Propagation Rate Constants Research Articles

To overcome the unconventional polymerization behavior of single-site symmetrical metallocene catalyst in the presence of borate

The β-H transfer of a propagating chain shows an unconventional polymerization behavior with single-site catalysts. In this work, we seek to address these challenges in the presence of different alkylaluminum cocatalysts. Adjusting the amount and type of cocatalyst in the polymerization process can affect molecular weight distribution (MWD) and chain ends formed via β-H transfer. The cocatalyst's elevated triethylelaluminum (TEA) by more than 50 % resulted in a drop in isoprene (IP) concentration, Mw, and activity, while pure TEA exhibited a smaller [C*]/[Zr] % than both pure Triisobutylaluminum (TIBA) and TIBA/TEA mixture. These results indicate that the type of alkylaluminum and its varying ratio affect the activation of metallocene catalysts. Secondly, this study also includes chain termination and transfer reactions and how comonomers participate in overcoming these issues. For this complicated process, we additionally performed the quench-labeling metal-polymer bonds technique (quantitative experiments (catalyst's active site)) leading to building a kinetic model that plays a significant role in mechanistic studies. The quantitative of active sites results indicate that the lower propagation rate constant (kp) was increased by nearly 20 % with TEA (25 %), and continuously increased with the TEA amount, meaning that TEA is a noticeable essential component in the cocatalyst for higher kp. The higher kpE and kpIP with TIBA might be associated with faster propagation and lower chain transfer reactions to Al−iBu and active centers and faster re-initiation of Al−iBu. The active center and 3,4 connections of IP are increased with increased TEA, meaning that the active site based on Al−Et bonds is facilitating more coordinated-to-IP through 3,4 connections. Finally, to clarify the impact of cocatalysts on MWD, a detailed theoretical splitting of the corresponding GPC was conducted. However, compared to PE MWD, TEA decreases the MWD of the polymers and becomes narrow. It is evident that introducing IP as a comonomer and TEA as a combined cocatalyst significantly reduces the chain transfer reaction that occurs during PE.

Real-time monitoring of vegetable oils photo-oxidation kinetics using differential photocalorimetry

This study introduced differential photocalorimetry (DPC) as a method for real-time monitoring of the photo-oxidation kinetics of vegetable oils. DPC measures the heat flow generated during the oxidation of oils upon light exposure. Experiments conducted with stripped linseed oil (SLSO), an oil depleted from its natural antioxidants, showed no induction time (τ). Conversely, spiking SLSO with increasing concentrations of trans-ferulic acid resulted in an induction time (τ) proportional to the antioxidant concentration (R2 = 0.99). A comparative study among different vegetable oils revealed that rice bran oil exhibited the highest resistant to photo-oxidation, followed by corn, soybean, and sunflower oils. The results are discussed in terms of sample oxidizability and antioxidant efficiency (A.E.), and validated through high-performance liquid chromatography with diode array detection (HPLC-DAD). Furthermore, the measured heat flow enabled the determination of the rates of inhibited (Rinh) and uninhibited (Runi) periods, as well as the rate constant of propagation (kp) and inhibition (kinh) reactions.

Influence of the reaction conditions on the Ziegler-Natta catalyzed ethylene polymerization: Kinetics and properties of the resulting polymers

This work conducts an investigation into how the polymerization conditions affect the kinetics of ethylene homopolymerization and the properties of the final polyethylene using a commercially available Ziegler-Natta catalyst with the formula TiCl4/MgCl2. By employing a mathematical model, we estimated the apparent propagation (kp), activation (ka), and deactivation (kd) rate constants under different reaction conditions, including cocatalyst and catalyst concentration, hydrogen/ethylene ratio, and polymerization temperature. Additionally, we examined the properties of the resulting polyethylene products, such as particle size, molecular weight (Mw), melting temperature, and % crystallinity. We found that the trend of polymer particle size was similar to that of the propagation rate constant under the employed polymerization conditions. Our results indicated that parameters enhancing the polymerization rate also increased kp and reduced crystallinity. The quantitative rate constants and polymer characteristics reported in this study provide valuable insights for industrial polyethylene manufacturers, allowing them to fine-tune plant operation conditions and achieve precise control over polymer particle properties. Furthermore, Density Functional Theory (DFT) calculations provided additional insights into the polymerization process, particularly regarding the role of hydrogen as a chain transfer agent and the fundamental significance of MgCl2, emphasizing the need for a minimal-dimensional model to evaluate this role.

