Polymerization Of E-caprolactone Research Articles

Hydrogen Bond Donors in the Catalytic Pocket: The Case of the Ring-Opening Polymerization of Cyclic Esters Catalyzed by an Amino-Propoxide Aluminum Complex

A new aluminum complex (NSO)AlMe2 featuring a hydrogen bond donor on the ligand backbone has been synthesized via the reaction of AlMe3 with 1-((2-(isopropylamino)phenyl)thio)propan-2-ol (NSO-H) and spectroscopically characterized. In the complex, the aluminum atom is in a distorted tetrahedral coordination sphere determined by the anionic oxygen and neutral nitrogen atoms of the ligand and by the two carbon atoms of the alkyl groups. After proper activation, the complex (NSO)AlMe2 was able to promote the ring-opening polymerization of L-, rac-lactide, ε-caprolactone and rac-β-butyrolactone. The polymerization of rac-lactide was faster than that of L-lactide: in a toluene solution at 80 °C, the high monomer conversion of 100 equivalents was achieved in 1.5 h, reaching a turnover frequency of 63 molLA·molAl–1·h–1. The experimental molecular weights of the obtained polymers were close to those calculated, assuming the growth of one polymer chain for one added alcohol equivalent and the polydispersity indexes were monomodal and narrow. The kinetic investigation of the polymerization led to the determination of the apparent propagation constants and the Gibbs free energies of activation for the reaction; the terminal groups of the polymers were also identified. The complex (NSO)AlMe2 was active in harsh conditions such as at a very low concentration or in the melt using technical-grade rac-lactide. A relatively high level of activity was observed in the ring-opening polymerization of ε-caprolactone and rac-β-butyrolactone. DFT calculations were performed and revealed the central role of the NH function of the coordinated ligand. Acting as a hydrogen bond donor, it docks the monomer in the proximity of the metal center and activates it toward the nucleophilic attack of the growing polymer chain.

A theoretical exploration of monomer activation mechanisms in bis-lithium N[sbnd]heterocyclic carbenes complexes for enhanced understanding of charge distribution in ring-opening polymerization of ε-caprolactone

A comprehensive examination was conducted on the ring-opening polymerization (ROP) mechanism of ε-caprolactone (ε-CL) employing bis-lithium N-heterocyclic carbene complexes (bisLiNHCs) in a theoretical framework. The modeled reactions were carried out utilizing density functional theory at B3LYP level. An activated-monomer mechanism was observed, characterized by occurrence of two distinct transition states. Initiating with activation of ε-CL via two lithium atoms from bisLiNHCs catalysts, the ensuing step involved nucleophilic addition of carbonyl group stemming from the lithium benzoxide (LiBnO) initiator. The ring opening ε-CL was accomplished via classical cleavage of acyl-oxygen bond. The determination of reaction barrier heights for ε-caprolactone with bisLiNHCs catalysts involved the examination of potential energy profiles. The computed energy profiles revealed exothermic characteristics for each ROP reaction, with the identification of a rate-determining step occurring at the second transition state, which entailed cleavage of acyl-oxygen bond from monomer. Furthermore, through comparisons catalytic capabilities of bisLiNHCs derivatives and energy barrier heights, it was observed that the length and flexibility of linker chain as well as steric effects from substituent groups, significantly influenced the geometric configuration. These specific variations induce alterations in both distance and angular orientation, which are pivotal aspects influencing the chelation dynamics between lithium and oxygen atoms.

Intensive Cycloalkyl-Fused Pyridines for Aminopyridyl-Zinc-Heteroimidazoles Achieving High Efficiency toward the Ring-Opening Polymerization of Lactides.

