Ordinary Polymer Research Articles

Mesoscopic segregation in binary liquid solutions: application of a model for block copolymers to non-macromolecular systems

In this work, an analogy between block copolymer phase behaviour and microdomain spacial organization in certain liquid organic/aqueous binary systems is discussed. The peculiar phase behaviour in block copolymers has been described by a segregation of the constituting blocks in domains of mesoscopic dimensions that do not lead to actual macroscopic phase separation, in contrast to what is observed in ordinary binary polymer mixtures. In the liquid non-macromolecular systems under investigation here, such events can be described as a self-association of the organic moiety leading to the formation of initially spherical microdomains that grow in size and progressively change their geometry into interpenetrating patterns, as one proceeds towards composition regions of low water content, until a collapse of the microdomains is reached, and a non-polar continuum is produced. At that point, a reversion in the microconfiguration of the binary mixture takes place. In this work, vibrational spectroscopic data for one of those systems, namely, tetramethylurea/water, were analysed in order to determine changes in structural/dynamic parameters throughout the whole range of solvent composition, with the aim of allowing inferences relative to organization patterns of the micro/meso-domains. Along with evidence from previous work, the results strongly suggest a close parallelism between phase behaviour in these non-macromolecular liquid systems and that observed for block copolymers.

Effects of Temperature and Molecular Weight on the Porous Structure Formation of Polymer Chemical Gels

The effects of temperature and molecular weight on the formation of inhomogeneous polymer gels, in which chemical gelation and phase separation take place simultaneously, were investigated. Slow chemical gelation by gamma ray irradiation was suitable for systematic analysis. In starting from ordinary polymer solutions, the characteristic wavenumber of the porous structure decreases very sharply with depth of temperature jump. However, with appropriate amount of pre-dose, the effects of temperature are almost taken over by those of the pre-dose. The shape of the phase boundary also contributes to this temperature insensitive region. Hence, pre-dose of polymer solutions, which induces the molecular weight build up, is an important factor that facilitates controlled preparations of inhomogeneous porous structures of chemical gel networks.

Dielectric relaxation behaviour of the side group liquid-crystalline polyacrylates having a segmented spacer

The dielectric relaxation behaviour and the alignment property of two kinds of liquid-crystalline (LC) polyacrylates, P-3EO-C6 and P-3EO-C11, having a segmented spacer, which consisted of binary components of an oligo(ethylene oxide) segment and an alkylene segment, was investigated to clarify the effect of the spacer structure on these properties. For P-3EO-C6 showing a glassy behaviour, δ-relaxation was observed in the lower temperature region compared with the case of an ordinary liquid-crystalline polymer with mesogenic side groups (SGLCP). The relaxation behaviour of the samples of both P-3EO-C6 and P-3EO-C11 indicated characteristically low values of ΔG‡. The microphase separation was supposed in the case of P-3EO-C11 to have a long alkylene segment. For the alignment behaviour of P-3EO-C6, the fully aligned sample could be achieved by applying an electric field. From these results, the advantage of the segmented spacer as an accelerator of the motion of a mesogenic group has been discussed in this paper.

Order-Disorder Transition of Symmetric Poly(styrene-b-2-vinylpyridine) in Bulk and Solution

Order-disorder transitions (ODT) of symmetric poly(styrene-b-2-vinylpyridine) in a common good solvent and bulk were determined by dynamic rheological and small-angle neutron scattering measurements. ODT conditions determined by both methods are consistent with each other and the degree of polymerization dependence of critical volume fraction in solution at almost constant temperature agrees with the theoretical prediction for semidilute solutions. However, semidilute behavior persists to a much higher concentration than for ordinary polymer solutions and the crossover from semidilute to concentrated regimes is not clear.

