Anionic Polymerization Of Styrene Research Articles

Effect of solvent on the initiation mechanism of living anionic polymerization of styrene: A computational study

For living anionic polymerization (LAP), solvent has a great influence on both reaction mechanism and kinetics. In this work, by using the classical butyl lithium-styrene polymerization as a model system, the effect of solvent on the mechanism and kinetics of LAP was revealed through a strategy combining density functional theory (DFT) calculations and kinetic modeling. In terms of mechanism, it is found that the stronger the solvent polarity, the more electrons transfer from initiator to solvent through detailed energy decomposition analysis of electrostatic interactions between initiator and solvent molecules. Furthermore, we also found that the stronger the solvent polarity, the higher the monomer initiation energy barrier and the smaller the initiation rate coefficient. Counterintuitively, initiation is more favorable at lower temperatures based on the calculated results of ΔGTS. Finally, the kinetic characteristics in different solvents were further examined by kinetic modeling. It is found that in benzene and n-pentane, the polymerization rate exhibits first-order kinetics. While, slow initiation and fast propagation were observed in THF due to the slow free ion formation rate, leading to a deviation from first-order kinetics.

General route to design polymer molecular weight distributions through flow chemistry

The properties of a polymer are known to be intrinsically related to its molecular weight distribution (MWD); however, previous methodologies of MWD control do not use a design and result in arbitrary shaped MWDs. Here we report a precise design to synthesis protocol for producing a targeted MWD design with a simple to use, and chemistry agnostic computer-controlled tubular flow reactor. To support the development of this protocol, we constructed general reactor design rules by combining fluid mechanical principles, polymerization kinetics, and experiments. The ring opening polymerization of lactide, the anionic polymerization of styrene, and the ring opening metathesis polymerization are used as model polymerizations to develop the reactor design rules and synthesize MWD profiles. The derivation of a mathematical model enables the quantitative prediction of the experimental results, and this model provides a tool to explore the limits of any MWD design protocol.

Practical Continuous‐Flow Controlled/Living Anionic Polymerization

AbstractA continuous‐flow reaction system was developed, allowing flow conditions of the entire system to be maintained at a predetermined constant level, which is one of the most significant factors for successful industrial application. Controlled/living anionic polymerization was selected as a model reaction since the characteristics of its polymer products, molecular weights, and molecular weight distributions are highly susceptible to changes in the relative flow rates of a monomer and initiator solutions. In flow microreactors, controlled/living anionic polymerization of styrene in tetrahydrofuran (THF)/hexane initiated by THF‐diluted n‐butyllithium (n‐BuLi) was examined. Poly(styrenes) of larger molecule sizes such as Mn > 15 000 were successfully synthesized. After continuous operation for four hours, ca. 0.5 kg of the polymer was readily produced with narrow molecular weight distribution, demonstrating the applicability of this continuous‐flow system for controlled/living anionic polymerization on considerably large scale with a view to its industrial usage in the future.

Grafting‐from Afforded Cyclic Graft Copolymers from Cyclic Anionic Macroinitiator via Lithiation of Tolyl Groups

AbstractCyclic graft copolymers consisting of poly(p‐methylstyrene) backbone and polystyrene branches with relatively low molecular weight distribution are synthesized with grafting‐from approach by living anionic polymerization of styrene from lithiated cyclic poly(p‐methylstyrene)s as multifunctional anionic macroinitiators for vinyl polymerizations. Precursors of the macroinitiators are prepared by ring‐closing metathesis reaction of α,ω‐divinyl‐terminated telechelic polymers. Subsequently, selective lithiation of tolyl groups in the cyclic polymers is conducted by s‐BuLi in the presence of tetramethylethylenediamine in cyclohexane in order to prepare the macroinitiators. Addition of styrene monomer into the cyclic macroinitiators provides shift in SEC to higher molecular weight due to graft polymerization from the macroinitiators to form cyclic graft copolymers. The unique polymer architecture of the obtained cyclic graft copolymers is confirmed by unimolecular observation by using atomic force microscopy.

The Mechanism of the Propagation in the Anionic Polymerization of Polystyryllithium in Non-Polar Solvents Elucidated by Density Functional Theory Calculations. A Study of the Negligible Part Played by Dimeric Ion-Pairs under Usual Polymerization Conditions.

