Homo-and Copolymerization of ε-Caprolactone and 2,2-Dimethyltrimethylene Carbonate by Rare Earth Initiators

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Synthesis and characterization of highly random copolymer of ϵ-caprolactone and D,L-lactide using rare earth catalyst

Highly random copolymers of ϵ-caprolactone (CL) and D ,L -lactide (LA) were synthesized by a new catalyst system, rare earth chloride–propylene oxide (PO) system. In the presence of propylene oxide, all rare earth chlorides tested are highly effective for the copolymerization. The influences of reaction conditions on the copolymerization catalyzed by the NdCl₃-5PO system have been investigated in detail. The reactivity ratios of ϵ-caprolactone and D ,L -lactide were determined and show that the copolymerization with this new rare earth catalyst is closer to ideal copolymerization than reported for other catalysts. The microstructure of copolymer analyzed by ¹³C-NMR shows that the monomer units in the copolymer is near to completely random distribution with a short average monomer sequence length. The DSC measurement confirms the high randomness of the chain structure. The mechanism studied by NMR indicates that the rare earth alkoxide generated by the reaction of rare earth chloride with propylene oxide initiates the copolymerization, and then proceeds via a “coordination-insertion” mechanism with acyl-oxygen bond cleavage of CL and LA. © 1996 John Wiley & Sons, Inc.     

Homopolymerization and Copolymerization of Adipic Anhydride with ε-Caprolactone Catalyzed by Rare Earth Trisphenolate

The ring-opening polymerization of adipic anhydride and the ring-opening copolymerization of adipic anhydride with ε-caprolactone catalyzed by single component rare earth trisphenolate have been reported. The structure of the copolymer poly（CL-b-AA） has been characterized by SEC, ^1H NMR and DSC.     

Homoleptic lanthanide guanidinate complexes: The effective initiators for the polymerization of trimethylene carbonate and its copolymerization with ε‐caprolactone

The ring‐opening polymerization of trimethylene carbonate (TMC) using homoleptic lanthanide guanidinate complexes [RNC(NR′₂)NR]₃Ln as single component initiators has been fully investigated for the first time. The substituents on guanidinate ligands and center metals show great effect on the catalytic activities of these complexes, that is, ? N(CH₂)₅ > ? NⁱPr₂ > ? NPh₂ (for R′), ? Cy > ? ⁱPr (for R), and Yb > Sm > Nd. Among them, [Ph₂NC(NCy)₂]₃Yb shows the highest catalytic activity. Some features and kinetic behaviors of the TMC polymerization initiated by [Ph₂NC(NCy)₂]₃Yb were studied in detail. The polymerization rate is first order, with the monomer concentration and M_n of the polymer increasing with the polymer yield increasing linearly. The results indicated the present system having “living character.” A mechanism that the polymerization occurs via acyl‐oxygen bond cleavage rather than alkyl‐oxygen bond cleavage was proposed. The copolymerization of TMC with ?‐caprolactone (ε‐CL) initiated by [Ph₂NC(NCy)₂]₃Yb was also tested. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1778–1786, 2005     

Cationic graft copolymerization of styrene onto poly(vinyl chloride) initiated by phosphorus trichloride

The effect of some organic halides on the cationic polymerization of styrene (St) initiated by phosphorus trichloride (PCl₃) was studied to clarify the initiation mechanism on the cationic polymerization. Addition of organic halides caused an acceleration to some extent. Further, cationic graft copolymerization of St onto poly(vinyl chloride) and polychloroprene was carried out. In each case, grafting efficiency was lower than 10%. These results in the cationic polymerization of St by PCl₃ in nitrobenzene support the assumption that the initiation step is caused by the dissociation of two molecules of PCl₃ to ion pairs.     

Synthesis and characterization of biodegradable poly(ester anhydride) based on ε‐caprolactone and adipic anhydride initiated by potassium poly(ethylene glycol)ate

Novel biodegradable poly(ester anhydride) block copolymers based on ε‐caprolactone (ε‐CL) and adipic anhydride (AA) were prepared by sequential polymerization. ε‐CL was first initiated by potassium poly(ethylene glycol)ate and polymerized into active chains (PCL‐O^?K⁺), which were then used to initiate the ring‐opening polymerization of AA. The effects of the AA feed ratio, solvent polarity, monomer concentration, and temperature on sequential polymerization were investigated. The copolymers, obtained under different conditions, were characterized by Fourier transform infrared, ¹H NMR, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). The GPC results showed that the weight‐average molecular weights of the block copolymers were approximately 6.0 × 10⁴. The DSC results indicated the immiscibility of the two components. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1511–1520, 2003     

