Ring-opening Polymerization Process Research Articles

Grafting of poly(ε-caprolactone) on electrospun gelatin nanofiber through surface-initiated ring-opening polymerization

ABSTRACTGelatin–polycaprolactone hybrid materials are being used in medicinal applications such as drug delivery, tissue engineering applications nowadays. In this study, gelatin–polycaprolactone graft copolymer was synthesized through ring-opening polymerization process instead of conventional grafting methods using potentially cytotoxic crosslinkers, or applying plasma, aminolysis reactions. Gelatin nanofiber (GNF) was produced by electrospinning process before immobilization of poly(ε-caprolactone). Ring-opening polymerization of ε-caprolactone was successfully initiated on the surface of GNF using tin(IV) isopropoxide and gelatin (primary amine functional groups) as an initiator and a coinitiator, respectively. The growing of polymer chains on GNF was indicated by both scanning electron microscope and energy-dispersive X-ray spectroscopy. Chemical structure was characterized through infrared spectrum, thermal behaviors and the material composition was analyzed with thermogravimetric analysis, wettability and hydrophilicity were determined by water contact angle measurements.

Facile Organocatalyzed Synthesis of Poly(ε-lysine) under Mild Conditions

Functional poly(amino acid)s such as poly(e-lysine) have many potential high-value applications. However, the effective chemosynthetic strategy for these materials remains a big challenge in polymer chemistry; the key issue is how to design and protect amino groups for the effective ring-opening polymerization (ROP). Our lab succeeded in chemosynthesis of poly(e-lysine) via delicate design of a 2,5-dimethylpyrrole protecting group and metal-catalyzed ROP processes, but harsh reaction conditions (e.g., ca. 260 °C) were required. Herein, we developed a superbase t-BuP4-catalyzed ROP of e-lactam derivatives, affording high molecular weight poly(e-lysine) bearing pendant protected amino groups with high monomer conversion (up to 95%). The organocatalytic polymerization could proceed at low reaction temperature (e.g., 60 °C) compatible with readily removable protecting groups, providing a sustainable and new methodology toward facile preparation of poly(e-lysine).

Organocatalytic Cellulose Dissolution and In Situ Grafting of ϵ‐Caprolactone via ROP in a Reversible DBU/DMSO/CO2System

AbstractThe facile dissolution of cellulose via its reversible reaction with CO2in the presence of 1, 8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) in DMSO provides a new efficient platform for derivatization of cellulose, on which serials of grafted poly‐(ϵ‐caprolactone) copolymers were successfully prepared through ring‐opening polymerization (ROP) under mild conditions without adding external catalysts. The strategy allows the preparation cellulose‐graft‐poly‐(ϵ‐caprolactone) copolymers with a molar substitution (MSPCL) of poly‐(ϵ‐caprolactone) ranging 2.29 to 8.01 under mild conditions. The results indicated that DBU acted as not only an important reagent to achieve cellulose dissolution, but it also acted as an organocatalyst for the subsequent ROP process. The grafting content of the prepared copolymers were characterized by1H NMR. Their physiochemical structures were determined by NMR, FTIR, GPC and WXRD, and thermal properties were studied by TGA and DSC.

Synthesis of graphene oxide/polybenzoxazine-based nitrogen-containing porous carbon nanocomposite for enhanced supercapacitor properties

A strategy for the fabrication of graphene oxide (GO) and nitrogen-containing porous carbon (NC) nanocomposites for high-performance supercapacitor electrodes was reported. Driven by the hydrogen bonding and covalent bonding between GO and benzoxazine, GO/NC nanocomposites with different GO content were prepared from a novel polybenzoxazine (PBZ) via a situ ring opening polymerization process coupled with KOH activation technique. The introduction of GO demonstrates a significant effect on the textural property, surface chemistry as well as the electrical conductivity of the nanocomposites, leading to remarkably improvement of the electrochemical behavior. A maximum specific capacitance of 405.6Fg−1 at a current density of 1.0Ag−1 was achieved for GO/NC nanocomposite electrode with GO content of 1.29wt. % in 6M KOH electrolyte solution. It also shows better rate capability (267.8Fg−1 at 40Ag−1) and cycle durability (95.8% capacitance retention over 5000 cycles) in comparison with the activated PBZ-based nanoporous carbon without GO. Additionally, the as-fabricated GO/NCs symmetric supercapacitor devices in 1M Na2SO4 can realize a wide operational voltage of 1.8V, and displays high energy density of 38.6 Wh kg−1 at the power density of 180Wkg−1, which still maintains 19.9 Wh kg−1 at 32.4kWkg−1.

