Synthesis and degradation of PLA-PCL-PLA triblock copolymer prepared by successive polymerization of ε-caprolactone and dl-lactide

A PLA-PCL-PLA triblock copolymer was synthesized by ring-opening polymerization of successively added ε-caprolactone and dl-lactide in the presence of ethylene glycol, using zinc powder as catalyst. The resulting copolymer was compression molded to yield circular films from which 10×10×0.4 mm³ square samples were cut. These samples were allowed to degrade in isoosmolar 0.13 M, pH 7.4 phosphate buffer at 37 °C. Various analytical techniques such as weighing, SEC, ¹H NMR, IR, DSC, X-ray, ESEM and CZE were used to monitor property changes during degradation such as water absorption, weight loss, molecular weight distribution, composition, bulk and surface morphologies, thermal behavior, and release of water-soluble oligomers into the aqueous phase. Comparison is made with a PCL homopolymer under similar ageing conditions. The presence of PLA sequences did not alter the ability of PCL segments to crystallize during degradation, in agreement with the microphase separation between PLA and PCL blocks. Large amounts of lactic acid-rich soluble degradation by-products were released into the solution between 18 and 25 weeks. Copolymer films cracked down under drying beyond 25 weeks' degradation, while the surface remained smooth. The copolymer exhibited faster degradation as compared with PCL homopolymer, a feature which is of great interest for temporary therapeutic applications.     

Hydrolytic degradation of poly(oxyethylene)–poly-(ε-caprolactone) multiblock copolymers

The degradation of poly(oxyethylene)–poly(ε-caprolactone) (POE–PCL) multiblock copolymers was investigated at 37°C in a 0.13M, pH 7.4 phosphate buffer selected to mimic in vivo conditions. The copolymers were obtained by coupling polycaprolactone diols and poly(ethylene glycol) diacids using dicyclohexylcarbodiimide as coupling agent. Various techniques, such as weighing, size exclusion chromatography, infrared, ¹H nuclear magnetic resonance, differential scanning calorimetry, and X-ray diffractometry, were used to monitor changes in total mass, water absorption, molar mass, thermal properties, degree of crystallinity, and composition. The results showed that introduction of POE sequences considerably increased the hydrophilicity of the copolymers as compared with PCL homopolymers. Nevertheless, the degradability of PCL sequences was not enhanced due to the phase separation between the two components. Significant morphological changes were also observed during the degradation. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 989–998, 1998     

Ring-opening polymerization of ε-caprolactone initiated by cyclopentadienyl sodium

Polymerization of ε-caprolactone had been investigated with cyclopentadienyl sodium as an initiator. The effects of reaction time, temperature, and concentration of the initiator on the yield and molecular weight of the polymer were discussed. It was shown that the high molecular weight of poly(ε-caprolactone) (13 × 10⁴) was obtained with cyclopentadienyl sodium initiator, and the mechanism of polymerization was also discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1273–1276, 1998     

Curing behaviour and mechanical properties of dicarboxylated telechelic poly(ε-caprolactone)s/styrene–(epoxidized butadiene)–styrene triblock copolymer reactive blends

End-carboxylated telechelic poly(ε-caprolactone)s (XPCLs) with different molecular weights were blended into a triblock copolymer of styrene–(epoxidized butadiene)–styrene (ESBS) to investigate the curing behaviour and the mechanical properties of the XPCL/ESBS binary reactive blend. It was found that the time–torque cure curve showed a significant torque increase after a very short induction period, in which the degree of the torque increase depended on the molecular weight of XPCL. This indicates that substantial crosslinking reaction takes place between the XPCLs and the epoxidized polybutadiene of the ESBS. Stress–strain curves of the blends after cure depended on the molecular weight of XPCL and the blend ratio. The XPCL/ESBS blends had sufficient thermal stability to show elastomeric behaviour at elevated temperature above the glass transition of the styrene domains of ESBS because of formation of crosslinking points between unlike polymer components by the reactive blending. © 1999 Society of Chemical Industry     

Polymerization of lactides and lactones. IV. Ring-opening polymerization of ε-caprolactone by rare earth phenyl compounds

