On the thermal behaviour of acetylphenyl-hydroxyaceticacid-4-nitrobenzyl esters

The 4-nitrobenzyl ester of acetylphenylhydroxyacetic acid differs in its melting behaviour from other nitrobenzyl esters of phenylhydroxyacetic or acetylphenylhydroxyacetic acids, the racemate having a higher melting point than the enantiomers. By means of thermal analysis, IR spectroscopy and X-ray diffractometry the ester can be shown to occur in two crystalline modifications. In the process of solidification of the molten mass, at first a modification of higher energy is formed, obviously being caused by an excess of one enantiomer, which is then exothermally rearranged in the lattice of the racemate.     

Crystallization and structure formation of block copolymers containing a glassy amorphous component

Formation of higher‐order structure in crystallization from microphase‐separated melts was studied for polystyrene–polyethylene (PS–PE) diblock copolymers and PS–PE–PS triblock copolymers with time‐resolved synchrotron small‐angle X‐ray scattering (SR–SAXS) techniques. The PE block was crystallized at temperatures when the PS block was in the glassy state. In both crystallization and melting processes, only the peak intensity in the SR–SAXS curve changed, however, the peak positions including higher‐order peaks did not change. This means that the microphase‐structure in the crystalline state was completely the same as that in the molten state. These behaviors were observed regardless of any melt microphase structure. Also, once a stable microphase structure was formed in the molten state, the structure was not changed even if crystallization and melting were repeated. Behavior of crystallization from such microphase‐separated melts was also studied. Apparent activation energies of crystallization were high for all block copolymers, compared with that for the PE homopolymer. In particular, the triblock copolymers showed higher apparent activation energies than the diblock copolymers. Both degrees of crystallinity and Avrami indices were greatly suppressed in crystallization from the cylindrical domain. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4199–4206, 2004     

Crystallization and melting of isotactic polypropylene crystallized from quiescent melt and stress‐induced localized melt

Temperature dependency of crystalline lamellar thickness during crystallization and subsequent melting in isotactic polypropylene crystallized from both quiescent molten state and stress‐induced localized melt was investigated using small angle X‐ray scattering technique. Both cases yield well‐defined crystallization lines where inverse lamellar thickness is linearly dependent on crystallization temperature with the stretching‐induced crystallization line shifted slightly to smaller thickness direction than the isothermal crystallization one indicating both crystallization processes being mediated a mesomorphic phase. However, crystallites obtained via different routes (quiescent melt or stress‐induced localized melt) show different melting behaviors. The one from isothermal crystallization melted directly without significant changing in lamellar thickness yielding well‐defined melting line whereas stress‐induced crystallites followed a recrystallization line. Such results can be associated with the different extent of stabilization of crystallites obtained through different crystallization routes. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 957–963     

Crystallization and melting behavior of isotactic polypropylene nucleated with individual and compound nucleating agents

In this study, α-phase nucleating agent (NA) 1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol (DMDBS), β-phase rare earth NA (WBG), and their compound NAs were introduced into isotactic polypropylene (iPP) matrix, respectively. Crystallization kinetics and subsequent melting behavior of the nucleated iPPs were comparatively studied by differential scanning calorimetry (DSC) under both isothermal and nonisothermal conditions. For the isothermal crystallization process, it is found that the Avrami model successfully described the crystallization kinetics. The active energy of nonisothermal crystallization of iPP was determined by the Kissinger method and showed that the addition of nucleating agents increased the activation energy. Melting behavior and crystalline structure of the nucleated iPPs are dependent on the nature of NAs and crystallization conditions. Higher proportion of β-phase can be obtained at higher content of β-nucleating agent and lower crystallization temperature or lower cooling rate.     

Morphology and melting behavior of semicrystalline poly(ethylene terephthalate). II. Annealed PET

Annealing of poly(ethylene terephthalate) samples crystallized under isothermal conditions above the crystallization temperature has a marked influence on their morphology and results in increased thermal stability of the crystalline structure as indicated by the melting point increase of the samples. The morphological transformation processes induced by annealing are very complex and depend on the thermal history of the samples, i.e., crystallization temperature and heating procedure. Depending on the nature of the processes occurring during annealing, various parameters characterizing the semicrystalline state of the samples can be affected such as the degree of crystallinity, the long spacing, the thickness of amorphous and crystalline layers, the crystal perfection, the fold-surface structure, and the mosaic structure of the crystalline lamellae. Annealing involves a solid-state transformation of the original crystalline structure including crystal perfection without thickening or a melting followed by recrystallization with crystal perfection and crystal thickening. The combination of differential scanning calorimetric (DSC) measurements and small-angle x-ray scattering is a powerful analytical tool to detect morphological changes and helps in deciding on the processes which are involved in the transformation of the microstructure upon annealing.     

