Living Anionic Polymerization Research Articles

Synthesis of α,ω-End Functionalized Polydienes: Allylic-Bearing Heteroleptic Aluminums for Selective Alkylation and Transalkylation in Coordinative Chain Transfer Polymerization.

There are still challenges in the preparation of difunctional stereoregular polydienes, especially for the construction of initiating chain-end functionalization. Coordinative chain transfer polymerization (CCTP) provides a way to achieve the goal but usually requires sophisticated functionalized catalysts as well as expensive chain transfer agents (CTAs). In this work, heteroleptic aluminum with oligo(dienyl) substituents (oligo-Al agents) were readily prepared by living anionic polymerization (LAP) technique. The oligo-Al agents used in Nd-mediated CCTPs of dienes exhibit highly selective alkylation and transalkylation features. Kinetics and transfer efficiency studies using 1 H NMR, 13 C NMR, 1 H-13 C HSQC, and Dosy NMR analyses revealed that the resulting polydienes possess substituents at the initiating chain-end that have transferred from the oligo-Al agents. The functionalization efficiency of the initiating chain-end is up to 99 %, and the molar mass regulation efficiency of heteroleptic aluminum is higher than that of the traditional CTA Ali Bu2 H (0.608 vs. 0.410). Based on the experimental results and density functional theory (DFT) calculations, we propose a mechanism in which allylic-Al acts as an efficient alkylating moiety in catalyst preformation and also as an effective transfer agent in polymerization. Taking advantage of these features, di-functionalized polyisoprene, polybutadiene, and poly(isoprene-co-butadiene) can be facilely synthesized.

Synthesis of α,ω‐End Functionalized Polydienes: Allylic‐Bearing Heteroleptic Aluminums for Selective Alkylation and Transalkylation in Coordinative Chain Transfer Polymerization

AbstractThere are still challenges in the preparation of difunctional stereoregular polydienes, especially for the construction of initiating chain‐end functionalization. Coordinative chain transfer polymerization (CCTP) provides a way to achieve the goal but usually requires sophisticated functionalized catalysts as well as expensive chain transfer agents (CTAs). In this work, heteroleptic aluminum with oligo(dienyl) substituents (oligo‐Al agents) were readily prepared by living anionic polymerization (LAP) technique. The oligo‐Al agents used in Nd‐mediated CCTPs of dienes exhibit highly selective alkylation and transalkylation features. Kinetics and transfer efficiency studies using 1H NMR, 13C NMR, 1H‐13C HSQC, and Dosy NMR analyses revealed that the resulting polydienes possess substituents at the initiating chain‐end that have transferred from the oligo‐Al agents. The functionalization efficiency of the initiating chain‐end is up to 99 %, and the molar mass regulation efficiency of heteroleptic aluminum is higher than that of the traditional CTA AliBu2H (0.608 vs. 0.410). Based on the experimental results and density functional theory (DFT) calculations, we propose a mechanism in which allylic‐Al acts as an efficient alkylating moiety in catalyst preformation and also as an effective transfer agent in polymerization. Taking advantage of these features, di‐functionalized polyisoprene, polybutadiene, and poly(isoprene‐co‐butadiene) can be facilely synthesized.

Quo Vadis Carbanionic Polymerization?

Living anionic polymerization will soon celebrate 70 years of existence. This living polymerization is considered the mother of all living and controlled/living polymerizations since it paved the way for their discovery. It provides methodologies for synthesizing polymers with absolute control of the essential parameters that affect polymer properties, including molecular weight, molecular weight distribution, composition and microstructure, chain-end/in-chain functionality, and architecture. This precise control of living anionic polymerization generated tremendous fundamental and industrial research activities, developing numerous important commodity and specialty polymers. In this Perspective, we present the high importance of living anionic polymerization of vinyl monomers by providing some examples of its significant achievements, presenting its current status, giving several insights into where it is going (Quo Vadis) and what the future holds for this powerful synthetic method. Furthermore, we attempt to explore its advantages and disadvantages compared to controlled/living radical polymerizations, the main competitors of living carbanionic polymerization.

Cooperative and Independent Effect of Modular Functionalization on Mesomorphic Performances and Microphase Separation of Well-Designed Liquid Crystalline Diblock Copolymers.

