Multiphase Polymer Research Articles

Formation and Properties of Model Crystalline Blends Comprising Diacetylene-Containing Polyester and Polyolefin. Tensile Behavior and Deformation Micromechanics

Model blends comprising a cross-polymerized diacetylene-containing polyester (PE) and poly-[ethylene-co-(vinyl acetate)] (EVA) were prepared and their mechanical properties evaluated. The dependence of the Young's modulus of the blends upon composition has been modeled by using a variety of theories for the deformation of multiphase polymers. Deformation of the cross-polymerized polyester phase in the blends was monitored by using Raman spectroscopy. The polyester phases within the blends produce well-defined Raman spectra in which the C?C stretching bands undergo significant stress-induced band shifts during deformation of the blends. The results show that the Raman technique allows direct measurement of the stress in the polyester phase in a blend, independent of the overall deformation of the blend. Simultaneous deformation and Raman spectroscopy studies, therefore, give a unique insight into the deformation micromechanics of polymer blends.

Fiber reinforcement and fracture resistance of PC/PBT/LCP ternary in situ composite

AbstractThe microstructures, mechanical properties, and fracture toughness of LCP (Vectra B950) reinforced PC/PBT blend with a 60/40 weight ratio have been studied. LCP of varying concentrations were investigated as rigid fillers in matrices of multiphase polymer blends. In this study, differences in microstructures and morphology between samples of two thicknesses (4 mm thick and 6 mm thick) and two geometries (dumbbell and rectangular) were compared using scanning electron microscopy (SEM). Given identical processing conditions, fibrous LCP structures were evident in the 4‐mm‐thick injection molded, dumbbell‐shaped samples, whereas the 6‐mm‐thick rectangular samples displayed spherical dispersion of LCP aggregates that embrittled the preblended ductile matrix. Tensile properties of the dumbbell specimens showed superior strengthening and stiffening whereby the tensile strength increased twofold and the modulus increased fourfold. Plane strain fracture toughness was slightly enhanced as the LCP content increased because of the fiber strengthening effect but the overall fracture performance of the in situ composites was relatively poor compared with PC/PBT. Experimental results were compared with those predicted in composite theory. Simplified micromechanics equations were developed to describe the tensile moduli of injection molded LCP reinforced blends that exhibited a strong skin‐core morphology.

高分子系多相構造：分子設計・制御・応用 多相高分子の結晶化の特性

高分子系多相構造：分子設計・制御・応用 多相高分子の結晶化の特性

Small-angle X-ray and neutron scattering studies from multiphase polymers

The thermodynamic understanding of complex polymer systems is presently undergoing important developments. Much of the experimental input is based on structural studies that use small-angle scattering of X-rays and neutrons. These techniques provide important insight into static phase behavior and polymer conformation. In recent years, dynamical aspects have also been probed by in situ studies under time-varying fields. Recent progress has been made in analysing block copolymer systems and complex polymer blends using small-angle scattering.

Phase Structure of Polymers by Dipolar-Induced Spin Diffusion: Model Spin Diffusion Calculations

The evolution of the spatial inhomogeneity of magnetization induced by spin diffusion is investigated theoretically for different models of a multiphase polymer solid. It is shown that the decay of the total magnetization associated with the domains where the magnetization initially resides is affected by the distributions in the size of the domains and the separation between them. The models examined include the two-phase/multidomain (2P-MD) case, in which the system consists of two phases with an infinite number of domains in each phase, and the two-phase/four-domain (2P-4D) model, in which the system has two phases with two domains in each. The spin diffusion equation is solved for these models by using a simple two-value distribution in the domain width or the domain separation. The solutions for the magnetization of the 2P-MD model show a slower decay in the long-time regime in comparison to those of the 2P-4D case. The solutions of the latter give a reasonable approximation to the former, provided that the spread in the distribution is sufficiently smaller than the average of the distribution. The simple two-phase/two-domain (2P-2D) model, in which the two phases are represented by a single domain each, is also investigated. In this case, the effect of the distribution is incorporated by taking an ensemble average. It is shown that there is no correct way of taking the average, and the results always yield erroneous long-time behavior for the magnetization. The results of the 2P-MD, 2P-4D, and 2P-2D models are applied to the spin diffusion experiment of a semicrystalline polypropylene film.

