Dissipative crystallization of aqueous mixtures of potassium salts of poly(riboadenylic acid) and poly(ribouridylic acid)

Dissipative drying patterns of aqueous mixtures of potassium salts of poly(riboadenylic acid) (KPolyA) and poly(ribouridylic acid) (KPolyU) were studied on a cover glass, a watch glass and a glass dish at room temperature. Accumulation of the polymers forming the broad rings near the outside edge and the inner area of the dried film was observed. The fine multiple ring structures formed when the affinity of the polymer with the substrate is strong. Microscopic drying patterns changed drastically depending on the location in the dried film. Microscopic drying patterns were mainly dendritic long rods and sword (halberd)-like rods. They are assigned to the crystals of double-stranded and triple-stranded helices of the A:U and A:2U complexes, respectively. Cross-like drying patterns are also observed originated from the salt-polymer interaction.     

Dissipative crystallization of aqueous mixtures of potassium salts of poly(riboguanylic acid) and poly(ribocytidylic acid)

Drying patterns of aqueous solutions of potassium salts of poly(riboguanylic acid) (KPolyG), poly(ribocytidylic acid) (KPolyC), and their mixtures KPolyG + KPolyC were studied on a cover glass, a watch glass, and a glass dish at room temperature. Accumulation of the polymers forming the broad rings near the outside edge and also in the inner area of the dried film was observed. The fine multiple ring structures formed, which supports the fact that the affinity of the polymer with the substrate is strong. Typical microscopic drying patterns of KPolyG, KPolyC, and KPolyG + KPolyC were spherulites, dendritic long rods, and sword (harberd)-like rods, respectively. The patterns changed depending on the location in the dried film. The dendritic long rods and sword-like rods were assigned to the crystals of double-stranded and/or triple-stranded helices of the G:C and 2G:C complexes. Cross-like drying patterns that originated from the salt-polymer interaction are also observed. The relationship between the polymer complexation of KPolyG + KPolyC systems and the drying patterns is similar to that of KPolyA (potassium salt of poly(adenylic acid)) + KPolyU (potassium salt of poly(uridylic acid)).     

Dissipative crystallization of sodium salt of deoxyribonucleic acid

Drying patterns of aqueous solutions of sodium salt of deoxyribonucleic acid (NaDNA) were studied on a cover glass, a watch glass, and a Petri glass dish at room temperature. Orientation of the rod-like single crystals of NaDNA molecules in the radial direction was observed especially at low polymer concentrations. The ratios of the size of the broad ring against initial size of the liquid on a cover glass and a watch glass were very small between 0.05 and 0.1 compared with those of the typical polyelectrolytes. Main cause is the compact conformation of NaDNA forming single or double stranded helix structures in the dried film. Microscopic drying patterns were long rods accompanied with the many short rods especially on a cover glass. Thick and short rods and dendritic crystals were fogrmed at the inward and outward areas of the dried films, respectively, on a watch glass and a Petri glass dish. Rod-like and dendritic crystals resembled the distorted hedrite and/or spherulite structures. Dissipative crystallization such as the orientation and accumulation of the single crystals of NaDNA were observed and the importance of the convectional and sedimentation processes was demonstrated during the course of crystallization.     

Dissipative crystallization of sodium salts of poly (d-glutamic acid), poly (l-glutamic acid), and their low molecular weight analogs

Drying dissipative patterns were observed at room temperature on a cover glass, a watch glass, and a Petri glass dish during the course of dryness of aqueous solution of sodium salts of poly (d-glutamic acid), poly (l-glutamic acid), and their low molecular weight analogs, monosodium d-glutamate, monosodium l-glutamate, and monosodium dl-glutamate. The low molecular weight analogs were hygroscopic and their drying patterns were observed in a dry box coexisted with the bags of desiccant. The broad rings, which are the typical macroscopic drying patterns, were observed for all the samples. Optical isomeric effects on the drying patterns were not recognized. Spherulite (or hedrite) and rod-like crystals from the assemblies of helical main chains of the polymers are formed mainly at the inner area from the broad ring (except central area) and the broad ring area, respectively. Coexistence of sodium chloride enhanced the crystal structures by the cooperative interactions between the polymers and the salts. The typical dissipative crystallization such as accumulation, segregation, and orientation effects of crystals were observed in the drying patterns.     

Cooperativity length evolution during crystallization of poly(lactic acid)

Effects of stereoregularity and crystallization mode on the amorphous phase dynamics are investigated for poly(lactic acid) PLA. An isothermal crystallization from the melt and a cold crystallization are imposed. For each PLA, the cold crystallization leads to the appearance of a less perfect crystalline phase and to an important rigid amorphous fraction RAF content (35%), although only 10% of RAF is generated after crystallization from the melt. Temperature Modulated Differential Scanning Calorimetry is used to determine the Cooperative Rearranging Regions (CRR) size at the glass transition temperature in the mobile amorphous phase MAP. It is shown that the CRR size in the MAP is not modified by the appearance and the spherulite growth. For the intra-spherulite MAP, a confining effect is evidenced, causing an amorphous phase thickness decrease during crystallization, and inducing a drastic CRR size reduction.     