The Influence of Annealing and Heavy Ion Irradiation of Multiple Melting and Crystallization in PBT Films

The influence of heavy ion-irradiation (Ar 5.5 MeV amu^-1, 5·10¹¹ ion cm^-2) on the melting and crystallization of two PBT films subjected to different modes of thermal treatment was investigated. Differences were observed between the processes occurring in both initial films, due to differences in crystalline phase content. The course of melting and crystallization in heavy ion-irradiated films during first heating, cooling and second heating differs from that in the initial films. The density data and DSC results indicate a decreased crystalline phase content in the PBT films after irradiation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Crystalline Morphology and Crystallization Kinetics of Melt-miscible Crystalline/Crystalline Polymer Blends of Poly（vinylidene fluoride） and Poly（butylene succinate-co-24mol% hexamethylene succinate）

Poly（vinylidene fluoride） （PVDF） and poly（butylene succinate-co-24 mol% hexamethylene succinate） （PBHS）, both crystalline polymers, formed melt-miscible crystalline/crystalline polymer blends. Both the characteristic diffraction peaks and nonisothermal melt crystallization peak of each component were found in the blends, indicating that PVDF and PBHS crystallized separately. The crystalline morphology and crystallization kinetics of each component were studied under different crystallization conditions for the PVDF/PBHS blends. Both the spherulitic growth rates and overall isothermal melt crystallization rates of blended PVDF decreased with increasing the PBHS composition and were lower than those of neat PVDF, when the crystallization temperature was above the melting point of PBHS component. The crystallization mechanism of neat and blended PVDF remained unchanged, despite changes of blend composition and crystallization temperature. The crystallization kinetics and crystalline morphology of neat and blended PBHS were further studied, when the crystallization temperature was below the melting point of PBHS component. Relative to neat PBHS, the overall crystallization rates of the blended PBHS first increased and then decreased with increasing the PVDF content in the blends, indicating that the preexisting PVDF crystals may show different effects on the nucleation and crystal growth of PBHS component in the crystalline/crystalline polymer blends.     

Phase behavior of crystalline blends of poly(tetrafluoroethylene) and of random fluorinated copolymers of tetrafluoroethylene

In the present article, we investigate by differential scanning calorimetry (DSC) the thermal behavior (melting, crystallization, and crystal–crystal transitions) far from equilibrium of blends constituted of two crystalline polymers. In particular, the following blends are examined: PTFE–PFMVE, PTFE–FEP, and FEP–PFMVE where PTFE is poly(tetrafluoroethylene), PFMVE is poly(tetrafluoroethylene‐co‐perfluoromethylvinylether), and FEP is poly(tetrafluoroethylene‐co‐hexafluoropropylene). The two last ones are random tetrafluoroethylene copolymers with small amounts of comonomer. Our results indicate that, under the experimental investigated conditions, the blends containing PTFE do not give cocrystallization on cooling from the melt, although under very rapid crystallization conditions, quenching, the presence of the copolymer would seem to slightly influence PTFE crystallization (lower peak temperatures are observed for the crystalline transitions and the melting with respect to those of the neat homopolymer). The behavior of the FEP–PFMVE blend is completely different; in fact, our results indicate the occurrence of cocrystallization, then miscibility in the crystalline phase, for almost all compositions and all investigated experimental conditions. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 679–689, 1999     

Crystallization behaviour of polyoxetanes: poly(oxetane), poly (3,3-dimethyloxetane) and poly(3,3-diethyloxetane)

The influence of the crystallization temperature on the melting behaviour and crystalline structure of polyoxetane (PTO), poly(3,3-dimethyloxetane) (PDMO) and poly(3,3-diethyloxetane) (PDEO) has been studied using differential scanning calorimetry (DSC) and X-ray techniques. When PTO is crystallized by cooling from the relaxed melt state, only the orthorhombic modification is obtained. However, PDMO and PDEO can be crystallized in two different modifications depending on crystallization temperature. The effect of the substituents in the stability of main chain conformations in crystalline state is discussed.     