Liquid crystalline block copolymers (LCBCPs) are promising for developing functional materials owing to an assembly of better functionalities. Taking advantage of differences in reactivity between alkynyl and vinyl over temperature during hydrosilylation, a series of LCBCPs with modular functionalization of the block copolymers (BCPs) are reported by independently and site-selectively attaching azobenzene moieties containing alkynyl (LC1 ) and Si-H (LC2 ) terminals into well-designed poly(styrene)-block-polybutadienes (PS-b-PBs) and poly(4-vinylphenyldimethylsilane)-block-polybutadienes (PVPDMS-b-PBs) produced from living anionic polymerization (LAP). By the principle of modular functionalization, it is demonstrated that mono-functionalized (PVPDMS-g-LC1 )-b-PB and PS-b-(PB-g-LC2 ) not only maintain independence but also have cooperative contributions to bi-functionalized (PVPDMS-g-LC1 )-b-(PB-g-LC2 ) in terms of mesomorphic performances and microphase separation, which is evident from differential scanning calorimetry (DSC) and polarized optical morphologies (POM) and identified by powder X-ray diffractions. With the application of the new principle of modular functionalization, local-crosslinked liquid crystalline networks (LCNs) with controlled functionality are successfully synthesized, which show well-controlled phase behaviors over molecular compositions.

Synthesis of well-defined PS-based Azo-liquid crystals with control of phase transitions and photo-behaviors for liquid crystal networks with photomechanical deformation

Benefiting from their good mechanical processability and high tunability, Si–H and vinyl-functionalized polystyrenes (PSs), i.e., poly(4-vinylphenyl)-dimethyl-silane (PVPDMS/PS-SiH) and poly(4-vinylphenyl)-1-butene (PVSt/PS-Vinyl), produced by living anionic polymerization (LAP) were treated with four vinyl- and Si–H-terminated azobenzene mesogens (Azo-Vinyl, Azo-SiH, AzoB-Vinyl, and AzoB-SiH, referred to as M1, M2, M3, and M4, respectively) via hydrosilylation for the fabrication of PS-based side-chain liquid crystal polymers (SCLCPs) containing different spacers, i.e., PS-SiC/SiOSi-Azo/AzoB. As a strategy for basic molecular control in PS-based SCLCPs, the cooperative influences of the spacers and the degree of polymerization (DP) on the mesomorphic transitions were explored. The phase transitions could be tuned slightly based on the DP but dramatically by adjusting the spacers. For example, the temperature ranges of mesomorphic formation (ΔT) were in the order PS-[SiOSi]-Azo (ΔT = 34–49 °C) < PS-[SiC]-Azo (ΔT = 49–60 °C) < PS-[SiOSi]-AzoB (ΔT = 154–164 °C) < PS-[SiC]-AzoB (ΔT = 162–193 °C). Taking advantage of the quantitative structure-property correlation of PS-based SCLCPs, PS-based liquid crystal networks (LCNs) were further designed for the photomechanical deformation. PS-based LCNs show good mechanical properties with a storage modulus of 120 MPa, controlled phase transitions, and glass transition temperatures (Tg) around room temperature. Crosslinked PS-based LCNs of rigid PS homopolymers with selective crosslinking can exhibit directional bending upon irradiation with UV light at 50 °C after stretching, and this was shown to be a photomechanical deformation, which expands the applicability of these materials.

Precise construction of polymer brush on a nanosilica surface via the combination of anionic polymerization and Ugi-4CR

In this paper, a novel process was presented to synthesize monomodal and bimodal polymer brushes by optimizing living anionic polymerization (LAP) and Ugi four-component reaction (Ugi-4CR). As a remarkable tool, LAP provides an efficient entrance to synthesize the di-endcapped polymer chains. Consequently, the α-terminal silicon oxide group enables polymer chains to be anchored on the surface of nanosilica particles, while the ω-terminal amino group enables Ugi-4CR to be used in the preparation of the multimodal brushes. Through the regulation of the graft density during the “grafting onto” process, the concentration of the amino groups on the nanoparticles involved in the Ugi reaction can be adjusted, and by changing the feeding ratio of aldehyde-terminated polystyrene, the efficiency of the Ugi reaction can be controlled, thereby achieving the synthesis of monomodal and bimodal polymer brushes. After precisely characterizing those polymer brushes, a flexible approach may be preliminarily raised for tuning the topological structure of the polymer chains on the nanoparticle surfaces.

