Reactive Compatibilization of Poly(trimethylene terephthalate)/Polypropylene Blends by Polypropylene‐graft‐Maleic Anhydride. Part 2. Crystallization Behavior

The crystallization behavior of uncompatibilized and reactive compatibilized poly(trimethylene terephthalate)/polypropylene (PTT/PP) blends was investigated. In both blends, PTT and PP crystallization rates were accelerated by the presence of each other, especially at low concentrations. When PP content in the uncompatibilized blends was increased to 50–60 wt%, PTT showed fractionated crystallization; a small PTT crystallization exotherm appeared at ～135°C besides the normal ～175°C exotherm. Above 70 wt% PP, PTT crystallization exotherms disappeared. In contrast, PP in the blends showed crystallization exotherms at 113–121°C for all compositions. When a maleic anhydride‐grafted PP (PP‐g‐MAH) was added as a reactive compatibilizer, the crystallization temperatures (T _c ) of PTT and PP shifted significantly to lower temperatures. The shift of PTT's T _c was larger than that of the PP, suggesting that addition of the PP‐g‐MAH had a larger effect on PTT's crystallization than on PP due to reaction between maleic anhydride and PTT.

The nonisothermal crystallization kinetics was analyzed by a modified Avrami equation. The results confirmed that PTT's and PP's crystallization was accelerated by the presence of each other and the effect varied with blend compositions. When the PP content increased from 0 to 60 wt%, PTT's Avrami exponent n decreased from 4.35 to 3.01; nucleation changed from a thermal to an athermal mode with three‐dimensional growths. In contrast, when the PTT content increased from 0 to 90 wt% in the blends, changes in PP's n values indicated that nucleation changed from a thermal (0–50 wt% PTT) to athermal (60–70 wt% PTT) mode, and then back to a thermal (80–90 wt% PTT) mode. When PP‐g‐MAH was added as a compatibilizer, the crystallization process shifted considerably to lower temperatures and it took a longer crystallization time to reach a given crystallinity compared to the uncompatibilized blends.     

Self‐Toughening and Self‐Reinforcing Injection‐Molded Isotactic Polypropylene via Midfrequency Vibration Field

The effect of vibration frequency on the mechanical properties of general grade polypropylene (PP) prepared by two types of vibration injection molding (VIM) was investigated. With the application of vibration injection molding, the mechanical properties of isotactic PP are improved. The yield strength was upgraded with the increment of vibration frequency and a peak occurs at a particular frequency for each VIM. The elongation at break was also raised by increased vibration frequency, and the vibration frequency also improves impact strength. Self‐reinforcing and self‐toughening polypropylene molded parts were found at high vibration frequency. The wide angle X‐ray diffraction (WAXD) curves and scanning electronic micrograph (SEM) micrographs have shown that, in the vibration field, the enhancement of mechanical properties can be attributed to the occurrence of a γ‐phase crystalline structure and a more pronounced elongation in shape than obtained by conventional injection moldings. In addition, smaller crystals of the β‐phase crystal form improve toughness.     

Crystallization Kinetics of Linear and Long‐Chain Branched Polypropylene

Isothermal crystallization kinetics of linear polypropylene (PP) and long‐chain branched (LCB) PPs were investigated on the basis of the Avrami theory. The Avrami exponents of LCB PPs are smaller than that of linear PP; moreover, they decrease with an increasing LCB level. The crystallization half‐time of LCB PP depends more strongly on the crystallization temperature than does that of linear PP. The Lauritzen‐Hoffman theory was used to study the effect of LCB on the crystal growth rate of PP. The fold surface free energy of LCB PP is lower than that of linear PP; moreover, it decreases with an increasing LCB level. However, when the LCB level is over a certain value, the fold surface free energy increases again. Furthermore, the crystal structures of linear PP and LCB PPs were studied by wide‐angle X‐ray diffraction (WAXD); it was observed that linear PP can crystallize in the α and β forms, while LCB PPs have only the α crystalline form. Moreover, the relative intensities of different α peaks were also influenced by the LCB level.     

