In vitro hydrolytic degradation of poly(?-caprolactone) grafted dextran fibers and films

We studied the hydrolytic degradation of poly(?-caprolactone) grafted dextran (PGD) fibers and films (matrices) prepared by electrospinning and solvent evaporation methods, respectively. In vitro degradation and erosion experiments were carried out in phosphate buffered saline (pH 7.4 ± 0.1) at 37 ± 1 °C for 150 days. Changes in molecular weights and morphologies of the PGD matrices were monitored as a function of degradation time. The extent of degradation was measured by physical weight loss, scanning electron microscopic (SEM) observations, Fourier transform-infrared (FT-IR) spectroscopy, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). During the progress of hydrolysis, GPC chromatograms appeared bi modal for fibers and bi and trimodal for the films. The crystallization temperature (T_c) and heat of fusion were significantly increased in both matrices; this indicated preferential hydrolytic degradation in amorphous regions followed by cleavage-induced crystallization. The biodegradation rates were faster for the films (28%) than fibers (23%). After 150 days of degradation, the pH was steady at 5.8 ± 0.3 for fibers and 6.1 ± 0.3 for films. The faster degradation of the films could be probably due to autocatalysis in the interior of the films and the degraded oligomers are hard to diffuse out into the surrounding solution due to its compact physical geometry. Thus, our preliminary results about the degradation of matrices suggested that PGD nanofibers could be excellent matrices in tissue engineering over the films.     

Synthesis and characterization of organic–inorganic macrocyclic molecular brushes with poly(ε-caprolactone) side chains

In this work, we reported the synthesis of a dodecahydroxyl-functionalized macrocyclic oligomeric silsesquioxane (MOSS). The novel 24-membered hydroxyl-functionalized MOSS was employed as a macroinitiator for the ring-opening polymerization of ε-caprolactone (CL) and the organic–inorganic macrocyclic molecular brushes with poly(ε-caprolactone) (PCL) side chains were successfully synthesized. The organic–inorganic macrocyclic molecular brushes were characterized by means of nuclear magnetic resonance spectroscopy (NMR) and gel permeation chromatography (GPC). The results of wide angle X-ray diffraction (XRD) indicate that the architecture of the organic–inorganic macrocyclic molecular brushes did not alter the structure of PCL crystals. Differential scanning calorimetry (DSC) shows that the architecture of organic–inorganic macrocyclic molecular brushes significantly affected the rearrangement of PCL crystals. Compared to linear PCL, the organic–inorganic macrocyclic molecular brushes possessed the improved thermal stability in terms of the temperatures at the maximum of degradation rate and the yields of degradation residues.     

Synthesis and characterization of calixarene-based poly(ε-caprolactone) stars catalyzed by yttrium complex

Two calixarene derivatives (2a, 2b) have been synthesized and used as macro-initiators to prepare star-shaped poly(ε-caprolactone)s (SPCLs) via controlled ringopening polymerization of ε-caprolactone in the presence of yttrium tris(2,6-di-tert-butyl-4-methylphenolate) [Y(DBMP)₃]. The molecular weight of SPCLs was characterized by end group ¹H-NMR analyses and size-exclusion chromatography (SEC). The results indicate that SPCLs based on a calix[4]arene derivative (2a) are well-defined four-arm star polymers with reasonably narrow molecular weight distributions in the given molecular weight range, while SPCLs based on a calix[6]arene derivative (2b) are star polymers with not so defined structures. Differential scanning calorimetry (DSC) analyses suggest that the maximal melting point, the crystallization temperature and the degree of crystallinity of SPCLs increases with the increasing molecular weight and are lower than those of the liner poly(ε-caprolactone) (LPCL) counterpart. Furthermore, polarized optical microscopy (POM) indicates that SPCL exhibits irregular spherulites with poor morphology and slower crystallization rate, whereas LPCL shows fast crystallization rate and good spherulitic morphology. __________ Translated from Acta Polymerica Sinica, 2007, 10: 967–973 [译自:高分子学报]     

Biodegradation of aliphatic polyesters soaked in deep seawaters and isolation of poly(?-caprolactone)-degrading bacteria