RING-OPENING POLYMERIZATION OF TRIMETHYLENE CARBONATE BY CALIX[8]ARENE-NEODYMIUM*

Ring-opening polymerization of trimethylene carbonate (TMC) with a rare earth calixarene compound as catalysthas been studied for the first time. The effect of TMC/Nd (molar ratio) and polymerization conditions were investigated indetail. It was found that calix[8]arene-neodymium is a highly effective catalyst for the bulk polymerization of TMC and giveshigh molecular weight (M_v = 60,000) polymer. The optimum conditions of TMC polymerization were found to be asfollows:TMC/Nd (molar ratio) = 2,000, 80℃, 16 h. The polymers were characterized by NMR, GPC and DSC. Studying themechanism by NMR showed that the polymerization of TMC catalyzed by calix[8]arene-neodymium proceeds via a cationicmechanism.     

Ring opening polymerization of propylene oxide by chitosan-supported rare earth catalytic system and its kinetics

Ring opening polymerization of propylene oxide in the presence of a new type of catalytic system composed of chitosan-supported rare earth complex, triisobutyl aluminium, and acetylacetone and its kinetics have been studied for the first time. It has been found that the characteristics of this catalytic system are of high catalytic activity, of higher stereoselectivity, and of a high molecular weight polymer of 2 × 10⁶. Kinetic studies show that the polymerization rate is first order with respect to monomer concentration and catalyst concentration, respectively. The apparent activation energy of the polymerization reaction is 37.1 kJ/mol. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2177–2182, 1997     

One‐step synthesis of polycarbonates bearing pendant carboxyl groups by lipase‐catalyzed ring‐opening polymerization

The ring‐opening polymerization of a monomer containing a free carboxylic acid group is reported for the first time. The monomer, 5‐methyl‐5‐carboxyl‐1,3‐dioxan‐2‐one (MCC), was copolymerized with trimethylene carbonate (TMC) in an enzymatic ring‐opening polymerization conducted in bulk at 80 °C. The low‐melting TMC comonomer also solubilized the high‐melting MCC monomer, allowing for solvent‐free polymerizations. Six commercially available lipases were screened, and Candida antarctica lipase‐B (Novozym‐435) and Pseudomonas cepacia lipase were selected to catalyze the copolymerization because of their higher monomer conversions. Higher molecular weight polymers (weight‐average molecular weight = 7800–9200) were prepared when Novozym‐435 was used, with less MCC incorporated into the copolymer than used in the monomer feed. However, Pseudomonas cepacia lipase showed good agreement between the molar feed ratios and the molar composition, but the molecular weights (weight‐average molecular weight = 3600–4800) were lower than those obtained when Novozym‐435 was used. ¹³C NMR spectral data were used for microstructural analysis, which suggested the formation of random, linear, and pendant carboxylic acid groups containing polycarbonates with hydroxyl groups at both chain ends. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1267–1274, 2002     

Copper(0)‐mediated radical copolymerization of vinyl acetate and acrylonitrile in DMSO at ambient temperature

In this work, Cu(0)‐mediated radical copolymerization of vinyl acetate (VAc) and acrylonitrile (AN) was explored. The polymerization was carried out at 25°C with 2,2′‐bipyridine as ligand and dimethyl sulfoxide as solvent. The copolymerization proceeded smoothly producing moderately controlled molecular weights at low VAc feed ratios. The high VAc feed ratios generated low polymerization rate and poorly controlled molecular weights. FTIR, ¹H NMR, and differential scanning calorimetry confirmed the successful obtaining of the copolymers. Based on ¹H NMR spectra, the reactivity ratios of VAc and AN were calculated to be 0.003 and 1.605, respectively. This work conveyed the first example for the Cu(0)‐mediated radical polymerization of AN and VAc, wherein VAc cannot be homopolymerized by Cu(0)‐mediated radical polymerization technique. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Magnesium complexes incorporated by sulfonate phenoxide ligands as efficient catalysts for ring‐opening polymerization of ε‐caprolactone and trimethylene carbonate

