Living anionic copolymerization of isoprene and styrene, initiated by alkyllithium compounds in nonpolar solvent, typically yields commercially relevant tapered copolymers, widely used as thermoplastic elastomers. Lewis base modifiers enable both gradient and microstructure control. Ether-type ligands with varying coordination number were systematically investigated in styrene/isoprene copolymerization in cyclohexane using in situ near-infrared spectroscopy, focusing on their electronic and steric effects and coordination behavior. Pronounced changes in reactivity ratios (rI ≫ rS to rI ≪ rS) enabled access to tapered, gradient, inverse-gradient, and inverse-tapered architectures with increasing modifier strength. NMR analysis revealed systematic polyisoprene (PI) microstructural variations, leading to increased vinyl (1,2- and 3,4-PI) content. In summary, the most promising bidentate modifier, 2,2-di(2-tetrahydrofuryl)propane (DTHFP), provides efficient architectural tuning by changing the modifier/lithium ratio, yielding random copolymers at concentrations as low as 0.25 equiv with respect to the sec-BuLi-initiator employed.

Abstract This work aims to shed light on the use of the highly available, yet unexplored dimethyl ether (DME) as a solvent for anionic polymerizations. DME is virtually nontoxic and does not lead to the formation of peroxides. The development of special techniques and setups, for the first time, enabled the use of liquid DME, exhibiting a vapor pressure of 6 bar at 25 °C, as a (co)solvent for the anionic polymerization of isoprene (I), β-myrcene (Myr), β-farnesene (Far), and styrene (S) using sec-butyllithium as an initiator. Propagation constants, kinetic orders, and activation energies of I, Myr, and Far in DME were determined at 0, 10, and 23 °C using in situ 1H NMR kinetics. The use of DME leads to faster monomer consumption compared to the less polar methyl tert-butyl ether (MTBE). Additionally, the effect of increasing amounts of DME on the reactivity ratios of S/I copolymerizations up to [DME]/[Li] = 450 in cyclohexane (CHx) was investigated using in situ near-infrared (NIR) spectroscopy. The necessary amount of polar ether modifier to reach random (i.e., rI ≈ rS ≈ 1) S/I incorporation inversely correlates with the polarity of the solvent, i.e., MTBE < DME < THF. Using in situ 1H NMR kinetics, the same trend could be established for the stability toward n-butyllithium in the respective ethers. NIR kinetics revealed that the polymerization rate of styrene in CHx at 20 °C is accelerated ≈18 times at [DME]/[Li] = 30. Lastly, the effect of Li, Na, K, Rb, and Cs naphthalenides on the microstructure of polyisoprene (PI) synthesized in DME at room temperature was determined and found to be comparable to PI synthesized in 1,4-dioxane.

The development of new bio-derived monomers that can reproduce or even outperform the material properties of fossil-based polymers plays an important role in polymer science. Here, we present 4,8-dimethyl-1,3,7-nonatriene (DMNT) for carbanionic polymerization. Accessible from bio-based citral via Wittig olefination, DMNT was successfully polymerized with sec-butyllithium in cyclohexane, leading to moderately narrow molecular weight distributions. Investigation of the polar modifier THF revealed unexpected microstructural changes, favoring the nearly quantitative formation of the 1,4-microstructure. To rationalize this observation, a lithiated intermediate of polymerization was isolated and characterized by X-ray diffraction. Extended NMR studies helped elucidate the solvent-dependent structure in solution, and DFT calculations on the propagation mechanism explained the unexpected microstructure formation in polar environments. This study combines the introduction of a new bio-derived monomer with unique anionic polymerization characteristics with the in-depth investigation of the underlying reactivity features, thereby combining polymer chemistry with molecular methods to clarify the underlying propagation mechanism.

The effect of lithium, sodium, and potassium tert-amylates on the kinetics of the statistical anionic copolymerization of styrene and isoprene in cyclohexane was investigated using in situ near-infrared (NIR) spectroscopy. The reactivity ratios and the related comonomer gradients can be adjusted over the entire range resulting in both random and inverted gradient copolymers. Lithium tert-amylate retards the polymerization at overstoichiometric concentrations. In contrast, even at low concentrations, sodium and potassium tert-amylate increase the rate of styrene polymerization due to a counterion exchange. Only 1/30 equiv of potassium tert-amylate relative to butyllithium is necessary to obtain random copolymers, which unexpectedly consist of short blocks. Remarkably, a high content of isoprene 1,4-units is maintained, leading to a low glass transition temperature of -55 °C of random or inversely tapered poly-(styrene-co-isoprene). Thus, in contrast to Lewis base modifiers, the diene microstructure can be decoupled from reaction kinetics, when potassium alkoxides are used.

