Viscometric investigation of intramolecular hydrogen bonding cohesional entanglement in extremely dilute aqueous solution of poly vinyl alcohol

An investigation of influence of cryogenic treatment on extremely dilute aqueous solution of poly(vinyl alcohol) (PVA) was performed by viscometry. The solution was frozen in liquid nitrogen or in a freezer at −25°C, then thawed at ambient temperature and concentrated by evacuation. The viscosity of the solution was measured using the dilute method. The experimental results indicated that the viscosity of the solution is related to N, the times of the freezing and thawing cycle, and the temperature for freezing. Undergoing a treatment of freezing and thawing, the viscosity of the solution is decreased, while it can be recovered the value of before the treatment as the solution had been heated at a high temperature. Thus, a conclusion may be obtained; that is, for an extremely dilute aqueous solution of PVA, which concentration is below C_gel, threshold concentration for gelation, an intramolecular hydrogen bonding cohesional entanglement can be formed by freezing as N < 5. However, in the case of N > 5, it not only formed an intramolecular hydrogen bonding but also produced an intermolecular hydrogen bonding. At the same time, the abnormal behavior of reduced viscosity of the solution in extremely dilute concentration region has been explained. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2421–2427, 1997     

Structural transformation from shish‐kebab crystals to micro‐fibrils through hot stretching process of gel‐spun ultra‐high molecular weight polyethylene fibers with high concentration solution

Structural evolution of gel‐spun ultra‐high molecular weight polyethylene fibers with high concentration solution via hot stretching process was investigated by in situ small‐angle X‐ray scattering, in situ wide‐angle X‐ray diffraction measurements, scanning electron microscopy, and differential scanning calorimetry. With the increase of stretching strain, the long period continuously increases at relative lower stretching temperature, while it first increases and then decreases rapidly at relative higher stretching temperature. The kebab thickness almost keeps constant during the whole hot‐stretching process and the kebab diameter continually decreases for all stretching temperatures. Moreover, the length of shish decreases slightly and the shish quantity increases although there is almost no change in the diameter of shish crystals during the hot stretching process. The degree of crystal orientation at different temperatures is as high as above 0.9 during the whole stretching process. These results indicate that the shish‐kebab crystals in ultra‐high molecular weight polyethylene fibers can transform continuously into the micro‐fibril structure composed mostly of shish crystals through the hot stretching process. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 225–238     

Excluded volume theory of rigid plates in solution using continuous orientation distributions

A new analytical theory has been developed for the thermodynamics of dilute‐to‐moderately concentrated solutions of rigid plates of arbitrary dimensions. The approach presented differs from most current theories by allowing for a continuous distribution of plate orientations rather than a small set of discrete orientations. With a few simple approximations, the theory is made tractable enough to allow for the straightforward determination of the thermodynamic properties. The results of the theory, which contains no adjustable parameters, are in good agreement with the results of Monte Carlo simulations of spatially sparse distributions of plates created by random sequential addition. An example set of the free energy of mixing curves and a phase diagram are also presented, and the prospects for future development of the theory are briefly discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2366–2377, 2000     

Synthesis and orientation study of a magnetically aligned liquid‐crystalline chitin/poly(acrylic acid) composite

A high magnetic field of 5 T was used to fabricate a magnetically aligned, optically anisotropic, liquid‐crystalline chitin/poly(acrylic acid) composite. The aligned mesophase was fixed by photoinitiated free‐radical polymerization. From an examination of polarized optical micrographs and an X‐ray diffraction study, a high degree of orientation of 0.70 was observed for the composite with a higher liquid‐crystalline chitin concentration (10.70 wt %); the orientation was reduced with a decreased chitin concentration at a given acrylic acid concentration. The X‐ray data for the developed composite showed a uniplanar orientation for the chitin crystallites, with its molecular long axes perpendicular to the direction of the magnetic field. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 711–714, 2003     

Poly(ethylene terephthalate) modified with aromatic bisester diamides: Thermal and oxygen barrier properties

