Structure,Properties and Biodegradation of Some Bacterial Copoly(hydroxyalkanoate)s

This article describes the relationships between not only comonomer-unit compositions but also their distributions and structures as well as properties for bacterial copoly(hydroxyalkanoate)s, including poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxy-propionate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxy-butyrate-co-4-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-mercapto-propionate). It was found that as-produced copoly(hydroxy-alkanoate)s have broad comonomer-unit compositional distributions, which we can control to some degree. The structure and properties of copoly(hydroxy-alkanoate)s depend not only on the chemical structure and the comonomer-unit composition but also on the comonomer-unit compositional distribution.     

PHBV-GMA与PHBV-GMA/PPC共混物中接枝物的热性能与形态结构

以甲基丙烯酸缩水甘油酯(GMA)单体对聚(3-羟基丁酸酯-3-羟基戊酸酯)(PHBV)接枝改性,得到的产物PHBV-GMA与封端后的聚碳酸亚丙酯(PPC)反应性共混。索氏抽提器提取PHBV-GMA和PHBV-GMA/PPC共混物,分别得到两种接枝产物PHBV-g-GMA和PHBV-g-PPC,用差示扫描量热法(DSC)、偏光显微镜(POM)以及原子力显微镜(AFM)研究其热性能和形态结构。结果发现,GMA接枝后,对PHBV结晶有成核效应。PPC接枝PHBV后,接枝物PHBV-g-PPC结晶度降低,球晶尺寸减小,PHBV和PPC两种大分子间的相分离程度降低,相容性明显提高。     

Mechanical spectroscopy study on biodegradable synthetic and biosynthetic aliphatic polyesters

Miscibility behavior and rheological properties with mechanical spectroscopy study of both poly(3-hydroxybutyrate) (PHB)/poly(ethylene oxide) (PEO) and biodegradable synthetic aliphatic polyester (BDP)/linear low density polyethylene (LLDPE) were investigated. Blends of BDP with LLDPE were immiscible, showing two separate T_g values in all compositions; whereas blends of PHB with PEO were miscible, showing a single T_g in the whole range of compositions. However, the shear viscosities of both synthetic and biosynthetic blend systems decrease with increasing shear rate. When a modified Cole-Cole plot of the blend system is further considered, the logG′-logG” plot shows little sensitivity to a variation in both LLDPE composition for synthetic BDP and PEO composition for biosynthetic PHB. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)) random copolymers were also investigated.     

Preparation,fractionation, and dilute-solution behavior of ABA poly(methyl methacrylate-b-α-methylstyrene) block copolymers

The preparation by anionic polymerization of six ABA poly(methyl methacrylate-b-α-methylstyrene) block copolymers and of sixteen poly(α-methylstyrene)s is described. The block copolymers, of similar molecular weight but with different chemical compositions, were fractionated by preparative gel permeation chromatography and their behavior in dilute solution was investigated using viscometry. The results obtained indicate that the intramolecular phase separation does not occur under the conditions utilized, the block copolymers assuming randomcoil configurations in all of the copolymer/solvent systems studied. Consequently the block copolymer molecules are more expanded than homopolymers of the same molecular weight. The series of poly(α-methylstyrene)s covered the molecular weight range 2.7 × 10³–1.3 × 10⁶ and enabled the determination of Mark–Houwink–Sakurada constants for poly(α-methylstyrene) in the solvents chosen for the block copolymer studies.     

NMR characterization of biodegradable polyesters

Biodegradable polyesters obtained by fermentation of Alcaligenes eutrophus are characterized with the aid of H, D, C NMR spectroscopy. Copolymers of 3-hydroxybutyrate and 3-hydroxyvalerate are Bernoullian or mixture of two Bernoullian copolymers depending on fermentation conditions. The reverse reaction was found in the reaction catalyzed by beta-ketothiolase during biosynthetic pathway. The fractional population of gauche and trans conformers around the skeletal CH-CH₂ bond is 0.6:0.4 for both poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) in chloroform. This result suggests the possibility of formation of isomorphic crystals between copolymers with different composition ratios.     

