Anionic Polymerization Research Articles

Tuning moduli of hybrid bottlebrush elastomers by molecular architecture

Polymeric elastomers made of bottlebrush chains are soft, solvent-free materials with precisely controllable moduli by network topology. However, fabrication methods of bottlebrush networks with precisely programmable topology are lacking. The aim of this study is to achieve precise control over the modulus of hybrid elastomers containing bottlebrush and linear strands by integrating a versatile experimental synthesis approach with Molecular Dynamics (MD) simulations. In this study, polydimethylsiloxane (PDMS) networks (G′=10−328 kPa) are made by crosslinking prepared and purified bottlebrush molecules where the precursors, side chains and backbone, are synthesized using well-controlled living anionic polymerization. This approach allows independent programming of the crucial topological parameters of bottlebrushes, such as length of both sides chain and backbone and grafting density. In addition to this versatile synthesis, MD simulations reveal the influence of network defects inevitably present in all polymer networks. This novel combining of fabrication method and simulation yields experimentally-measured structural shear and Young's moduli which are in better agreement with theoretical predictions. Importantly, these bottlebrush-containing networks have no solvent or additives and notably, by removing ungrafted side chains impurities before network formation, results in soft, solvent-free elastomers with Young's moduli as low as E∼30 kPa with adhesiveness far lower than commercial silicone products of similar stiffness.

Novel BODIPY-Based Photobase Generators for Photoinduced Polymerization.

Photobase generators (PBGs) are compounds that utilize light-sensitive chemical-protecting groups to offer spatiotemporal control of releasing organic bases upon targeted light irradiation. PBGs can be implemented as an external control to initiate anionic polymerizations such as thiol-ene Michael addition reactions. However, there are limitations for common PBGs, including a short absorption wavelength and weak base release that lead to poor efficiency in photopolymerization. Therefore, there is a great need for visible-light-triggered PBGs that are capable of releasing strong bases efficiently. Here, we report two novel BODIPY-based visible-light-sensitive PBGs for light-induced activation of the thiol-ene Michael "click" reaction and polymerization. These PBGs were designed by connecting the BODIPY-based light-sensitive protecting group with tetramethylguanidine (TMG), a strong base. Moreover, we exploited the heavy atom effect to increase the efficiency of releasing TMG and the polymerization rate. These BODIPY-based PBGs exhibit extraordinary activity toward thiol-ene Michael addition-based polymerization, and they can be used in surface coating and polymer network formation of different thiol and vinyl monomers.

Tuning the morphology of silicon containing copolymers via macromolecular architecture effect

We demonstrate the successful synthesis of linear and non-linear star block copolymers consisting of the highly segregated polystyrene (PS) and poly(dimethylsiloxane) (PDMS) blocks through sequential anionic polymerization combined with chlorosilane chemistry. To study the macromolecular architecture effect on the adopted morphology star block copolymers with six equivalent diblock arms [(PS-b-PDMS)6] were synthesized and compared with their linear diblock copolymer precursors as well as with the corresponding star block copolymers with smaller arm number (2, 3, 4) but identical molecular characteristics. After verifying the molecular and thermal characteristics, bulk studies were carried out through transmission electron microscopy and small angle X-ray scattering. Well-defined structures with enhanced order and similar domain spacing values, irrespective of the architecture complexity of the samples, were observed. The better order of star block copolymers suggests an alternative way to further reduce the lower limit of repeating period by tuning the architecture which is important for the potential future use of the copolymers for nanotechnology related applications. The findings of the specific study are related to the effects of the increased conformational restriction of the inner block. Herein, we show morphological transformations in the (PS-b-PDMS)6 copolymers having non symmetric volume fraction ratios when compared to their linear diblock precursors and triblock copolymers which has not been observed in previous relevant (PS-b-PDMS)n studies that involved stars with less than six arms. To establish the structure/property relationship as a function of arm number, a series of samples involving the diblock precursor, the triblock, the three-, four- and six- arm star block copolymers was prepared, and a systematic comparison was conducted.

