PHB Block Research Articles

Synthesis of novel biodegradable elastomers based on poly[3-hydroxy butyrate] and poly[3-hydroxy octanoate] via transamidation reaction

Poly(3-hydroxyalkanoate)s (PHAs) are a class of polymers receiving attention because of their potential as renewable, biodegradable and high-technology properties. Unlike most short chain length (scl) PHAs such as poly(3-hydroxybutyrate) (PHB), medium chain length (mcl) PHAs such as poly(3-hydroxyoctanoate) (PHO) exhibit low crystallinity and are elastomeric in character. PHB-b–PEG-b–PHO block copolymers can combine both properties in block copolymer matrix. In this study, we report the synthesis of the block copolymers combining the PHB and PHO blocks. Transamidation reactions of PHB with polyethylene glycol with primary amine yield equimolar amounts and PHB with amine ends. PHO reacts with the modified PHB containing the amine end to give PHB-b–PEG-b–PHO block copolymers. Structural analysis of the products was performed by using 1H–, 13C, heteronuclear single quantum coherence NMR techniques. Thermal and mechanical properties of the block polymers were also evaluated.

Codelivery for Paclitaxel and Bcl-2 Conversion Gene by PHB-PDMAEMA Amphiphilic Cationic Copolymer for Effective Drug Resistant Cancer Therapy.

Antiapoptotic Bcl-2 protein's upregulated expression is a key reason for drug resistance leading to failure of chemotherapy. In this report, a series of biocompatible amphiphilic cationic poly[(R)-3-hydroxybutyrate] (PHB)-b-poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) copolymer, comprising hydrophobic PHB block and cationic PDMAEMA block, is designed to codeliver hydrophobic chemotherapeutic paclitaxel and Bcl-2 converting gene Nur77/ΔDBD with enhanced stability, due to the micelle formation by hydrophobic PHB segment. This copolymer shows less toxicity but similar gene transfection efficiency to polyethyenimine (25k). More importantly, this codelivery approach by PHB-PDMAEMA leads to increased drug resistant HepG2/Bcl-2 cancer cell death, by increased expression of Nur77 proteins in the Bcl-2 present intracellular mitochondria. This work signifies for the first time that cationic amphiphilic PHB-b-PDMAEMA copolymers can be utilized for the drug and gene codelivery to drug resistant cancer cells with high expression of antiapoptosis Bcl-2 protein and the positive results are encouraging for the further design of codelivery platforms for combating drug resistant cancer cells.

Effect of atactic poly(3-hydroxybutyrate) block on the crystallization and degradation behavior of 6-arm poly(l-lactide)-b-atactic poly(3-hydroxybutyrate)

6-arm poly(l-lactide) (6a-PLLA) homopolymer and a series of 6-arm poly(l-lactide)-b-atactic poly(3-hydroxybutyrate) (6a-PLLA-b-PHB) diblock copolymers were synthesized by ring-opening polymerization in the presence of Zn compound as catalyst and D-mannitol as initiator. The two block segments were found to be miscible according to the single Tg detected by the DSC. The structure effect of atactic PHB (ataPHB) block on the thermal stability, crystallization kinetic, melting behavior, and enzymatic degradation of diblock copolymer were investigated. The TGA results indicated that the thermal degradation of block copolymers started from the ataPHB block and thereby enhanced the thermal stability of PLLA block. No obvious changes were observed in the nucleation mechanism and crystal structure of the PLLA block, but the amorphous ataPHB block interrupted its crystallization, and induced lower crystallization rate and imperfect crystals. The enzymatic degradation rate of PLLA domains was determined in the presence of proteinase K. It was found that the erosion rate is strongly dependent on the length of ataPHB blocks. The degradation behavior was discussed from two aspects, i.e., the molecular mobility and retardation effect from ataPHB block.

