Relaxation processes in a block copoly(ether-ester) elastomer investigated by the spin probe method

Relaxation processes in the soft segment phase of a block copoly(ether-ester) elastomer were investigated using the spin probe method. Rotational mobility of the two probes, differing in sizes, were analysed and the results were interpreted based on the relaxation diagram. It was found that the change in mobility of the probes, as detected by the change in ESR line shape, in the slow rotation region corresponds to the β-relaxation, whereas that in the rapid rotation region corresponds to the α + β-relaxation. The analysis of probe mobilities, including the way they rotate, indicates the necessity of inclusion of rotational anisotropy in the interpretation of the behaviour of probes of different size.     

The crystallization behavior and the mechanical properties of segmented poly(ether ester) thermoplastic elastomers

The isothermal melt crystallization of three segmented copoly(ether ester)s based on PBT as the hard and PTMO as the soft segments differing in their hard segment content was investigated. The kinetics of crystallization was studied using polarizing microscopy and DSC. Two regimes of crystallization were observed. Spherulitic structures of low crystallinity are formed via predominantly athermal nucleation in regime I at supercoolings ΔT_u < 30°C. Ill-defined aggregations of lamellae grow at ΔT_u > 30°C. The crystallization follows an apparent Avrami-equation; the Avrami-constants cannot be explained in terms of a simple model. The structure of the samples was investigated by SAXS and compared to the structure of samples crystallized by rapid quenching and subsequent annealing. Much higher long spacings are obtained on isothermal crystallization. The long spacing increases with decreasing ΔT_u. It increases at constant ΔT_u with decreasing average hard segment length contrary to the samples crystallized by subsequent annealing of the quenched melt. In this case polymers differing in composition do not differ with regard to the long spacing obtained at constant ΔT_u. The modulus in the Hookean-range as derived from stress-strain curves at T > T_g does not reflect the details of the morphology or chain architecture but it is found to depend logarithmically on the volume fraction of crystallinity in the sample. Data of pure PBT are described by the same relationship.     

Preparation and mesomorphic properties of new thermotropic liquid-crystalline copoly(urethane-carbonate)s

New thermotropic liquid-crystalline (LC) copoly(urethane-carbonate)s (4) with high inherent viscosities were prepared by melt polycondensation from 6,6′-(4,4′-biphenylylenedioxy)dihexanol (1) and a mixture of aliphatic bis(phenyl carbamate)s (2) and bis(phenyl carbonate)s (3) in high yields. The polymers characterized by FTIR spectra and elemental analyses show good solubilities in organic solvents such as chloroform. Flexible films were cast from the polymer solutions. Their thermotropic LC properties were evaluated by differential scanning calorimetry and observation under the polarizing microscope equipped with a hot stage. These measurements indicate that the polymers form stable LC mesophases and possess block-like sequence distributions.     

Preparation,properties and complex formation ability of poly(ether-ester)s of poly(ethylene glycol)s and 2,6-pyridinedicarboxylic acid

Poly(ether-ester)s of poly(ethylene glycol)s (PEGs) and 2,6-pyridinedicarboxylic acid (PDA) were synthesized by polycondensation of PDA and PEG in the presence of dicyclohexylcarbodiimide and dimethylaminopyridine and by polycondensation of acyl chloride of PDA and PEG in the presence of triethylamine at 45°C. The polymers were characterized by GPC, UV, IR and ¹H and ¹³C NMR spectroscopy. The complex formation between poly(acrylic acid) (PAA) or poly(methacrylic acid) (PMA) and the poly(ether-ester)s was studied. It occurs below the critical polyether chain length necessary for complex formation because of the stabilizing effect of the PDA hydrophobic residues.     

Preparation of well-defined poly(ether-ester) macromers: photogelation and biodegradability

Two series of poly(ether-ester)-based bis-functional macromers terminated with acrylate groups and a well-defined number of ester bonds were synthesized. One series had a chain of 1, 3 or 5 ester bonds at both ends of the central poly(ethylene glycol) block (molecular weight, about 1000), while the other had an alternating structure of oligo(ethylene glycol) each of them linked to two ester bonds, in which 6 or 10 ester bonds were incorporated equally in the macromer molecules and the total molecular weight was adjusted by about 1000. Irradiation of all poly(ether-ester) macromers mixed with camphorquinone resulted in the formation of gels. Gel yield increased and hydrophilic properties of the gels produced decreased with irradiation time. The elastic modulus of the gels decreased with the number of ester bonds. Upon incubation in a PBS solution (pH 8.04), all gels were gradually degraded with time. At 3 weeks of incubation, the degradation ratio increased linearly with the number of ester bonds per unit of molecular weight of the macromers. The order of in vivo degradation rates determined from weight loss was similar to that of the in vitro study. Thus, these poly(ether-ester) macromers may be useful for biodegradable biomaterials or tissue engineering scaffolds.     