Surface-Initiated Living Anionic Polymerization of Functional Methacrylates from the Surface of Organic Particles

Surface-Initiated Living Anionic Polymerization of Functional Methacrylates from the Surface of Organic Particles

Effect of chain architecture on the structure, dynamics, and rheology of thermoresponsive poloxamer hydrogels and associated blends.

Poloxamers, ABA triblock polymers composed of a poly(propylene oxide) (PPO) midblock (B) and poly(ethylene oxide) (PEO) endblocks (A), are widely studied for biomedical applications. Aqueous poloxamer 407 (P407; also referred to as F127) undergoes a solution-to-gel transition with increasing temperature, driven by the formation and ordering of micelles onto periodic lattices; however, the gel temperature and resulting modulus has limited tunability. Here, reverse P407 (RP407), a BAB polymer of the same composition and molar mass but the inverted architecture, is synthesized via anionic polymerization. The micellization and gelation temperatures of RP407 are higher than that of P407 and the PPO endblocks allow for intermicelle bridging; however, both single-component solutions favor body-centered cubic (BCC) packings. Further, aqueous RP407 displays a "soft gel" region with interesting rheological behavior, including viscoelastic aging and thermal hysteresis. Combining P407 and RP407 yields solutions with intermediate transition temperatures and alters the size and micelle packing. While the single-component solutions produce BCC packings, the blends form close-packed structures and larger micelles of higher aggregation numbers. Blends of P407 with an analogous AB diblock (E111P32) display similar behavior, whereas RP407/diblock blends form intermediate-sized BCC-packed micelles. These differences in packing and aggregation alter the local environments within the gels, which could have implications for applications such as drug delivery and protein stabilization.

Trivinylphosphine Oxide: Synthesis, Characterization, and Polymerization Reactivity Investigated Using Single-Crystal Analysis and Density Functional Theory.

Organophosphorus chemicals are versatile and important in industry. Trivinylphosphine oxide (TVPO), for example, exhibited a promising precursor as a flame-retardant additive for industrial applications. Density functional theory (DFT) simulations were used to explore the kinetic and thermodynamic chemical processes underlying the nucleophilic addition reactions of TVPO in order to better understand their polymerization mechanisms. An experimental X-ray single-crystal study of TVPO supported this work's theory based on its computed findings. TVPO was prepared using POCl3 and VMB in a temperature-dependent reaction. TVPO, the thermodynamically favourable product, is preferentially produced at low temperatures. The endothermic anionic addition polymerization reaction between TVPO and VMB begins when the reaction temperature rises. An implicit solvation model simulated TVPO and piperazine reactions in water, whereas a hybrid model modelled VMB interactions in tetrahydrofuran. The simulations showed a pseudo-Michael addition reaction mechanism with a four-membered ring transition state. The Michael addition reaction is analogous to this process.

Polyampholyte Polymers‐Based Sensors: A Review on Stimuli and Applications

AbstractPolyampholytes are a specific type of zwitterionic materials composed of monomers with both positive and negative charges. These materials can be synthesized through various methods, such as free radical, anionic, or cationic polymerization, or by modifying existing polymers through postpolymerization processes. Polyampholytes possess unique properties that make them attractive for a wide range of applications, particularly in sensor technology. They can undergo conformational changes in response to external stimuli like pH variations, temperature fluctuations, or changes in salt concentration. These properties have led to their application in biosensors, salt and ion sensors, pH sensors, fluorescence‐based sensors, strain sensors, and thermosensitive sensors. It is worth noting that in some cases polyampholytes can respond to multiple stimuli simultaneously. Overall, polyampholytes are drawing great attention for their excellent mechanical properties including self‐healing, high toughness, and fatigue resistance. Thus, this review is focused on advances that are made to develop polyampholyte polymer‐based sensors in different applications.