Poly[(R)‐3‐hydroxybutyrate)]/poly(styrene) blends compatibilized with the relevant block copolymer

AbstractA novel triblock copolymer PS–PHB–PS based on the microbial polyester Poly[(R)‐3‐hydroxybutyrate)] (PHB) and poly(styrene) (PS) was prepared to be used as compatibilizer for the corresponding PHB/PS blends. It was prepared in a three‐step procedure consisting of (i) transesterification reaction between ethylene glycol and a high‐molecular‐weight PHB, (ii) synthesis of bromo‐terminated PHB macroinitiator, and (iii) atom transfer radical polymerization polymerization of styrene initiated by the PHB‐based macroinitiator. Fourier transform infrared, gel permeation chromatography, 1H‐, and 13C‐NMR spectroscopies were used to determine the molecular structure and/or end‐group functionalities at each step of the procedure. Although thermogravimetric analysis showed that the block copolymer underwent a stepwise thermal degradation and had better thermal stability than their respective homopolymers, differential scanning calorimetry displayed that the PHB block in the copolymer could not crystallize, and thus generating a total amorphous structure. Atomic force microscopy images indicated that the block copolymer was phase segregated in a well‐defined morphological structure with nanodomain size of ∼40 nm. Contact angle measurements proved that the wettability properties of the block copolymer were in between those of the PHB and PS homopolymers. Blends analyzed for their morphology and thermal properties showed good miscibility and had well‐defined morphological features. Polymer blends exhibited lower crystallinity and decreased stiffness which was proportional to the amount of compatibilizer content in the blends. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Threading α-Cyclodextrin through Poly[(R,S)-3-hydroxybutyrate] in Poly[(R,S)-3-hydroxybutyrate]−Poly(ethylene glycol)−Poly[(R,S)-3-hydroxybutyrate] Triblock Copolymers: Formation of Block-Selected Polypseudorotaxanes

A series of polypseudorotaxanes were synthesized from α-cyclodextrin (α-CD) and poly[(R,S)-3-hydroxybutyrate]−poly(ethylene glycol)−poly[(R,S)-3-hydroxybutyrate] (PHB−PEG−PHB) triblock copolymers with flanking PHB blocks of different lengths and the middle PEG block of Mn 3000 Da. Formation of inclusion complexes was confirmed by X-ray diffraction data, with α-CD adopting channel-type crystalline structures. The 1H NMR spectroscopy and thermogravimetric analysis results confirmed the presence of both host and guest molecules, and the compositions determined thereof from the two techniques were in good agreement. In the presence of excess α-CD, complexation stoichiometries between ethylene oxide units and α-CD for all polypseudorotaxanes were near the theoretical value of 2 despite the different lengths of PHB chains of the copolymers. Together with differential scanning calorimetry measurements where crystallization of the middle PEG block of the copolymers was completely absent while the glass transition of atactic PHB was detected, α-CD was thought to selectively cover the middle PEG block leaving telechelic PHB uncovered. The hypothesis was further substantiated by kinetic measurements; precipitation due to aggregation of the stable polypseudorotaxanes was slower with longer PHB chains. These findings demonstrated the successful threading of α-CD over the atactic PHB chain, which was previously thought to be impossible due to the mismatch in cross-sectional area. The study has highlighted the importance of block-selected molecular recognition of α-CD on PEG in the formation of stable polypseudorotaxanes of a block copolymer. The above revelations have interesting implications pertaining to design and synthesis of functional materials based on polypseudorotaxanes.

Enzymatic Preparation of Novel Thermoplastic di-Block Copolyesters Containing Poly[(R)-3-hydroxybutyrate] and Poly(ϵ-Caprolactone) Blocks via Ring-Opening Polymerization

