Controlled synthesis and characterizations of amphiphilic poly[(R,S)-3-hydroxybutyrate]-poly(ethylene glycol)-poly[(R,S)-3-hydroxybutyrate] triblock copolymers

Well-defined biodegradable amphiphilic triblock copolymers consisting of atactic poly[(R,S)-3-hydroxybutyrate] (PHB) and poly(ethylene glycol) (PEG) as the side hydrophobic block and middle hydrophilic block were synthesized via ring opening polymerization of (R,S)-β-butyrolactone from PEG macroinitiators and characterized using NMR, GPC, FT-IR, XRD, DSC and TG analyses. The controlled synthesis was made possible by the facile synthesis of pure PEG macroinitiators through a TEMPO-mediated oxidation. Constituting 40-70 wt% of the copolymer content, PHB blocks grown were amorphous while PEG formed crystalline phase when segment was sufficiently long. While hindering PEG crystallization, atactic PHB mixed well with amorphous PEG to give single T_g in all the copolymers. The copolymers exhibited two-step thermal degradation profile starting with PHB degradation from 210 to 300 °C, then PEG from 350 to 450 °C.     

Scaling laws and internal structure for characterizing electrospun poly[(R)-3-hydroxybutyrate] fibers

Using chloroform/dimethylformamide (CF/DMF) co-solvent, electrospinning of poly[(R)-3-hydroxybutyrate] (PHB) solutions was carried out at ambient temperature. The effects of the applied voltage (V), flow-rate (Q), and solution viscoelastic properties on the Taylor cone, electrified jet, and fiber morphology were investigated. In addition, the electric field developed by the needle-plate electrode configuration was calculated using a finite element analysis to reveal the tip-to-collector (H) effect. Among the processing parameters (V, Q and H), it was found that Q played a key role in determining the jet diameter (d_j) and electrospun fiber diameter (d_f), and scaling laws existed between them, i.e., d_j-Q^0.61 and d_f-Q^0.33. The diameter reduction ratios of D_o/d_j (D_o is the needle diameter) and d_j/d_f were measured as 50-120 and 5-10, respectively; it suggested that major jet stretching took place in the straight electrified jet region, and further chain orientation could be gained by the subsequent process of jet whipping. By changing PHB concentrations from 5 to 15 wt%, the solution viscosity (η_o) was increased from 100 to 4900 cP, whereas the surface tension and solution conductivity remained unchanged; it provided a good model solution to exclusively reveal the η_o effect on the electrospinning process. Our results showed that the η_o-dependence of d_j and d_f also followed simple scaling laws: d_j-η_o^0.06, and d_f-η_o^0.39, with a prefactor depending on the processing variables, mainly the flow-rate. Regardless of the PHB concentrations used, the obtained PHB fibers showed a similar crystallinity fraction of ca. 0.63 and possession of major α-crystals together with a small amount of β-crystals with zigzag chain conformation.     

Polybinaphthyls incorporating chiral (R) or (S)-2,2′-binaphthyland oxadiazole moieties by Stille reaction

Chiral polymers P-1 and P-2 were prepared by the polymerization of (R)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthyl ((R)-M-1) and (S)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthyl ((S)-M-1) with 2,5-bis[(4-tributylstannyl)phenyl]-1,3,4-oxadiazole (M-2) via Pd(PPh₃)₄ catalyzed Stille coupling reaction. 1,3,4-Oxadiazole unit not only has high electron affinity, high thermal and oxidative stability, but also serves as a good chromophore. Polymers have strong blue fluorescence due to the efficient energy migration from the extended π-electronic structure of the polymers to the chiral binaphthyl core and can be expected to have potential application in the materials of fluorescent sensors. Circular dichroism (CD) spectra of polymers P-1 and P-2 are almost identical except that they gave opposite signals at each wavelength. The long wavelengths CD effect of P-1 and P-2 can be regarded as the more extended conjugated structure in the repeating unit and a high rigidity of the polymer backbone.     

