Ring‐opening polymerization of lactide, ε‐caprolactone and their copolymerization catalyzed by β‐diketiminate zinc complexes

A series of zinc silylamido complexes bearing non‐symmetric β ‐diketiminate ligands were synthesized and structurally characterized. Ring‐opening polymerization (ROP) of rac ‐lactide catalyzed by these zinc complexes afforded heterotactic polylactides at room temperature (P _r = 0.79 ~ 0.83 in THF). The steric and electronic characteristics of the ancillary ligands showed significant influence on the polymerization performance of the corresponding zinc complexes. All these zinc complexes also showed moderate activities toward the polymerization of ε ‐caprolactone at ambient temperature in toluene, producing polycaprolactones (PCLs) with high molecular weights and moderate polydispersities. PCL‐b ‐PLLA copolymers could be obtained via three different copolymerization strategies (one‐pot polymerization, and sequential addition of the two monomers in either order) by adopting complex 6 as the initiator through the adjustment of reaction temperatures. The diblock nature of the copolymers was confirmed by ¹³C NMR spectroscopy and DSC analysis.     

Ring‐opening polymerization of ε‐caprolactone via the bismuth‐2‐mercaptoethanol complex

A complex consisting of one Bi³⁺ ion and two 2‐mercaptoethanol units (BiME₂) was used as initiator for the ring‐opening polymerization of ε‐caprolactone in bulk. A kinetic comparison showed that BiME₂ is as reactive as initiator as Sn‐octanoate and more reactive than Bi‐hexanoate. The difference to BiHex₃ decreased at higher temperatures and upon addition of an alcohol as coinitiator. When tetra(ethylene glycol) was used as coinitiator, it was completely incorporated into the poly(εCL) chain, so that telechelic polylactones having two OH‐endgroups were formed. In the absence of a coinitiator, 2‐mercaptoethanol or its disulfide were incorporated in the form of ester groups. Furthermore, it was found by MALDI‐TOF mass spectrometry that small amounts of cyclic oligolactones (detected up to a degree of polymerization of 17) were formed under all reaction conditions. Higher temperatures and longer times favored a higher content of cycles. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3175–3183, 2006     

Synthesis,characterization, and catalytic activity of titanium iminophenoxide complexes in relation to the ring‐opening polymerization of L‐lactide and ε‐caprolactone

This study synthesized a series of titanium iminophenoxide complexes and investigated their suitability as catalysts for the ring‐opening polymerization of L ‐lactide (L ‐LA) and ε‐caprolactone (CL). Complexes with bidentate ligands demonstrate higher catalytic activity than their tridentate counterparts since the third coordination atom needs to contend with L ‐LA and CL. Differences in the geometric framework of bidentate ligands also influence the catalytic activity. Type II ligands (N, N‐trans form of Ti complex) prevent the coordination of monomers to Ti thereby decreasing the initiation rate. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Tridentate anilido‐aldimine magnesium and zinc complexes as efficient catalysts for ring‐opening polymerization of ε‐caprolactone and L‐lactide

A novel tridentate anilido‐aldimine ligand, [o‐C₆H₄(NHAr)? HC?NCH₂CH₂NMe₂] (Ar = 2,6‐ⁱPr₂C₆H₃, L ‐H, 1 ), has been prepared by the condensation of N, N‐dimethylethylenediamine with one molar equivalent of 2‐fluoro‐benzaldehyde in hexane, followed by the addition of the lithium salt of diisopropylaniline in THF. Magnesium (Mg) and zinc (Zn) complexes supported by the tridentate anilido‐aldimine ligand have been synthesized and structurally characterized. Reaction of L ‐H ( 1 ) with an equivalent amount of MgⁿBu₂ or ZnEt₂ produces the monomeric complex [ L MgⁿBu] ( 2 ) or [ L ZnEt] ( 3 ), respectively. Experimental results show that complexes 2 and 3 are efficient catalysts for ring‐opening polymerization of ε‐caprolactone (CL) and L ‐lactide (LA) in the presence of benzyl alcohol and catalyze the polymerization of ε‐CL and L ‐LA in a controlled fashion yielding polymers with a narrow polydispersity index. In both polymerizations, the activity of Mg complex 2 is higher than that of Zn complex 3 , which is probably due to the higher Lewis acidity and better oxophilic nature of Mg²⁺ metal. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4927–4936, 2009     

Ring opening insertion polymerization of ε‐caprolactone with hydrogen phosphonate initiators