Mixing of perfluorooctanesulfonic acid (PFOS) potassium salt with dipalmitoyl phosphatidylcholine (DPPC)

Perfluorooctane-1-sulfonic acid (PFOS) is emerging as an important persistent environmental pollutant. To gain insight into the interaction of PFOS with biological systems, the mixing behavior of dipalmitoylphosphatidylcholine (DPPC) with PFOS was studied using differential scanning calorimetry (DSC) and fluorescence anisotropy measurements. In the DSC experiments the onset temperature of the DPPC pretransition (Tp) decreased with increasing PFOS concentration, disappearing at XDPPC < or = 0.97. The main DPPC phase transition temperature showed a depression and peak broadening with increasing mole fraction of PFOS in both the DSC and the fluorescence anisotropy studies. From the melting point depression in the fluorescence anisotropy studies, which was observed at a concentration as low as 10 mg/L, an apparent partition coefficient of K = 5.7 x 10(4) (mole fraction basis) was calculated. These results suggest that PFOS has a high tendency to partition into lipid bilayers. These direct PFOS-DPPC interactions are one possible mechanism by which PFOS may contribute to adverse effects, for example neonatal mortality, in laboratory studies and possibly in humans.     

Oriented crystallization of poly(L‐lactic acid) in uniaxially oriented blends with poly(vinylidene fluoride)

This article describes the oriented crystallization of poly(L ‐lactic acid) (PLLA) in uniaxially oriented blends with poly(vinylidene fluoride) (PVDF). Uniaxially drawn films of PLLA/PVDF blend with fixed ends were heat‐treated in two ways to crystallize PLLA in oriented blend films. The crystal orientation of PLLA depended upon the heat‐treatment process. The crystal c‐axis of the α form crystal of PLLA was highly oriented in the drawing direction in a sample cold‐crystallized at T_c = 120 °C, whereas the tilt‐orientation of the [200]/ [110] axes of PLLA was induced in the sample crystallized at T_c = 120 °C after preheating at T_p = 164.5–168.5 °C. Detailed analysis of the wide‐angle X‐ray diffraction (WAXD) indicated that the [020]/ [310] crystal axes were oriented parallel to the drawing direction, which causes the tilt‐orientation of the [200]/ [110] axes and other crystal axes. Scanning electron microscopy (SEM) suggested that oriented crystallization occurs in the stretched domains of PLLA with diameters of 0.5–2.0 μm in the uniaxially drawn films of PVDF/PLLA = 90/10 blend. Although the mechanism for the oriented crystallization of PLLA was not clear, a possibility was heteroepitaxy of the [200]/[110] axes of the α form crystal of PLLA along the [201]/[111] axes of the β form crystal of PVDF that is induced by lattice matching of d₁₀₀(PLLA) ≈ 5d₂₀₁(PVDF). © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1376–1389, 2008     

Fast crystallization of poly(ethylene terephthalate)

The crystallization of poly(ethylene terephthalate) (PET) was studied in the presence of nucleating agents and promoters. The effect of both by themselves and in concert was investigated using differential scanning calorimetry. The aim of this work is to find conditions of fast crystallization of PET. Sodium benzoate(SB) and Surlyn® (S) substantially increase the crystallization rate of PET at higher temperature owing to a reduction in the energy barrier towards primary nucleation, but they accelerate crystallization even more at lower temperature with an additional improvement of the molecular mobility of PET chains. Chain scission of PET caused by the reaction with the nucleating agents was proven by determination of molecular weight. The addition of S alone led to a lower reduction in molecular weight. A series of N-alkyl-p-toluenesulfonamides (ATSAs) were shown to effectively promote molecular motion of the PET chains, leading to an increase in crsytallization rate at lower temperature. A remarkable acceleration of crystallization of PET was attained at lower temperature when S and ATSA were added together. When the content of ATSA is low, S has the dominant influence due to its dual effect of decreasing energy barrier towards nucleation and promoting molecular motion of PET chains. A further increase of crystallization rate of PET was found only after an addition of ATSA of above 5 wt.%.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthdayThis work was supported by State Science and Technology Commission, and partially by National Science Foundation.     