Chain stiffness of liquid crystalline polyesters. 1. Characteristic ratio and persistence length

Calculations of the characteristic ratios (C∞) and persistence lengths (Lp) of novel liquid crystalline polyesters (LCPEs) containing the dihydroxy-α-methylstilbene (DHαMS) fragment were performed. The RIS Metropolis Monte Carlo (RMMC) method was used. RMMC enables the direct estimation of several key conformational properties of polymer chains from atomistic simulations. Calculations were also performed for a single-chain analogue of VECTRA ™ A900 (a commercial LCPE). The results, including the similar calculated exponential decrease of C∞ and Lp with increasing absolute temperature, were very similar. The DHαMS isophthalate repeat unit, which is present at 10% by mole in the DHαMS-based LCPE, introduces ‘kinks’ and reduces the calculated C∞ and Lp to the same level as for VECTRA ™ A900. If it is replaced by DHαMS terephthalate, C∞ and Lp increase to almost 20% greater than those of VECTRA™ A900 which does not contain any moieties with a propensity to introduce kinks. Finally, DHαMS polycarbonate was calculated to be much stiffer than an ordinary random coil polymer, but much more flexible than any of the LCPEs which were modelled.

Electro-optical study of nematic elastomer gels

We report on an electro-optical study of a liquid-crystal--polymer composite system. This system is made by dissolving a small amount of acrylate monomers (8%) plus crosslinkers in a nematic liquid crystal, and then photopolymerizing the homogeneous mixture. These nematic gels show properties different from those of ordinary nematics or polymer stabilized liquid crystals. By studying the electric field induced Frederiks transition, some basic properties of the nematic gels can be deduced. We compare the experimental results to a simple phenomenological model of the nematic gel, involving a characteristic length scale of order 1 $\ensuremath{\mu}$m, which is also visible as speckles, an effective internal aligning field of a few statvolts per cm, and an increased rotational viscosity on the order of ${10}^{4}$ P. We indicate how a microscopic model might relate the first two of these parameters.

Researches on Polymer Surfaces: Structure and Dynamics. Non-linear Macroscopic Pattern Formation on Polymer Film Surface.

This article reviews non-linear macroscopic pattern formation on polymer film surfaces. As a result of solvent evaporation from a dilute polymer solution heated from below, the free surface of the as-cast polymer film undulates and exhibits a two-dimensional pattern due to the undulation. For an ordinary polymer, a hexagonal (or polygonal) pattern was obtained. This pattern, due to surface undulation, was found to be ascribed to convection existing in the solution. On the other hand, a very peculiar concentric-ring pattern was observed for an SBS film, where SBS designates polystyrene-block-polybutadiene-block-polystyrene triblock copolymers. Note that this sample forms lamellar microdomain structures with a ca. 22 nm identity period. In this pattern, a set of concentric rings contained in a cellular compartment is a unit constituent and was found to be a set of wrinkles on the surface. The mechanism of formation of the concentricring pattern is presented in this article, and moreover, control of the morphology of the pattern is discussed.

Near-IR Multiplex Bandpass Spectrometer Utilizing Polymer Filters

A simple near-infrared spectrometer is described that utilizes ordinary polymer sheets as near-IR spectral filters. Examples of filter materials include polymethyl methacrylate, polyvinyl chloride (PVC), and organic solutions immobilized in a PVC matrix. The polymers were prepared by using solvent-molding techniques as well as with a thermoforming process. Each filter substance passes multiple bands of near-IR radiation. The performance of the spectrometer is demonstrated in selected quantitative and qualitative near-IR analytical applications. The applicability of the designed multiplex bandpass spectrometer in determining trace levels of water in methanol, dimethyl sulfoxide, and propylene glycol is examined. Additionally, the utility of the spectrometer in the determination of glucose concentration in aqueous solutions is studied.