The model precatalyst sp3- and sp2-N dinitrogen-coordinated zinc-heteroimidazole has been used as an efficient catalyst for the ring-opening polymerization of cyclic esters. Subsequent to our exceptional active 5,6,7-trihydroquinolin-8-amine-zinc catalysts for the ring-opening polymerization (ROP) of ε-caprolactone, various pyridine-fused cycloalkanones (ring size from five to eight) are developed for the correspondent fused amine-pyridine derivatives and their zinc-heteroimidazole chloride complexes Zn1-Zn8 (LZnCl2) bearing N-diphenylphosphinoethyl pendants. Activated with two equivalents of LiN(SiMe3)2, the title zinc complexes efficiently promote the ROP of L-lactide (L-LA) in situ; among them, Zn4/2Li(NSiMe3)2 catalyzed 500 equivalent L-LA at 80 °C with 92% conversion in 5 min (TOF: 5520 h-1). Under the same conditions, the catalytic efficiency for the ROP of rac-LA by Zn1-Zn8/2Li(NSiMe3)2 was slightly lower than that for L-LA (highest TOF: 4440 h-1). In both cases, cyclooctyl-fused pyridyl-zinc complexes exhibited higher activity than others, while the cycloheptyl-fused zinc complexes showed the lowest activity. The microstructure analysis of the polymers showed they possessed a linear structure capped with CH3O as major and cyclic structure as minor. In this work, all the ligands and zinc complexes were well characterized by 1H/13C/31P NMR, FT-IR spectroscopy as well as elemental analysis.

Catalytic Investigation of ε-caprolactone Polymerization through Schiff BaseTitanium (IV) Complexes

Background: The ring-opening polymerization (ROP) reaction has provided an efficient and convenient route to prepare polyesters of high molecular weight, low polydispersity index, and high optical purity. The poly(ε-caprolactone) (PCL) and poly(lactide) (PLA) were prepared through ROP reaction of ε-caprolactone and D, L-lactide, respectively. These compounds have a huge industrial demand and become an interest among the scientific community to develop more economically and eco-friendly catalysts for ROP reactions. Methods: Three Schiff base ligands, 2-((benzo[d]thiazole-2-ylimino)methyl)phenol, L1; 2-(1-benzo[d]thiazole-2-ylimino)ethyl)phenol, L2; and 2- ((benzo[d]thiazole-2-ylimino)methyl)-5-methoxyphenol, L3; were prepared by the reaction of 2-aminobenzothiazole with 2-hydroxybenzaldehyde, 2-hydroxyacetophenone and 2-hydroxy-4-methoxybenzaldehyde in 1:1 molar ratio. In anticipation of interesting stereochemistry, reactivity, and catalytic potential against ε-caprolactone polymerization, three Titanium(IV) complexes (1 – 3) of these Schiff base ligands were synthesized. All the prepared compounds were characterized by elemental analysis, molar conductance, FT-IR, UV-Vis, 1H-NMR, 13C{1H}-NMR and FAB-Mass spectroscopic technique. Geometry was optimized with the help of DFT. Results: Complex 3 gives a much higher yield (87.7%) in comparison to 1 and 2. The order of catalytic efficiency for complexes is 3>1>2. With the increase in temperature, the % yield was found to decrease, and results are in support of moderate to good potency of synthesized catalysts. Conclusion: Complexes were screened for catalytic potency against ε-Caprolactone polymerization reaction. A most plausible mechanism for the polymerization was also proposed.

Aluminum complexes with sulfur containing pyridine based ligands: Synthesis, structure and catalysis

New pyridinyl SN-bi- (1) and SNS-tridentate (3) ligands were obtained by hydrothiolation of substituted alkenes with thioacetic acid. A number of these, as well as the known SN- (2) and SNO- (4, 5) ligands were used in the synthesis of methylaluminum complexes. Molecular structure of the monoligand, [2,6-MePy(CH2CMe2S)]AlMe2 (1a), [2,6-MePy(CH2CH2CMe2S)]AlMe2 (2a), [2,6-Py(CH2CMe2S)2AlMe] (3a) and [2,6-Py(CH2CH2CMe2SH)(CH2CH2CMe2O)AlMe2]2 (5a), and the diligand, [2,6-MePy(CH2CMe2S)]2AlMe (1b), complexes were studied in solution (NMR spectroscopy) and in crystal (1a, XRD); the dependence between the ligand and the complex structure formed was established. The catalytic activity of 1-3a, 5a and 1b in the ring-opening polymerization of ε-caprolactone was studied in bulk, indicating high control of the process.

