Nonisothermal crystallization studies on poly(4‐hydroxybutyric acid‐alt‐glycolic acid)

The crystallization behavior of a new sequential polyester constituted by glycolic acid and 4‐hydroxybutyric acid has been studied under nonisothermal conditions. Nonisothermal melt crystallization has been followed by means of hot‐stage optical microscopy (HSOM), with experiments performed at different cooling rates. Two crystallization regimes have been found, which is in good agreement with previous isothermal studies and with the different spherulitic morphologies that were observed. The kinetics of both glass and melt crystallizations has also been studied by differential scanning calorimetry (DSC) and considering the typical Avrami, Ozawa, and Cazé analyses. Only the last gave Avrami exponents, which were in good agreement with those measured under isothermal conditions, suggesting a spherulitic growth with a predetermined nucleation. Isoconversional data of melt and glass nonisothermal crystallizations have been combined to obtain the Hoffman and Lauritzen parameters. Results again indicate the existence of two crystallization regimes with nucleation constants close to those deduced from isothermal DSC experiments. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 121–133, 2008     

Crystallization kinetics of PGBG4: A sequential poly(ester amide) derived from glycine, 1,4‐butanediol,and adipic acid

Isothermal crystallization kinetics of a new sequential poly(ester amide) derived from glycine, 1,4‐butanediol, and adipic acid was investigated with differential scanning calorimetry and optical microscopy. The Avrami analysis was performed to obtain the kinetic parameters of primary and secondary crystallization. The experimental data indicate a heterogeneous nucleation with spherical growth geometry for the primary crystallization, whereas a linear growth within formed spherulites is characteristic of the last crystallization stages. The Lauritzen–Hoffman analysis was also undertaken to determine the different crystallization regimes, having estimated the corresponding nucleation constants. Temperature dependence of the normalized crystallization‐rate constants was tested with different theoretical equations. These allow an estimation of a temperature close to 90 °C for the maximum crystallization rate. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 903–912, 2003     

Crystallization and morphology of poly(vinylidene fluoride)/poly(3‐hydroxybutyrate) blends. III. Crystallization and phase diagram by differential scanning calorimetry

The crystallization of poly(vinylidene fluoride) (PVDF)/poly(3‐hydroxybutyrate) (PHB) blends was studied with differential scanning calorimetry, from which the phase diagram was derived. Strong miscibility was underlined by the large negative Flory–Huggins interaction parameter (?0.25). The crystallization of the blend components differed remarkably. Whereas PVDF always crystallized in the surroundings of a homogeneous melt, PHB crystallized in a volume that was confined by the already existing PVDF spherulites, partly in their surroundings and partly inside. Under isothermal conditions, PVDF usually crystallized regularly in three dimensions with predominant quench‐induced athermal nucleation. The Avrami exponent for PVDF dendritic spherulitic growth was, however, distinctly smaller than that for compact growth, and this revealed the two‐dimensional lamellar growth inside. This deviation from ideal Avrami behavior was caused by the development of compositional inhomogeneities as PVDF crystallization proceeded, and this decelerated the kinetics. PHB crystallized three‐dimensionally with mixed thermal and athermal nucleation outside the PVDF spherulites. Inside the PVDF spherulites, PHB crystallization proceeded in a fibrillar fashion with thermal nucleation; the growth front followed the amorphous paths inside the dendritic PVDF spherulites. The crystallization was faster than that in the melt of uncrystallized PVDF. Solid PVDF acts possibly heterogeneously nucleating, accelerating PHB crystallization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 287–295, 2005     

Crystallization kinetics and morphology of poly(butylene succinate‐co‐adipate)

The crystallization kinetics of biodegradable poly(butylene succinate‐co‐adipate) (PBS/A) copolyester was investigated by using differential scanning calorimetry (DSC) and polarized optical microscopy (POM), respectively. The Avrami and Ozawa equations were used to analyze the isothermal and nonisothermal crystallization kinetics, respectively. By using wide‐angle X‐ray diffraction (WAXD), PBS/A was identified to have the same crystal structure with that of PBS. The spherulitic growth rates of PBS/A measured in isothermal conditions are very well comparable with those measured by nonisothermal procedures (cooling rates ranged from 0.5 to 15 °C/min). The kinetic data were examined with the Hoffman–Lauritzen nucleation theory. The observed spherulites of PBS/A with different shapes and textures strongly depend on the crystallization temperatures. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3231–3241, 2005     