Solid-state relaxations in linear low-density (1-octene comonomer), low-density,and high-density polyethylene blends

Extensive thermal and relaxational behavior in the blends of linear low-density polyethylene (LLDPE) (1-octene comonomer) with low-density polyethylene (LDPE) and high-density polyethylene (HDPE) have been investigated to elucidate miscibility and molecular relaxations in the crystalline and amorphous phases by using a differential scanning calorimeter (DSC) and a dynamic mechanical thermal analyzer (DMTA). In the LLDPE/LDPE blends, two distinct endotherms during melting and crystallization by DSC were observed supporting the belief that LLDPE and LDPE exclude one another during crystallization. However, the dynamic mechanical β and γ relaxations of the blends indicate that the two constituents are miscible in the amorphous phase, while LLDPE dominates α relaxation. In the LLDPE/HDPE system, there was a single composition-dependent peak during melting and crystallization, and the heat of fusion varied linearly with composition supporting the incorporation of HDPE into the LLDPE crystals. The dynamic mechanical α, β, and γ relaxations of the blends display an intermediate behavior that indicates miscibility in both the crystalline and amorphous phases. In the LDPE/HDPE blend, the melting or crystallization peaks of LDPE were strongly influenced by HDPE. The behavior of the α relaxation was dominated by HDPE, while those of β and γ relaxations were intermediate of the constituents, which were similar to those of the LLDPE/HDPE blends. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1633–1642, 1997     

The influence of wood flour and compatibilizer (<Emphasis Type="Italic">m</Emphasis>-TMI-<Emphasis Type="Italic">g</Emphasis>-PP) on crystallization and melting behavior of polypropylene

Wood flour/polypropylene composites (WPC) were prepared by melt extruding with different wood flour (WF) loadings. The non-isothermal crystallization and melting was studied with different WF loadings, for W40P60 and W40P60M6, the melting was investigated after non-isothermal and isothermal crystalline. Comparing with neat polypropylene, the melting behavior of the composites, both non-isothermally and isothermally, was investigated by differential scanning calorimetry (DSC). The results showed that WF was an effective heterogeneous nucleating agent, as evidenced by an increase in the crystallization temperature and the crystallinity for melt crystallization of PP with increasing WF content. For the non-isothermal samples, the origins of the double melting behaviors were discussed, based on the DSC results of PP. The XRD measurements confirmed that no crystalline transition existed during the non-isothermal crystallization process. With m-TMI-g-PP adding, due to compatibilization phenomenon were probably responsible for decreasing T _m, X _c. In the DSC scan after isothermal crystallization process, the single melting behaviors were found and each melting endotherm had a different origin.     

Can Classic Avrami Theory Describe the Isothermal Crystallization Kinetics for Stereocomplex Poly(lactic acid)?

Classic Avrami model and its modifications have found diverse applications in describing the thermal and phase behaviors of inorganic metals and organic polymers.The direct introduction of classic Avrami equation to offer quantitative analyses of crystallization kinetic parameters for enantiomeric poly(lactic acid) (PLA) blends may,however,lead to contradictory conclusions.As revealed by this study,during the characterization of isothermal melt and cold crystallization for stereocomplex PLA containing equal-weight poly(L-lactic acid) and poly(D-lactic acid),the kinetic parameters yielded by Avrami equation are not in line with the classic crystallization hypotheses or the direct morphological observations.The underlying mechanisms,to some extent,lie in the generation of stereocomplex crystals (SCs) during the cooling/heating which affects the subsequent crystallization dynamics.The huge gap between the melting enthalpies of 100％ crystalline SCs (142 J/g) and homo-crystals (HCs,93 J/g) is most likely responsible for the confusing kinetic parameters acquired from the deduction of Avrami equation,which is based on the integration of enthalpies as a function of crystallization time.This prompts for great care that the classic Avrami equation is not applicable to accurately describe the crystallization kinetics of stereocomplex PLA,given the generation of SCs prior to crystallization and the coexistence of HCs and SCs during crystallization.     

