Chemoselective Polymerization Research Articles

A one-pot approach towards polycarbonate-b-polyester block copolymers via chemoselective polymerization catalyzed by a one-component phosphonium borane Lewis pair

Chemoselective polymerization from a mixture of l-LA, CHO and CO2 enables the synthesis of PLLA, PCHC or PCHC-b-PLLA achieved by PBB-Br. The chemoselectivity depends on the nature of the growing polymer chain end.

Synthesis of Sequence-Controlled Homopolymer via Anionic Self-Alternating and Chemoselective Polymerization of 4-Vinyl-1,1-diphenylethylene Derivatives

Synthesis of Sequence-Controlled Homopolymer via Anionic Self-Alternating and Chemoselective Polymerization of 4-Vinyl-1,1-diphenylethylene Derivatives

Molecular design of ferrocene-based novel polymer using click chemistry via chemoselective polymerization and investigation of electrical properties as organic Schottky diode

Organic Schottky diodes are electronic devices that consist of a metal–semiconductor junction formed with an organic polymer as the semiconductor material. This work synthesized cinnamic acid side chain bearing polymer and its ferrocene-modified polymer. Thermal stability, dielectric and electrical properties of the initial polymer and the modified one were examined and the addition of a ferrocene unit to the initial polymer clearly improved the optical and electrical properties of the target polymer. Due to the influence of ferrocene, the dielectric constant increased from 8.69 to 18.92. Additionally, it was discovered that the ac conductivity value raised from 6.40x10−9 to 2.64x10−8. The Al/modified-polymer/p-Si structure exhibits an ideality factor of 2.22, a barrier height of 0.61 eV, and a reverse bias current of 1.28 10−5 A in the dark, according to the I-V measurements. These results demonstrated the fabricated diodes have a rectifier behavior. This diode exhibits unique electrical properties due to the characteristics of the organic polymer.

Original Fluorinated Non-Isocyanate Polyhydroxyurethanes

New fluorinated polyhydroxyurethanes (FPHUs) with various molar weights were synthesized via the polyaddition reaction of a fluorinated telechelic bis(cyclocarbonate) (bis-CC) with a diamine. The fluorinated bis-CC was initially synthesized by carbonylation of a fluorinated diepoxide, 1,4-bis(2',3'-epoxypropyl)perfluorobutane, in the presence of LiBr catalyst, in high yield. Then, several reaction conditions were optimized through the model reactions of the fluorinated bis-CC with hexylamine. Subsequently, fluorinated polymers bearing hydroxyurethane moieties (FPHUs) were prepared by reacting the bis-CC with different hexamethylenediamine amounts in bulk at 80 °C and the presence of a catalyst. The chemoselective polymerization reaction yielded three isomers bearing primary and secondary hydroxyl groups in 61-82% yield. The synthesized fluorinated CCs and the corresponding FPHUs were characterized by 1H, 19F, and 13C NMR spectroscopy. They were compared to their hydrogenated homologues synthesized in similar conditions. The gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) data of the FPHUs revealed a higher molar mass and a slight increase in glass transition and decomposition temperatures compared to those of the PHUs.

Chemoselective Synthesis of Tyrosine‐Based Polymers and Comparison of Their Thermal, Kinetic, and Dielectric Properties

AbstractBoth synthetic chemistry and polymer science, benefiting from click chemistry, have paved the way for the easy synthesis and use of polymer compounds in various application areas. In this work, a chemoselective polymerization reaction (for the synthesis of polymer 1) in which click reaction occurred in a further step (for the synthesis of polymer 2) was carried out through the monomer obtained from the reaction of tyrosine with propargyl amine (PA) and methyl methacrylate. Polymer 2 was synthesized from azido end chalcone and the polymer carrying alkyne in its side chain by using the click chemistry. The average activation energy of polymers 1 and 2 were 116.95 and 81.54 kJ mol−1, respectively. The thermal and dielectric properties of both polymers were compared. The results indicated that the alkyne ends in polymer 1 are completely converted into triazole rings after the click reaction, and polymer 2 gained more thermal stability and dielectric property compared to polymer 1. Dielectric constant (ϵ′) of polymer 2 (16.42) increased about 2.70 fold after the addition of the chalcone group to polymer 1 (6.09). These results indicate that polymer 2 with a high dielectric constant is a potential compound to use in electronic applications such as capacitors.