Thermal properties of poly(alkylene dicarboxylate)s derived from 1,12‐dodecanedioic acid and even aliphatic diols

A series of new aliphatic polyesters derived from 1,12‐dodecanedioic acid and different diols with an even number of methylene units have been studied to assess the effect of the chemical structure on the final thermal properties of the materials. The polyesters have high thermal stability and are fast crystallizing polymers, with crystallization rate similar to that of polyethylene (PE). This behavior is connected to the fact that long aliphatic chains assume conformational characteristics very similar to that of PE. However, the polyester prepared from ethanediol shows a peculiar behavior (for example, double melting peak, melting and crystallization temperatures, which do not fit the trend of those of the other samples and ringed spherulites) owing to a probable different conformation, deviating from the all‐trans planar typical of PE. In the isothermal crystallization studies, a bell‐shape trend has been found for the crystallization rate as a function of the number of ? (CH₂)? units in the diol. The high crystallization rate of the sample with long ? (CH₂)? sequences has been attributed to the high chain flexibility and, thus, high mobility in the molten state and ease of chain folding. By reducing the aliphatic sequence length, instead, implications of the structural characteristics of the samples are probably involved. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1053–1067, 2007     

Melting behavior,crystallization kinetics,and crystal structure of poly(2‐hydroxyethoxybenzoate)

The melting behavior and crystallization kinetics of poly(2‐hydroxyethoxybenzoate) (PHEBA) were investigated with differential scanning calorimetry and hot‐stage optical microscopy. The observed multiple endotherms, commonly displayed by polyesters, were influenced by the crystallization temperature. By the application of the Hoffman–Weeks method to the melting temperatures of isothermally crystallized samples, a value of 232 °C was obtained for the equilibrium melting temperature. Isothermal crystallization kinetics were analyzed according to Avrami's treatment. Values of Avrami's exponent n close to 3 were obtained, independently of the crystallization temperature, in agreement with a crystallization process originating from predetermined nuclei and characterized by three‐dimensional spherulitic growth. In fact, space‐filling banded spherulites were observed by hot‐stage optical microscopy at all crystallization temperatures explored, with the band spacing increasing with increasing crystallization temperature. The rate of crystallization became lower as the crystallization temperature increased as usual at low undercooling, with the crystallization process controlled by nucleation. The equilibrium heat of fusion was determined by differential scanning calorimetry and wide‐angle X‐ray scattering measurements. Finally, the crystal phase of PHEBA was investigated with wide‐angle X‐ray scattering, and a triclinic unit cell was hypothesized. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1354–1362, 2002     

Crystallization and morphology of poly(vinylidene fluoride)/poly(3‐hydroxybutyrate) blends. II. Morphology and crystallization kinetics by time resolved X‐ray scattering

The development of the morphology in poly(vinylidene fluoride)/poly(3‐hydroxybutyrate) (PVDF/PHB) blends upon isothermal and anisothermal crystallization is investigated by time‐resolved small‐ and wide‐angle X‐ray scattering. The components are completely miscible in the melt but crystallize separately; they crystallize stepwise at different temperatures or sequentially with isothermal or anisothermal conditions, respectively. The PVDF crystallizes undisturbed whereas PHB crystallizes in a confined space that is determined by the existing supermolecular structure of the PVDF. The investigations reveal that composition inhomogeneities may initially develop in the remaining melt or in the amorphous phases of the PVDF upon crystallization of that component. The subsequent crystallization of the PHB depends on these heterogeneities and the supermolecular structure of PVDF (dendritically or globularly spherulitic). PHB may form separate spherulites that start to grow from the melt, or it may develop “interlocking spherulites” that start to grow from inside a PVDF spherulite. Occasionally, a large number of PVDF spherulites may be incorporated into PHB interlocking spherulites. The separate PHB spherulites may intrude into the PVDF spherulites upon further growth, which results in “interpenetrating spherulites.” Interlocking and interpenetrating are realized by the growth of separate lamellar stacks (“fibrils”) of the blend components. There is no interlamellar growth. The growth direction of the PHB fibrils follows that of the existing PVDF fibrils. Depending on the distribution of the PHB molecules on the interlamellar and interfibrillar PVDF regions, the lamellar arrangement of the PVDF may contract or expand upon PHB crystallization and the adjacent fibrils of the two components are linked or clearly separated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 974–985, 2004     