(R,R)-salen/salan-based polymer fluorescence sensors for Zn detection

(R,R)-salen-based polymer fluorescence sensor P-1 could be synthesized by the polymerization of 5,5′-(isoquinoline-5,8-diylbis(ethyne-2,1-diyl))-bis(3-tert-butyl-2-hydroxybenzaldehyde) (M-1) with (R,R)-1,2-diaminocyclohexane (M-2) via nucleophilic addition-elimination reaction, and (R,R)-salan-based polymer sensor P-2 could be obtained by the reduction reaction of P-1 with NaBH₄. The fluorescence response behaviors of two chiral polymers P-1 and P-2 on Zn²⁺ were investigated by fluorescence spectra. The fluorescence intensities of P-1 and P-2 can exhibit gradual enhancement upon addition of Zn²⁺. Compared with other cations, such as Na⁺, K⁺, Mg²⁺, Ca²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Ag⁺, Cd²⁺, Cr³⁺ and Pb²⁺, Zn²⁺ can lead to the pronounced fluorescence enhancement as high as 22.8-fold for P-1 and 3.75-fold for P-2, respectively. The results show that P-1 and P-2 incorporating (R,R)-salen/salan moieties as receptors in the polymer main chain backbone can exhibit high sensitivity and selectivity for Zn²⁺ detection.     

Surface structure of folded-chain crystals of poly(R-3-hydroxybutyrate) of different chain length

The structure of the crystalline-amorphous interface of poly(R-3-hydroxybutyrate) (PHB) of different molar mass is evaluated by analysis of the rigid amorphous fraction and by analysis of the degree of reversible melting and crystallization. The rigid amorphous fraction of low-molar-mass PHB of 5 kDa is only 5-10%, and at best half of that of high-molar-mass PHB of almost 500 kDa, despite identical crystallinity. This result is paralleled by observation of distinctly larger degree of reversible melting and crystallization in PHB of high molar mass. The larger rigid amorphous fraction and higher degree of reversible melting and crystallization in PHB of high molar mass, consistently and independently, prove enhanced covalent coupling of crystals and amorphous structure, and/or de-coupling of segments of macromolecules which traverse between phases, respectively. The distinct isolation of crystals in PHB of low molar mass is discussed in terms of absence of wide loops/folds, long-chain cilia, and tie-molecules.     

Analysis of inner structure in high-strength biodegradable fibers by X-ray microtomography using synchrotron radiation

The observation of the inner structure of materials without pretreatment or damage is a very useful analytical method in the field of materials science as well as in medicine and biology. We have carried out a three-dimensional (3D) analysis of biodegradable polyester bacterial-poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate] (P(3HB-co-3HV)) fibers with high tensile strength (1.07 GPa) using X-ray microtomography with synchrotron radiation. The inner structure of the fibers was visualized at a spatial resolution of 1 μm. There are many fine voids for one-step-drawn P(3HB-co-3HV) fibers after isothermal crystallization from the result of X-ray microtomography. This revealed that the clear streak reflection along the equator in small-angle X-ray scattering is caused by these fine voids. The recalculated tensile strength of one-step-drawn P(3HB-co-3HV) fibers after isothermal crystallization is suggested to be 2.02 GPa, taking the cross-section area with 52.7% (polymer region) into consideration. These fine voids in fibers seemed to be generated by the volume changes due to the contraction of polymer chains during isothermal crystallization.     

Influence of the swelling history on the swelling kinetics of stimuli-responsive poly[(N-isopropylacrylamide)-co-(methacrylic acid)] hydrogels

