixtures of styrene and 1,4‐divinylbenzene containing 10–80 mol% of the divinyl crosslinker, or even pure crosslinker. In all cases, soluble hyperbranched polymers are obtained up to moderate monomer conversions. The effects of crosslinker and HV iodine(III) compound concentrations on the polymerization outcome are studied systematically.

Dynamic Monte Carlo Simulation of Olefin Block Copolymers (OBCs) Produced via Chain‐Shuttling Polymerization: Effect of Kinetic Rate Constants on Chain Microstructure

AbstractOlefin block copolymers (OBCs) are thermoplastic elastomers with unique statistical multiblock structures produced by chain‐shuttling polymerization. In this study, a dynamic Monte Carlo model is used to simulate the effect of changing chain‐shuttling (kCS), catalyst deactivation (kd), and chain transfer (ktr) rate constants on the microstructure of OBCs made in a semi‐batch reactor. The simulations show how each rate constant governs different aspects of the OBC chains and provide guidelines on how to fine‐tune OBC microstructure to achieve precisely designed multiblock structures.

Bifunctional Initiators as Tools to Track Chain Transfer during the CROP of 2-Oxazolines.

Detailed kinetic studies during the cationic ring-opening polymerization (CROP) of 2-ethyl-2-oxazoline (EtOx) are conducted using four bifunctional bromo-type initiators in N,N-dimethylformamide (DMF) at 140 °C. Serving as models to quantify chain transfer to monomer occurring during the CROP initiated by monofunctional initiators, size exclusion chromatography (SEC) resolves a second molar mass distribution with lower molar mass at initial [monomer] to [initiation site] ratios ([M]0 /[I]0 ) of 25, while the resolution is insufficient at [M]0 /[I]0 of 10. Slightly slow initiation is revealed at [M]0 /[I]0 = 25, which prohibits the derivation of chain transfer rates by fitting of the size exclusion chromatography (SEC) data. Although conventional kinetic plots give no indication of significant amounts of chain transfer, the molar mass distributions resolved by SEC can unambiguously be identified as such by matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) in both the high as well as the low m/z regions of the mass spectra.

Modeling and Experimentation of RAFT Solution Copolymerization of Styrene and Butyl Acrylate, Effect of Chain Transfer Reactions on Polymer Molecular Weight Distribution

AbstractChain transfer reactions widely exist in the free radical polymerization and controlled radical polymerization, which can significantly influence polymer molecular weight and molecular weight distribution. In this work, the chain transfer reactions in modeling the reversible addition–fragmentation transfer (RAFT) solution copolymerization are included and the effects of chain transfer rate constant, monomer concentration, and comonomer ratio on the polymerization kinetics and polymer molecular weight development are investigated. The model is verified with the experimental RAFT solution copolymerization of styrene and butyl acrylate, with good agreements achieved. This work has demonstrated that the chain transfer reactions to monomer and solvent can have significant impacts on the number‐average molecular weight (Mn) and dispersity (Ð).

Steric and Solvation Effects on Polymerization Kinetics, Dormancy, and Tacticity of Zr-Salan Catalysts

1-Hexene polymerization using four zirconium-based amine bis(phenolate) catalysts, Zr[2-R-4-tBu-ONNO]Bn2 (where R = methyl (1), ethyl (2), isopropyl (3), and tert-butyl (4)), was examined to establish the effect of ligand sterics on kinetics and stereocontrol of olefin polymerization. For each catalyst, a rich data set was obtained including monomer consumption, molecular weight evolution, end-group analysis, and active site counts. A set of reaction specific rate constants was determined for catalysts 2–4. In addition to the standard elementary reaction steps of initiation, propagation, mis-insertion, and chain transfer, these catalysts undergo isomerization leading to dormancy. This isomerization is particularly prominent in bromobenzene and for less sterically hindered complexes. Across the series 2–4, ligand steric properties have a systematic effect on both insertion and chain transfer rate constants. This relationship was rationalized using the Sterimol steric parameters. The rates of propagation an...

Synthesis of random and block copolymers of vinyl chloride and vinyl acetate by RAFT miniemulsion polymerizations mediated by a fluorinated xanthate

ABSTRACTReversible addition–fragmentation chain transfer miniemulsion (co)polymerizations of vinyl acetate (VAc) and vinyl chloride (VC) are conducted in the presence of a fluorinated xthanate (X1). VAc miniemulsion polymerization can be well controlled by X1, and PVAc with small polydispersity index (PDI, <1.20) are obtained. X1 also shows well mediative effect to VC‐VAc miniemulsion copolymerization, while the PDI of VC‐VAc copolymer is greater than that of PVAc since a chain transfer rate to VC is greater than that to VAc. PVAc‐b‐PVC copolymers are synthesized by VC miniemulsion polymerizations mediated by X1‐terminated PVAc. PDIs of PVAc‐b‐PVC copolymers are greater than that of PVAc and VC‐VAc random copolymers with close monomer compositions, and increase with the increase of VC conversion. This is caused by the increased chain transfer to monomer and the formation of monomer‐rich and polymer‐rich phases during the VC polymerization stage. As‐prepared PVAc‐b‐PVC copolymers exhibit a micro‐phase separated morphology. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45074.

