Isothermal crystallization kinetics of PEO in poly(ethylene terephthalate)-poly(ethylene oxide) segmented copolymers. I. Effect of the sofi-block length

The isothermal crystallization kinetics of poly(ethylene oxide) (PEO) block in two poly(ethylene terephthalate) (PET)-PEO segmented copolymers was studied with differential scanning calorimetry. The Avrami equation failed to describe the overall crystallization process, but a modified Avrami equation, the Q equation, did. The crystallizability of the PET block and the different lengths of the PEO block exerted strong influences on the crystallization process, the crystallinity, and time final morphology of the PEO block. The mechanism of nucleation and the growth dimension of the PEG block were different because of the crystallizability of time PET block and the compositional heterogeneity. The crystallization of the PEO block was physically constrained by the microstructure of time PET crystalline phase, which resulted in a lower crystallization rate. However, this influence became weak with the increase in the soft-block length. (C) 2000 John Wiley & Sons, Inc.

Spatially-confined crystallization of poly(vinylidene fluoride)

Nanometre-sized poly(vinylidene fluoride) (PVDF) particle domains in a confined space were obtained by blending PVDF with excess poly(methyl methacrylate) (PMMA). When these particles were small enough they showed beta -form structure, which was different from the structure of bigger particles or PVDF bulk. However, the beta -form was thermodynamically metastable because it could eventually be transformed to a more stable phase by annealing at a certain temperature. Larger particle domains were of identical phase to the bulk, indicating that small size favours the formation of the beta -form. (C) 2000 Society of Chemical Industry.

Morphology, crystallization behaviors, and mechanical properties of PA1010/HIPS and PA1010/HIPS-g-MA blends

The binary blends of polyamide 1010 (PA1010) with the high-impact polystyrene (HIPS)/maleic anhydride (MA) graft copolymer (HIPS-g-MA) and with HIPS were prepared using a wide composition range. Different blend morphologies were observed by scanning electron microscopy according to the nature and content of PA1010 used. Compared with the PA1010/HIPS binary blends, the domain sizes of dispersed-phase particles in PA1010/HIPS-g-MA blends were much smaller than that in PA1010/HIPS blends at the same compositions. It was found that the tensile properties of PA1010/HIPS-g-MA blends were obviously better than that of PA 1010/HIPS blends. Wide-angle xray diffraction analyses were performed to confirm that the number of hydrogen bonds in the PA1010 phase decreased in the blends of PA1010/HIPS-g-MA. These behaviors could be attributed to the chemical interactions between the two components and good dispersion in PA1010/HIPS-g-MA blends.

Nonisothermal crystallization kinetics of ethylene terephthalate-ethylene oxide segmented copolymers with two crystallizing segments

The nonisothermal crystallization behavior of ethylene terephthalate-ethylene oxide segmented copolymers has been studied by means of differential scanning calorimetry (DSC). The kinetics of ET-EO segmented copolymer under nonisothermal crystallization conditions has been analyzed by the Ozawa equation. During the crystallization of the high-T-m segments (PET), the low-T-m segments (PEO) act as a noncrystalline diluent, the crystallization behavior of PET obeys the Ozawa theory. When the PEO segments begin to crystallize, the PET phase is always partially solidified and the presence of the spherulitic microstructure of PET profoundly influences the crystallization behavior, which results in that the overall crystallization process does not obey the Ozawa equation. (C) 2000 Elsevier Science Ltd. All rights reserved.

Phase behavior of polymer blends

The present report deals with some results on phase behavior, miscibility and phase separation for several polymer blends casting from solutions. These blends are grouped as the amorphous polymer blends, blends containing a crystalline polymer or two crystalline polymers. The blends of PMMA/PVAc were miscible and underwent phase separation at elevated temperature, exhibited LCST behavior. The benzoylated PPO has both UCST and LCST nature. For the systems composed of crystalline polymer poly(ethylene oxide) and amorphous polyurethane, of two crystalline polymers poly(epsilon-caprolactone) and poly[3,3,-bis-(chloromethyl) oxetane], appear a single T-g, indicating these blends are miscible. The interaction parameter B's were determined to be -14 J cm(-3), -15 J cm(-3) respectively. Phase separation of phenolphthalein poly(ether ether sulfone)/PEO blends were discussed in terms of thermal properties, such as their melting and crystallization behavior.

Isothermal and nonisothermal crystallization of poly(aryl ether ketone ketone) with all-para phenylene linkage

Isothermal and nonisothermal crystallization behavior for PEKK(T) was studied using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and electron diffraction (ED). In the isothermal crystallization process, the Avrami parameters obtained were n = 2.33-2.69, which shows crystal growth of two-dimensional extensions consistent with our observations by TEM. The lamellar thickness increases with the crystallization temperature of PEKK(T) crystallized isothermally from the melt. However, for the nonisothermal crystallization of PEKK(T), the results from the modified Avrami analysis show two different crystallization processes. Avrami exponents n(1) = 3.61-5.30, obtained from the primary crystallization process, are much bigger than are the secondary n(2) = 2.26-3.04 and confirmed by the observation of the spherulite morphology. PEKK(T) crystallized isothermally from the melt possesses the same crystal structure (Form I) as that from nonisothermal melt crystallization. The results from TEM observation show that the spherulite radius decreases with an increasing cooling rate. (C) 2001 John Wiley & Sons, Inc.