Hydrophilically-modified poly(ε-caprolactone) with zwitterionic sulfobetaine/tertiary amine and their self-assemblies in water

To achieve hydrophilic modification of poly(ε-caprolactone) (PCL), a series of amphiphilic copolymers, poly(ε-caprolactone)-b-poly(N,N-dimethylaminoethyl methacrylate-co-sulfobetaine methacrylate) (PCDSs), were synthesized with varying sulfobetaine compositions using a three-step synthetic strategy. Firstly, the hydroxyl-terminated polymer, PDMAEMA-OH was synthesized through free radical polymerization using AIBN as an initiator and 2-mercaptoethanol as a chain transfer agent. Subsequently, the block copolymer poly(ε-caprolactone)-b- poly(N,N-dimethylamino ethylmethacrylate) (PCD) was prepared through ring-opening polymerization of PDMAEMA-OH and ε-caprolactone employing Sn(OCt)2 as the catalyst. Finally, zwitterionization of the tertiary amine groups in PCD was achieved by treating it with 1,3-propane sultone (1,3-PS) in THF to obtain the desired PCDSs copolymers. The chemical compositions and the structures of PCDSs were confirmed by 1H nuclear magnetic resonance (1H NMR) spectroscopy and gel permeation chromatography (GPC). Additionally, self-assembly behavior in water was systematically investigated for both PCD and PCDSs copolymers. The results showed that these copolymers could form stable, pH-responsive micelles with diameters less than 150 nm via solvent evaporation method while also exhibiting efficient loading and release capabilities for the anti-tumor drug doxorubicin (DOX). Furthermore, cytotoxicity assay revealed low cell cytotoxicity of PCDS micelles towards L929, HeLa, and MCF-7 cells; however DOX-loaded PCDS micelles (PCDS/DOX), particularly those composed of 47% sulfobetaine content exhibited significant inhibitory effects on HeLa and MCF-7 cells along with enhanced cellular uptake efficiency. These findings highlight that pH-responsive zwitterionic sulfobetaine-based polymeric micelles derived from the PCDSs hold great promise for effective DOX delivery.

Influence of the steric bulk of a trityl group in the formation of molecular metallosilicates

The molecular silanol (Ph3CO)(iPrO)2Si(OH) was designed to evaluate the degree of steric bulk the trityl moiety imposes on the Si–OH group. The reactivity of the silanol was evaluated by the formation of three metallosilicates with lithium, aluminum, and gallium, and their molecular structures and the degree of association were determined. Hirshfeld atom refinement or DFT calculation, and QTAIM analysis of the electron density in all compounds were used to analyze the bonding situation in the metallosilicate moieties and determine the strength of the intermolecular hydrogen bonds formed by the silanol. Finally, ring-opening polymerization of ε-caprolactone was used as another criterion for the evaluation of the steric bulk imposed by the trityl group.

N-Butyltin(IV) trichloride initiator for the solvent-free ring-opening polymerization of ε-caprolactone: evaluation of the structure-reactivity relationship of tin(IV) derivatives

n-Butyltin(IV) trichloride initiator for the solvent-free ring-opening polymerization of ε-caprolactone: evaluation of the structure-reactivity relationship of tin(IV) derivatives

Synthesis and Characterization of Graft Copolymers with Poly(ε-caprolactone) Side Chain Using Hydroxylated Poly(β-myrcene-co-α-methyl styrene).

Graft copolymers have unique application scenarios in the field of high-performance thermoplastic elastomers, resins and rubbers. β-myrcene (My) is a biomass monomer derived from renewable plant resources, and its homopolymer has a low glass transition temperature and high elasticity. In this work, a series of tapered copolymers P(My-co-AMS)k (k = 1, 2, 3) were first synthesized in cyclohexane by one-pot anionic polymerization of My and α-methyl styrene (AMS) using sec-BuLi as the initiator. PAMS chain would fracture when heated at high temperature and could endow the copolymer with thermal degradation property. The effect of the incorporation of AMS unit on the thermal stability and glass transition temperature of polymyrcene main chain was studied. Subsequently, the double bonds in the linear copolymers were partially epoxidized and hydroxylated into hydroxyl groups to obtain hydroxylated copolymer, which was finally used to initiate the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) to synthesize the graft copolymer with PCL as the side chain. All these copolymers before and after modifications were characterized by proton nuclear magnetic resonance (1H NMR), gel permeation chromatography (GPC), thermogravimetry analysis (TGA), and differential scanning calorimeter (DSC).

