Enhanced crystallization of poly(L‐lactide‐co‐ε‐caprolactone) in the presence of water

Poly(L ‐lactide‐co‐ε‐caprolactone) [P(LLA‐CL)], which is used in biodegradable biomedical materials such as drug‐delivery systems, surgical sutures, orthopedics, and scaffolds for tissue engineering, has been reported to crystallize upon storage in a dry state even at room temperature; this results in rapid changes in the mechanical properties. In biomedical applications, P(LLA‐CL) is used in the presence of water. This study investigated the effects of water on the crystallization of P(LLA‐CL) at 37°C in phosphate buffered solution, which was anticipated to alter its mechanical properties and hydrolytic degradation behavior. Surprisingly, the crystallinity of P(LLA‐CL) in the presence of water rapidly increased in 6–12 h and then slowly increased up to 120 h. The period of time for the initial rapid crystallization increase in the presence of water was much shorter than that in the absence of water. The obtained information would be useful for the selection, preparation, and use of P(LLA‐CL) in various biomedical applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Morphology and hydrolysis of PCL/PLLA blends compatibilized with P(LLA‐co‐ϵCL) or P(LLA‐b‐ϵCL)

The effect of the compatibilizers, P(LLA‐co‐?CL) and P(LLA‐b‐?CL), on the morphology and hydrolysis of the blend of poly(?‐caprolactone) (PCL) and poly(L ‐lactide) (PLLA) was investigated. An addition of P(LLA‐co‐?CL) or P(LLA‐b‐?CL) into the blend could enhance the compatibility between the dispersed PCL domains and the PLLA matrix. The size of the PCL domains in the PLLA/PCL (70/30) blend containing P(LLA‐co‐?CL) reduced more significantly with an increase in the content of the compatibilizer than that in the blend containing P(LLA‐b‐?CL). The molecular weight of the PLLA/PCL blend films compatibilized with P(LLA‐co‐?CL) or P(LLA‐b‐?CL) decreased during the hydrolysis and the decrease of the molecular weight of the blend films compatibilized with P(LLA‐co‐?CL) was much more significant than that of the blend films compatibilized with P(LLA‐b‐?CL). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1892–1898, 2002     

Synthesis and characterization of poly(L‐lactide‐co‐ϵ‐caprolactone)‐b‐poly(L‐lactide) biodegradable diblock copolyesters: Effect of the block lengths on their thermal properties

Poly(L ‐lactide‐co‐ε‐caprolactone)‐b‐poly(L ‐lactide) [P(LL‐co‐CL)‐b‐PLL] diblock copolyesters were synthesized in a two‐step process with 1‐dodecanol (DDC) and stannous octoate as the initiating system. In the first‐step reaction, a 50:50 mol % amorphous poly(L ‐lactide‐co‐ε‐caprolactone) [P(LL‐co‐CL)] copolyester was synthesized via the bulk copolymerization of L ‐lactide and ε‐caprolactone, which was followed by the polymerization of the PLL crystalline block at the end chain in the second‐step reaction. The yielded copolyesters were characterized with dilute‐solution viscometry, gel permeation chromatography, ¹H‐ and ¹³C‐NMR, and differential scanning calorimetry methods. The molecular weights of the P(LL‐co‐CL) copolyesters from the first‐step reaction were controlled by the DDC concentrations, whereas in the second‐step reaction, the molecular weights of the P(LL‐co‐CL)‐b‐PLL diblock copolyesters depended on the starting P(LL‐co‐CL) copolyester molecular weights and L ‐lactide/prepolymer molar ratios. The starting P(LL‐co‐CL) copolyester molecular weights and PLL block lengths seemed to be the main factors affecting specific thermal properties, including the melting temperature (T_m), heat of melting (ΔH_m), crystallizing temperature (T_c), and heat of crystallizing (ΔH_c), of the final P(LL‐co‐CL)‐b‐PLL diblock copolyester products. T_m, ΔH_m, T_c, and ΔH_c increased when the PLL block lengths increased. However, these thermal properties of the diblock copolyesters also decreased when the P(LL‐co‐CL) block lengths increased. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Synthesis and characterization of ABA type tri‐block copolymers derived from p‐dioxanone,L‐lactide and poly(ethylene glycol)