Facile Synthesis of Amphiphilic Bottlebrush Block Copolymers Bearing Pyridine Pendants via Click Reaction from Protected Alkyne Side Groups

We present the facile synthetic platform for the production of amphiphilic bottlebrush block copolymers bearing pyridine pendants through combination of living anionic polymerization (LAP), ring-op...

A polymerization-induced self-assembly process for all-styrenic nano-objects using the living anionic polymerization mechanism

By combination of the living anionic polymerization (LAP) mechanism with the polymerization-induced self-assembly (PISA) technique, the all-styrenic diblock copolymer poly(p-tert-butylstyrene)-b-polystyrene (PtBS-b-PS) based LAP PISA was successfully developed.

Living anionic copolymerization of DPE derivatives containing alkynyl with controlled kinetic behaviors and monomer sequence

Alkyne functional group plays a significant and versatile role in the post-polymerization modifications to prepare advanced materials. We found an inevitable side reaction, specifically a coupling reaction between poly(styryl)lithiums and alkynes protected with trimethylsilyl groups, when alkyne-contained 1,1-diphenylethylene (DPE) derivative was incorporated into a polymer chain through living anionic polymerization (LAP) method in the previous study. Herein, we redesigned the structure of alkynyl-functionalized DPE derivative by introducing more bulky protecting group (i.e. 1-phenyl-1′-[4-[2-(triisopropylsilyl)ethynyl]phenyl]ethylene, DPE-TPSE), and found that this strategy is effective for restraining the side reaction through investigating the end-capping reaction. However, the phenomenon of multi peaks in SEC is still existed in the copolymerization with scant feeding of DPE-TPSE, which was revealed by Kinetic Monte Carlo simulation and can be attributed to excessively low cross-over of P-DPE-Li to P-St-Li for high reactivity of DPE-TPSE. Further, this unexpected phenomenon was completely eliminated by introducing another electron-donating methoxyl group into the DPE structure (i.e. 1-(4-methyloxyphenyl)-1′-[4-[2-(triisopropylsilyl)ethynyl]phenyl]ethylene, DPE-OTPSE) and the in situ1H NMR method was applied to precisely analyze the kinetics and sequence for the copolymerization with DPE-OTPSE. The apparent kinetic constants for DPE-OTPSE and St (KOTPSE and KSt) are calculated to be 4.35 × 10-4 min−1 and 3.15 × 10-4 min−1, respectively, and the rSt is calculated to be 0.27, which indicates the sequence of DPE-OTPSE units in chain presents gradient feature.

Synthesis of ultrahigh molecular weight bottlebrush block copolymers of ω-end-norbornyl polystyrene and polymethacrylate macromonomers

Well-controlled polystyrene-polymethacrylate bottlebrush block copolymers (BBCPs) of ultrahigh molecular weight using ω-end-norbornyl polystyrene as the macromonomer for the first block were synthesized by combining living anionic polymerization (LAP) and ring-opening metathesis polymerization (ROMP). The ω-end-norbornyl polystyrene (NB-PSt), poly(tert-butyl methacrylate) (NB-PtBMA), poly(methyl methacrylate) (NB-PMMA), and poly(benzyl methacrylate) (NB-PBzMA) macromonomers (MMs) were synthesized by the LAP. The ROMP of the MMs led to poly(NB-g-St) (molecular weight, Mn = 1515 kDa, and dispersity, Ð = 1.12), poly(NB-g-tBMA) (Mn = 1470 kDa, Ð = 1.49), poly(NB-g-MMA) (Mn = 1128 kDa, Ð = 1.42), and poly(NB-g-BzMA) (Mn = 941 kDa, Ð = 1.16) bottlebrush homopolymers at degree of polymerization (DP) of 500. Synthesis of the BBCP, P(NB-g-St)-b-P(NB-g-tBMA) was well-controlled with high molecular weight and a low dispersity (Mn = 3002 kDa, Ð = 1.17) with a total DP of 976. The self-assembly of the resulting BBCP films revealed periodic lamellar morphologies with characteristic photonic crystal properties.