The synthesis and properties of poly(ethylene terephthalate) (PET) copolymers containing four bisester diamide structural units are reported. Two of the bisester diamides consist of three para‐substituted aromatic rings, and the other two consist of three meta‐substituted aromatic rings. The copolymers have been characterized by nuclear magnetic resonance, differential scanning calorimetry, and dilute solution viscometry. Three of the copolymers can be compression‐molded into amorphous films for oxygen barrier testing, and one of these three films can be oriented for additional barrier testing. The three amorphous films all have lower permeabilities than unoriented PET. However, this difference diminishes upon the orientation of the polymer films. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1668–1681, 2004     

Response of a biphasic poly(n‐hexyl isocyanate)/p‐xylene solution to applied high electric fields

The effect of a high electric field on a solution of a lyotropic liquid‐crystalline polymer, poly(n‐hexyl isocyanate) in p‐xylene, was studied. The application of a high‐voltage alternating‐current electric field to the biphasic solution resulted in an elongation of the nematic domains in the field direction, the degree of elongation varying approximately with the square of the electric field. At a constant field, the extent of elongation decreased, varying inversely with the frequency in an exponential fashion. The domain structure and thus the molecular orientation were examined to explain these electric field effects. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1124–1133, 2005     

On the nature of phase separation of polymer solutions at high extension rates

Experiments with stretching moderately concentrated polymer solutions have been carried out. Model experiments were carried out for poly(acrylonitrile) solutions in dimethyl siloxane. Just the choice of concentrated solutions allowed for a clear demonstration of a demixing effect with the formation of two separate phases—an oriented polymer fiber and solvent drops sitting on its surface. An original experimental device for following all subsequent stages in the demixing process was built. It combined two light beams, one transverse to the fiber and a second directed along (inside) the fiber, the latter played the role of an optical line. This gives a unique opportunity to observe processes occurring inside a fiber. The process of demixing starts from the volume phase separation across the whole cross section of a fiber at some critical deformation and the propagation of the front of demixing along the fiber. Then a solvent cylindrical skin appears which transforms into a system of separate droplets. New experimental data are discussed based on a comparison of the current different points of view on the phenomenon of deformation‐induced phase separation: thermodynamic shift of the equilibrium phase transition temperature, growth of stress‐induced concentration fluctuations in two‐component fluids, and mechanically pressing a solvent out from a polymer network. The general belief is that a rather specific (so‐called “beads‐on‐a‐string”) structure of a filament is realized in stretching dilute solutions: beads of a polymer solution connected by oriented polymer bridges forming a single object. The situation in stretching moderately concentrated solutions appears quite different: real phase separation was observed. So, the alternative phenomenon to the formation of the “beads‐on‐a‐string” structure has been experimentally proven. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 559–565     

Micro‐FT‐IR study of stretching a single filament: Polymorphic transition in nylon 6

The polymorphic transition (γ → α conversion) in a single nylon 6 filament under stretching has been explored for the first time by using micro‐FT‐IR spectroscopy. The content of γ‐form deceases with straining while the amount of α‐form gradually increases, suggesting γ → α conversion. A two‐step mechanism, that is, melting and recrystallization, seems pertinent for the γ → α conversion considering that the γ‐form shows somewhat reversible and the α‐form keeps nearly intact upon unloading. Moreover, stress‐induced γ → α conversion at large strain can be well correlated with the molecular orientation in the amorphous phase and thus a serial arrangement between the γ crystals and amorphous phase along the stretching direction is proposed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 898–902, 2009     

