Crystallization behavior of P(EN‐co‐ET) copolyesters: Crystallization kinetics and morphology revealed by DSC,time‐resolved SAXS analysis,and TEM

The crystallization kinetics and morphology of PEN/PET copolyesters were investigated using differential scanning calorimetry (DSC), time‐resolved small‐angle X‐ray scattering (TR‐SAXS), and transmission electron microscopy (TEM). The Avrami exponents obtained using DSC were approximately 3 for homo PEN and 4 for all the copolyesters. The 3‐parameter Avrami model was successfully fitted to the invariants with respect to the time obtained from TR‐SAXS, and the exponent values were similar to those obtained from DSC. Moreover, the Avrami rate constants obtained from TR‐SAXS showed marked temperature‐sensitive decreases in all samples, like those obtained from DSC. This indicates that not only could changes in morphological parameters be obtained from the analysis of TR‐SAXS data but also crystallization kinetics. The changes in the morphological parameters determined from the SAXS data indicate that the minor components, dimethyl terephthalate (DMT) segments, are rejected into the amorphous phase during crystallization. In the TEM study, copolyesters crystallized at temperature above 240 °C grew into both the α‐ and β‐form, although 240 °C is the optimum condition for the β‐form crystal. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 805–816, 2005     

Morphology of homogeneous copolymers of ethylene and 1‐octene. III. Structural changes during heating as revealed by time‐resolved SAXS and WAXD

The structural changes of two linear polyethylenes, LPEs, with different molar mass and of two homogeneous copolymers of ethylene and 1‐octene with comparable comonomer content but different molar mass were monitored during heating at 10 °C per minute using synchrotron radiation SAXS. Two sets of samples, cooled at 0.1 °C per minute and quenched in liquid nitrogen, respectively, were studied. All LPEs display surface melting between room temperature and the end melting temperature, whereas complete melting, according to lamellar thickness, only occurs at the highest temperatures where DSC displays a pronounced melting peak. There is recrystallization followed by isothermal lamellar thickening if annealing steps are inserted. The lamellar crystals of slowly cooled homogeneous copolymers melt in the reverse order of their formation, that is, crystals melt according to their thickness. Quenching creates unstable crystals through the cocrystallization of ethylene sequences with different length. These crystals repeatedly melt and co‐recrystallize during heating. The exothermic heat due to recrystallization partially compensates the endothermic heat due to melting resulting in a narrow overall DSC melting peak with its maximum at a higher temperature than the melting peak of slowly cooled copolymers. With increasing temperature, the crystallinity of quenched copolymers overtakes the one of slowly cooled samples due to co‐recrystallization by which an overcrowding of leaving chains at the crystal surfaces is avoided. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1975–1991, 2000     

Characterization of stress‐strain behavior for binary blends of isotactic polypropylene with ethylene‐α‐olefin copolymer

The characterization of the mechanical nonlinear behavior of isotactic polypropylene/ethylene‐1‐hexene copolymer blends with various kinds of morphology was carried out using a nonlinear constitutive equation in which the plastic deformation and the anharmonicity of elastic response are taken into account. It was found that the mechanical nonlinearity of the incompatible blends showing phase separation is much greater than that of the compatible blends having rubbery components in the interlamellar regions. Moreover, the mechanical behavior is governed by the plastic deformation for the incompatible blends, whereas the anharmonicity strongly affects the mechanical behavior for the compatible blends. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1513–1521, 1999     

Origin of the double melting peaks of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) with a high HV content as revealed by in situ synchrotron WAXD/SAXS analyses

We here reported the dual melting behaviors with a large temperature difference more than 50 °C without discernible recrystallization endothermic peak in isomorphous poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (P(HB‐co‐HV)) with a high HV content of 36.2 mol %, and the structure evolution upon heating was monitored by in situ synchrotron wide‐angle X‐ray diffraction/small‐angle X‐ray scattering (WAXD/SAXS) to unveil the essence of such double endothermic phenomena. It illustrated that the thinner lamellae with the larger unit cell and the thicker crystals having the smaller unit cell were melted around the first low and second high melting ranges, respectively. By analyzing in situ WAXD/SAXS data, and then coupling the features of melting behavior, the evolution of the parameters of both crystal unit cell and lamellar crystals, we proposed that the thinner unstable lamellae possess a uniform structure with HV units total inclusion, and the thicker stable lamellae reflect the sandwich structure with HV units partial inclusion. It further affirmed that the thicker sandwich and thinner uniform lamellae formed during the cooling and subsequent isothermal crystallization processes, respectively. These findings fully verify that it is the change of structure of lamellae rather than the melting/recrystallization that is responsible for double melting peaks of isomorphous P(HB‐co‐36.2%HV), and enhance our understanding upon multiple endothermic behaviors of polymers. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1453–1461     