Threading-the-Needle: Compatibilization of HDPE/iPP blends with butadiene-derived polyolefin block copolymers

Management of the plastic industry is a momentous challenge, one that pits enormous societal benefits against an accumulating reservoir of nearly indestructible waste. A promising strategy for recycling polyethylene (PE) and isotactic polypropylene (iPP), constituting roughly half the plastic produced annually worldwide, is melt blending for reformulation into useful products. Unfortunately, such blends are generally brittle and useless due to phase separation and mechanically weak domain interfaces. Recent studies have shown that addition of small amounts of semicrystalline PE-iPP block copolymers (ca. 1 wt%) to mixtures of these polyolefins results in ductility comparable to the pure materials. However, current methods for producing such additives rely on expensive reagents, prohibitively impacting the cost of recycling these inexpensive commodity plastics. Here, we describe an alternative strategy that exploits anionic polymerization of butadiene into block copolymers, with subsequent catalytic hydrogenation, yielding E and X blocks that are individually melt miscible with PE and iPP, where E and X are poly(ethylene-ran-ethylethylene) random copolymers with 6 wt% and 90 wt% ethylethylene repeat units, respectively. Cooling melt blended mixtures of PE and iPP containing 1 wt% of the triblock copolymer EXE of appropriate molecular weight, results in mechanical properties competitive with the component plastics. Blend toughness is obtained through interfacial topological entanglements of the amorphous X polymer and semicrystalline iPP, along with anchoring of the E blocks through cocrystallization with the PE homopolymer. Significantly, EXE can be inexpensively produced using currently practiced industrial scale polymerization methods, offering a practical approach to recycling the world's top two plastics.

Self-Assembly of Polymer-Modified FePt Magnetic Nanoparticles and Block Copolymers.

The fabrication of nanocomposites containing magnetic nanoparticles is gaining interest as a model for application in small electronic devices. The self-assembly of block copolymers (BCPs) makes these materials ideal for use as a soft matrix to support the structural ordering of the nanoparticles. In this work, a high-molecular-weight polystyrene-b-poly(methyl methacrylate) block copolymer (PS-b-PMMA) was synthesized through anionic polymerization. The influence of the addition of different ratios of PMMA-coated FePt nanoparticles (NPs) on the self-assembled morphology was investigated using transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). The self-assembly of the NPs inside the PMMA phase at low particle concentrations was analyzed statistically, and the negative effect of higher particle ratios on the lamellar BCP morphology became visible. The placement of the NPs inside the PMMA phase was also compared to theoretical descriptions. The magnetic addressability of the FePt nanoparticles inside the nanocomposite films was finally analyzed using bimodal magnetic force microscopy and proved the magnetic nature of the nanoparticles inside the microphase-separated BCP films.

Effect of styrene–butadiene–styrene triblock copolymer structure on the rheological properties of high content SBS polymer modified asphalts

Styrene-butadiene-styrene triblock copolymer (SBS) is a thermoplastic elastomer synthesized through the anionic polymerization. The effects of SBS structure including diblock content, molecular weight and styrene content on the properties of high content SBS polymer modified asphalts (HCPMA) with 8wt% were studied. The structure of SBS was characterized by the Size Exclusion Chromatography. The rheological properties of HCPMA were analyzed by performance grading, linear amplitude sweep and zero shear viscosity. The results show that the increasing diblock content decreases the melt viscosity, and improves the workability and the thermal-cracking resistance of HCPMA. However, it reduces the high-temperature performance and fatigue resistance. Higher molecular weight of SBS improves the high-temperature properties and fatigue resistance of HCPMA, but worsens the workability and hot-storage stability. Asphalts modified by SBS with a higher styrene content show better workability and high-temperature properties, while a higher butadiene content in SBS shows better hot-storage stability and thermal-cracking resistance of HCPMA. When the styrene content of SBS is 30%, the binder represents the best fatigue resistance. The results also show that rheological tests characterize HCPMA more precisely than the conventional methods.

Thin film and bulk morphology of PI-PS-PMMA miktoarm star terpolymers with both weakly and strongly segregated arm pairs

