Temperature‐Sensitive Amorphous Polyurethanes

Abstract

Shape‐memory polymers based on segmental polyurethanes (PUs) were synthesized from 1,3‐butane diol (1,3‐BD), hexamethylene diisocyanate (HDI), and 4,4′‐diphenylmethane diisocyanate (MDI), and characterized in terms of thermomechanical, dynamic mechanical, rheological, and thermal properties. It was found that soft segments (1,3‐BD and HDI) and hard segments (1,3‐BD and MDI) were well phase mixed to give a single glass transition temperature (T _g) that was easily controlled by hard segment content. With the increase in hard segment content, T _g, melt viscosity, rubbery plateau, modulus, relaxation time, and shape recovery increased, and shape fixability for repeated cycles decreased.     

Effect of Stereodefects Distribution on Rheological Behavior of Isotactic Polypropylene

A series of five isotactic polypropylenes (iPP) used commercially for producing biaxial oriented polypropylene film (BOPP), which had similar average degrees of isotacticity but different stereodefects distribution, was studied. Xylene solubles (XS) at different temperatures and high temperature solution ¹³C NMR were used to characterize the stereodefects distribution of the five samples. These samples gradually became more random following the order of sample A to E. The plateau modulus (G ⁰ _N ≈ 0.2 MPa at 190°C) of these samples was lower than those of metallocene-catalyzed polypropylenes with very narrow molecular weight distributions (MWD) (G ⁰ _N ≈ 0.4 MPa at 190°C), indicating that the influence of MWD on G ⁰ _N cannot be neglected. The storage modulus and complex viscosity of the five samples decreased gradually with the widened stereodefects distribution, due to the formation of a less constrained network that finally caused the reduction of G ⁰ _N and the increase of the flow activation energy. The rheological behavior of the BOPP resin samples could be well related to the results of XS and ¹³C NMR, implying that the rheological measurement can be adopted as a simple and efficient method to characterize the stereodefects distribution of isotactic polypropylene.     

Effect of Surface Structure of Nano-CaCO3 Particles on Mechanical and Rheological Properties of PVC Composites

To study the effect of different surface structures on resultant mechanical and rheological properties, nano-CaCO₃ particles were treated with isopropyl tri-stearyl titanate (H928), isopropyl tri-(dodecylbenz-enesulfonyl) titanate (JN198), and isopropyl tri-(dioctylpyrophosphato) titanate (JN114). Scanning electron microscopy (SEM) and dynamic mechanic analysis (DMA), carried out to characterize the effective interfacial interaction between the nano-CaCO₃ particles and a poly(vinyl chloride) (PVC) matrix, indicated that JN114 treated nano-CaCO₃ particles had the strongest interfacial interaction with a PVC matrix, while H928 treated nano-CaCO₃ had the weakest. The rheological and mechanical properties of PVC/nano-CaCO₃ composites were investigated as a function of surface structure and filler volume fraction. The tensile yield stress and elongation at break decreased with the increasing of calcium carbonate content while tensile modulus increased. PVC filled with JN114 treated nano-CaCO₃ had the highest tensile modulus and tensile yield stress, while those filled with H928 treated nano-CaCO₃ had the highest elongation at break at the same filler content. The impact strength of PVC/nano-CaCO₃ composites increased with the increasing of CaCO₃ content, and PVC composites filled with JN198 treated nano-CaCO₃ particle had a higher impact strength than those with JN114 or H928 treated, with the value reaching 23.9 ± 0.7 kJ/m² at 11 vol% CaCO₃, four times as high as that of pure PVC. Rheological properties indicated that a suitable interfacial interaction and a good dispersion of inorganic filler in a PVC matrix could reduce the viscosity of PVC/nano-CaCO₃ composites. The interfacial interaction was quantitatively characterized by semiempirical parameters calculated from the tensile strength of PVC/nano-CaCO₃ composites to confirm the results from the SEM and DMA experiments.     

