Degradation of a poly(ester urethane) elastomer. II. Kinetic modeling of the hydrolysis of a poly(butylene adipate)

In preparation for studying the kinetics of the hydrolysis of Estane® 5703, published hydrolysis data for a similar poly(butylene adipate) (herein called 63 PBA) have been modeled. Poly(ester urethanes) are known to degrade by acid‐catalyzed hydrolysis of the ester links, and the data on 63 PBA show that this degradation is reversible at low relative humidities (RHs). Previous work with these data was unable to fit them with concentration‐independent rate coefficients. It is shown herein that, with the water‐concentration model of the preceding article and the A_AC2 mechanism of reversible hydrolysis/esterification, the experimental kinetic data that vary across temperature, RH, and starting molecular weight can be fit with a single set of concentration‐independent rate coefficients. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 192–200, 2002     

Degradation of a poly(ester urethane) elastomer. I. Absorption and diffusion of water in Estane® 5703 and related polymers

In preparation for studying the hydrolytic degradation of Estane® 5703 and related poly(ester urethane) elastomers, the absorption (solubility) and diffusion of water in these polymers have been examined experimentally and modeled theoretically. Weight gain and loss experiments have been carried out. The amount of water absorbed per gram of sample was linear at low relative humidities (RHs) but curved upward at higher RHs. This curvature was not fit by Henry's law or the Flory–Huggins equation but was easily fit by a water‐cluster model. Diffusion coefficients were determined by fitting the time dependence of the sample weights, and the diffusion appeared Fickian to within experimental uncertainty. The similarity of related polymers was used to determine the approximate temperature dependence of the absorption. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 181–191, 2002     

Hydrolytic aging of crystallizable shape memory poly(ester urethane): Effects on the thermo-mechanical properties and visco-elastic modeling

The shape memory functionality of a segmented poly(ester urethane) and its hydrolytically aged specimens has been studied by cyclic thermo-mechanical measurements with an imposed strain of 100%. The shape memory effect was triggered by a melting transition in the soft segment phase. Aging was enforced by immersion in hot de-ionized water. In the course of the immersion the tensile properties (secant moduli, stress and strain at yield and break) were impaired by hydrolysis. Advanced specimen embrittlement finally led to rupture during the first thermo-mechanical cycle. This happened after 68 days of aging at 55 °C and correspondingly after 8 days at 80 °C. The residual strain after the first cycle, which was about 25%, increased significantly with aging time. Therefore, the total strain recoverability became ever smaller: aged specimens needed conditioning by at least two cycles for a full development of shape recoverability. Likewise the recovery force decreased continuously. Despite these degradation effects, it was observed that the shape fixity and the cycle-related shape recovery of appropriately conditioned specimens (number of cycles N > 2) remained on a constant high level (at round 100% and between 90% and 100%, respectively) throughout the whole aging period. These observations are discussed within the framework of a simplified model of the behavior of crystallizable shape memory polymers. The amorphous state of the polymer is described by the equation of the linear visco-elastic solid. As for the semi-crystalline state the material is assumed to react elastically with respect to deviations from the configuration, which was frozen up under constraint conditions. The curves of the dependence of the material behavior on aging time at 55 °C match perfectly those at 80 °C when the time axis is adjusted by a factor of 8.5, from which the apparent activation energy for hydrolytic aging in the amorphous state of 82 kJ mol⁻¹ could be deduced.     

Shape memory poly(ester urethane) with improved hydrolytic stability

In two hydrolytic degradation studies the tensile (mechanical) and functional (thermo-mechanical) properties of a hydrolysis-stabilized shape memory poly(ester urethane) and its non-stabilized analog were investigated. Hydrolytic degradation was enforced by specimen immersion in de-ionized water at 80 °C. Significant differences in the fundamental shape memory parameters were monitored as function of aging time for the stabilized and non-stabilized polymer. This included the ability to recover strain (shape recoverability) and stress (stress recoverability) on heating after shape programming. Hydrolysis-related mechanical and functional changes were correlated with morphological ones, detected by differential scanning calorimetry (DSC). The shape memory poly(ester urethane), which was protected by a carbodiimide-based hydrolysis stabilizer, revealed significantly improved resistance towards hydrolysis with respect to various mechanical and shape memory parameters.     