The kinetics of anionic polymerization of β‐myrcene initiated by sec ‐butyllithium were examined in saturated and unsaturated hydrocarbon solvents, i.e. cyclohexane, cyclohexene, 4‐vinylcyclohexene and dl ‐limonene. Polymerizations usually proceeded in a living manner, i.e. in the absence of termination and chain transfer reactions, in all solvents, to produce well‐defined polymyrcenes with high content (>85%) of cis ‐1,4 units. However, polymyrcenyllithium chains exhibited limited long‐term stability in 4‐vinylcyclohexene solution, most probably due to chain transfer to solvent. Reaction orders with respect to the concentration of active chains were found to be one‐quarter in cyclohexane increasing to one‐half in unsaturated solvents, indicating that the polymyrcenyllithium chains are present as tetrameric or dimeric associates, respectively. Apparent activation energies were found to be 81 kJ mol −1 in cyclohexane and 77 kJ mol −1 in dl ‐limonene solution, which are close to the values obtained by quantum chemical calculations. © 2025 The Author(s). Polymer International published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The statistical anionic copolymerization of 4-trimethylsilylstyrene (TMSS) with isoprene (I) in cyclohexane was investigated using in situ near-infrared (NIR) spectroscopy in the presence of various amounts of the polar modifier tetrahydrofuran (THF). Polymers with narrow molecular weight distribution of 85-138 kg/mol and dispersities of 1.09-1.22 were obtained. By increasing modifier content, the reactivity ratios can be adjusted over a wide range from r(TMSS) < r(I) to r(TMSS )>> r(I). Compared to the system styrene/isoprene (S/I) only a minute amount of modifier (0.5 eq THF relative to lithium) is sufficient to alter the reactivity ratios, resulting in an ideally random copolymerization, which validates the higher reactivity of TMSS compared to styrene. Using these reactivity ratios, molar and volume composition gradients were calculated. Additionally, the glass transition temperature and microstructure of the polyisoprene units were investigated via differential scanning calorimetry and proton nuclear magnetic resonance. The results are encouraging for the use of these materials in high-end applications like membranes.

Ferulic acid, a natural cinnamic acid derivative with hydroxyl and methoxy group, was quantitatively converted into protected functional styrene monomers via 4-vinylguaiacol (VG) as an intermediate. In a facile and scalable two-step reaction including decarboxylation followed by protection reactions, the monomers 1-ethoxy ethoxy-VG and tert -butyldimethylsilyl-VG were obtained in high yields. Living anionic polymerization of the acetal (1ethoxy ethoxy-) and silyl ( tert -butyldimethylsilyl-) protected styrenes proceeded to well-defined polymers with narrow MWD, although the reaction temperatures in THF were dependent on the protecting groups of the monomers. Deprotection of the acetal and silyl groups was conveniently attained under acidic conditions both in THF and water, resulting in well-defined poly(vinylguaiacol). In addition, demethylation with boron tribromide was performed to obtain poly(vinylcatechol) copolymers, which were used to complex Fe(III). Random copolymerization was observed for the statistical EE -VG and styrene copolymerization in THF at -95 degrees C. Aiming at a fully biobased approach, 4-isopropylstyrene was synthesized from cuminaldehyde by Wittig reaction, and the copolymerization of the latter with EE -VG was also performed, resulting in multi -hydroxyl functional macroinitiators after deprotection, which were employed for subsequent L-lactide and 4-methyl-epsilon-caprolactone grafting.