A series of triblock co‐polymers, consisting of a poly(ethylene glycol) (PEG) central block joined to two blocks of random p‐dioxanone‐co‐L ‐lactide copolymers were synthesized by ring‐opening polymerization of p‐dioxanone (PDO) and L ‐lactide (LLA) initiated by PEG in the presence of stannous 2‐ethylhexanoate catalyst. The resulting copolymers were characterized by various techniques including ¹H and ¹³C NMR and FTIR spectroscopies, gel permeation chromatography, inherent viscosity, wide‐angle X‐ray diffractometry (WAXD) and differential scanning calorimetry (DSC). The conversion of PDO and L ‐lactide into the polymer was studied various mole ratios and at different polymerization temperature from ¹H NMR spectra. Results of WAXD and DSC showed that the crystallinity of PEG macroinitiator was greatly influenced by the composition of PDO and L ‐lactide in the copolymer. The triblock copolymers with low molecular weight were soluble in water at below room temperature. © 2003 Society of Chemical Industry     

Fabrication and properties of core‐shell structure P(LLA‐CL) nanofibers by coaxial electrospinning

In this article, core‐shell structure nanofibers were fabricated by coaxial electrospinning with biodegradable copolymer Poly(L ‐Lactic‐ε‐Caprolactone) [P(LLA‐CL) 50 : 50] as shell and bovine serum albumin (BSA) as core. Morphology and microstructure of the nanofibers were characterized by scanning electron microscopy and transmission electron microscopy. The mechanical properties were investigated by stress‐strain tests. In vitro degradation rates of the nanofibrous membranes were determined by measuring their weight loss when immersed in phosphate‐buffered saline (pH 7.4) for a maximum of 14 days. Release behavior of BSA was measured by an ultraviolet‐visible spectroscopy, and the results demonstrated that BSA could release from P(LLA‐CL) nanofibers in a steady manner. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Part 7. Effects of poly(L‐lactide‐co‐ϵ‐caprolactone) on morphology,structure, crystallization,and physical properties of blends of poly(L‐lactide) and poly(ϵ‐caprolactone)

Blended films of poly(L ‐lactide) [ie poly(L ‐lactic acid)] (PLLA) and poly(?‐caprolactone) (PCL) without or mixed with 10 wt% poly(L ‐lactide‐co‐?‐caprolactone) (PLLA‐CL) were prepared by solution‐casting. The effects of PLLA‐CL on the morphology, phase structure, crystallization, and mechanical properties of films have been investigated using polarization optical microscopy, scanning electron microscopy, differential scanning calorimetry and tensile testing. Addition of PLLA‐CL decreased number densities of spherulites in PLLA and PCL films, and improved the observability of spherulites and the smoothness of cross‐section of the PLLA/PCL blend film. The melting temperatures (T_m) of PLLA and PCL in the films remained unchanged upon addition of PLLA‐CL, while the crystallinities of PLLA and PCL increased at PLLA contents [X_PLLA = weight of PLLA/(weight of PLLA and PCL)] of 0.4–0.7 and at most of the X_PLLA values, respectively. The addition of PLLA‐CL improved the tensile strength and the Young modulus of the films at X_PLLA of 0.5–0.8 and of 0–0.1 and 0.5–0.8, respectively, and the elongation at break of the films at all the X_PLLA values. These findings strongly suggest that PLLA‐CL was miscible with PLLA and PCL, and that the dissolved PLLA‐CL in PLLA‐rich and PCL‐rich phases increased the compatibility between these two phases. © 2003 Society of Chemical Industry     

Regulation of the mechanical properties and heat resistance of the poly(l‐lactide‐co‐trimethylene carbonate) copolymer by the incorporation of a stereocomplex crystal and graphene oxide

Stereocomplex crystals of polylactide and graphene oxide (GO) were simultaneously used to regulate the mechanical properties and heat resistance of a poly(l ‐lactide‐co‐trimethylene carbonate) [P(LLA‐co‐TMC)] copolymer. The crystallization behaviors in the nonisothermal cold‐crystallization process of P(LLA‐co‐TMC)–poly(d ‐lactide) (PDLA) blends and P(LLA‐co‐TMC)–PDLA–GO composites were investigated by differential scanning calorimetry, wide‐angle X‐ray diffraction, and polarized optical microscopy. Data from the crystallization kinetics and the crystallization active energy indicated that GO both promoted nucleation and limited growth during the stereocomplex crystallization process. Three kind of samples (without crystallization, with low crystallinity, and with high crystallinity) were used to investigate the mechanical properties and heat resistance. We found a decrease in the elongation at break when the stereocomplex crystal and GO contents were increased, and this was accompanied by an improvement in the tensile strength. The change in the storage modulus value determined by dynamic mechanical analysis demonstrated that both the stereocomplex crystal and GO effectively improved the heat resistance. These results indicate that this study provided a new strategy for fabricating a P(LLA‐co‐TMC) copolymer with good comprehensive properties at was entirely different from common chemical crosslinking methods. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45248.     