Isotactic poly(propylene‐co‐1‐pentene‐co‐1‐hexene) terpolymers: Synthesis,molecular characterization,and evidence of the trigonal polymorph

Terpolymers based on propylene with 1‐pentene and 1‐hexene as comonomeric units are satisfactorily synthesized using a metallocene catalyst. Thus, several terpolymers are prepared with distinct overall compositions in comonomers as well as three different 1‐pentene/1‐hexene ratios at a given composition to evaluate the influence on polymerization activity, intrinsic viscosity, and microstructural details. The new trigonal δ polymorph is observed in those quenched terpolymers with a global content in comonomers of about 14 mol %, independently of the ratio between both comonomers. However, preliminary results indicate a profound influence of that ratio on the crystallization rate. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3251–3259     

Stereospecific polymerization of 1‐hexene catalyzed by ansa‐metallocene/methylaluminoxane systems under high pressures

Stereospecific polymerization of 1‐hexene under high pressures (up to 1,000 MPa = ca. 10,000 atm) using metallocene/methylaluminoxane (MAO) catalysts was investigated. Several C₂‐symmetric ansa‐metallocenes, their meso‐isomers, and two C_s‐symmetric ansa‐metallocenes were employed as catalyst precursors. In the course of this study, novel C₂‐symmetric germylene‐bridged ansa‐metallocenes, (rac‐[Me₂Ge(η⁵‐C₅H‐2,3,5‐Me₃)₂MCl₂] (M = Zr, rac‐4a; M = Hf, rac‐4b), have been prepared. High pressures induced enhancement of the catalytic activity and the molecular weight of the polymers in most of the catalysts. The maximum of both the catalytic activity and the molecular weight of the polymers was mostly observed at 100–500 MPa in each catalyst, although the enhanced ratio was smaller than that observed for nonbridged metallocenes. Isospecificity of the C₂‐symmetric ansa‐metallocene catalysts was essentially maintained even under high pressure. Highly isotactic polyhexene ([mmmm] = 91.6%) with very high molecular weight (M_w = 2,360,000) was achieved by rac‐4b under 250 MPa. High pressures slightly decreased syndiotacticity when the C_s‐symmetric ansa‐metallocene, isopropylidene(1‐η⁵‐cyclopentadienyl)(9‐η⁵‐fluorenyl)zirconium dichloride 5, was employed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 283–292, 1999     

Kinetics,polymer molecular weights,and microstructure in zirconocene‐catalyzed 1‐hexene polymerization

1‐Hexene was polymerized by rac‐(dimethylsilyl)bis(4,5,6,7‐tetrahydro‐1‐indenyl)zirconium dichloride catalyst and methylaluminoxane cocatalyst over the temperature range 0–100 °C. The polymerization rate, polymer molecular weight, and polymer microstructure (stereospecificity and regiospecificity) were studied as a function of the temperature and the concentrations of monomer, catalyst, and cocatalyst. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3802–3811, 2000     

Microstructure of metallocene isotactic propylene‐co‐1‐pentene‐co‐1‐hexene terpolymers

This study aims at characterizing in depth the microstructure of propylene‐co‐1‐pentene‐co‐1‐hexene terpolymers, which have been recently reported to develop the isotactic polypropylene δ trigonal polymorph when the total comonomer content is high enough. Such a specific crystalline form had been only reported so far in the analogous copolymers containing either 1‐pentene or 1‐hexene. A comparative ¹³C NMR study in solution of the aforementioned terpolymers and copolymers allows asserting the random insertion of both comonomers during chain growth under the polymerization conditions used. The reaction parameters, mainly catalyst and temperature, have been chosen for the purpose of assuring relatively high molar mass polymers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2537–2547     

