Melting behavior of isotactic polystyrene

The melting behavior of isotactic polystyrene, crystallized from the melt and from dilute solutions in trans-decalin, has been studied by differential scanning calorimetry and solubility measurements. The melting curves show 1, 2, or 3 melting endotherms. At large supercooling, crystallization from the melt produces a small melting endotherm just above the crystallization temperature T_c. This peak originates from secondary crystallization of melt trapped within the spherulites. The next melting endotherm is related to the normal primary crystallization process. Its peak temperature increases linearly with T_c, yielding an extrapolated value for the equilibrium melting temperature T_c° of 242 ± 1°C as found before. By self-seeding, crystallization from the melt could be performed at much higher temperature to obtain melting temperatures as high as 243°C, giving rise to doubt about the value of T_c° found by extrapolation. For normal values of T_c and heating rate, an extra endotherm appears on the melting curve. Its peak temperature is the same for both melt-crystallized and solution-crystallized samples, and independent of T_c, but rises with decreasing heating rate. From the effects of heating rate and partial scanning on the ratio of peak areas and of previous heat treatment on dissolution temperature, it is concluded that this peak arises from the second one by continuous melting and recrystallization during the scan.     

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.     

New insights into the multiple melting behaviors of the semicrystalline ethylene‐hexene copolymer: Origins of quintuple melting peaks

A semicrystalline ethylene‐hexene copolymer (PEH) was subjected to a simple thermal treatment procedure as follows: the sample was isothermally crystallized at a certain isothermal crystallization temperature from melt, and then was quenched in liquid nitrogen. Quintuple melting peaks could be observed in heating scan of the sample by using differential scanning calorimeter (DSC). Particularly, an intriguing endothermic peak (termed as Peak 0) was found to locate at about 45 °C. The multiple melting behaviors for this semicrystalline ethylene‐hexene copolymer were investigated in details by using DSC. Wide‐angle X‐ray diffraction (WAXD) technique was applied to examine the crystal forms to provide complementary information for interpreting the multiple melting behaviors. Convincing results indicated that Peak 0 was due to the melting of crystals formed at room temperature from the much highly branched ethylene sequences. Direct heating scans from isothermal crystallization temperature (T_c, 104–118 °C) were examined for comparison, which indicated that the multiple melting behaviors depended on isothermal crystallization temperature and time. A triple melting behavior could be observed after a relatively short isothermal crystallization time at a low T_c (104–112 °C), which could be attributed to a combination of melting of two coexistent lamellar stack populations with different lamellar thicknesses and the melting‐recrystallization‐remelting (mrr) event. A dual melting behavior could be observed for isothermal crystallization with both a long enough time at a low T_c and a short or long time at an intermediate T_c (114 °C), which was ascribed to two different crystal populations. At a high T_c (116–118 °C), crystallizable ethylene sequences were so few that only one single broad melting peak could be observed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2100–2115, 2008     

Polymorphism and transcrystallization of syndiotactic polystyrene composites filled with carbon nanotubes

Syndiotactic polystyrene (sPS) composites filled with well-dispersed multi-walled carbon nanotubes (CNTs) were readily prepared through a coagulation method. Fourier-transform infrared spectroscopy and wide-angle X-ray diffraction revealed the effect of CNTs on the polymorphism of sPS. When crystallized from the melted state, the formation of the β-form was always favored after CNT addition regardless of crystallization conditions (isothermal or non-isothermal). In the case where liquid nitrogen was used to quench the melt, the uncrystallized material that was not able to crystallize in the extremely short crystallization time crystallized in the α form upon subsequent cold crystallization. Regardless of the CNT content, the glass transition and equilibrium melting temperature of the sPS matrix were unchanged at ∼96 and 290 °C, respectively. With a gradual increase in CNT loading, the sPS crystallization rate initially increased but then reached a plateau value at high CNT concentrations because of the reduction in chain mobility. Moreover, the Avrami exponent was changed from 2.8 for samples at low CNT contents to 2.0 for samples with a CNT concentration above 0.1 wt.%, at which the rheological threshold was approached and a polymer-CNT hybrid network was formed. The enhanced crystallization kinetics was attributed to the high nucleating ability of CNTs to induce a transcrystalline layer (TCL) at its surface, as revealed by transmission electron microscopy. For composites with low levels of CNT, the growth of sPS spherulites in the bulk between CNTs prevailed. Provided that the CNT-related networks were developed, the two-dimensional growth of cylindrical TCL at the CNT surface became dominant and led to the expected Avrami exponent.     