Effects of copolymer microstructure on the properties of electrospun poly(l‐lactide‐co‐ε‐caprolactone) absorbable nerve guide tubes

The main objective of this work has been to study the effects of copolymer microstructure, both chemical and physical, on the microporosity, in vitro hydrolytic degradability and biocompatibility of electrospun poly(l ‐lactide‐co‐ε‐caprolactone), PLC, copolymer tubes for potential use as absorbable nerve guides. PLC copolymers with L : C compositions of 50 : 50 and 67 : 33 mol % were synthesized via the ring‐opening copolymerization of l ‐lactide (L) and ε‐caprolactone (C) at 120°C for 72 h using stannous octoate (tin(II) 2‐ethylhexanoate) and n‐hexanol as the initiating system. Electrospinning was carried out from solution in a dichloromethane/dimethylformamide (7 : 3 v/v) mixed solvent at room temperature. The in vitro hydrolytic degradation of the electrospun PLC tubes was studied in phosphate buffer saline over a period of 36 weeks. The microporous tubes were found to be gradually degradable by a simple hydrolysis mechanism leading to random chain scission. At the end of the degradation period, the % weight retentions of the PLC 50 : 50 and 67 : 33 tubes were 15.6% and 70.2%, respectively. Pore stability during storage as well as cell attachment and proliferation of mouse fibroblast cells (L929) showed the greater potential of the PLC 67 : 33 tubes for use as temporary scaffolds in reconstructive nerve surgery. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4357–4366, 2013     

Hydrolytic Degradation of Amorphous Films of L‐Lactide Copolymers with Glycolide and D‐Lactide

Summary: Films of poly(L ‐lactic acid) (PLLA) and copolymers of L ‐lactide (LLA) with either glycolide [P(LLA‐GA)](81/19) or D ‐lactide [P(LLA‐DLA)](77/23) were prepared and an effect of comonomer type on the hydrolytic degradation of the films was studied in phosphate‐buffered solutions at 37 °C. The degraded films were investigated using gravimetry (weight loss and water absorption), gel permeation chromatography, DSC, X‐ray diffractometry, tensile testing and polarization optical microscopy. To exclude the effects of molecular weight and crystallinity on hydrolytic degradation, the films were prepared from polymers with similar molecular weights and were made amorphous by melt quenching. It was found that the hydrolytic degradation rate decreased in the order P(LLA‐GA) > P(LLA‐DLA) > PLLA. The hydrolytic degradation rate constant of PLLA and LLA copolymer films increased with increasing the water absorption (hydrophilicity), or with decreasing the initial glass transition temperature or the L ‐lactyl unit sequence length, indicating that the hydrolytic degradation rate of the copolymers was closely related to these three parameters. The crystallization of P(LLA‐GA) film occurred within hydrolytic degradation for 20 weeks.

M_n of PLLA and LLA copolymer films as a function of hydrolytic degradation time.     

Blends of aliphatic polyesters. VIII. Effects of poly(L‐lactide‐co‐ε‐caprolactone) on enzymatic hydrolysis of poly(L‐lactide), poly(ε‐caprolactone), and their blend films