Chemo- and Stereoselective Polymerization of Polar Divinyl Monomers by Rare-Earth Complexes

Chemoselective polymerization of divinyl monomers is a promising strategy to access functional polymers via postpolymerization, which however, encounters a cross-linking problem. Herein, we report ...

Chemoselective Polymerization of Fully Biorenewable α-Methylene-γ-Butyrolactone Using Organophosphazene/Urea Binary Catalysts Toward Sustainable Polyesters

Despite the great potential of biorenewable α-methylene-γ-butyrolactone (MBL) to produce functional, recyclable polyester, the ring-opening polymerization (ROP) of MBL remains a challenge due to th...

Chemoselective Polymerization of Epoxides from Carboxylic Acids: Direct Access to Esterified Polyethers and Biodegradable Polyurethanes.

Carboxylic-acid-initiated ring-opening polymerization (ROP) of epoxides is a fast approach to esterified polyethers which are cleavable at the termini or centers. A major challenge lies in conventional ROP methods because of the lability of ester groups formed in the initiation step. Here, we describe chemoselective ROP of epoxides from aliphatic, aromatic, and methacrylic carboxylic acids using two-component metal-free catalysts. Transesterification is clearly absent so that well-defined α-(carboxylic ester)-ω-hydroxy polyethers are generated in one step from monocarboxylic acids. The livingness of the ROP is verified despite the slow initiation mode. The ester end group can be readily cleaved from the polyether hydrolytically. An α,ω-dihydroxy poly(propylene oxide) with two central ester groups is generated from a diacid initiator and transformed in situ by the same catalyst to polyurethane which shows distinct enzymatic degradability. This study provides convenient access to α,ω-heterobifunctional polyethers with cleavable, releasable, or modifiable end groups and to biodegradable polyether-based materials.

Continuous flow rare earth phenolates catalyzed chemoselective ring-opening polymerization

A novel chemoselective polymerization methodology was established by employing rare earth catalysis and microflow technology. The microscale effect (inner size and flow rate) on chemoselectivity and polymerization kinetic were investigated for the model system of mercapto-alcohol initiating ring-opening polymerizations (ROP) of caprolactone (ε-CL) in the presence of lanthanum tris(2,6-di-tert-butyl-4-methylphenolate)s. By reducing the inner diameter (ID) of the microreactor tube from 4 mm to 0.5 mm, the chemoselectivity (thiol fidelity) was firstly increased from 63% into 74% and then decreased to 69%. Faster flow rates enabled better chemoselective (82% at 667 μL min−1 vs 63% at 167 μL min−1). The chemoselective polymerization kinetics were compared between batch reactor and microreactor with varied ID. In contrast to the batchwise reaction, flow chemistry brought great benefits in the chemoselective polymerization, including faster polymerization, higher thiol fidelity, more controlled molecular weight and distributions. Microreactor with 2 mm ID showed better performance than that with 1 mm ID, which was consistent with the results of microscale effect study. Six varied rare earth phenolates were utilized to demonstrate the versatility of microflow system and resultant polymer exhibited thiol fidelity over 87%. By applying this continuous flow chemoselective ROP strategy, series of well-defined thiol-terminated poly poly(ε-caprolactone)s were efficiently synthesized under optimized flow conditions with high thiol fidelity (>91%) and varied molecular weights (3440–15,090 g mol−1). This work would provide deep insight into microflow technology and chemoselective polymerization.