The influence of the swelling history on the swelling behavior of poly[(N-isopropylacrylamide)-co-(methacrylic acid)] P[(N-iPAAm)-co-(MAA)] random copolymers hydrogels synthesized by free radical polymerization in solution of N-iPAAm and MAA comonomers crosslinked with tetraethylene glycol dimethyl acrylate (TEGDMA) has been studied. The swelling behavior under pH 7 at 18, 29, 39 and 49 °C of this series of copolymers, previously soaked either at pH 2 or 7 has been investigated. The swelling kinetics of these two series of samples displays different behavior as function of the composition and temperature. However, the equilibrium swelling values only show slight dependences on the previous soaking pH and temperature. When samples are soaked at pH 7, then the swelling at pH 7 follows a first order kinetics, irrespective of the copolymer composition or the temperature at which the experiment has been carried out. In this case, the swelling process is very fast and depends only slightly on temperature. The first order rate constant increases with the MAA content in the hydrogel. Furthermore, the swelling rate of copolymer hydrogels soaked at pH 2, show strong dependence on composition and temperature. They follow an autocatalytic swelling kinetics due to the disruption of hydrogen bond arrangements. An initial slow water uptake is followed by an acceleration process, in which water molecules inside the gel help the next water molecules to come in. Two rate constants, a first-order rate constant and an autocatalytic one have been obtained from the kinetics analysis. They have revealed different temperature dependence which may be due to a balance between hydrophobic and hydrogen bond interactions. The temperature dependence of the swelling kinetics is stronger and more complex for copolymers treated under pH 2 than for copolymers soaked under pH 7.     

Pure gas and vapor permeation properties of poly[1-phenyl-2-[p-(trimethylsilyl)phenyl]acetylene] (PTMSDPA) and its desilylated analog, poly[diphenylacetylene] (PDPA)

The permeabilities of He, H₂, N₂, O₂, CO₂, CH₄, C₂H₆, C₃H₈, and n-C₄H₁₀ in poly[1-phenyl-2-[p-(trimethylsilyl)phenyl]acetylene] (PTMSDPA) and poly[diphenylacetylene] (PDPA) are presented and compared to those of poly(1-trimethylsilyl-1-propyne) (PTMSP), poly(1-phenyl-1-propyne) (PPP), and polysulfone. Like PTMSP, PTMSDPA, a disubstituted glassy acetylene-based polymer, exhibits higher permeabilities to organic vapors than to permanent gases due to its rigid polyacetylene backbone and bulky side groups, which provide a relatively high fractional free volume (FFV) value of 0.26. Desilylation was performed on PTMSDPA. The resulting material, PDPA, is totally insoluble in common organic solvents, so it has much higher chemical resistance than PTMSDPA. Additionally, due to its insolubility in polymerization solvents, desilylation provides the only known route to high molar mass PDPA. The FFV of the resulting membrane (PDPA) is reduced by approximately 12% relative to that of PTMSDPA. This leads to a decrease in gas permeability values and selectivity of organic vapors relative to nitrogen. For example, the oxygen permeability is reduced from 1200 to 500 Barrers upon desilylation. The pure gas selectivities decrease from 9 to 3 for n-C₄H₁₀/N₂ and from 26 to 9 for C₃H₈/N₂.     

可降解弹性体聚癸二酸丙二醇柠檬酸酯的合成及其性能

通过癸二酸与1,2-丙二醇反应,生成中间体癸二酸聚酯二元醇,然后将中间体与柠檬酸(CA)在一定条件下熔融缩聚制得了一种可降解弹性体聚癸二酸丙二醇柠檬酸酯(PPSC).考察了催化剂和带水剂种类及酸醇比(摩尔比)对中间体合成工艺的影响,对中间体和PPSC进行了表征,初步研究了PPSC的物理机械性能和体外降解性能.结果表明,以对甲苯磺酸为催化剂、苯为带水剂,在酸醇比为1∶ 4的条件下可合成较低相对分子质量的中间体癸二酸聚酯二元醇;PPSC弹性体的玻璃化转变温度在0 ℃以下,于室温及人体温度下处于高弹态;PPSC为适度交联的、低模量高伸长的弹性体,其在37 ℃、pH值为7.4的磷酸盐缓冲溶液中具有较快的降解性(降解度超过50%).     