The synthesis of a fully biobased thermoplastic elastomer (TPE) is presented as an alternative to classical styrene/isoprene-derived TPEs. Limitations of classical systems, e.g., the microstructure of dienes or elaborate multistep addition pathways can be overcome by the combination of bifunctional initiation in the scarcely used, moderately polar solvent methyl tert-butyl ether (MTBE) and by using the monomers beta-farnesene and nopadiene. The monomers can be derived from renewable sugar cane and pine tree feedstocks. Excellent control of carbanionic copolymerization is confirmed by in situ NMR kinetics. The study reveals that two-sided tapered ABA triblock copolymers are accessible in a one-step approach, capitalizing on a difunctional initiator in MTBE. The material properties can be tuned in a broad range-highly elastic materials with elongation exceeding 1300% as well as tough materials with Young's modulus exceeding 500 MPa were obtained. Small-angle Chi-ray scattering, temperature-modulated differential scanning calorimetry, rheology, and dielectric spectroscopy were employed to relate the material properties to the phase state. They revealed local phase segregation accompanied by respective glass temperatures, albeit in the absence of long-range order.

The moderately polar solvent methyl tert-butyl ether (MTBE) was investigated as the reaction medium for the carbanionic polymerization of the 1,3-dienes isoprene and beta-farnesene. Key characteristics of MTBE, e.g., 50 times longer half-life of n-butyllithium in MTBE compared to that in tetrahydrofuran, and polymerization rate constants were determined. In situ H-1 NMR kinetics showed a polymerization rate in MTBE in between the commonly utilized solvents cyclohexane and tetrahydrofuran for diene polymerization. Remarkably, the living polydienyllithium chains in MTBE are predominantly present as nonaggregated unimers. The copolymerization of styrene and isoprene in cyclohexane with an increasing MTBE fraction was investigated via in situ near-infrared kinetics. The gradient structure successively changes to random monomer incorporation and ultimately yields an inverted yet still almost random incorporation in pure MTBE, reflected by the reactivity ratios r(S)(MTBE) = 1.82 and r(I)(MTBE) = 0.55. A spotlight is placed on the great potential of this highly available, albeit rarely used solvent for anionic polymerization.

In-depth understanding of copolymerization kinetics and the resulting polymer microstructure is crucial for the design of materials with well-defined properties. Further, insights regarding the impact of solvents on copolymerization kinetics allows for precisely tuned materials. In this regard, in situ H-1 NMR spectroscopy enables precise monitoring of the living anionic ring-opening copolymerization (AROP) of ethylene oxide (EO) with the glycidyl ethers allyl glycidyl ether (AGE) and ethoxy vinyl glycidyl ether (EVGE), respectively. Determination of reactivity ratios reveals slightly higher reactivity of both glycidyl ethers compared to EO, emphasizing a pronounced counterion chelation effect by glycidyl ethers in AROP. Implementation of density functional theory (DFT) calculations further illustrates the complexation capability of ether-containing side groups in glycidyl ethers, in analogy to crown ethers ("crown ether effect"). Investigation of the copolymerization in i) THF-d(8) and ii) DMSO-d(6) shows an increasing disparity of reactivity ratios for both glycidyl ethers compared to EO, clearly related to decreasing solvent polarity.

Motivated by the need for sustainable, bio-based materials, the living anionic polymerization of the under-explored terpene monomer beta-ocimene (Oc) was investigated for the first time. Homopolymers with Mn up to 50 kg mol-1 of the Oc isomeric mixture (E:Z = trans:cis = 70:30) were synthesized in cyclohexane and analyzed with respect to molecular weight control, dispersity, microstructure, and glass transition temperature, Tg. Employing styrene as a comonomer, diblock copolymers, and a series of statistical copolymers with Mn up to 20 kg mol-1 with varying comonomer compositions offered the opportunity to tailor the glass transition of the copolymers. Real-time 1H nuclear magnetic resonance (NMR) kinetics indicated a remarkably divergent reactivity of the trans and cis isomers. This unveiled the unique observation that the homopolymerization of Oc is in fact a copolymerization of the cis and trans isomers, which one might name as "stereo-copolymerization" (rtrans = 3.16; rcis = 0.32). Kinetic studies of the statistical copolymerization of the Oc isomeric mixture with styrene revealed an astonishingly contradictory reactivity of the two isomers (rtrans < rcis). The reactivity differences of the cis and trans isomers in the polymerization were utilized to isolate the individual isomers for the first time. Subsequently, they were independently homo-and copolymerized with styrene. The complex mechanism of these polymerizations and the rather high polymer dispersities (D approximate to 1.6-2) are discussed using various kinetic models supported by density functional theory modeling. The surprisingly different behavior of the two isomers with styrene was validated experimentally via a 1H NMR-monitored chemical titration.