Investigation of the Locked-Unlocked Mechanism in Living Anionic Polymerization Realized with 1-(Tri-isopropoxymethylsilylphenyl)-1-phenylethylene.

Reported is an intriguing advance in living anionic polymerization (LAP) by a "locked-unlocked" mechanism in which the living anionic species can be quantitatively locked by end-capping with 1-(tri-isopropoxymethylsilylphenyl)-1-phenylethylene (DPE-Si(O-iPr)3 ) and can be unlocked by adding the key, sodium 2,3-dimethylpentan-3-olate (NaODP). These new insights into this mechanism were carefully confirmed by designing reactions involving sequential feeding of quantitative DPE-Si(O-iPr)3 and traditional monomers mixed with NaODP, and subsequently characterizing the corresponding samples, taken during the feeding process, by GPC, NMR, and MALDI-TOF-MS techniques. The switch from the locked to unlocked state was clearly confirmed by these characterization techniques. The putative locked-unlocked mechanism in the LAP was simulated by the Gaussian method. This intriguing mechanistic finding of LAP reactions is expected to supplement the existing knowledge and facilitate the tailoring of specific structures for these polymerizations.

Investigation of the Locked‐Unlocked Mechanism in Living Anionic Polymerization Realized with 1‐(Tri‐isopropoxymethylsilylphenyl)‐1‐phenylethylene

AbstractReported is an intriguing advance in living anionic polymerization (LAP) by a “locked‐unlocked” mechanism in which the living anionic species can be quantitatively locked by end‐capping with 1‐(tri‐isopropoxymethylsilylphenyl)‐1‐phenylethylene (DPE‐Si(O‐iPr)3) and can be unlocked by adding the key, sodium 2,3‐dimethylpentan‐3‐olate (NaODP). These new insights into this mechanism were carefully confirmed by designing reactions involving sequential feeding of quantitative DPE‐Si(O‐iPr)3 and traditional monomers mixed with NaODP, and subsequently characterizing the corresponding samples, taken during the feeding process, by GPC, NMR, and MALDI‐TOF‐MS techniques. The switch from the locked to unlocked state was clearly confirmed by these characterization techniques. The putative locked‐unlocked mechanism in the LAP was simulated by the Gaussian method. This intriguing mechanistic finding of LAP reactions is expected to supplement the existing knowledge and facilitate the tailoring of specific structures for these polymerizations.

Sequence Features of Sequence-Controlled Polymers Synthesized by 1,1-Diphenylethylene Derivatives with Similar Reactivity during Living Anionic Polymerization

Living anionic polymerization (LAP) is the primary representative method of living polymerization and exhibits the ability to synthesize sequence-regulated functionalized polymers. However, there has always been a lack of special features for LAP to guide these cutting-edge syntheses in sequence-controlled polymers. In this study, the copolymerizations of a series of alkyl-substituted 1,1-diphenylethylene derivatives (DPE-alkyls), which display similar reactivities but different structures, and St were performed. In addition, the processes of whole chain propagation were monitored by the in situ 1H NMR method. The results show that changing the alkyl type of DPE-alkyls has little influence on their sequence distributions during copolymerization. Therefore, we could deduce a reasonable principle called “sequence equivalence” in LAP: the copolymers of different DPE derivatives and St would have identical sequence structures when DPE derivatives exhibit exactly the same reactivity ratio (rSt) during the copolymerization under the same conditions. Furthermore, the combination of in situ 1H NMR experiments and kinetic Monte Carlo model (KMC) simulations was conducted synchronously. The results of simulations show that the KMC model not only can simulate detailed information for LAP of DPE derivative and St but also could quantify the precision of the corresponding sequence distributions. Additionally, the KMC model that we constructed for the simulation of sequence control in LAP can give us a new insight into the possibility of sequence tailoring. Next, the relationship among the glass transition temperatures (Tgs), types of alkyl substituent, and sequence structures of DPE derivative units in the chains was investigated. Through DSC analysis, this study’s results indicated that polymers with similar sequences but different alkyl substituents present contrasting differences in thermal property. These results could provide a broader understanding of the thermal properties of polymers.