Renewable agricultural fibers as reinforcing fillers in plastics

Thermal properties such as melting and crystallization are important aspects in understanding the morphology and its contribution to the physical properties of semicrystalline polymers, such as polypropylene. The inclusion of fillers, which are small particles dispersed in the continuous polymer phase, often complicates the predictability of these properties by acting as nucleating agents or defect origins. This paper discusses the creation and use of empirical models based on experimental data for predicting and optimizing the thermal properties of agricultural filler-polypropylene (AgFiller-PP) composites, including peak melting temperature (T _m), peak crystallization temperature (T _c) and percent of crystallinity (X _c). Experiments were performed using differential scanning calorimetry (DSC) to gather data necessary for building appropriate prediction models. Finally, additional experiments were carried out to test the prediction results generated by the models.     

Multiple melting behavior of poly(butylene succinate). II. Thermal analysis of isothermal crystallization and melting process

The multiple melting behavior of poly(butylene succinate) (PBSu) was studied with differential scanning calorimetry (DSC). Three different PBSu resins, with molecular weights (MWs) of 1.1 × 10⁵, 1.8 × 10⁵, and 2.5 × 10⁵, were isothermally crystallized at various crystallization temperatures (T_c) ranging from 70 to 97.5 °C. The T_c dependence of crystallization half‐time (τ) was obtained. DSC melting curves for the isothermally crystallized samples were obtained at a heating rate of 10 K min⁻¹. Three endothermic peaks, an annealing peak, a low‐temperature peak L, and a high‐temperature peak H, and an exothermic peak located between peaks L and H clearly appeared in the DSC curve. In addition, an endothermic small peak S appeared at a lower temperature of peak H. Peak L increased with increasing T_c, whereas peak H decreased. The T_c dependence of the peak melting temperatures [T_m(L) and T_m(H)], recrystallization temperature (T_re), and heat of fusion (ΔH) was obtained. Their fitting curves were obtained as functions of T_c. T_m(L), T_re, and ΔH increased almost linearly with T_c, whereas T_m(H) was almost constant. The maximum rate of recrystallization occurred immediately after the melting. The mechanism of the multiple melting behavior is explained by the melt‐recrystallization model. The high MW samples showed similar T_c dependence of τ, and τ for the lowest MW sample was longer than that for the others. Peak L increased with MW, whereas peak H decreased. In spite of the difference of MW, T_m(L), T_m(H), and T_re almost coincided with each other at the same T_c. The ΔH values, that is crystallinity, for the highest MW sample were smaller than those for the other samples at the same T_c. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2039–2047, 2005     

Calorimetric analysis of the multiple melting behavior of melt-crystallized poly(l-lactic acid) with a low optical purity

The polymorphous crystallization and multiple melting behavior of poly(l-lactic acid) (PLLA) with an optical purity of 92 % were investigated after isothermally crystallized from the melt state by wide-angle X-ray diffraction and differential scanning calorimetry. Owing to the low optical purity, it was found that the disordered (α′) and ordered (α) crystalline phases of PLLA were formed in the samples crystallized at lower (<95 °C) and higher (≥95 °C) temperatures, respectively. The melting behavior of PLLA is different in three regions of crystallization temperature (T _c) divided into Region I (T _c < 95 °C), Region II (95 °C ≤ T _c < 120 °C), and Region III (T _c ≥ 120 °C). In Region I, an exothermic peak was observed between the low-temperature and high-temperature endothermic peaks, which results from the solid–solid phase transition of α′-form crystal to α one. In Region II, the double-melting peaks can be mainly ascribed to the melting–recrystallization–remelting of less stable α crystals. In Region III, the single endotherm shows that the α crystals formed at higher temperatures are stable enough and melt directly without the recrystallization process during heating.     