A series of three homologous ABC miktoarm star terpolymers having a polyisoprene (PI), a polystyrene (PS) and a poly(methyl methacrylate) (PMMA) arm, is synthesized by living anionic polymerization. While the volume fraction of the PI and the PS blocks are kept equal and constant, the volume fraction of the PMMA block is varied. The room temperature bulk structure is characterized using small-angle X-ray scattering and transmission electron microscopy, while the structure of thin films is investigated using scanning electron microscopy, atomic force microscopy and X-ray reflectometry. For both bulk and thin films, it is found that the sample with the lowest volume fraction of PMMA has a morphology distinctly different from the two samples with larger PMMA volume fraction. All data for both bulk and thin film samples are consistent with an alternating lamellar structure for the lowest PMMA volume fraction sample. The two higher PMMA volume fraction samples show standing rod structure, however the details of the packing in the PMMA matrix differ depending on sample thickness. Overall, a structure with PI domains screened from interacting with PMMA by a PS shell is seen for both samples. In bulk, core-shell cylinders pack hexagonally, while a 100 nm thin film of the sample with the largest volume fraction of PMMA shows a square-lattice packing. The structuring is driven by two factors: i) the strong segregation of the PI-PMMA arm pair together with the weak segregation of the two arm pairs with a PS block and ii) the geometrical constraints resulting from the star architecture. No wetting layers are observed for any of the thin film samples, neither at the air-polymner surface or at the polymer-substrate interface.

Superbase‐enabled anionic polymerization of poly(alkyl cyanoacrylate)s: achieving well‐defined structures and controlled molar masses

AbstractPoly(alkyl cyanoacrylate)s (PACAs) find extensive use as adhesives in engineering and medicine. However, their high reactivity often leads to wide molar mass dispersity and uncontrolled chain‐end functionalities. Achieving precise polymer structures is crucial, particularly for medical applications to prevent oligomer toxicity. The conventional anionic polymerization of cyanoacrylates initiated by water results in high molar mass dispersities (Ð) and low end‐group functionalities. Nonetheless, under specific conditions, anionic polymerization holds the potential for controlling the molar mass and Ð of PACAs. Here, we demonstrate the synthesis of well‐defined PACAs by employing minute quantities (1%) of superbases to activate a functional thiophenol (PhSH) initiator. This strategy enables the attainment of adjustable molecular weights (Mn > 20 kg mol−1) and moderate dispersities (Ð < 1.4) for homopolymers and block copolymers. The selective initiation by thiophenol is confirmed through 1H DOSY NMR analysis. Furthermore, the controlled homo‐ and copolymerization of ACA derivatives highlights the remarkable performance of the superbase in conjunction with PhSH. © 2023 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.

Living/Controlled Anionic Polymerization of Glycolide in Fluoroalcohols: Toward Sustainable Bioplastics.

Ring-opening polymerization (ROP) is a promising approach to accessing well-defined polyesters with superior (bio)degradability and recyclability. However, the living/controlled polymerization of glycolide (GL), a well-known sustainable monomer derived from carbon monoxide/dioxide, has never been reported due to the extremely low solubility of its polymer in common solvents. Herein, we report the first living/controlled anionic ROP of GL in strong protic fluoroalcohols (FAs), which are conventionally considered incompatible with anionic polymerization. Well-defined polyglycolide (PGA, Đ < 1.15, Mn up to 55.4 kg mol-1) and various PGA-based macromolecules are obtained at room temperature for the first time. NMR titration and computational studies revealed that FAs simultaneously activate the chain end and monomer without being involved in initiation. Low-boiling-point FAs and PGA can be recycled through simple distillation and sublimation at 220 °C in vacuo, respectively, providing a promising sustainable alternative for tackling plastic pollution problems.

Impact of pendant substituents on post-polymerization functionalization and electronic properties in stereoregular non-conjugated pendant electroactive polymers

Recent reports on non-conjugated pendant electroactive polymers (NCPEPs) have demonstrated the significance of altering structural variables specifically the stereoregularity, the nature of the pendant group and the length of the spacer connecting that group to the backbone for tuning of their optoelectronic properties. The only synthetic approach that allows for selectively studying the effects of tuning these variables without additional superimposed effects of varied molecular weights and tacticities is the post-polymerization functionalization methodology in which parent polymers are synthesized first and then functionalized with the respective pendant groups and spacers. However, specifically for tuning of the pendant group itself, the scope of such post-polymerization functionalization methods remains largely underexplored. Here, the compatibility of the established photochemical thiol-ene post-polymerization method with various pendant groups is investigated for functionalization of stereoregular and stereorandom poly(allyl methacrylates) made via anionic polymerization using an organolithium initiator. Carbazole and a family of four 3,6-disubstituted carbazoles with phenyl, methoxy, nitrile and t-butyl substituents were investigated as the respective pendant groups. With the phenyl, methoxy and nitrile substituted pendant groups limitations of the scope of the thiol-ene methodology due to limited solubility and vulnerability to photochemical side reactions could be demonstrated. In contrast, t-butyl substituents did not impede the post-polymerization functionalization. The corresponding functionalized NCPEPs were characterized and effects of substitution of the carbazole pendant group with t-butyl groups on the optoelectronic properties of the polymers are discussed. Overall, this work demonstrates critical limitations of the thiol-ene functionalization method as well as their origin when applied to differently substituted pendant groups.