Polymerization and copolymerization of β-butyrolactone and benzyl-β-malolactonate by aluminoxane catalysts

High molecular weight poly-β-hydroxybutyrate (PHB) and poly (β-hydroxybutyrate-co-β-benzyl malate) [P (HB? BM)], were prepared by ring-opening polymerization reactions of racemic β-butyrolactone (BL) and racemic β-benzyl malolactonate (BM) using two types of oligomeric aluminoxane catalysts prepared by the reaction of water with either triethyl-aluminum (EAO) or triisobutylaluminum (IBAO). The stereoregularities, crystallinities, and molecular weights were determined for both the PHB homopolymers and the P (HB? BM) copolymers by nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), and gel permeation chromatography (GPC). All homopolymers and copolymers obtained could be separated into acetone-soluble and acetone-insoluble fractions. In every case the latter had higher degrees of crystallinity, higher molecular weights and higher degrees of stereoregularity (84–87% isotactic dyads) than the former. Hence all of the polymers obtained from both types of catalysts apparently had stereoblock isotactic structures. Copolymer compositions and monomer dyad sequence distributions were determined by NMR spectroscopy.     

Application of solid phase peptide synthesis to engineering PEO–peptide block copolymers for drug delivery

This work describes a simple, versatile solid-phase peptide-synthesis (SPPS) method for preparing micelle-forming poly(ethylene oxide)-block-peptide block copolymers for drug delivery. To demonstrate its utility, this SPPS method was used to construct two series of micelle-forming block copolymers (one of constant core-composition and variable length; the other of constant core length and variable composition). The block copolymers were then used to study in detail the effect of size and composition on micellization. The various block copolymers were prepared by a combination of SPPS for the peptide block, followed by solution–phase conjugation of the peptide block with a proprionic acid derivative of poly(ethylene oxide) (PEO) to form the PEO-b-peptide block copolymer. The composition of each block component was characterized by mass spectrometry (MALDI and ES-MS). Block copolymer compositions were characterized by ¹H NMR. All the block copolymers were found to form micelles as judged by transmission electron microscopy (TEM) and light scattering analysis. To demonstrate their potential as drug delivery systems, micelles prepared from one member of the PEO-b-peptide block copolymer series were physically loaded with the anticancer drug doxorubicin (DOX). Micelle static and dynamic stability were found to correlate strongly with micelle core length. In contrast, these same micellization properties appear to be a complex function of core composition, and no clear trends could be identified from among the set of compositionally varying, fixed length block copolymer micelles. We conclude that SPPS can be used to construct biocompatible block copolymers with well-defined core lengths and compositions, which in turn can be used to study and to tailor the behavior of block copolymer micelles.     

Macromolecular size of polyelectrolytes containing ammonium and sulfonic acid groups, as determined by light scattering

The macromolecular dimensions of fractionated polyelectrolytes poly(4-vinylpyridine) quaternized (PVPyQ), poly[(3-methacryloylamino) propyltrimethyl ammonium chloride] (PMPTA), poly(diallyl dimethyl ammonium chloride) (PDDA), and poly[(3-methacryloylamino) propyltrimethyl ammonium chloride-co-2-acrylamido-2-methyl-1-propanesulfonic acid] P(MPTA-co-APSA), were determined by light scattering, using aqueous electrolyte as solvent. PVPyQ, PMPTA, and P(MPTA-co-APSA) of various comonomer compositions were synthesized by radical polymerization. All polymers were fractionated by membrane ultrafiltration. Light scattering measurements on dialyzed solutions give good Zimm plots from which the average molecular weight, , mean squared radius of gyration, 〈s²〉, and second virial coefficient, A₂, were determined. No significant selective sorption of the electrolyte by the polyelectrolytes was detected. Positive A₂ values are obtained in all cases, corresponding to good solvent conditions, however, the interpenetration function, Ψ, has low values (0.01-0.10), showing that the excluded volume effect is relatively low. In PDDA, the dependence of 〈s²〉 on suggests that the coil of this polyelectrolyte is contracted by branching. In the ammonium-sulfonic copolymers, the comonomer stoichiometric feed 1:1 yields an insoluble copolymer (possible complex formation between amino and sulfonic groups). The soluble copolymers (with unbalanced comonomer compositions) have dimensions similar to the homopolymers, and not appreciably dependent on composition; hence no contraction due to complex formation is detected in these copolymers.     