Enzymatic modification of a microbial polyester was achieved by the ring-opening polymerization of epsilon-caprolactone (CL) with low-molecular weight telechelic hydroxylated poly[( R)-3-hydroxybutyrate] (PHB-diol) as initiator and Novozym 435 (immobilized Candida antarctica Lipase B) as catalyst in anhydrous 1,4-dioxane or toluene. The ring-opening polymerization was investigated at different conditions with two different types of PHB-diols: PHB-diol(P), containing a primary OH and a secondary OH end groups, and PHB-diol(M), consisting of 91% PHB-diol(P) and 9% PHB-diol containing two secondary OH end groups. The reactions were followed by GPC analyses of the resulting polymers at different time points, and the optimal conditions were established to be 70 degrees C at a weight ratio of CL/enzyme/solvent of 8:1:24. The ring-opening polymerization of CL with PHB-diol(M) (Mn of 2380, NMR) at the molar ratio of 50:1 under the optimal conditions in 1,4-dioxane gave the corresponding poly[HB(56 wt %)-co-CL(44 wt %)] with Mn (NMR) of 3900 in 66% yield. Polymerization of CL and PHB-diol(P) ( Mn of 2010, NMR) at the same condition in toluene gave the corresponding poly[HB(28 wt %)-co-CL(72 wt %)] with Mn (NMR) of 7100 in 86% yield. Both polymers were characterized by (1)H and (13)C NMR and IR analyses as di-block copolyesters containing a PHB block with a secondary OH end group and a poly(epsilon-caprolactone) (PCL) block with a primary OH end group. NMR analyses and control experiments suggested no formation of random copolymers and no change of the PHB block during the reaction. The enzymatic ring-opening polymerization was selectively initiated by the primary OH group of PHB-diol, whereas the secondary OH group remained as an end group in the final polymers. The thermal properties of the di-block poly(HB-co-CL)s were analyzed by DSC, with excellent T g values for the elastomer domain: poly[HB(56 wt %)- co-CL(44 wt %)] with M n (NMR) of 3900 demonstrated a T g of -57 degrees C, Tm of 145, 123, and 53 degrees C; and poly[HB(28wt%)-co-CL(72wt%)] with Mn (NMR) of 7100 gave a Tg of -60 degrees C, Tm of 147 and 50 degrees C. Thus, the selective enzymatic ring-opening polymerization with PHB-diol as macro-initiator provides a new method for the preparation of PHB-based block copolymers as biomaterials with good thermoplastic properties and novel structures containing functional end groups.

In vitro cytotoxicity, hemolysis assay, and biodegradation behavior of biodegradable poly(3‐hydroxybutyrate)–poly(ethylene glycol)–poly(3‐hydroxybutyrate) nanoparticles as potential drug carriers

Nanoparticles based on amorphous poly(3-hydroxybutyrate)-poly(ethylene glycol)-poly(3-hydroxybutyrate) (PHB-PEG-PHB) are potential drug delivery vehicles, and so their cytotoxicity and hemolysis assay were investigated in vitro using two kinds of animal cells. The PHB-PEG-PHB nanoparticles showed excellent biocompatibility and had no cytotoxicity on animal cells, even when the concentrations of the PHB-PEG-PHB nanoparticle dispersions were increased to 120 microg/mL. Moreover, no hemolysis was detected with the PHB-PEG-PHB nanoparticles, suggesting that the PHB-PEG-PHB nanoparticles were obviously much hemocompatible for drug delivery applications. In the presence of intracellular enzyme esterase, the biocompatible PHB-PEG-PHB nanoparticles might be hydrolyzed, and their biodegradable behavior was monitored by the fluorescence spectrum and the pH meter. The initial biodegradation rate of the PHB-PEG-PHB nanoparticles was closely related to the enzymatic amount and the PHB block length. Compared with that obtained from the fluorescence determination, the initial biodegradation rate from pH measurement was faster. The biodegraded products mainly consisted of 3HB monomer and dimer, which were the metabolites present in the body.

Synthesis, Characterization, and Morphology Studies of Biodegradable Amphiphilic Poly[(R)-3-hydroxybutyrate]-alt-Poly(ethylene glycol) Multiblock Copolymers

Novel biodegradable amphiphilic alternating block copolymers based on poly[(R)-3-hydroxybutyrate] (PHB) as biodegradable and hydrophobic block and poly(ethylene glycol) (PEG) as hydrophilic block (PHB-alt-PEG) were successfully synthesized through coupling reaction. Their chemical structures have been characterized by using gel permeation chromatography, (1)H nuclear magnetic resonance, and Fourier transform infrared spectroscopy. Differential scanning calorimetry (DSC) analysis revealed that both PHB and PEG blocks in PHB-alt-PEG block copolymers can crystallize to form separate crystalline phase except in those with a short PEG block (M(n) 600) only PHB crystalline phase has been observed. However, due to the mutual interference from each other, the melting transition of both PHB and PEG crystalline phases shifted to lower temperature with lower crystallinity in comparison with corresponding pure PHB and PEG. The crystallization behavior of PHB block and PEG block has also been studied by X-ray diffraction, and the results were in good agreement with those deduced from DSC study. The surface morphologies of PHB-alt-PEG block copolymer thin films spin-coated on mica have been visualized by atomic force microscopy with tapping mode, indicating formation of laterally regular lamellar surface patterns. Static water contact angle measurement revealed that surface hydrophilicity of these spin-coated thin films increases with increasing PEG block content.