Crystallization and morphology of poly(ethylene‐2,6‐naphthalene dicarboxylate) in the presence of nucleating agents

The crystallization and morphology of poly(ethylene‐2,6‐naphthalene dicarboxylate) (PEN) containing, as nucleating agents, a sodium salt of a copolymer of ethylene and acrylic acid or a sodium salt of a copolymer of ethylene and methacrylic acid, were investigated with differential scanning calorimetry, polarized optical microscopy, and small‐angle light scattering. The nucleating agents accelerated the crystallization rate at high temperatures by decreasing the surface free energy barrier hindering nucleation. Meanwhile, the nucleating agents with flexible chains could also improve the mobility of the PEN chains and increase the crystallization rate at low temperatures. Hedrites were observed when PEN was crystallized at high temperatures, whereas crystallization at low temperatures led to the formation of spherulites. Similar but smaller morphologies were obtained in the presence of nucleating agents. With nucleating agents, the spherulites formed at low temperatures were less perfect, although the optical properties of the spherulites were not influenced. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2387–2394, 2002     

Crystallization kinetics for low‐ether‐content polyether–polyester block copolymers with amide linkages

A series of low‐ether‐content polyether–polyester block copolymers with amide linkages were synthesized. Their crystallization kinetics and mechanisms were investigated. The crystallization kinetics were analyzed via Avrami treatment; an average value of 1.8 for the Avrami index was thus obtained. Athermal nucleation was evidenced by observations of a linear boundary between impinged spherulites under polarized light microscopy and transmission electron microscopy. The development of spherulitic morphology with a hedgehog texture was attributed to the mechanism of lamellar branching. On the basis of the morphological observations and Avrami analysis, a crystallization mechanism through a heterogeneous nucleation process with homogeneous lamellar branching was proposed. No regime transition was found for polyether–polyesters in the examined temperature ranges, and the crystallization was identified as regime I kinetics on the basis of a Lauritzen Z test. The copolymerization of poly(ether amide)s with polyesters led to a significant suppression of the crystallization rate of polyester crystals. The suppression was explained as the result of a dilution effect in nucleation combined with an increasing nucleation barrier. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2469–2480, 2001     

Structure,morphology, and crystallization process of isotactic polypropylene/hydrogenated hydrocarbon resin blends

The structure, morphology, and isothermal and nonisothermal crystallization of isotactic polypropylene/low‐molecular‐mass hydrocarbon resin blends (iPP/HR) (up to 20% in weight of HR) have been studied, using optical and electron microscopy, wide‐ and small‐angle X‐ray and differential scanning calorimetry. New structures and morphologies can be activated, using appropriate preparation and crystallization conditions and blend composition. For every composition and crystallization condition, iPP crystallizes in α‐form, with a spherulitic morphology. The size of iPP spherulites increases with resin content, whereas the long period decreases. In the range of crystallization temperatures investigated, HR modifies the birefringence of iPP spherulites, favoring the formation of radial lamellae and changing the ratio between tangential and radial lamellae. Spherulitic radial growth rates, overall crystallization rates, and melting temperatures are strongly affected by resin, monotonically decreasing with resin content. This confirms miscibility in the melt between the two components of the blends. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3368–3379, 2004     

Miscibility and crystallization behavior of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) and methoxy poly(ethylene glycol) blends

Poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) (PHB‐HHx) and methoxy poly(ethylene glycol) (MPEG) blends were prepared using melt blending. The single glass transition temperature, T_g, between the T_gs of the two components and the negative χ value indicated that PHB‐HHx and MPEG formed miscible blends over the range of compositions studied. The Gordon–Taylor equation proved that there was an interaction between PHB‐HHx and MPEG in their blends. FTIR supported the presence of hydrogen bonding between the hydroxyl group of MPEG and the carbonyl group of PHB‐HHx. The spherulitic morphology and isothermal crystallization behavior of the miscible PHB‐HHx/MPEG blends were investigated at two crystallization temperatures (70 and 40 °C). At 70 °C, melting MPEG acted as a noncrystalline diluent that reduced the crystallization rate of the blends, while insoluble MPEG particles acted as a nucleating agent at 40 °C, enhancing the crystallization rate of the blends. However, no interspherulitic phase separation was observed at the two crystallization temperatures. The constant value of the Avrami exponent demonstrated that MPEG did not affect the three‐dimensional spherulitic growth mechanism of PHB‐HHx crystals in the blends, although the MPEG phase, such as the melting state or insoluble state, influenced the crystallization rate of the blends. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2852–2863, 2006     