Effect of transfer agent, temperature and initial monomer concentration on branching in poly(acrylic acid): A study by 13C NMR spectroscopy and capillary electrophoresis

Branching has been investigated in poly(acrylic acid) synthesized by conventional radical polymerization with and without chain transfer agent (CTA) at different temperatures and initial monomer concentrations. The average number of branches per monomer unit (i.e. degree of branching) was quantified by solution-state 13C NMR spectroscopy. The heterogeneity of branching (dispersity of the electrophoretic mobility distributions) was measured by capillary electrophoresis in the critical conditions (CE-CC). The degree of branching (DB) increases with the reaction temperature due to a rise in the frequency of reactions leading to branches, while the heterogeneity of branching remains steady. DB is lower in polymer synthesized with CTA. This decrease is due to either the CTA quenching the mid-chain radicals or a reduction of the rate of chain transfer to polymer relative to (chain-end) propagation. No influence of initial monomer concentration on DB and on the heterogeneity of branching was observed.

Free Radical Polymerization Behavior of the Vinyl Monomers from Plant Oil Triglycerides

A one-step method of plant oil direct transesterification was used to synthesize new vinyl monomers from sunflower (SFM), linseed (LSM), soybean (SBM), and olive (OVM) oils. The degree of unsaturation in plant oil fatty acids was used as a criterion to compare the free radical polymerization behavior of new monomers. The number-average molecular weight of plant oil-based homopolymers synthesized in toluene in the presence of AIBN at 75 °C varies at 11 000–25 000 and decreases as follows: poly(OVM) > poly(SFM) > poly(SBM) > poly(LSM), corresponding to increasing degree of unsaturation in the monomers. Rate of polymerization depends noticeably on the degree of unsaturation in monomers. Due to the allylic termination, chain propagation coexists with effective chain transfer during polymerization. The obtained values of CM (ratio of chain transfer and propagation rate constants) depends on monomer structure as follows: CM(LSM) > CM(SBM) > CM(SFM) > CM(OVM). 1H NMR spectroscopy shows that the fraction of the r...

Ethylene Polymerizations Using Parallel Pressure Reactors and a Kinetic Analysis of Chain Transfer Polymerization

We demonstrate a method for high-throughput catalyst screening using a parallel pressure reactor starting from the initial synthesis of a nickel α-diimine ethylene polymerization catalyst. Initial polymerizations with the catalyst lead to optimized reaction conditions, including catalyst concentration, ethylene pressure and reaction time. Using gas-uptake data for these reactions, a procedure to calculate the initial rate of propagation (kp) is presented. Using the optimized conditions, the ability of the nickel α-diimine polymerization catalyst to undergo chain transfer with diethylzinc (ZnEt2) during ethylene polymerization was investigated. A procedure to assess the ability of the catalyst to undergo chain transfer (from molecular weight and 13C NMR data), calculate the degree of chain transfer, and calculate chain transfer rates (ke) is presented.

Ethylene Polymerizations Using Parallel Pressure Reactors and a Kinetic Analysis of Chain Transfer Polymerization.

We demonstrate a method for high-throughput catalyst screening using a parallel pressure reactor starting from the initial synthesis of a nickel α-diimine ethylene polymerization catalyst. Initial polymerizations with the catalyst lead to optimized reaction conditions, including catalyst concentration, ethylene pressure and reaction time. Using gas-uptake data for these reactions, a procedure to calculate the initial rate of propagation (kp) is presented. Using the optimized conditions, the ability of the nickel α-diimine polymerization catalyst to undergo chain transfer with diethylzinc (ZnEt2) during ethylene polymerization was investigated. A procedure to assess the ability of the catalyst to undergo chain transfer (from molecular weight and 13C NMR data), calculate the degree of chain transfer, and calculate chain transfer rates (ke) is presented.

Why Are Organotin Hydride Reductions of Organic Halides So Frequently Retarded? Kinetic Studies, Analyses, and a Few Remedies

Kinetic data for reduction of organic halides (RX) by tri-n-butylstannane (SnH) reveal a serious flaw in the current view of the kinetic radical chain: the tacit but unproven assumption that the speed of reaction is determined by the slowest propagation step. Our results show this is rarely true for reductive chains and that the observed rate is in fact controlled by unseen side-reactions of propagating R(•) and Sn(•) radicals with the solvent (notably, benzene!) or solvent impurities (e.g., trace benzophenone dryness indicator in THF) or, crucially, with allylic-CH and conjugated unsaturated groups in substrates and products. Most R(•) and/or Sn(•) radicals are therefore converted into relatively inert delocalized species A(•) and/or B(•) that inhibit the chain. Retardation in the degraded chain is given by a simple sum of terms, each being the ratio of the chain-transfer rate divided by the rate of chain-return. The model kinetic equation is linear and easy to ratify, interpret, and apply: to calculate retarding rate constants, optimize reaction conditions, and identify additives or "remedies" that repair the chain and accelerate reaction. The present work is thus expected to have a helpful impact on the practice and design of SnH radical chain based (and related) syntheses.