Alcohol- and Water-Tolerant Living Anionic Polymerization of Aziridines

Living anionic polymerization gives access to well-defined polymers, but it demands strict purification of reagents and solvents. This work presents the azaanionic polymerization (AAROP) of aziridines as a robust living polymerization technique, with the ease of controlled radical polymerizations. AAROP does not require inert atmosphere and remains living in the presence of large amounts of water or alcohols. Mesyl-, tosyl-, or brosyl-activated aziridines were polymerized with up to 100-fold excess of a protic impurity with respect to the initiator and still being active for chain extension. This allowed the preparation of polyols by anionic polymerization without protective groups, as only minor initiation occurred from the alcohols. The tolerance toward protic additives lies in the electron-withdrawing effect of the activating groups, decreasing the basicity of the propagating species, while maintaining a strong nucleophilic character. In this way, competing alcohols and water are only slightly involved...

Precise Synthesis of Bottlebrush Block Copolymers from ω-End-Norbornyl Polystyrene and Poly(4-tert-butoxystyrene) via Living Anionic Polymerization and Ring-Opening Metathesis Polymerization

A facile and efficient synthetic grafting-through strategy for preparing well-defined bottlebrush block copolymers (BBCPs) was developed through a combination of living anionic polymerization (LAP) and ring-opening metathesis polymerization (ROMP). ω-End-norbornyl polystyrene (NPSt) and poly(4-tert-butoxystyrene) (NPtBOS) were synthesized by LAP using terminator of chlorine moiety containing silane-protecting amine and coupled with a subsequent amidation using norbornyl activated ester. Bottlebrush homopolymers of NPSt were obtained by ROMP with ultrahigh molecular weights (MWs, Mw = 2928 kDa) and narrow molecular weight distributions (MWDs, Đ = 1.07) at high degree of polymerizations (DPw = 1084). Well-defined BBCPs with ultrahigh MWs (Mw ∼ 3055 kDa) and narrow MWDs (Đ ∼ 1.13) were synthesized through sequential ROMP of NPSt with NPtBOS. The effect of ultrahigh MWs was investigated by self-assembly of the BBCPs in which the phase-separated BBCPs presented periodic lamellar structures and exhibited structural colors from blue to pink.

Preparation of periodic copolymers by living anionic polymerization mechanism assisted with a versatile programmed monomer addition mode

Assisted by a versatile programmed monomer addition mode, the well-defined periodic Poly(styrene-per-isoprene) [Poly(St-per-Is)] copolymers are innovatively prepared by living anionic polymerization (LAP) of a general monomer pair of styrene and isoprene. For comparison, the random Poly(St-ran-Is) and diblock PS-b-PI copolymers are also synthesized. The Differential Scanning Calorimetry (DSC) analysis shows that the periodic Poly(St-per-Is) copolymers always have relatively higher glass transition temperature (Tgs) than the corresponding random Poly(St-ran-Is) analogues with the same molar ratio [St]/[Is] and close molecular weight (MW). The Tgs of copolymers follow a general tendency of Tg,Poly(St-per-Is) > Tg,PS-b-PI > Tg,Poly(St-ran-Is). The reason is rationalized to the different sequence of styrene and isoprene units arranged along the copolymers.

Study on the Mechanism of a Side Coupling Reaction during the Living Anionic Copolymerization of Styrene and 1-(Ethoxydimethylsilyphenyl)-1-phenylethylene (DPE-SiOEt).

A 1,1-diphenylethylene (DPE) derivative with an alkoxysilyl group (DPE-SiOEt) was synthesized. It was end-capped with poly(styryl)lithium (PSLi) and then copolymerized with styrene via living anionic polymerization (LAP) in a non-polar solvent at room temperature. The observed side coupling reaction was carefully investigated by end-capping the polymer. Changes in molecular weight support the plausibility of a mechanism involving living anionic species (PSLi or lithiated DPE-end-capped polystyrene, PSDLi) and the alkoxysilyl groups. Through a series of copolymerizations with different feed ratios, the kinetics of the side coupling reaction were also studied. The results showed that the side reactions could be controlled using an excess feed of DPE-SiOEt, a potentially useful strategy for the synthesis and application of well-defined alkoxysilyl-functionalized polymers via LAP.