Two novel sulfonate phenol ligands—3,3′‐di‐tert‐butyl‐2′‐hydroxy‐5,5′,6,6′‐tetramethyl‐biphenyl‐2‐yl 4‐X‐benzenesulfonate (X?CF₃, L^CF3 ‐H, and X?OCH₃, L^OMe ‐H)—were prepared through the sulfonylation of 3,3′‐di‐tert‐butyl‐5,5′,6,6′‐tetramethylbiphenyl‐2,2′‐diol with the corresponding 4‐substituted benzenesulfonyl chloride (1 equiv.) in the presence of excess triethylamine. Magnesium (Mg) complexes supported by sulfonate phenoxide ligands were synthesized and characterized structurally. The reaction of MgⁿBu₂ with L‐H (2 equiv.) produces the four‐coordinated monomeric complexes ( L^CF3 )₂Mg ( 1 ) and ( L^OMe )₂Mg ( 2 ). Complexes 1 and 2 are efficient catalysts for the ring‐opening polymerization of ε‐caprolactone (ε‐CL) and trimethylene carbonate (TMC) in the presence of 9‐anthracenemethanol; complex 1 catalyzes the polymerization of ε‐CL and TMC in a controlled manner, yielding polymers with the expected molecular weights and narrow polydispersity indices (PDIs). In ε‐CL polymerization, the activity of complex 1 is greater than that of complex 2 , likely because of the greater Lewis acidity of Mg²⁺ metal caused by the electron‐withdrawing substitute trifluoromethyl (? CF₃) at the 4‐position of the benzenesulfonate group. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3564–3572, 2010     

Isothiourea‐based lewis pairs for homopolymerization and copolymerization of 2,2‐dimethyltrimethylene carbonate with ε‐caprolactone and ω‐pentadecalactone

In this study, the homopolymerization of 2,2‐dimethyltrimethylene carbonate (DTC) and its copolymerizations with ε‐caprolactone (CL) were carried out in detail using the isothiourea‐based Lewis pairs comprised 2,3,6,7‐tetrahydro‐5H‐thiazolo(3,2‐a)pyrimidine and magnesium halides (MgX₂) with benzyl alcohol (BnOH) as the initiator. The copolymerization of DTC and CL via one‐pot addition produced randomly sequenced copolymers. On the other hand, a well‐defined linear poly(ε‐caprolactone)–block–poly(2,2‐dimethyltrimethylene carbonate) (PCL‐b‐PDTC) diblock copolymer was prepared by simple sequential ring‐opening polymerization of CL and DTC. In addition, poly(ω‐pentadecalactone)–block–PDTC diblock copolymer was successfully prepared by the same strategy. Moreover, PDTC–poly(ethylene glycol) (PEG)–PDTC triblock copolymer was synthesized in the presence of PEG 2000. The effects of different polymerization conditions on the polymerization reactions have been systematically discussed. The resulting polymers were characterized by the ¹H and ¹³C NMR spectra, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐ToF MS). The block copolyester structures were confirmed by the ¹³C NMR spectroscopy and DSC characterizations. These results indicated that the supposed mechanism was a dual catalytic mechanism. The proposed mechanism involved activation of the monomer via coordination to the MgX₂, and the initiator alcohol was deprotonated by base. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2349–2355     

Copolymerization with the feeding of one of the comonomers: Cationic activated monomer copolymerization of ε‐caprolactone with ethylene oxide

The cationic copolymerization of ε‐caprolactone with ethylene oxide (EO) under the conditions of activated monomer polymerization, that is, with a low‐molecular‐weight diol as an initiator and BF₃ etherate as a catalyst, was studied. To ensure the uniform composition of the resulting copolymers (telechelic oligodiols), the copolymerization was conducted with incremental feeding of the EO comonomer, which was more reactive in the cationic process. ¹H NMR analysis of samples isolated at different stages of the copolymerization indicated that the average composition of the copolymer was indeed nearly constant over the course of the copolymerization. Matrix‐assisted laser desorption/ionization time‐of‐flight spectra of the products revealed, however, that for the same degree of polymerization, macromolecules containing different numbers of EO units were present. The observed distribution was compared with the distribution simulated under the assumption that the probability of incorporating a given unit depended only on the feed composition (nearly constant during the copolymerization). With this assumption, a good agreement between the observed and simulated spectra was obtained. This indicated that, even when the optimum conditions for the formation of a uniform copolymer were created, the individual macromolecules differed in composition because of the statistical character of the copolymerization. The results of differential scanning calorimetry analysis were compatible with such a conclusion; two melting peaks appeared on differential scanning calorimetry curves when a sample was heated immediately after fast cooling, and this may indicate the presence of different types of crystallites. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3788–3796, 2005     

Preparation and characterization of chitosan‐graft‐poly (ϵ‐caprolactone) with an organic catalyst