Biodegradable photo-crosslinked poly(ether-ester) networks for lubricious coatings

Biodegradable poly(ether-ester) networks were synthesized by UV photopolymerization and their lubrication performances were evaluated. Polyethers such as poly(ethylene glycol) (PEG), poly(propylene glycol) (PPG), and poly(tetramethylene glycol) (PTMG) were copolymerized with oligomers of D,L-lactic acid and terminated with acrylate groups to form photopolymerizable macromers. 1H NMR and IR spectra confirmed the chemical structures of copolymers and diacrylated macromers. Crosslinked polymer networks were formed upon UV-initiated free-radical polymerization. Gel contents, water contents, and contact angles were measured to characterize the crosslinked networks. In vitro degradation times of the crosslinked networks at 37 degrees C in 1 N NaOH varied from 20 min to 7 days depending on the crosslinking density (molecular weight of macromer) and the hydrophilic susceptibility (types of polyethers). The crosslinked polymers were coated on stainless-steel needles to investigate the lubrication properties by measuring penetration and drag forces through rubber stoppers. The maximum improvement in penetration force over control was 41% in the needle coated with PPG-based polymer networks (molecular weight of PPG = 4000). These materials can potentially be used as biodegradable lubricants for coating various medical products to replace the existing non-degradable silicone-based materials currently used.     

Structure and properties of segmented poly(ether-ester)s, 7. Model triblock copolyesters of monodisperse block length

Synthesis and characterization of model triblock copolyesters, in which the two end-blocks are based on tetramethylene terephthalate and the middle block is oligo(oxytetramethylene), are described. These model copolyesters, which are essentially monodisperse, and similarly prepared segmented block copolyesters with monodisperse blocks exhibit the same dependency of the melting temperature on the degree of polymerization of the ester blocks as polydisperse technical copoly(ether-ester)s.     

Syntheses and properties of elastic copoly(ester-urethane)s containing a phospholipid moiety and the fabrication of nanosheets

In these years, we have investigated the syntheses of novel diamine and diol monomers containing phosphorylcholine (PC) group to obtain biocompatible polymers, the backbone components of which were thermally stable and mechanically strong. In this study, the preparations of elastic copoly(ester-urethane)s containing PC group and polycarbonate segment were carried out by polycondensation and polyaddition using a diol monomer containing PC group and polycarbonate diol. It was found that the obtained polymers exhibited the high-thermal stability up to 200?°C and the elasticity derived from the soft segment. The introduction of PC group was effective to improve the resistance to the adhesions of proteins and platelets on the polymer films, which was the result of surface properties derived from the PC moiety. In addition, we tried to prepare ultra-thin polymer films composed of copoly(ester-urethane)s, so-called nanosheets. As a result, the desired nanosheets were successfully fabricated and the obtained nanosheets exhibited the high adhesive strength, indicating that the nanosheets could conform closely to the desired surfaces due to their exquisite flexibility and low roughness.     

Biodegradable poly(ether-ester) multiblock copolymers for controlled release applications

Multiblock poly(ether-ester)s based on poly(ethylene glycol), butylene terephthalate, and butylene succinate units were synthesized by a two-step melt polycondensation reaction, with the aim of developing a new series of degradable polymers for controlled release applications. The copolymers were characterized with respect to their composition (NMR), thermal properties (DSC), and swelling. The main focus was on the degradation kinetics and release properties of the copolymers. The crystallinity and swelling could be tailored by the PEG segment length and the ratio of the building units. With increasing mol fraction succinate in the hard segment, the swelling increased. The in vitro degradation was found to occur by molecular weight decrease and mass loss. Substitution of the aromatic terephthalate units by aliphatic succinate units increased the degradation rate of the copolymers. Polymers with PEG segments of 1000 kg/mol showed a more pronounced degradation than copolymers containing shorter and longer PEG segments. Model proteins were successfully incorporated and released from the poly(ether-ester) films. Depending on the size of the protein, the release mechanism was based on diffusion of the protein and degradation of the matrix.     