To investigate biodegradability of so-called biodegradable plastics in deep sea, degrading behavior of aliphatic polyesters poly(?-caprolactone) [PCL], poly(β-hydroxybutyrate/valerate) [PHB/V], and poly(butyrene succinate) [PBS] in deep seawaters were evaluated at Rausu, Toyama, and Kume, Japan. After 12 months of soaking in deep seawaters, PCL and PHB/V fibers became brittle or completely ruined. Although breaking strength of PBS fibers maintained approximately 95% of the initial values, for all 3 fibers, many pinholes and cracks were observed on the surfaces. These results imply that examined 3 aliphatic polyesters are degradable also at deep sea though the degradation rates would vary with the material structures. From the deep seawaters assessed, 5 PCL-degrading bacteria were isolated, which were found to belong to the genuses Pseudomonas, Alcanivorax, and Tenacibaculum, as assessed by phylogenetic analysis using 16S rRNA gene sequencing. It was also confirmed that all these bacteria degrade PCL fibers in vitro. In addition, these strains were found to prefer conditions of low temperature (4-10 °C) and high hydrostatic pressure.     

Synthesis and characterization of isomeric 4- and 8-(σ-CHCHPh)-closo-ruthenacarboranes with η:η-phosphacarbocyclic ligand

Reactions of [3,3-(PPh₃)₂-3-Cl-3-H-3,1,2-closo-RuC₂B₉H₁₁] (1) and its exo-nido isomer [exo-5,6,10-{Ru(Ph₃P)₂Cl}-5,6,10-(μ-H)₃-10-H-7,8-nido-C₂B₉H₈] (2) with NH₄PF₆ in methanol or ethanol solution followed by heating in the presence of an excess of phenylacetylene (3) affords a mixture of two isomeric closo species [3,3-{(1′-3′-η³):(5′,6′-η²)-ortho-C₆H₄PPh₂CHC(Ph)CHCHPh}-8-(σ-CHCHPh)-3,1,2-closo-RuC₂B₉H₁₀] (4) and [3,3-{(1′-3′-η³):(5′,6′-η²)-ortho-C₆H₄PPh₂CHC(Ph)CHCHPh}-4-(σ-CHCHPh)-3,1,2-closo-RuC₂B₉H₁₀] (5) in which boron vertexes in β- and α-sites with respect to the cage carbons bear the (E)-CHCHPh group. The X-ray diffraction study of 4 together with the multinuclear NMR data for 4 and 5 revealed that such an unusual η³:η²-phosphacarbocyclic ligand in both isomeric complexes is formed by specific insertion of the initially metal-bound PPh₃ group into the chain of two alkyne molecules coupled in a “head-to-tail” fashion around the metal vertex.     

Synthesis and micellar characterization of thermosensitive amphiphilic poly(ε-caprolactone)-b-poly(N-vinylcaprolactam) block copolymers

Poly(ε-caprolactone)-b-poly(N-vinylcaprolactam) (PCL-b-PVCL) block copolymers were synthesized as new biocompatible, thermosensitive, amphiphilic block polymers by a combination of ring-opening polymerization and reversible addition–fragmentation chain transfer (RAFT) polymerization, and their thermosensitive micellar behavior was examined. The PCL macro-chain-transfer agent was first synthesized by converting the end group of PCL-OH to O-ethyl xanthate, which was subsequently used for the RAFT polymerization of N-vinylcaprolactam. The critical micelle concentration of PCL-b-PVCL (M _n,NMR?=?56,300?g/mol, polydispersity index?=?1.18) was 0.026?mg/mL. The mean diameter of the PCL-b-PVCL micelles determined by transmission electron microscopy was 55?±?25?nm. The PCL-b-PVCL micelles exhibited repetitive aggregation and dispersion during reversible cooling and heating cycles between 20 and 40?°C due to the thermosensitive behavior of the PVCL shell. Overall, the PCL-b-PVCL block copolymers have potential applications in thermosensitive drug delivery applications.     

Synthesis and characterization of silver—poly(methylmethacrylate) nanocomposites

The optical properties of silver nanoparticles embedded in poly(methylmethacrylate) (PMMA) was investigated as well as the influence of silver nanoparticles on the thermal properties of polymer matrix. The average size and particle size distribution of silver nanoparticles was determined using transmission electron microscopy. The obtained transparent nanocomposite films were optically characterized using UV-Vis and FTIR spectroscopy. Thermal stability of polymer matrix was improved upon incorporation of small amount of silver nanoparticles. Also, silver nanoparticles have pronounced effect on thermo-oxidative stability of PMMA matrix. The glass transition temperatures of nanocomposites are lower compared to the pure polymer.     