In this work, ring opening insertion polymerization (ROIP) of ε‐caprolactone (ε‐CL) using a series of hydrogen phosphonates (H‐phosphonates) as initiators was investigated. The ROIP occurred by a coordination‐insertion mechanism containing two steps. First, the carbonyl carbon was attacked by the phosphorus atom of the H‐phosphonate tautomerization (a phosphine‐like structure) and the acyl‐oxygen bond was broken. An intermediate was formed by the coordination of the former carbonyl carbon and acyl‐oxygen of ε‐CL to phosphorus atom. Then the phosphorus‐alkoxide of H‐phosphonate was cleavaged to form acyl‐alkoxide bond. Poly(ε‐caprolactone) (PCL)‐inserted H‐phosphonates (PCL‐HPs), which was not only the product of the occurred ROIP but also the initiator for the next ROIP, were produced. After 60 min of microwave irradiation (510 W), PCL with a number‐average molar mass of 7800 g/mol and monomer conversion over 92% was obtained. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6214–6222, 2009     

Titanium complexes of dialkanolamine ligands as initiators for living ring‐opening polymerization of ε‐caprolactone

The titanium complexes with one ( 1a , 1b , 1c ) and two ( 2a , 2b ) dialkanolamine ligands were used as initiators in the ring‐opening polymerization (ROP) of ε‐caprolactone. Titanocanes 1a and 1b initiated living ROP of ε‐caprolactone affording polymers whose number‐average molecular weights (M_n) increased in direct proportion to monomer conversion (M_n ≤ 30,000 g mol^?1) in agreement with calculated values, and were inversely proportional to initiator concentration, while the molecular weight distribution stayed narrow throughout the polymerization (M_w/M_n ≤ 1.2 up to 80% monomer conversion). ¹H‐NMR and MALDI‐TOF‐MS studies of the obtained poly(ε‐caprolactone)s revealed the presence of an isopropoxy group originated from the initiator at the polymer termini, indicating that the polymerization takes place exclusively at the Ti–OⁱPr bond of the catalyst. The higher molecular weight polymers (M_n ≤ 70,000 g mol^?1) with reasonable MWD (M_w/M_n ≤ 1.6) were synthesized by living ROP of ε‐caprolactone using spirobititanocanes ( 2a , 2b ) and titanocane 1c as initiators. The latter catalysts, according MALDI‐TOF‐MS data, afford poly(ε‐caprolactone)s with almost equal content of α,ω‐dihydroxyl‐ and α‐hydroxyl‐ω(carboxylic acid)‐terminated chains arising due to monomer insertion into “Ti–O” bond of dialkanolamine ligand and from initiation via traces of water, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1230–1240, 2010     

Ring‐opening polymerization of ϵ‐caprolactam and ϵ‐caprolactone via microwave irradiation

A novel process for synthesizing nylon‐6 and poly(?‐caprolactone) by microwave irradiation of the respective monomers, ?‐caprolactam and ?‐caprolactone, is described. The ring opening of ?‐caprolactam to produce nylon‐6 was performed in a microwave oven by the forward power being controlled to about 90–135 W in the presence of an ω‐aminocaproic acid catalyst (10 mol %) and for periods of 1–3 h at temperatures varying from 250 to 280 °C. The ring opening of ?‐caprolactone to produce poly(?‐caprolactone) was performed in a microwave oven by the forward power being controlled to about 70–100 W for a period of 2 h in the presence of stannous octoate with and without 1,4‐butanediol over a temperature range of 150–200 °C. The yields, conditions of the reactions, and properties of the products generated relative to the thermal processes are discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2264–2275, 2002     

Ring‐opening polymerization of ϵ‐caprolactone initiated with different ruthenium derivatives: Kinetics and mechanism studies

End‐functionalized polyesters have been synthesized by ring‐opening polymerization (ROP) of ?‐caprolactone (CL) initiated with five different ruthenium derivatives in the presence of a series of alcohols as transfer agents. Mechanistic studies were performed for ROP of CL with RuCl₂(PPh₃)₃ ( I ), TpRuCl(PPh₃)₂ ( II ), and TpRuCl(PHPh₂)(PPh₃) ( III ) as catalysts in the presence or absence of benzyl alcohol (BzOH). Obtained molecular weights are proportional to CL/BzOH ratio, but there is not a direct relationship with CL/ruthenium complex ratios. ¹H and ¹³C NMR spectroscopy revealed the existence of benzyl ester end‐groups. Catalysis involves (a) dissociation of ruthenium complexes, (b) coordination of the lactone CL, (c) coordination of the BzOH with the formation of a metal alkoxide, (d) transfer from the alkoxyl ligand to the coordinated lactone, and (e) ring‐opening of CL by oxygen‐acyl bond cleavage. The proposed mechanism is supported by ¹H, ¹³C, and ³¹P NMR, gel permeation chromatography (GPC), and MALDI‐TOF analysis of the polymers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6926–6942, 2006     

Ring-opening Polymerization of 6-Caprolactone by Lanthanide Tris（ 2,6- dimethylphenolate ） s

Lanthanide tris ( 2,6-dimethylphenolate ) s [ Ln ( ODMP)3 ] were used as iniliators for ring-opening polymerization of e-caprolac-tone (CL) for the first time. The influence of different rare earth elements and solvents was investigated. ^1H NMR spectral data of polycaprolactone (PCL) obtained showed that the poly-merization mechanism is in agreement with the coordination-in-sertion mechanism and the selective cleavage of the acyl-oxygen bond of CL.     