Isothermal anionic polymerization of ε‐caprolactam to polyamide‐6: Kinetic modeling and application for production process

AbstractThe in‐situ anionic polymerization of ε‐caprolactam (ε‐CL) to polyamide‐6 enables the production of large, near net shape fiber reinforced composites by thermoplastic resin transfer molding. For the propagation of the flow front as well as for the progress of the solidification, the simultaneous processes of polymerization and crystallization and the corresponding reaction kinetics play a central role. To investigate these processes, preparation of reactive mixtures consisting of ε‐CL, activator, and initiator was carried out under inert atmosphere. A solvent‐based activator and initiator were used, which hardly have been studied in the literature so far. In analogy to the resin transfer molding process, quasi‐isothermal differential scanning calorimetry measurements were performed at various temperatures and the released enthalpy and the degree of crystallization were determined. From these isothermal measurements, a two‐stage semi‐empirical kinetic model was established for a solvent‐based system for the first time, which reproduces the experimental data with high precision. To apply the obtained kinetic model to a thermoplastic resin transfer molding process it was finally correlated to dielectric sensor data, allowing real‐time prediction of the total conversion.

Ketyl Radical Anion Mediated Radical Polymerization and Anionic Ring-Opening Polymerization to Give Polymers with Low Molecular Weight Distribution.

The development of novel polymerization capable of yielding polymers with low molecular weight distribution (Đ) is essential and significant in polymer chemistry, where monofunctional initiator contains only one initiation site in these polymerizations generally. Here, ketyl radical anion species is introduced to develop a novel Ketyl Mediated Polymerization (KMP), which enables radical polymerization at carbon radical site and anionic ring-opening polymerization at oxygen anion site, respectively. Meanwhile, polymerization and corresponding organic synthesis generally couldn't be performed simultaneously in one pot. Through KMP, organic synthesis and polymerization are achieved in one pot, where small molecules (cyclopentane derivates) and polymers with low Đ are successfully prepared under mild condition simultaneously. At the initiation step, both organic synthesis and polymerization are initiated by single electron transfer reaction with ketyl radical anion formation. Cyclopentane derivates are synthesized through 3-3 coupling reaction and cyclization. Polystyrene and polycaprolactone with low Đ and a full monomer conversion are prepared by KMP via radical polymerization and anionic ring-opening polymerization, respectively. This work therefore enables both organic synthesis and two different polymerizations from same initiation system, which saves time, labour, resource and energy and expands the reaction mode and method libraries of organic chemistry and polymer chemistry.

Synthesis and Characterization of Furan-Based Non-Ionic Surfactants (fbnios).

Two series of furan-based non-ionic surfactants (fbnios) were prepared by a combination of Williamson ether synthesis and anionic polymerization of ethylene oxide (EO). The reaction of 1-bromooctane and 1-bromododecane with 2,5-bis(hydroxymethyl)furan after deprotonation with potassium tert-butoxide yielded the corresponding alkane furfuryl alcohols (Cx-F-OH with x = 8 or 12). Deprotonation of Cx-F-OH with potassium tert-pentoxide enabled the anionic polymerization of EO, which yielded four C8-F-EOy samples with y = 3, 6, 9, and 14 and four C12-F-EOy samples with y = 9, 12, 18, and 23. The chemical composition of the fbnios was determined by NMR and matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-ToF MS) analysis, while their dispersity (Đ) was characterized by gel permeation chromatography (GPC) and MALDI-ToF MS. The purity of the Cx-F-EOy samples exceeded 92%, and they were produced with narrow molecular weight distributions (Đ ≤ 1.02, as determined by GPC analysis). The critical micelle concentration (CMC) of the Cx-F-EOy samples was determined by surface tension and pyrene fluorescence measurements. These showed that the CMC of the fbnios could be tuned by adjusting the molecular parameters x and y, with the CMC increasing for decreasing x and increasing y. In particular, the CMC of the C8-F-EOy and C12-F-EOy samples was significantly higher and lower, respectively, than for typical non-ionic surfactants (nios) like the Triton X and Brij surfactant families. The efficiency, effectiveness, and cross section of the EOy headgroup of the fbnios were also determined. Together, the CMC, efficiency, and effectiveness of the fbnios demonstrate that this new surfactant family displays tensioactive properties that match and even exceed those of traditional nios, suggesting that they could extend further the already broad range of applications for nios.