Living and Chemoselective (Co)polymerization of Polar Divinyl Monomers Mediated by Bulky Lewis Pairs

A near 100% initiation efficiency and 100% regioselectivity at the methylacrylic C═C bond was realized by bulky Lewis pairs-mediated polymerization of polar divinyl monomers such as 4-vinylbenzyl methacrylate at mild conditions, affording soluble polymers bearing pendant active vinyl groups with narrow dispersities. A delicate combination of Lewis acid and base with suitable steric hindrance is necessary for achieving high initiation efficiency and activity. The livingness and robustness of the bulky Lewis pair polymerization systems provide a simple and convenient route to produce various di- or tri-block copolymers by the stepwise addition of the different monomers, as well as the copolymer in random distribution by the use of the mixed monomers.

Organocatalyzed chemoselective ring-opening polymerizations

A novel metal-free and protecting-group-free synthesis method to prepare telechelic thiol-functionalized polyesters is developed by employing organocatalysis. A scope of Brønsted acids, including trifluoromethanesulfonic acid (1), HCl.Et2O (2), diphenyl phosphate (3), γ-resorcylic acid (4) and methanesulfonic acid (5), are evaluated to promote ring-opening polymerization of ε-caprolactone with unprotected 6-mercapto-1-hexanol as the multifunctional initiator. Among them, diphenyl phosphate (3) exhibits great chemoselectivity and efficiency, which allows for simply synthesis of thiol-terminated poly(ε-caprolactone) with near-quantitative thiol fidelity, full monomer conversion, controlled molecular weight and narrow polydispersity. Kinetic study confirms living/controlled nature of the organocatalyzed chemoselective polymerizations. Density functional theory calculation illustrates that the chemoselectivity of diphenyl phosphate (3) is attributed to the stronger bifunctional activation of monomer and initiator/chain-end as well as the lower energy in hydroxyl pathway than thiol one. Moreover, series of tailor-made telechelic thiol-terminated poly(δ-valerolactone) and block copolymers are efficiently generated under mild conditions.

Chemoselective Polymerization of Polar Divinyl Monomers with Rare-Earth/Phosphine Lewis Pairs.

This work reports the chemoselective polymerization of polar divinyl monomers, including allyl methacrylate (AMA), vinyl methacrylate (VMA), and 4-vinylbenzyl methacrylate (VBMA), by using simple Lewis pairs comprised of homoleptic rare-earth (RE) aryloxide complexes RE(OAr)3 (RE = Sc (1), Y (2), Sm (3), La (4), Ar = 2,6-tBu2C6H3) and phosphines PR3 (R = Ph, Cy, Et, Me). Catalytic activities of polymerizations relied heavily upon the cooperation of Lewis acid and Lewis base components. The produced polymers were soluble in common organic solvents and often had a narrow molecular weight distribution. A highly syndiotactic poly(allyl methacrylate) (PAMA) with rr ~88% could be obtained by the scandium complex 1/PEt3 pair at −30 °C. In the case of poly(4-vinylbenzyl methacrylate) (PVBMA), it could be post-functionalized with PhCH2SH. Mechanistic study, including the isolation of the zwitterionic active species and the end-group analysis, revealed that the frustrated Lewis pair (FLP)-type addition was the initiating step in the polymerization.

Chemoselective polymerization platform for flow synthesis of functional polymers and nanoparticles

A chemoselective polymerization platform was designed for flow synthesis of telechelic thiol-functionalized polymers, amphiphilic block copolymers and noble metal nanoparticles. By assembling Novozyme435 packed tubular reactor, α-thiol-ω-hydroxyl telechelic poly(ε-caprolactone) were efficiently obtained via metal-free and protecting-group-free ring-opening polymerizations. Fast polymerization, high end group fidelity, controlled molecular weight and distribution were achieved under the flow conditions. The resultant mercapto-polymer solution derived from the enzymatic process was directly pumped into the subsequent microreactor system (isolation-step-free) to prepare amphiphilic poly(N-vinylpyrrolidone)-block-poly(ε-caprolactone). Relative narrower molecular weight distribution was observed in contrast to the batch mode. Moreover, silver nanoparticles were facilely fabricated in flow fashion by using mercapto-polymer solution as the stabilizer without isolation. The surface plasma resonance band absorption of nanoparticles could be adjusted by regulating the flow rates. This chemoselective polymerization platform would provide a powerful toolbox for the novel polymer and nanomaterial preparations.