Synthesis and characterization of trimethoxysilyl-functionalized poly(phthalazinone ether ketone)

A novel alkoxysilyl-functionalized poly(phthalazinone ether ketone)(PPEK)was prepared for the boundary lubricant application in micro-electro-mechanical system(MEMS).The synthesis of functionalized PPEK was started from the hydro- xylation of PPEK,then following with the corresponding ring-opening reaction of 3-glycidoxypropyltrimethoxysilane(GPTMS). The structures of the functional PPEK were confirmed by FTIR,~1H NMR,~(29)Si NMR,and UV-vis spectrum.     

Synthesis and biodegradation of poly(2-pyrrolidone-co-ε-caprolactone)s

Copolyesteramides of 2-pyrrolidone with ε-caprolactone were synthesized by ring-opening copolymerization. The copolymers were random-like and their melting temperature and heat of fusion were dependent on the polymer composition. Biodegradation by a polyamide 4 (PA4) degrading microorganism showed rapid degradation in the region of amide-rich polymer composition. On the contrary, enzymatic hydrolysis using a lipase resulted in a different tendency, that is, ester-rich copolymers hydrolyzed rapidly. Activated sludge makes copolymers degrade to CO₂ in wide polymer composition ratio. Copolyesteramides are expected to be applied as an environmentally-friendly plastics or bioabsorbable polymers in medical fields.     

Synthesis and characterization of dendronized poly(methylsiloxane) with appendent Fréchet-type dendrons

A new kind of dendronized poly(methylsiloxane) (3a and 3b) with appendent Fre-chet-type poly(aryl ether) dendrons has been synthesized and characterized by GPC, DSC, TGA, fluorescence and UV-Vis spectra.     

Synthesis and characterization of poly(styrene/α-t-butoxy-ω-vinylbenzyl-polyglycidol) microspheres

Polystyrene microspheres with polyglycidol (polyGL) in a surface layer were synthesized in batch radical emulsifier-free emulsion copolymerizations of styrene and surfmers, α-t-butoxy-ω-vinylbenzyl-polyGL macromonomers (VB-polyGL). Macromonomers with number-average molecular weight Mˉ _n=950 (VB-polyGL950) and Mˉ _n=2700 (VB-polyGL2700) were used for these polymerizations. In all syntheses the initial concentrations of styrene and initiator (K₂S₂O₈) were constant. The initial macromonomer-to-styrene ratios were varied from 1.10 × 10⁻³ to 1.64 × 10⁻² mol/mol and from 3.46 × 10⁻⁴ to 3.47 × 10⁻³ mol/mol for VB-polyGL950 and VB-polyGL2700, respectively. The diameters of microspheres obtained were smaller for the syntheses with higher concentrations of macromonomers. Syntheses with VB-polyGL950 yielded microspheres with number-average diameters (Dˉ _n) from 216 to 900 nm and with a bimodal diameter distribution. The number-average diameters of microspheres obtained with VB-polyGL2700 varied from 220 to 650 nm, depending on the initial concentration of macromonomer. Their diameter distributions were monomodal, with a diameter polydispersity parameter (ratio of weight-average and number-average diameters) in the range 1.007≤Dˉ _w/Dˉ _n≤1.022. For each type of microsphere the fraction of polyGL in a surface layer and the surface concentration of sulfate anions were determined. The fraction of polyGL in the surface layer was related to the initial monomer composition in the polymerizing mixture. Adsorption of human serum albumin onto surfaces of some poly(styrene/VB-polyGL) microspheres was up to 10 times lower than for the polystyrene microspheres obtained in a similar emulsifier-free emulsion polymerization of styrene. Received: 26 September 2000/Accepted: 19 February 2001     

Synthesis and characterization of poly(L-lactide-co-ε- caprolactone) copolymers: influence of sequential monomer addition on chain microstructure

A series of copolymers with various compositions were synthesized by one-step and two-step bulk ring-opening polymerizations of L -lactide (LA) and ε-caprolactone (CL) using stannous octoate [Sn(Oct)₂] and 1-hexanol as the initiating system. For the sequential two-step polymerization, a poly(ε-caprolactone) (PCL) prepolymer was polymerized first to a percent conversion of approximately 70% and LA then added in order to produce a copolymer with a chain microstructure different from that obtained from the corresponding one-step reaction. The resulting copolymers were characterized using a combination of nuclear magnetic resonance spectroscopy (¹H- and ¹³C-NMR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and gel permeation chromatography (GPC). The average sequence lengths of the lactidyl ( ) and caproyl ( ) units, the degree of randomness (R) and the transesterification coefficient (T_(II)) were calculated from the ¹³C-NMR spectra. The appearance of a signal due to CapLCap sequences was directly attributable to transesterification of lactidyl (LL) units. It was found that both and values from the two-step syntheses were significantly longer than from the corresponding one-step syntheses, leading to different semi-crystalline morphologies and chain microstructures. The copolymers all showed at least some blocky chain structure as a result of the significant difference in monomer reactivity (LA > CL) between LA and CL. Thermal properties including stability depended on both composition and chain microstructure which could be controlled by the method of synthesis. From their DSC curves, the two-step copolymers were seen to be semi-crystalline whereas the one-step copolymers were mainly amorphous. A more blocky microstructure, as obtained from the two-step method, appeared to result in a lower thermal stability. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis, characterization and self-assemble behavior of chitosan-O-poly(ε-caprolactone)