Chitosan‐graft‐poly(ϵ‐caprolactone) was prepared via the ring‐opening graft polymerization of ϵ‐caprolactone (CL) through chitosan with 4‐dimethylaminopyridine as a catalyst and water as a swelling agent. The graft content of PCL within the graft copolymer was adjusted by the feed ratio of CL to chitosan, and the highest grafting concentration of PCL was up to about 400%. Fourier transform infrared, ¹H NMR, and two‐dimensional heteronuclear single quantum coherence analyses indicated that the amino group (NH₂ CH‐2) of chitosan initiated the graft polymerization of CL through the backbone of chitosan, and the hydroxyl group (HO CH_2–6) of chitosan did not participate in initiating the graft polymerization. The percentage of amino groups initiating the graft polymerization decreased with an increasing molar ratio of CL to chitosan in the feed, and this was attributed to the fact that the graft polymerization system increasingly became heterogeneous with an increasing feed ratio of CL to chitosan. The physical properties of the graft copolymers were characterized by thermogravimetric analysis and wide‐angle X‐ray diffraction, respectively. These suggested that the introduction of PCL grafts through the chitosan backbone would to some extent destroy the crystalline structure of chitosan, and the PCL grafts existed in an amorphous structure. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5353–5361, 2006     

Cationic ring‐opening polymerization behavior of a five‐membered cyclic thiocarbonate having a spiro‐linked adamantane moiety

This work deals with the synthesis and cationic ring‐opening polymerization behavior of a novel five‐membered cyclic thiocarbonate bearing a spiro‐linked adamantane moiety, tricyclo[3.3.1.1^3,7]decane‐2‐spiro‐4′‐(1′,3′‐dioxolane‐2′‐thione) ( TC2 ). The cationic ring‐opening polymerization of TC2 did not proceed with trifluoromethanesulfonic acid, methyl trifluoromethanesulfonate, triethyloxonium tetrafluoroborate (Et₃OBF₄), boron trifluoride etherate (BF₃OEt₂), titanium tetrachloride, or methyl iodide as the initiator, presumably because of the steric hindrance of the adamantane moiety. However, the cationic ring‐opening copolymerization of TC2 with five‐ or six‐membered cyclic thiocarbonates, that is, 1,3‐dioxolane‐2‐thione, 1,3‐dioxane‐2‐thione, 5‐methyl‐1,3‐dioxane‐2‐thione, or 5,5‐dimethyl‐1,3‐dioxane‐2‐thione, initiated by BF₃OEt₂ or Et₃OBF₄, proceeded to afford the corresponding copolymer via a selective ring‐opening direction. The increase in the feed ratio of TC2 in the copolymerization increased the unit ratio derived from TC2 in the copolymer; however, the molecular weight of the copolymer decreased. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 699–707, 2003     

Heteroleptic Tin(II) Initiators for the Ring‐Opening (Co)Polymerization of Lactide and Trimethylene Carbonate: Mechanistic Insights from Experiments and Computations

The tin(II) complexes {LO^x}Sn(X) ({LO^x}^?=aminophenolate ancillary) containing amido ( 1 – 4 ), chloro ( 5 ), or lactyl ( 6 ) coligands (X) promote the ring‐opening polymerization (ROP) of cyclic esters. Complex 6 , which models the first insertion of L ‐lactide, initiates the living ROP of L ‐LA on its own, but the amido derivatives 1 – 4 require the addition of alcohol to do so. Upon addition of one to ten equivalents of iPrOH, precatalysts 1 – 4 promote the ROP of trimethylene carbonate (TMC); yet, hardly any activity is observed if tert‐butyl (R)‐lactate is used instead of iPrOH. Strong inhibition of the reactivity of TMC is also detected for the simultaneous copolymerization of L ‐LA and TMC, or for the block copolymerization of TMC after that of L ‐LA. Experimental and computational data for the {LO^x}Sn(OR) complexes (OR=lactyl or lactidyl) replicating the active species during the tin(II)‐mediated ROP of L ‐LA demonstrate that the formation of a five‐membered chelate is largely favored over that of an eight‐membered one, and that it constitutes the resting state of the catalyst during this (co)polymerization. Comprehensive DFT calculations show that, out of the four possible monomer insertion sequences during simultaneous copolymerization of L ‐LA and TMC: 1) TMC then TMC, 2) TMC then L ‐LA, 3) L ‐LA then L ‐LA, and 4) L ‐LA then TMC, the first three are possible. By contrast, insertion of L ‐LA followed by that of TMC (i.e., insertion sequence 4) is endothermic by +1.1 kcal mol^?1, which compares unfavorably with consecutive insertions of two L ‐LA units (i.e., insertion sequence 3) (?10.2 kcal mol^?1). The copolymerization of L ‐LA and TMC thus proceeds under thermodynamic control.     