Poly(L ‐lactide), that is, poly(L ‐lactic acid) (PLLA), poly(ε‐caprolactone) (PCL), and their blend (50/50) films containing different amounts of poly(L ‐lactide‐co‐ε‐caprolactone) (PLLA‐CL), were prepared by solution casting. The effects of added PLLA‐CL on the enzymatic hydrolysis of the films were investigated in the presence of proteinase K and Rhizopus arrhizus lipase by use of gravimetry. The addition of PLLA‐CL decreased the proteinase K–catalyzed hydrolyzabilities of the PLLA and PLLA/PCL (50/50) films as well as the Rhizopus arrhizus lipase‐catalyzed hydrolyzability of the PCL and PLLA/PCL (50/50) films. The decreased enzymatic hydrolyzabilities of the PLLA and PCL films upon addition of PLLA‐CL are attributable to the fact that the PLLA‐CL is miscible with PLLA and PCL and the dissolved PLLA‐CL must disturb the adsorption and/or scission processes of the enzymes. In addition to this effect, the decreased enzymatic hydrolyzabilities of the PLLA/PCL (50/50) films upon addition of PLLA‐CL can be explained by the enhanced compatibility between the PLLA‐rich and PCL‐rich phases arising from the dissolved PLLA‐CL. These effects result in decreased hydrolyzable interfacial area for PLLA/PCL films. The decrement in proteinase K–catalyzed hydrolyzability of the PLLA film upon addition of PLLA‐CL, which is miscible with PLLA, was in marked contrast with the enhanced proteinase K–catalyzed hydrolyzability of the PLLA film upon addition of PCL, which is immiscible with PLLA. This confirms that the miscibility of the second polymer is crucial to determine the proteinase K–catalyzed hydrolyzabilities of the PLLA‐based blend films. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 412–419, 2003     

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     

Synthesis and characterization of star‐shaped poly(ethylene glycol)‐block‐poly(L‐lactic acid) copolymers by melt polycondensation

Compared with linear diblock or triblock poly(ethylene glycol)‐block‐poly(L ‐lactic acid) copolymer (PEG‐b‐PLLA), star‐shaped PEG‐b‐PLLA (sPEG‐b‐PLLA) copolymers exhibit smaller hydrodynamic radius and lower viscosity and are expected to display peculiar morphologies, thermal properties, and degradation profiles. Compared with the synthesis routine of PEG‐b‐PLLA form lactide and PEG, the traditional synthesis routine from LA and PEG were suffered by the low reaction efficiency, low purity, lower molecular weight, and wide molecular weight distribution. In this article, multiarm sPEG‐b‐PLLA copolymer was prepared from multiarm sPEG and L ‐lactic acid (LLA using an improved method of melt polycondensation, in which two types of sPEG, that is, sPEG₁ (four arm, Mn = 4300) and sPEG₂ (three arm, Mn = 3200) were chosen as the core. It was found the molecular weight of sPEG‐b‐PLLA could be strongly affected by the purity of LLA and sPEGs, and the purification technology of vacuum dewater and vacuum distillation could help to remove most of the impurities in commercial available LLA. The polymers, including sPEG and sPEG‐b‐PLLA with varied core (sPEG₁ and sPEG₂) and LLA/sPEG feeding ratios, were characterized and confirmed by ¹H‐NMR and ¹³C‐NMR spectroscopy, Fourier transform infrared spectroscopy (FT‐IR) and gel permeation chromatography, which showed that the terminal hydroxyl group in each arm of sPEGs had reacted with LLA to form sPEG‐b‐PLLA copolymers with fairly narrow molecular weight distribution. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Biodegradable elastomers based on ABA triblocks: influence of end‐block crystallinity on elastomeric character

ABA triblock copolymers, based on biodegradable monomers, namely ε‐caprolactone (CL) and L ‐lactide (LLA), were synthesized and studied. The end‐blocks were mostly poly(L ‐lactide) while the middle segments were a random copolymer of PCL and PLLA. Synthesis of these copolymers was performed by varying the end‐block segment length while retaining a fixed middle‐block segment length and vice versa. Nuclear magnetic resonance studies confirmed the designed structure of the copolymers and their thermal properties were studied with differential scanning calorimetry. Mechanical and thermomechanical properties were determined with an Instron tester and by dynamic mechanical analysis, respectively. The elastomeric character of the copolymers was verified by cyclic test as well as by creep and recovery measurements. Changes made to the middle‐ and end‐block segment lengths had a significant influence on the mechanical properties of the copolymers, especially their extendibility and recoverability. An increase in the crystallinity of the end‐blocks in the copolymers caused a drop in their elastomeric character. In cyclic testing, under conditions of 50% and 150% strain, copolymers with low end‐block crystallinity could recover more than 85% whereas copolymers with high crystallinity showed reduced recovery values as low as 60%. Copyright © 2011 Society of Chemical Industry     