Syntheses of amphiphilic biodegradable copolymers of poly(ethyl ethylene phosphate) and poly(3-hydroxybutyrate) for drug delivery

Biodegradable and amphiphilic triblock copolymers poly(ethyl ethylene phosphate)-poly(3-hydroxy-butyrate)-poly(ethyl ethylene phosphate) (PEEP-b-PHB-b-PEEP) have been successfully synthesized through ring-opening polymerization. The structures are confirmed by gel permeation chromatography and NMR analyses. Crystallization investigated by X-ray diffraction reveals that the block copolymer with higher content of poly(ethyl ethylene phosphate) (PEEP) is more amorphous, showing decreased crystallizability. The obtained copolymers self-assemble into biodegradable nanoparticles with a core-shell micellar structure in aqueous solution, verified by the probe-based fluorescence measurements and transmission electronic microscopy (TEM) observation. The hydrophobic poly(3-hydroxybutyrate) (PHB) block serves as the core of the micelles and the micelles are stabilized by the hydrophilic PEEP block. The size and size distribution are related to the compositions of the copolymers. Paclitaxel (PTX) has been encapsulated into the micelles as a model drug and a sustained drug release from the micelles is observed. MTT assay also demonstrates that the block copolymers are biocompatible, rendering these copolymers attractive for drug delivery. Supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No.20060358036)     

Melting and thermal history of poly(hydroxybutyrate-co-hydroxyvalerate) using step-scan DSC

Melting behaviour and crystal morphology of poly(3-hydroxybutyrate) (PHB) and its copolymer of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with various hydroxyvalerate (HV) contents [5 wt.% (PHB5HV), 8 wt.% (PHB8HV) and 12 wt.% (PHB12HV)] have been investigated by conventional DSC, step-scan differential scanning calorimetry (SDSC) and hot-stage polarised optical microscopy (HSPOM). Crystallisation behaviour of PHB and its copolymers were investigated by SDSC. Thermal properties were investigated after different crystallisation treatments, fast, medium and slow cooling. Multiple melting peak behaviour was observed for all polymers. SDSC data revealed that PHB and its copolymers undergo melting–recrystallisation–remelting during heating, as evidenced by exothermic peaks in the IsoK baseline (non-reversing signal). An increase in degree of crystallinity due to significant melt–recrystallisation was observed for slow-cooled copolymers. PHB5HV showed different crystal morphologies for various crystallisation conditions. SDSC proved a convenient and precise method for measurement of the apparent thermodynamic specific heat (reversing signal) HSPOM results showed that the crystallisation rates and sizes of spherulites were significantly reduced as crystallisation rate increased.     