Amphiphilic Biodegradable Poly(ϵ-caprolactone)-Poly(ethylene glycol) – Poly(ϵ-caprolactone) Triblock Copolymer Synthesis by Maghnite-H+ as a Green Catalyst

Amphiphilic biodegradable (PCL-PEG-PCL) triblock copolymers have been successfully prepared by the ring opening polymerization of ?-caprolactone (CL) in the presence of poly(ethylene glycol) (PEG) at 80°C employing Maghnite-H⁺ a non-toxic Montmorillonite clay as catalyst. Maghnite-H⁺ reacts as a solid source of protons to induce ?-caprolactone polymerization. The triblock architecture, molecular weight and thermal properties of the copolymers were characterized by NMR spectra, GPC and DSC analyses. The effect of Maghnite-H⁺ proportion and PEGs on the rate of copolymerization and on average molecular weight of resulting copolymers was studied. A cationic mechanism for the copolymerization reaction was proposed.     

Synthesis and properties of poly(carbonate‐co‐ester)s obtained by cationic ring‐opening copolymerization of spiroorthocarbonate and ε‐caprolactone

Cationic ring‐opening copolymerization behavior of 1,5,7,11‐tetraoxaspiro[5.5]undecane (SOC1) and ε‐caprolactone (CL), and the thermal behavior of the obtained copolymers are described. When SOC1 and CL were cationically copolymerized under various feed ratios using BF₃OEt₂ as the initiator in CH₂Cl₂ at 25 °C, the corresponding copolymers were obtained in 77–99% yields. The ¹H NMR spectroscopic analysis of the copolymers revealed that the copolymer compositions were almost identical to the feed ratios, and the diad ratios of SOC1–SOC1/SOC1–CL and CL–SOC1/CL–CL are 48.0/52.0 and 54.3/45.7. These observations proved the random structures of the copolymers without containing the long blocks of the homopolymer sequences. Differential scanning calorimetric (DSC) analysis revealed that the melting points and melting entharpies decreased with the increase of the SOC1 unit compositions, suggesting that the copolymers gain flexibility as the SOC1 unit increases. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2937–2942, 2006     

Homopolymerization and copolymerization kinetics of trimethylene carbonate bearing a methoxyethoxy side group

The polymerization kinetics of 5‐[2‐{2‐(2‐methoxyethoxy)ethyoxy}‐ethoxymethyl]‐5‐methyl‐trimethylene carbonate (TMCM‐MOE3OM) synthesized using the organocatalyst 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) were studied and compared to those with the commonly used catalyst/initiator for ring‐opening polymerization of cyclic carbonates and esters, stannous 2‐ethylhexanoate. Further, the utility of each of these catalysts in the copolymerization of TMCM‐MOE3OM with trimethylene carbonate (TMC) and l ‐lactide (LLA) was examined. Regardless of conditions with either catalyst, homopolymerization of TMCM‐MOE3OM yielded oligomers, having number average molecular weight less than 4000 Da. The resultant molecular weight was limited by ring‐chain equilibrium as well as through monomer autopolymerization. Interestingly, autopolymerization of TMC was also achieved with DBU as the catalyst. Copolymerization with TMC using stannous 2‐ethylhexanoate as the catalyst yielded random copolymers, while diblock copolymers were formed by copolymerization with LLA. With DBU as the catalyst, copolymers with LLA could not be formed, while blocky copolymers were formed with TMC. These findings should be useful in the incorporation of this monomer in the design of polymer biomaterials. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 544–552     

Polymerization of trimethylene carbonate in aqueous solutions: Reaction mechanism and characterization

Polymerization of a trimethylene carbonate (TMC) in an aqueous solution was investigated by gel permeation chromatography, Fourier transform infrared spectroscopy, and nuclear magnetic resonance. The polymerization reaction proceeded rapidly in the aqueous solution and high conversion was achieved in a relatively short time. 1,3‐Propanediol (PPD) formed by hydrolysis of TMC was used as the initiator. The TMC oligomer obtained by ring‐opening polymerization had a TMC unit backbone with terminal 3‐hydroxypropyl groups at both chain ends. The oligomer underwent transesterification reaction with elimination of PPD, resulting in a gradual increase in the molecular weight of the product. The molecular weight was affected by the concentration of TMC. The thermal properties of the polymers were investigated by differential scanning calorimetry. Polymers within the molecular weight (M_n) range from 6.0 × 10³ to 2.3 × 10⁴ g/mol crystallized, and endothermic peaks corresponding to the melting temperature were observed. The glass transition temperature increased with the molecular weight of the polymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1485–1492, 2010