Rheological Characterization of Poly(3,3′-Diaminodiphenylsulfone Terephthaloylchloride) Solutions in Dimethylsulfoxide

Steadyshear and oscillatory shear rheological measurements were performed to characterize the solution rheological behavior of poly(3,3′-diaminodiphenylsulfone terephthaloylchloride) (P(3,3′-DDS-TPC)) in dimethyl sulfoxide (DMSO). The effects of temperature, concentration, and weight-average molar mass () on the rheological properties were investigated. From the temperature dependence of zero-shear viscosity, the flow activation energies, E_η, of P(3,3′-DDS-TPC)/DMSO solutions were calculated. Both the overlap concentration, C*, and the entanglement concentration, C_e, were determined from the concentration dependence of the specific viscosity η_sp. All the P(3,3′-DDS-TPC) solutions, we studied, can be separated into three regimes: the dilute, semidilute-unentangled, and entangled regime with slopes of 1, 1.3, and 3.9, of concentration versus η_sp plots, respectively, which are consistent with scaling predictions for flexible polymers in a good solvent.     

Synthesis and surface properties of submicron barium sulfate particles

Barium sulfate particles were synthesized in the presence of EDTA at room temperature. X-ray diffractometry (XRD), Fourier transform infrared resonance (FTIR) and scanning electron microscopy (SEM) were used to characterize the structure and morphology of BaSO₄ particles. The effect of the preparation parameters on the particle size distribution and morphology was investigated. The conditional formation constants of Ba-EDTA at different pH values were calculated. The results show that the size and morphology of BaSO₄ particles can be effectively controlled by adding EDTA in the precipitation process. Among all the operation conditions, the pH value has significant effect on the particle size. The obtained barium sulfate particles are spherical and well dispersed at pH = 9-10. Zeta potentials of BaSO₄ were measured at different pH. The isoelectric point (IEP) of barium sulfate colloid appears at pH 6.92. The model of the solid-solution interface at a particle of BaSO₄ was presented. The FTIR result indicates that the surface of the prepared BaSO₄ absorbs the functional groups of EDTA, which lower the IEP of the barium sulfate particles.     

Drastic change of rheological behaviour of Precipitated Calcium Carbonate (PCC) formulations induced by water sorption onto mineral filler surface

The water sorption properties of Precipitated Calcium Carbonate (PCC) formulations have been studied in relation to the rheological behaviour. Uncoated mineral fillers (median diameter 0.85 μm) have been dispersed in an organic liquid used as plasticizer, a dioctylphthalate (DOP), at a concentration of 25% by weight (volume fraction of about 11%). Water sorption isotherms onto PCC in air and in the organic matrix have been constructed. Measurement of water concentration in the DOP permits a complete evaluation of water exchanges at the inorganic (mineral)/organic (plasticizer) interface. Evolutions of yield stress, storage modulus and loss modulus have been determined as functions of the water activity in the system. A drastic change of rheological properties has been observed for water activities above 0.3.     

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.     

Synthesis of nanoparticles and its effect on properties of elastomeric nanocomposites

Calcium carbonate (CaCO₃) nanoparticles (9, 15, and 21 nm) were synthesized by solution spray of CaCl₂ and NH₄HCO₃ with sodium lauryl sulfate (SLS) as a stabilizing agent, and their effect was studied on polybutadiene rubber (PBR) with variations in wt% loading (4, 8, and 12%). The results of PBR nanocomposites were compared with commercial CaCO₃ (40 μm) and fly ash (75 μm) filled PBR microcomposites. Properties such as tensile strength, young modulus, elongation at break, glass transition temperature, decomposition temperature, and abrasion resistances were determined. Profound effect in properties was observed, because nanometric size of CaCO₃ particles synthesized using solution spray technique. Maximum improvement in mechanical and flame retarding properties was observed at 8 wt% of filler loading. This increment in properties was more pronounced in 9-nm size CaCO₃. The results were not appreciable above 8 wt% of nanofillers because of agglomeration of nanoparticles. In addition, an attempt was made to consider modeling Young’s modulus of PBR–nano CaCO₃ which was predicted by modified Halpin–Tsai equation. It was observed that the predication by the Guth equation and modified Halpin–Tsai equation agreed very well with experimental, whereas the Halpin–Tsai equation can only applied to predict the modulus of rubber nanocomposites in the range of low addition of nanofiller, which agrees the Nielsen equation.     