Preparation and characterization of biodegradable nanoparticles based on amphiphilic poly(3-hydroxybutyrate)–poly(ethylene glycol)–poly(3-hydroxybutyrate) triblock copolymer

Amphiphilic triblock copolymers of poly(3-hydroxybutyrate)–poly(ethylene glycol)–poly(3-hydroxybutyrate) (PHB–PEG–PHB) were directly synthesized by the ring-opening copolymerization of β-butyrolactone monomer using PEG as macroinitiator. Their structure, thermal properties and crystallization were investigated by 1H NMR, differential scanning calorimetry (DSC) and X-ray diffraction. It was found that both PHB and PEG blocks were miscible. With the increase in the PHB block length, the triblock copolymers became amorphous because amorphous PHB block remarkably depressed the crystallization of the PEG block. Biodegradable nanoparticles with core-shell structure were prepared in aqueous solution from the amphiphilic triblock copolymers, and characterized by 1H NMR, SEM and fluorescence. The hydrophobic PHB segments formed the central solid-like core, and stabilized by the hydrophilic PEG block. The nanoparticle size was close related to the initial concentrations of the nanoparticle dispersions and the compositions of the triblock copolymers. Moreover, the PHB–PEG–PHB nanoparticles also showed good drug loading properties, which suggested that they were very suitable as delivery vehicles for hydrophobic drugs.

Compositional study and cytotoxicity of biodegradable poly(ester urethane)s consisting of poly[( R)-3-hydroxybutyrate] and poly(ethylene glycol)

Biodegradable PHB–PEG multi-block polyurethane copolymers comprising PHB blocks ( M n: 1100, 1740 and 3240) and PEG blocks ( M n: 1960, 3250, 4150 or 7950) were synthesized followed by characterization by GPC, 1H NMR, and FT-IR. The PHB contents ranged from 9 to 62% by weight. The copolymers displayed improved thermal stabilities compared with their respective precursors. The morphological structures of the copolymers were studied by FT-IR, DSC and XRD. FT-IR revealed the existence of amorphous and crystalline phases of PHB. Both DSC and XRD analyses showed that separate crystalline phases are formed by PEG and PHB blocks in the copolymers. Upon annealing, the melting transition temperature ( T m), melting enthalpy (Δ H m) and the fractional crystallinity ( X c) of the PEG block increased when the length of PEG incorporated into the copolymer increased. These values were higher when the PHB block length is shorter as the shorter PHB chain does not disrupt the crystallization of PEG as much as the longer PHB chain. A similar disruptive effect on the crystallization of PHB segments was observed by varying PEG chain lengths but the effect is less pronounced compared with the PEG segments. A comparison of the swelling properties of the poly(ester urethane)s showed that the length and crystalline properties of the PHB block significantly affects the water uptake properties of the copolymers. The crystalline properties and the water uptake capacities of the copolymers could be fine-tuned by consideration of the length of the PHB and PEG block incorporated. The results of the cytotoxicity tests demonstrated that the poly(PHB/PEG) urethanes were non-cytotoxic and could potentially be used for biomedical purposes.