Characterization of the interaction of poly(ethylene oxide) with nanosize fumed silica: Surface effects on crystallization

Poly(ethylene oxide) (PEO) of 4600 molar mass (PEO‐4600) was crystallized from methanol in the presence of hydrophilic fumed silicas (A380, A200, and OX50) with nominal surface areas of 380, 200, and 50 m²/g and a hydrophobic fumed silica (R812s) modified with methyl groups. The composites were characterized by thermogravimetric analysis and differential scanning calorimetry. The inhibition of crystallization and the tendency for chain reorganization after melting were in the order of A380 > A200 > OX50 > R812s, respectively, that is, both were least for the hydrophobic silica and increased with increasing specific surface area for the hydrophilic silica. The interaction of PEO with the silica increased in the melt state as compared with the solution‐cast samples, resulting in enhanced suppression of crystallization. The following took place at a high silica content: (1) crystallization occurred at crystallization temperatures [T_c < T_c (bulk)], suggesting that the silica inhibited crystallization; (2) crystallites with melt temperatures [T_m < T_m (bulk)] were observed, indictive of smaller and/or less perfect crystals; and (3) melt entropies [ΔS_m (surface) < ΔS_m (bulk)] suggested that the interaction of surface silanols, Si_sOH, with PEO decreased both the melt entropy and crystallite size/perfection. Crystallinity was observed in solution‐cast composites when there were greater than ～0.03 PEO molecules/nm² for native and ～0.01 PEO molecules/nm² for methylated fumed silica, similar to reported plateau equilibrium adsorption values from methanol. These results were consistent with a model in which PEO interacted more strongly with native fumed silica as compared with hydrophobically modified silica because of hydrogen bonding of the ether oxygens of PEO with the acidic silanols, preventing chain mobility and crystallization. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1978–1993, 2003     

Melting behavior of a poly(ether‐block‐amide) copolymer melt‐crystallized under quiescent,isothermal conditions

Segmented poly(ether‐block‐amide) copolymers are typically known as polyamide‐based thermoplastic elastomers consisting of hard, crystallizable polyamide block and flexible, amorphous polyether block. The melting characteristics of a poly(ether‐block‐amide) copolymer melt‐crystallized under various quiescent, isothermal conditions were calorimetrically investigated using differential scanning calorimetry (DSC). For such crystallized copolymer samples, their crystalline structures under ambient condition and the structural evolutions upon heating from ambient to complete melting were characterized using ambient and variable‐temperature wide‐angle X‐ray diffractometry (WAXD), respectively. It was observed that dependent of specific crystallization conditions, the copolymer samples exhibited one, two, or three melting endotherms. The ambient WAXD results indicated that all melt‐crystallized copolymer samples only exhibited γ‐form crystals associated with the hexagonal habits of the polyamide homopolymer, whereas variable‐temperature WAXD data suggested that upon heating from ambient, a melt‐crystallized copolymer might exhibit so‐called Brill transition before complete melting. Based on various DSC and variable‐temperature WAXD experimental results obtained in this study, the applicability of different melting mechanisms that might be responsible for multiple melting characteristics of various crystallized PEBA copolymer samples were discussed. It was postulated that the low (T _m1) endotherm was primarily because of the disruption of less thermally stable, short‐range ordered structure of amorphous polyamide segments of the copolymer, which was only formed after the completion of primary crystallization via so‐called annealing effects. The intermediate (T_m2) and high (T_m3) endotherms were attributed to the melting of primary crystals within polyamide crystalline microdomains of the copolymer. The appearance of these two melting endotherms might be somehow complicated by thermally induced Brill transition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2035–2046, 2008     

Crystal orientation and melting behavior of poly(ɛ-Caprolactone) under one-dimensionally “hard” confined microenvironment

Crystal orientation and melting behavior of poly(ε-caprolactone) in a diblock copolymer of poly(ε-caprolactone)-block-poly(2,5-bis[4-methoxyphenyl]oxycarbonyl)styrene) (PCL-b-PMPCS) was investigated. The degrees of polymerization of the PCL and PMPCS block are 200 and 98, respectively. With the PMPCS in a columnar liquid crystalline phase, the diblock is rod-coil one, which exhibits a lamellar phase morphology with the PCL layer thickness of 15.2 nm. Since the glass transition temperature of PMPCS block is much higher than the melting temperature of PCL, the crystallization of PCL is in a one-dimensionally "hard" confinement environment. Mainly on the basis of two-dimensional wide-angle X-ray diffraction experiments, we identified the orientation of PCL isothermally crystallized at various crystallization temperatures (Tcs). At high Tcs (Tc≥10℃), the c-axis of the PCL crystal is along the layer normal of the microphase-separated sturcture. Decreasing Tc can result in the tilting of PCL c-axis with respect to the layer normal. The lower the Tc is, the more the c-axis inclines. Meanwhile, the b-axis of PCL remains perpendicular to the layer normal. At a very low Tc of -78℃, the orientation of the PCL crystals is completely random. For the samples isothermally crystallized at Tc≤10℃, double melting behavior can be observed. While the low temperature endotherm reflects the melting of the crystals originally formed at the Tc applied, the high temperature one is associated with the crystals subjected to the process of recrystallization/reorganization upon heating due to the annealing effect.     