Crystallization behavior of biodegradable amphiphilic poly(ethylene glycol)‐poly(L‐lactide) block copolymers

Poly(ethylene glycol)‐poly(L ‐lactide) diblock and triblock copolymers were prepared by ring‐opening polymerization of L ‐lactide with poly(ethylene glycol) methyl ether or with poly(ethylene glycol) in the presence of stannous octoate. Molecular weight, thermal properties, and crystalline structure of block copolymers were analyzed by ¹H‐NMR, FTIR, GPC, DSC, and wide‐angle X‐ray diffraction (WAXD). The composition of the block copolymer was found to be comparable to those of the reactants. Each block of the PEG–PLLA copolymer was phase separated at room temperature, as determined by DSC and WAXD. For the asymmetric block copolymers, the crystallization of one block influenced much the crystalline structure of the other block that was chemically connected to it. Time‐resolved WAXD analyses also showed the crystallization of the PLLA block became retarded due to the presence of the PEG block. According to the biodegradability test using the activated sludge, PEG–PLLA block copolymer degraded much faster than PLLA homopolymers of the same molecular weight. © 1999 John Wiley amp; Sons, Inc. J Appl Polym Sci 72: 341–348, 1999     

Study of novel biodegradable thermo‐sensitive hydrogels of methoxy‐poly(ethylene glycol)‐block‐polyester diblock copolymers

A series of biodegradable thermo‐sensitive hydrogels were synthesized by ring‐opening polymerization of methoxy‐poly(ethylene glycol) (mPEG) and various ester monomers, i.e. D ,L ‐lactide, glycolide, β‐propiolactone, δ‐valerolactone and ε‐caprolactone. The copolymers were characterized using ¹H NMR spectroscopy and gel permeation chromatography. The micelle properties were also measured. The results indicated that the diblock copolymers formed nano‐micelles at low concentrations in aqueous phase. The lower critical solution temperatures of the diblock copolymers were above 35 °C at 1 wt%. As the temperature increased above room temperature, the diblock copolymer solutions underwent a sol‐to‐gel phase transition, which was manifested in viscosity increases, indicative of the formation of a gel. The mPEG–polyester diblock copolymer solutions exhibited sol‐gel transition behavior as a function of temperature and polymer concentration. Copyright © 2010 Society of Chemical Industry     

Shape‐memory behaviors of biodegradable poly(L‐lactide‐co‐ϵ‐caprolactone) copolymers

A series of biodegradable poly(L ‐lactide‐co‐?‐caprolactone) (PCLA) copolymers with different chemical compositions are synthesized and characterized. The mechanical properties and shape‐memory behaviors of PCLA copolymers are studied. The mechanical properties are significantly affected by the copolymer compositions. With the ?‐caprolactone (?‐CL) content increasing, the tensile strength of copolymers decreases linearly and the elongation at break increases gradually. By means of adjusting the compositions, the copolymers exhibit excellent shape‐memory effects with shape‐recovery and shape‐retention rate exceeding 95%. The effects of composition, deformation strain, and the stretching conditions on the recovery stress are also investigated systematically. A maximum recovery stress around 6.2 MPa can be obtained at stretching at T_g ? 15°C to 200% deformation strain for the PCLA70 copolymer. The degradation results show that the copolymers with higher ?‐CL content have faster degradation rates and shape‐recovery rates, meanwhile, the recovery stress can maintain a relative high value after 30 days in vitro degradation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Poly(N‐isopropylacrylamide‐co‐hydroxyethyl methacrylate) graft copolymers and their application as carriers for drug delivery system