Shear‐Enhanced Nucleation of Isotactic Polypropylene in Limited Space

The nucleation rate was measured by directly counting the number of nuclei, which were developed while an isotactic polypropylene melt was flowing under shear in a thin film. The nucleation rate was enhanced with an increased rate of shear, e.g., by a factor of 10 larger at the rate of shear of 14 s^?1 compared with the quiescent state, at 134°C. The ratio of the shear‐enhanced nucleation rate to the nucleation rate in the quiescent state was larger at a higher temperature of crystallization, i.e., about 10 times at 134°C to 590 times at 140°C. The increase of the nucleation rate under shear flow was explained by a reduction of the lateral and end (fold) surface free energies; the product σ _s ² σ _e decreased to 3.2×10^?7 for the sheared melt, from 6.0×10^?7 (J m^?2)³ for the isotropic state. The free energy reduction was caused by transition of the nucleus formation mode from three‐dimensional folded chain nuclei to two‐dimensional bundle nuclei, in which chains lie down on the glass substrate, aligning parallel to the flow direction.     

Synthesis and Thermal Behavior of Silica‐Graft‐Polypropylene Nanocomposites Studied by Step‐Scan DSC and TGA

Silica graft poly(propylene) (silica‐g‐PP) nanocomposites were successfully prepared by radical grafting copolymerization and ring‐opening reaction. Their thermal properties were studied by step‐scan differential scanning calorimetry (SDSC) and thermogravimetric analysis (TGA). The exothermic peaks in the IsoK baseline (C_p,IsoK, nonreversing signal) of SDSC reveal that PP and silica‐g‐PP nanocomposites undergo melting‐recrystallization‐remelting during heating. The peak temperatures of recrystallization and remelting shift upward with the existence of nanoparticles in the PP matrix. The thermal degradation kinetics of silica‐g‐PP nanocomposites were investigated using nonisothermal TGA and the Flynn‐Wall‐Ozawa method. The results indicate that the thermal stability was significantly improved with increasing silica content, mainly because of the physical‐chemical adsorption of the volatile degradation products on the nanoparticles that delays their volatilization during decomposition, and the covalent interaction between nanoparticles and PP chains, which will also reduce the breakage of PP backbone chains.     

Investigation of the Melt‐Crystallization of Polypropylene by a Temperature Slope Method

Abstract

To investigate the in‐situ ordering process of isotactic polypropylene (iPP) from a melt state, a stationary growth front was prepared by the temperature slope crystallization (TSC) method. During the melt‐crystallization, iPP was crystallized into the α‐phase or β‐phase depending on the crystallizing conditions. The mechanism of the melt‐crystallization at the growth front was precisely observed by wide‐angle and small‐angle x‐ray scattering (WAXS and SAXS) using a strong synchrotron beam. In the TSC apparatus, the sample was crystallized in between a heater, controlled to 220°C, and a cooler, cooled by water to 25°C. We define the z‐axis parallel to the temperature gradient. A‐lamellae and B‐lamellae are also defined as those whose lamellar normal are perpendicular and parallel to the z‐axis, respectively. In a sample‐stop (SS) stage before the TSC, the original α‐phase lamellae became thicker, approaching to the melt‐solid boundary by annealing. The annealing process showed that the α‐phase B‐lamellae remained and the SAXS reflection was stronger on the meridian near the melt‐solid boundary in the SS stage. In the beginning of the TSC, the α‐phase B‐lamellae developed as a primary crystallization. During secondary crystallization under high supercooling, the SAXS cross pattern appeared showing that the α‐phase developed both A‐ and B‐lamellae. As the growth direction of A‐lamellae is parallel to the z‐axis, A‐lamellae grow faster than B‐lamellae. By the self‐epitaxial mechanism on the side surface of the A‐lamellae, the B‐lamellae grow on the base of the A‐lamellae. Following appearance of a spontaneous β‐nucleus, the β‐phase lamellae grew preferentially, excluding the α‐phase, and occupied the whole area of the sample. In this case also, A‐lamellae are advantageous to grow because of the growth direction parallel to the z‐axis. As a result, the SAXS β‐phase reflection appeared on the equator.     

The Preparation and Study on Ultrahigh Molecular Weight Polypropylene Gel‐spun Fibers

A novel polypropylene (PP) fiber was prepared by using gel spinning/crystallization from dilute solutions of ultrahigh molecular weight isotactic polypropylene (i‐UHMWPP), and subsequently drawing at various temperatures. The influence of drawing temperature on the properties of the resulted fibers was investigated. We found that the draw‐ability and mechanical as well as crystallization properties of the fibers obtained were dramatically improved with increasing drawing temperature. When the drawing temperature is below the α‐crystal relaxation temperature of PP, which was measured by wide‐angle X‐ray diffraction (WAXD) analysis as 100–120°C, the fibers are characterized by lower crystallinity and smaller crystals with less perfection, resulting in brittle fracture and subsequently poor mechanical durability. With drawing at temperatures above the α‐crystal relaxation temperature of PP, a novel UHMWPP fiber with Young's modulus of 27 GPa and tensile strength of 1.3 GPa was obtained. Higher crystallinity and larger crystals with better perfection and orientation were observed in this fiber.     