Ring-opening polymerization of ε-caprolactone (CL) has been initiated with rare earth phenyl compounds in both bulk and solution. These rare earth phenyl initiators can give polycaprolactone (PCL) with high yield and high molecular weight. The polymerization mechanism is through a coordination-deprotonation-insertion process, by which the monomer inserts on the Ln O bond of rare earth enolate. The efficiency of rare earth phenyl compounds for CL is high. The effects of reaction conditions, such as reaction time, reaction temperature, and monomer/initiator molar ratio, on the polymerization are discussed. The polymer was characterized by FTIR, ¹H-NMR. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1401–1408, 1999     

Ring-opening homopolymerization and copolymerization of lactones. Part 2. enzymatic degradability of poly(β-hydroxybutyrate) stereoisomers and copolymers of β-butyrolactone with ε-caprolactone and δ-valerolactone

In this study, we have prepared poly([R,S ]-β-hydroxybutyrate) (P([R,S ]-β-HB) or PHB) from [R ,S]-β-butyrolactone ([ R,S]-β-BL), using different aluminoxane catalyst systems (triethylaluminium/water, triisobutylaluminium/water, trioctylaluminium/water and tetraisobutyldialuminoxane/water). By varying the ratio of catalyst to water and using a method of fractionation of polymers, PHB with different isotactic diad fractions (i) (from 0.41 to 0.72) and crystallinities were obtained. Copolymers poly(butyrolactone-co-caprolactone) (P(BL-co-CL)) and poly(butyrolactone-co-valerolactone) (P(BL-co-VL)) have also been synthesized from the ring-opening copolymerization of [ R,S]-β-BL with either ε-caprolactone (CL) or δ-valerolactone (VL) using tetraisobutyldialuminoxane (TIBAO) catalyst. The enzymatic degradability of these polymers was studied in aerobic and anaerobic media. The objective of this work was to determine the influence of the tacticity and crystallinity of the polymers on their degree of biodegradation and on their initial degradation rate. It was shown that the degradation rate measured for bacterial PHB 100% [R] was the highest and the degree of aerobic biodegradation reached after 36 days was around 94%. A 40–50% biodegradation was obtained for synthetic PHB, highly isotactic and predominantly syndiotactic. The non-crystalline and atactic PHB synthesized from TIBAO catalyst had a very high degree of biodegradation of around 88%. This result may suggest that not only are the [R ]-BL units hydrolysed but also the [S ]-BL units. The influence of the crystallinity on the initial degradation rate was observed for the copolymers P(BL-co-CL) and P(BL-co -VL) of various feed ratios. All these copolymers synthesized from TIBAO catalyst, exhibit a high degree of biodegradation of around 85% except for copolymers containing a very high portion of unsubstituted units, CL or VL. The anaerobic biodegradation of PHB and copolymers P(BL-co -CL) is much lower than the aerobic biodegradation, as are the initial rates, even for bacterial P([R ]-HB). © 1999 Society of Chemical Industry     

Enzyme-catalyzed polymerization and degradation of copolyesters of ε-caprolactone and γ-butyrolactone

Copolymers of γ-butyrolactone (γ-BL) and ε-caprolactone (ε-CL) were successfully synthesized by ring-opening polymerization using Novozyme-435 (immobilized lipase B from Candida antartica) as catalyst. Copolymers with different compositions were obtained and characterized by ¹H NMR, ¹³C NMR, GPC, DSC and X-ray diffraction. Increasing the [BL]/[CL] feed ratio resulted in decreases of molecular weight (M_n) of copolymers and reaction yield. Moreover, the BL contents in the copolymers varied according to the feed ratio. The T_m of the copolymers decreased from 58 to 49 °C with increase in BL content from 0 to 14%. The resulting copolymers were all semicrystalline with a PCL-type crystalline structure. Solution cast films were allowed to degrade in a pH 7.0 phosphate buffer solution containing Pseudomonas lipase. Weight loss data showed that the degradation rate of copolymers in the presence of Pseudomonas lipase decreased with the increase of BL contents.     

Ring-opening homo- and copolymerization of lactones. Part 1. Homo- and copolymerization of racemic β-butyrolactone with ε-caprolactone and δ-valerolactone by tetraisobutyldialuminoxane (TIBAO) catalyst

Copolymers of racemic β-butyrolactone (β-BL) with ε-caprolactone (ε-CL) (P(BL-co-CL)) and δ-valerolactone (δ-VL) (P(BL-co-VL)) were prepared by ring-opening polymerization reactions using the commercial aluminoxane catalyst tetraisobutyldialuminoxane (TIBAO). The yields, molecular weights, compositions and crystallinities were determined for both copolymers by gel permeation chromatography (GPC), nuclear magnetic resonance (¹H NMR) spectroscopy and differential scanning calorimetry (DSC). A detailed study by ¹³C NMR spectroscopy has been made to determine monomer diad sequence distributions. These results and those of reactivity ratios indicate that the co-polymers may consist of compatible blocks of BL units and VL units of variable size. © 1998 SCI.     

