A single active site metal center of neodymocene chloride for the ring‐opening polymerization of ε‐caprolactone

A germyl‐bridged lanthanocene chloride, Me₂Ge(^tBu‐C₅H₃)₂LnCl (Ln = Nd; (Cat‐ Nd ), was prepared and successfully used as single catalyst to initiate the ring‐opening polymerization of ε‐caprolactone (ε‐CL) for the first time. Under mild conditions (60°C,[ε‐CL]/[Ln] = 200, 4 h), Cat‐ Nd efficiently catalyzes the polymerization of ε‐CL, giving poly(ε‐caprolactone) (PCL) with high molecular weight (MW) (>2.5 × 10⁴) in high yield (>95%). The effects of molar ratio of [ε‐CL]/Cat‐Nd, polymerization temperature and time, as well as solvent were determined in detail. When the polymerization is carried out in bulk or in petroleum ether, it gives PCL with higher MW and perfect conversion (100%). The higher catalytic activity of this neodymocene chloride could be ascribed to the bigger atom in the bridge of bridged ring ligands. Some activators, such as NaBPh₄, KBH₄, AlEt_3, and Al(i‐Bu)₃, can promote the polymerization of ε‐CL by Cat‐ Nd, which leads to an increase both in the polymerization conversion and in the MW of PCL. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 1212–1217, 2012     

Ring‐opening polymerization of ε‐caprolactone by a new yttrium complex: Y[2,2′‐ethylidene‐bis(4,6‐di‐tert‐butylphenoxy)]2(ethylene glycol dimethyl ether)Na(ethylene glycol dimethyl ether)3

The main aims of the work reported here were to synthesize and characterize a new 2,2′‐ethylidene‐bis(4,6‐di‐tert‐butylphenol) (EDBPH₂)‐based bimetal yttrium complex, Y(EDBP)₂(DME)Na(DME)₃ (1c; where DME is ethylene glycol dimethyl ether), which was employed as an efficient initiator for the ring‐opening polymerization of ε‐caprolactone (ε‐CL). From single‐crystal X‐ray diffraction, the solid structure of this new bimetal initiator was well established. Experimental results show that 1c initiates the ring‐opening polymerization of ε‐CL to afford poly(ε‐CL) with a narrow molecular weight distribution (M_w/M_n = 1.09–1.36, 65 °C). Based on an in situ NMR study, a plausible coordination–insertion mechanism is then proposed. The bimetal complex 1c can be used as an initiator for the ring‐opening polymerization of ε‐CL with some living characteristics. A study of the mechanism reveals that DME displacement in 1c by ε‐CL is involved in the initiation process and the propagation may proceed through three pathways by Na? O insertion or Y? O insertion. Copyright © 2009 Society of Chemical Industry     

Ring‐opening polymerization of trimethylenecarbonate and its copolymerization with ϵ‐caprolactone by lanthanide (II) aryloxide complexes

Lanthanide metal (II) 2,6‐di‐tert‐butylphenoxide complexes (ArO)₂Ln(THF)₃ (Ln = Sm 1 , Yb 2 ) alone have been developed to catalyze the ring‐opening polymerization of trimethylenecarbonate (TMC) and random copolymerization of TMC and ε‐caprolactone (ε‐CL) for the first time. The influence of reaction conditions, such as initiator, initiator concentration, polymerization temperature, and polymerization time, on monomer conversion, molecular weight, and molecular weight distribution of the resulting PTMC was investigated. It was found that the divalent complex 1 showed higher activity for the polymerization of TMC than complex 2 . The random structure and thermal behavior of the copolymers P(TMC‐co‐CL) have been characterized by ¹H NMR, ¹³C NMR, GPC, and DSC analysis. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Direct grafting of ε‐caprolactone on solid core/mesoporous shell silica spheres by surface‐initiated ring‐opening polymerization

Poly(?‐caprolactone) (PCL) was formed on Solid core/mesoporous shell (SCMS) silica surface by surface‐initiated ring‐opening polymerization (SI‐ROP). The SI‐ROP of ?‐caprolactone was achieved by heating a mixture of SCMS silica, ?‐caprolactone and the tin(II) 2‐ethylhexanoate [Sn(Oct)₂] in a anhydrous toluene for 20 h at different temperatures viz. 40, 60, and 80°C. The PCL grafted SCMS silica was characterized by fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), X‐ray, differential scanning calorimetry and scanning electron microscopy (SEM). The FTIR spectroscopic analysis reveals the formation of ester linkage between PCL and hydroxyl terminated SCMS silica. TGA investigation shows increase in PCL content on SCMS silica surface with increase in reaction temperature. The SEM photographs clearly show the formation of PCL polymer on the SCMS silica surface without altering the spherical nature of SCMS silica. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Ring opening polymerization of ε‐caprolactone initiated by decamolybdate anion: Determination of kinetic and thermodynamic parameters by DSC and 1H‐NMR