Biodegradable nanoparticles of amphiphilic triblock copolymers based on poly(3-hydroxybutyrate) and poly(ethylene glycol) as drug carriers

New amorphous amphiphilic triblock copolymers of poly(3-hydroxybutyrate)-poly(ethylene glycol)-poly(3-hydroxybutyrate) (PHB-PEG-PHB) were synthesized using the ring-opening copolymerization of beta-butyrolactone monomer. They were characterized by fluorescence, SEM and (1)H NMR. These triblock copolymers can form biodegradable nanoparticles with core-shell structure in aqueous solution. Comparing to the poly(ethylene oxide)-PHB-poly(ethylene oxide) (PEO-PHB-PEO) copolymers, these nanoparticles exhibited much smaller critical micelle concentrations and better drug loading properties, which indicated that the nanoparticles were very suitable for delivery carriers of hydrophobic drugs. The drug release profile monitored by fluorescence showed that the release of pyrene from the PHB-PEG-PHB nanoparticles exhibited the second-order exponential decay behavior. The initial biodegradation rate of the PHB-PEG-PHB nanoparticles was related to the enzyme amount, the initial concentrations of nanoparticle dispersions and the PHB block length. The biodegraded products detected by (1)H NMR contained 3HB monomer, dimer and minor trimer, which were safe to the body.

Dynamic and Static Light Scattering Studies on Self-Aggregation Behavior of Biodegradable Amphiphilic Poly(ethylene oxide)−Poly[(R)-3-hydroxybutyrate]−Poly(ethylene oxide) Triblock Copolymers in Aqueous Solution

The self-aggregation behavior of two amphiphilic poly(ethylene oxide)-poly[(R)-3-hydroxybutyrate]-poly(ethylene oxide) (PEO-PHB-PEO) triblock copolymer samples with nearly identical PHB block lengths but different PEO block lengths, PEO-PHB-PEO(2000-810-2000) and PEO-PHB-PEO(5000-780-5000), was studied with dynamic and static light scattering (DLS and SLS), in combination with fluorescence spectroscopy and transmission electron microscopy (TEM). The formation of polymeric micelles by the two PEO-PHB-PEO triblock copolymers was confirmed with fluorescence technique and TEM. DLS analysis showed that the hydrodynamic radius (R(h)) of the monodistributed polymeric micelles increased with an increase in PEO block length. The relative thermostability of the triblock copolymer micelles was studied by SLS and DLS at different temperatures. The aggregation number and the ratio of the radius of gyration over hydrodynamic radius were found to be independent of temperature, probably due to the strong hydrophobicity of the PHB block. The combination of DLS and SLS studies indicated that the polymeric micelles were composed of a densely packed core of hydrophobic PHB blocks and a corona shell formed by hydrophilic PEO blocks. The aggregation numbers were found to be approximately 53 for PEO-PHB-PEO(2000-810-2000) micelles and approximately 37 for PEO-PHB-PEO(5000-780-5000) micelles. The morphology of PEO-PHB-PEO spherical micelles determined by DLS and SLS measurements was further confirmed by TEM.

Synthesis and characterization of biodegradable triblock copolymers based on bacterial poly[(R)‐3‐hydroxybutyrate] by atom transfer radical polymerization

AbstractBiodegradable poly(tert‐butyl acrylate)–poly[(R)‐3‐hydroxybutyrate]–poly (tert‐butyl acrylate) triblock copolymers based on bacterial poly[(R)‐3‐hydroxybutyrate] (PHB) were synthesized by atom transfer radical polymerization. The chain architectures of the triblock copolymers were confirmed by 1H NMR and 13C NMR spectra. Gel permeation chromatography analysis was used to estimate the molecular weight characteristics and lengths of the PHB and poly(tert‐butyl acrylate) blocks of the copolymers. The thermal properties of the copolymers were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). TGA showed that the triblock copolymers underwent stepwise thermal degradation and had better thermal stability than their respective homopolymers, whereas DSC analyses showed that a microphase‐separation structure was formed only in the triblock copolymers with the longer PHB block. As a similar result, from wide‐angle X‐ray diffraction experimentation, the crystalline phase of PHB could not be seen evidently in the triblock copolymers with the shorter PHB block. The enzymatic hydrolysis of the copolymer films was carried at 37 °C and pH 7.4 in a potassium phosphate buffer with an extracellular PHB depolymerase from Penicillum sp. The biodegradability of the triblock copolymers increased with an increase in the PHB block content. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4857–4869, 2005