Production of specific copolymers of polyhydroxyalkanoates from industrial waste

Polyhydroxyalkanoates, biodegradable plastics with the desired physical and chemical properties of conventional synthetic plastics, are extensively investigated. In this study, specific bacterial strains produced specific copolymers from food waste. Copolymers of HB and HV (poly[3-hydroxybutyrate-co-3-hydroxyvalerate]) were obtained using various ratios of butyric acid (C₄) and valeric acid (C₅) as carbon sources. The C₄ to C₅ ratio affected the melting points of the copolymers. Melting and glass transition temperatures and many other thermal properties are important parameters relative to in-service polymer applications. Higher ratios of butyrate to valerate gave higher melting points. When a mixed culture of activated sludge was employed to produce copolymers using food wastes as nutrients, the obtained copolymers showed various monomer compositions. Copolymers with a higher portion of HV were obtained using soy waste; copolymers with less HV were obtained using malt wastes. Pure strains, (i.e., Alcaligenes latus DSM 1122, and DSM 1124, Staphylococcus spp., Klebsiella spp.) produced specific copolymers from food waste. Only Klebsiella spp. produced different copolymers; the ratios of HB:HV were 93:7 and 79:21 from malt waste and soy waste, respectively. The other strains produced polymers of 100% HB. Selecting industrial food wastes as carbon sources can further reduce the cost of producing copolymers. Open Laboratory of Chirotechnology of the Institute of Molecular Technology for Drug Discovery and Synthesis The University Grants Committee Area of Excellence Scheme, Hong Kong     

Phase Behavior and Thermal Properties for Binary Blends of Bacterial Poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate)s with Narrow‐Comonomer‐Unit Compositional Distribution

The miscibility and the effect of compositional distribution on physical properties were investigated for binary blends of biosynthesized poly(3‐hydroxybutyrate) [P(3HB)] and comonomer compositionally fractionated poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate)s [P(3HB‐co‐3HH)] with narrow compositional distribution. Biosynthesized P(3HB‐co‐3HH) samples were compositionally fractionated using solvent (chloroform)/nonsolvent (n‐heptane) mixtures. The binary blends of fractionated P(3HB‐co‐3HH)s with different 3HH unit content were prepared by casting from solution in chloroform. The miscibility and the thermal properties of these blends were analyzed by differential scanning calorimetry (DSC). It was found that the two components are miscible in the amorphous phase when the difference in 3HH unit content between the two component polymers of these blends is less than 20 mol‐%, subsequently they are immiscible when the difference is larger than 30 mol‐%. By comparing the thermal properties of the binary blends of fractions, with those for the fractions themselves, and with those for the bacterially as‐produced unfractionated copolyesters, the effects of compositional distribution on the properties of copolyesters were discussed.

Glass transition temperatures of blends PHB/H10, H10/H20, and PHB/H20 versus total 3HH unit content in the blends. The solid lines are the best fits of the experimental results of the P(3HB‐co‐3HH) fractions with narrow compositional distribution.     

Separation and composition distribution determination of triblock copolymers by thermal field-flow fractionation

Thermal field-flow fractionation (ThFFF) is used to separate a linear triblock copolymer of polystyrene, poly(tert-butyl acrylate), and poly(methyl methacrylate) by composition. Fractions were collected and subjected to off-line NMR analysis. The resultant mole fraction versus retention time plots for each of the three polymer components confirmed the success of the separation and yielded the composition distribution of the copolymer. The composition distribution was also obtained using a second approach that involved solving a series of equations comprised of polymer thermal diffusion coefficients and quasi-elastic light scattering, differential refractometry, and UV detector responses. Both sets of data showed similar trends of composition variations in each polymer component as a function of retention time. However, discrepancies were observed in the mole fraction values. The ability to compositionally separate and to determine composition distribution of copolymers is important as demonstrated by the presence of diblock impurities in the ThFFF with off-line NMR results.     

Photooxidative and pyrolytic degradation of methyl methacrylate-alkyl acrylate copolymers