The aim of this work is the kinetic and thermodynamic study (by differential scanning calorimetry (DSC) and proton nuclear magnetic resonance (¹H‐NMR)) of the polymerization of ε‐caprolactone initiated by ammonium decamolybdate. By means of isothermal kinetics, enthalpies of reaction in the range 150–160°C, as well as constant rates of polymerization (using an nth‐order kinetics function model), were determined. From an Arrhenius plot, activation energy (E_a = 85.3 kJ/mol) and preexponential factor (A = 1.78 × 10⁸ min^?1) were estimated. Using dynamic methods, crystallization and melting temperatures for the polymer obtained in situ were derived. Kinetic data for polymerization (obtained by ¹H‐NMR) were fitted to 13 different model reaction functions. It was found that power law equations represent better the conversion versus time plots for this system. On the basis of experimental facts, a coordination‐insertion mechanism involving molybdenum(V) species is proposed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Kinetics study of Ti[O(CH2)4OCHCH2]4 initiated ring‐opening polymerization of ε‐caprolactone by differential scanning calorimetry

Chemical shrinkage was used for the in situ measurement of the progressing chemical stabilization reactions and the influence of ozone during the stabilization of polyacrylonitrile. A method for evaluating the activation energy through the sensitivity temperature is presented. The calculated results show that the activation energies were 161.57 kJ/mol in air and 181.23 kJ/mol in ozone-enriched air. Therefore, the chemical reactions were postponed during stabilization in ozone-enriched air. Ozone seemed to act in three ways: first, ozone promoted the formation of the serious skin–core structure. Second, ozone accelerated the chemical reactions and shortened the stabilization time at lower heating rates. Third, ozone postponed the chemical reactions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Elaboration of Poly(ε‐caprolactone)‐g‐TiNbO5 Nanocomposites via in situ Metal Complex Initiated Intercalative Polymerization

Summary: The preparation of poly(ε‐caprolactone)‐g‐TiNbO₅ nanocomposites via in situ intercalative polymerization of ε‐caprolactone initiated by an aluminium complex is described. These nanocomposites were obtained in the presence of HTiNbO₅ mineral pre‐treated by AlMe₃, but non‐modified by tetraalkylammonium cations. These hybrid materials obtained have been characterized by Fourier transform infrared absorption spectroscopy, wide‐angle X‐ray scattering, scanning electron microscopy, and dynamic mechanical analysis. Layered structure delamination and homogeneous distribution of mineral lamellae in the poly(ε‐caprolactone) (PCL) is figured out and strong improvement of the mechanical properties achieved. The storage modulus of the nanocomposites is enhanced as compared to pure PCL and increases monotonously with the amount of the filler in the range 3 to 10 wt.‐%.

SEM image of the fractured surface of a PCL‐TiNbO₅ nanocomposite film.     

Ring‐opening copolymerization of L‐lactide with ε‐caprolactone initiated by diphenylzinc

Copolymerization of mixtures of L ‐lactide and ε‐caprolactone has been initiated by diphenylzinc. The reaction conditions were investigated, to discover the effects on yield, molecular weight and microstructure of copolymers obtained. The temperature used varied between 50 and 120 °C, the molar ratio of monomer to initiator ranged between 90 and 1440 mol/mol, and the molar ratio of ε‐caprolactone to L ‐lactide employed was between 100/0 and 0/100 mol/mol. Copolymers were characterized by ¹H‐NMR, ¹³C‐NMR, DSC and gel permeation chromatography. The results indicate that incorporation of L ‐lactide to the growing chain is preferred and ε‐caprolactone is copolymerized after most of the L ‐lactide has been depleted. The microstructure of obtained copolyesters was affected considerably by transesterification reactions. It was observed that increasing reaction temperature, reaction time and concentration initiator was advantageous to the transesterification. The crystallinity of copolyester obtained was determined by differential scanning calorimetry. The results are in good agreement with both molar composition and sequence distribution of copolyesters. Copyright © 2006 Society of Chemical Industry     