Electron Energy-Loss Spectrum Profiling of Polymer-Polymer Interfaces

The spatially-resolved structure and composition of amorphous or semicrystalline polymer-polymer interfaces are poorly understood. The absence of atomic-level periodicity precludes many of the transmission electron-optical techniques that have been so fruitful in studying interfaces in polycrystalline inorganic materials. Similarly, there has been relatively little work done on spatially-resolved spectroscopic analysis of polymer-polymer interfaces to determine chemical widths, largely because of concerns over electron-beam damage. Digital microscope control and parallel spectral acquisition provide for low-dose exposure, quantification of dose, and efficient data collection which open new windows to study polymer interfaces.This research is studying various multiphase polymer systems by focused-probe spectroscopic analysis to identify appropriate spectral features, data acquisition protocols, and background-modeling/data-processing algorithms in order to establish chemical widths characteristic of specific polymer-polymer interfaces (1). This research uses a 200keV Philips CM20 FEG TEM/STEM with a Gatan 666 PEELS spectrometer and an Emispec digital data acquisition/control system.

Spin diffusion and spin-lattice relaxation in multiphase polymers

A model which treats spin diffusion and spin-lattice relaxation in multiphase polymers on the same footing is proposed. This new approach allows for more accurate determination of domain sizes and interfacial thickness in the probed polymers. In a poly(styrene-b-isoprene) copolymer example a significant improvement in the agreement between the NMR measurements and the simulated results can be obtained with the incorporation of a spin-lattice relaxation term into the spin diffusion process. The obtained microphase structural parameters are similar to the small angle X-ray scattering results. In addition, the spin-lattice relaxation times (T1) in different domains can be predicted reasonably well based on T1s of the component homopolymers and on the microphase structure in the present model.

Morphological studies of Cu(I)‐complexed bipyridine‐containing block copolymers by combined transmission electron microscopy techniques

The design of molecular species which can form well‐defined macromolecular architectures by spontaneous, recognition‐directed self‐assembly of their components is a major goal in supramolecular chemistry. We synthesized block copolymers with polyether and bipyridine or oligo‐(bipyridine) containing segments where the latter could form double‐helical structures by metal complexation. Upon complexation with Cu(I) these systems showed a dramatic change in the thermal and mechanical properties from a waxy system to a thermoplastic elastomeric behaviour. This effect could be explained by the formation of a multiphase polymer system consisting of domains of bipyridine or oligo(bipyridine) Cu(I) complexes in a matrix of amorphous soft segments.In the solution‐cast films both nitrogen and copper could be detected with electron energy‐loss spectroscopy. Element spectroscopic imaging pictures of the net nitrogen and copper element distribution were identical and revealed a microphase‐separated system with identical morphological structures. High‐resolution bright‐field images revealed fine structures (interference lines) which were in accordance with stacks of [Cu(I)(bpy)2] complexes. Electron diffraction patterns showed that the supramolecular order could be perfected through annealing.

Prediction and manipulation of the phase morphologies of multiphase polymer blends: 1. Ternary systems

The dispersed phases of a multiphase polymer blend will either form an encapsulation-type phase morphology or the phases will remain separately dispersed, depending on which morphology has the lower free energy. We have developed a model to predict phase morphologies of multiphase polymer blends. Calculations based on the model suggest that interfacial tensions play the major role in establishing the phase structure of a multiphase system, with a less significant role played by the surface areas of the dispersed phases. The model further shows that the phase structure of a multiphase polymer blend can be converted from one type to another by changing the interfacial tensions between one or more pairs of the components using interfacially-active agents such as block or graft copolymers. We have applied the model to different ternary blends of polystyrene, polyethylene, polypropylene and poly(methyl methacrylate), and have compared the predicted morphologies of these blends with experimental results. In each case, the predicted morphologies agree with those found experimentally. In addition, we have successfully converted the phase structures of these blends from one type to another by using interfacially-active block copolymers.

Modulated differential scanning calorimetry: 8. Interface development between films of polyepichlorohydrin and poly(vinyl acetate)

A thermal method with the potential to determine the weight fraction and the interfacial thickness in multiphase polymer materials is described. The extent of interdiffusion, and hence the development of an interface between two miscible polymers, polyepichlorohydrin and poly(vinyl acetate), with time at 100°C has been studied by means of modulated-temperature differential scanning calorimetry. This polymer pair is known to be miscible. By measurement of the change of increment of heat capacity in the glass transition region, the total interface content can be determined. With increasing time, the interfacial thickness increases. The average interfacial thickness is about 0.1 mm after a diffusion time of 4180 min. The interfacial thickness grows at t 1 2 , where t is the diffusion time, and the interdiffusion coefficient is about 6.25 × 10 −11 cm 2 s −1, assuming that the diffusion rates of the two polymers are equal.