聚酯-酰胺的水解降解行为

研究了各种条件下聚酯-酰胺的水解降解行为及其与结构之间的关系。结果表明：酯键含量越高,质量损失就越快。聚合物的降解受酸、碱催化。根据SEM观察提出了可能发生的降解机理：表面腐蚀、非晶区腐蚀、晶区破坏到全部降解。     

Hydrolytic degradation and functional stability of a segmented shape memory poly(ester urethane)

In order to understand the effects of water and hydrolytic ageing on semi-crystalline poly(ester urethane) and its shape memory functionality, water immersion experiments at elevated temperature have been performed on a model substance and various parameters were monitored: change of the melting/crystallisation temperatures, substantial increase in crystallinity, temperature dependence of the water diffusion coefficient and solubility, hydrogen-bonding index and phase mixing by peak deconvolution of the FT-IR carbonyl region and day-to-day tensile and thermo-mechanical cyclic tensile tests. A rising fraction of freezable water agglomerates in the polymer was found for specimens cooled from the immersion temperature. The degradation process could be divided into three phases: an induction phase, a phase of continuous degradation and a phase of accelerated degradation. Shape recovery remains fairly constant during phase one and decreases slowly during phase two. The increase in crystallinity in phase two is accompanied by an increase in shape fixing ability.     

Synthesis and hydrolysis behaviour of poly(ester anhydrides) from polylactone precursors containing alkenyl moieties

Hydroxyl-group functional polylactones were prepared and converted to acid- terminated polyesters in a reaction with a series of alkenylsuccinic anhydrides containing 8, 12, or 18 carbons in their alkenyl chains. These polyester precursors were then linked into higher molecular weight poly(ester anhydrides) containing alkenyl moieties in their polyester blocks. The hydrolysis behaviour of the poly(ester anhydrides) was found to depend on the thermal properties of the polyester precursors. For poly(ester anhydrides) prepared from low molecular weight prepolymers with thermal transitions below 37 degrees C, the presence of hydrophobic alkenyl chains in the polyester precursors slowed the rate of weight loss. Poly(ester anhydrides) prepared from higher molecular weight prepolymers showed the opposite weight-loss behaviour; i.e., the crystallinity and thermal transitions of the alkenyl chain-containing poly(ester anhydrides) were low, and the weight loss was faster than for poly(ester anhydrides) without the alkenyl chains. The differences in length of the alkenyl chain, as such, had little effect on the hydrolysis behaviour and thermal properties of the poly(ester anhydrides).     

A Non-isocyanate Route to Poly(ester urethane) with High Molecular Weight: Synthesis and Effect of Chemical Structures of Polyester-diol

A series of non-isocyanate linear high molecular weight poly(ester urethane)s(PETUs)were prepared through an environmentallyfriendly route based on dimethyl carbonate,1,6-hexanediol and 1,6-hexanediamine.In this route,the polyurethane diol was first prepared by the reaction between bis-1,6-hexamethylencarbamate(BHC)and 1,6-hexanediol.A series of polyester soft segments of polyurethane have been synthesized from the polycondensation of adipic acid and different diols,including butanediol,hexanediol,octanediol and decanediol.The subsequent polycondensation of polyurethane diol and polyester diol led to linear PETUs.The resultant polymers were characterized by GPC,FTIR,¹H-NMR,¹³C-NMR,DSC,WAXD,TGA and tensile test.The results indicated that PETUs possess weight-average molecular weights higher than 1×10⁵ and the tensile strength as high as 10 MPa.The thermal properties,crystallization behavior,microphase separation behavior and morphology were studied by DSC and AFM,and the results indicated that the degree of phase separation was affected by two factors,the crystallization and hydrogen bonding interaction between soft segment and hard segment.     

Impact properties,phase structure,compatibility, and fracture morphology of polyamide‐1010/thermoplastic poly(ester urethane) elastomer blends

Blends of polyamide‐1010 (PA1010) and a thermoplastic poly(ester urethane) elastomer (TPU) were prepared by melt extrusion. The impact properties, phase structure, compatibility, and fracture morphology under impact were investigated for PA1010/TPU blends. The results indicated that TPU enhanced the impact strength of PA1010, and the best impact modification effect of the blends was obtained with 20 wt % TPU. The phase structure was investigated with scanning electron microscopy, and the compatibility was investigated with dynamic mechanical analysis and small‐angle X‐ray scattering. The study of the fracture morphology of PA1010/TPU blends indicated that the fracture surface of the blends had special features, consisting of many fibrillar elastomer particles and a conglutination–multilayer structure, as well as many small tubers on this structure. These fracture phenomena could not be found on the fracture surface of pure PA1010. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1177–1185, 2005     