Asymmetric penta‐armed poly(ε‐caprolactone)s with short‐chain phosphazene core: synthesis,characterization, and in vitro degradation

A novel hydroxyl‐terminated short‐chain penta‐armed phosphazene was prepared. This penta‐armed compound was studied as an initiator for the synthesis of asymmetric penta‐armed poly(ε‐caprolactone)s in the presence of stannous octoate. The effect of molar ratio of monomer to initiator was investigated. Thermal analysis revealed that the penta‐armed poly(ε‐caprolactone)s possessed lower melting point and crystallinity than linear ones. The penta‐armed poly(ε‐caprolactone)s with long chain‐length exhibited higher onset decomposition temperature and maximum decomposition temperature than linear ones owing to the presence of the phosphazene core. The in vitro degradation of linear and penta‐armed PCL was performed in phosphate buffer solution at 37 and 55 °C. Copyright © 2005 Society of Chemical Industry     

Esterification on solid support by surface‐initiated ring‐opening polymerization of ε‐caprolactone from benzylic hydroxyl‐functionalized Wang resin bead

Biodegradable poly(ε‐caprolactone) (PCL) was formed on benzylic hydroxyl‐functionalized Wang resin surface by surface‐initiated ring‐opening polymerization (SI‐ROP). The SI‐ROP of ε‐caprolactone was achieved first by treating Wang resin with Tin(II) 2‐ethylhexanoate [Sn(Oct)₂] to form Tin(II) complex, and then followed by polymerization of ε‐caprolactone in anhydrous toluene at 60°C. Thus, the polymer‐grafted Wang resin was characterized by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), optical microscopy (OM), and field‐emission scanning electron microscopy (FE‐SEM). The FTIR spectroscopic analysis of polymer‐grafted Wang resin (Wang‐g‐PCL) reveals the formation of ester linkage between PCL and hydroxyl‐terminated Wang resin. The DSC thermogram shows melting peak corresponding to PCL polymer on Wang resin surface. Thermogravimetric investigation shows increase in PCL content on the Wang resin surface in terms of percentage of weight loss with increase in reaction time. The formation of polymeric layers on the Wang resin surface can be directly visualized from OM and SEM images. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis of functionalizable and biodegradable polymers via ring‐opening polymerization of 5‐benzyloxy‐trimethylene carbonate and ε‐caprolactone

The biomedical applications of poly(ε‐caprolactone) (PCL) were limited for its high hydrophobicity and crystallinity. In this study, we copolymerized CL with amorphous 5‐hydroxyl‐trimethylene carbonate (HTMC) to solve the problem. The 5‐benzyloxy‐trimethylene carbonate (BTMC) was synthesized to copolymerize with CL, then hydrogenolyzed to obtain hydroxyl pendant groups. A serial of copolymers with different BTMC molar ratio were synthesized and their chemical structures and thermal properties were thoroughly studied with NMR, FT‐IR, GPC, XRD, DSC, and TGA. Finally we examined the water contact angle of the copolymers. DSC and XRD results showed that the PCL segments in the copolymers crystallized below 16.8%. BTMC molar content and the crystallinity of the copolymers increased after hydrolysis. With the introduced hydroxyl pendant groups, the deprotected copolymers improved their hydrophilic property significantly, and the copolymer with 9.3% HTMC molar content had static water contact angle as low as 36.5°. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Functionalization of multi‐walled carbon nanotubes with poly(ε‐caprolactone) using click chemistry

Multi‐walled carbon nanotubes (MWNTs) were covalently functionalized with poly(ε‐caprolactone) (PCL) using click chemistry. First, chlorine moiety‐containing PCL was synthesized by the copolymerization of α‐chloro‐ε‐caprolactone with ε‐caprolactone monomer using ring opening polymerization, and further converted to azide moiety‐containing PCL. The alkyne‐functionalized MWNTs were prepared with the treatment of p‐amino propargyl ether using a solvent free diazotization procedure. The covalent functionalization of alkyne‐derived MWNTs with azide moiety‐containing PCL was accomplished using Cu(I)‐catalyzed [3+2] Huisgen dipolar cycloaddition click chemistry. The PCL‐functionalization of MWNTs was confirmed by the measurements of Fourier transform infra‐red, NMR, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and Characterization of Biodegradable Poly(ε‐caprolactone)‐Polyglycolide‐Poly(ethylene glycol) Monomethyl Ether Random Copolymer