Structure investigation of narrow banded spherulites in polyhydroxyalkanoates by microbeam X-ray diffraction with synchrotron radiation

Narrow banded structures of spherulites of poly[(R)-3-hydroxybutyrate] (P(3HB)) and its copolymers, with different second monomer unit of 4-hydroxybutyrate, 3-hydroxyhexanoate or 6-hydroxyhexanoate, were investigated by microbeam X-ray diffraction with Fresnel Zone Plate technique in synchrotron radiation (SPring-8). Radial scanning of spherulites were performed in 2 or 4 μm steps with 0.5 μm beam diameter of fine microfocus beam. The X-ray diffraction patterns for P(3HB) homopolymer spherulites showed the change of crystal orientation along the radial direction (a-axis), while the b- and c-axes rotated around a-axis. The intensities in microbeam X-ray diagrams of spherulites for P(3HB) copolymers changed periodically as function of the distance along the radial direction. The periodicity measured by X-ray diffraction was matched with narrow band spacing (15-25 μm) observed by polarized optical microscopy.     

4-间甲苯胺-3-吡啶磺酰胺的合成工艺改进

以4-羟基吡啶-3-磺酸为原料,经氯化、氨解、缩合等3个步骤制备了4-间甲苯胺-3-吡啶磺酰胺,对氯化后处理、缩合反应及其精制进行了改进,总收率75%.     

Different thermal behaviors of microbial polyesters poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)

Various methods were employed to study the thermal behaviors of a novel microbial polyhydroxyalkanoate (PHA) terpolyester, namely, poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) (PHBVHHx) compared with poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx). PHBVHHx showed higher crystallization rate and degree of crystallinity. PHBVHHx exhibited also different multiple melting behaviors from PHBHHx. The WAXD results demonstrated that the crystal lattice of PHBVHHx was more compact than that of PHBHHx, suggesting stronger interaction between chain stems. DSC and in-situ heating WAXD studies revealed that PHBVHHx showed a partial melting-lamellar thickening-remelting process during heating, while PHBHHx demonstrated a melting-rapid formation of new crystals-remelting process. It is proposed that the simultaneous introduction of 3-hydroxyvalerate and 3-hydroxyhexanoate monomers into poly(3-hydroxybutyrate) improves the mobility of chain stems along the chain direction, leading to easier intralamellar slip during heating or drawing, further resulting in improvement of mechanical properties, which was supported by the DMA tests. Consequently, we establish a relationship between the thermal behavior and the mechanical properties of biodegradable plastics, which we believe is applicable to other polymers as well.     

Co‐electrospun composite nanofibers of blends of poly[(amino acid ester)phosphazene] and gelatin

Electrospinning is known as a simple and effective fabrication method to produce polymeric nanofibers suitable for biomedical applications. Many synthesized and natural polymers have been electrospun and reported in the literature; however, there is little information on the electrospinning of poly[(amino acid ester)phosphazene] and its blends with gelatin. Composite nanofibers were made by co‐dissolving poly[(alaninoethyl ester)_0.67(glycinoethyl ester)_0.33phosphazene] (PAGP) and gelatin in trifluoroethanol and co‐electrospinning. The co‐electrospun composite nanofibers from different mixing ratios (0, 10, 30, 50, 70 and 90 wt%) of gelatin to PAGP consisted of nanoscale fibers with a mean diameter ranging from approximately 300 nm to 1 µm. An increase in gelatin in the solution resulted in an increase of average fiber diameter. Transmission electron microscopy and energy dispersive X‐ray spectrometry measurements showed that gelatin core/PAGP shell nanofibers were formed when the content of gelatin in the hybrid was below 50 wt%, but homogeneous PAGP/gelatin composite nanofibers were obtained as the mixing ratios of gelatin to PAGP were increased up to 70 and 90 wt%. The study suggests that the interaction between gelatin and PAGP could help to stabilize PAGP/gelatin composite fibrous membranes in aqueous medium and improve the hydrophilicity of pure PAGP nanofibers. Copyright © 2009 Society of Chemical Industry     

Solid-state NMR study on the structure and mobility of the noncrystalline region of poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

The noncrystalline structures of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) copolymers were studied by variable temperature solid-state wide-line ¹H NMR and solid-state high-resolution ¹³C NMR spectroscopy. It is found that at room temperature there exists a rich and rigid component in the noncrystalline region of PHB and PHBV. The content of this component decreases with the increase in 3-hydroxyvalerate content in PHBV and with the increase in temperature. The brittleness of PHB may be partly attributed to the rigidness of the noncrystalline region at room temperature, while the improvement of the properties of PHBV may come from the enhanced mobility of the noncrystalline region.     