Poly(1-adamantyl acrylate): Living Anionic Polymerization, Block Copolymerization, and Thermal Properties

Living anionic polymerization of acrylates is challenging due to intrinsic side reactions including backbiting reactions of propagating enolate anions and aggregation of active chain ends. In this study, the controlled synthesis of poly(1-adamatyl acrylate) (PAdA) was performed successfully for the first time via living anionic polymerization through investigation of the initiation systems of sec-butyllithium/diphenylethylene/lithium chloride (sec-BuLi/DPE/LiCl), diphenylmethylpotassium/diethylzinc (DPMK/Et2Zn), and sodium naphthalenide/dipenylethylene/diethylzinc (Na-Naph/DPE/Et2Zn) in tetrahydrofuran at −78 °C using custom glass-blowing and high-vacuum techniques. PAdA synthesized via anionic polymerization using DPMK with a large excess (more than 40-fold to DPMK) of Et2Zn as the ligand exhibited predicted molecular weights from 4.3 to 71.8 kg/mol and polydispersity indices of around 1.10. In addition, the produced PAdAs exhibit a low level of isotactic content (mm triads of 2.1%). The block copolymers of AdA and methyl methacrylate (MMA) were obtained by sequential anionic polymerization, and the distinct living property of PAdA over other acrylates was demonstrated based on the observation that the resulting PAdA-b-PMMA block copolymers were formed with no residual PAdA homopolymer. The PAdA homopolymers exhibit a very high glass transition temperature (133 °C) and outstanding thermal stability (Td: 376 °C) as compared to other acrylic polymers such as poly(tert-butyl acrylate) and poly(methyl acrylate). These merits make PAdA a promising candidate for acrylic-based thermoplastic elastomers with high upper service temperature and enhanced mechanical strength.

Precise Synthesis of Block and Miktoarm Star‐Branched Polymers Containing Polythiophene Segments with Low Dispersity by Combination of Living Anionic Polymerization and Catalyst‐Transfer Polycondensation Systems

In this Talent article, the synthesis of well‐defined block and miktoarm star‐branched polymers is described by the combination of living anionic polymerization (LAP) and Kumada catalyst‐transfer polymerization (KCTP), mostly focusing on poly(3‐alkylthiophene) (P3AT)‐based block copolymers and miktoarm star‐branched polymers. The two synthetic methodologies are introduced as follows: (a) a chain‐extension method using chain‐end‐functional polymers via site transformation reaction, and (b) a linking reaction method between two polymer building blocks. The most promising method (b) can further be divided into four different approaches, (b‐1) direct addition reaction of living anionic polymers with chain‐end‐functional P3HT; (b‐2) “Click” reaction between two chain‐end‐functional polymers; (b‐3) direct coupling reaction of living anionic polymers with chain‐end‐functional P3HT; and (b‐4) ionic bond formation of chain‐end‐functional polymers. Based on the recent progresses in synthetic methodologies, versatile block copolymers and miktoarm star‐branched polymers have been successfully produced, well controlling the molecular weights (MW) and dispersities (ÐM). image

Living anionic polymerization of 4‐diphenylphosphino styrene for ABC triblock copolymers

Living anionic polymerization of 4-diphenylphosphino styrene (DPPS) achieved unprecedented poly(S-b-I-b-DPPS) ABC triblock copolymers with predictable molecular weights and narrow polydispersities. In situ Fourier transform infrared spectroscopy probed the anionic polymerization, monitoring vinyl disappearance during sequential monomer addition for kinetic analysis. Varying the concentration of reinforcing, polystyrenic external blocks enabled diverse compositions with tunable thermomechanical properties and tailored morphology. Dynamic mechanical analysis confirmed the presence of microphase separation in the triblock copolymers and revealed a broad temperature range (ca 100 oC) for a plateau region and onset of flow temperatures above 100 oC. Small-angle X-ray scattering and atomic force microscopy collectively revealed solid state morphologies of the triblock copolymers and probed phase separation at the nanoscale. Well-defined poly(S-b-I-b-DPPS) ABC triblock copolymers with tunable structure − property relationships now permit phosphorus-containing thermoplastic elastomers for emerging applications. © 2016 Society of Chemical Industry