(Z)-N-(pyridin-2-yl)benzimidate dimethylaluminum complexes: synthesis, structures and ring-opening polymerization of ε-caprolactone

The easy synthesis and characterization of three new N,O-coordination aluminum complexes (Al1-Al3) bearing (Z)-N-(pyridin-2-yl)benzimidate ligand are presented, as well as their ring-opening polymerization (ROP) of ε-caprolactone (ε-CL). The three aluminum complexes were simply synthesized by single-step reactions of unsubstituted and substituted N-(pyridin-2-yl)benzamides (RC5H4N)NHCOC6H5 (R = H, 1; R = 5-Me, 2; R = 6-Me, 3) with AlMe3; The reactions involved the tautomerization of the original N-(pyridin-2-yl)amide ligands to (Z)-configurational N-(pyridin-2-yl)imidates which acts as N,O-bidentate ligands. Molecular structures of the three obtained aluminum complexes were determined by NMR spectroscopy, single-crystal X-Ray diffraction and elemental analysis. The aluminum complexes (Al1-Al3) were found to catalyze the ring-opening polymerization of ε-caprolactone with moderate activities. The GPC test showed that the produced polycaprolactones with narrow molecular weight distributions (Mw/Mn < 1.14) when the polymerization time within 25 min. For the present system, the introduction of electron-donating methyl substituents at the pyridine ring of the ligand resulted in an apparent increase in catalytic activity. Particularly, among the three investigated aluminum complexes, Al3 showed the highest activity up to 99% conversion rate with [CL]0/[Al]0/[BnOH]0 = 100/1/1 at 80°C for 25 min.

Effect of Keratin Waste on Poly(ε-Caprolactone) Films: Structural Characterization, Thermal Properties, and Keratinocytes Viability and Proliferation Studies

Keratin extracted (KE) from chicken feathers was used for the production of composite films comprising poly(ε-caprolactone) (PCL) and keratin (PCL/KE films). The process involved the extraction of keratin from chicken feathers using a 0.1 M NaOH solution, followed by characterization via sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The PCL was synthesized through the ring-opening polymerization (ROP) of ε-caprolactone (ԑ-CL) with Sn(Oct)2 as a catalyst. Films were prepared via solvent casting, including pure PCL films and those enriched with different weight percentages of KE (10%, 15%, 25%, and 30%). The films were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TG), and scanning electron microscopy (SEM). SEM analysis revealed a more uniform incorporation of KE within the PCL matrix in the case of the 15% keratin-enriched film (PCL/KE15) as compared to other keratin percentages. The thermal analysis showed a positive influence of keratin on the thermal stability of the films. Keratinocytes viability and proliferation tests on the PCL/KE15 film demonstrated compatibility with cells. Collectively, these results hold relevance for potential biomedical applications of PCL/KE films.

Synthesis of PEGylated amphiphilic block copolymers with pendant linoleic moieties by combining ring-opening polymerization and click chemistry.

This study focused on synthesizing and characterizing PEGylated amphiphilic block copolymers with pendant linoleic acid (Lin) moieties as an alternative to enhance their potential in drug delivery applications. The synthesis involved a two-step process, starting with ring-opening polymerization of ε-caprolactone (CL) and propargylated cyclic carbonate (MCP) to obtain PEG-b-P(CL-co-MCP) copolymers, which were subsequently modified via click chemistry. Various reaction conditions were explored to improve the yield and efficiency of the click chemistry step. The use of anisole as a solvent, N-(3-azidopropyl)linoleamide as a substrate, and a reaction temperature of 60°C proved to be highly efficient, achieving nearly 100% conversion at a low catalyst concentration. The resulting copolymers exhibited controlled molecular weights and low polydispersity, confirming the successful synthesis. Furthermore, click chemistry allows for the attachment of Lin moieties to the copolymer, enhancing its hydrophobic character, as deduced from their significantly lower critical micelle concentration than that of traditional PEG-b-PCL systems, which is indicative of enhanced stability against dilution. The modified copolymers exhibited improved thermal stability, making them suitable for applications that require high processing temperatures. Dynamic light scattering and transmission electron microscopy confirmed the formation of micellar structures with sizes below 100 nm and minimal aggregate formation. Additionally, 1H NMR spectroscopy in deuterated water revealed the presence of core-shell micelles, which provided higher kinetic stability against dilution.