Monte Carlo simulation studies of the interfaces between polymeric and other solids as models for fiber‐matrix interactions in advanced composite materials

AbstractAs a coarse‐grained model for dense amorphous polymer systems interacting with solid walls (i.e., the fiber surface in a composite), the bond fluctuation model of flexible polymer chains confined between two repulsive surfaces is studied by extensive Monte Carlo simulations. Choosing a potential for the length of an effective bond that favors rather long bonds, the full temperature region from ordinary polymer melts down to the glass transition is accessible. It is shown that in the supercooled state near the glass transition an “interphase” forms near the walls, where the structure of the melt is influenced by the surface. This “interphase” already shows up in static properties, but also has an effect on monomer mobilities and the corresponding relaxation behavior of the polymer matrix. The thickness of the interphase is extracted from monomer density oscillations near the walls and is found to be strongly temperature dependent. It is ultimately larger than the gyration radius of the polymer chains. Effects of shear deformation on this model are simulated by choosing asymmetric jump rates near the moving wall (large jump rate in the direction of motion, and a small rate against it). It is studied how this dynamic perturbation propagates into the bulk of the polymer matrix.

Morphology of associated polymer blends: one-end-aminated polystyrene/one-end-car☐ylated or sulfonated poly(ethylene glycol)

Small-angle X-ray scattering (SAXS) profiles have been measured for blends of one-end-aminated polystyrene (APS) and one-end-car☐ylated or -sulfonated poly(ethylene glycol) (CPEG or SPEG) with weight fraction of 50/50 per cent. In the profiles of blend solutions in toluene (TL), PS/CPEG/TL and APS/SPEG/TL with solvent weight fraction of 0.2 at 80°C, there exists a scattering maximum around a Bragg spacing of 203Åfor the system containing SPEG, whereas there is no peak for the system containing CPEG. Similarly, the scattering peak is absent in the profile of the blend APS/CPEG without solvent, and is observed in that of APS/SPEG at 80°C. The APS/SPEG blend sample cooled to a temperature below the melting point of SPEG shows a more intense SAXS peak than that at higher temperature. The similarly cooled blend of APS/CPEG exhibits a weak scattering maximum, and its position is nearly identical to that of pure CPEG. From these observations and previous studies on the phase diagram of blend solutions in TL, it has been suggested that the APS/SPEG blend behaves like a diblock copolymer owing to the strong association between the terminal amino and sulfonic acid groups, and an ordered structure that is similar to those observed in diblock copolymers is formed even in bulk melt and concentrated solution. Because of the weak association between amino and car☐yl groups, the APS/CPEG system behaves like an ordinary polymer blend, and crystallization of the CPEG chain may occur in a similar manner to the homopolymer in the macroscopically separated domain.

New polymer systems exhibiting microphase separation transition with the formation of nano‐microstructures

AbstractThe concept of microphase separation was up to now widely applied mainly to the conformational transitions in block‐copolymer solutions and melts. However, recently it became obvious that this concept has a much more general meaning. It was shown that microphase separation transition can be observed in random copolymers, interpenetrating polymer networks, polyelectrolyte mixtures, poor solvent polyelectrolyte solutions, ionomer solutions and melts, polymer blends and solutions with nonlocal entropy of mixing. In all these examples the emerging microdomain structures correspond to the nanometer scale, therefore the study of these effects can lead to the new ways of obtaining polymer materials with controlled nano‐microstructure.In this presentation the review of our recent findings on microphase separation in some of the above‐mentioned systems will be presented.1. The problem of microphase separation in the systems containing weakly charged polyelectrolytes (polyelectrolyte mixtures and poor solvent polyelectrolyte solutions) will be considered. From the methodic point of view, it will be shown that this problem can be solved by direct minimization of the free energy, without the use of “weak segregation” or “strong segregation” assumptions which are common in the theory of block‐copolymers. The final phase diagrams exhibit wide macroscopic phase separation regions, which is their main difference from the corresponding phase diagrams for block‐copolymer systems. The formation of microdomains is thus coupled with macroscopic phase separation: in most of the cases microdomain structure is formed in one of the coexisting phases after macroscopic phase separation takes place [1] ‐ [2].2. The formation of the multiplet structure in ionomer melts and solutions can be also considered as the microphase separation in the random copolymer system with the formation of the “micelles” (or clusters) of ionic links. The parallels with micelle formation in block‐copolymer systems can be established if one considers a new “superstrong segregation regime” for block‐copolymer microstructures. This regime can be indeed observed for diblock copolymers with one ionomeric and one neutral block [3].3. The microphase separation transition in ordinary polymer blends and solutions is also possible. The conditions for this effect are: (i) significant entropic contribution to polymer/polymer or polymer/solvent miscibility, (ii) the nonlocal character of this contribution with a high value of the nonlocality radius. It is argued that one can expect that the entropy nonlocality radius increases in the vicinity of the glass transition for the blend or polymer solutions (in the latter case solvent molecules act like “poor solvent plasticisers”). Computer simulation data supporting the theoretical prediction of microphase separation transition in these systems will be presented [4] ‐ [5].