Preparation of Biodegradable Cationic Polycarbonates and Hydrogels through the Direct Polymerization of Quaternized Cyclic Carbonates.

Polymers exhibiting both antimicrobial and biodegradable properties are of great interest for next generation materials in healthcare. Among those, cationic polycarbonates are one of the most promising classes of materials because of their biodegradability, low toxicity, and biocompatibility. They are typically prepared by a chemical postmodification after the polymer has been synthesized. The main problem with the latter is the challenges of ensuring and verifying complete quaternization within the polymer structure. Herein, we report the first example of synthesizing and polymerizing charged aliphatic cyclic carbonates with three different alkane pendant groups (N-methyl, N-butyl, and N-hexyl) by ring-opening polymerization (ROP). These charged eight-membered cyclic carbonates displayed extraordinary reactivity and were even polymerizable in polar solvents (e.g., DMSO) and in catalyst free conditions that are generally unobtainable for other ring opening polymerization processes. A computational study was carried out and the findings were in agreement with the experimental data in regards to the dramatic increase in reactivity of the charged monomer over their neutral analogs. Furthermore, a series of hydrogels were prepared using the different charged eight-membered cyclic carbonates, and we found it to have a significant impact on the hydrogels' ability to swell and degrade in water. Finally, the hydrogels demonstrated antibacterial activity against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive). These materials could be ideal candidates for biologically relevant applications where cationic structure is required.

Block copolymer synthesis in one shot: concurrent metal-free ATRP and ROP processes under sunlight

A completely metal-free strategy was developed by combining Atom Transfer Radical Polymerization (ATRP) and Ring Opening Polymerization (ROP) for the syntheses of block copolymers.

The Quest for Converting Biorenewable Bifunctional α-Methylene-γ-butyrolactone into Degradable and Recyclable Polyester: Controlling Vinyl-Addition/Ring-Opening/Cross-Linking Pathways.

α-Methylene-γ-butyrolactone (MBL), a naturally occurring and biomass-sourced bifunctional monomer, contains both a highly reactive exocyclic C═C bond and a highly stable five-membered γ-butyrolactone ring. Thus, all previous work led to exclusive vinyl-addition polymerization (VAP) product P(MBL)VAP. Now, this work reverses this conventional chemoselectivity to enable the first ring-opening polymerization (ROP) of MBL, thereby producing exclusively unsaturated polyester P(MBL)ROP with Mn up to 21.0 kg/mol. This elusive goal was achieved through uncovering the thermodynamic, catalytic, and processing conditions. A third reaction pathway has also been discovered, which is a crossover propagation between VAP and ROP processes, thus affording cross-linked polymer P(MBL)CLP. The formation of the three types of polymers, P(MBL)VAP, P(MBL)CLP, and P(MBL)ROP, can be readily controlled by adjusting the catalyst (La)/initiator (ROH) ratio, which is determined by the unique chemoselectivity of the La-X (X = OR, NR2, R) group. The resulting P(MBL)ROP is degradable and can be readily postfunctionalized into cross-linked or thiolated materials but, more remarkably, can also be fully recycled back to its monomer thermochemically. Computational studies provided the theoretical basis for, and a mechanistic understanding of, the three different polymerization processes and the origin of the chemoselectivity.

Insight into the Thermal Ring-Opening Polymerization of Phospha[1]ferrocenophanes.