Dielectric Spectroscopy of Anisotropic Polypropylene/Nylon‐66 Blends Containing Carbon Black

The relationships of the dielectric properties and structure of polypropylene (PP)/nylon (Ny) blends containing carbon black (CB) were studied. Dielectric anisotropy was found in blends exhibiting an oriented fibrillar Ny network covered by CB particles. In the Ny fibril direction the composites are conductive, while in the perpendicular direction they are insulating, as indicated by the different frequency dependence of the AC conductivity in the two orthogonal directions. However, once CB is located within both the Ny and the PP the dielectric behavior is isotropic. This was further confirmed by Cole‐Cole plots, which, for the first time, were found to fit numerical predictions of the “resistor‐capacitor” (RC) model. The CB network formed upon the surface of the Ny fibrils is denser and/or better structured than that formed within the Ny phase. Thus, the former can be envisioned as a 2D system, as suggested by the values of the scaling exponents of the AC conductivity and permittivity with frequency, which have a lower activation energy for charge transport. The dielectric measurements were found helpful in elucidating the CB network structure.     

Correlation Between Structural and Dynamic‐Mechanical Transitions of Different Syndiotactic Polypropylene Polymorphs

Abstract

We prepared several well‐characterized syndiotactic polypropylene (sPP) polymorphs so as to correlate their thermal and dynamic‐mechanical behaviors. A sample was crystallized in pure form I at 100°C; a second sample containing only the trans‐planar mesophase was prepared by directly drawing a quenched sample at 0°C; a third sample, drawn at room temperature, contained both the trans‐planar mesophase and a fraction of the helical form II. By annealing this sample at increasing temperatures, we obtained a series of samples containing either trans‐planar mesophase, or form II and form I crystallinities.

In the dynamic‐mechanical analysis, the sample containing form I crystallinity showed only the amorphous glass transition, at 19°C, before melting at a high temperature. The trans‐planar mesophase transformed, at temperatures higher than 50°C, into the helical forms, and this transition was completed at 80°C. The dynamic mechanical curve of the sample containing only the mesophase showed a peak, centered at 50°C, which could be clearly associated to this transition. The sample containing the trans‐planar mesophase and the helical form II, showed in the dynamic‐mechanical curve a third peak that can be associated with the melting recrystallization of form II into the most stable form I. These results are important, because it was possible to directly correlate the structural transitions of the sPP polymorphs to the dynamic‐mechanical behavior. Moreover, a dynamic‐mechanical analysis could help recognize the presence of the trans‐planar mesophase or of the helical form II in more complex structural organizations.     

Reaction‐Induced Phase‐Separation in Polyoxyethylene/Polystyrene Blends. II. Structure Development

Abstract

The morphology development in model polymer blends was investigated in relation to the processing pathway. Reaction‐induced phase separation was used to make polyoxyethylene (POE) and polystyrene (PS) blends from a solution of POE/styrene. As the styrene underwent polymerization by photo‐initiation with ultraviolet light, phase separation, and phase inversion were induced, whereby the POE became the matrix phase. Optical microscopy showed that liquid–liquid (L–L) phase separation occurred soon after the styrene polymerization was initiated. Nucleation and growth was identified as the mechanism of L–L phase separation. Polystyrene/styrene‐rich domains formed in a POE/styrene‐rich matrix. The domain size developed until arrested by the POE liquid–solid phase separating and crystallizing, since the experiments were conducted below the melt temperature of POE. The POE crystal growth process also followed a nucleation and growth mechanism. The time to the onset of crystallization was observed to decrease as the POE content increased, until the POE formed a saturated solution in styrene. As the crystallization onset time decreased, the PS‐rich domain size also decreased. The phase diagram previously established can now be used to describe (and predict) the number density and size of the PS‐rich domains in the POE matrix of the blends.     

