Synthesis and characterization of poly(beta-hydroxybutyrate) and poly(epsilon-caprolactone) copolyester by transesterification

To synthesize the copolyester of poly(beta-hydroxybutyrate) (PHB) and poly(epsilon-caprolactone) (PCL), the transesterification of PHB and PCL was carried out in the liquid phase with stannous octoate as the catalyzer. The effects of reaction conditions on the transesterification, including catalyzer concentration, reaction temperature, and reaction time, were investigated. The results showed that both rising reaction temperature and increasing reaction time were advantageous to the transesterification. The sequence distribution, thermal behavior, and thermal stability of the copolyesters were investigated by C-13 NMR, Fourier transform infrared spectroscopy, differential scanning calorimetry, wide-angle X-ray diffraction, optical microscopy, and thermogravimetric analysis. The transesterification of PHB and PCL was confirmed to produce the block copolymers. With an increasing PCL content in the copolyesters, the thermal behavior of the copolyesters changed evidently. However, the introduction of PCL segments into PHB chains did not affect its crystalline structure. Moreover, thermal stability of the copolyesters was little improved in air as compared with that of pure PHB.

Compatibilization by main-chain thermotropic liquid crystalline ionomer of blends of PBT/PP

The miscibility and mechanical properties of the blends of polybutylene terephthalate (PBT) and polypropylene (PP) with a liquid crystalline ionomer (LCI) containing a sulfonate group on the terminal unit as a compatibilizer were assessed. SEM and optical microscopy (POM) were used to examine the morphology of blends of PBT/PP compatibilized by LCI. DSC and TGA were used to discuss the thermal properties of PBT/PP blends with LCI and without LCI. The experimental results revealed that the LCI component affect, to a great extent, the miscibility and crystallization process and mechanical property of PBT/PP blends, The fact is that increasing LCI did improve miscibility of PBT/PP blends and the addition of 1% LCI to the PBT/PP blends increased the ultimate tensile strength and the ultimate elongation.

Morphological study on water-borne conducting polyaniline-poly(ethylene oxide) blends

Conducting polyaniline-poly(ethylene oxide) blends were prepared from their aqueous solutions. The blends displayed an electrical conductivity percolation threshold as low as 1.83 wt % of polyaniline loading. As demonstrated by scanning electron microscopy, polarized optical microscopy, and wide-angle X-ray diffraction studies, the conducting polyaniline took a fibrillar morphology in the blend, and it existed only in the amorphous phase of poly(ethylene oxide). A three-phase model combining morphological factors instead of a two-phase model was proposed to explain the low-conductivity percolation threshold.

Synthesis and properties of three novel series of monomers containing para-methoxyazobenzene as the mesogenic group

Three novel series of monomers, namely n-1-bromo-[4-(4-methoxyphenylazo)phenyloxy]-alkanes (Bn, n = 3, 6, 10), n-[4-(4-methoxyphenylazo) phenyloxy]alkyloxy-4-methoxybenzene (Cn, n = 3, 6, 10) and n-[4-(4-methoxyphenylazo)phenyloxyl]alkyloxy-[4-methoxy-2,5-bis-(chloromethyl)] benzene (Dn, n = 3, 6, 10) were synthesized and characterized with FTIR, H-1 NMR, UV-visible and fluorescence spectroscopy. Their thermal behaviour was studied by different scanning calorimetry and polarizing optical microscopy. The results show that B3, B6 and C6 exhibit monotropic nematic liquid crystalline behaviour.