Intermacromolecular Complexation due to Specific Interactions. 2. Nonradiative Energy Transfer Fluorospectroscopy and Nuclear Magnetic Resonance Monitoring Miscibility-Complexation Transition

The difference in chain arrangements between ordinary miscible blends and polymer complexes could be monitored by a nonradiative energy transfer (NRET), when part of one of the constituents, i.e., poly(methyl methacrylate) (PMMA), was labeled with fluorescence donor (c) and another part with acceptor (a). In blends composed of PMMA-a, PMMA-c, and modified polystyrene [PS(OH)] carrying hexafluoro-α-hydroxypropyl groups, a gradual decrease of the energy transfer efficiency was observed accompanying the transition from miscibility to the pairing of interacting polymer chains as the hydroxyl content in PS(OH) increases, from 2 to 10 mol%. Solid-state 1 H NMR relaxation measurements failed to reflect the transition. However, evidence of complexation between PMMA and PS(OH) with a high hydroxyl content was obtained by NMR NOE measurements in the blend solutions

NMR and x‐ray studies on the morphology of thermoreversible polyacrylonitrile gels

AbstractThe morphology of thermoreversible polyacrylonitrile–propylene carbonate (PAN‐PC) gels was examined using solid‐state carbon‐13 nuclear magnetic resonance (NMR) spectroscopy and x‐ray diffraction. Following complete dissolution of the polymer at elevated temperature and cooling of the concentrated PAN‐PC solutions, a gel was formed. The PAN‐PC gels consisted of regions of mobile polymer chains, rich in PC, “cross‐linked” by regions of rigid polymer. The mobile regions of the gels showed solution‐type NMR spectra with resolution of tacticity effects. The rigid component detected by NMR would correspond to the crysttallites detected previously by x‐ray diffraction. Wide‐angle x‐ray diffractograms of the gels showed different peaks when compared with the dry polymer powder. After solvent extraction and drying of the gel, the diffractogram reverted to that of the original dry powder. This new result is the strongest evidence to support the view advanced earlier that the new peaks found in the diffraction pattern of the wet gels arises from solvated polymer crystallites rather than from ordinary polymer crystallites. © 1993 John Wiley & Sons, Inc.

Raman studies of intact and sodium doped 13C‐substituted poly‐p‐phenylene

AbstractThe Raman and infrared spectra of 13C‐substituted poly‐p‐phenylene (PPP) and the Raman spectra of Na‐doped PPP excited at 488.0 and 1064 nm were observed and compared with the corresponding spectra for the ordinary (12C) polymer. 13C substitution is shown to be useful for characterizing not only the bands of intact PPP but also those of polarons and bipolarons generated in Na‐doped PPP. The number of Raman bands observed for bioplarons (and also for polarons) is greater than that for intact PPP. This observation is explained as the result of the loss of translational symmetry in the regions of these local excitations.

A mathematical model and numerical estimation of setting stresses in polymer composites molded under hydrostatic pressure

The effect of compression molding (i.e. molding under hydrostatic pressure) on the magnitude and distribution of setting stresses in particle-reinforced polymer composites is investigated using the finite element method. Models based on fairly random arrangements of the reinforcing particles are used, with different particle size gradations, as well as different aggregate-to-resin ratios. An analytical expression of the maximum setting stresses in these composites is introduced. A non-linear constrained optimization technique is used to obtain the mathematical model parameters which aid in a reasonable numerical estimation of the maximum setting stresses in real systems. The numerical results show that externally applied hydrostatic pressure helps diminish some of the local setting stresses. However, this relief becomes insignificant at the interface between aggregate particles and the resin domains where local setting stresses are maximum. This indicates that the practice of compression molding does not have a significant effect in reducing local setting stresses in ordinary polymer concrele systems.