Glycine N-Thiocarboxyanhydride: A Key to Glycine-Rich Protein Mimics.

Glycine-rich proteins (GRPs) containing a high content of glycine residues (>30%) possess unique structural stability. However, the controllable synthesis of glycine-rich poly(amino acid)s (PAAs) to mimic GRPs has not been realized yet due to the poor solubility of polyglycine segments. We developed a novel method to synthesize glycine-rich PAAs via the controlled ring-opening copolymerization of glycine-N-thiocarboxyanhydrides (Gly-NTA) with sarcosine-N-carboxyanhydride and ε-Cbz-l-lysine-N-carboxyanhydride. The random copolymerization is evidenced by a kinetic study that shows that the propagation rate constant of Gly-NTA is close to those of comonomers. The copolymers exhibit predictable molecular weights between 4.5 and 24.6 kg/mol and tunable glycine incorporation, varying from 10.3 to 59.2%. Poly(Gly-r-Sar) samples with various glycine contents form nanoparticles or a hydrogel in water. Remarkably, the β-sheet folding of poly(Gly-r-Lys) remains intact in a neutral environment where the amine groups are protonated. Overall, the strategy paves the way to engineer glycine-rich PAAs and thereby expands their applications.

Mechanistic study on hydrogen effects in propylene polymerization with MgCl2-supported Ziegler-Natta catalysts: New evidences from active center counting and reaction kinetics

Propylene polymerizations catalyzed by MgCl2/Di/TiCl4-AlEt3/siloxane in the absence and presence of hydrogen were studied by determining the time-dependent changes of catalytic activity, number of active centers and active center distribution. Three types of active centers with high, medium and very low stereoselectivity were differentiated by fractionating the polymer into three parts. Chain propagation rate constant of each type of active centers was estimated by linear fitting/extrapolating the time-dependent change of apparent propagation rate constant. The centers with high (Ci*), medium (Cm*) and low (Ca*) stereoselectivity responded to addition of hydrogen differently. Adding hydrogen caused marked increase of Ci*, but its propagation rate constant (kpi) was evidently reduced. In contrast, numbers of Cm* and Ca* were only slightly affected, but their propagation rate constants were evidently enhanced by hydrogen. The different hydrogen responses of Ci* with those of Cm* and Ca* were explained by two kinds of hydrogen activation mechanisms.

Hydroxyl radical-initialized polymerization and degradation of N-vinylpyrrolidone in lipid and aqueous environments

Poly(N-vinylpyrrolidone) (PVP) is an industrial polymer that has many uses in cosmetic, pharmaceutical, and biomedical formulations due to its low toxicity. Nonetheless, the destruction of PVPs by free radicals such as HO• under physiological conditions and in the environment may result in the formation of dangerous compounds, especially in case of the further reaction of the transition state of the monomer N-vinylpyrrolidone (NVP) with HO•. A comprehensive study of the mechanism and kinetics of the radical reactions of the monomer NVP has not yet been carried out. Here we report on quantum chemical computations of the radical polymerization and degradation of the NVP in reactions with the hydroxyl radical in aqueous and lipidic media. It was found that the reaction of NVP with HO• radical has an overall rate constant of koverall(app) = 3.64×109 and 6.16×109 M−1 s−1 in pentyl ethanoate and water, respectively. The good agreement between the calculated rate constant in koverall(f) = 1.86×109 M−1 s−1 at pH ≈ 7.0) and experimental data (k(NVP + HO•) = 1.2–2.0 × 109 M−1 s−1 validates the accuracy of the computational method. The propagation rate constant (kp) was 3.80×103 M−1 s−1 in water, which is also in good agreement with experimental data under the studied conditions: kp(calculated)/kp(experimental) = 0.22−0.42. The RAF(C7)-FHT(C5-H) reaction was the primary mechanism for the radical initiation of NVP in the lipid medium, whereas the RAF(C6)-SET reaction was responsible for the initiation in an aqueous solution. Secondary interactions of the intermediates with the hydroxyl radical yielded a range of products that were assessed and found to be less hazardous to the environment than NVP.