Organocatalytic and Chemoselective Polymerization of Multivinyl-Functionalized γ-Butyrolactones.

Achieving complete chemoselectivity in the polymerization of multivinyl polar monomers is an important yet challenging task, currently achievable only by metal- or metalloid-mediated polymerization processes but in a noncatalytic fashion. Now this work shows that organic N-heterocyclic carbene (NHC) catalysts effect rapid, chemoselective, and catalytic polymerization of multivinyl-functionalized γ-butyrolactones, particularly γ-vinyl-α-methylene-γ-butyrolactone (VMBL). Thus, the NHC-catalyzed polymerization of VMBL not only is quantitatively chemoselective, proceeding exclusively via polyaddition across the conjugated α-methylene double bond while leaving the γ-vinyl double bond intact, but also requires only an exceptionally low catalyst loading of 50 ppm, thus, exhibiting a remarkably high catalyst turnover frequency of 80000 h-1 and producing on average 33.6 polymer chains of Mn = 73.8 kg/mol per NHC molecule. The resulting PVMBL can be either thermally cured into cross-linked materials or postfunctionalized with the thiol-ene "click" reaction to achieve complete conversion of the pendant vinyl group on every repeat unit into the corresponding thioether.

Chemoselective Polymerizations from Mixtures of Epoxide, Lactone, Anhydride, and Carbon Dioxide.

Controlling polymer composition starting from mixtures of monomers is an important, but rarely achieved, target. Here a single switchable catalyst for both ring-opening polymerization (ROP) of lactones and ring-opening copolymerization (ROCOP) of epoxides, anhydrides, and CO2 is investigated, using both experimental and theoretical methods. Different combinations of four model monomers-ε-caprolactone, cyclohexene oxide, phthalic anhydride, and carbon dioxide-are investigated using a single dizinc catalyst. The catalyst switches between the distinct polymerization cycles and shows high monomer selectivity, resulting in block sequence control and predictable compositions (esters and carbonates) in the polymer chain. The understanding gained of the orthogonal reactivity of monomers, specifically controlled by the nature of the metal-chain end group, opens the way to engineer polymer block sequences.

Highly Active Half-Metallocene Yttrium Catalysts for Living and Chemoselective Polymerization of Allyl Methacrylate

Highly active half-metallocene amidinate yttrium catalysts for chemoselective and living polymerization of allyl methacrylate are reported. The living characteristics of allyl methacrylate polymerization have been proved by three sets of experiments. The generated polymers exhibit good solubility in DMF, well-controlled molecular weights, and narrow molecular weight distributions (Đ < 1.10). The kinetic studies revealed that the catalyst systems follow a living monometallic coordination–addition polymerization mechanism. The present study is first example for rare earth metal-catalyzed living coordination–addition polymerization of polar divinyl monomers.

Lewis Pair Polymerization of Acrylic Monomers by N‐Heterocyclic Carbenes and B(C6F5)3