X-ray scattering and thermal analysis study of the effects of molecular weight on phase structure in blends of poly(butylene terephthalate) with polycarbonate

Blends of Poly(butylene terephthalate), PBT, with Polycarbonate, PC, were studied for a range of molecular weights and blend compositions. Blends were available in PBT/PC compositions 80/20 and 40/60, and with M_w designated by H (high) or L (low). Samples were prepared by melt crystallization, or by cold crystallization following a rapid quench from the melt. Addition of PC reduces the crystallization kinetics of PBT so that the resulting crystals are more perfect than those which form in the homopolymer. Degree of crystallinity of the blends followed the rank ordering: L/L > L/H > H/L = H/H. The glass transition behavior was investigated using dynamic mechanical analysis (DMA) and modulated differential scanning calorimetry (MDSC). All blends exhibited two glass transitions at intermediate temperatures between the T_gs of the homopolymers, indicating existence of a PBT-rich phase and a PC-rich phase. Blends L/L were most, and H/H the least, miscible. Small-angle X-ray scattering was performed at room temperature on cold crystallized blends, or at elevated temperature during melt crystallization. The long period was consistently larger, and the linear stack crystallinity was consistently smaller, in blends L/L or H/L. These results indicate that in blends containing low M_w PC, there is more PC located within the PBT-rich phase. The long period was consistently smaller in cold crystallized samples, while the linear stack crystallinity was nearly the same, regardless of melt or cold crystallization treatment. Reduction of the average long period in cold crystallized samples could result from crystallization of PBT within the PC-rich phase. This is consistent with thermal analysis results, which indicate that cold crystallized samples have greater overall crystallinity than melt crystallized samples. A hypothetical liquid phase diagram is presented to explain the differences between melt and cold crystallized blends. © 1996 John Wiley & Sons, Inc.     

SAXS and DSC studies of the crystallization and melting phenomena of poly(ϵ‐caprolactone)

The relationships between the crystallization temperature, T_c, the crystal thickness, d_c and the melting peak temperature, T_m of poly(ϵ‐caprolactone) have been determined by carrying out time‐ and temperature‐dependent small angle x‐ray scattering experiments. A two‐step melting has been suggested, resulting in the occurrence of two well defined independent boundary lines, indicating the transformation from melt into the partially crystalline state. For crystallization temperatures lower than 40°C, during heating, more pronounced peak shifts are observed with the final melting of the crystallites having the same thickness of d_c ≈︁ 7 nm. In this region, it is evident that crystals have relatively good stabilities, since they have fairly uniform thickness. At higher temperatures, above 40°C, T_m increases with T_c, together with the thickness. The transformation of the melt into the partially crystalline state depicts a two‐step process, beginning with the formation of a well defined initial structure with lower order, which is subsequently stabilized.     

Self‐decelerated crystallization in poly(butylene terephthalate)/poly(ε‐caprolactone) blends

Isothermal crystallization of poly(butylene terephthalate) (PBT) blended with oligomeric poly(ε‐caprolactone) (PCL) is investigated by polarized optical microscopy and differential scanning calorimetry at various temperatures (T_c). The growth rate of PBT spherulites is found to depend on time (t), as the spherulite radius (r) linearly increases with t at the early stages of crystallization (r ∝ t), then, with the progress of phase transition, the spherulite radius becomes dependent on the square root of the time (r ∝ t^1/2) until termination of crystal growth. The nonlinear advance of the crystal growth front is caused by a varied composition of the melt phase in contact with the growing crystals, due to diffusion of mobile PCL chains away from the spherulite surface. The melt phase becomes spatially inhomogeneous, causing self‐deceleration of PBT crystallization until a limit composition that prevents further crystallization is reached in the melt. The maximum crystallinity achievable during isothermal crystallization decreases with T_c. The lowering of the temperature after termination of the isothermal crystallization allows to complete the crystal growth, but the final developed crystallinity still depends on T_c, being lower at higher T_cs. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3148–3155, 2007     

Fractionated and Confined Crystallization of Polybutene-1 in Immiscible Polypropylene/Polybutene-1 Blends