The elementary processes occurring in the anionic polymerization of styrene with dimerically associated polystyryllithium (propagation during the anionic polymerization of dimeric polystyryllithium) in the gas phase and cyclohexane were studied using MX062X/6-31+G(d), a recently developed density functional theory (DFT) method and compared with the polymerization of styrene with non-associated polystyryllithium, which was described in a previous study. The most stable transition state in the reaction of styrene with dimeric polystyryllithium has a structure in which the side chains of styrene and the two chain end units of polystyryllithium are located in the same direction around the Li atom near the reactive site. The relative enthalpy for this transition state in cyclohexane is 28 kJ·mol−1, which is much lower than that for the reaction of non-associated polystyryllithium (51 kJ·mol−1). However, the relative free energy (which determines the rate constant) for the former is 93 kJ·mol−1, which is greater than that for the latter by 7 kJ·mol−1, indicating that the latter reaction (reaction with non-associated polystyryllithium) is advantageous over the former (reaction with dimeric polystyrylllithium). Their rates of reaction are also affected by initiator concentrations; in the case of reactions with low initiator concentrations, from which high molecular weight polymers are usually obtained, the rate of reaction corresponding to non-associated polystyryllithium is much larger than that corresponding to dimeric polystyryllithium.

Molecular Weight Distribution of Polymers Produced by Anionic Polymerization Enables Mixability Evaluation

In the anionic polymerization of styrene using a flow microreactor, there was a strong correlation between the molecular weight distribution (Mw/Mn) of the polymer and the mixing speed. By taking advantage of this relationship, a new type of mixability evaluation was developed using the flow microreactor system. The new method allowed the mixability to be evaluated at 0 °C or a lower temperature with high accuracy. With the ability to be applied for a wider range of reaction conditions, it offers a great advantage over other evaluation procedures such as the Dushman reaction, which requires reaction temperatures to be above 0 °C. The presented method is a promising alternative as a new evaluation technique for mixing efficiency.

ω-Norbornenyl Macromonomers: In Situ Synthesis by End-Capping of Living Anionic Polymers Using a Norbornenyl-Functionalized α-Phenyl Acrylate and Their Ring-Opening Metathesis Polymerization

An operationally simple approach to preparation of ω-norbornenyl macromonomers (MMs) is reported. Reaction of exo-N-(6-hydroxyhexyl)-5-norbornene-2,3-dicarboximide or exo-N-(10-hydroxydecyl)-5-norbornene-2,3-dicarboximide with α-phenyl acrylate (α-PhA) led to novel end-capping agents, NBxPhA [x is 6 (n-hexyl) or 10 (n-decyl)]. Living anionic polymerization of styrene and methyl methacrylate followed by capping with NBxPhA yielded the desired MMs, ω-norbornenyl polystyrene (NBxPS) and ω-norbornenyl poly(methyl methacrylate) (NBxPMMA). These MMs, formed with controlled molecular weights (Mn = 2–5 kDa) and low dispersity (Đ = 1.02–1.07), upon ring-opening metathesis polymerization (ROMP) resulted in P(NB-g-PS) and P(NB-g-PMMA) bottlebrush homopolymers with ∼95% and ∼75% yield, respectively, signifying efficient end-capping efficiency. The factors affecting synthesis of NBxPS and NBxPMMA and their subsequent ROMP, such as [NBxPhA]/[sec-BuLi] ratio, the length of alkyl spacer, and varying molecular weights of ...

Direct through anionic, cationic, and radical active species: Terminal carbon–halogen bond for “controlled”/living polymerizations of styrene

ABSTRACTIn this work, we examined the synthesis of novel block (co)polymers by mechanistic transformation through anionic, cationic, and radical living polymerizations using terminal carbon–halogen bond as the dormant species. First, the direct halogenation of growing species in the living anionic polymerization of styrene was examined with CCl4 to form a carbon–halogen terminal, which can be employed as the dormant species for either living cationic or radical polymerization. The mechanistic transformation was then performed from living anionic polymerization into living cationic or radical polymerization using the obtained polymers as the macroinitiator with the SnCl4/n‐Bu4NCl or RuCp*Cl(PPh3)/Et3N initiating system, respectively. Finally, the combination of all the polymerizations allowed the synthesis block copolymers including unprecedented gradient block copolymers composed of styrene and p‐methylstyrene. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 465–473

Nanopatterning via Self-Assembly of a Lamellar-Forming Polystyrene-block-Poly(dimethylsiloxane) Diblock Copolymer on Topographical Substrates Fabricated by Nanoimprint Lithography.