Liquid‐like structure of polymer solutions near the overlap concentration

The light scattering structure factor S( q , c) has been measured for a series of concentrations near the overlap value c* for solutions of high molecular weight poly(α‐methyl styrene) in the good solvent toluene. Scattering functions near and above overlap are characterized by a maximum as a function of scattering vector q . Scattering functions have also been calculated for these conditions using the measured second virial coefficient and radius of gyration, as reported previously for dilute solutions. The scattering function is factored into an intramolecular part that is described by a Debye function with no adjustable parameters and an intermolecular part that depends on the coil–coil pair correlation function, as suggested by Flory and Bueche. The pair correlation function is calculated using the Percus–Yevick theory of liquids and the Flory–Krigbaum potential for coil–coil interactions, as suggested by Frank Stillinger. Good agreement is obtained for the most concentrated dilute solutions, but as the overlap concentration is approached significant discrepancies are observed. The thermodynamic value of the scattering function, S(0, c), is overestimated by the theory. This discrepancy is discussed in terms of the importance of three‐body interactions, the failure of the Flory–Krigbaum potential in semidilute solutions and the limited precision of the standard protocol for calculating the measured scattering function in nondilute solutions. The observed maximum in the scattering function near overlap is not quantitatively reproduced by the theory. This discrepancy is discussed in terms of the failure of the shape of the Flory–Krigbaum potential to accurately reflect the energy of overlap for chains separated by distances near twice the radius of gyration. The mean‐field nature of the potential ignores the increased probability of interactions of linear neighboring segments. Well into the overlap region, the calculated scattering function poorly describes the observed results. The failure of the Flory–Bueche approximation in semidilute solutions is discussed as well as the effect of a changing radius of gyration as a function of concentration on the intramolecular scattering function. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 703–710, 2006     

Dynamics of solutions of triblock copolymers in a selective solvent: Effect of varying copolymer concentration

We have used static and dynamic light scattering and pulsed field gradient NMR to study the effect of varying concentration on the dynamics of the triblock copolymer, polystyrene block poly(ethylene, butylene) block polystyrene (PS‐PEB‐PS), dissolved in n‐heptane, a selective solvent for the middle block. The correlation function for a dilute solution with c = 0.49 % (w/v) corresponds to the translational diffusion of micelles. At intermediate concentrations [1.1 ≤ c ≤ 2.6 % (w/v)], the correlation functions can be fitted to the sum of a single exponential and stretched exponential functions. The slower mode is due to the diffusion of polydisperse clusters formed by random association of triblock copolymer molecules and the faster one again represents micelles. A complex behavior is observed in the semidilute region [4.0 ≤ c ≤ 6.9 % (w/v)]. Three dynamic processes can be extracted from the correlation function: (i) The fast diffusive mode is the collective diffusion mode in the physical gel, (ii) the middle, relaxational mode, is probably due to the local movement of insoluble domains trapped in the network of the physical gel, and (iii) the slow diffusive mode implies the existence of large‐scale inhomogeneities in the system. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1312–1322, 2000     

Coil‐stretch transition in deformation flows

We present a novel Monte‐Carlo lattice model for the study of the coil‐stretch transition for polymer chains in deformation flows. Our results indicate that elongational flows are much more effective than shear flows in stretching polymer chains, in full agreement with experimental observation. Our model data also show that the ε˙_c∼M^−1.5 powerlaw observed experimentally for the dependence of critical flow rate on polymer molecular weight can be fully explained through a nonuniform stretching of the chain by the flow. A higher powerlaw exponent is predicted in more affine deformation cases. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2422–2428, 2000     

Alignment effect of attapulgite on the mechanical properties of poly(vinyl alcohol)/attapulgite nanocomposite fibers

Poly(vinyl alcohol) (PVA)/attapulgite (AT) nanocomposite fibers have been prepared by wet spinning. The morphology and mechanical properties of the modified PVA fibers have been characterized with transmission electron microscopy, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), birefringence measurements, and mechanical testing. The PVA/AT nanocomposite fibers show much higher tensile strength, initial modulus, and work to break than pure PVA fibers with the same draw ratio. SEM observations demonstrate that the AT nanorods can align orderly along the fiber axis by stretching and have good adhesion to the fiber matrix. The results of birefringence measurements prove that the modified fibers have higher orientation than pure PVA fibers after stretching. The results of DSC analysis indicate that the crystallinity of the PVA fibers can be increased by the addition of AT. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1995–2000, 2006     