Aluminum Complexes Bearing Aminoquinoline Ligands with Different Pendant Donors: Remarkable Impact of Hemilability on the Ring-Opening Polymerization of ε-Caprolactone

Aluminum Complexes Bearing Aminoquinoline Ligands with Different Pendant Donors: Remarkable Impact of Hemilability on the Ring-Opening Polymerization of ε-Caprolactone

Non-isothermal kinetics of the organocatalytic ring-opening polymerization of ε-caprolactone with metal-free α‑hydroxy acids: Eco-friendly and facile synthesis process

Metal-free and green α‑hydroxy acids (AHA) such as l-malic (MA), DL-mandelic acid (MDL), and citric acid (CA) were successfully and effectively utilized as an effective initiator for the solvent-free ring-opening polymerization (ROP) of ε-caprolactone (ε-CL). The performance of AHAs in the polymerization of ε-CL was completely and powerfully investigated via the non-isothermal differential scanning calorimetry (DSC). The proceed of ROP of ε-CL with AHAs could be real-time monitored by the obtained polymerization exotherms at different heating rates. The polymerization exotherms obtained from the ROP of ε-CL with CA occurred at a lower temperature range than MA, and MDA, respectively. From the kinetics study, the average activation energy (Ea) values for the ROP of ε-CL with CA (38.0 ± 1.8 kJ mol−1) were lower than MA (45.2 ± 3.6 kJ mol−1) and MDA (48.8 ± 6.2 kJ mol−1). Using the first-order model fitting, the values of pre-exponential factor (lnA0) for the ROP of ε-CL with CA, MA, and MDA were 7.0 ± 0.3, 8.5 ± 0.2, and 8.9 ± 0.3, respectively. The effectiveness of AHAs in the synthesis of PCL was clarified by conducting a larger-scale (4.0000 g) polymerization using conventional heating and microwave (MW) irradiation methods. From conventional heating, the green AHAs produced PCL with the number average molecular weight (Mn) and dispersity (Đ) values in the range of 5.18 × 103 - 1.43 × 104 g mol−1 and 1.14–2.02, respectively. The irradiation by MW could enhance the synthesis of PCL by reducing the synthesis time. By using the MW power of 450 W and irradiation time of 30 min, the PLC was obtained from the ROP of ε-CL with MA and MDA initiators, and the Mn of the obtained PCL from MW heating was 4.28 × 103 - 8.45 × 103 g mol−1. The mechanism for the ROP of ε-CL with all AHAs was proposed through the activated monomer mechanism.

Extended Hydrogen-Bonded Molybdenum Arrays Derived from Carboxylic Acids and Dianilines: ROP Capability of the Complexes and Parent Acids and Dianilines