Miscibility, crystallization kinetics, and morphology of poly(beta-hydroxybutyrate) and poly(methyl acrylate) blends

The miscibility, spherulite growth kinetics, and morphology of binary blends of poly(beta-hydroxybutyrate) (PHB) and poly(methyl acrylate) (PMA) were studied with differential scanning calorimetry, optical microscopy, and small-angle X-ray scattering (SAXS). As the PMA content increases in the blends, the glass-transition temperature and cold-crystallization temperature increase, but the melting point decreases. The interaction parameter between PHB and PMA, obtained from an analysis of the equilibrium-melting-point depression, is -0.074. The presence of an amorphous PMA component results in a reduction in the rate of spherulite growth of PRE. The radial growth rates of spherulites were analyzed with the Lauritzen-Hoffman model. The spherulites of PHB were volume-filled, indicating the inclusion of PMA within the spherulites. The long period obtained from SAXS increases with increased PMA content, implying that the amorphous PMA is entrapped in the interlamellar region of PHB during the crystallization process of PHB. All the results presented show that PHB and PMA are miscible in the melt. (C) 2000 John Wiley & Sons, Inc.

The single crystal-like banded textures in the films of a thermotropic liquid crystalline poly(aryl ether ketone) containing a lateral chloro group

The banded textures in the films of a thermotropic liquid crystalline poly(aryl ether ketone) containing a lateral chloro group have been studied by means of transmission electron microscopy(TEM), electron diffraction(ED) and atomic force microscopy (AFM). The crystallization-induced Landed texture without external shear can be formed when the thin films were annealed at the temperature range(320-330 degrees C) of the liquid crystalline state from the melt, The results show that the banded regions have high orientation of single crystal based on the orthorhombic packing and the growing direction of the Lands is along the b axis of the crystals, This kind of single crystal-like bands is due to the different orientation of the packing molecular chains, The molecular chains of the dark bands in the bright field electron micrograph are perpendicular to the film plane, while the ones of the bright Lands are tilt along the b axis with the tilt angle upto +/-20 degrees.

Study on the properties of poly(beta-hydroxybutyrate) grafted with maleic anhydride

The thermal stability, crystallization behavior and biodegradability of poly(beta -hydroxybutyrate) (PHB) grafted with maleic anhydride (MA) were studied by DSC,TGA, optical microscopy and WAXD. The results showed that thermal stability of maleated PHB was obviously improved, comparing with that of pure PHB. The temperature of decomposition was enhanced about 20 degreesC After grafting MA, the crystallization behavior of PHB changed evidently. The rate of spherulite growth decreased, the crystallization temperature from the melt state reduced, and the cold crystallization temperature from the glass state increased. With the increase in graft degree, the banding texture of spherulite became more distinct and orderly. Moreover, the introduction of MA groups promoted the biodegradation of PHB.

Studies on the nature of the macromolecular condensed state of "nascent" ultra high molar mass polyethylene

Ultra high molar mass polyethylene (UHPE) powder as polymerized in a slurry process has been studied, in its nascent state, after recrystallization on rapid cooling from the melt and after hot compression molding to a film, by DSC, effect of annealing the recrystallized specimen at 120 similar to 130 degreesC, morphology by polarizing optical microscopy and small angle X-ray scattering. Based on the experimental results obtained the macromolecular condensed state of the nascent UHPE powder is a rare case of a multi-chain condensed state of non-interpenetrating chains, involving interlaced extended chain crystalline layers and relaxed parallel chain amorphous layers. On melting, a nematic rubbery state of nanometer size domain resulted. The nematic-isotropic transition temperature was judged from literature data to be at least 220 degreesC, possibly higher than 300 degreesC, the exact temperature is however not sue because of chain degradation at such high temperatures. The recrystallization process from the melt is a crystallization from a nematic rubbery state. The drop of remelting peak temperature by 10 K of the specimen recrystallized from its melt as compared to the nascent state has its origin in the decrease both of the crystalline chain stem length and of the degree of crystallinity. The remelting peak temperature could be returned close to that of the nascent state by annealing at 120 similar to 130 degreesC.