A facile strategy was proposed for synthesizing chitosan-O-poly(ε-caprolactone) (CS-O-PCL). Stoichiometric sodium dodecyl sulfate-chitosan complex (SCC) which was soluble in common organic solvents was adopted as an intermediate. Regioselective conjugation of PCL onto SCC could be achieved through condensation reaction between isocyanate-terminated PCL and hydroxyl groups of chitosan. The grafting level of PCL could be modulated by varying PCL/SCC weight ratio. SDS was removed from SCC-O-PCL using trihydroxymethylamine (Tris) as a decomplexation agent. The self-assemble behavior of the amphiphilic copolymers was studied by fluorometry, TEM and laser light scattering. The morphology of the CS-O-PCL nanoparticles was found to be dependent on PCL grafting level. Both spherical micelles and vesicle could be formed by dialysis method.     

Synthesis of poly(ε-caprolactone) diols and EO-CL block copolymers and their characterization by liquid chromatography and MALDI-TOF-MS

Polymers of ε-caprolactone were synthesized by microwave-assisted polymerization initiated with polyethylene glycols (PEG 200 and PEG 300) and monodisperse diols (mono-, di-, tri-, tetra- and hexaethylene glycol) and tin octoate as catalyst. These polymers were characterized by different chromatographic techniques (SEC, LAC and LCCC) and MALDI-TOF-MS. A comparison with commercially available polycaprolactone diols with molecular weight 530 and 830 showed that the new polymers had a much higher content of triblock structures, while the commercial samples contained considerable amounts of diblocks.     

Synthesis and characterization of alkoxy derivatives with double-headed initiators for the preparation of poly(ε-caprolactone)-β-polyacrylonitrile (PCL-β-PAN) and poly(l-lactide)-β-polyacrylonitrile (PLLA-β-PAN) copolymers

The synthesis of simple single source molecular precursor based on metal alkoxides of the type,[(MMPEP)Al(μ-OBnCH₂Cl)]₂ (1),[(MMPEP-H)Li·(BnOH)]₂ (2) and[(MMPEP-H)Li·(HOB-nCH₂Cl)]₂ (3) has been reported herein. Complex 1 was prepared by the reaction of[(MMPEP)Al(CH₃)(Et₂O)] with p-(chloromethyl)benzyl alcohol. The reaction of 2,2′-methylene-bis(4,6-di(1-methyl-1-phenylethyl)phenol) (MMPEP-H₂) with ⁿBuLi, BnOH or p-(chloromethyl)benzyl alcohol was added to give complexes 2 and 3, respectively. Among them, only complex 1 shows excellent catalytic properties towards ring-opening polymerization (ROP) of ε-caprolactone. However, complexes 2 and 3 are active for ROP of l-lactide only. Block copolymers of poly(ε-caprolactone)-β-polyacrylonitrile and poly(l-lactide)-β-polyacrylonitrile were synthesized by using a technique known as atom transfer radical polymerization (ATRP) and the ring opening polymerization (ROP). TEM micrograph of PCL-β-PAN shows the microphase property with the help of self-assembly.     

Synthesis and characterization of inclusion complexes of aliphatic-aromatic poly(Schiff base)s with β-cyclodextrin (highlight)

This paper describes the formation of polymer inclusion complexes(polymer-CD-ICs) between β-cyclodextrin(β-CD) and aliphatic-aromatic poly(Schiff base)s. Fourier transform infrared(FTIR) spectroscopy, ¹H nuclear magnetic resonance spectroscopy(¹H-NMR), thermogravimetric analysis(TGA) and X-ray diffraction(XRD) have been used to observe the formation of polymer-CD-ICs. In FTIR spectra, the characteristic peaks of β-CD at 3391 cm⁻¹ shifted to 3418 cm⁻¹ and the intense peak at 1602 cm⁻¹ due to the –C = N– stretching vibration diminished after formation of inclusion complexes. Compared the ¹H-NMR of polymer-CD-ICs with β-CD, the chemical shift of the protons H-3, H-5 have shifted to higher field after the formation of inclusion complexes, which is perhaps due to the interaction of these protons with polymers. The TGA analysis revealed that the polymer-CD-ICs had better thermal stability than β-CD, suggesting that the polymer increased the stability of β-CD. The X-ray diffraction patterns displayed that the strong peak for both polymer-CD-ICs at approximately 20.0° (2θ) may confirm their IC formation.     