Homoepitaxial crystallization in films of a thermotropic liquid crystalline chloro-poly(aryl ether ketone)

The homoepitaxial crystallization in the films of a thermotropic liquid crystalline chloro-ply(aryl ether ketone) is studied by transmission electron microscopy (TEM) and electron diffraction (ED). The homoepitaxy takes place in the temperature range 330-320 degreesC, in which a highly-ordered smectic crystalline phase of the copolymer with a single-crystal-like banded structure is formed during the cooling process from the isotropic melt. The homoepitaxial crystallizations with angles of 32 degrees and 122 degrees between the two b axes are the major populations observed, and possess epitaxial contact planes of (100)(I)-(210)(II) and (010)(I)-(210)(II); respectively.

Size-affected crystallization of trans-1,4-polybutadiene

By using different catalyst systems, two trans-1,4-polybutadiene (TPBD) samples with different tr trans-content and molecular weight were synthesized. The phase transition of two samples from monoclinic form to hexagonal phase was revealed by differential calorimeter scanning and X-ray, respectively. The small-angle X-ray scattering measurements showed the remarkable discrepancy of phase transition and melting point between the two samples was attributed to the different lamellar thickness of crystals: The crystals with different crystalline morphology and lamellar thickness were developed by casting different concentration TPBD solutions. Transmission electron microscopy morphology observations proved that annealing the specimen at the temperature above the phase transition point for different times resulted in the different lamellae thickening of monoclinic form. It means that annealing the TPBD in its hexagonal phase will also slightly favor the increase of both the phase transition temperature and melting point of hexagonal phase. (C) 2001 Elsevier Science Ltd. All rights reserved.

Effect of physical aging on the microstructure and the crystallization of amorphous poly(aryl ether ether ketone ketone) (PEEKK)

Physical aging of poly(aryl ether ether ketone ketone) (PEEKK) has been investigated. Heat flow responses were measured after annealing the amorphous samples obtained by quenching the melt into an ice-water bath close to, but below, the glass transition temperature. The extent of aging is related to the supercooling from the glass transition temperature and to the aging time. The activation energy of the aging process, which was estimated by a Williams-Watt expression, is similar in magnitude to that obtained for the cold crystallization for the aged samples. The quenched glass is a metastable glass. The conformation of molecular chains rearranges with physical aging which results in the formation of a denser packing in the amorphous phase. The dense amorphous phase may form an initial nucleus for crystallization. Isothermal cold crystallization of the aged samples was carried out. The Avrami equation was used to determine the kinetic parameters, and the Avrami constant n is about 2. An Arrhenius expression was used to evaluate the activation energy of relaxation upon physical aging and the activation energy of transportation upon isothermal crystallization. The activation energy of relaxation is similar in magnitude to that of crystallization for aged samples. Results obtained are interpreted as kinetic effects associated with the glass formation process.

Miscibility and crystallization behavior of poly(beta-hydroxybutyrate)/poly(ethylene oxide) blends

The miscibility and crystallization behavior of poly(beta-hydroxybutyrate) (PHB)/poly(ethylene oxide) (PEO) blends were studied by differential scanning calorimetry(DSC) and polarizing microscopy (POM). It is found that the miscibility is related to the composition of the blends. When the PEO content is over 20 percent, the miscible blends turn into partially miscible and the phase separation can be observed with POM. The addition of the PEO influences not only the morphology of PHB crystals and the radial growth rate of spherulites, but also the cold crystallization temperature.

Isothermal crystallization kinetics and melting behavior of poly(beta-hydroxybutyrate)/poly(vinyl acetate) blends

The overall isothermal crystallization kinetics and melting behavior of poly(beta-hydroxybutyrate) (PHB)/poly(vinyl acetate) (PVAc) blends were studied by using differential scanning calorimetry(DSC). The Avrami analysis indicates that the addition of PVAc into PHB results in the decrease in the overall crystallization rate of the PHB phase, but does not affect PHB's nucleation mechanism and geometry of crystal growth. The activation energy of the overall process of crystallization increases with the increasing PVAc content in the blends. The phenomenon of multiple melting endotherms is observed, which is caused by melting and recrystallization during the DSC heating run. (C) 1998 Elsevier Science Ltd. All rights reserved.

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.

Novel morphology in ring-banded spherulites from single-phase mixtures of poly(epsilon-caprolactone) with poly(styrene-co-acrylonitrile)

Novel morphology of ring-banded spherulites in the surface of poly(epsilon-caprolactone)/poly(styrene-co-acrylonitrile) (PCL/SAN) blends was discovered and studied by SEM and TEM. The ring-banded spherulites separate into those exhibiting a very dark contrast, of relatively regular bundles of lamellae and others appearing with a much brighter intensity, of a coarse and irregular aggregates of lamellae. The origin of the novel morphology is not due to different crystalline structures as in the case of isotactic polypropylene because only one crystal structure exists in PCL/SAN blends. The formation may reflect whether spherulites in PCL/SAN blends are nucleated at the bottom surface or at the top (free) surface.

Crystallization behavior of blends of high-density polyethylene with novel linear low-density polyethylene

Blends of high-density polyethylene (HDPE) with novel linear low-density polyethylene (LLDPE) samples in the whole range of compositions were investigated by means of differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD). The LLDPEs are ethylene/octene-1 copolymers prepared with a single-site catalyst, with a narrower distribution of branches compared to Ziegler-Natta type polymers. It was found that cocrystallization or separate crystallization in the blends profoundly depends on the content of branches in the LLDPE, while the critical branch content of the novel LLDPE for separate crystallization is much lower than that of commercial LLDPE (prepared with Ziegler-Natta catalysts). This implies that the miscibility of linear and branched polyethylene is also affected by the distribution of branches. The marked expansion of the unit cell in cocrystals, which are formed by HDPE with the novel LLDPE, indicates that the branches are included in the crystal lattice during the cocrystallization process. The result is very helpful to understand the phenomenon that the unit cell dimensions of commercial branched polyethylene are larger than those of linear polyethylene.