Side Chain Dipole Orientation and Its Effect on Microphase Separation: Experiment and Simulation via Structural Isomer Variation

We use experiments and molecular dynamics simulations in an investigation of structural isomer–property relationships in block copolymers (BCPs) that allow us to isolate the effects of dipole orientation on microphase separation and χ. We combine anionic polymerization of a single parent BCP with post-polymerization thiol-epoxy “click” chemistry with a series of structural isomers of fluorinated thiophenols to synthesize structural isomeric BCPs (SI-BCPs). The resulting SI-BCPs possess identical molecular weight and dispersity, such that only the isomerism can affect microphase separation. Domain periodicity of the SI-BCPs is measured with small angle X-ray scattering, from which χ is estimated. The value of χ for each SI-BCP shows a significant dependence on the position of fluorine atoms on the phenyl ring of the thiophenol. Simulation results show a strong correlation between the dipole moment orientation of the appended thiol and χ, which is also observed in simulations of a BCP of the structural isomers poly(2-vinylpyridine) and poly(4-vinylpyridine). This work illustrates a little-known facet of the structure–property relationship of BCP materials and provides another tool for the molecular engineering of BCPs.

Bio-based non-flammable foams with a circular end-of-life based on the self-foaming process

For conventional polymeric foams, over-utilization of harmful precursors and the problem with waste management are driving scientists to develop sustainable foaming methods and make polymeric foams from renewable precursors. This study developed a self-foaming system to create a lignin carbonate foam (LCF) from two non-toxic carbon storage precursors: lignin and ethylene carbonate (EC). Specifically, kraft lignin, in its isolated salt form, referred to as lignophenolate, is copolymerized with EC via the anionic ring-opening polymerization. Under the optimal condition, the gelation and solidification of the copolymers could coincide with trapping in-situ generated CO2 blowing gas from the copolymers to make the foams. Its unique composition endows the materials with comparable performances with those benchmark plastic foams (for example polyurethane foam, expanded polystyrene) considering the mechanical performances, thermal stability, shape fidelity, and non-flammability. Moreover, the carbonate linkages in LCFs render them to be reshaped or depolymerized with valuable precursors for end-of-life recycling. This study opens new avenues to fabricate polymeric foams from carbon storage precursors through a self-foaming process for applications in the construction industry.

Poly(dimethyl-diphenyl-imide)siloxane/phenolic-based double network hybrid resin coatings for ablation thermal protection

Organic-inorganic hybridization is an important way to improve ablation resistance of phenolic resin coatings (PR). However, long molecular chain silicone by copolymerization is less compatible with PR and hybrid resin will form sea-island phase, which is not favorable for further improvement of ablation resistance. Therefore, how to achieve a combination of long chain and compatibility is a major challenge. In this work, the poly(dimethyl-diphenyl-imide)siloxane (PMPI) containing imide and phenyl was synthesized by anionic ring-opening polymerization and copolymerization. Then, it was hybridized with PR to obtain PMPI/PR-based double network hybrid resin coatings with nano co-continuous phase. The oxyacetylene ablation test suggests that the resin coatings with medium phenyl content has the lowest linear ablation rate (0.055 mm/s), which is 74 % lower compared to PR (0.21 mm/s). In addition, the mechanism by which PMPI enhances ablation resistance is discussed. This work provides a promising approach to develop higher performance ablative-resistant resin coatings.