Sequence ordered copoly(arylester-carbonate)s: synthesis and characterization

A new class of ester-carbonate monomers was prepared by reaction of monomethylcarbonate of bisphenol-A with tere/isophthaloyl chloride. Self polycondensation of these monomers in presence of titanium tetraisopropoxide as catalyst resulted in the formation of copoly(arylester-carbonate)s having an ester to carbonate ratio of 2: 1. Copoly(arylester-carbonate)s rich in either carbonate groups were also prepared by copolymerization of ester-carbonate monomer with dimethyl terephthalate and the bismethylcarbonate of bisphenol-A. The polymer structure was established by ¹ H NMR and IR spectroscopy. The ordered sequence of estercarbonate groups in the polymer was established by ¹³C NMR spectroscopy.     

Preparation and thermal properties of semi-rigid homo- and copoly(imide-carbonate)s based on 4,4′-oxydiphthalimide

New aromatic-aliphatic semi-rigid homo- and copoly(imide-carbonate)s 7 containing the 4,4′-oxydiphthalimide ring system were prepared by melt polycondensation of N,N′-bis(6-hydroxyhexyl)-4,4′-oxydiphthalimide ( 4 ) and/or 6,6′-(4,4′-biphenyldiyldioxy)dihexanol ( 5 ) with hexamethylene diphenyl dicarbonate in the presence of zinc acetate, and their thermal and mesomorphic properties were evaluated. The assigned structures of the monomer and the polymers were identified by Fourier-transform infrared and ¹³C nuclear magnetic resonance spectroscopy and elemental analyses. Differential scanning calorimetry measurements, observation of the texture by means of a polarizing microscope equipped with a hot stage and powder X-ray analyses at various temperatures demonstrated that only the biphenyl moiety-rich polymers from nematic phases, but the 4,4′-oxydiphthalimide moiety-rich polymers exhibit no liquid-crystalline melts. It was suggested that the mesogenic character of the 4,4′-oxydiphthalimide ring system is low. The glass transition temperature steps decrease with the biphenyl moiety content. Thermogravimetry/differential thermal analysis (TG-DTA) measurements indicated that the polymers are thermostable up to 300°C in air.     

Preparation of Biocompatible,UV-Cured Fumarated Poly(ether-ester)-Based Tissue-Engineering Hydrogels

The aim of this study was to develop biodegradable, photo-polymerizable in situ gel-forming systems prepared from a fumaric acid monoethyl ester (FAME) modified poly(lactide-co-glycolide) (PLGA) co-polymer. By reacting lactide and glycolide in the presence of stannous octoate as a catalyst and 2-ethyl,2-hydroxymethyl 1,3-propanediol as an initiator, hydroxyl terminated branched PLGA was synthesized. Afterwards, at room temperature hydroxyl terminated branched PLGA was reacted with fumaric acid monoethyl ester (FAME). N,N′-dicyclohexylcarbodiimide and triethylamine were used as a coupling agent and catalyst, respectively. The gel percentage, equilibrium mass swelling, degradation profile and polymerization kinetics of the hydrogels were investigated. All of the results were influenced by the amount of FAME modified PLGA co-polymer. Biocompatibility of the hydrogels was examined by using MTT cytotoxicity assay. According to the results, hydrogels are biocompatible and cell viability percentage depends on the amount of PLGA co-polymer. While the amount was 15% in hydrogel composition, cell viability was 100%, but after increasing the PLGA co-polymer amount to 30% the viability reduced to 78%.     

蒸汽灭菌对聚醚酯材料及其血管细胞相容性的影响

探讨了蒸汽灭菌对聚乙二醇对苯二甲酸酯/聚对苯二甲酸丁二醇酯多嵌段共聚物(PEGT/PBT)性能的改变而导致对血管细胞相容性的影响.血管细胞能在紫外辐照灭菌的PEGT/PBT膜片上较好地黏附生长,而在蒸汽灭菌的膜片表面几乎无法黏附生长.使用差示扫描量热分析、静态接触角、光电子能谱、表面羧基测定、核磁共振和扫描电镜等分析测试方法对灭菌前后膜片的本体性能和表面性能进行表征.结果表明,蒸汽灭菌没有改变材料表面形貌和材料的组成.但是在蒸汽灭菌过程中PEGT/PBT链段发生重新取向,亲水性软段PEGT和材料的端羧基在表面富集,使得材料表面亲水性增加、硬段的结晶度有所增加.可能由于端羧基和表面聚乙二醇增多导致蛋白在材料表面的吸附减少,而致使血管细胞无法在蒸汽灭菌的膜片上黏附生长.     