Effects of Internal Electron Donor on Distribution and Reactivity of Active Centers in Ethylene/1‐Hexene Copolymerization with MgCl2‐Supported Ziegler‐Natta Catalyst

AbstractEthylene/1‐hexene copolymerization with two MgCl2‐supported Ziegler‐Natta catalysts containing no internal electron donor or diethylphthalate (DEP) is conducted for different polymerization time . Effects of DEP on active center distribution are studied by fractionating each copolymer sample into boiling n‐heptane soluble (C7‐sol) and insoluble (C7‐ins) fractions, and counting the number of active centers in the copolymer fractions . The main effect of introducing DEP in the catalyst are reduction in the Ti content and significant increase in the proportion of active centers producing C7‐ins fraction. The propagation rate constants of ethylene insertion (kpE) and 1‐hexene insertion (kpH) are respectively estimated by linear fitting/extrapolating the change of apparent propagation rate constants (kpi)a with polymer yield according to a simplified multi‐grain particle model. In both catalysts, kpE in the C7‐ins fraction is 9–12 times larger than that in the C7‐sol fraction, and kpH in the C7‐ins fraction is 3–4 times larger than that in the C7‐sol fraction. The two groups of active centers have distinctly different catalytic properties. Introducing DEP reduced the kpE and kpH values and the extent of diffusion limitation . In summary, addition of electron donor in MgCl2‐supported Z‐N catalyst significantly changed the active center distribution and catalytic properties of its two groups of active centers.

Random and block architectures of N-arylitaconimide monomers with methyl methacrylate

Abstract “Itaconimide” is the members of imide (–CO–NH–CO–) family with reactive exocyclic double bond and it is easily obtained from the renewable resource i.e. D-glucose. The polymerization of various N-arylitaconimide (NAI) monomers with methyl methacrylate (MMA) have been reported to improve the glass transition temperature (T g) and thermal stability of poly(methyl methacrylate) (PMMA). In literature, these studies have been done mostly using conventional free radical polymerization methods, which restricts the architecture of copolymers to “random” only. The block copolymers of NAI and MMA are an important due to the combination of glassy PMMA and thermally stable poly(NAI), which offers its applications for higher temperature service. The architectural control of polymers in provisions of its topology, composition, and various functionalities is possibly obtained using reversible-deactivation radical polymerizations (RDRPs). In RDRPs, the concentration of free radical is controlled in such a way that the termination reactions are minimized (normally in range of 1–10 mol%), and not allowed to obstruct with the desired architecture. However, this is possible by achieving (or by establishing) a rapid dynamic equilibrium between propagating radical and dormant species (i.e. R–X). Among all RDRPs, the atom transfer radical polymerization (ATRP) is very popular and adaptable method for the synthesis of polymers with specifically controlled architecture. Two different architectures of NAI and MMA copolymers are reported using ATRP process. The effect of various pedant groups on the rate constants of propagation (k p) and thermal properties NAI and MMA copolymers is studied. The poly(NAI-ran-MMA)-b-poly(MMA) are stable up to 200 °C and degraded in three steps. Whereas, the poly(NAI-ran-MMA)-b-poly(NAI) are stable up to 330 °C and degraded in two steps. The density functional theory methods are used for calculation of equilibrium constants (K ATRP) for the ATRP process for the series of laboratory synthesized alkyl halides. A good agreement was observed between the experimentally determined and theoretically calculated K ATRP values. The mechanistic studies are carried for poly(NAI-ran-MMA) copolymer system using statistical model discrimination method along with 1H decoupled 13C NMR spectroscopy. For studying the mechanism of copolymerization of NAI and MMA via ATRP methods, “trimer model or penultimate model” will be more accurate than “dimer model or terminal model”.