From reactions involving sodium molybdate and dianilines [2,2′-(NH2)C6H4]2(CH2)n (n = 0, 1, 2) and amino-functionalized carboxylic acids 1,2-(NH2)(CO2H)C6H4 or 2-H2NC6H3-1,4-(CO2H)2, in the presence of Et3N and Me3SiCl, products adopting H-bonded networks have been characterized. In particular, the reaction of 2,2′-diaminobiphenyl, [2,2′-NH2(C6H4)]2, and 2-aminoterephthalic acid, H2NC6H3-1,4-(CO2H)2, led to the isolation of [(MoCl3[2,2′-N(C6H4)]2}{HNC6H3-1-(CO2),4-(CO2H)]·2[2,2′-NH2(C6H4)]2·3.5MeCN (1·3.5MeCN), which contains intra-molecular N–H∙∙∙Cl H-bonds and slipped π∙∙∙π interactions. Similar use of 2,2′-methylenedianiline, [2,2′-(NH2)C6H4]2CH2, in combination with 2-aminoterephthalic acid led to the isolation of [MoCl2(O2CC6H3NHCO2SiMe3)(NC6H4CH2C6H4NH2)]·3MeCN (2·3MeCN). Complex 2 contains extensive H-bonds between pairs of centrosymmetrically-related molecules. In the case of 2,2′ethylenedianiline, [2,2′-(NH2)C6H4]2CH2CH2, and anthranilic acid, 1,2-(NH2)(CO2H)C6H4, reaction with Na2MoO4 in the presence of Et3N and Me3SiCl in refluxing 1,2-dimethoxyethane afforded the complex [MoCl3{1,2-(NH)(CO2)C6H4}{NC6H4CH2CH2C6H4NH3}]·MeCN (3·MeCN). In 3, there are intra-molecular bifurcated H-bonds between NH3 H atoms and chlorides, whilst pairs of molecules H-bond further via the NH3 groups to the non-coordinated carboxylate oxygen, resulting in H-bonded chains. Complexes 1 to 3 have been screened for the ring opening polymerization (ROP) of both ε-caprolactone (ε-CL) and δ-valerolactone (δ-VL) using solvent-free conditions under N2 and air. The products were of moderate to high molecular weight, with wide Ð values, and comprised several types of polymer families, including OH-terminated, OBn-terminated (for PCL only), and cyclic polymers. The results of metal-free ROP using the dianilines [2,2′-(NH2)C6H4]2(CH2)n (n = 0, 1, 2) and the amino-functionalized carboxylic acids 1,2-(NH2)(CO2H)C6H4 or 2-H2NC6H3-1,4-(CO2H)2 under similar conditions (no BnOH) are also reported. The dianilines were found to be capable of the ROP of δ-VL (but not ε-CL), whilst anthranilic acid outperformed 2-aminoterephthalic acid for both ε-Cl and δ-VL.

Aluminum Tris(2-pyridyl)borates: Structure, reactivity and catalysis

Tris(2-pyridyl)borates are emerging scorpionate ligands distinguished by their robustness and modularity, as well as their strong electron-donicity. Metal tris(2-pyridyl)borates show a strong tendency toward six-coordinate, pseudooctahedral metal geometries with static κ3-ligation. Most exceptions involve sterically hindered tris(2-pyridyl)borates. We report four-coordinate alkylaluminum complexes with the sterically unhindered ligand phenyl tris(2-pyridyl)borate (Tpy–), using single-crystal XRD, variable-temperature NMR, and computational modelling to characterize their structure and dynamics. Thus proton exchange between TpyH and trialkylaluminum gave four-coordinate complexes TpyAlR2 (–R = methyl, ethyl, and isobutyl), the first κ2-complexes of sterically unhindered tris(2-pyridyl)borates. Moreover, pyridine coordination in TpyAlR2 complexes is fluxional, showing NMR symmetry down to −80 °C. Computational modelling suggests that pyridine exchange occurs through a higher energy five-coordinate κ3-conformation. By contrast, the analogous gallium complex TpyGaMe2 is also κ2, but NMR does not show pyridine interconversion even up to 70 °C. Alternatively, proton exchange involving TpyH, trialkylaluminums, and acids gives κ3, four-coordinate cations with the composition [TpyAlR]+ (–R = methyl, ethyl, and isobutyl), in addition to an unusual protonated tris(2-pyridyl)borate complex [TpyHAliBu2]+. Furthermore, reaction of TpyH with two equivalents of AlMe3 gave the first bimetallic tris(2-pyridyl)borate complex TpyAl2Me5, with distinct κ2- and κ1-bound aluminum sites. Finally, we characterize controlled polymerization of ε-caprolactone by these complexes at high temperatures.

Computational evaluation of zirconocene catalysts for ε-caprolactone cationic ring-opening polymerization

This quantum chemical study presents the ligand effect and a structure–property relationship in the cationic ring-opening polymerization (CROP) of ε-caprolactone using zirconocene catalysts. We first examined the effects of catalyst structure on the initiation and chain propagation steps of the CROP process. A total of 54 catalyst structures were investigated to understand the influence of the ligand structure on the stability of the catalyst–monomer complex and polymerization activity. The properties of the catalysts were analyzed in terms of ancillary ligands, ligand substituents, and bridging units. Calculations showed that the polymerization follows a proposed cationic mechanism, with ring opening occurring via alkyl-bond cleavage. A correlation between complex stability and activation energy was also observed, with ligand substituents dominating in both steps. While the ancillary ligands directly affect the HOMO energy level, the bridges are mainly responsible for the catalyst geometries, resulting in reduced complex stability and higher activation energy for the propagation step. This study contributes to a better understanding of the structural characteristics of zirconocene catalysts, which offers guidance for improving CROP activities in lactone polymerization.