Nonisothermal crystallization behaviors of polypropylene with α/β nucleating agents

In this work, the nonisothermal crystallization and subsequent melting behaviors of polypropylene (PP) nucleated with different nucleating agents (NAs) have been studied. α‐phase NA 1,3:2,4‐bis (3,4‐dimethylbenzylidene) sorbitol (DMDBS, Millad 3988), β‐phase NA aryl amides compound (TMB‐5), and their compounds were introduced into PP matrix, respectively. The results show that the nonisothermal crystallization behaviors and crystalline structures of PP with compounded NAs are dependent on the composition of NAs. In the sample of PP with 0.1 wt % DMDBS and 0.1 wt % TMB‐5, the nucleation efficiency (NE) of TMB‐5 is much higher than that of DMDBS and PP crystallizes mainly nucleated by TMB‐5, and in this condition, β‐phase PP is the main crystallization structure. For the sample of PP with 0.2 wt % DMDBS and 0.2 wt % TMB‐5, 0.2 wt % DMDBS has higher NE than 0.2 wt % TMB5, and α‐phase is the main crystalline structure. The cooling rate is proved to be very important in controlling the nonisothermal crystallization behavior and the final crystalline structure of nucleated PP. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1853–1867, 2008     

Analysis of crystallization behavior and crystal modifications of poly(butylene‐2,6‐naphthalene dicarboxylate)

Information on the crystalline structure and the properties of poly(butylene‐2,6‐naphthalene dicarboxylate) (PBN) has not been well reported until now, but it is known that there are two different crystal modifications in PBN, as follows: one is formed in isotropic samples by annealing (α form); another appears by annealing with tension (β form). The relation between the crystal modifications and the kinetics of isothermal crystallization for PBN was investigated using in‐situ Fourier transform infrared spectroscopy (FTIR) and wide‐angle X‐ray diffraction (WAXD). The melting behavior of each crystalline form was also studied by means of FTIR and differential scanning calorimetry (DSC) measurements. From the analysis of the melt‐crystallized PBN specimens, the two crystalline forms coexisted in the isotropic samples melt‐crystallized at 230°C, but only the α crystal modification was observed in the films annealed at lower temperatures. In addition, it was revealed that, at 230°C, the β modification was formed only in the primary crystallization process. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 561–574, 1999     

Phase and state transition effects on dielectric, mechanical, and thermal properties of polyols

The present study investigated the glass transition, crystallisation and melting behaviour of erythritol, xylitol, and glucitol (sorbitol) using dielectric analysis (DEA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). Sorbitol and xylitol were plasticised by water and their glass transition temperatures decreased when water content was increased. Erythritol crystallised rapidly, and its water plasticisation behaviour could not be determined. Melting of the crystalline polyols occurred at their specific melting temperatures. Melts of erythritol and xylitol crystallised on recooling and no glass transition was apparent on reheating. Quench cooled sorbitol melt remained amorphous and showed a glass transition on reheating. Glass transition and crystallisation were apparent in the DSC thermogram and the dielectric and the dynamic mechanical spectra of mixtures of amorphous and crystalline xylitol.     

MULTIPLE MELTING TRANSITIONS IN POLYURETHANE-UREA ELASTOMERS UNDER EXTENSION

Two melting transitions were observed in linear segmented polyurethane-urea elastomers underextension using thermal, mechanical and X-ray diffraction techniques, and the results are compared.These data indicate both strain-induced and temperature-induced crystallization in the stretchedclastomers, which may result from two different types of crystallites with different melting tempera-tures. These have been assigned as type 1 appearing around 60℃, and type 2 around 30℃. Thetype 1 crystallization can be induced by stretching at room temperature to large strain, and is mechani-cally reversible, but the type 2 crystallization is mainly induced by cooling below its crystallizationtemperature. These two crystalline structures are interchangeable under suitable conditions. Atelongations greater than 300%, the low temperature peak observed on fusion thermograms disappearsor combines with the high temperature peak. When the temperature of the sample is over the meltingpoint of the type 1 crystal, irreversible melting occurs and only the type 2 crystal develops on cooling.The results of stress-strain and stress hysteresis experiments at different temperatures indicate therelative importance of strain-induced and temperature-induced crystallization on the mechanicalproperties of these materials.     