Micellization Phenomena of Biodegradable Amphiphilic Triblock Copolymers Consisting of Poly(β-hydroxyalkanoic acid) and Poly(ethylene oxide)

This paper reports the studies on micelle formation of new biodegradable amphiphilic poly(ethylene oxide)-poly[(R)-3-hydroxybutyrate]-poly(ethylene oxide) (PEO-PHB-PEO) triblock copolymer with various PHB and PEO block lengths in aqueous solution. Transmission electron microscopy showed that the micelles took an approximately spherical shape with the surrounding diffuse outer shell formed by hydrophilic PEO blocks. The size distribution of the micelles formed by one triblock copolymer was demonstrated by dynamic light scattering technique. The critical micellization phenomena of the copolymers were extensively studied using the pyrene fluorescence dye absorption technique, and the (0,0) band changes of pyrene excitation spectra were used as a probe for the studies. For the copolymers studied in this report, the critical micelle concentrations ranged from 1.3 x 10(-5) to 1.1 x 10(-3) g/mL. For the same PEO block length of 5000, the critical micelle concentrations decreased with an increase in PHB block length, and the change was more significant in the short PHB range. It was found that the micelle formation of the biodegradable amphiphilic triblock copolymers consisting of poly(beta-hydroxyalkanoic acid) and PEO was relatively temperature-insensitive, which is quite different from their counterparts consisting of poly(alpha-hydroxyalkanoic acid) and PEO.

Role of intermolecular interaction between hydrophobic blocks in block-selected inclusion complexation of amphiphilic poly(ethylene oxide)-poly[( R)-3-hydroxybutyrate]-poly(ethylene oxide) triblock copolymers with cyclodextrins

The influence of hydrophobic interaction between poly[( R)-3-hydroxybutyrate] blocks on block-selected inclusion complexation between amphiphilic poly(ethylene oxide)-poly[( R)-3-hydroxybutyrate]-poly(ethylene oxide)) (PEO-PHB-PEO) triblock copolymers and α-cyclodextrin (α-CD) or γ-cyclodextrin (γ-CD) was studied by X-ray diffraction, differential scanning calorimetry (DSC), FTIR and 1H NMR. Due to the stronger hydrophobic interaction at higher temperature, the amphiphilic triblock copolymer tends to aggregate to form tighter core-shell sphere with PHB block in the core and PEO in the corona. Therefore, the CD threaded onto PEO blocks cannot further slide onto the PHB block, which resulted in a highly block-selected inclusion complex formation. Moreover, the DSC results indicated that the triblock copolymer coalesced from its ICs with hot water showed an increase in microphase separation compared with the as-synthesized triblock copolymer, which further supports our hypothesis that CD only selectively includes PEO blocks of the triblock copolymer at higher temperature.

Synthesis and properties of graft copolymers based on poly(3-hydroxybutyrate) macromonomers.

Graft copolymers of poly(methyl methacrylate) with poly(3-hydroxybutyrate), PHB, segments as long side chains were prepared by the macromonomer method. PHB macromonomers were prepared from the esterification of oligomers with 2-hydroxyethyl methacrylate at their carboxylic acid end. Esterification products displayed low polydispersity indices (ca. 1.2) and a functionality of over 83%, with a Mn of 2,020. Using free radical polymerization methods, the macromonomers were copolymerized with methyl methacrylate to yield graft (comb type) copolymers at different comonomer feed ratios. The graft copolymers contained from 0.5 to 14 mol-% of PHB blocks, with a glass transition temperature decreasing from 100 to 3 degrees C.

Synthesis and Characterization of Novel Thermoplastic Polyester Containing Blocks of Poly[(R)-3-hydroxyoctanoate] and Poly[(R)-3-hydroxybutyrate