Surface modification of Mg2B2O5 whisker and its effect on the mechanical properties and thermostability of polycarbonate/Mg2B2O5w composites

The Mg₂B₂O₅ whiskers (Mg₂B₂O₅w) were modified by boric acid ester (BE) coupling agent and used to prepare polycarbonate (PC) composites. Surface wettability test and evaluation of dispersibility of BE-modified Mg₂B₂O₅w (BE-Mg₂B₂O₅w) in n-heptane were carried out by water contact angle measurement and polarizing microscopy, respectively. The surface chemical characteristics of BE-Mg₂B₂O₅w and estimation of the amount of tightly bonded organic modifier were examined by Fourier transform infrared spectrometry (FT-IR) and thermogravimetric analysis (TGA), respectively. The influence of BE-Mg₂B₂O₅w on the mechanical property, morphology and thermostability of PC composites was investigated by using universal testing machine, scanning electron microscopy (SEM), dynamic mechanical analysis (DMA) and TGA, respectively. It was found that BE was successfully grafted to the surface of Mg₂B₂O₅w, and the hydrophobic BE-Mg₂B₂O₅w leads to high ratio of adhesion work to interfacial tension between PC and BE-Mg₂B₂O₅w, and its better dispersibility in n-heptane. Furthermore, the incorporation of BE-Mg₂B₂O₅w into PC matrix resulted in higher tensile properties of PC/BE-Mg₂B₂O₅w than that of PC/Mg₂B₂O₅w composites and lower maximum weight loss rate than that of PC. The storage modulus of the PC/Mg₂B₂O₅w composites increased obviously as a function of whisker content, especially for the composites with BE-Mg₂B₂O₅w, but the T_g value changed little.     

Morphology,miscibility and mechanical properties of PMMA/PC blends

This study deals with some results on morphology, miscibility and mechanical properties for polymethyl methacrylate/polycarbonate (PMMA/PC) polymer blends prepared by solution casting method at different concentration between 0 and 100 wt%. Dynamic storage modulus and tan δ were measured in a temperature range from 30 to 180°C using dynamical mechanical analyzer (DMA). The value of the storage modulus was found to increase with the addition of the PC in the matrix. Transition temperature of pure PMMA and pure PC is found to be 83.8 and 150°C, respectively. The result shows that the two polymers are miscible for whole concentration of PC in PMMA. The distribution of the phases in the blends was studied through scanning electron microscopy (SEM). Also the mechanical properties like elongation at break and fracture energy of the PMMA/PC blends increase with the increase in concentration of PC in PMMA.     

Melt blends of san with phenoxy

Melt blends of styrene-co-acrylonitrile (SAN) with phenoxy were prepared over a full range of compositions and were evaluated in terms of morphological, rheological, thermal, and mechanical properties. Viscosity-composition plots showed a crossover with the additivity line at 50/50 (SAN/phenoxy by weight), and deviations from semicircles in Cole‐Cole plots were seen for 70/30, 50/50, and 30/70 blends. Scanning electron micrographs (SEM) of the blends showed a two-phase morphology with a finer dispersion and well-elongated fibrils seen when SAN formed the dispersed phase. The glass transition temperature (T _g) of SAN was almost unchanged in the blends, whereas T _g of phenoxy was increased over 5°C. Tensile modulus and strength generally showed synergistic effects in phenoxy-rich blends. In the 10/90 blend, the ultimate elongation was greater than for pure phenoxy, and a dramatic drop of Izod impact strength was observed.     

Rheological Investigations of Copolymers of N-(Substituted Maleimide)s with Styrene in Dimethylsulfoxide

The viscoelastic behavior of poly(N-(4-formylphenoxy-4′-carbonylphenyl)maleimide-co-styrene) and poly(N-(4-carboxyphenyl)maleimide-co-styrene) in dimethylsulfoxide is investigated. The rheological parameters (elastic modulus, viscous modulus, loss tangent) were determined at different temperatures in the range 20°C–80°C. Poly(N-(4-carboxyphenyl)maleimide-co-styrene) exhibits a Newtonian behavior in the frequency range from 0.05 to 700 rad/s at all temperatures. For poly(N-(4-formylphenoxy-4′-carbonylphenyl)maleimide-co-styrene), a shear thinning behavior was observed at temperatures below 40°C (pseudoplastic behavior), whereas at higher temperatures the sample exhibits Newtonian flow throughout the studied frequencies range. The activation energies of the flow (calculated by using the zero shear viscosity values) give indications about the intensity of polymer-polymer interactions as a function of the maleimide monomer structure.     