Summary: Poly(ε‐caprolactone)‐polyglycolide‐poly(ethylene glycol) monomethyl ether random copolymers were synthesized from ε‐caprolactone (ε‐CL), glycolide (GA) and poly(ethylene glycol) monomethyl ether (MPEG) using stannous octoate as catalyst at 160 °C by bulk polymerization. The copolymers with different composition were synthesized by adjusting the weight ration of reaction mixture. The resultant copolymer with a weight ratio (10:15:75) of MPEG2000, GA, and CL was characterized by IR, ¹H NMR, GPC and DSC. The new biodegradable copolymer has potential for medical applications since it is combined with properties of PCL, PGA and MPEG.

     

Novel biodegradable amphiphilic poly(ε‐caprolactone)/poly(N‐vinylpyrrolidone) blends via successive in situ polymerizations

In this study, biodegradable blends of poly(ε‐caprolactone) (PCL) and poly(N‐vinylpyrrolidone) (PVP) were prepared by a new strategy in the following steps: (1) free radical polymerization of N‐vinyl‐2‐pyrrolidone (NVP) in ε‐caprolactone (CL); (2) ring‐opening polymerization of ε‐caprolactone in the presence of PVP to obtain the target blends. The structure of the blends was confirmed by FTIR and ¹H NMR, and the molecular weight of PCL and PVP were determined by GPC. SEM study revealed that this polymerization method could decrease the disperse phase size and improve the interphase when compared with solution‐blending method. The phase inversion occurred when PVP content was 15–20 wt %. Subsequently, the PCL sphere dispersed in PVP matrix and its size decreased with the increase of PVP content. The contact angle results showed that PVP has a profound effect on hydrophilic properties of PCL/PVP blends. PCL/PVP blends are believed to be promising for drug delivery, cell therapy, and other biomedical applications. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Surface‐initiated ring‐opening polymerization of ϵ‐caprolactone from the surface of PP film

This article presents the ring‐opening polymerization of ε‐caprolactone (ε‐CL) from PP film modified with an initiator layer composed of ? OSn(Oct) groups. This method consists of two steps: (1) Sn(Oct)₂ exchanged with the hydroxyl groups on the surface of PP film, forming the ? OSn(Oct) groups bonded on the surface; (2) surface‐initiated ring‐opening polymerization of ε‐CL with the ? OSn(Oct) groups. The initiator layer is characterized by attenuated total reflectance‐Fourier transform infrared (ATR‐FTIR), contact angles, and X‐ray photoelectron spectroscopy (XPS). The growth of PCL chains from the initiator layer through ring‐opening polymerization is successfully achieved. ATR‐FTIR, XPS, and scanning electron microscope (SEM) are also used to characterize the grafted film. XPS results reveal that the PCL chains cover the surface of PP film after 4 h. The SEM images reveal that the PCL chain clusters grow into regular spheroidal particles, which can be changed into other different morphology by treated with different solvents. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Biodegradable poly(vinyl alcohol)‐graft‐ poly(ε‐caprolactone) comb‐like polyester: Microwave synthesis and its characterization

Poly(vinyl alcohol)‐initiated microwave‐assisted ring opening polymerization of ε‐caprolactone in bulk was investigated, and a series of poly(vinyl alcohol)‐graft‐poly(ε‐caprolactone) (PVA‐g‐PCL) copolymers were prepared, with the degree of polymerization (DP) of PCL side chains and the degree of substitution (DS) of PVA by PCL being in the range of 3–24 and 0.35–0.89, respectively. The resultant comb‐like PVA‐g‐PCL copolymers were confirmed by means of FTIR, ¹H NMR, and viscometry measurement. The introduction of hydrophilic backbone resulted in the decrease in both melting point and crystallization property of the PVA‐g‐PCL copolymers comparing with linear PCL. With higher microwave power, the DP of PCL side chains and DS of PVA backbone were higher, and the polymerization reaction proceeded more rapidly. Both the DP and monomer conversion increased with irradiation time, while the DS increased first and then remained constant. With initiator in low concentration, the DP and DS were higher, while the monomer was converted more slowly. Microwaves dramatically improved the polymerization reaction in comparison of conventional heating method. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104, 3973–3979, 2007     