AbstractThis work has uncovered the first highly active and efficient Lewis pair polymerization (LPP) system based on N‐heterocyclic carbene (NHC)/B(C6F5)3 pairs for converting acrylic monomers into medium‐ to high‐molecular weight polymers. The study has systematically examined steric and electronic effects of three 1,3‐dialkyl(Me, iPr, tBu)imidazol‐2‐ylidene NHCs on the LPP of three classes of acrylic monomers, including linear methyl methacrylate (MMA), cyclic biorenewable γ‐methyl‐α‐methylene‐γ‐butyrolactone (γMMBL), and difunctional allyl methacrylate (AMA). For MMA polymerization, IiPr is not only the most active (∼3× and ∼120× more active than IMe and ItBu, respectively), but also the most effective NHC, especially under low NHC loading conditions. Kinetic results are consistent with a bimolecular, activated monomer propagation mechanism. In the case of the more reactive γMMBL, the polymerization by NHC/B(C6F5)3 in CH2Cl2 is extremely rapid, with all three NHCs achieving quantitative monomer conversion in 1 min and thus reaching a high turnover frequency of≥48,000 h−1. The molecular weight (MW) of PγMMBL can be tuned by adjusting the [γMMBL]/[NHC] ratio, and thus high MW polymers with relatively narrow MW distributions can be readily synthesized (e.g., from Mn=1.41×105 g mol−1, Đ=1.08 to Mn=4.89×105 g mol−1, Đ=1.20). The LPP by NHC/B(C6F5)3 is completely chemoselective, as demonstrated by the polymerization of AMA, which selectively polymerizes the conjugated vinyl group while leaving the non‐conjugated vinyl group in the allyl moiety intact, thanks to its activated monomer propagation mechanism. The resulting PAMA is syndiotactic (rr=83 %), uncross‐linked, and soluble in common solvents, thus suitable for further functionalization. This quantitatively chemoselective polymerization by NHC/B(C6F5)3 should provide a facile, yet powerful, approach to functional acrylic polymers.

Chemoselective polymerization control: from mixed-monomer feedstock to copolymers.

A novel chemoselective polymerization control yields predictable (co)polymer compositions from a mixture of monomers. Using a dizinc catalyst and a mixture of caprolactone, cyclohexene oxide, and carbon dioxide enables the selective preparation of either polyesters or polycarbonates or copoly(ester-carbonates). The selectivity depends on the nature of the zinc–oxygen functionality at the growing polymer chain end, and can be controlled by the addition of exogeneous switch reagents.

Chemoselective Polymerization Control: From Mixed‐Monomer Feedstock to Copolymers

AbstractA novel chemoselective polymerization control yields predictable (co)polymer compositions from a mixture of monomers. Using a dizinc catalyst and a mixture of caprolactone, cyclohexene oxide, and carbon dioxide enables the selective preparation of either polyesters or polycarbonates or copoly(ester‐carbonates). The selectivity depends on the nature of the zinc–oxygen functionality at the growing polymer chain end, and can be controlled by the addition of exogeneous switch reagents.

Asymmetric Polymerization of (S)-N-Maleoyl-L-Leucine Allyl Ester and Chiral Recognition Ability of Its Polymer as Chiral Stationary Phase for HPLC

(S)-N-Maleoyl-L-leucine allyl ester ((S)-ALMI), a kind of N-substituted maleimide having two double bonds with different reactivities, was newly synthesized from maleic anhydride, L-leucine, and allyl alcohol. Asymmetric polymerizations were carried out to obtain optically active polymers. Poly((S)-ALMI) obtained by anionic polymerization with n-butyllithium/(S,S)-(1-ethylpropylidene)-bis(4-benzyl-2-oxazoline) (n-BuLi/Bnbox) complex in THF showed the highest negative specific rotation of −429.1°. Chemoselective polymerization behaviors of (S)-ALMI on the two reactive groups were elucidated. In anionic polymerizations, only the double bond in the maleimide moiety exclusively took part in the polymerization, affording the corresponding poly((S)-ALMI) with the allyl pendant group. In radical polymerizations, the solvents strongly affect the radical polymerization behaviors of (S)-ALMI. Chiroptical properties and structures of the poly((S)-ALMI)s obtained were investigated by GPC, CD, XRD, and NMR measurements. The methods of preparing chiral stationary phases (CSPs) for high performance liquid chromatography (HPLC) and the chiral recognition ability of the optically active poly((S)-ALMI) were also discussed.