Mechanical properties of magnetically oriented epoxy

The microstructure of an epoxy system oriented in high magnetic fields (15–25 T) has been observed to consist of highly oriented domains at the molecular level along the direction of the applied field. The changes in the microstructure have been characterized as a function of the magnetic‐field strength and have been investigated microscopically and with wide‐angle X‐ray diffraction. The mechanical properties of the epoxy have been examined in light of nanoindentation experiments at different load levels. The basic results of the experimental investigations for the effect of high magnetic fields on the structure and property of the epoxy are presented. Nanoindentation testing has revealed large differences in the nanomechanical behavior for thermomagnetically processed epoxy specimens. The differences can be ascribed to the microstructural changes (reorientation) of the polymer at the molecular level. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1586–1600, 2004     

Orientation and relaxation study of polystyrene: Polystyrene/poly(phenylene oxide) blends

Polarization modulation infrared linear dichroism has been used to study the molecular orientation and relaxation of polystyrene/poly(2,6‐dimethyl 1,4‐phenylene oxide) (PS/PPO) miscible blends, containing up to 20% PPO, during and after a rapid uniaxial deformation above T_g. In general, it is found that both the PS and PPO chain orientation functions increase with stretching rate and PPO content, and decrease with temperature. For all blends investigated, between T_g + 5 and T_g + 13 °C, the relaxation occurs at the same rate for PS and PPO and, therefore, the relaxation times calculated are similar indicating, under those conditions, a strong relaxation coupling between the two polymers at both short and long times. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1405–1415, 2000     

Restraining the aggregation of photoluminescent 1‐pyrenecarboxylic acid by hydrogen bonding to poly(methyl methacrylate)

Hydrogen bonds between the carboxylic acid in photoluminescent 1‐pyrenecarboxylic acid (PCA) and the ester carbonyl group in poly(methyl methacrylate) (PMMA) can be used to restrain the aggregation of the fluorescent PCA molecules and to enhance the emission efficiency of the resulting PMMA/PCA films. Primarily, PCA is added to PMMA in THF (or in toluene) to make homogeneous mother solutions for the further preparation of solid PMMA/PCA films. The concentration and chain conformation of PMMA in the mother solution are crucial to controlling the dispersion of PCAs in solution and, therefore, the extent of aggregation in the so‐derived films. The results from solution emissions suggest that PCAs in dilute solutions are easy to disperse, and less PMMA is required for the effective exclusion of aggregation in comparison with PCAs in concentrated solutions. In addition, the solvents THF and toluene play different roles in the arrangement of the PMMA chains and the emission behavior of the incorporated PCA in the dilute and semidilute regimes. With appropriate solution preparation conditions, the resulting films have photoluminescence quantum efficiencies ranging from 0.83 to 0.93, and the best value of 0.93 has been obtained from a film containing a small PCA content of 0.24 wt %. This result indicates that the fluorophore arrangements, rather than the content, govern the final emission efficiency. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 920–929, 2007     

Preparation and properties of high‐pretilt‐angle polyimides based on an alicyclic dianhydride and long alkyloxy side‐group‐containing diamines

A series of polyimides were prepared by a solution polycondensation reaction between 3‐carboxylmethylcyclopentane‐1,2,4‐tricarboxylic dianhydride and 4‐alkyloxybenzene‐1,3‐diamines in N‐methyl‐2‐pyrrolidone and chemical imidization with triethylamine and acetic anhydride. These polyimides possess great organo‐solubility, high optical transparency, and high pretilt angles. They are soluble not only in strong polar aprotic organic solvents such as N‐methyl‐2‐pyrrolidone, N,N‐dimethylacetamide, N,N‐dimethylformamide, m‐cresol, and 1,4‐butyrolactone but also in common low‐boiling‐point solvents such as chloroform and tetrahydrofuran, and some are even soluble in acetone. They exhibit high transparency at wavelengths greater than 320 nm. They can generate pretilt angles greater than 5°, and some can even achieve pretilt angles greater than 10°. The pretilt angle of a polyimide increases with the increasing length of the alkyloxy side group. The polyimides possess glass‐transition temperatures between 180 and 230 °C and thermal decomposition temperatures (onset temperatures) of about 435 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1943–1950, 2000     