A mixture of cis/trans isomers of phospha[1]ferrocenophanes equipped with one iPr group at the α position to the bridging PhP moiety was prepared. Both isomers (cis-4 and trans-4) were obtained as racemates and could be separated so that their thermal properties were investigated individually. The molecular structure of cis-4 was determined by single-crystal X-ray analysis showing a tilt angle α=26.35(8)°. Interconversion between both isomers occurred in the melt at elevated temperatures and revealed that the trans isomer is thermodynamically more stable. Structural and thermodynamic data was complemented by DFT calculations (B3PW91/6-311+G(d,p) and B3PW91-D3(BJ)/6-311+G(d,p)). Performance of thermal ring-opening polymerization (ROP) of trans-4 at 230 °C gave polymers and cyclic oligomers. Gel permeation chromatography (GPC) of the sulfurized polymer resulted in a molecular weight of 62.5 kDa (Mw ) and a polydispersity index of 1.39 (PDI). Mass spectrometric analysis of the oligomers showed the presence of cyclic species from dimers to heptamers. After sulfurization, preparative thin layer chromatography led to the separation of three isomeric dimers. Structural characterization of these dimers by single-crystal X-ray analysis led to the conclusion that the Fe-Cp bond breaks during the thermal ROP process. A mechanism similar to the known mechanism of the photolytic ROP of ferrocenophanes is proposed.

Complex Structured Fluorescent Polythiophene Graft Copolymer as a Versatile Tool for Imaging, Targeted Delivery of Paclitaxel, and Radiotherapy.

Advances in polymer chemistry resulted in substantial interest to utilize their diverse intrinsic advantages for biomedical research. Especially, studies on drug delivery for tumors have increased to a great extent. In this study, a novel fluorescent graft copolymer has been modified by a drug and targeting moiety and the resulting structure has been characterized by alterations in fluorescent intensity. The polythiophene based hybrid graft copolymer was synthesized by successive organic reactions and combination of in situ N-carboxy anhydride (NCA) ring opening and Suzuki coupling polymerization processes. Initially, targeted delivery of the graft copolymer was investigated by introducing a tumor specific ligand, anti-HER2/neu antibody, on the structure. The functionalized polymer was able to differentially indicate HER2-expressing A549 human lung carcinoma cells, whereas no signal was obtained for Vero, monkey kidney epithelial cells, and HeLa, human cervix adenocarcinoma cells. After integrating paclitaxel into the structure, cell viability, cell cycle progression, and radiosensitivity studies demonstrate HER2/neu targeting polymers were most effective to inhibit cell proliferation. Importantly, the graft copolymer used had no cytotoxic effects to cells, as evidenced by cell viability and cell cycle analysis. This work clearly confirms that a specially designed and fabricated graft copolymer with a highly complex structure is a promising theranostic agent capable of targeting tumor cells for diagnostic and therapeutic purposes.

Aromatic triblock polymers from natural sources as protective coatings for stone surfaces

ABSTRACTAromatic triblock polymers were synthesized, characterized, and tested as protective coatings for stone surfaces. Syntheses were carried out by a ring opening polymerization process from specifically synthesized monomers ((3S)‐6‐methyl‐3‐phenyl‐1,4‐dioxan‐2,5‐dione or 1,4‐benzodioxepin‐3‐methyl‐2,5‐dione) and a perfluoropolyether diol (Fluorolink D10‐H), as chain initiator. Polymers were characterized through spectroscopic and analytical techniques while their stability under photo‐oxidative conditions was tested using a Solar Box. An excellent stability to environmental conditions was noticed with very low degradation during accelerated aging tests up to 1000 h, as detected by FTIR, molecular weight, DSC and weight loss. Furthermore, these polymers formed an excellent protective coating on the stone surface as shown by capillary water absorption test. Finally, as expected, very stable coatings were obtained as shown by aging tests. The stone surface showed negligible changes of color and a good hydrorepellency confirming a good durability of treatments. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43377.

Completely recyclable biopolymers with linear and cyclic topologies via ring-opening polymerization of γ-butyrolactone.