Influence of the Norbornene Anchor Group in Ru-Mediated Ring-Opening Metathesis Polymerization: Synthesis of Bottlebrush Polymers

Ring-opening metathesis polymerization (ROMP) mediated by Grubbs’ third-generation catalyst [G3, (H2IMes)(Cl)2(pyr)2RuCHPh] is widely used to make bottlebrush polymers by polymerization of a macromonomer (MM), typically a low molecular weight polymer functionalized with a norbornene. Termed the grafting-through method, this strategy requires a high degree of living character (“livingness”) to form well-defined bottlebrush polymers. Here, we studied how various anchor groups, the series of atoms connecting the polymerizable norbornene unit to the polymer side-chain, affect livingness in ROMP in a series of exo-norbornene polystyrene MMs. First, we calculated the HOMO and HOMO/LUMO gap energies of MM structures containing five different anchor groups using density functional theory methods, finding that these energies spanned a range of 10 kcal/mol. We then performed kinetics experiments on each MM with target backbone degrees of polymerization (Nbb) of 100 to measure the propagation rate constant (kp,obs) under identical conditions. A positive correlation between the HOMO energy and measured kp,obs values emerged, revealing a 7-fold variation in kp,obs values across the five MMs, suggesting different degrees of livingness among the anchor groups. A series of studies targeting Nbb values ranging from 100 to 2000 further highlighted these differences: The MMs with high kp,obs values reached higher conversions at high target Nbb values with lower dispersities (D̵) than the MMs with lower kp,obs values. Finally, we evaluated the synthesis of bottlebrush pentablock copolymers using the MMs at the two extremes by injecting an MM aliquot into a catalyst solution five consecutive times, allowing for polymerization of each block before the next injection. MM conversion at each step was higher, and the D̵ values for each block were lower for the MM with the highest kp anchor group compared to the lowest kp anchor group. Taken together, these studies highlight how the anchor group dramatically affects both kp and livingness in ROMP, which is crucial for the synthesis of precise bottlebrush (co)polymers.

Influence of the Norbornene Anchor Group in Ru-Mediated Ring-Opening Metathesis Polymerization: Synthesis of Linear Polymers

Ring-opening metathesis polymerization (ROMP) mediated by Grubbs’ first-generation catalyst [G1, (PCy3)2(Cl)2RuCHPh] and Grubbs’ third-generation catalyst [G3, (H2IMes)(Cl)2(pyr)2RuCHPh] can exhibit living characteristics for some monomer classes, most commonly substituted norbornenes. Here, we studied how various anchor groups, the series of atoms connecting the polymerizable norbornene unit to a functional group, affect livingness in ROMP in a series of small-molecule exo-norbornene monomers. We first designed and calculated the HOMO energy of 61 monomers using density functional theory methods, finding that these energies spanned a range of 25 kcal/mol. We then performed kinetics experiments using 1H NMR spectroscopy to measure the propagation rate constant (kp,obs) under identical conditions for eight selected monomers with different anchor groups across the range of HOMO energies. We observed a positive correlation between the HOMO energy or the HOMO/LUMO energy gap and measured kp,obs values for both catalysts, revealing a 30-fold and a 10-fold variation in kp,obs values across the series for G1 and G3, respectively. Interestingly, we observed a plateau for the three monomers with the highest HOMO energies for G3 catalyst, suggesting that above a certain level, the HOMO energy no longer influenced the rate-determining step under the conditions studied here. Chelation studies revealed that only one of the eight monomers showed measurable binding of electron-rich groups on the monomer to the catalyst, but with no apparent effect on kp. Finally, we utilized 1H NMR spectroscopy to measure the rate of catalyst decomposition in the presence of each monomer, a key termination pathway in ROMP. Ultimately, we determined that the anchor group did not substantially affect catalyst decomposition, a proxy for the termination rate constant (kt). In sum, these combined computational and experimental studies collectively demonstrate that livingness in ROMP of exo-norbornene monomers using G1 and G3 catalysts, as measured by relative kp/kt ratios, is primarily controlled by the kp of the anchor group, which is correlated with the HOMO energy.