Melting and crystallization behavior of polyhedral oligomeric silsesquioxane‐capped poly(ε‐caprolactone)

In this study, we investigated the melting and crystallization behavior of polyhedral oligomeric silsesquioxane (POSS)‐capped poly(ε‐caprolactone) PCL with various lengths of PCL chains by means of X‐ray diffraction and differential scanning calorimetry. This organic–inorganic macromolecule possesses a tadpole‐like structure in which the bulky POSS cage is the “head” whereas PCL chain the “tail”. The novel organic–inorganic association result in the significant alterations in the melting and crystallization behavior of PCL. The POSS‐terminated PCL displayed the enhanced equilibrium melting points compared to the control PCL. Both the overall crystallization rate and the spherulitic growth rate of the POSS‐terminated PCLs increased with increasing the concentration of POSS (or with decreasing length of PCL chain in the hybrids). The analysis of Avrami equation shows that the crystallization of the POSS‐terminated PCL preferentially followed the mechanism of spherulitic growth with instantaneous nuclei. It is found that the folding free energy of surface for the POSS‐terminated PCLs decreased with increasing the concentration of POSS. It is found that the folding free energy of surface for the POSS‐terminated PCLs decreased with increasing the concentration of POSS. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2201–2214, 2007     

Crystallization kinetics and morphology of biodegradable poly(butylene succinate‐co‐propylene succinate)s

The crystallization behavior of biodegradable poly(butylene succinate) and copolyesters poly(butylene succinate‐co‐propylene succinate)s (PBSPS) was investigated by using ¹H NMR, DSC and POM, respectively. Isothermal crystallization kinetics of the polyesters has been analyzed by the Avrami equation. The 2.2‐2.8 range of Avrami exponential n indicated that the crystallization mechanism was a heterogeneous nucleation with spherical growth geometry in the crystallization process of polyesters. Multiple melting peaks were observed during heating process after isothermal crystallization, and it could be explained by the melting and recrystallization model. PBSPS was identified to have the same crystal structure with that of PBS by using wide‐angle X‐ray diffraction (WAXD), suggesting that only BS unit crystallized while the PS unit was in an amorphous state. The crystal structure of polyesters was not affected by the crystallization temperatures, too. Besides the normal extinction crosses under the POM, the double‐banded extinction patterns with periodic distance along the radial direction were also observed in the spherulites of PBS and PBSPS. The morphology of spherulites strongly depended on the crystallization temperature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 420–428, 2007     

Spherulitic growth rates and morphology of absorbable poly(p‐dioxanone) homopolymer and its copolymer by hot‐stage optical microscopy

Hot‐stage optical microscopy was used to study the crystal morphology, nucleation, and spherulitic growth rates of poly(p‐dioxanone) (PDS) homopolymer and an 89/11 PDS/glycolide segmented block copolymer. A wide range of crystallization conditions were experimentally accessible, allowing the inspection of various morphological features and accurate estimations of characteristic growth parameters, including radial growth and nucleation rates. Although the regime analysis of the crystallization kinetics indicated no breaks in the growth rate curve, the isothermal data were in excellent agreement with the Hoffman–Lauritzen theory. Spherulitic growth rates obtained from optical measurements are compared with values of the half‐time of crystallization determined earlier by differential scanning calorimetry. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 3073–3089, 2001     

Peptide‐poly(ε‐caprolactone) biohybrids by grafting‐from ring‐opening polymerization: Synthesis,aggregation, and crystalline properties