Poly(N‐isopropylacrylamide‐co‐hydroxyethyl methacrylate) [P(NIPAM‐co‐HEMA)] copolymer was synthesized by controlled radical polymerization from respective N‐isopropylacrylamide (NIPAM) and hydroxyethyl methacrylate (HEMA) monomers with a predetermined ratio. To prepare the thermosensitive and biodegradable nanoparticles, new thermosensitive graft copolymer, poly(L ‐lactide)‐graft‐poly(N‐isoporylacrylamide‐co‐hydroxyethyl methacrylate) [PLLA‐g‐P(NIPAM‐co‐HEMA)], with the lower critical solution temperature (LCST) near the normal body temperature, was synthesized by ring opening polymerization of L ‐lactide in the presence of P(NIPAM‐co‐HEMA). The amphiphilic property of the graft copolymers was formed by the grafting of the PLLA hydrophobic chains onto the PNIPAM based hydrophilic backbone. Therefore, the graft copolymers can self‐assemble into uniformly spherical micelles ò about 150–240 nm in diameter as observed by the field emission scanning electron microscope and dynamic light scattering. Dexamethasone can be loaded into these nanostructures during dialysis with a relative high loading capacity and its in vitro release depends on temperature. Above the LCST, most of the drugs were released from the drug‐loaded micelles, whereas a large amount of drugs still remains in the micelles after 48 h below the LCST. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Totally bioresorbable composites prepared from poly(l‐lactide)‐co‐(trimethylene carbonate) copolymers and poly(l‐lactide)‐co‐(glycolide) fibers as cardiovascular stent material

This paper aims to evaluate the potential of totally bioresorbable composites as cardiovascular stent material. Copolymers were synthesized by ring‐opening polymerization of L ‐lactide (LLA) and 1,3‐trimethylene carbonate (TMC) with LLA‐TMC ratios of 3/1, 4/1, and 5/1 and characterized by nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). Wt. 5% of poly(L ‐lactide)‐co‐(glycolide) (PLGA) fibers are used to reinforce PTMC‐LLA copolymer matrices to prepare totally bioresorbable composites. Heat treatment under vacuum and oxygen plasma treatment are applied to improve the mechanical performance of the composites in terms of eliminating the imperfections inside, enhancing interfacial affinity, surface roughness, and enriching surface oxidative chemical bonds. After plasma treatment, the viscosity and tensile strength of the fibers decrease, but the surface chemical bonds are enriched and surface roughness is increased. The composites with 15‐min plasma‐treated fibers and 2 h heat treatment exhibit the highest tensile strength of 46 MPa, i.e., very close to that of PLLA (48 MPa), which is usually used as biodegradable stent material. Moreover, the tensile modulus of the above composite is 1711 MPa, which is only 34% of PLLA's modulus (4985 MPa). Therefore, novel composites with sufficient tensile strength and better flexibility are obtained as promising cardiovascular stent material. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Synthesis and characterization of poly(ϵ‐caprolactone)–poly(L‐lactide) diblock copolymers with an organic amino calcium catalyst

The quasiliving characteristics of the ring‐opening polymerization of ?‐caprolactone (CL) catalyzed by an organic amino calcium were demonstrated. Taking advantage of this feature, we synthesized a series of poly(?‐caprolactone) (PCL)–poly(L ‐lactide) (PLA) diblock copolymers with the sequential addition of the monomers CL and L ‐lactide. The block structure was confirmed by ¹H‐NMR, ¹³C‐NMR, and gel permeation chromatography analysis. The crystalline structure of the copolymers was investigated by differential scanning calorimetry and wide‐angle X‐ray diffraction analysis. When the molecular weight of the PLA block was high enough, phase separation took place in the block copolymer to form PCL and PLA domains, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2654–2660, 2006     

Properties and degradation behavior of surface functionalized MWCNT/poly(L‐lactide‐co‐ε‐caprolactone) biodegradable nanocomposites

In this research, poly(L ‐lactide‐co‐ε‐caprolactone) (PLACL) reinforced with well‐dispersed multiwalled carbon nanotubes (MWCNTs) nanocomposites were prepared by oxidization and functionalization of the MWCNT surfaces using oligomeric L ‐lactide (LA) and ε‐caprolactone (CL). It is found that the surface functionalization can effectively improve the dispersion and adhesion of MWCNTs in PLACL. The surface functionalization will have a significant effect on the physical, thermomechanical, and degradation properties of MWCNT/PLACL composites. The tensile modulus, yield stress, tensile strength, and elongation at break of composite increased 49%, 60%, 70%, and 94%, respectively, when the concentration of functionalized MWCNTs in composite is 2 wt %. The in vitro degradation rate of nanocomposites in phosphate buffer solution increased about 100%. The glass transition temperature (T_g) of composites was decreased when the concentration of functionalized MWCNTs is 0.5 wt %. With further increasing the concentration of functionalized MWCNTs, the T_g was increased. The degradation kinetics of nanocomposites can be engineered and functionalized by varying the contents of pristine or functionalized MWCNTs. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011