Different compositions of poly(methyl methacrylate-co-methyl acrylate) (PMMAMA), poly(methyl methacrylate-co-ethyl acrylate) (PMMAEA) and poly(methyl methacrylate-co-butyl acrylate) (PMMABA) copolymers were synthesized and characterized. The photocatalytic oxidative degradation of all these copolymers were studied in presence of two different catalysts namely Degussa P-25 and combustion synthesized titania using azobis-iso-butyronitrile and benzoyl peroxide as oxidizers. Gel permeation chromatography (GPC) was used to determine the molecular weight distribution of the samples as a function of time. The GPC chromatogram indicated that the photocatalytic oxidative degradation of all these copolymers proceeds by both random and chain end scission. Continuous distribution kinetics was used to develop a model for photocatalytic oxidative degradation considering both random and specific end scission. The degradation rate coefficients were determined by fitting the experimental data with the model. The degradation rate coefficients of the copolymers decreased with increase in the percentage of alkyl acrylate in the copolymer. This indicates that the photocatalytic oxidative stability of the copolymers increased with increasing percentage of alkyl acrylate. From the degradation rate coefficients, it was observed that the photocatalytic oxidative stability follows the order PMMABA > PMMAEA > PMMAMA. The thermal degradation of the copolymers was studied by using thermogravimetric analysis (TGA). The normalized weight loss and differential fractional weight loss profiles indicated that the thermal stability of the copolymer increases with an increase in the percentage of alkyl acrylate and the thermal stability of poly(methyl methacrylate-co-alkyl acrylate)s follows the order PMMAMA > PMMAEA > PMMABA. The observed contrast in the order of photostability and thermal stability of the copolymers was attributed to different mechanisms involved for the scission of polymer chain and formation of different products in both the processes.     

聚β－羟基烷酸酯热分解行为的直接裂解质谱研究

用ＤＰＭＳ、ＴＧ、ＤＴＡ等方法研究了聚β－羟基丁酸酯（ＰＨＢ）及其共聚物Ｐ（ＨＢ－ｃｏ－ＨＶ）的热分解行为和某些结构性质．能提供多至７个链节重复单元的裂解碎片．可较好地反应共聚物的组成和分布．结果表明：聚β－羟基烷酸酯的热分解具有较高的选择性，通过β－Ｈ转移反应形成由羧基和烯烃结尾的齐聚物．齐聚物准分子离子可进一步脱去一分子水．     

Synthesis of Poly(glutamic acid-co-aspartic acid) via Combination of N-carboxyanhydride Ring Opening Polymerization with Debenzylation简

The random copolymers of glutamic acid （LG） and aspartic acid （ASP）, poly（LG-co-ASP）, with designed compositions could be successfully synthesized via combination of N-carboxyanhydride ring opening copolymerization with debenzylation. Ring opening copolymerizations of y：benzyl-L-glutamate N-carboxyanhydride （BLG-NCA） and β-benzyl-Laspartate N-carboxyanhydride （BLA-NCA） were carried out by using different amines including triethylamine （TEA）, diethylamine, n-hexylamine （NHA）, triphenylamine, diphenylamine or aniline as initiators. All the 6 amines were highly efficient to get well-defined poly（BLG-co-BLA） copolymers with designed compositions although the polymerizations proceeded via different mechanisms （normal amine mechanism or/and activated monomer mechanism）, which are based on chemical structure of amines. The molecular weights of poly（BLG-co-BLA） copolymers could be mediated by both TEA concentration and polymerization time. Then, debenzylation ofpoly（BLG-co-BLA） copolymers was conducted to prepare the corresponding hydrophilic random eopolymers of poly（LG-co-ASP） with a-subunit structure in ASP structural units. The contents of LG structural units in poly（LG-co-ASP） copolymers matched with those of BLG-NCA in NCA-monomer feeds in ring opening copolymerizations initiated by NHA or TEA and were closed to the theoretical line. The diblock copolymer of poly（BLG-b-BLA） could also be synthesized via living NCA ring opening copolymerization by sequential addition of BLG- NCA and BLA-NCA.     

Controlled synthesis of styrene-n-butyl acrylate copolymers with various chain microstructures mediated by dibenzyl trithiocarbonate

Copolymers of styrene and n-butyl acrylate are synthesized via pseudoliving radical copolymerization mediated by dibenzyl trithiocarbonate as a reversible addition fragmentation chain transfer agent. In a wide range of monomer feed compositions, narrowly dispersed compositionally uniform copolymers of desired molecular masses are formed, and their gradient structures are controlled by the compositions of the initial monomer feeds. The effects of the compositions, the chain microstructures, and the compositional homogeneity of the copolymers on their glass-transition temperatures are studied.     