Biocompatibility and degradation of poly(ether-ester) microspheres: in vitro and in vivo evaluation

Microspheres of a hydrophobic and a hydrophilic poly(ether–ester) copolymer were evaluated for their in vitro and in vivo biocompatibility and degradation. The microspheres prior to and after sterilization were tested for in vitro cytotoxicity. The in vivo biocompatibility of the poly(ethylene glycol) terephthalate and poly(butylene terephthalate) (PEGT/PBT) microspheres was evaluated subcutaneously and intramuscularly for 24 weeks in rabbits. The in vivo degradation of the microspheres was studied microscopically and compared to the in vitro degradation. The in vitro and in vivo studies showed the biocompatibility of the microspheres of both the hydrophobic and the hydrophilic PEGT/PBT copolymer. Extracts of these microspheres showed no cytotoxic reactivity in the in vitro cytotoxicity test. Sterilization of the microspheres by gamma irradiation did not affect the cytotoxicity. PEGT/PBT microspheres injected subcutaneously and intramuscularly in rabbits showed a mild tissue response in vivo, in terms of the inflammatory response, the foreign body reaction and the granulation tissue response. Although an in vitro degradation experiment showed a decrease in molecular weight due to hydrolysis, the in vivo degradation of the microspheres was slower than previously published.     

Modification of poly(ether urethane)elastomers by incorporation of poly(isobutylene)glycol. Relation between polymer properties and thrombogenicity

Non-polar hydrophobic poly(isobutylene)glycol (PIBG) was substituted for poly(tetramethylene ether)glycol (PTMEG) in poly(ether urethanes) based on 4,4'-methylenebis-(phenylisocyanate) (MDI) and 1,4-butanediol (BD) as chain extender. Two series of polyurethanes differing in their soft segment length, polymer composition, and hard segment content were studied by dynamic mechanical analysis (DMA) and static, as well as dynamic, contact angle measurements. The thrombogenicity of these polymers was characterized by studying the adhesion and activation of platelets using ELISA for GMP 140 and fluorescence microscopy. It was found by DMA that in PIBG-containing polyurethanes (PUE) exist soft domains containing hard segments, strictly separated hard segment domains, and hard segments partially mixed with soft segments. Contact angle measurements revealed that 25% PIBG or even less, are sufficient for a remarkable enrichment of these non-polar soft segments on the polymer surface. The platelet adhesion/activation on these materials was demonstrated to increase with the rise in hard segment content, as well as with an enhancement of the PIBG content. However, comparison of PIBG-containing PUE with medical applied polypropylene and pellethane expressed that PUE with PIBG content equal or less 25% have excellent haemocompatibility.     

Structure and properties of segmented poly(ether esters), 4. Compatibility of oligo(tetramethylene terephthalate)s with oligoethers and block copoly(ether ester)s

The mutual compatibility of oligo(tetramethylene terephthalate)s 1a—d and their compatibility with oligoethers 2, 3 , and 4 and block copoly(ether ester)s 5a—c based on poly(tetramethylene terephthalate) and poly(oxytetramethylene) is reported. From the binary phase diagrams of the oligoesters it is concluded that the oligoesters do not cocrystallize and the melt of the lower melting compound is not a good solvent for the higher melting homologue. For the trimer/pentamer ( 1b/1c )-blend the eutectic composition contains 3 mole-% of the pentamer 1c . Oligo(oxytetramethylene) ( 3 ) is a better solvent for the oligoesters than oligo(oxyethylene) ( 2 ). The addition of an oligoester to the block copoly(ether ester) induces a change in the phase behaviour of the polymer, resulting in a melting point of the blend higher than for the pure polymer or oligomer.     