Kinetic modeling of cationic ring-opening polymerization for the synthesis of biodegradable poly(ε-caprolactone)

Ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) is an efficient way to produce a widely used biodegradable polymer, i.e., poly(ε-caprolactone) (PCL). Compared to coordination ROP, ionic ROP receives great attentions in recent years due to mild reaction conditions and well-defined polymer microstructure. To fully exploit the potential of ionic ROP, in this work, a mathematical kinetic model for activated monomer mechanism (AMM) based cationic ROP of ε-CL was developed based on method of moments (MoM). Using the developed model, we estimated the values of the kinetic coefficients of monomer activation and monomeric units’ protonation reactions. The simulated results are found to be in good agreement with experimental data, as well as the benchmark by kinetic equation. Moreover, the simulations reveal the crucial role of transesterification reaction in molar mass distribution broadening and how the concentrations of acid and alcohol affect the monomer conversion and average molar masses of the polymer. Finally, the model was successfully extended to a newly reported system using trityl tetrafluoroborate (TrBF4) as catalyst, proving the universality of our model. This study provides deeper understanding of the cationic ROP and allows to optimize process conditions to increase the industrial sustainability of PCL-based materials.

Highly solvent-dependent naphthalene diimide-based fluorescent polymer sensors for detecting p-xylene

P-xylene (PX), as one of xylenes, is a kind of very important chemical raw material. It is generally fabricated using methanol (MeOH) and toluene (TOL), and serves as a useful intermediary. However, it is difficult to use a simple and convenient tool to distinguish it from TOL and MeOH. Herein, we reported a simple naphthalene diimide-based polycaprolactone polymer (NDI-PCL) as a high-sensitive fluorescent sensor for xylene detection from MeOH and TOL. NDI-PCL was synthesized via ring-opening polymerization (ROP) of ε-caprolactone. NDI-PCL showed a remarkable fluorescence change from blue to green and yellow because of the formation of charge transfer (CT) interaction between naphthalene diimide (NDI) and aromatic solvents. NDI-PCL was successfully applied as the high-sensitive sensor for discriminating binary solvent mixtures such as PX in TOL, MeOH in PX, and MeOH in TOL, and their limit of detection (LOD) were as low as 19 ppm, 16 ppm and 9 ppm. These excellent fluorescence properties ensured that NDI-PCL indicated great potential application in detecting aromatic solvents.

A comparative study of titanium complexes bearing 2-(arylideneamino)phenolates and 2-((arylimino)methyl)phenolates as catalysts for ring-opening polymerization of ε-caprolactone and L-lactide.

Titanium complexes bearing 2-(arylideneamino)phenolates and 2-((arylimino)methyl)phenolates were synthesized, and their catalytic activities in the polymerization of ε-caprolactone and L-lactide were studied. Among five-membered ring Ti complexes bearing 2-(arylideneamino)phenolates, FCl-Ti exhibited the highest level of catalytic activity ([CL] : [FCl-Ti] = 100 : 1, where [CL] = 2 M, and conv. = 86% at 60 °C after 9 h). For six-membered ring Ti complexes bearing 2-((arylimino)methyl)phenolates, SCl-Ti exhibited the highest level of catalytic activity ([CL] : [SCl-Ti] = 100 : 1, where [CL] = 2 M, and conv. = 88% at 60 °C after 118 h). The five-membered ring Ti complexes bearing 2-(arylideneamino)phenolates exhibited a higher level of catalytic activity (6.1-12.8 fold for the polymerization of ε-caprolactone and 6.2-23.0 fold for the polymerization of L-lactide) than the six-membered ring Ti complexes bearing 2-((arylimino)methyl)phenolates. The density functional theory (DFT) results revealed that the free energy of the first transition state FH-Ti-TS1 is 36.49 kcal mol-1 which is lower than that of SH-Ti-TS1 (46.58 kcal mol-1), which was ascribed to the fact that the Ti-Nim bond (2.742 Å) of FH-Ti-TS1 is longer than that of SH-Ti-TS1 (2.229 Å) and reduces the repulsion between ligands.