13Carbon nuclear magnetic resonance of ethylene–propylene–1‐hexene terpolymers

We report the complete ¹³C NMR characterization of a series of ethylene–propylene–1‐hexene terpolymers obtained with the metallocenic system rac‐ethylene bis‐indenyl zirconium dichloride, with different comonomer ratios. A detailed study of ¹³C NMR chemical shifts, triad sequence distributions, monomer‐average sequence lengths, and reactivity ratios for these terpolymers is presented. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2474–2482, 2004     

New high impact polystyrene: Use of poly(1‐hexene) and poly(1‐hexene‐co‐hexadiene) as impact modifiers

In this study, polystyrene (PS) was melt blended with different amounts of poly1‐hexene (PH) and poly(1‐hexene‐co‐hexadiene) (COPOLY) and the blends were compared with conventional PS/polybutadiene (PS/PB) one. Scanning electron microscope revealed that the dispersion of PH and COPOLY in PS matrix was more uniform with the appearance of small particles in PS matrix; however, in the case of PS/PB blends, the fracture surface showed nonhomogenous morphology with the appearance of bigger rubber particles. Based on Differential Scanning Calorimetry (DSC) and dynamic mechanical thermal analysis results, T_g of the blends decreased in comparison with it in neat PS. Impact strength of PS/PH and PS/COPOLY blends was considerably higher than that in PS/PB and significantly higher than the value for neat PS. Tensile test showed substantial improvement in stress at yield and better elongation at break for COPOLY containing blend than the samples containing PH and PB rubbers. Also, blending of PS with 10% of the rubbers was considered in the presence of dicumylperoxide as a probable grafting/cross‐linking agent to produce XPS/COPOLY10 and XPS/PB10 samples, respectively. IR results of the nonsoluble solvent extracted gel showed that COPOLY and PB were grafted to PS matrix during melt blending, which caused higher impact strength in the related samples.     

Crystal structure and morphologies of polypropylene homopolymer and propylene‐ethylene random copolymer: Effect of the substituted 1,3,5‐benzenetrisamides

Four different substituted 1,3,5‐benzenetrisamides were synthesized and two of them were reported for the first time. Their effects on the crystal structure and morphologies of the iPP homopolymer (PPH) and propylene‐ethylene random copolymers (PPR) were investigated. The results showed that they had versatile nucleating ability among the different crystal forms of PPH. The N,N′,N′′‐tris‐tert‐butyl‐1,3,5‐benzene‐tricarboxamide, N,N′,N′′‐tris‐cyclohexyl‐1,3,5‐benzene‐tricarboxamide, and N,N′,N′′‐tris‐isopropyl‐1,3,5‐benzene‐tricarboxamide suppressed the formation of detectable spherulites with the common α‐form of the PPH, as well as the N,N′,N′′‐n‐butyl‐1,3,5‐benzene‐tricarboxamide induced the spherulites of the β‐form. The combination of the ethylene segment and the nucleating agent facilitated the formation of the γ‐form. These trisamides had limited effects on the packing of the PPH segments but induced more compacted packing of the PPRs. The nucleation mechanism of such compounds was discussed for the first time, it was found that the nucleation ability of these compounds rooted in matching of their dimension of the b‐axis with dimension of the c‐axis of iPP, and their butterfly‐shape further enhanced it. The (001) face of the trisamides was in contact with the (010) face of iPP. This epitaxial crystallization led to preferential growth along the b‐axis, and the ethylene segment indeed enhanced this effect. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1067–1078, 2008     

Mono‐ and binuclear nickel catalysts for 1‐hexene polymerization

Polymerization of 1‐hexene was carried out using a mononuclear (MN) catalyst and two binuclear (BN₁ and BN₂) α‐diimine Ni‐based catalysts synthesized under controlled conditions. Ethylaluminium sesquichloride (EASC) was used as an efficient activator under various polymerization conditions. The highly active BN₂ catalyst (2372 g poly(1‐hexene) (PH) mmol^?1 cat) in comparison to BN₁ (920 g PH mmol^?1 cat) and the MN catalyst (819 g PH mmol^?1 cat) resulted in the highest viscosity‐average molecular weight (M_v) of polymer. Moreover, the molecular weight distribution (MWD) of PH obtained using BN₂/EASC was slightly broader than those obtained using BN₁ and MN (2.46 for BN₂ versus 2.30 and 1.96 for BN₁ and MN, respectively). These results, along with the highest extent of chain walking for BN₂, were attributed to steric, nuclearity and electronic effects of the catalyst structures which could control the catalyst behaviour. Differential scanning calorimetry showed that the glass transition temperatures of polymers were in the range ? 58 to ?81 °C, and broad melting peaks below and above 0 °C were also observed. In addition, longer α‐olefins (1‐octene and 1‐decene) were polymerized and characterized, for which higher yield, conversion and molecular weight were observed with a narrower MWD. The polymerization parameters such as polymerization time and polymerization temperature showed a significant influence on the productivity of the catalysts and M_v of samples.     