Why only half of the added ansa-metallocene catalyst active in the E/P/diene polymerization: catalyst evaluation in terms of active center [Zr]/[C*] fraction and polymerization propagation rate constants

To understand how the silyl-bridged metallocene catalysts rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2 behave against dienes under the same reaction condition because of its importance as a commercial polymerization catalyst and ethylene propylene diene monomers (EPDM). Adding diene depressed the catalytic activity, especially 5-ethylidene-2-norbornene (ENB) exerted the most substantial deactivation effect. Firstly, we examine the (ENB, vinyl norbornene (VNB) and 4-vinylcyclohexene (VCH)) non-conjugated and conjugated (isoprene (IP), butadiene (BD)) diene and address how polymerization catalysts behave against these dienes. For example, the catalytic activity was enhanced with IP and BD (3–3.3106 gm/mmolMt·h) compared to ENB, VNB and VCH. The VNB incorporation rate was prolonged (5.4 mol%), but with IP and BD, it was relatively moderate. E/P/IP and E/P/BD with higher incorporation of E produced a higher MW, which means that the chain transfer reaction with ethylene is slower than P. Secondly, we address how the dienes exocyclic and exocyclicπ bonds of non-conjugated and conjugated properties of IP and BD affect the kinetic measurements such as active centers [Zr]/[C*] fraction, EPDM chain propagation, termination, and isomerization. Finally, we compare [Zr]/[C*] and kpPE, kpP and kpDienes for different EPDM. After collecting these kinetic parameters, we can describe the mechanism’s intricacy and the existence of considerable catalyst dormancy with dienes under identical reaction conditions.

Estimation of the chain propagation rate constants of propylene polymerization and ethylene‐1‐hexene copolymerization catalyzed with MgCl2‐supported Ziegler–Natta catalysts

AbstractIn olefin polymerization with MgCl2‐supported Ziegler–Natta (Z–N) catalysts, the apparent propagation rate constant (kp)a calculated by Rp = (kp)a [C*] CMe (CMe is equilibrium monomer concentration in the reaction system) declines with reaction time for gradually developed monomer diffusion limitation in the polymer/catalyst particles. In this work, a simplified multi‐grain particle model was proposed to build correlation between (kp)a and other kinetic parameters that can be determined experimentally. Rate profiles of propylene polymerization and ethylene‐1‐hexene copolymerization by three MgCl2‐supported Z–N catalysts were determined, and the (kp)a data was calculated using [C*] determined by quench‐labelling the propagation chains with acyl chloride. Decline of (kp)a in each polymerization process was precisely fitted by the linear correlation between lg(kp)a and [(ρcatmp)/(ρpmcat) + 1]1/3 developed on the particle model. Real propagation rate constant (kp) was estimated by extrapolating the fitting line to the starting point of polymerization, where no concentration gradient exists. According to the particle model, the slope of the lg(kp)a versus [(ρcatmp)/(ρpmcat) + 1]1/3 line (lgd) represents the degree of monomer diffusion limitation. Variations of parameter d found in the studied reaction systems can be reasonably explained based on the knowledge of olefin diffusion in the polymer phase.

Optimization of Grade Transitions in Bulk Poly(propylene) Polymerizations

AbstractIn the present paper, a dynamic optimization problem regarding grade transitions in bulk poly(propylene) polymerization processes is formulated and solved for the first time. Initially, a detailed dynamic process model is presented and implemented, comprising mass and energy balances, some of the polymer properties (such as the melting flow index and the xylene solubles) and regulatory control loops. Additionally, the effects of cocatalyst and electron donor on the propagation rate constant are taken into account. Then, the dynamic optimization problem is formulated and an evolutionary algorithm is used to solve the resulting nonlinear programming problem. It is shown that there is significant coupling among the manipulated variables and the controlled performance and polymer property variables, which adds complexity to the grade transition problem and demands the simultaneous manipulation of multiple variables during transitions. Despite the inherent open‐loop unstable nature of the analyzed process, it is shown that smooth grade transition trajectories can be accomplished through proper adjustment of the objective function weights. Finally, it is shown that the obtained optimum trajectories can significantly diminish the transition time, which can be of paramount importance for the plant economics.

Validation of an Extended Kinetic Model of Free‐RadicalN‐Vinylpyrrolidone Polymerization

AbstractTo predict the polymer properties produced by free‐radical polymerization ofN‐vinylpyrrolidone (NVP) in aqueous solution a detailed kinetic model has been developed. The kinetic model allows to calculate the chain length distribution, the number of branching points, and the number of terminal double bonds (TDB). The latter is accounted for since TDBs are a precondition for branching. While monomer conversion can be predicted sufficiently using independently determined rate constants for propagation and termination, here the predictions of structural properties by a newly developed extended kinetic model to experimental findings are compared. Polymer produced in a continuous stirred tank reactor is analyzed by gel permeation chromatography (GPC), field flow fractionation (FFF), and high‐pressure liquid chromatography (HPLC).