Kinetics and Modeling of Vinyl Acetate Graft Polymerization from Poly(ethylene glycol)

A kinetic model for the graft polymerization of VAc from PEG was developed using the method of moments. Experiments were carried out to verify the model. The effect of various parameters, such as initiator concentration, temperature, and PEG molecular weight on the polymerization kinetics was examined. Polymerization rate, grafting efficiency, graft copolymer molecular weight, and PEG grafted ratio were measured. The model was in good agreement with the experimental data. No gel effect was observed at the studied PEG/VAc weight ratio of 1:1. The chain transfer constant to PEG was correlated to be . The model was also applied in a semi‐batch reaction and compared with the experimental results.

     

Water‐disintegrative and biodegradable blends containing poly(L‐lactic acid) and poly(butylene adipate‐co‐terephthalate)

In this study, novel biodegradable materials were successfully generated, which have excellent mechanical properties in air during usage and storage, but whose structure easily disintegrates when immersed in water. The materials were prepared by melt blending poly(L ‐lactic acid) (PLLA) and poly(butylene adipate‐co‐terephthalate) (PBAT) with a small amount of oligomeric poly(aspartic acid‐co‐lactide) (PAL) as a degradation accelerator. The degradation behavior of the blends was investigated by immersing the blend films in phosphate‐buffered saline (pH = 7.3) at 40 °C. It was shown that the PAL content and composition significantly affected morphology, mechanical properties, and hydrolysis rate of the blends. It was observed that the blends containing PAL with higher molar ratios of L ‐lactyl [LA]/[Asp] had smaller PBAT domain size, showing better mechanical properties when compared with those containing PAL with lower molar ratios of [LA]/[Asp]. The degradation rates of both PLLA and PBAT components in the ternary blends simultaneously became higher for the blends containing PAL with higher molar ratios of [LA]/[Asp]. It was confirmed that the PLLA component and its decomposed materials efficiently catalyze the hydrolytic degradation of the PBAT component, but by contrast that the PBAT component and its decomposed materials do not catalyze the hydrolytic degradation of the PLLA component in the blends. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Synthesis and characterization of crystallizable aliphatic thermoplastic poly(ester urethane) elastomers through a non-isocyanate route

A simple non-isocyanate route is developed for synthesizing crystallizable aliphatic thermoplastic poly(ester urethane) elastomers(TPEURs) with good thermal and mechanical properties. Three prepolymers of1,6-bis(hydroxyethyloxycarbonylamino) hexane(BHCH), i.e. Pre PBHCHs, were prepared through the self-transurethane polycondensation of BHCH. A poly(butylene adipate) prepolymer(Pre PBA) with terminal HO― groups was prepared and used as a polyester glycol. A series of TPEURs were prepared by the co-polycondensation of the Pre PBHCHs with Pre PBA at 170 ℃ under a reduced pressure of 399 Pa. The TPEURs were characterized by gel permeation chromatography, FTIR,1H-NMR, differential scanning calorimetry, thermogravimetric analysis, wide-angle X-ray diffraction, atomic force microscopy, and tensile test. The TPEURs exhibited M_n up to 23300 g/mol, M_w up to 51100 g/mol, Tg ranging from-33.8 ℃ to-3.1 ℃, T_m from 94.3 ℃ to 111.9 ℃, initial decomposition temperature over 274.7 ℃, tensile strength up to18.8 MPa with a strain at break of 450.0%, and resilience up to 77.5%. TPU elastomers with good crystallization and mechanical properties were obtained through a non-isocyanate route.     