Ring-opening polymerization (ROP) is a powerful synthetic methodology for the chemical synthesis of technologically important biodegradable aliphatic polyesters from cyclic esters or lactones. However, the bioderived five-membered γ-butyrolactone (γ-BL) is commonly referred as 'non-polymerizable' because of its low strain energy. The chemical synthesis of poly(γ-butyrolactone) (PγBL) through the ROP process has been realized only under ultrahigh pressure (20,000 atm, 160 °C) and only produces oligomers. Here we report that the ROP of γ-BL can, with a suitable catalyst, proceed smoothly to high conversions (90%) under ambient pressure to produce PγBL materials with a number-average molecular weight up to 30 kg mol(-1) and with controlled linear and/or cyclic topologies. Remarkably, both linear and cyclic PγBLs can be recycled back into the monomer in quantitative yield by simply heating the bulk materials at 220 °C (linear polymer) or 300 °C (cyclic polymer) for one hour, which thereby demonstrates the complete recyclability of PγBL.

Comparative Study of Aluminum Complexes Bearing N,O- and N,S-Schiff Base in Ring-Opening Polymerization of ε-Caprolactone and L-Lactide.

A series of Al complexes bearing Schiff base and thio-Schiff base ligands were synthesized, and their application for the ring-opening polymerization of ε-caprolactone (CL) and l-lactide (LA) was studied. It was found that steric effects of the ligands caused higher polymerization rate and most importantly the Al complexes with N,S-Schiff base showed significantly higher polymerization rate than Al complexes with N,O-Schiff base (5-12-fold for CL polymerization and 2-7-fold for LA polymerization). The reaction mechanism of CL polymerization was investigated by density functional theory (DFT). The calculations predicted a lower activation energy for a process involved with an Al complex bearing an N,S-Schiff base ligand (17.6 kcal/mol) than for that of an Al complex bearing an N,O-Schiff base ligand (19.0 kcal/mol), and this magnitude of activation energy reduction is comparable to the magnitude of rate enhancement observed in the experiment. The reduction of activation energy was attributed to the catalyst-substrate destabilization effect. Using a sulfur-containing ligand to decrease the activation energy in the ring-opening polymerization process may be a new strategy to design a new Al complex with high catalytic activity.

Cellulose Dissolution and In Situ Grafting in a Reversible System using an Organocatalyst and Carbon Dioxide.

Cellulose is a promising renewable material, but cannot easily be processed homogeneously owing to the stiffness of the molecules and the dense packing of its chains, due to intermolecular hydrogen bonds. Cellulose processability can be improved by chemical modification. The reversible reaction of cellulose with carbon dioxide in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) allows dissolution of cellulose in dimethyl sulfoxide (DMSO). This DMSO solution is an effective medium for grafting L-lactide (LLA) from cellulose by ring-opening polymerization (ROP) under mild conditions, allowing to prepare cellulose-graft-poly(L-lactide) co-polymers with a molar substitution (MSPLLA ) of poly(L-lactide) in the range of 0.37-5.32, at 80 °C. This makes DBU not only an important reagent to achieve cellulose dissolution, but it also acts as organocatalyst for the subsequent ring-opening polymerization process. Characterization of the structure and thermal properties of the co-polymers by a variety of techniques reveals that they have a single glass-transition temperature (Tg ), which decreases with increasing MSPLLA . Thus, the modification results in a transformation of the originally semirigid cellulose into a thermoplastic material with tunable Tg . The carbon dioxide dissolution strategy is an efficient platform for cellulose derivatization by homogeneous organocatalysis.

Synthesis of multifunctional ABC stars with a reduction-labile arm by consecutive ROP, RAFT and ATRP processes