The self-assembly of a lamellar-forming polystyrene-block-poly(dimethylsiloxane) (PS-b-PDMS) diblock copolymer (DBCP) was studied herein for surface nanopatterning. The DBCP was synthesized by sequential living anionic polymerization of styrene and hexamethylcyclotrisiloxane (D3). The number average molecular weight (Mn), polydispersity index (Mw/Mn) and PS volume fraction (φps) of the DBCP were MnPS = 23.0 kg mol−1, MnPDMS = 15.0 kg mol−1, Mw/Mn = 1.06 and φps = 0.6. Thin films of the DBCP were cast and solvent annealed on topographically patterned polyhedral oligomeric silsesquioxane (POSS) substrates. The lamellae repeat distance or pitch (λL) and the width of the PDMS features (dL) are ~35 nm and ~17 nm, respectively, as determined by SEM. The chemistry of the POSS substrates was tuned, and the effects on the self-assembly of the DBCP noted. The PDMS nanopatterns were used as etching mask in order to transfer the DBCP pattern to underlying silicon substrate by a complex plasma etch process yielding sub-15 nm silicon features.

Anionic Polymerization of Styrene and 1,3-Butadiene in the Presence of Phosphazene Superbases.

The anionic polymerization of styrene and 1,3-butadiene in the presence of phosphazene bases (t-BuP4, t-BuP2 and t-BuP1), in benzene at room temperature, was studied. When t-BuP1 was used, the polymerization proceeded in a controlled manner, whereas the obtained homopolymers exhibited the desired molecular weights and narrow polydispersity (Ð < 1.05). In the case of t-BuP2, homopolymers with higher than the theoretical molecular weights and relatively low polydispersity were obtained. On the other hand, in the presence of t-BuP4, the polymerization of styrene was uncontrolled due to the high reactivity of the formed carbanion. The kinetic studies from the polymerization of both monomers showed that the reaction rate follows the order of [t-BuP4]/[sec-BuLi] >>> [t-BuP2]/[sec-BuLi] >> [t-BuP1]/[sec-BuLi] > sec-BuLi. Furthermore, the addition of t-BuP2 and t-BuP1 prior the polymerization of 1,3-butadiene allowed the synthesis of polybutadiene with a high 1,2-microstructure (~45 wt %), due to the delocalization of the negative charge. Finally, the one pot synthesis of well-defined polyester-based copolymers [PS-b-PCL and PS-b-PLLA, PS: Polystyrene, PCL: Poly(ε-caprolactone) and PLLA: Poly(L-lactide)], with predictable molecular weights and a narrow molecular weight distribution (Ð < 1.2), was achieved by sequential copolymerization in the presence of t-BuP2 and t-BuP1.

Enhancement of mechanical and optical performance of commercial polystyrenes by blending with siloxane‐based copolymers

ABSTRACTWell‐defined poly(styrene‐block‐dimethylsiloxane) copolymers (PS‐b‐PDMS) with low polydispersity index (Mw/Mn) and different compositions were synthesized by sequential anionic polymerization of styrene (S) and hexamethyl(ciclotrisiloxane) (D3) monomers. Synthesized PS‐b‐PDMS copolymers were characterized by 1H‐nuclear magnetic resonance, size exclusion chromatography, Fourier transform infrared spectroscopy, and transmission electron microscopy. The physicochemical characterization determined that block copolymers have molar mass values close to ∼135,000 g mol−1, narrow Mw/Mn &lt; 1.3, and chemical composition ranging from low to intermediate PDMS content. Blends of these copolymers with a commercial polystyrene (PS) were obtained by melt mixing and subsequently injection. Films obtained were flexible, and showed lower transparency than the original PS matrix. On the other hand, a 10 wt % incorporation of PS‐b‐PDMS copolymers leads to better mechanical performance by enhancing elongation at break (∼8.8 times higher) and opacity values (∼18 times higher). In addition, UV–Vis barrier capacity of the resulting blends is also increased (up to 400% higher). © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45122.