Novel block copolyester containing biocompatible and biodegradable biopolyester blocks was prepared by polycondensation of telechelic hydroxylated poly[(R)-3-hydroxyoctanoate] (PHO-diol) and telechelic hydroxylated poly[(R)-3-hydroxybutyrate] (PHB-diol) with terephthaloyl chloride (TeCl). Reaction of PHO-diol (Mp of 2100), PHB-diol (Mp of 3200), and TeCl at a ratio of 1.3:1:2.1 gave the block co-polyester PHOHBTe in 86% yield with a molecular weight Mp of 7200 (GPC). The chemical structure of the copolyester was confirmed by 1H-, 13C-, and COSY-NMR and IR spectra. On average, 2 PHO-diol, 1 PHB-diol, and 2 TeCl were incorporated in each molecule of the block copolyester PHOHBTe. For comparison, polyester PHOTe with a Mp of 7100 (GPC) was prepared in 81% yield by reaction of PHO-diol and terephthaloyl chloride at a molar ratio of 1:1.2. NMR analysis suggested that PHOTe contains 3 PHO and 3 Te units on average. While PHOTe containing no PHB block is soft-sticky, PHOHBTe containing both soft PHO and hard PHB blocks showed good thermoplastic properties with Tm of 129 and 140 °C and a Tg of −41 °C. Thus, for the first time, block copolyester containing PHO and PHB blocks has been prepared and demonstrated to be thermoplastic.

Compatibility of Block Copolymers on Blends of Polysulfone and Semiaromatic Polyester Crystalline Polymer

Two block copolymers, polysulfone–polyethylene terephthalate (PSF–PET) and polysulfone–polyhydroxybenzoate (PSF–PHB), were synthesized in order to compatibilize the blends of polysulfone (PSF) and a semiaromatic thermotropic liquid crystalline polymer (TLCPA1). A PSF–PET block copolymer exhibits better compatibility. Only 2% of PSF–PET copolymer can reduce the interfacial tension of a PSF and TLCPA1 phase, which makes TLCPA1 form of fine microfiber phase and distributes in a PSF matrix uniformly. Furthermore, the blend containing 2% PSF–PET exhibits better mechanical properties than uncompatibilized blends. Comparatively speaking, the PSF–PHB block copolymer shows poor compatibility to PSF/TLCP blends. The compatibility comparison of copolymers having different block lengths shows that the compatibility of a copolymer depends on not only its composition but also its block length.

Compatibilizing capability of poly(β-hydroxybutyrate-,co-ϵ-caprolactone) in the blend of poly(β-hydroxybutyrate) and poly(ϵ-caprolactone)

In order to increase the miscibility in the blend of poly(β-hydroxybutyrate) [PHB] and poly(e-caprolactone) [PCL], PHB/PCL copolyesters were used as compatibilizers. These PHB/PCL copolyesters were synthesized by transesterification in solution phase. The melting point [Tm] depression, which was not observed in PHB/PCL blend without compatibilizer, was observed when PHB/PCL copolyesters as compatibilizers were added to the PHB/PCL blend system. As the amount of compatibilizer added to the blend increased, the crystallization temperature [Tc] of PCL in the blend increased and Tc of PHB in the blend decreased. The difference in Tc between PHB and PCL was gradually reduced. When the sequence length of PHB block and PCL block in the PHB/PCL copolyester increased, the miscibility of the blend increased. This is evidenced by the depression in the Tm of PHB and PCL in the blend and by the decrease in the difference of Tc between PHB and PCL. From the polarizing optical micrographs, the phase separation in PHB/PCL blend was observed. However, in the presence of PHB/PCL copolyester, the spherulite of PHB grows in equilibrium with one phase melt.

Blends of Linear Low-Density Polyethylene and a Diblock Copolymer of Hydrogenated Polybutadiene and Methyl Methacrylate

Blends of linear low-density polyethylene (LLDPE) and a diblock copolymer of hydrogenated polybutadiene and methyl methacrylate [P(HB-b-MMA)] were studied by transimission electron microscope (TEM), differential scanning calorimetry (DSC), and wide angle X-ray diffraction (WAXD). At 10 wt% block copolymer content, block copolymer chains exist as spherical micelles and cylindrical micelles in LLDPE matrix. At 50 wt% block copolymer content, block copolymer chains mainly form cylindrical micelles. The core and corona of micelles consist of PMMA and PHB blocks, respectively. DSC results show that the total enthalpy of crystallization of the blends varies linearly with LLDPE weight percent, indicating no interactions in the crystalline phase. In the blends, no distortion of the unit cell is observed in WAXD tests.