In this work,the crystallization of immiscible polypropylene(PP)/polybutene-1(PB)blends,in particular the effect of crystal morphology of PP(HTC,high Tm component)on the subsequent crystallization behavior of PB(LTC,low Tm component)was studied.Herein,we firstly indicated that PP/PB blends were not completely compatible but characterized as the LCST-like phase diagram above the melting temperature of PP.Crystallization of PP at different crystallization temperatures brought about different PP crystal morphologies and PB was segregated and confined at different locations.Much larger-sized domain of PB component appeared in PP spherulites resulting from the effects of non-negligible phase separation and the slower PP crystallization rate as PP crystallized at high temperature.As temperature continued to fall below Tm of PB,the fractionated and confined crystallization of PB occurred in the framework of PP spherulites,reflected by the decreased crystallization temperature(Tc)of PB and the formation of form I′beside form II.Notably,if PP previously crystallized at high Tc,fractionated crystallization of PB became predominant and confined crystallization of PB became weak due to the much wider droplet-size distribution of PB domains.     

Long periods in slow-cooled linear and branched polyethylene: Part II

It is shown that the long periods L in slow-cooled polyethylene materials obey the general law L = L⁰ + αr_w, where r_w is the weight average dimension of the coil before crystallization, and L⁰ is a parameter of the order of l_c, the crystalline core thickness, which increases as the cooling rate V decreases. α is a parameter independent of M and V but decreasing with the number of long-chain branches per molecule. The two terms in the above relation are, respectively, the contributions of crystalline and amorphous layers. For cooling rates from 800°C/min to 0.2°C/min, it is shown that the temperature T_c of crystallization is constant; hence the change of morphology (long period, crystalline core thickness, crystallinity) cannot be explained by supercooling. The increase in long period and crystallite thickness in slow-cooled materials with decreasing cooling rate is interpreted in terms of annealing of the crystallized materials between the crystallization temperature T_c and the secondary transition temperature T_αc. Crystallization proceeds by a two-step process of solidification and annealing. During the annealing stage, the mobility of the chains in the crystalline phase is due to defects; the kinetics of thickening is then governed by the mobility (or nucleation) of the defects appearing above T_αc. In the proposed model of crystallization, the assumption that the energy of activation is proportional to T_αc explains the observed laws L ≡ l_c ≡ log t_a, where the annealing time t_a is equal to (T_c ? T_αc)/V. The model applies also to polymers crystallized from the melt and subsequently annealed.     

Comparison of the properties of waterborne polyurethane/multiwalled carbon nanotube and acid‐treated multiwalled carbon nanotube composites prepared by in situ polymerization

A series of waterborne polyurethane (WBPU)/multiwalled carbon nanotube (CNT) and WBPU/nitric acid treated multiwalled carbon nanotube (A‐CNT) composites were prepared by in situ polymerization in an aqueous medium. The optimum nitric acid treatment time was about 0.5 h. The effects of the CNT and A‐CNT contents on the dynamic mechanical thermal properties, mechanical properties, hardness, electrical conductivity, and antistatic properties of the two kinds of composites were compared. The tensile strength and modulus, the glass‐transition temperatures of the soft and hard segments (T_gs and T_gh, respectively), and ΔT_g (T_gh − T_gs) of WBPU for both composites increased with increasing CNT and A‐CNT contents. However, these properties of the WBPU/A‐CNT composites were higher than those of the WBPU/CNT composites with the same CNT content. The electrical conductivities of the WBPU/CNT1.5 and WBPU/A‐CNT1.5 composites containing 1.5 wt % CNTs (8.0 × 10⁻⁴ and 1.1 × 10⁻³ S/cm) were nearly 8 and 9 orders of magnitude higher than that of WBPU (2.5 × 10⁻¹² S/cm), respectively. The half‐life of the electrostatic charge (τ_1/2) values of the WBPU/CNT0.1 and WBPU/A‐CNT0.1 composites containing 0.1 wt % CNTs were below 10 s, and the composites had good antistatic properties. From these results, A‐CNT was found to be a better reinforcer than CNT. These results suggest that WBPU/A‐CNT composites prepared by in situ polymerization have high potential as new materials for waterborne coatings with good physical, antistatic, and conductive properties. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3973–3985, 2005     

A study of phase separation of crystalline and miscible polymer blends. Poly(ε-caprolactone)/poly(styrene-co-acrylonitrile)