Confinement Effects on the Crystallization Kinetics and Self-Nucleation of Double Crystalline Poly(p-dioxanone)-b-poly(ϵ-caprolactone) Diblock Copolymers

The morphology, crystallization and self nucleation behavior of double crystalline diblock copolymers of poly(p-dioxanone) (PPDX) and poly(ϵ-caprolactone) (PCL) with different compositions have been studied by different techniques, including optical microscopy (OM), atomic force microscopy (AFM) and differential scanning calorimetry (DSC). The two blocks crystallize in a single coincident exotherm when cooled from the melt. The self-nucleation technique is able to separate into two exotherms the crystallization of each block. We have gathered evidences indicating that the PPDX block can nucleate the PCL block within the copolymers regardless of the composition. This effect is responsible for the lack of homogeneous nucleation or fractionated crystallization of the PCL block even when it constitutes a minor phase within the copolymer (25% or less). Nevertheless, we were able to show that decreasing amounts of PCL within the diblock copolymer still produces confinement effects that retard the crystallization kinetics of the PCL component and decrease the Avrami index. On the other hand evidence for confinement was also obtained for the PPDX block, since as its content is reduced within the copolymer, a depression in its self-nucleation and annealing temperatures were observed.     

Ion transport and relaxation in phosphonium poly(ionic liquid) homo- and co-polymers

In the present work, a poly(ionic liquid) (PIL), poly(triphenyl-4-vinylbenzylphosphonium chloride) and a series of its random copolymers with nonionic hydrophobic poly(methyl methacrylate) (PMMA) are synthesized by conventional free radical polymerization (CFRP) and reversible addition-fragmentation chain-transfer (RAFT) polymerization. The understanding of some fundamental aspects about ion transport and relaxation mechanism in PIL and PIL copolymers are investigated using dielectric spectroscopy via several theoretical models. The influence of copolymer compositions, physical blending of neat PIL and PMMA, size of counter anions (Cl⁻ and TFSI⁻) and variation of molecular weights on thermal stability, moisture sensitivity, ionic transport and relaxation properties are also studied. An enhancement of thermal stability and ionic transport property of the PIL copolymer is observed compared to those of the physically mixed blend of two homopolymers with same compositions. The incorporation of hydrophobic PMMA segment definitely decreases the moisture content in PIL copolymers than the PIL itself. In all these PIL- based systems, the temperature dependence of ionic conductivity, relaxation time and ion diffusivity are well described by Vogel-Tammann-Fulcher model. The studies of some fundamental properties of these new PIL copolymers with less moisture sensitivity may help in using them as potential polymer electrolytes in energy storage devices.     

Evolution of concentric spherulites in crystalline-crystalline poly(3-hydroxybutyrate-co-3-hydroxyvalerate)-b-poly(ethylene glycol) copolymers

Crystalline-crystalline poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly (ethylene glycol) (PEG) block copolymers (PHEGs) were synthesized by telechelic hydroxylated PHBV2000 and PEG with different number-average molecular weights. The synthesized PHEGs were analyzed using gel permeation chromatography and proton nuclear magnetic resonance. The cooling curves of the differential scanning calorimetry showed that the range of the melt-crystallization temperature of the PEG and PHBV blocks in the PHEGs partially overlapped. The spherulite of each PEG block and each PHBV block in the PHEGs crystallizes individually, but nucleated in the same site to form a concentric spherulite. The observations of the hot-stage polarized microscope (HSPM) showed that the first spherulite growth acted as a template for the later spherulite growth in the PHBV-b-PEG concentric spherulite. The spherulite growth rate of individual spherulite from the PEG block and PHBV block in PHEGs depends on the crystallization environment. The evolution of concentric spherulites in PHEGs at different crystallization conditions was studied in this study.