High-Resolution NMR Study on Hydrogen Bondings in Polyether Polyurethane Zwitterionomers

Hydrogen bondings formed in polyether-polyurethane zwitterionomers based on 4,4′-diphenylmethane diisocyanate (MDI), methyl diethanolamine (MDEA), and polytetramethylene oxide glycol (PTMO) were studied in concentrated solutions with high resolution 1H NMR spectroscopy. By comparing with the results of a previous wide line NMR study, a direct relationship was found between the degree of phase separation and the amounts of various kinds of hydrogen bondings formed in the system. The formation of hard segment micelles in concentrated solution is proved and high resolution NMR is demonstrated to be a powerful tool to study the morphology of the multiphase polymers.

Synthesis and properties of sulfonated polyurethane ionomers with anions in the polyether soft segments

A series of polyether (PTMO, PEO) polyurethane ionomers having different contents of sodium sulfonate groups in the soft segments have been synthesized. The reaction of transesterification was involved in the incorporation of the sodium sulfonate groups in the polyether. The polyurethane ionomers were characterized by means of dynamic mechanical thermal analysis, differential scanning calorimetry, and small-angle x-ray scattering. Solid-state ionic conductivity was also measured. As the ionization level increased, the compatibility of the hard and soft segments increased and the glass transition region of the soft segment became broader. These samples had relatively higher moduli and good film-forming ability. Moreover, this kind of ionomer provides a very promising ionic conductive multiphase polymer with a single ion transport mechanism. © 1997 John Wiley & Sons, Inc.

Prediction and manipulation of the phase morphologies of multiphase polymer blends: II. Quaternary systems

We have applied our model concerning the phase structures of multiphase polymer blends to quaternary blends of polyethylene, polypropylene, polystyrene and poly(methyl methacrylate) of different overall compositions. Predictions of the phase morphologies of such multicomponent blends are based on minimization of the total interfacial free energy of the system. We compare predictions of the model with experimental observations, and show agreement in every case between the predicted and experimental morphologies. Furthermore, we show that the phase structure of a quaternary blend can be converted from one type of phase morphology to another, e.g. from an encapsulation type to the dispersion type, by using an interfacially active block copolymer. This shows the possibility of adjusting the phase morphologies of multicomponent systems as desired.

The study of multiphase polymer-blend morphologies by HVEM

Multiphase polymer blends are important in the polymer industry. Most commercial blends consist of two main polymers combined with a third, compatibilizing polymer, typically a graft or block copolymer. The most common examples are those involving the impact modification of a brittle thermoplastic by the microdispersion of a rubber into the matrix. Recently, a model of ternary polymer blends has provided a wealth of morphologies for examination. Even though this model can give an excellent basis for the design of a polymer blend, experimental verification is necessary. A correlation of blend properties such as impact strength with blend morphology must also be made. The focus is to confirm the predicted morphologies in binary and ternary blends using HVEM.The polymer blends were produced by compositional quenching. In this process, the polymers were dissolved in a solvent. The solution was pumped through a heat exchanger and then flashed across a needle valve to remove the solvent.

Rheo-physics of multiphase polymer systems by K. Sondergaard and J. Lyngaae-Jorgensen, Technomic Publishing Co., Inc, Lancaster, PA, 1995, 576 pp.

Rheo-physics of multiphase polymer systems by K. Sondergaard and J. Lyngaae-Jorgensen, Technomic Publishing Co., Inc, Lancaster, PA, 1995, 576 pp.

Measuring Polymer Microstructure using Spatially-Resolved Eels in the Stem

ABSTRACTImage contrast for the examination of multiphase polymers in the transmission electron microscope (TEM) usually requires differential staining by a heavy element (Os, Ru, U). Staining methods have provided a wealth of microstructural information in polymers, but there are situations, particularly where high resolution is needed, where staining is undesirable or impossible. This research has collected microstructural information from multiphase polymers without heavy-element stains using spatially-resolved electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM). The technique is known as spectrum imaging. The principal problems facing spectrum imaging in polymer applications are: (1) the identification of spectral fingerprints distinguishing different polymer phases; and (2) the extraction of meaningful microstructural data from large data sets where the signal is weak due to instrumentation and materials constraints. This paper describes applications of spectrum imaging to PE/PS and HDPE/Nylon 6 blends. The aim is to identify adequate spectral features and establish data acquisition and extraction procedures for applications to general, unstained, multiphase polymers.