Wetting characteristics and blood clotting on surfaces of copoly(gamma-Benzyl-L-glutamate, gamma-hydroxyethyl-L-glutamine)

The film surface of poly(gamma-benzyl-L-glutamate) (PBLG) was modified with 2-aminoethanol to enhance its hydrophilicity. Controlling the reaction conditions of PBLG and 2-aminoethanol, various types of copoly(gamma-benzyl-L-glutamate, gamma-hydroxyethyl-L-glutamine) film surfaces were obtained. Surface free energy (gamma sv), the dispersive component of gamma sv (gamma dsv), the nondispersive component of gamma sv (gamma psv), and the interfacial free energy of polymer surface with water (gamma sw), which were obtained by using the contact angle measurement and calculation method proposed by Andrade et al., were changed remarkably by the aminolysis. The gamma sv value increased after 2 h of aminolysis from 48.2 (PBLG) to 65.3 dyn/cm and gradually increased to around 70 dyn/cm after 12 h reaction. (gamma dsv) and (gamma psv) changed from 31.0 and 17.2 dyn/cm (PBLG) to 26.5 and 44.3 dyn/cm, respectively. These parameters of the material surfaces, modified over 12 h reaction, were found to be similar to those of the surfaces of canine aorta, vein, and human fibrin membrane. Blood clotting times on these polymer surfaces were comparatively longer than on siliconized glass surfaces.     

Enzymatic hydrolysis of copoly(N-hydroxypropyl-L-glutamine/L-leucine) hydrogels in vitro

Two component random copolypeptide hydrogels consisting of N-hydroxyalkyl L-glutamine and L-leucine were prepared by carrying out aminolysis reactions with 3-amino-1-propanol(P) together with crosslinking reactiors with 1,8-octamethylenediamine (OMDA) on hydrogels of the starting copolymers consisting of γ-methyl-L-glutamate(M) and L-leucine(L). The relation between their bulk structure and properties was investigated with regard to the swelling ratio in water, aqueous vapor permeability, tensile properties, and enzymatic degradation behavior in a pseudoextracellular fluid (PECF). The tensile property of the hydrogels was highly dependent on the swelling ratio in PECF, and on the hydrophobicity of the side chains, whose behavior was typical of an elastomer. It was shown that a common relation was obtained between the rate of water vapor permeabilities and the swelling ratio of hydrogels in PECF regardless of the difference of the nature of side chains. Biodegradation of the hydrogels in vitro by bromelain indicated that the degradation took place in bulk rather than on surface, and that the rate of degradation was also highly dependent on the swelling ratio of samples as well as on the hydrophobicity of the side chains of samples.     

Synthesis and evaluation of poly(diol citrate) biodegradable elastomers

Herein, we report the synthesis and evaluation of a novel family of biodegradable and elastomeric polyesters, poly(diol citrates). Poly(diol citrates) were synthesized by reacting citric acid with various diols to form a covalent cross-linked network via a polycondensation reaction without using exogenous catalysts. The tensile strength of poly(diol citrates) were as high as 11.15+/-2.62 MPa and Young's modulus ranged from 1.60+/-0.05 to 13.98+/-3.05 MPa under the synthesis conditions that were investigated. Elongation was as high as 502+/-16%. No permanent deformation was found during mechanical tests. The equilibrium water-in-air contact angles of measured poly(diol citrates) films ranged from 15 degrees to 53 degrees . The mechanical properties, degradation and surface characteristics of poly(diol citrates) could be controlled by choosing different diols as well as by controlling the cross-link density of the polyester network. Various types of poly(diol citrate) scaffolds were fabricated to demonstrate their processing potential. These scaffolds were soft and could recover from deformation. In vitro and in vivo evaluation using cell culture and subcutaneous implantation, respectively, confirmed cell and tissue compatibility. The introduction of poly(diol citrates) will expand the repertoire of currently available biodegradable polymeric elastomers and should help meet the requirements of tissue engineering applications.     

Amino alcohol-based degradable poly(ester amide) elastomers

Currently available synthetic biodegradable elastomers are primarily composed of crosslinked aliphatic polyesters, which suffer from deficiencies including (1) high crosslink densities, which results in exceedingly high stiffness, (2) rapid degradation upon implantation, or (3) limited chemical moieties for chemical modification. Herein, we have developed poly(1,3-diamino-2-hydroxypropane-co-polyol sebacate)s, a new class of synthetic, biodegradable elastomeric poly(ester amide)s composed of crosslinked networks based on an amino alcohol. These crosslinked networks feature tensile Young's modulus on the order of 1MPa and reversable elongations up to 92%. These polymers exhibit in vitro and in vivo biocompatibility. These polymers have projected degradation half-lives up to 20 months in vivo.