Biodegradable Poly(ε‐Caprolactone)‐Based Graft Copolymers Via Poly(Linoleic Acid): In Vitro Enzymatic Evaluation

Well‐defined graft copolymers based on poly(ε‐caprolactone) (PCL) via poly(linoleic acid) (PLina), are derived from soybean oil. Poly(linoleic acid)‐g‐poly(ε‐caprolactone) (PLina‐g‐PCL) and poly(linoleic acid)‐g‐poly(styrene)‐g‐poly(ε‐caprolactone) (PLina‐g‐PSt‐g‐PCL) were synthesized by ring‐opening polymerization of ε‐caprolactone initiated by PLina and one‐pot synthesis of graft copolymers, and by ring‐opening polymerization and free radical polymerization by using PLina, respectively. PLina‐g‐PCL, PLina‐g‐PSt‐g‐PCL3, and PLina‐g‐PSt‐g‐PCL4 copolymers containing 96.97, 75.04 and 80.34 mol% CL, respectively, have been investigated regarding their enzymatic degradation properties in the presence of Pseudomonas lipase. In terms of weight loss, after 1 month, 51.5 % of PLina‐g‐PCL, 18.8 % of PLina‐g‐PSt‐g‐PCL3, and 38.4 % of PLina‐g‐PSt‐g‐PCL4 were degraded, leaving remaining copolymers with molecular weights of 16,140, 83,220 and 70,600 Da, respectively. Introducing the PLina unit into the copolymers greatly decreased the degradation rate. The molar ratio of [CL]/[Lina] dramatically decreased, from 21.3 to 8.4, after 30 days of incubation. Moreover, reduced PCL content in PLina‐g‐PSt‐g‐PCL copolymers decreased the degradation rate, probably due to the PSt enrichment within the structure, which blocks lipase contact with PCL units. Thus, copolymerization of PCL with PLina and PSt units leads to a controllable degradation profile, which encourages the use of these polymers as promising biomaterials for tissue engineering applications.     

Synthesis and characterization of poly(ethylene glycol)-b-poly (l-lactide)-b-poly(l-glutamic acid) triblock copolymer

A biodegradable amphiphilic triblock copolymer of poly(ethylene glycol)-b-poly(l-lactide)-b-poly(l-glutamic acid) (PEG-b-PLLA-b-PLGA) was obtained by catalytic hydrogenation of poly(ethylene glycol)-b-poly(l-lactide)-b-poly(γ-benzyl-l-glutamic acid) (PEG-b-PLLA-b-PBLGA) synthesized by the ring-opening polymerization (ROP) of N-carboxyanhydride of γ-benzyl-l-glutamate (BLG-NCA) with amino-terminated MPEG-b-PLLA-NH₂ as a macroinitiator. MPEG-b-PLLA-NH₂ converted from MPEG-b-PLLA-OH first reacted with tert-Butoxycarbonyl-l-phenylalanine (Phe-^NBOC) and dicyclohexylcarbodiimide (DCC) and then deprotected the tert-butoxycarbonyl group. MPEG-b-PLLA-OH was prepared by ROP of l-lactide with monomethoxy poly(ethylene glycol) in the presence of stannous octoate. The triblock copolymer and its diblock precursors were characterized by ¹H NMR, FTIR, GPC and DSA (drop shape analysis) measurements. The lengths of each block polymers could be tailored by molecular design and the ratios of feeding monomers. The triblock polymer PEG-b-PLLA-b-PLGA containing carboxyl groups showed obviously improved hydrophilic properties and could be a good potential candidate as a drug delivery carrier.     

Molecular motion in poly(amino acid)s: 6. Molecular motion in a β-form crystal of poly(γ-methyl-d-glutamate)

The molecular motion in a β-form crystal of fully annealed poly(γ-methyl-d-glutamate) was investigated by means of an X-ray diffractometer and an infra-red spectrophotometer. The interchain periodicity (chains are bound side by side with intermolecular hydrogen bonds) increases linearly with increasing temperature, indicating ordinary thermal expansion of the lattice. The intersheet periodicty (sided chains pack into sheets) increases linearly up to 150°C and then the slope of the temperature dependence of the periodicty increases owing to the onset of active segmental motion of the side chains.It is evident from the temperature dependence of the wavenumber of the maximum of the infra-red absorption for NH stretching in the crystal that thermal expansion in the direction of the hydrogen bond is hardly affected by the segmental motion of the side chain.     