Second‐Order Dispersion Forces. I. Equations of Motion

Equations of motion for polarization on the S–P atomic transition in a weak resonance field have been derived taking into account the Van der Waals interaction between atoms. The case of two atoms is considered within the Wigner–Weisskopf formalism and generalized to the case of identical atoms in a weak resonance field, where the saturation is negligible. It is found that two equations of motion are necessary: one of them for the polarization and another one for an effective polarization relaxation rate.     

Nonisothermal Crystallization Nucleation of In‐Situ Fibrillar and Spherical Inclusions in Poly (Phenylene Sulfide)/Isotactic Polypropylene Blends

Nonisothermal crystallization nucleation and its kinetics of in‐situ fibrillar and spherical dispersed phases in poly (phenylene sulfide) (PPS)/isotactic polypropylene (iPP) blends are discussed. The PPS/iPP in‐situ microfibrillar reinforced blend (MRB) was obtained via a slit‐die extrusion, hot stretching, and quenching process, while PPS/iPP common blend with spherical PPS particles was prepared by extrusion without hot stretching. Morphological observation indicated that the well‐defined PPS microfibrils were in situ generated. The diameter of most microfibrils was surprisingly larger than or equal to the spherical particles in the common blend (15/85 PPS/iPP by weight). The nonisothermal crystallization kinetics of three samples (microfibrillar, common blends, and neat iPP) were investigated with differential scanning calorimetry (DSC). The PPS microfibrils and spherical particles could both act as heterogeneous nucleating agents during the nonisothermal crystallization, thus increasing the onset and maximum crystallization temperature of iPP, but the effect of PPS spherical particles was more evident. For the same material, crystallization peaks became wider and shifted to lower temperature when the cooling rate increased. Applying the theories proposed by Ozawa and Jeziorny to analyze the crystallization kinetics of neat iPP, and microfibrillar and common PPS/iPP blends, both of them could agree with the experimental results.     

Polypropylene–MAlN (M = Ti,Cr) interface interactions

We have studied the influence of transition metal (M = Ti, Cr) and nonmetal (N, O) valence electron concentration, surface defects, and radicals on the interaction of polypropylene and cubic M_0.5Al_0.5N (002) and (111) surfaces using ab initio calculations. For the ideal and defected surface, the work of separation is low and not affected by valence electron concentration, implying weak interactions. Striking differences occur for radicals, where an increase by two orders of magnitude is observed. This may be understood based on the electronic structure. Radicals give rise to strong bonding across the interface and hence strong interactions.     

Rheological Properties,Morphology, and Thermal Performance of E‐MA‐GMA/PC Blend

Blends of ethylene–methyl acrylate–glycidyl methacrylate terpolymer (E‐MA‐GMA, a random terpolymer) and polycarbonate (PC) were prepared in a Haake torque rheometer and the rheological properties, phase morphology, and thermal behavior were investigated. The graft reactions of PC terminal hydroxyl groups with the epoxy groups of E‐MA‐GMA and the in situ formation of the E‐MA‐GMA‐g‐PC copolymers at the interface were illustrated by the improved mixing torque and melt viscosity in E‐MA‐GMA/PC blends. Typical variation and significant deformation of the dispersed phase was observed in E‐MA‐GMA/PC blends with different composition, where PC was the matrix. With the E‐MA‐GMA content increasing, a complex co‐continuous phase structure with some dispersed E‐MA‐GMA particles wrapped in the continuous PC phase was present, indicating strengthened interfacial adhesion. When the E‐MA‐GMA content was higher than the PC component, fibrous structure of the dispersed PC phase in the E‐MA‐GMA matrix was caused by shear flow and interfacial interaction. DSC studies showed that the melting point of E‐MA‐GMA shifted to lower temperature with the increase of PC content, indicating that the enhanced interaction and graft structure hindered the process of crystallization and crystal growth.     

Electrospinning of Continuous,Large Area,Latticework Fiber onto Two‐Dimensional Pin‐array Collectors

The fiber spinning technique of electrospinning has been optimized in order to prepare unidirectionally aligned and structurally oriented fibers. For this paper, we designed a new device based on a 2D period collector fabrication and electrostatic fields analysis to obtain a large area latticework fibers pattern. The pattern was composed of polyvinylpyrrolidone (PVP)‐based sub‐micron fibers with diameters ranging from 910 nm to 1300 nm, which have potential applications in tissue cell cultures.     