Structural parameters, electronic structures, elastic stiffness and thermal properties of M2PC (M=V, Nb, Ta)

Using pseudo-potential plane-wave method based on the density functional theory in conjunction with the generalized gradient approximation, structural parameters, electronic structures, elastic stiffness and thermal properties of M₂PC, with M=V, Nb, Ta, were studied. The optimized zero pressure geometrical parameters are in good agreement with the available results. Pressure effect, up to 20 GPa, on the lattice parameters was investigated. Electronic properties are studied throughout the calculation of densities of states and band structures. The elastic constants and their pressure dependence were predicted using the static finite strain technique. We performed numerical estimations of the bulk modulus, shear modulus, Young's modulus, Poisson's ratio and average sound velocity for ideal polycrystalline M₂PC aggregates in framework of the Voigt-Reuss-Hill approximation. We estimated the Debye temperature and the theoretical minimum thermal conductivity of M₂PC.     

Thickness dependence of elastic modulus of polycarbonate interphase

The oligomer of bis-phenol A (oligo-PC) with M _w = 1300 and bis-phenol A polycar-bonate (PC) with M _w = 20 000 were deposited onto E-glass surface using SiCl₄ as the grafting and cross-linking agent. Thickness of the deposited layers was varied from 30 to 10⁶ nm and the layers were investigated as prepared and after thermal annealing at 245°C for 10 min in the air. Vibrational piezoelectric resonator technique and the speed of Rayleigh wave measurement were used to determine elastic moduli of the ultra thin layers deposited on flat E-glass substrate as a function of their thickness. In all cases, increase of the Young modulus of the interphase, E _i, with decreasing layer thickness, t _i, was observed. At a given thickness, the E _i of PC layer was significantly lower than that for the oligo-PC layer. Thermal annealing of the deposited PC layer resulted in a significant increase of its E _i compared to the as received layer. No significant change was observed for oligo-PC interphases. Increase of the shear strength of the interface, τ _a, with reducing interphase thickness, t _i, was observed. The observed increase of E _i with the decreasing t _i was ascribed to the reduction of the molecular mobility of chains near solid surface compared to their mobility in the bulk. Most probably, the observed increase of E _i after thermal annealing of PC was caused by rearrangement of both segment density distribution in individual PC coils near the solid surface and cooperative rearrangements of multiple PC chains. Since the oligomers attached to the surface attained presumably more regular extended conformations with lower conformation entropy compared to the PC random coils, the effect of thermal annealing was negligible. In agreement with theoretical predictions, increase of E _i at the same extent of interfacial interactions resulted in the observed increase of the τ _a measured using the single embedded fiber test.     

Morphology and dynamic mechanical properties of poly(acrylonitrile-butadiene-styrene)/polycarbonate/clay nanocomposites prepared by melt mixing

The morphology and dynamic mechanical properties of poly(acrylonitrile-butadienestyrene) (ABS)/polycarbonate (PC)/clay nanocomposites were investigated. From the studies of the transmission electron microscopy (TEM) analysis of the ABS/PC (70/30 wt%) nanocomposites with clay, it was observed that most of the clay existed in the ABS phase and the interface of the ABS and PC. From the studies of the scanning electron microscopy (SEM), droplet size of the PC in the ABS/PC/clay nanocomposites did not change significantly with the clay and has been found to be from 1.0 to 1.5 μm when the clay was added up to 5 phr. The small difference of the droplet size of the PC was maybe due to the similar values of the viscosities of the dispersed phase (PC) and continuous phase (ABS). From the dynamic mechanical properties of the ABS/PC/clay nanocomposites, the storage modulus was increased by the addition of the clay at the rubbery state between 120 and 150°C. From the studies of the tan δ of the ABS/PC/clay nanocomposites, it was shown that double tan δ peaks were observed. The height of the lower temperature tan δpeak was decreased from 4.5 to 3.3 when the clay was increased up to 5 phr. The decrease of the height of the lower tan δ peak in the ABS/PC/clay nanocomposites suggested that the ABS chain motion was restricted by the clay in the ABS phase.     