Stress overshoot of polymer solutions at high rates of shear; Polystyrene with bimodal molecular weight distribution

Overshoot of shear stress, σ, and the first normal stress difference, N₁, in shear flow was investigated for dilute solutions of polystyrene with very high molecular weight in concentrated solution of low M PS. In the case that the matrix was a nonentangled system, behavior of overshoot was similar to that of dilute solution of high M PS in pure solvent. The magnitudes of shear, γ_σm and γ_Nm, corresponding to the peaks of σ and N₁ lay on the universal functions of γ˙τ_R, respectively, proposed for dilute solutions in pure solvent. Here τ_R is the Rouse relaxation time for high M PS in the blend evaluated from dynamic modulus at high frequencies. In the case that the matrix was an entangled system, an additional σ peak was observed at high rates of shear at times corresponding to γ_σm = 2–3. This peak can be assigned to the motion of low M chains in entanglement network. When the matrix was entangled, stress overshoot was observed even at relatively low rates of shear, say γ˙τ_R < 10⁻². This is probably due to the motion of high M chains in entanglement of all the chains. In this case the γ_σm and γ_Nm values were higher than those expected for entangled chains of monodisperse polymer in pure solvent. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2043–2050, 2000     

Styrene‐butadiene copolymers with different butadiene microstructure: Mechanical,swelling, and orientational properties

Results of equilibrium stress‐strain and swelling experiments are reported for styrene‐butadiene copolymers of varying butadiene microstructure. The orientation of polymer chains was investigated under uniaxial elongation by birefringence and infrared dichroism spectroscopies which probe orientation on a segmental scale. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2449–2456, 2000     

AC electric field‐assisted assembly and alignment of cellulose nanocrystals

In this article, we describe an efficient physical electric‐field‐assisted method to study self‐assembly and orientation of cellulose nanocrystals. When applying an alternating voltage to a cellulose nanocrystals suspension deposited onto a thin gap of coplanar lithographically patterned metallic electrodes, a highly homogeneous orientation of cellulose nanocrystals is obtained. Parameters such as strength and frequency of the applied electric field and cellulose nanocrystals aspect ratios were studied to determine how they affect cellulose nanocrystals assembly and orientation. The prepared films were analyzed by atomic force microscopy, and the results suggest that the alignment of cellulose nanocrystals generated films is greatly influenced by the frequency and the strength of the applied electric field. The orientation of cellulose nanocrystals becomes more homogeneous with increasing electric field higher than 2000 V/cm with a frequency ranging between 10⁴ and 10⁶ Hz. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1430–1436, 2008     

Oxygen‐barrier properties of cold‐drawn polyesters

The improvement of oxygen‐barrier properties of glassy polyesters by orientation was examined. Poly(ethylene terephthalate) (PET), poly(ethylene naphthalate), and a copolymer based on PET in which 55 mol % of the terephthalate was replaced with bibenzoate (PET‐BB55) were oriented by constrained uniaxial stretching. In a fairly narrow window of stretching conditions near the glass‐transition temperature, it was possible to achieve uniform extension of the polyesters without crystallization or stress whitening. The processes of orientation and densification correlated with the conformational transformation of glycol linkages from gauche to trans. Oxygen permeability, diffusivity, and solubility decreased with the amount of orientation. A linear relationship between the oxygen solubility and polymer specific volume suggested that the cold‐drawn polyester could be regarded as a one‐phase densified glass. This allowed an analysis of oxygen solubility in accordance with free‐volume concepts of gas permeability in glassy polymers. Orientation was seen as the process of decreasing the amount of excess‐hole free volume and bringing the nonequilibrium polymer glass closer to the equilibrium (zero‐solubility) condition. Cold drawing most effectively reduced the free volume of PET‐BB55. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 862–877, 2002