Proton and Carbon‐13 NMR Studies of the Phencyclone Adducts of Medium Alkyl Chain‐Length N‐n‐Alkylmaleimides. Hindered Rotations and Magnetic Anisotropic Effects. Ab initio Calculations for Optimized Structures

Abstract

The Diels–Alder adducts, 3a–e, of phencyclone, 1, have been prepared from a series of N‐n‐alkylmaleimides, 2, with medium chain‐length n‐alkyl groups. The maleimides were obtained by cyclodehydration of the N‐n‐alkylmaleamic acids, 4, formed from reaction of maleic anhydride with the corresponding n‐alkylamines. The five adducts prepared included derivatives from n‐heptyl, 3a; n‐octyl, 3b; n‐nonyl, 3c; n‐decyl, 3d; and n‐dodecyl, 3e. The NMR spectra of the adducts were studied in CDCl₃ at ambient temperatures at 300 MHz for proton and 75 MHz for carbon‐13, with full proton assignments achieved by high‐resolution COSY45 spectra for the aryl and the alkyl regions. Slow exchange limit (SEL) spectra were observed for both ¹H and ¹³C spectra showing slow rotation on the NMR timescales of the unsubstituted bridgehead phenyl groups. Endo Diels–Alder adduct stereochemistry was supported by striking magnetic anisotropic shielding effects in the ¹H spectra of the alkyl groups, with the NCH₂ CH ₂ signal of each adduct appearing upfield of tetramethylsilane (TMS) at ca. ?0.32 ppm. Proton NMR spectra for precursor maleamic acids and maleimides are reported, with some solvent effects found (CDCl₃ vs. d ₆‐acetone) for the carbon‐bound HC?CH protons of 4. Ab initio molecular modeling calculations at the Hartree‐Fock level using the 6‐31G* basis set have been performed for two key conformers of the phencyclone adduct of N‐n‐octylmaleimide, as a representative structure for these hindered adducts, to estimate geometric parameters for the adduct. A syn conformer, with the alkyl chain directed into the adduct cavity, was found to be ca. 0.23 kcal/mol lower energy than an anti conformer (in which the alkyl chain was directed away from the phenanthrenoid moiety).     

Structural Characterization of RF‐Sputtered a‐C:N Thin Films by Raman,IR, and X‐ray Reflectometry Spectroscopies

Abstract

Amorphous carbon nitride thin films (a‐C:N) were deposited from a carbon target, at room temperature onto silicon substrates, by reactive RF sputtering in a gas mixture of argon and nitrogen. The structural properties of these films have been studied by Raman, infrared (IR), and X‐ray reflectometry spectroscopies. Both the IR and Raman spectra of the a‐C:N films reveal the presence of C–C, C?C, C?N, and C≡N bonding types. The Raman spectra analysis shows, an increase of the C≡N triple bonds content when the concentration of nitrogen C(N₂) in the gas mixture is increased. The Raman intensities ratio between the disorder (D) and graphitic (G) bands increases with C(N₂) suggesting an increased disorder with the incorporation of nitrogen in the carbon matrix. The effect of C(N₂) on the density of a‐C:N films was also investigated by X‐ray reflectometry measurement. The increase of the nitrogen concentration C(N₂) was found to have a significant effect on the density of the films: as C(N₂) increases from 0 to 100%, the density of the a‐C:N films decreases slightly from 1.81 to 1.62 g/cm³. The low values of density of the a‐C:N films were related (i) to the absence of C–N single bonds, (ii) to the increase of disorder introduced by the incorporation of nitrogen in the carbon matrix, and (iii) to the presence of the bands around 2350 cm^?1 and 3400 cm^?1 associated with the C–O bond stretching modes and the O–H vibration, respectively, suggesting a high atmospheric contamination by oxygen and water. The presence of these bands suggests the porous character of the studied samples.     

Electroluminescence and Spectral Properties of N9‐Isobutyl‐2‐Oxo‐3‐Phenyl‐3N‐Benzo[F]Chromene‐9‐Sulfonamide

Experimental data on the synthesis and spectral properties (UV, IRFourier, xray photoelectronic, and luminescence spectra) of the sulfonamide derivative of benzocoumarin in an isopropanol solution and in a film applied by thermal vacuum deposition (TVD film) are reported. The use of TVD films of the investigated substance as electroluminophors is shown to be promising.