L,L‐Lactide and ε‐Caprolactone Block Copolymers by a ‘Poly(L,L‐lactide) Block First’ Route

L,L ‐lactide (LA) and ε‐caprolactone (CL) block copolymers have been prepared by initiating the poly(ε‐caprolactone) (PCL) block growth with living poly(L,L ‐lactide) (PLA*). In the previous attempts to prepare block copolymers this way only random copolyesters were obtained because the PLA* + CL cross‐propagation rate was lower than that of the PLA–CL* + PLA transesterification. The present paper shows that application of Al‐alkoxide active centers that bear bulky diphenolate ligands results in efficient suppression of the transesterification. Thus, the corresponding well‐defined di‐ and triblock copolymers could be prepared.

     

Ring‐opening polymerization of ε‐caprolactone catalyzed by Yttrium trisphenolate in the presence of 1,2‐propanediol. Do both primary and secondary hydroxyl groups initiate polymerization?

Although the ring‐opening polymerization (ROP) of ε‐caprolactone (CL) in toluene at 100 °C can be initiated by yttrium trisphenolate (Y(OC₆H₅)₃), in the presence of 1,2‐propanediol (PD) the ROP gives much better, that is, controlled polymerizations. In this case, the molecular weights (MWs) are controlled by the CL/PD molar ratios with primary and secondary hydroxyl groups both initiating the ROP and the MW distributions are narrow. The chain transfers between the active yttrium alkoxides and the residual hydroxyl groups on the PD and/or the chain ends appear to be much faster than chain propagation, consistent with the living character of the ROP. Computational studies support these facile reactions with estimated activation free energies in the 3.0–4.5 kcal/mol range compared with about 25–30 kcal/mol for the polymerization. Intramolecular transfer within the PD is predicted to be negligible having a calculated activation energy of 19 kcal /mol. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Grafting of poly(ε‐caprolactone) onto maghemite nanoparticles

We report the coating of maghemite (γ‐Fe₂O₃) nanoparticles with poly(ε‐caprolactone) (PCL) through a covalent grafting to technique. ω‐Hydroxy‐PCL was first synthesized by the ring‐opening polymerization of ε‐caprolactone with aluminum isopropoxide and benzyl alcohol as a catalytic system. The hydroxy end groups of PCL were then derivatized with 3‐isocyanatopropyltriethoxysilane in the presence of tetraoctyltin. The triethoxysilane‐functionalized PCL macromolecules were finally allowed to react on the surface of maghemite nanoparticles. The composite nanoparticles were characterized by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). Effects of the polymer molar mass and concentration on the amount of polymer grafted to the surface were investigated. Typical grafting densities up to 3 μmol of polymer chains per m² of maghemite surface were obtained with this grafting to technique. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6011–6020, 2004     

Homoleptic lanthanide metallocenes and their derivates: syntheses,structural characterization and their catalysis for ring‐opening polymerization of ε‐caprolactone

Homoleptic lanthanide metallocenes Cp′₃Ln [Cp′ = methylcyclopentadienyl, Ln = Y ( 1 ), Er ( 2 ), Sm ( 3 ); Cp′ = cyclopentadienyl, Ln = Er ( 4 ) and Sm ( 5 )] have been found to be a novel type of initiators for the ring‐opening polymerization (ROP) of ε‐caprolactone (ε‐CL). Among them, complex 1 shows the highest catalytic activity for ROP of ε‐CL. In addition, a novel neutral trifluoroethoxo yttrium complex [(MeC₅H₄)₂Y(µ‐OCH₂CF₃)]₂ ( 6 ) has been synthesized by the reaction of 1 with trifluoroethanol in 1:1 molar ratio in toluene and characterized by single‐crystal X‐ray structural analysis. Preliminary study shows that the catalytic activity of tris(methylcyclopentadienyl)yttrium complex 1 is higher than that of bis(methylcyclopentadienyl)yttrium complex 6 . The mechanism of the present polymerization was studied by NMR spectra. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis of biodegradable thermoplastic elastomers from ε‐caprolactone and lactide