Ring-opening polymerization of ϵ-caprolactone initiated by rare earth complex catalysts

The polymerization of caprolactone (ϵ-CL) was initiated by yttrium triisopropoxide {Y(OPⁱ_r)₃}, bimetallic isopropoxide of yttrium and aluminum {Y[Al(OPⁱ_s)₄]₃}, yttrium and tin(II) {Y[Sn(OPⁱ_r)₃]₃}, and tin(II) and yttrium {Sn[Y(OPⁱ_r)₄]₂}, respectively. The polymerization was carried out through coordinative insertion of a monomer into the free metal-oxygen bond. The molecular weight and yield of poly(ϵ-caprolactone) (PCL) were affected drastically by the mol % of the initiator to the monomer (C_o/M_o). The results showed that Y(OPⁱ_r)₃ and Sn[Y(OPⁱ_r)₄]₂ were more effective than were {Y[Al(OPⁱ_r)₄]₃} and {Y[Sn(OPⁱ_r)₃]₃} for the polymerization of ϵ-CL. When polymerization was conducted at 5°C using Y(OPⁱ_r)₃ as the initiator or at 10°C using Sn[Y(OPⁱ_r)₄]₄ as the initiator, polymers with a molecular weight of 45.9 × 10³ or 54.0 × 10³ and high yield resulted in 30 or 5 min, respectively. The polymer was characterized by FTIR, H-NMR, and GPC. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1295–1299, 1997     

Thermal properties of poly(styrene-block-ε-caprolactone) in blends with poly(vinyl methyl ether)

The thermal characteristics of a styrene-ε-caprolactone diblock copolymer, P(S-b-CL), in blends with poly(vinyl methyl ether) (PVME) were studied by DSC. The glass transition temperatures show that PVME is only dissolved in the PCL block. It segregates from the PCL block at low temperatures. The addition of PVME leads to increasing crystallinity of the PCL block in a certain range of composition. However, degrees of crystallinity do not change significantly with crystallization temperature. Optical inspection revealed that the PCL block does not form spherulites. The crystallization kinetics of the PCL block has been systematically studied. The rate constants of crystallization for different blends decrease exponentially with crystallization temperature, whereas the rates of crystallization are scarcely affected by PVME content. The Avrami exponents were found close to two.     

Synthesis and characterization of poly(oxyethylene)–poly(caprolactone) multiblock copolymers

Novel poly(oxyethylene)/poly(caprolactone) POE/PCL copolymers were synthesized by step growth polymerization of poly(ε-caprolactone) diols and poly(ethylene glycol) diacids using dicyclohexylcarbodiimide as coupling agent. The reaction was performed at room temperature and yielded multiblock copolymers with predetermined POE and PCL block lengths. The resulting copolymers were characterized by various analytical techniques including SEC, IR, ¹H NMR, DSC and X-ray diffractometry. Data showed that the properties of these polymers can be modulated by adjusting the chain lengths of the macromonomers. In particular, one or two crystalline structures can exist within the copolymers of various crystallinities. © 1998 SCI.     

Incorporation of active nano-hybrids into poly(ε-caprolactone) for local controlled release: Antifibrinolytic drug

The antifibrinolytic drug trans-4-(aminomethyl)cyclohexanecarboxylate (tranexamic anions) was intercalated by anion exchange into Mg/Al layered double hydroxide (LDH). The hybrid, of formula [Zn_0.65Al_0.35(OH)₂]Trx_0.24(CO₃)_0.055 × 1.5H₂O, was characterized by chemical and thermal analyses and X-ray powder diffraction.Different amounts of the hybrid material were incorporated into poly(ε-caprolactone) by high energy ball milling technique and processed as films. The composite materials were analyzed by X-ray diffractometry, thermogravimetry and FT-IR spectroscopy to clarify the filler-polymer structural organization. An investigation of the mechanical properties of the composite showed an improvement of mechanical parameters, in particular the elastic modulus, when compared to of the pristine polymer. Thus, the inorganic component, even in small quantities, beside acting as a reservoir of active molecular anions, can improve the physical properties.A new method for the quantitative determination of tranexamic anions by infrared spectroscopic analysis was proposed and the release process of the tranexamic anions from the composite into a physiological solution was monitored. The release consisted of two stages: a first stage, very rapid as a burst, in which a small fraction of intercalated drug was released and of a second stage over longer time, much slower than the first.The composites are very promising in the preparation of new hybrid polymeric materials to be used for the molecular delivery of drugs in topical applications, as suture threads or medicate scaffolds.     