Skin-core morphology ofin situ composites based on polycarbonate and a liquid crystalline polymer

The outstanding mechanical properties of an engineering liquid crystalline polymer (LCP) can be attributed to the self-reinforcement effect due to its rigid rod-like molecular structure [1-4]. High strength and high stiffness liquid crystalline polymer fibres, e.g. Kevlar and Vectran have been developed and commercialized [5, 6]. Recently there has been increasing interest in blending thermotropic liquid crystalline polymers with conventional isotropic polymers. Liquid crystalline polymer fibre reinforcement can be formed in situ in an isotropic polymer matrix via a melt blending process [7-26]. The structure and morphology of the in situ composites may be controlled by varying the processing conditions and theological history of the blends. Blends of LCPs with conventional polyesters [7, 8], nylon [9], polycarbonate [10-13], polystyrene [11, 14], polypropylene [15, 16], polysulphone [17], poly[ether imide] [18] and poly[phenylene sulphide] [19] have been studied. For extrusion-blended materials, the structure and mechanical properties were found to be closely related to the extrusion conditions, in particular the draw-down ratio. Most researchers have attempted to explain the changes in mechanical properties in terms of the morphology of the LCP phase in the blends, with the most widely used techniques to study the morphology being scanning electron microscopy (SEM) and X-ray diffraction (XRD) [7, 12]. Transmission electron microscopy (TEM) has been widely used to study the crystalline structure of liquid crystalline fibres [4, 6, 20, 21] and the morphology of multiphase polymer systems [22]. Analysis has revealed detailed information on the crystalline structure of aramid and thermotropic liquid crystalline polyester fibres and the development of skin-core morphology of such fibres [4, 21 ]. These findings were related to the properties and sample processing conditions. The work reported in this letter is concerned with the application of the TEM technique to the analysis of blends of a liquid crystalline polymer and polycarbonate. The microstructure and morphology

Modulated differential scanning calorimetry: 4. Miscibility and glass transition behaviour in poly(methyl methacrylate) and poly(epichlorohydrin) blends

The differential of heat capacity signal, d C p/d T, from modulated-temperature differential scanning calorimetry (M-T d.s.c.) was used to elucidate the miscibility and glass transition behaviour of poly(methyl methacrylate) (PMMA) and poly(epichlorohydrin) (PECH) blends. The conclusion reached was the same as that reported by Higgins and co-workers (Clark, J.N., Higgins, J.S., Kim, C.K. and Paul, D.R. Polymer 1992, 33, 3137) from small-angle neutron scattering, but different from that of Fernandes (Fernandes, A.C. Ph.D. Dissertation, University of Texas at Austin, 1986) from a d.s.c. study. This M-T d.s.c. study reveals that PECH/PMMA blends are not fully miscible. More detailed information was obtained from the d C p/d T signal. In this blend system, there were PMMA-rich, PECH-rich phases and interfaces, indicating that the blend is partially miscible. The breadth of the glass transition region, Δ T g, can be used to judge polymer-polymer miscibility. For polymer blends, Δ T g as a miscibility criterion was considered to obey the following relation: Δ T g = w 1 Δ T g,1 + w 2 Δ T g,2 where w 1 and w 2 are the weight fractions for polymer 1 and polymer 2, and Δ T g,1 and Δ T g,2 are the glass transition widths for polymer 1 and polymer 2, respectively. Partial miscibility results in a broad transition region. The width of the transition may be indicative of the presence of microphase separation and of interfaces. The M-T d.s.c. d C p/d T signal provides increased sensitivity and resolution for studying polymer-polymer miscibility and multiphase polymer materials.

Calculation of deformative and thermal properties of multiphase composite materials filled with composite or hollow spherical inclusions by the effective medium method

A theoretical investigation was carried out to examine the possibilities of a structural approach to prediction of elastic constants, creep functions, and thermal properties of multiphase polymer composite materials filled with composite or hollow spherical Inclusions of several types. The problem of determining effective properties of the composite was solved by generalizing the effective medium method, a variant of the self-consistent method, for the case of a four-phase kernel-shell-matrix-equivalent homogeneous medium model. Exact analytical expressions for the bulk modulus thermal expansion coefficient, thermal conductivity coefficient, and specific heat were obtained. The solution for the shear modulus is given in the form of a nonlinear equation whose coefficients are the solution of a system of 12 linear equations.

Reactive recycling of multiphase polymer systems through electron beam

Recycling of polymer structural materials leads to two main obstacles: degradation of macromolecular chains and incompatibility of different polymer components. Both obstacles can be avoided by applying a reactive additive which acts as a functional compatibilizer. Electron-beam processing has been successfully applied to produce multiphase polymer composites using recycled polyester fibers, wood fibers, glass fibers and minerals as reinforcements in thermoplastic matrix.