The phase separation of a crystalline and miscible polymer blend, poly(ε-caprolactone) /poly(styrene-co-acrylonitrile) (PCL/SAN), has been studied by differential scanning calorimetry (DSC), using a SAN containing 28.3% of acrylonitrile units. Several phenomena can be associated with the occurrence of phase separation depending upon the composition of the mixture. Following annealing at high temperatures, below and above the phase separation temperature T_c, three cases can be distinguished. In Case I, there is no sign of crystallization during quenching and DSC scanning, but a melting peak is observed at T_c, and above. In Case II, there is no crystallization on quenching but it does occur during the DSC run; the shift of the crystallization peak can then be related to T_c. In Case III, there is crystallization on quenching, and additional crystallization during the DSC run; the change of area of the crystallization peak is indicative of T_c. From these observations, the phase diagram of the system was determined. © 1993 John Wiley & Sons, Inc.     

Crystallization kinetics and melting behavior of metallocene short‐chain branched polyethylene fractions

Metallocene polyethylene (mPE) fractions are recognized as being more homogeneous with respect to short‐chain branch (SCB) distribution as compared with unfractionated mPEs. Differential scanning calorimetry and polarized optical microscopy (POM) were used to study the influences of SCB content on the crystallization kinetics, melting behavior, and crystal morphology of four butyl‐branched mPE fractions. The parent mPE of the studied fractions was also investigated for comparative purposes. mPE fractions showed a much simpler crystallization behavior as compared with their parent mPE during the cooling experiments. The Ozawa equation was successfully used to analyze the nonisothermal crystallization kinetics of the fractions. The Ozawa exponent n decreased from about 3.5 to 2 as the temperature declined for each fraction, indicating the crystal‐growth geometry changed from three‐dimensional to two‐dimensional. For isothermal crystallization, the fraction with a lesser SCB content exhibited a higher crystallization temperature (T_c) window. The results from the Avrami equation analysis showed the exponent n values were around 3 (with minor variation), which implied that the crystal‐growth geometry is pseudo‐three‐dimensional. Both of the activation energies for nonisothermal and isothermal crystallization were determined for each fraction with Kissinger and Arrhenius‐type equations, respectively. Double melting peaks were observed for both nonisothermally or isothermally crystallized specimens. The high‐melting peak was confirmed induced via the annealing effect during heating scans. The Hoffman–Weeks plot was inapplicable in obtaining the equilibrium melting temperature (T_m°) for each fraction. The relationship between T_c and T_m for the fractions is approximately T_m = T_c (°C) + 8.3. The POM results indicated that the crystals of parent or fractions formed under cooling conditions did not exhibit the typical spherulitic morphology as a result of the high SCB content. © 2002 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 325–337, 2002     

Multiple melting behavior of poly(butylene succinate). I. Thermal analysis of melt‐crystallized samples

The multiple melting behavior of poly(butylene succinate) (PBSu) was studied with differential scanning calorimetry (DSC). Three different PBSu resins, with molecular weights of 1.1 × 10⁵, 1.8 × 10⁵, and 2.5 × 10⁵, were cooled from the melt (150 °C) at various cooling rates (CRs) ranging from 0.2 to 50 K min^?1. The peak crystallization temperature (T_c) of the DSC curve in the cooling process decreased almost linearly with the logarithm of the CR. DSC melting curves for the melt‐crystallized samples were obtained at 10 K min^?1. Double endothermic peaks, a high‐temperature peak H and a low‐temperature peak L, and an exothermic peak located between them appeared. Peak L decreased with increasing CR, whereas peak H increased. An endothermic shoulder peak appeared at the lower temperature of peak H. The CR dependence of the peak melting temperatures [T_m(L) and T_m(H)], recrystallization temperature (T_re), and heat of fusion (ΔH) was obtained. Their fitting curves were obtained as functions of log(CR). T_m(L), T_re, and ΔH decreased almost linearly with log(CR), whereas T_m(H) was almost constant. Peak H decreased with the molecular weight, whereas peak L increased. It was suggested that the rate of the recrystallization decreased with the molecular weight. T_m(L), T_m(H), T_re, and T_c for the lowest molecular weight sample were lower than those for the others. In contrast, ΔH for the highest molecular weight sample was lower than that for the others. If the molecular weight dependence of the melting temperature for PBSu is similar to that for polyethylene, the results for the molecular weight dependence of PBSu can be explained. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2411–2420, 2002