Molecular dynamics of chiral semi-crystalline poly(R)-(3-hydroxyalkanoates)

The inversion-recovery cross-polarization (IRCP) sequence used for measuring cross-relaxation time (T_CH) is modified to obtain signals that show exponential or spin-lock (SL) decay to zero. The new sequence may, therefore, be analogously abbreviated as SLCP. Poly(R)-(3-hydroxybutyrate-co-3-hydroxyhexanoate) {P(HB-HHx) (85:15)} is found to be more mobile than poly(R)-(3-hydroxybutyrate) {PHB} in the crystalline regions. The molecular-level evidence by solid state nuclear magnetic resonance (NMR) that the P(HB-HHx) chain is more flexible than PHB is echoed by the dynamic frequency sweep measurements of the biopolymer melts, which show that the PHB melt has an unusual rheological response with the dynamic loss moduli dominating the storage moduli at all frequencies. This is most likely to be caused by the local anisotropic melt structures due to the long persistence length of PHB in the melt. Upon cooling the PHB melt to the solid state, such high levels of anisotropy may be frozen into the solid causing lower chain mobility, and hence giving rise to lower toughness. The incorporation of longer side chain unit to the main chain gives rise to a dynamic rheological response in P(HB-HHx) similar to that of an isotropic melt. This is believed to be due to the enhanced chain flexibility, and hence reduced persistence length. This further allows P(HB-HHx) to be processed into a more uniform isotropic morphology, and hence with improved mechanical toughness.     

Synthesis,crystallinity and degradation properties of biodegradable poly[(sebacic anhydride)‐co‐caprolactone] triblock copolymers

BACKGROUND: A series of novel biodegradable poly[(sebacic anhydride)‐co‐caprolactone] (PSA‐co‐PCL) triblock copolymers were prepared by melt condensation of acylated PSA and monofunctional hydroxyl‐terminated PCL prepolymers. These copolymers could be used as novel drug delivery carriers with expected good drug permeability due to the PCL component. The degradation rate and mode can be modulated by varying the ratio of monomers in the copolymer. RESULTS: The homopolymers and copolymers were characterized using ¹H NMR, gel permeation chromatography and differential scanning calorimetry (DSC). ¹H NMR confirmed the formation of triblock copolymers that comprise a middle PSA block and two side PCL blocks. DSC revealed that the melting temperature and degree of crystallinity for both sebacic anhydride (SA) and caprolactone (CL) components are strongly composition dependent, implying the hindrance effect of the two components on the crystallinity. In vitro degradation experiments showed that the mass loss is significantly accelerated for samples in base buffer solution and more rapid for the copolymers with a higher SA content. Scanning electron microscopy revealed that for SA‐rich copolymer, PSA(80 wt%)‐co‐PCL, surface erosion dominated the degradation mode of the sample. In contrast, for CL‐rich copolymer, PSA(20 wt%)‐co‐PCL, a micropore structure developed at a degradation time of 155 h along the edges of the sample, owing to the hydrolysis of SA. CONCLUSION: It is concluded that the rate and mode of degradation of these copolymers can be tuned by varying the composition of the copolymers. Copyright © 2007 Society of Chemical Industry     