Mechanical,Thermal, and Surface Properties of Ultrahigh Molecular Weight Polyethylene/Polypropylene Blends

Various compositions of ultrahigh molecular weight polyethylene/polypropylene (UHMWPE/PP) blends were prepared in decalin, with the rheological, mechanical, thermal, and surface properties of the blends being determined using the solution cast film. Viscosity and mechanical properties of the blends decreased below the additivity value with increasing PP content implying that PP molecules disturb the entanglement of UHMWPE. Contact angle of the blend films with a water drop increased with increasing content of PP. The atomic force microscope (AFM) images showed that the surface of cast UHMWPE was very smooth whereas that of cast PP was very uneven. For blends, the surface became rough and uneven with increasing content of PP. The melting temperature of PP (T _mP) decreased in the blends with increasing UHMWPE content while that of UHMWPE (T _mU) remained almost constant in blends.     

Effect of viscosity ratio of the components of thermoplastic and liquid-crystalline polymer blends on the properties

The effects of viscosity ratio on the rheological and mechanical properties of the blends of four thermoplastics of low viscosity and a liquid crystalline polymer (LCP) were studied. A polyamide of reduced crystallinity (amorphous PA), a polycarbonate (PC), a polyethylene-terephthalate (PET), and a cyclic polyolefin (COC) were investigated with the copolymer of 2-hydroxy-6-naphthoic acid (HNA) and 4-hydroxybenzoic acid (HBA) (Vectra A type LCP). The LCP content changed in the range of 0–50 w/w%. The mechanical properties were determined by tensile tests on injection molded test bars in parallel and perpendicular directions to the flow. Except for the PC/LCP blends, the viscosity decreased with increasing LCP content, the tensile strength increased significantly in the parallel and decreased in the perpendicular direction indicating formation of fibrillar phase morphology. In the case of PC/LCP blends, a reinforcing effect was observed at low LCP contents, but above 20 w/w% the viscosity increased and the parallel tensile strength dropped to the value measured in the perpendicular direction. The loss of the reinforcing effect might originate from chemical reactions of the two polymers.     

Mechanical Properties,Rheology, and Crystallization of Epoxy-Resin-Compatibilized Polyamide 6/Polycarbonate Blends: Effect of Mixing Sequences

Blends of polyamide 6 (PA6)/polycarbonate (PC)/epoxy resin (EP) were melt blended with three different mixing sequences. Their mechanical properties, crystallization, and rheological behaviors, as well as the morphology, were investigated via mechanical testing, differential scanning calorimetry (DSC), dynamic rheometry, and scanning electron microscopy (SEM). It was noted that the mixing sequences affected the distribution of EP in the PA6 matrix, as well as the reactivity of EP with PA6 and PC. Mechanical testing showed that the blends prepared by the first (S₁, blending PA6, PC, and EP simultaneously) and second mixing sequences (S₂, blending PC with a premixture of PA6/EP) had higher notched Izod impact strengths due to the formation of PA6-EP-PC block copolymer (named as the AEC structure) during compounding, as evidenced by the results of dynamic rheology and SEM. Whereas for the third sequence (S₃, blending PA6 with a premixture of PC/EP), EP could barely react with PA6 and PC, leading to little formation of AEC structure, which resulted in a poor notched Izod impact strength of the blends. The incorporation of EP actually acted as a plasticizer to improve the elongation at break of the S₃ blends. In addition, the DSC results and SEM observations showed that there were distinct differences in the crystallization and morphology of the samples prepared by the different mixing sequences.     

Determination of elastic constants of Na0.5Bi0.5TiO3 from ab initio calculations

Elastic constants and bulk modulus for the tetragonal, rhombohedral, and cubic phase of Na_0.5Bi_0.5TiO₃ crystal were calculated from the first principles. From the calculated elastic constants, other structural properties such as bulk modulus, shear modulus, Young's modulus, and Poisson's ratio can be derived using respective relationships from Voight–Reuss–Hill approximation; bulk modulus was calculated as an example in this article. It was shown that elastic constants show different behavior for compression and elongation. The different values of elastic constants have been calculated for the direction parallel to the bismuth layer (crystallographic a(b)-axis) and the perpendicular direction (crystallographic c-axis). It seems to be caused by bismuth layer structure oxides of Na_0.5Bi_0.5TiO₃ crystal.