Surface modification of starch nanocrystals through ring‐opening polymerization of ε‐caprolactone and investigation of their microstructures

Bionanoparticles of starch obtained by submitting native potato starch granules to acid hydrolysis conditions. The resulted starch nanoparticles were used as core or macro initiator for polymerization of ε‐caprolactone (CL). Starch nanoparticle‐g‐polycaprolactone was synthesized through ring‐opening polymerization (ROP) of CL in the presence of Sn(Oct)₂ as initiator. The detailed microstructure of the resulted copolymer was characterized with NMR spectroscopy. Thermal characteristic of the copolymer was investigated using DSC and TGA. By introducing PCL, the range of melting temperature for starch was increased and degradation of copolymer occurred in a broader region. X‐ray diffraction and TEM micrographs confirmed that there was no alteration of starch crystalline structure and morphology of nanoparticles, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Homoleptic lanthanide amidinate complexes: A single‐component initiator for ring‐opening polymerization of trimethylene carbonate and copolymerization with ϵ‐caprolactone

The ring‐opening polymerization of trimethylene carbonate (TMC) using homoleptic lanthanide amidinate complexes [CyNC(R)NCy]₃Ln as single component initiators has been fully investigated for the first time. The substituents on amidinate ligands and center metals show great effect on the catalytic activities of these complexes, that is, Me > Ph, and La > Nd > Sm > Yb. Among them, [CyNC(Me)NCy]₃La shows the highest catalytic activity. Some features of the TMC polymerization initiated by [CyNC(Me)NCy]₃La were studied in detail. 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 initiated by [CyNC(Me)NCy]₃La was also tested. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 22–28, 2006     

Synthesis and characterization of poly(p‐phenylene)‐graft‐poly(ε‐caprolactone) copolymers by combined ring‐opening polymerization and cross‐coupling processes

2,5‐Dibromo‐1,4‐(dihydroxymethyl)benzene was used as initiator in ring‐opening polymerization of ε‐caprolactone in the presence of stannous octoate (Sn(Oct)₂) catalyst. The resulting poly(ε‐caprolactone) (PCL) macromonomer, with a central 2,5‐dibromo‐1,4‐diphenylene group, was used in combination with 1,4‐dibromo‐2,5‐dimethylbenzene for a Suzuki coupling in the presence of Pd(PPh₃)₄ as catalyst or using the system NiCl₂/bpy/PPh₃/Zn for a Yamamoto‐type polymerization. The poly(p‐phenylenes) (PPP) obtained, with PCL side chains, have solubility properties similar to those of the starting macromonomer, ie soluble in common organic solvents at room temperature. The new polymers were characterized by ¹H and ¹³C NMR and UV spectroscopy and also by GPC measurements. The thermal behaviour of the precursor PCL macromonomer and the final poly(p‐phenylene)‐graft‐poly(ε‐caprolactone) copolymers were investigated by thermogravimetric analysis and differential scanning calorimetry analyses and compared. Copyright © 2004 Society of Chemical Industry     

Structure and morphology of poly(β‐hydroxybutyrate) synthesized by ring‐opening polymerization of racemic (R,S)‐β‐butyrolactone with distannoxane derivatives

Predominantly syndiotactic poly((R,S)‐β‐hydroxybutyrate) (PHB) was synthesized by ring‐opening polymerization of racemic β‐butyrolactone with distannoxane derivatives as catalysts. We have studied the polymerization of (R,S)‐β‐BL using distannoxane derivatives as catalysts and the effects of polymerization time on crude yield and molecular weight of the polymers obtained. Then, a more detailed study of the characterization of polymers obtained using hydroxy‐ and ethoxy‐distannoxanes was performed. ¹³C NMR spectroscopy resolved stereosequences in synthetic PHB at the diad level for the carbonyl carbon and at the triad level for the methylene carbon. These analyses show that distannoxane catalysts produce preferentially syndiotactic polyesters (syndiotactic diads fraction from 0.56 to 0.61). Triad stereosequence distribution of PHB samples agrees favourably with the Bernoullian statistical model of chain‐end control, where ideally Φ = 4(mm) (rr)/(mr + rm)² = 1 for perfect chain‐end control. Polymer samples synthesized from distannoxane catalysts are composed of two distinct transition endotherm components with peak temperatures of approximately 42 °C and 75 °C. The formation of two melting endotherms may be due to the presence of two different crystalline structures. © 2000 Society of Chemical Industry