The chemomechanical properties of microbial polyhydroxyalkanoates

Microbially produced polyhydroxyalkanoates (PHAs) are fully biodegradable biopolyesters that have attracted much attention recently as alternative polymeric materials that can be produced from biorenewable and biowaste resources. The properties of these biological polymers are affected by the same fundamental principles as those of fossil-fuel derived polyolefins, with a broad range of compositions available based on the incorporation of different monomers into the PHA polymer structure, and with this broad range tailoring subsequent properties. This review comprehensively covers current understanding with respect to PHA biosynthesis and crystallinity, and the effect of composition, microstructure and supramacromolecular structures on chemomechanical properties. While polymer composition and microstructure are shown to affect these properties, the review also finds that a key driver for determining polymer performance properties is compositional distribution. From this review it follows that PHA–PHA blend compositions are industrially important, and the performance properties of such blends are discussed. A particular need is identified for further research into the effect of chemical compositional distribution on macromolecular structure and end-use properties, advanced modeling of the PHA accumulation process and chain growth kinetics for better process control.     

The domain structure and mobility of semi-crystalline poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate): A solid-state NMR study

Solid-state NMR techniques have been employed to investigate the domain structure and mobility of the bacterial biopolymeric metabolites such as poly(3-hydroxybutyrate) (PHB) and its copolymers poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) containing 2.7 mol% (PHBV2.7) and 6.5 mol% (PHBV6.5) 3-hydroxyvalerate. Both single-pulse excitation with magic-angle spinning (SPEMAS) and cross-polarization magic-angle spinning (CPMAS) ¹³C NMR results showed that these biopolymers were composed of amorphous and crystalline regions having distinct molecular dynamics. Under magic-angle spinning, ¹H T_1ρ and ¹³C T₁ showed two processes for each carbon. Proton relaxation-induced spectral editing (PRISE) techniques allowed the neat separation of the ¹³C resonances in the crystalline regions from those in the amorphous ones. The proton spin-lattice relaxation time in the tilted rotating frame, , measured using the Lee-Goldburg sequence with frequency modulation (LGFM) as the spin-locking scheme, was also double exponential and significantly longer than ¹H T_1ρ. The difference between for the amorphous and crystalline domains was greater than that of ¹H T_1ρ. Our results showed that the differences could be exploited in LGFM-CPMAS experiments to separate the signals from two distinct regions. ¹H spin-diffusion results showed that the domain size of the mobile components in PHB, PHBV2.7 and PHBV6.5 were about 13, 24 and 36 nm whereas the ordered domain sizes were smaller than 76, 65 and 55 nm, respectively. The results indicated that the introduction of 3-hydroxyvalerate into PHB led to marked molecular mobility enhancement in the biopolymers.     

Behaviour of poly(β-hydroxybutyric acid) in dilute solution

The refractive indices of poly(β-hydroxybutyric acid) (PHB) at four wavelengths have been determined via different procedures. Viscometric and light scattering measurements have been made on solutions of eight samples of PHB (M_w = 20·9 × 10³?929 × 10³ g mol^?1) in 2,2,2-trifluoroethanol. From the dependences of intrinsic viscosity and of radius of gyration on molar mass, the conformation of PHB in dilute solution is shown to be that of a random coil. The findings are discussed in relation to existing conflicting evidence on the conformation of this polymer.     

Dielectric relaxation spectroscopy of poly[(R)‐3‐hydroxybutyrate] (PHB) during crystallization

The dielectric response of poly [(R)‐3‐hydroxybutyrate] (PHB) was investigated as a function of time after quenching a film from the melt to a crystallization temperature of 20 °C. In the frequency range investigated (20 to 10⁶ Hz) a relaxation maximum was observed–attributable to the glass transition–which could be analysed by the Havriliak–Negami relation. Changes in the complex dielectric constant were monitored both during spherulite growth (primary crystallization) and subsequently during a period of progressive crystallization (secondary crystallization) at room temperature. The relaxation strength changed only slightly during primary crystallization and its peak position remained at a constant frequency. Subsequently a continuous decrease in relaxation strength occurred, indicating considerable changes in molecular mobility after spherulite growth had been completed. The results provide further evidence that molecular mobility in the amorphous regions decreases significantly with time, and that this would be the reason why PHB shows embrittlement on ageing at room temperature. Copyright © 2004 Society of Chemical Industry