Catalytic effect of DMSO in metal‐catalyzed radical polymerization mediated by disproportionation facilitates living and immortal radical polymerizations

AbstractDMSO, an interesting solvent for copper‐catalyzed living radical polymerization (LRP) mediated by disproportionation, does not exhibit the greatest disproportionation of Cu(I)X into Cu(0) and Cu(II)X2. Under suitable conditions, DMSO provides 100% conversion and absence of termination, facilitating the development of complex‐architecture methodologies by living and immortal polymerizations. The mechanism yielding this level of precision is being investigated. Here we compare Cu(0)‐wire‐catalyzed LRP of methyl acrylate mediated by disproportionating ligands tris(2‐dimethylaminoethyl)amine, Me6‐TREN, tris(2‐aminoethyl)amine, TREN, and Me6‐TREN/TREN = 1/1 in presence of eight disproportionating solvents, some more efficient than DMSO in disproportionation. Unexpectedly, we observed that all solvents increased the rate of polymerization when monomer concentration decreased. This reversed trend from that of conventional LRPs demonstrates catalytic effect for disproportionating solvents. Above a certain concentration, the classic concentration‐rate dependence was observed. The external order of reaction of the apparent rate constant of propagation, kpapp on solvent concentration demonstrated the highest order of reaction for the least disproportionating DMSO. Of all solvents investigated, DMSO has the highest ability to stabilize Cu(0) nanoparticles and therefore, yields the highest activity of Cu(0) nanoparticles rather than their greatest concentration. The implications of the catalytic effect of solvent in this and other reactions were discussed.

Kinetic Modeling of a Poly(N-vinylcaprolactam-co-glycidyl methacrylate) Microgel Synthesis: A Hybrid In Silico and Experimental Approach

Synthesizing microgels with new functionalities is vital for applications in various disciplines; yet microgel synthesis kinetics are mostly unknown. We present a bottom-up approach to model the synthesis of N-vinylcaprolactam-based microgels functionalized with glycidyl methacrylate. The existing synthesis model requires parameter values for unknown reaction rates, which we estimate by a hybrid approach based on quantum chemical calculations and experimental data. Using quantum mechanics, we compute propagation rate constants and enthalpies of the underlying polymerization reactions. We estimate 7 out of 21 reaction parameter values using the reaction calorimetry measurements and a mechanistic process model. Our hybrid approach averages a coefficient of determination of 0.97 for the enthalpy transfer rate over time during microgel synthesis. Our approach illustrates that quantum chemistry methods and physical experiments can be integrated into models toward better understanding and designing of pVCL/GMA microgel synthesis processes.

The alkoxy radical polymerization of N-vinylpyrrolidone in organic solvents: theoretical insight into the mechanism and kinetics.

Poly(N-vinylpyrrolidone) (PVP) is a polymer with many applications in cosmetic, pharmaceutical, and biomedical formulations due to its minimal toxicity. PVP can be synthesized through radical polymerization in organic solvents; this well-known industrial process is thoroughly characterized experimentally, however, quantum chemical modeling of the process is scarce: the mechanism and kinetics have not been thoroughly investigated yet. In this work, the mechanism and kinetics of the alkoxy radical polymerization of N-vinylpyrrolidone in organic solvents, namely isopropanol (IP) and toluene (TL), were successfully modeled by computational chemistry. The initiator radicals di-tert-butyl peroxide (TBO˙) and dicumyl peroxide (CMO˙) as well as the solvents isopropanol and toluene, were shown to be capable of assisting in the initiation reactions. The rate constant was influenced by the combination of initiators and solvent and the values of the rate constant of propagation were approximately 101-103 M-1 s-1. The radical polymerization of NVP with dicumyl peroxide as an initiator was comparable to that of di-tert-butyl peroxide in all of the examined organic solvents, whereas the solvents had less of an effect.