Geminal poly(silyl ester)s: Highly labile degradable polymers

Geminal silyl ester linkages were used for the backbone construction of linear polymers, which exhibit rapid cleavage in the presence of atmospheric water. A series of poly(gem-silyl ester)s with two ester groups flanking each silicon atom were synthesized, in order to probe the effects of different silyl-substituted side-chain groups upon the physical and chemical properties. The transsilylation condensation reaction of bis(trimethylsilyl) terephthalate with dichlorodiisopropylsilane, dichlorodicyclohexylsilane, dichloromethyl-n-octadecylsilane, and dichloromethyl-4-methylphenethylsilane gave the four poly(gem-silyl ester)s with two isopropyl, two cyclohexyl, one methyl plus one octadecyl, and one methyl plus one 4-methyl-phenethyl side-chain groups per silicon, respectively. The polymers were characterized by NMR (¹H, ¹³C, and ²⁹Si), infrared spectroscopy (IR), size-exclusion chromatography (SEC), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Hydrolytic degradation studies of the polymers solvated in tetrahydrofuran and as bulk samples in the solid state were performed in the presence of atmospheric water as the nucleophilic cleavage agent, and the molecular weight loss was monitored by SEC. Poly(diisopropylsilyl terephthalate) (1a) and poly(dicyclohexylsilyl terephthalate) (1b) were found to be more stable towards nucleophilic degradation in comparison to poly(methyl-n-octadecylsilyl terephthalate) (1c) and poly(methyl-4-methylphenethylsilyl terephthalate) (1d), due to the presence of sterically bulky isopropyl or cyclohexyl groups attached to the silicon atoms. All of the polymers degraded into small molecules upon hydrolysis, with the exception that the degradation products of 1c and 1d self-condensed in the solid state to form the respective polysiloxanes. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3606–3613, 1999     

PEGylated poly(ester amide) elastomer scaffolds for soft tissue engineering

Biodegradable synthetic elastomers with tunable mechanical and physicochemical properties remain attractive materials for soft tissue engineering. We have recently synthesized novel poly(1,3‐diamino‐2‐hydroxypropane‐co‐glycerol sebacate)‐co‐poly(ethylene glycol) (APS‐co‐PEG) biodegradable elastomers. This class of PEGylated elastomers has widely tunable mechanical and degradation properties compared wtih currently available biodegradable elastomers. To further investigate the biological application of this class of elastomers, we fabricated hybrid APS‐co‐PEG/polycaprolactone (PCL) porous scaffolds by electrospinning. The fiber morphology, chemical composition, mechanical properties, degradability, and cytocompatibility of hybrid APS‐co‐PEG/PCL electrospun scaffolds were characterized. These scaffolds exhibited a wide range of mechanical properties and similar cytocompatibility to PCL scaffolds. Importantly, PEGylation inhibited platelet adhesion on all APS‐co‐PEG/PCL electrospun scaffolds when compared with PCL and APS/PCL scaffolds, suggesting a potential role in mitigating thrombogenicity in vivo. Additionally, APS‐25PEG/PCL scaffolds were found to be mechanically analogous to human heart valve leaflet and supported attachment of human aortic valve cells. These results reveal that hybrid APS‐co‐PEG/PCL scaffolds may serve as promising constructs for soft tissue engineering, especially heart valve tissue engineering. Copyright © 2017 John Wiley & Sons, Ltd.     

Improvement in Toughness of Polylactide by Melt Blending with Bio-based Poly（ester）urethane

Polylactide （PLA） was successfully toughened by blending with bio-based poly（ester）urethane （TPU） elastomers which contained bio-based polyester soft segments synthesized from biomass diols and diacids. The miscibility, mechanical properties, phase morphology and toughening mechanism of the blend were investigated. Both DSC and DMTA results manifested that the addition of TPU elastomer not only accelerated the crystallization rate, but also increased the final degree of crystallinity, which proved that TPU has limited miscibility with PLA and has functioned as a plasticizer. All the blend samples showed distinct phase separation phenomenon with sea-island structure under SEM observation and the rubber particle size in the PLA matrix increased with the increased contents of TPU. The mechanical property variation of PLA/TPU blends could be quantitatively explained by Wu＇s model. With the variation of TPU, a brittle-ductile transition has been observed for the TPU/PLA blends. When these blends were under tensile stress conditions, the TPU particles could be debonded from the PLA matrix and the blends showed a high ability to induce large area plastic deformation before break, which was important for the dissipation of the breaking energy. Such mechanism was demonstrated by tensile tests and scanning electron microcopy （SEM） observations.     