Effect of Y2O3 addition on viscosity and crystallization of the lithium aluminosilicate glasses

The melting and crystallization behaviors of lithium aluminosilicate (LAS) glasses containing Y₂O₃ were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis (DTA) and viscosity test. Effects of Y₂O₃ on the viscosity of LAS glasses were investigated from the softening point temperature to melting temperature. It was indicated that the introduction of yttria effectively decreased the melting temperature and viscosity of LAS glasses. The DTA and XRD results showed that yttria controlled the crystallization of LAS glasses by increasing the crystallization peak temperature (T_p) and activation energies (E), and the main crystalline phase of glass-ceramics was β-spodumene.     

Solution grown isotactic polystyrene crystals. II. Kinetics of thermal changes by x-ray diffraction

The present paper is a study of the annealing, melting, and recrystallization behavior of solution grown isotactic polystyrene crystals in order to elucidate changes both in total lamellar thickness and in the thickness of the crystalline “core” as a function of temperature. The lamellar thickness was obtained from x-ray long spacings and the core thickness from the broadening of appropriate reflections, both assessed by a high sensitivity x-ray detector system able to produce records within a few minutes during time dependent processes. The x-ray results were correlated with differential scanning calorimetry (DSC) measurements. On heating, first the usual annealing effects with little net melting were observed, but on increasing the temperature large changes in long spacing, which were reversible with temperature, were seen accompanied by only small changes in crystal core thickness. The second effect was found to be associated with a substantial degree of melting. Even after heating above the temperature where complete melting was indicated by DSC, the recrystallization rate was found to decrease as the melt temperature was increased and to be much faster than on cooling from the usual melts. Strikingly, this recrystallization was accompanied by a decrease in long period with time even under isothermal conditions. It is inferred that the memory of the preceding crystalline stack is preserved throughout the melting range and even beyond this, far into the molten state. This “seeding” effect is intrinsic to the polymer even if its nature cannot be specified. The principal effects in question can then be explained by envisaging that randomly placed lamellas gradually disappear within the stack on melting and successively reappear on crystallization during cooling. These ideas agree well with previous work on reversible long spacing changes in polyethylene (see ref. 9) and are likely to be of wider generality for melting and recrystallization phenomena in systems having stacked lamellar morphologies.     

Analysis of the complex thermal behavior of poly(L‐lactic acid) film. II. Samples crystallized from the melt

The complex thermal behavior of poly(l ‐lactic acid) films crystallized from the melt, either isothermally or nonisothermally, was studied by differential scanning calorimetry (DSC), wide angle X‐ray diffraction, and small angle X‐ray scattering. The variation of the thermal behavior with crystallization temperature, time, and cooling rate was documented and analyzed. After nonisothermal crystallization at low cooling rates that develop high crystallinity, an obvious double melting peak appears at modest heating rates (e.g., 10 °C/min). At higher heating rates, these samples exhibit only single melting. However, an unusual form of double melting occurs under the majority of the conditions studied under either isothermal or nonisothermal conditions. In this case, double melting is marked by the appearance of a recrystallization exotherm just prior to the final melting that obscures the observation of the melting of the crystals formed during the initial crystallization process. The occurrence of double melting in melt‐crystallized samples was concluded to be the result of a melt‐recrystallization process occurring during the subsequent DSC heating scan; it is a function of crystalline perfection, not the initial crystallinity, nor whether or not the crystallization reached completion at the crystallization temperature. Many other very interesting observations are also discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3378–3391, 2006     

Syntheses and properties of phosphorus-containing copolyamides

Caprolactam was copolymerized with 1,5-dioxo-1-methyl-4-azaphosphepane or methylphosphacaprolactam. The molecular weight of the resulting copolymers decreased with increasing concentration of the thermally labile phosphorus moieties. Copolymers based on ≥40% caprolactam were shown to be crystalline by differential scanning calorimetry and x-ray techniques. As the concentration of the phosphorus structures in the copolymers increased, the glass transition and crystallization temperatures increased while the melting temperatures, crystallinities, and thermal stabilities decreased. Melt blends of nylon 6 and polymethylphosphacaprolactam were shown by differential scanning calorimetry, a selective extraction technique, and elemental analysis to contain appreciable amounts of block copolyamides, and no crystalline random structures were detected. The thermal stabilities of the melt blends were similar to those of random copolymers having comparable concentrations of the phosphorus-containing sequences.