Synthesis and properties of poly(isosorbide 2,5-furandicarboxylate-co-ε-caprolactone) copolyesters

Bio-based poly(isosorbide 2,5-furandicarboxylate-co-ε-caprolactone) (PIFCL) copolyesters were synthesized from 2,5-furandicarboxylic acid, isosorbide and ε-caprolactone. The obtained copolyesters were characterized by ¹H NMR, ¹³C NMR, intrinsic viscosity, GPC, DSC, TGA and tensile testing. The NMR characterization results confirmed the insertion of lactones units into poly(isosorbide 2,5-furandicarboxylate) (PIF) chains. All PIFCL copolyesters were amorphous with T_{D, 5%} higher than 300 °C. The glass transition temperatures of PIFCLs with FDCA molar ratio from 74% to 45% were within the range of 132.1 °C and 72.4 °C. Tensile testing revealed that introduction of ε-caprolactone into PIF chain imparted PIFCL with excellent mechanical performance, typically, PIFCL polyseter with FDCA molar ratio of 45% had a Young's modulus 858 ± 92 MPa, a tensile strength 44 ± 4 MPa and an elongation at break 480 ± 45%.     

Synthesis and characterization of poly(ethylene glycol) based β-cyclodextrin polymers

A series of novel water soluble β-cyclodextrin (βCD) polymers has been synthesized from functionalized poly(ethylene glycol) (PEG). The chemical composition of the polymers has been characterized by ¹H NMR and the βCD content is found to be between 48 and 33% (w/w). The molecular weight has been determined by Size Exclusion Chromatography (SEC) and depends on the ratio between βCD and PEG, varying from 2.1 × 10⁴ to 8.6 × 10⁴ g mol^?1. The physico chemical properties have been characterized by differential scanning calorimetry (DSC), viscometry and isothermal titration calorimetry (ITC). ITC shows that the polymers have association constants comparable to βCD with different guest molecules, indicating a good accessibility of the CDs.     

Synthesis and structural characterization of η-allyl(α-diimine)nickel(II) complexes bearing trimethylsilyl groups

A set of isomeric para- and meta-trimethylsilylphenyl ortho-substituted N,N-phenyl α-diimine ligands [(Ar-NC(Me)-(Me)CN-Ar) Ar=2,6-di(4-trimethylsilylphenyl)phenyl (16); Ar=2,6-di(3-trimethylsilylphenyl)phenyl (17)] have been synthesized through a two-step procedure. The palladium-catalysed cross-coupling reaction between 2,6-dibromophenylamine (7) and 4-trimethylsilylphenylboronic acid (8), 3-trimethylsilylphenylboronic acid (9) was used to prepare 4,4^′-bis(trimethylsilyl)-[1,1^′;3^′,1″]terphenyl-2^′-ylamine (10) and 3,3^′-bis(trimethylsilyl)-[1,1^′;3^′,1″]terphenyl-2^′-ylamine (11). The di-1-adamantylphosphine oxide Ad₂P(O)H (13) and di-tert-butyl-trimethylsilylanylmethylphosphine tert-Bu₂P-CH₂-SiMe₃ (14) were used for the first time as ligands for the Suzuki coupling. The condensation of 2,2,3,3-tetramethoxybutane (15) with anilines 10 and 11 afforded α-diimines 16 and 17. The reaction of π-allylnickel chloride dimer (18), α-diimines (16), (17) and sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (BAF) (19) or silver hexafluoroantimonate (20) led to two sets of isomeric complexes [η³-allyl(Ar-NC(Me)-(Me)CN-Ar)Ni]⁺ X⁻, [Ar=2,6-di(4-trimethylsilylphenyl)phenyl, X=BAF (3), X=SbF₆ (4); Ar=2,6-di(3-trimethylsilylphenyl)phenyl, X=BAF (5), X=SbF₆ (6)]. The steric repulsion of closely positioned trimethylsilyl groups in 4 caused the distortion of the nickel square planar coordination by 17.6° according to X-ray analysis.