Precise Synthesis and Surface Characterization of End‐Functionalized Polystyrene with Perfluoroalkyl Group via Ionic Bond Formation of Diethylamino End‐Group with Perfluoroalkylcarboxylic Acid

Well‐defined polystyrene end‐functionalized with N,N‐diethylamino group (PS‐NEt2) is prepared by a living anionic polymerization of styrene, followed by an end‐capping reaction with a 1,1‐diphenylethylene derivative bearing with the corresponding functional group. The PS‐NEt2 is applied for the reaction with C8F17COOH in order to introduce the ionic‐bonded C8F17 group, i.e., C8F17COO−N+H(C2H5)2 at the polymer chain end. Surface characterization of the resulting polymer film is performed by an X‐ray photoelectron spectroscopy and a contact angle measurement. These results clearly show that the C8F17COO−N+H(C2H5)2 end‐group concentrates at the top of film surface similar to the original C8F17 group. The ionic‐bonded C8F17COOH is found to be removed by a treatment of the film surface with methanol. Moreover, the C8F17COO−N+H(C2H5)2 end‐group that remained inside film appears at the top of film surface by annealing the methanol‐treated film, indicating the surface reconstruction by environmental changes. image

New Vistas on the Anionic Polymerization of Styrene in Non-Polar Solvents by Means of Density Functional Theory.

The elementary processes of anionic styrene polymerization in the gas phase and in cyclohexane were studied using M062X (a recently developed density functional theory (DFT) method) combined with the 6-31+G(d) basis sets, in order to clarify the complicated phenomena caused by the association of the active chain-ends and elucidate the details of the polymerization mechanism. Three types of HSt2Li (a model structure of polystyryllithium chain-ends) were obtained; the well-known first structure in which Li is coordinated to the side chain, the second structure in which Li is coordinated to the phenyl ring, (both without the penultimate unit coordination), and the third structure in which Li is coordinated to both the chain-end unit and the penultimate styrene unit. Although the third HSt2Li is the most stable as expected, the free energy for the transition state of its reaction with styrene is higher than those for the other two transition states due to its steric hindrance. The free energy for the transition state of the reaction of the second HSt2Li with styrene is the lowest, suggesting that the route through it is the predominant reaction path. The penultimate unit effect, slower addition of styrene to HSt2Li than to HStLi, is attributed to coordination of the penultimate styrene units of the polystyryllithium dimer (one of the starting materials) to its Li atoms. The calculated enthalpy for the reaction barrier of the second HSt2Li with styrene in cyclohexane was found to agree with the observed apparent activation energy in benzene.

Synthesis of polyolefin‐block‐polystyrene through sequential coordination and anionic polymerizations

ABSTRACTTwo representative bulk polymers, polyolefin (PO) and polystyrene (PS), were molecularly connected to form PO‐block‐PS by sequentially performing coordination and anionic polymerizations in one pot. Ethylene/1‐octene copolymerization was performed using a typical ansa‐metallocene catalyst, rac‐[Me2Si(2‐methylindenyl)]2ZrCl2, in the presence of (benzyl)2zinc to grow PO‐chains at the Zn site. Anionic styrene polymerization was subsequently performed using nBuLi·(tmeda) (tmeda, N,N,N′,N′‐tetramethylethylenediamine) initiator to consecutively grow PS‐chains at the Zn site. The composition and the molecular weight of the PO‐blocks were controllable depending on the feed amounts of 1‐octene and (benzyl)2zinc (1‐octene fraction: ∼20, ∼40 wt %; PO‐Mw, 77,000–174,000) and the PS‐block size was also controlled (PS‐Mn, ∼21,000) with the complete conversion of the styrene monomer. Formation of block copolymers was evident in the GPC curves, TEM images, and strain‐stress curves. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3110–3118

"Shaping" the Future of Molecular Weight Distributions in Anionic Polymerization.

Varying molecular weight distributions (MWDs) have the potential to precisely tune polymer properties, but this approach remains relatively unexplored owing to a lack of synthetic methods that provide control over the exact makeup of a distribution. Herein, we report a simple and highly efficient strategy for addressing this challenge through temporal regulation of initiation in the anionic polymerization of styrene. This method yields unprecedented control over the shape of the polymer MWD and facilitates the synthesis of diblock copolymers with controlled MWD compositions. Importantly, we show that the MWD symmetry has a marked influence on the stiffness of poly(styrene-block-isoprene) copolymers, which demonstrates that varying MWD shape is an effective method for altering polymer properties.