Crystallization behavior and morphology of β‐nucleated isotactic polypropylene with different stereo‐defect distribution

Aiming at further investigating the combination effect of concentration of β‐nucleating agent (β‐NA) and stereo‐defect distribution on the crystallization behavior of β‐nucleated isotactic polypropylene (β‐iPP), in this study, the crystallization behavior and polymorphic morphology of twoβ‐iPP resins with nearly same average isotacticity (PP‐A and PP‐B) but different uniformities of stereo‐defect distribution were investigated by differential scanning calorimetry (DSC), wide angle X‐ray diffraction (WAXD) and polarized optical microscopy (POM). The results of DSC and WAXD showed that the addition of TMB‐5 increases the crystallization temperature and decreases the spherulite sizes of both PP‐A and PP‐B, and reduces their crystallization energy barriers as well; however, the polymorphic behaviors of PP‐A and PP‐B exhibit different dependence on the TMB‐5 concentration. For PP‐A with less uniform distribution of stereo‐defects, β‐phase can be observed only when the TMB‐5 concentration is no less than 0.1 wt.%, while for PP‐B with more uniform stereo‐defect distribution, addition of 0.01 wt.% TMB‐5 can induce the formation of β‐phase. Moreover, the analysis of POM indicated that the crystalline morphologies of both PP‐A and PP‐B change greatly with the TMB‐5 concentration, and the variation features of PP‐A and PP‐B are quite different from each other. PP‐B with more uniform stereo‐defect distribution was more favorable for the formation of large amount of β‐phase in the presence of wide concentration range of TMB‐5. The different polymorphic behaviors and their different dependences on the β‐NA concentration were related to the different uniformities of stereo‐defect distribution of the samples, since the distribution of stereo‐defects could restrain the regular insertion of molecular chains during crystallization and thus determine the tendency the α‐phase crystallization of the sample. Copyright © 2014 John Wiley & Sons, Ltd.     

Morphology and Crystallization Behavior of Poly(butylene succinate)‐Based Ionomers (PBSi)

Summary: The crystallization behavior of a poly(butylene succinate)‐based ionomer (PBSi) was analyzed by morphological observations and synchrotron small‐angle X‐ray scattering (SAXS) experiments. The spherulitic morphology of PBSi is composed of irregular lamellae propagating outwards from the center with ionic clusters isolated from the crystalline lamellae. Synchrotron radiation SAXS profiles revealed that the re‐crystallization during heating process was effectively retarded with increasing ionic content, suggesting that the presence of ion aggregates affects the extent of diffusion of chains towards crystallization.

PBSi‐3 was isothermally crystallized at 85 °C for 30 min (400×). The spherulites of PBSi‐3 showed an irregular ringed pattern without a distinct center of spherulite.     

Ethylene–propylene copolymerization behavior of ansa‐dimethylsilylene(fluorenyl)(amido)dimethyltitanium complex: Application to ethylene–propylene–diene or ethylene–propylene–norbornene terpolymers

Copolymerization behavior of ethylene (E) and propylene (P) using ansa‐dimethylsilylene(fluorenyl)(amido)dimethyltitanium complex was investigated. P was more reactive than E regardless of the chain‐end monomer unit, which was very unusual in the coordination polymerization system. The terpolymerizations of E, P and norbornene (NB) or 5‐ethylidene‐2‐norbornene (5E2N) were also performed. The each content in the E/P/NB terpolymer was independently controlled by the initial concentration of NB and E/P feed ratio. Glass transition temperature (T_g) of the terpolymer was raised in proportion to the NB content and close to that of the corresponding NB/E random copolymer with the same NB content. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 685–691     

The effect of electron beam irradiation on dynamic shear rheological behavior of a poly (propylene‐co‐ethylene) heterophasic copolymer