This article reports the synthesis and the properties of novel thermoplastic elastomers of A‐B‐A type triblock copolymer structure, where the hard segment A is poly(l ‐lactide) (PLLA) and the soft segment B is poly(ε‐caprolactone‐stat‐d ,l ‐lactide) (P(CL‐stat‐DLLA)). The P(CL‐stat‐DLLA) block with DLLA content of 30 mol % was applied because of its amorphous nature and low glass transition temperature (T_g = approximately ?40 °C). Successive polymerization of l ‐lactide afforded PLLA‐block‐P(CL‐stat‐DLLA)‐block‐PLLAs, which exhibited melting temperature (T_m = approximately 150 °C) for the crystalline PLLA segments and still low T_g (approximately ?30 °C) of the soft segments. The triblock copolymers showed very high elongation at break up to approximately 2800% and elastic properties. The corresponding d ‐triblock copolymers, PDLA‐block‐P(CL‐stat‐DLLA)‐block‐PDLAs (PDLA = poly(d ‐lactide)) were also prepared with the same procedure using d ‐lactide in place of l ‐lactide. When the PLLA‐block‐P(CL‐stat‐DLLA)‐block‐PLLA was blended with PDLA‐block‐P(CL‐stat‐DLLA)‐block‐PDLA, stereocomplex crystals were formed to enhance their T_m as well as tensile properties. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 489–495     

Synthesis and characterization of poly(L‐lactide‐co‐ε‐caprolactone) (B)‐poly(L‐lactide) (A) ABA block copolymers

ABA triblock copolymers of L ‐lactide (LL) and ε‐caprolactone (CL), designated as PLL‐P(LL‐co‐CL)‐PLL, were synthesized via a two‐step ring‐opening polymerization in bulk using diethylene glycol and stannous octoate as the initiating system. In the first‐step reaction, an approximately 50:50 mol% P(LL‐co‐CL) random copolymer (prepolymer) was prepared as the middle (B) block. This was then chain extended in the second‐step reaction by terminal block polymerization with more L ‐lactide. The percentage yields of the triblock copolymers were in excess of 95%. The prepolymers and triblock copolymers were characterized using a combination of dilute‐solution viscometry, gel permeation chromatography (GPC), ¹H‐ and ¹³C‐NMR, and differential scanning calorimetry (DSC). It was found that the molecular weight of the prepolymer was controlled primarily by the diethylene glycol concentration. All of the triblock copolymers had molecular weights higher than their respective prepolymers. ¹³C‐NMR analysis confirmed that the prepolymers contained at least some random character and that the triblock copolymers consisted of additional terminal PLL end (A) blocks. From their DSC curves, the triblock copolymers were seen to be semi‐crystalline in morphology. Their glass transition, solid‐state crystallization, and melting temperature ranges, together with their heats of melting, all increased as the PLL end (A) block length increased. Copyright © 2005 John Wiley & Sons, Ltd.     

Microwave‐assisted graft polymerization of ε‐caprolactone onto magnetite

The graft polymerization of ε‐caprolactone (ε‐CL) onto magnetite was carried out under microwave irradiation in the presence of tin(II) 2‐ethylhexanoate. The molar ratio of ε‐CL to tin(II) 2‐ethylhexanoate was 300, whereas the molar ratio of ε‐CL to magnetite was 5. The chemical structures of the obtained poly(ε‐caprolactone) coated magnetic nanoparticles were characterized by FTIR and XPS spectroscopy. These magnetic‐polymer hybrid nanostructures were further investigated by X‐ray diffraction and magnetization measurements. The morphology of the magnetic core‐shell nanostructures were determined by TEM. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5397–5404, 2009     

Two‐Step Backbiting Reaction in the Ring‐Opening Polymerization of γ‐Acryloyloxy‐ε‐caprolactone Initiated with Aluminium Isopropoxide

γ‐Acryloyloxyethyl‐γ‐butyrolactone is formed as a byproduct when the polymerization of γ‐acryloyloxy‐ε‐caprolactone is initiated with aluminium isopropoxide in toluene. The extent of this side reaction decreases with decreasing temperature and is dependent on whether the reaction is stopped as soon as monomer conversion is complete or not. A two‐step backbiting mechanism is proposed for this intramolecular transesterification reaction.     

Preparation of Poly(ε‐caprolactone)/Clay Nanocomposites by Microwave‐Assisted In Situ Ring‐Opening Polymerization

PCL/clay nanocomposites were prepared by microwave‐assisted in situ ROP of ε‐caprolactone in the presence of either unmodified clay (Cloisite® Na⁺) or clay modified by quaternary ammonium cations containing hydroxyl groups (Cloisite 30B). This PCL showed significantly improved monomer conversion and molecular weight compared with that produced by conventional heating. An intercalated structure was observed for the PCL/Cloisite Na⁺ nanocomposites, while a predominantly exfoliated structure was observed for the PCL/Cloisite 30B nanocomposites. Microwave irradiation proved to be an effective and efficient method for the preparation of PCL/clay nanocomposites.