Ring-banded spherulite surface structure of poly(epsilon-caprolactone) in its miscible mixtures with poly(styrene-co-acrylonitrile)

The surface structure of the ring-banded spherulites in polymer blends PCL/SAN (90/10) was studied by optical microscopy, SEM, and TEM, respectively. It is interesting to find that the surface structure of the ring-banded spherulites in polymer blends PCL/SAN (90/10) is made up of the convex bands. The landscape of the convex bands on the surface has been little emphasized before. Radial fibrils are arranged on the bands. Details of the radial fibrils on the bands can be observed by TEM. The landscape of the convex bands on the surface and twisting of lamellae in the convex bands for PCL/SAN blends may be useful to explain the formation mechanism of the ring banded spherulites in polymer blends or even in homopolymers. (C) 1999 John Wiley & Sons, Inc.

Synthesis and characterization of novel crosslinkable side-chain liquid crystalline polyesters

Crosslinkable side-chain liquid crystalline polyesters PCn from N-[n-(4-(4-nitrophenylazo)phenyloxy)alkyl]diethanolamine (Cn, n = 3, 5, 6, 10) as mesogenic monomers and maleic anhydride were synthesized and characterized. The thermal properties of PCn's were studied by means of DSC, polarized optical microscopy (POM) and wide angle X-ray diffraction (WAXD), and the results showed that all the polymers studied exhibit enantiotropic liquid crystallinity. In the molar mass independent region, the relatively high content of cis -CH=CH- groups in the polymer backbone of PC3 causes an increase of the melting temperature (T-m) and a decrease of T-g and isotropisation temperature (T-i). The crosslinking of PCn in the radical polymerization with styrene was confirmed by FTIR spectroscopy. The absorption band at 1300 cm(-1) attributed to the in-plane C-H-bending vibration of trans -CH=CH- in the polymer backbone disappeared after crosslinking, indicating that the trans -CH=CH- functions are consumed in the crosslinking polymerization of styrene.

Morphological and structural studies of sPS/aPS blends

The morphology and structure of the syndiotactic polystyrene (sPS)/atactic polystyrene (aPS) blends with various compositions have been studied by means of DSC, optical microscopy, SAXS, and WAXD. The results show that aPS is miscible with amorphous region of sPS. There is no macroscopic evidence that aPS forms separated domains in the blends. The decrease in crystallinity of sPS in the blends implies segregation of the aPS to the interfibrillar regions of the spherulites of sPS. The constancy of interlamellar distance and melting points indicates that the fibrillar structural units of sPS is unchanged on addition of aPS to sPS, and the unchanging parameters of the sPS unit cells mean that aPS does not enter the unit cells of sPS.

Miscibility and crystallization of PHB PMA blends

The miscibility, crystallization behavior and morphological structure of PHB/PMA blends have been studied by the differential scanning calorimeter (DSC) and polarized optical microscopy (POM). The chemical repeat units of the two components of the blend are isomers. The results indicate that PHB and PMA are miscible in the melt. The addition of PMA into PHB results in a depression in the spherulite growth rate of PHB. With increasing PMA content in the blends, the texture of PHB spherulite becomes more open.

Crystallization of micelles and matrix in dilute diblock copolymer/homopolymer solutions

The crystallization, morphology, and crystalline structure of dilute solid solutions of tetrahydrofuran-methyl methacrylate diblock copolymer (PTHF-b-PMMA) in poly(ethylene oxide) (PEO) and PTHF have been studied with differential scanning calorimetry (DSC), X-ray, and optical microscopy. This study provides a new insight into the crystallization behavior of block copolymers. For the dilute PTHF-b-PMMA/PEO system containing only 2 to 7 wt % of PTHF content, crystallization of the PTHF micellar core was detected both on cooling and on heating. Compared the crystallization of the PTHF in the dilute solutions with that in the pure copolymer, it was found that the crystallizability of the PTHF micellar core in the solution is much greater than that of the dispersed PTHF microdomain in the pure copolymer. The stronger crystallizability in the solution was presumably due to a softened PMMA corona formed in the solution of the copolymer with PEG. However, the "soft" micelles formed in the solution (meaning that the glass transition temperatures (T-g) of the micelle is lower than the T-m of the matrix phase) showed almost no effects on the spherulitic morphology of the PEO component, compared with that of the pure PEO sample. In contrast, significant effects of the micelles with a "hard" PMMA core (meaning that the T-g of the core is higher than the T-m of the PTHF homopolymer) on the nucleation, crystalline structure, and spherulitic morphology were observed for the dilute PTHF-b-PMMA/PTHF system. (C) 1998 John Wiley & Sons, Inc.