Well‐defined peptide‐poly(ε‐caprolactone) (Pep‐PCL) biohybrids were successfully synthesized by grafting‐from ring‐opening polymerization (ROP) of ε‐caprolactone (CL) using designed amine‐terminated sequence‐defined peptides as macroinitiators. MALDI‐TOF‐MS and ¹H NMR analyses confirmed the successful attachment of peptide to the PCL chain. The gel permeation chromatography (GPC) measurement showed that the Pep‐PCL biohybrids with controllable molecular weights and low polydispersities (PDI <1.5) were obtained by this approach. The aggregation of Pep‐PCL hybrid molecules in THF solution resulted in the formation of micro/nanospheres as confirmed through FESEM, TEM, and DLS analyses. The circular dichroism study revealed that the secondary structure of peptide moiety was changed in the peptide‐PCL biohybrids. The crystallization and melting behavior of Pep‐PCL hybrids were somewhat changed compared with that of neat PCL of comparable molecular weight as revealed by DSC and XRD measurements. In Pep‐PCL biohybrids, extinction rings were observed in the PCL spherulites, in contrast with the normal spherulite morphology of the neat PCL. There was a substantial decrease (4–5 folds) in the spherulitic growth rate after the incorporation of peptide moiety at the end of PCL chain as measured by polarizing optical microscopy. Pseudomonas lipase catalyzed enzymatic degradation was studied for Pep‐PCL hybrids and neat PCL. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Study of clay nanocomposites of the biodegradable polyhexamethylene succinate. Application of isoconversional analysis to nonisothermal crystallization

Nanocomposites of organomodified montmorillonites and the biodegradable polyester derived from hexanediol and succinic acid were prepared by the solution‐casting method using chloroform as solvent. Samples were studied by means of X‐ray diffraction and transmission electron microscopy. Intercalated structures differentiated by the stacking mode between silicate layers were observed. The highest variability in interlayer spacing was found when C30B organoclay was added. In this case, hydroxyl groups of the modifier could interact with polar carbonyl groups of the polyester. Thermal stability and crystallization behavior under both isothermal and nonisothermal conditions were evaluated. The overall crystallization rate of the intercalated nanocomposites was higher than that of the neat polyester due to a significant increase in their nucleation density, which compensated for their lower crystal growth rate. Isoconversional analysis was used to determine effective activation energies and to estimate nucleation and transport energy parameters from nonisothermal hot crystallization experiments. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2234–2248, 2008     

Microwave assisted hydroxyalkylamidation of poly(ethylene‐co‐acrylic acid) and formation of grafted poly(ϵ‐caprolactone) side chains

The microwave assisted amidation of poly(ethylene‐co‐acrylic acid) (PEAA) with 2‐(2‐aminoethoxy)ethanol was performed to yield a hydroxy functionalized poly(ethylene) based copolymer (PEAAOH) in a single step. PEAAOH was used as a polyinitiator for the ring‐opening polymerization of ε‐caprolactone. The obtained graft copolymers were studied via ¹H NMR spectroscopy, gel permeation chromatography, differential scanning calorimetry, polarized optical microscopy, and scanning electron microscopy. Microscopy methods show a crystallization behavior of banded spherulites. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3659–3667, 2007     

Miscibility,crystallization kinetics,and morphology of poly(β‐hydroxybutyrate) and poly(methyl acrylate) blends

The miscibility, spherulite growth kinetics, and morphology of binary blends of poly(β‐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 PHB. 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. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1860–1867, 2000     

Crystallization kinetics of poly(ethylene oxide) from its melt and from mixtures with tetrahydronaphthalene and oligo(ethylene oxide‐block‐dimethylsiloxane)

The crystallization of poly(ethylene oxide) (PEO) from the pure state and from its mixtures with oligo(dimethyl siloxane‐b‐ethylene oxide) (COP) and tetrahydronaphthalene (THN) was investigated. The crystallization kinetics was studied isothermally and nonisothermally with an automated device that monitored the light passing through the corresponding liquids as functions of time and/or temperature. The rate was strongly influenced by the concentration of COP in the mixture. A substantial decrease in the induction time (the time required for the onset of crystallization) and a considerable shift in the crystallization temperature (the transition from a liquid state to a solid state) to higher temperatures were observed as the concentration of COP rose. This behavior was attributed to the differences in the interaction parameters of PEO with THN and COP. The isothermal crystallization kinetics was analyzed on the basis of the Avrami equation. Modified approaches (Avrami and Ozawa) were used for the evaluation of nonisothermal crystallization. In the initial state of crystallization, a power law held true for the augmentation of the radii of spherulites with time for all mixtures, regardless of the concentration of COP. Different spherulitic morphologies were observed, depending on the COP concentration. With rising COP contents, the structures changed from being needlelike to being compact. These findings were all examined in terms of the isothermal variation of the degree of supercooling resulting from changes in the compositions of the mixtures. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 820–829, 2004