Determination of kinetic parameters of N-vinylpyrrolidone radical polymerization in water by Pulsed Electron Polymerization−Size Exclusion Chromatography (PEP−SEC)

Propagation step of radical polymerization of N-vinylpyrrolidone (NVP) in aqueous solutions has been studied by a recently introduced method, Pulsed Electron Polymerization−Size Exclusion Chromatography (PEP−SEC). Propagation rate constants have been determined at various initial monomer concentrations and reaction temperatures. It has been shown that the kinetic data, their concentration dependence, activation energy (Ea) and preexponential factor (A) in the Arrhenius equation obtained by PEP−SEC are very similar to those obtained by the well-established Pulsed Laser Polymerization−Size Exclusion Chromatography (PLP−SEC). These results support the correctness of the new PEP−SEC technique, which is expected to have some advantages over the classical PLP−SEC, in particular by its applicability to studying polymerization in nontransparent systems and lack of any chemical initiators and can be developed into a method alternative or complementary to PLP−SEC.

Progress toward Polymerization Reaction Monitoring with Different Dienes: How Small Amounts of Dienes Affect ansa-Zirconocenes/Borate/Triisobutylaluminium Catalyst Systems.

The objectives of this work were to address the fundamental characteristics of ansa-zirconocene catalyzed E/diene copolymerization and E/diene/1-hexene and E/diene/propylene terpolymerizations, and the quantitative relationship between diene structure and polymer chain propagation rate constant in term of quantifiable catalytic active sites. One of the most important but unknown factors in olefins ansa-zirconocene complexes is the distribution of the catalyst between sites actively participating in polymer chain formation and dormant sites. A set of ethylene/dienes copolymerizations, and ethylene/dienes/1-hexene and ethylene/dienes/1-hexene terpolymerizations catalyzed with ansa-zirconocenes/borate/triisobutylaluminium (rac-Et(Ind)2ZrCl2/[Ph3C][B(C6F5)4]/triisobutylaluminium (TIBA) were performed in toluene at 50 °C To determine the active center [C*]/[Zr] ratio variation in the copolymerization of E with different dienes and their terpolymerization with 1-hexene and propylene, each polymer propagation chain ends were quenched with 2-thiophenecarbonyl, which selectively quenches the metal–polymer bonds through acyl chloride. The ethylene, propylene, 1-hexene, and diene composition-based propagation rate constants (kpE, kpP, kp1-H, and kpdiene), thermal (melting and crystalline) properties, composition (mol% of ethylene, propylene, 1-hexene, and diene), molecular weight, and polydispersity were also studied in this work. Systematic comparisons of the proportion of catalytically [Zr]/[C*] active sites and polymerization rate constant (kp) for ansa-zirconocenes catalyzed E/diene, E/diene/1-hexene, and E/diene/propylene polymerization have not been reported before. We evaluated the addition of 1-hexene and propylene as termonomers in the copolymerization with E/diene. To make a comparison for each diene under identical conditions, we started the polymerization by introducing an 80/20 mole ratio of E/P and 0.12 mol/L of 1-hexene in the system. The catalyst behavior against different dienes, 1-hexene, and propylene is very interesting, including changes in thermal properties, cyclization of 1-hexene, and decreased incorporation of isoprene and butadiene, changes in the diffusion barriers in the system, and its effect on kp.

Living polymerization in nano-scale volumes. Impact of process conditions on polymerization kinetics and product characteristics

Living polymerization processes, irreversible and reversible, proceeding in a large number of isolated (no mass exchange) nano-scale reactors (droplets) were modeled using stochastic (Monte Carlo) and deterministic simulations and analytical solutions of derived mathematical equations. Monomer and living unimer used as initiator were redistributed in droplets uniformly or accordingly to the Poisson distribution, resulting in nanoreactors containing a small number of growing chains. Stochasticity of reactions involving low number of molecules affects the concentration of monomer and chain length distributions in individual droplets, both differing from ones accounted in macroscopic system. The developed mathematical description, based on values of rate constants of propagation (kp) and depropagation (kd) reactions and on initial monomer and living unimer concentrations, as well as numerical simulations, allow predicting kinetics of the process and of several characteristics of the products resulting therefrom, e.g. chain length distribution. Moreover, they allow also following evolution of droplet subpopulations that differ in composition. Moreover, for the reversible process the equilibrium monomer concentration in a droplets system [M]eq can be calculated. As living ionic and coordination polymerization and the controlled radical polymerization in nano-scale dispersions are rather little explored the theoretical predictions shown in this work could facilitate their further development.