A facile synthesis using a Grignard reaction was employed to prepare the silicon containing functional monomer 4-allyldimethylsilylstyrene (4ADSS). Detailed studies regarding the living nature of anionic polymerization of 4ADSS and its polymerization via the styrene vinyl bond in cyclohexane at room temperature were conducted, and P4ADSS samples with M-n up to 80 kg mol(-1) were accessible. This evidences that the 4ADSS structure disables undesired proton transfer side reactions, as known for the carbon-based analogue functional monomer 4-but-3-enyl-styrene. Real-time H-1 NMR kinetics of the statistical copolymerization of 4ADSS with styrene (r(4ADSS) = 3.55; r(S) = 0.047) revealed a remarkable gradient microstructure in the resulting copolymers. Based on this observation, a library of well-defined gradient copolymers P(4ADSS-co-S) with Mn in the range of 5-50 kg mol(-1) was synthesized, varying 4ADSS content. A comprehensive discussion regarding the glass transition temperatures (T-g) of the synthesized homo- and copolymers is presented. Furthermore, thiol-ene click reactions at the pendant allyl moiety of P(4ADSS-co-S) were explored to introduce functional groups. Likewise, P(4ADSS-co-S) copolymers were subjected to hydrosilylation reactions, and the impact of the introduced siloxane moieties on the glass transition of the resulting copolymers is presented. Both thiol-ene reactions as well as hydrosilylation of the P(4ADSS-co-S) copolymers proceeded quantitatively. Consequently, copolymerization of 4ADSS provides access to a wide range of polystyrene-based functional materials with specific applications using versatile post-polymerization chemistry.

The protected functional diene monomer 2,2,4,4-tetramethyl-5-(3-methylenepent-4-en-1-yl)-1,3-dioxolane (myrcene dioxolane, MyrDOL) is introduced, based on beta-myrcene. The monomer is suitable for carbanionic polymerization because its acetal functionality as a protective group for diols is stable under carbanionic conditions. The polymerization of MyrDOL in cyclohexane at 25 degrees C using sec-butyllithium as an initiator resulted in homopolymers with well-controlled molecular weights in the range 4.0-31 kg mol(-1) (SEC, PMMA calibration, and MALDI-TOF) and low dispersities, D, between 1.07 and 1.13. In pronounced contrast to polymyrcene, which contains 95% 1,4-myrcene microstructure (synthesis in cyclohexane by anionic polymerization, T-g = -67 degrees C), microstructure characterization of P(MyrDOL) shows 30-33% of 3,4-units and a T-g of 11 degrees C. The acetal groups can be quantitatively removed under mild conditions by using acidic deprotecting agents (e.g., DOWEX resin), resulting in well-defined poly(myrcene-2,3-diol). The copolymerization of MyrDOL with the dienes myrcene, styrene, and isoprene was investigated in great detail via in situ H-1 NMR kinetics. The substitution pattern of the 1,3-diene in combination with the polarity of the monomer has a significant influence on the copolymerization behavior, resulting in disparate reactivity ratios and formation of tapered copolymers in statistical copolymerizations. Myrcene copolymers with varying MyrDOL content, in the range 10-100 mol % MyrDOL, were synthesized (D <= 1.15) and characterized regarding their glass transition temperatures and polydiene microstructure. An increase in the 3,4-microstructure content was observed as a consequence of both increasing MyrDOL content and polarity of the polymerization medium, resulting in an increase in T-g from -67 to 9 degrees C. The protected, functional MyrDOL monomer is promising with respect to polar, hydroxyl-functional rubbers.