Universal calibration for thermal field‐flow fractionation

AbstractExperiments have shown that the thermal diffusion coefficient of a polymer is independent of the sample's molecular weight. According to the relationship between the ordinary diffusion coefficient and polymer molecular weight, a universal calibration method for thermal field‐flow fractionation (FFF) has been created. This method has been examined experimentally by three polymers of different chemical composition with different molecular weight in three organic solvents. It is shown that this method is useful both in terms of calibrating a thermal FFF system with some readily available polymer standard, for use with unknown samples of known thermal diffusivity, and in terms of determining the thermal diffusion coefficient of the unknown sample under conditions where its molecular weight can be measured by other methods.

Optically detected electron paramagnetic resonance and fluorescence study on geminate ion recombination in low-density polyethylene doped with pyrene

The optically detected electron paramagnetic resonance (ODEPR) spectrum of pyrene-doped low-density polyethylene has been studied. This is the first ODEPR spectrum observed on an ordinary polymer, and its intensity was comparable to that of spectra recorded in viscous solutions. The dependence of the ODEPR and fluorescence spectra on the concentration of pyrene as well as temperature led us to deduce the geminate recombination process in this inhomogeneous material. We found that: (1) charge recombination occurs mainly through electron hopping between the solute pyrenes. (2) Hole hopping between the pyrenes following hole transfer from the polymer matrix to the solute on the ODEPR timescale is allowed only at high temperatures and high solute concentrations.

Electrical conductivity of polydiacetylene P(4BCMU) gel: 2. A percolation model for elasticity and conductivity

Tensile stress and electrical conductivity were studied on gels formed from toluene solutions of a polydiacetylene, poly[5,7-dodecadiyn-1,12-diol-bis (n-butoxycarbonylmethyl urethane)], abbreviated to P(4BCMU). The gels exhibited stress-strain curves concave upwards, that is, opposite to the behaviour of ordinary flexible polymer networks. This behaviour indicates that the elasticity is not due to the conformational entropy due to deformation of the stiff ribbon-like P(4BCMU) molecules. The direct current conductivity σ dc, the alternating current conductivity σ ac and Young's modulus E increased with concentration C in proportion to C 0.88, C 0.89, and C 1.07, respectively. The similarity in the concentration dependences of σ dc, σ ac and E is explained with a percolation model. The σ ac was almost independent of frequency in the range of 0.1–100 kHz.

Probability theory and polymer physics

This study applies the theory of stochastic processes to the equilibrium statistical physics of polymers in solution. The topics treated include random copolymers and randomly branching polymers, with self-consistent mean field effects. A new and more natural way of dealing with Boltzmann weighting is discussed, which makes it possible from the beginning of a calculation to consider only the “physical” polymer conformations. We also show that in general the random copolymer problem can be reduced to the ordinary polymer problem, and treat the self-consistent field problem for a general branching polymer.

The sol/gel contribution to the behavior of γ‐irradiated poly(vinylidene fluoride)

AbstractPoly(vinylidene fluoride) films were γ‐irradiated in the dose range of 1–20 Mrad, resulting in up to 74% gel. The irradiated polymer undergoes both crosslinking and chain scission, about 5 : 3 events, respectively. Swelling measurements indicate an increasing crosslink density with the gel content, already at the lower doses. Thermal analysis of the gel fraction and the unextracted irradiated samples shows that although crosslinking affects the crystallization, degree of crystallinity, and the melting characteristics, the behavior of the crosslinked material is predominantly controlled by the extractable sol fraction which consists of the more mobile original chains, branched chains, and degraded ones. The crosslinks, already at low density, retard the development of ordinary crystalline polymer morphology.