This study aims at versatile synthesis of 3-arm ABC-type (A=poly( e -caprolactone), PCL; B=poly( N -isopropylacrylamide), PNIPAM; C=poly( tert -butyl acrylate), P t BA, or poly(acrylic acid), PAA) miktoarm star copolymers with a reducible disulfide linkage. Using 2-((2-((2-hydroxymethyl-2-((2-bromo-2-methyl)propionyloxy)methyl)propionyloxy)ethyl)disulfanyl)ethyl 4-cyano-4-(phenylcarbonothioylthio)pentanoate (HBCP) as a heterotrifunctional initiator, consecutive ring-opening polymerization (ROP) of e -caprolactone (CL), reversible addition-fragmentation chain transfer (RAFT) polymerization of N -isopropy-lacrylamide (NIPAM) and atom transfer radical polymerization (ATRP) of tert -butyl acrylate ( t BA) afforded ABC1 star, and followed by a subsequent hydrolysis to give ABC2 star. 1H nuclear magnetic resonance (1H NMR) and gel permeation chromatography (GPC) analyses revealed the desired stars and their precursors had well-controlled molecular weight and relatively low polydispersity (PDI￡1.12). As confirmed by GPC analysis, the disulfide linkage in ABC1 star could be efficiently cleaved upon reductive stimulus, during which the topology was converted from star terpolymer to mixtures of homopolymer (B) and diblock copolymer (AC1). In addition to acting as nanocarriers for stimuli-triggered drug delivery systems, ABC stars with terminal bromide, dithiobenzoate and hydroxyl functionalities are expected to form other reduction-cleavable multicomponent copolymers such as (BC- graft -A) m and dendritic graft copolymers via postpolymerization modification. Our research affords a straightforward “core-first” method to construct multifunctional star terpolymers with stimuli-responsive arms and reduction-labile linkage.

High glass transition temperature polyester coatings for the protection of stones

ABSTRACTCopolymers of lactic acid with mandelic or salicylic acid were synthetized through ring‐opening polymerization (ROP) and tested as protective coatings for stones. Most notably, glass transition temperature (Tg), hydrophobicity, and UV barrier properties were increased, making these materials more suitable as protective coating for outdoor stones than poly(lactic acid). A Tg of 76°C was obtained for the alternating copolymer lactic acid/mandelic acid and it was considerably higher than the one of poly(lactic acid) with similar molecular weight (50–55°C). Furthermore, the introduction of a perfluorinated moiety as chain‐end group, using a perfluoro alcohol as initiator of the ROP process, allowed to increase the hydrophobicity and stability of the new coatings. These polymers showed a good protective efficiency when applied on marble stones and preliminary stability tests under solar light showed low degradation, good stability to photo‐oxidative conditions, and negligible color changes after an aging time of 1000 h. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42323.

Methoxyaryl substituted aluminum ketiminate complexes and its activity in ring opening polymerization processes

The synthesis of dimethyl aluminum (LoAlMe2) and chloromethyl aluminum (LoAlMeCl) complexes containing ketiminate ligand [(2-MeO)C6H4]N(H)C(Me)=CHC(Me)=O (LoH) is reported along with the preparation of Lo3Al from LoH and LiAlH4, and ionic [Lo′Al(thf)3]I from LoAlMe2 and I2. In the later complex the pseudooctahedral geometry of the aluminum ion by terdentate ligand {[(2-O)C6H4]NC(Me)=CHC(Me)=O}2− (Lo′), originated from Lo ligand by the methyl group abstraction, and three THF molecules are observed. Structures of these complexes were determined by X-ray techniques. The activity of LoAlMe2 and LoAlMeCl as initiators of ring opening polymerization of ε-caprolactone, trimethylene carbonate and l-lactide, and (co)polymerization of cyclohexene oxide and carbon dioxide was studied.

Experimental and computational studies of ring-opening polymerization of ethylene brassylate macrolactone and copolymerization with ε-caprolactone and TBD-guanidine organic catalyst

The ring-opening polymerization (ROP) of ethylene brassylate, catalyzed by the cyclic guanidine 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) is reported. Several experimental parameters were evaluated for bulk ROP process and polyesters, resulting in molecular weights between 3 and 15 kg mol−1. End-group analysis by 1H nuclear magnetic resonnance (NMR) and matrix assisted laser desorption ionization time of flight computational studies supports the dual behavior of TBD, which can act as both a catalyst and initiator of the polymerization process. Under optimum conditions, semicrystalline poly(ethylene brassylate-co-e-caprolactone) random copolymers were synthesized. Depending on the comonomer content, our results showed a range of melting temperatures between 39 and 69 °C. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 552–561

Organocatalyzed Synthesis of Aliphatic Polyesters from Ethylene Brassylate: A Cheap and Renewable Macrolactone.