Synthesis and real-time 1H NMR kinetic studies on the living anionic copolymerization of 4-trimethylsilylstyrene (4TMSS), an electronically intricate monomer, are reported. Statistical copolymers of 4TMSS with styrene (S) and isoprene (I) with Mn up to 50 kg mol-1 were synthesized and analyzed with respect to dispersity, comonomer composition, and glass-transition temperatures, Tg. Access to well-defined di- and triblock copolymers ensured comprehensive synthetic control. Real-time 1H NMR kinetic measurements unraveled an enthralling gradient microstructure (r4TMSS = 2.76; rS = 0.087 and rI = 3.28; r4TMSS = 0.15) in the copolymers. The sequence distribution provided by a tandem MALDI-MS2 study validated an enhanced reactivity of 4TMSS in comparison to styrene in cyclohexane at room temperature. Furthermore, the kinetics of 4TMSS homopolymerization revealed detailed mechanistic insights. The possibility to tailor Tg and hydrophobicity of the copolymers by varying the 4TMSS content provides a promising approach to design copolymer-based materials for high-end applications, for example, in gas separation membranes.

We synthesized highly branched polybutadienes by anionic self-condensing vinyl copolymerization (ASCVCP) of a butyllithium/divinylbenzene (DVB)-based initiator monomer (inimer) and butadiene. The molecular structure of polybutadienes was evaluated by SEC with MALLS and viscosity detection. SEC/viscosity measurements confirmed the branched structure of the obtained polymers. Examination of polymerization of two isomers of divinylbenzene, i.e., para- and meta-DVB, revealed differences in the mechanism. MALDI-ToF mass spectrometric analysis in the case of p-divinylbenzene indicates macroinimer formation as the first step, followed by condensation of the macroinimers into a highly branched polymer with narrowly distributed polybutadiene segments. The living nature of the polymerization allowed further amino-functionalization of the hyperbranched polybutadienes or subsequent growth of (meth)acrylate arms leading to hyperstar molecules. The reactivity of the primary amino groups in the amino-functionalized copolymers was used in the grafting-onto reaction, i.e., amide formation with w-carboxy-poly(N-isopropylacrylamide), leading to another type of hyperstar. To the best of our knowledge, these are the first examples of hyperstars with a polybutadiene copolymer core described to date.

Polar modifiers strongly affect the statistical anionic copolymerization of biobased β-myrcene with styrene, leading to a variety of morphologies.

Thermoplastic elastomers (TPEs) combine the features of vulcanized thermoset rubbers and thermoplastic materials in their phase-separated microdomain structure. As a consequence soft, flexible and resilient materials are obtained, which can be high-speed processed from the melt state. In the last decades, a variety of polymerization strategies has been proven successful to synthesize block copolymers for TPE materials on an industrial scale. Motivated by the outstanding properties of natural rubber (cis-1,4-polyisoprene), the alkyllithium initiated anionic polymerization of isoprene and butadiene plays a key role for the flexible block of TPEs. The synthesis of ABA-type triblock copolymers based on styrene and 1,3-dienes leads to phase-segregated systems which do not require chemical crosslinking. The living character of the carbanionic chain end was utilized in numerous studies to synthesize complex, defined comonomer sequences by multi-step synthesis. Systematic variation of numerous parameters, e.g., block size and sequence allowed to correlate the resulting mechanical and morphological properties with polymer structure. In this review the focus is placed on multiblock structures and gradient copolymers, addressing key parameters of the molecular architecture to enable a general concept for the design of TPE materials with tailor-made properties. The choice of monomers, also bio-based diene structures such as β-myrcene or β-farnesene is another parameter. The major focus is put on the direct, i.e. statistical anionic copolymerization kinetics as the method of choice to synthesize rather complex multiblock sequences in a one-pot reaction. On-line spectroscopic methods are presented that enable to monitor the monomer consumption during the copolymerization, which directly translates to the comonomer incorporation and gradient formation. To enable precise insight into the comonomer composition of the formed chains, an overview of the theory of copolymerization and the determination of reactivity ratios is given. Kinetic Monte Carlo simulation (kMC) is a versatile tool. Based on experimentally determined kinetic rate constants, the copolymerization can be performed in silico. This enables access to relevant parameters, as for example the conversion as a function of the time as well as the composition and monomer sequence in individual chains, which allow rational design and evaluation of synthetic experiments.