Soft Graphoepitaxy for Large Area Directed Self‐Assembly of Polystyrene‐block‐Poly(dimethylsiloxane) Block Copolymer on Nanopatterned POSS Substrates Fabricated by Nanoimprint Lithography

Polyhedral oligomeric silsequioxane (POSS) derivatives have been successfully employed as substrates for graphoepitaxial directed self‐assembly (DSA) of block copolymers (BCPs). Tailored POSS materials of tuned surface chemistry are subject to nanoimprint lithography (NIL) resulting in topographically patterned substrates with dimensions commensurate with the BCP block length. A cylinder forming polystyrene‐block‐polydimethylsiloxane (PS‐b‐PDMS) BCP is synthesized by sequential living anionic polymerization of styrene and hexamethylcyclotrisiloxane. The patterned POSS materials provide a surface chemistry and topography for DSA of this BCP and after solvent annealing the BCP shows well‐ordered microphase segregation. The orientation of the PDMS cylinders to the substrate plane could be controlled within the trench walls by the choice of the POSS materials. The BCP patterns are successfully used as on‐chip etch mask to transfer the pattern to underlying silicon substrate. This soft graphoepitaxy method shows highly promising results as a means to generate lithographic quality patterns by nonconventional methods and could be applied to both hard and soft substrates. The methodology might have application in several fields including device and interconnect fabrication, nanoimprint lithography stamp production, nanofluidic devices, lab‐on‐chip, or in other technologies requiring simple nanodimensional patterns.

Preparation, characterization, and properties of poly(styrene-b-sulfonated isoprene)s membranes for proton exchange membrane fuel cells (PEMFCs)

A series of poly(styrene-b-isoprene) block copolymers (PSI) were synthesized by sequential anionic polymerization of styrene and isoprene. Poly(styrene-b-sulfonated isoprene) block copolymers (PSsI) were prepared via reacting the double bonds of the isoprene block with 1,4-dioxane/sulfur trioxide. The spherical-shaped ionic clusters within the PSsI membranes produce a comparable proton conductivity (10−1S/cm above 60°C) but benefits from approximately 50% lower methanol permeability than that of Nafion-117. Properties, such as proton conductivity and water content values, of PSsI membranes correlate highly to the content of the sulfonated isoprene block in PSsI samples even in the cases of similar IEC. As the hydrophilic block length is increased, the water content and proton conductivity also increased.

Self-assembly of thioether functionalized fullerenes on gold and their activity in electropolymerization of styrene

Fulleropyrrolidine alkylaromatic sulphides were found to form uniform coating on the gold surface through the thioether sulphur anchoring group and can initiate the anionic polymerization of styrene under electrochemical conditions.

Synthesis of high molecular weight poly(styrene-b-methyl methacrylate) using a plug flow reactor system by anionic polymerization

Sequential anionic polymerizations of styrene and methyl methacrylate and 2-vinylpyridine in tetrahydrofuran (THF) were conducted in a plug flow reactor system with a static mixer. Polymers [polystyrene (PS), Mn: 120×103 g·mol−1, Mw/Mn: 1.08), poly(methyl methacrylate) (PMMA, Mn: 28×103 g·mol−1, Mw/Mn: 1.09), poly(2-vinylpyridine) (P2VP, Mn: 53×103 g·mol−1, Mw/Mn: 1.08), and PS-b-PMMA (Mn: 117×103 g·mol−1, Mw/Mn: 1.12)] with a precisely controlled high molecular weight were obtained using a 1,1-diphenylhexyllithium initiator in a plug flow reactor system. PS-b-PMMA, PMMA, and P2VP were obtained in the presence of LiCl. The molecular weight distribution, which was related to the mixing efficiency of the static mixer, decreased with increasing flow rate. Additionally, the molecular weight of the polymers could be adjusted by varying the flow rates. Open image in new window

Lithium battery with solid polymer electrolyte based on comb-like copolymers

In this paper we report on the synthesis of comb-like copolymers as solid polymer electrolytes (SPE). The synthesis involved anionic polymerization of styrene (St) and 4-vinylanisole (VA) as the followed by grafting of poly(ethylene glycol) monomethyl ether methacrylate (PEGMA) by Atom Transfer Radical Polymerization (ATRP). The comb-like copolymer's structure was analyzed by Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). The membranes were made by solvent casting and the morphologies were analyzed by atomic forces microscopy (AFM) and scanning electron microscopy (SEM). We observed that a nano and micro phase separation occurs which improves ionic conductivity. The ionic conductivities were determined by AC Impedance, which showed that the SPEs have good conductivities (10−5 Scm−1) at room temperature owing to the negligible values (<10 kJ mol−1) of the activation energies for conductivity. The batteries with these polymers exhibit a capacity of 146 mAh g−1 at C/24, and no evidence of degradation after intense cycling was observed. However, poor cycle life was observed at C/6 and C/3, which is a consequence of several factors. We partially explain that behavior by arguing that whereas PEO lightly “solvates” Li+ thus slowing Li-ion mobility, and PEGMA chains “solvate” Li ions too strongly, trapping and inhibiting their mobility.