Miscibility and crystallization of poly(beta-hydroxybutyrate)/poly(vinyl acetate-co-vinyl alcohol) blends

Poly(vinyl acetate-co-vinyl alcohol) copolymers (P(VAc-co-VA)) were synthesized by hydrolysis-alcoholysis of PVAc. The miscibility, crystallization, and morphology of poly(P-hydroxybutyrate) (PHB) and P(VAc-co-VA) blends were studied by differential scanning calorimetry, optical microscopy (OM), and SAXS. It is found that the P(VAc-co-VA)s with vinyl alcohol content of 9, 15, and 22 mol % will form a miscible phase with the amorphous part of PHB in the solution-cast samples. The melting-quenched samples of PHB/P(VAc-co-VA) blends with different vinyl alcohol content show different phase behavior. PHB and P(VAc-co-VA9) with low vinyl alcohol content (9% mel) will form a miscible blend in the melt state. PHB and P(VAc-co-VA15) with 15 mol % vinyl alcohol will not form miscible blends while PHB/P(VAc-co-VA15) blend with 20/80 composition will form a partially miscible blend in the melt state. PHB and P(VAc-co-VA22) with 22 mol % vinyl alcohol are not miscible in the whole composition range. The single glass transition temperature of the blends within the whole composition range suggests that PHB and P(VAc-co-VA9) are totally miscible in the melt. The crystallization kinetics was studied from the whole crystallization and spherulite growth for the miscible blends. The equilibrium melting point of PHB in the PHB/P(VAc-co-VA9) blends, which was obtained from DSC results using the Hoffman-Weeks equation, decreases with the increase in P(VAc-co-VA9) content. The negative value of the interaction parameter determined from the equilibrium melting point depression supports the miscibility between the components. The kinetics of spherulitic crystallization of PHB in the blends was analyzed according to nucleation theory in the temperature range studied in this work. The best fit of the data to the kinetic theory is obtained by employing WLF parameters and the equilibrium melting points obtained by DSC. The addition of P(VAc-co-VA) did not affect the crystalline structure of PHB, as shown by the WAXD results. The long periods of blends obtained from SAXS increase with the increase in P(VAc-co-VA) content. It indicates that the amorphous P(VAc-co-VA) was rejected to interlamellar phase corporating with the amorphous part of PHB.

Miscibility and crystallization behavior of solution-blended PEEK/PI blends

Miscibility and crystallization behavior of solution-blended poly(ether ether ketone)/polyimide (PEEK/PI) blends were investigated by using DSC, optical microscopy and SAXS methods. Two kinds of PIs, YS-30 and PEI-E, which consist of the same diamine but different dianhydrides, were used in this work. The experimental results show that blends of PEEK/YS-30 are miscible over the entire composition range, as all the blends of different compositions exhibit a single glass transition temperature. The crystallization of PEEK was hindered by YS-30 in PEEK/YS-30 blends, of which the dominant morphology is interlamellar. On the other hand, blends of PEEK/PEI-E are immiscible, and the effect of PEI-E on the crystallization behavior of PEEK is weak. The crystallinity of PEEK in the isothermally crystallized PEEK/YS-30 blend specimens decreases with the increase in PI content. But the crystallinity of PEEK in the annealed samples almost keeps unchanged and reaches its maximum value, which is more than 50%. The spherulitic texture of the blends depends on both the blend composition and the molecular structure of the PIs used. The more PI added, the more imperfect the crystalline structure of PEEK. (C) 1998 John Wiley & Sons, Inc.