Synthesis and characterization of poly(itaconate ester)s with etheric side chains

The synthesis and characterization of poly(itaconate ester)s with short poly(ethylene oxide) side chains have been studied. It was found that the monomer syntheses via esterification of itaconic acid resulted in incomplete esterification leaving up to 35 mol % monomers with carboxylic acid functionality. These acid groups were then incorporated into the polymers. This acid incorporation has not previously been reported, nor have the properties of the copolymers been studied. Techniques were developed to effectively remove the acid impurities to generate pure homopolymers. Titration and gas chromatographic techniques were developed to study the amount of acid impurity in the monomers, and titration was also used to characterize the polymers. Size exclusion chromatography and differential scanning calorimetry were used to study both the homopolymers and copolymers. It was found that the location and breadth of the glass transition is a function of acid content. Finally, isomerization of the itaconate monomers to the inactive mesaconate was also found to be a problem during the synthesis. Pure mesaconate and citraconate monomers were synthesized and characterized by ¹H-NMR. © 1993 John Wiley & Sons, Inc.     

Synthesis and characterization of block poly(ester‐ether‐urethane)s from bacterial poly(3‐hydroxybutyrate) oligomers

Telechelic hydroxylated poly(3‐hydroxybutyrate) (PHB‐diol) oligomers have been successfully synthesized in 90–95% yield from high molar mass PHB by tin‐catalyzed alcoholysis with different diols (mainly 1,4‐butanediol) in diglyme. The PHB‐diol oligomers structure was studied by nuclear magnetic resonance, Fourier transformed infrared spectroscopy MALDI‐ToF MS, and size exclusion chromatography, whereas their crystalline structures, thermal properties and thermal stability were analyzed by wide angle X‐ray scattering, DSC, and thermogravimetric analyses. The kinetic of the alcoholysis was studied and the influence of (i) the catalyst amount, (ii) the diol amount, (iii) the reaction temperature, and (iv) the diol chain length on the molar mass was discussed. The influence of the PHB‐diol molar mass on the thermal stability, the thermal properties and optical properties was investigated. Then, tin‐catalyzed poly(ester‐ether‐urethane)s (PEEU) of M_n = 15,000–20,000 g/mol were synthesized in 1,2‐dichloroethane from PHB‐diol oligomers (P_ester) with modified 4,4'‐MDI and different polyether‐diols (P_ether) (PEG‐2000, PEG‐4000, and PPG‐PEG‐PPG). The influence of the PHB‐diol chain length, the P_ether/P_ester ratio, the polyether segment nature and the PEG chain length on the thermal properties and crystalline structures of PEEUs was particularly discussed. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1949–1961     

Synthesis of trans‐4‐hydroxy‐L‐proline‐based telechelic prepolymers and poly(ester‐urethane)

The synthesis of hydroxyproline‐based telechelic prepolymers by the condensation polymerization of trans‐4‐hydroxy‐N‐benzyloxycarbonyl‐L ‐proline methyl ester was investigated. All the polymerizations were carried out in the melt with stannous octoate as the catalyst and with different diols. The products were characterized by differential scanning calorimetry, proton nuclear magnetic resonance, infrared spectrophotometry, and inherent viscosity (η_inh). According to the analytic results, the η_inh value of the prepolymers depended on the kind and amount of diols that were added. With an increase in the 1,6‐hexanediol feed from 2 to 10 mol %, there was a decrease in η_inh from 0.78 to 0.41 along with a decrease in the glass‐transition temperature (T_g ) from 63 to 42 °C. When 2 mol % of different kinds of diols were used, η_inh ranged from 0.78 to 0.21, and T_g varied from 70 to 43 °C. These new prepolymers could be linked to poly(ester‐urethane) by the chain extender 1,6‐hexamethylene diisocyanate. The poly(ester‐urethane) was amorphous, and the T_g was 76 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2449–2455, 2000     

Study on sequence distribution of segmented poly(urethane urea)s by 13C-NMR spectroscopy: Effect of polymerization procedures

The segmented poly(urethane urea) copolymers were synthesized by one- and two-step polymerization procedures. The copolymers were based on 4,4′-diphenylmethane diisocyanate, 3,5-diethyltoluene diamine, and ethylene oxide-capped poly(propylene oxide) diol. The mean sequence lengths of polyurethane soft block and polyurea hard block as well as the sequence distribution of the hard block in the copolymers were estimated from the signals of aromatic carbons in ¹³C-NMR spectra. The results indicated that two-step polymerization led to longer mean sequence lengths and broader hard block sequence distribution than one-step polymerization did. © 1996 John Wiley & Sons, Inc.