The use of organocatalysts for the polymerization of ethylene brassylate, a commercially available, cheap, and renewable macro(di)lactone is reported for the first time. Ethylene brassylate was polymerized by ring-opening polymerization under bulk and solution conditions at 80 °C. Polymerizations were carried out in the presence of several organic catalysts, such as dodecylbenzenesulfonic acid (DBSA), diphenyl phosphate (DPP), p-toluenesulfonic acid (PTSA) and bases, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 1,2,3-tricyclohexylguanidine (TCHG), and 1,2,3-triisopropylguanidine (TIPG), using benzyl alcohol as initiator. Results agreed with a ring opening polymerization process in which the rate of polymerization was accelerated by the catalysts presence in the order of TBD > PTSA > DBSA > DPP > TIPG > TCHG. Complementary computational studies supported the experimental results. The obtained poly(ethylene brassylate) aliphatic polyesters were characterized by NMR, SEC, MALDI-TOF, DSC, and TGA. They showed molecular weights ranging from 2 to 13 kg mol-1 and polydispersity index between 1.5 and 2. Poly(ethylene brassylate) is a semicrystalline polyester similar to poly(ε-caprolactone) with slightly higher melting and glass transition temperatures (Tm = 69 °C, Tg = -33 °C) and good thermal stability.

Dinuclear Zinc–N‐Heterocyclic Carbene Complexes for Either the Controlled Ring‐Opening Polymerization of Lactide or the Controlled Degradation of Polylactide Under Mild Conditions

AbstractWe describe the synthesis of the new Zn–N‐heterocyclic carbene (NHC) alkoxide complexes [(S,CNHC)ZnCl(OBn)]2 (5) and [(O,CNHC)ZnCl(OBn)]2 (6) for use as ring‐opening polymerization (ROP) initiators for lactide polymerization. Complexes 5 and 6 are readily available through an alcoholysis reaction between BnOH and the corresponding Zn–NHC ethyl species [(S,CNHC)ZnCl(Et)] (3) and [(O,CNHC)ZnCl(Et)] (4), and species 3 and 4 were obtained from the reaction of ZnEt2 with the N‐methyl‐N'‐ethylphenylsulfide (1⋅HCl) and N‐methyl‐N'‐ethylmethylether (2⋅HCl) imidazolium salts, respectively. Both solution and solid‐state structural data for Zn benzyloxide species 5 and 6 agree with dimeric structures under the studied conditions (reaction conditions: CH2Cl2 or THF, room temperature). A computational analysis of species 3 and 4 supports a dimeric structure in solution. The ZnII alkoxide species 5 and 6 were found to mediate either the ROP of lactide (in an effective and controlled manner) to produce chain length‐controlled polylactide (PLA) or, in the presence of an alcohol source such as MeOH, the controlled degradation of PLA through extensive transesterification reactions to afford methyl lactate as the major product. A thorough DFT computational analysis of the ROP of lactide initiated by complex 5 was performed, which revealed that the operating coordination–insertion mechanism was assisted by the second Zn center, leading to a lower‐energy ROP process; this result may be of interest for the future design of well‐defined and high‐performance metal‐based catalysts.

Reactor Modeling and Recipe Optimization of Ring-Opening Polymerization: Block Copolymers

This paper addresses reactor modeling and recipe optimization of semibatch ring-opening polymerization processes for making block copolymers. Two rigorous reactor models are developed on the basis of the population balance and method of moments, respectively. The complete polymerization process model also includes vapor–liquid equilibrium equations from applying Flory–Huggins theory. The accuracies of both reactor models are validated against historical plant data by adjusting model parameters such as kinetic rate constants. The recipe optimization problem is formulated to design the optimal reactor operating policy to minimize polymerization time and incorporate additional process constraints in accordance with final product properties and process safety requirements. The resulting dynamic optimization problem is translated to a nonlinear program by using the simultaneous collocation method, and further solved by the interior point method. In the case study example, both reactor models show satisfactory matches between their predictions and the historical plant data. The recipe optimization with both models demonstrates significant process improvement and reductions in batch operating time. Moreover, the moment model shows superiority over the population balance model in terms of computational efficiency.