In this study the effect of electron beam irradiation on rheological properties of a poly (propylene‐co‐ethylene) heterophasic copolymer is evaluated. Using dynamic viscoelastic measurement in the linear viscoelastic range of deformation, it is observed that the complex viscosity and dynamic modulus of polypropylenes were decreased by increasing the irradiation dose. Polypropylene heterophasic copolymers consist of ethylene propylene rubber phase dispersed in polypropylene homopolymer matrix. The high energy electron beams simultaneously affect both isotactic polypropylene (iPP) matrix and ethylene propylene dispersed phase. The molecular chains of polypropylene homopolymer phase breakdown to smaller species, those are prone to degradation and branching as well. Increase in the melt flow rate behavior and shifting the cross‐over point to higher frequencies and increase in melt strength are due to this phenomenon. At the same time, the ethylene propylene phase of the polypropylene copolymer cross‐links due to irradiation, and a significant effect on the rheological behavior of samples are observed. The mathematical modeling of complex viscosity behavior revealed the conformity of experimental data with modified Carreau equation. Copyright © 2010 John Wiley & Sons, Ltd.     

A WAXD/SAXS/DSC study on the melting behavior of Ziegler–Natta and metallocene catalyzed isotactic polypropylene

A small- and wide-angle X-ray scattering study was performed on two metallocene catalyzed isotactic polypropylene (miPP) resins. The results were compared with two similar molecular weight Ziegler–Natta catalyzed isotactic polypropylene (zniPP) materials. Wide-angle X-ray diffraction (WAXD) results showed the existence of two crystalline structures in the metallocene samples, the α-monoclinic and γ-orthorhombic crystal structure, with increasing relative amounts of γ-orthorhombic phase as the lamellae thickness increased. Differential scanning calorimetry (DSC) scans exhibited a melting peak for each crystal structure. The metallocene resins had the same equilibrium melting temperature (186 ± 2 °C) as the high tacticity Ziegler–Natta (ZNHT) resin, whereas a second Ziegler–Natta resin had a lower equilibrium melting temperature (178 ± 2 °C). The equilibrium melting temperature for the γ-orthorhombic crystal structure in the metallocene resins was found to be 178 ± 4 °C. The results were explained by the distribution of defects within the miPP chains, generating higher fold surface free energies for the miPP resins. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3050–3064, 1999     

Poly(1‐hexene) with long methylene sequences and controlled branches obtained by a thermostable α‐diimine nickel catalyst with bulky camphyl backbone

1‐Hexene polymerizations catalyzed by α‐diimine nickel complexes after activation with modified methylaluminoxane were performed at various reaction temperatures. Effects of catalyst structure and polymerization temperature on activity and polymer microstructure were evaluated in detail. Bulky catalyst 1b with camphyl backbone exhibited good control ability and greatly enhanced thermal stability to be capable of polymerizing 1‐hexene at 80°C. The poly(1‐hexene)s with long methylene sequences and dominate branches (methyl and butyl) were synthesized using catalyst 1b . Differential scanning calorimetry analysis further confirmed that long polymethylene block (? (CH₂)_n? , n > 20) was formed in the poly(1‐hexene)s with melting point of 64°C obtained by catalyst 1b on the basis of initial branched model polyethylene. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Crystallization behavior and morphological development of isotactic polypropylene with an aryl amide derivative as β‐form nucleating agent

This article reports crystallization behaviors of isotactic polypropylene (iPP) with an aryl amide derivative (TMB‐5) as β‐form nucleating agent. The effects of nucleating agent concentration, thermal history and assemble morphology of nucleating agent on the crystallization behaviors of iPP were studied by differential scanning calorimetry, X‐ray diffraction, and polarized optical microscopy. The results indicated that the TMB‐5 concentration should surpass a threshold value to get products rich in β‐iPP. The diverse morphologies of TMB‐5 are determined by nucleating agent concentration and crystallization condition. At higher concentrations, the recrystallized TMB‐5 aggregates into needle‐like structure, which induces mixed polymorphic phases on the lateral surface and large amount of β modification around the tip. High β nucleation efficiency was obtained at the lowest studied crystallization temperature, which is desirable for real molding process. TMB‐5 prefers to recrystallize from the melt at higher concentration and lower crystallization temperature. The difference in solubility, pertinent to concentration and crystallization temperature, determined the distinct crystallization behaviors of iPP. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1725–1733, 2008