The statistical anionic copolymerization of isoprene (I) and styrene (S) is commonly used to synthesize tapered block copolymers, enabling control of the phase behavior by adjusting the order-disorder transition temperature, T-ODT. Alkyllithium initiation in hydrocarbons is known to afford tapered block copolymers of I and S in one step. The effect of tetrahydrofuran (THF) on the copolymerization kinetics and the resulting copolymers was systematically investigated by increasing the [THF]/[Li] ratio from 0 to 2500 (0 to 29%(vol) THF). For this purpose, in situ near-infrared (NIR) spectroscopy was employed as a versatile and fast method to track the highly accelerated consumption of the individual monomers. Changes in the I/S comonomer sequence and in the polyisoprene (PI) regioisomers, caused by variation of the THF concentration, were independently determined via NMR and in situ NIR spectroscopy. Reactivity ratios were determined as a function of the [THF]/[Li] ratio. They revealed a gradual reversal from r(I) >> r(S) over r(I) approximate to r(S) to r(I) << r(S). Corresponding changes in the copolymer composition profile up to a complete inversion are evident in thermal properties and morphologies. Although all copolymers possess the same comonomer composition (50%(mol) = 57%(vol) polystyrene (PS) units), small-angle X-ray scattering and transmission electron microscopy give evidence of a wide variation in bulk morphologies depending on the gradient profile. Overall, the phase diagram is symmetric, and the succession of phases bears certain similarities to the PI-b-PS case. This is discussed in terms of the increasing incompatibility of PS with 3,4-PI and the more symmetric polymer conformational parameter. The degree of segregation, as well as the nanodomain structure, was found to control the mechanical properties, showing a remarkably different viscoelastic response leading to either hard/brittle or ductile/soft materials. The accessibility of tailored gradient profiles, as well as their in-depth understanding by simply using THF as a microstructural modifier, opens a variety of possible applications. As an example, the synthesis of a PI-selective hydrogenated tapered triblock, possessing a THF-modified, phase-compatibilizing tapered block incorporated in the well-established SIS block architecture, is presented.

ABSTRACTWell‐defined polystyrene homopolymers with surface‐adhesive triethoxysilyl end group were synthesized via living carbanionic polymerization, epoxide end‐functionalization and subsequent hydrosilylation with triethoxysilane. Grafting‐to performance of polymers with various molecular weight (Mn = 3000–14,000 g mol−1) to a silicon surface was examined in dependence of reaction time, polymer concentration, solvent and number of alkoxysilyl end groups. Crosslinkable polymers for surface modification were synthesized by statistical carbanionic copolymerization of 4‐vinylbenzocyclobutene (4‐VBCB) and styrene, followed by epoxide end‐functionalization and triethoxysilane modification (Mn = 4000–14,000 g mol−1). The copolymers were characterized by 1H‐NMR, THF‐SEC, and matrix‐assisted laser desorption and ionization time‐of‐flight mass spectrometry. In situ 1H‐NMR kinetic studies in cyclohexane‐d12 provided information regarding the monomer gradient in the polymer chains, with styrene being the more reactive monomer (rs = 2.75, r4‐VBCB = 0.23). Thin polymer films on silicon wafers were prepared by grafting‐to surface modification under conditions derived for the polystyrene homopolymer. The traceless, thermally induced crosslinking reaction of the benzocyclobutene units was studied by DSC in bulk as well as in 3–6 nm thick polymer films. Crosslinked films were analyzed by atomic force microscopy, ellipsometry, and nanoindentation, showing smooth polymer films with an increased modulus. © 2019 The Authors. Journal of Polymer Science published by Wiley Periodicals, Inc. J. Polym. Sci. 2020, 58, 181–192

Block copolymer (BCP) self-assembly is one of the most versatile concepts for the bottom-up design of functional nanostructures in materials science, nanomedicine and nanotechnology. While BCPs have been extensively studied regarding their microphase separation in bulk and the self-assembly in solution, only recently BCPs were investigated for their ability to form internally ordered microparticles. In this review, we discuss two emerging concepts: (i) the microphase separation of BCPs in the spherical confinement of evaporating emulsion droplets and (ii) the self-assembly of highly asymmetric BCPs under concentrated conditions. While the first concept yields solid and compact multicompartment microparticles suited for the synthesis of shape-anisotropic nanoparticles, photonic colloids, and actuators, the latter produces highly regular porous microparticles with exceptional interfacial area (BCP cubosomes and hexosomes). Despite distinct differences in the origin of both fields, commonalities in shape and morphology suggest an underlying formation mechanism that may link both research directions.