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     

Phase behavior of poly(ε-caprolactone)/ poly (vinylidene fluoride) blends

The miscibility of blends of poly (ε-caprolactone) (PCL)/poly(vinylidene fluoride) (PVDF) was studied by measuring the cloud point, melting point depression and crystallization kinetics. Lower critical solution temperature (LCST) behavior was observed at PCL-rich compositions, whilst it was not observed at high compositions of PVDF. However it is possible that an LCST could exist below the melting point of PVDF. From analysis of the melting point depression, the Flory interaction parameter x₁₂, was calculated from the Nishi-Wang equation and the value was found to be-1.5. The crystallization rate of PCL increased with increasing amount of PVDF in the blend. The spinodal curve for PCL/PVDF blends was simulated by using the lattice-fluid theory.     

Morphology and electrical properties of carbon black-filled poly(ε-caprolactone)/poly(vinyl butyral) blends

Electrical properties of poly(ε-caprolactone) (PCL)/poly(vinyl butyral) (PVB) blends containing carbon black (CB) were studied as a function of a small amount of PVB content and a wide range of molecular weight of PVB. For samples with the same CB content, the intensity of positive temperature coefficient (I_PTC, defined as the ratio of peak resistivity to resistivity at room temperature) of the blends was increased, with PVB content greatly and molecular weight of PVB weakly. As the band spacings of PCL spherulites in PCL/PVB blends decrease with PVB content and molecular weight of PVB, the changes of the positive temperature coefficient property are ascribed to the morphological difference (i.e., period of twisted lamellae) in the blends. We confirmed our previous conclusion that the origin of the positive temperature coefficient phenomenon is the changes of the distribution of the CB on the melting of the crystalline phase. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 193–199, 1998     

Poly(ϵ-caprolactone)/poly(ethylene oxide) diblock copolymer II. Nonisothermal crystallization and melting behavior

The nonisothermal crystallization behavior and melting process of the poly(ϵ-caprolactone) (PCL)/poly(ethylene oxide) (PEO) diblock copolymer in which the weight fraction of the PCL block is 0.80 has been studied by using differential scanning calorimetry (DSC). Only the PCL block is crystallizable, the PEO block with 0.20 weight fraction cannot crystallize. The kinetics of the PCL/PEO diblock copolymer under nonisothermal crystallization conditions has been analyzed by Ozawa's equation. The experimental data shows no agreement with Ozawa's theoretical predictions in the whole crystallization process, especially in the later stage. A parameter, kinetic crystallinity, is used to characterize the crystallizability of the PCL/PEO diblock copolymer. The amorphous and microphase separating PEO block has a great influence on the crystallization of the PCL block. It bonds chemically with the PCL block, reduces crystallization entropy, and provides nucleating sites for the PCL block crystallization. The existence of the PEO block leads to the occurrence of the two melting peaks of the PCL/PEO diblock copolymer during melting process after nonisothermal crystallization. The comparison of nonisothermal crystallization of the PCL/PEO diblock copolymer, PCL/PEO blend, and PCL and PEO homopolymers has been made. It showed a lower crystallinity of the PCL/PEO diblock copolymer than that of others and a faster crystallization rate of the PCL/PEO diblock copolymer than that of the PCL homopolymer, but a slower crystallization rate than that of the PCL/PEO blend. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1793–1804, 1997     

Synthesis and characterization of fullerene grafted poly(ε‐caprolactone)

The fullerene grafted poly(ε‐caprolactone) (PCL) was successfully synthesized with a graft efficiency of 80%. The fullerene moieties grafted onto the PCL chain aggregate into 1–2 μm particles so that a physical pseudo‐network is formed. Because of the existence of the network structure, the fullerene grafted PCL film can retain its shape at much higher temperatures than that of pure PCL film, as observed in dynamic mechanical tests. It shows a hydrophobic gelling behavior in chloroform solution. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008