Quiescent and strain-induced crystallization of poly(p-phenylene terephthalamide) from sulfuric acid solution

Quiescent and strain-induced crystallization of poly(p-phenylene terephthalamide) (PPTA) from sulfuric acid solution has been studied. Negative spherulites (SA-PPTA spherulites) are formed from hot concentrated solutions by cooling. The spherulite consists of radiating fibrous lamellae several hundred angstroms wide. The electron diffraction pattern indicates that PPTA molecules are oriented perpendicular to the long axes of the fibrous lamellae and that the [010] or [110] direction of the modification I crystal and [010] direction of the modification II crystal are parallel to the long axes of the fibrous lamellae. The width of the lamellae is much smaller than the chain length of the starting PPTA. It appears that hydrolysis of PPTA during melting crystallization determines the chain length, i.e., the width of the fibrous lamella. Stacked, lamellar structures like “row structures” are formed under shear. The longer axes of the fibrous lamellae are oriented perpendicular to the shear direction. It is confirmed by electron diffraction studies that the PPTA molecules are oriented parallel to the shear direction. Well-developed fibrils with the PPTA molecules oriented to the fibril axis, are formed by adding the SA-PPTA spherulites to water with vigorous stirring.     

Folded chain crystallization of poly(N-vinylcarbazole)

A study of the morphology of thermally induced crystallization in poly(N-vinylcarbazole) has shown the formation of folded chain lamellae. Diffraction analysis of multiple and single lamellae indicates a paracrystalline structure with hexagonal symmetry about the chain axis and an interchain spacing of 12.00 Å. No sharp reflections due to chain axis periodicity were observed and the chain axis period was calculated from the crystalline density extrapolated to 100% crystallinity. This gave a chain axis period/monomer unit of 2.16 Å consistent with an isotactic 3/1 screw axis and a basic trigonal structure with a = 12.00 Å and c = 6.47 Å.     

Stress-induced crystallization of poly(ethylene terephthalate)

Quenched amorphous films of poly(ethylene terephthalate) (PET) are stretched at temperatures less than T_g; changes in density, wide-angle x-ray diffraction, and small-angle light scattering are observed. The density increase upon stretching is attributed to an increase in crystallinity accompanied by an increase in the intensity of somewhat diffuse wide-angle x-ray diffraction and of both V_V and H_V small-angle light scattering patterns. The formation of oriented rodlike superstructure may be discerned from small-angle light scattering. Annealing of these samples increases the crystallinity as measured from density and leads to an increase in the perfection of crystalline and supercrystalline structure as measured by wide-angle x-ray diffraction and small-angle light scattering. The rodlike morphology changes to form spherulitelike aggregates as observed by small-angle light scattering and light micrographs. A model is proposed to explain the observations. Studies are extended to stretching films of PET above their T_g and observing changes in birefringence, density, wide-angle x-ray diffraction and small-angle light scattering as a function of elongation and stretching temperature. The formation of defomed spherulitelike superstructure may be discèrned from light micrographs. Results are compared with those obtained upon stretching films below T_g.     

Complexation between poly(acrylic acid) and poly(vinylpyrrolidone): Influence of the molecular weight of poly(acrylic acid) and small molecule salt on the complexation

Poly(acrylic acid) (PAA) with different molecular weight and poly(vinylpyrrolidone) (PVP) were prepared by free radical polymerization using 2,2′-azoisobutyronitrile (AIBN) as initiator in anhydrous methanol for PAA, and in distilled water for PVP. Then, the complexation between PAA and PVP in aqueous solution was studied by UV transmittance measurement and fluorescence probe technique. The result shows that (1) at low pH, the formation of complexation between PAA and PVP bases on the intermacromolecular hydrogen bond and the composition of the formed complex is around 3:2 (the unit molar ratio of PAA to PVP) at pH 2.60 over the range of pH investigated. (2) The cooperative interaction through the formation of hydrogen bond among active sites plays an important role in complex formation, and depends on the pH of solution, the required minimum chain length of poly(acrylic acid). (3) The hydrogen bond is not affected by small molecular salt, which only affects those carboxylic groups without forming hydrogen bond on the PAA chain.     

Crystallization kinetics of a commercial poly(lactic acid) based on characteristic crystallization time and optimal crystallization temperature

Journal of Thermal Analysis and Calorimetry - A model is proposed to fit differential scanning calorimetry (DSC) isothermal crystallization curves obtained from the molten state at different...     

Proton,phosphorus and carbon nuclear magnetic relaxation studies on the interaction of poly(riboadenylic acid) with Cu2+

Interaction between poly(riboadenylic acid) (poly(A)) and Cu²⁺ in neutral aqueous (D₂O) solution has been studied by ¹H, ³¹P, and ¹³C nuclear magnetic resonance. electron-nuclear hyperfine coupling constant and apparent electron-nuclear distances were determined by measurement of T₁ and T₂ values as a function of temperature. The apparent distance from Cu²⁺ to H(2), H(8), H(1′), and phosphorus nuclei were estimated to be 4.1, 3.7, 5.1, and 3.1 Å from these results. Cu²⁺ was found to coordinate directly to the phosphate groups of poly(A) (Type I complex). Simultaneously there are bindings of Cu²⁺ directly to one of the nitrogen atoms of adenine ring, mainly to N(7) (Type II complex) and either N(1) or N(3) (Type III complex).     

Alkaline-solution-induced crystallization in poly(butylene terephthalate)

Subtle crystalline structure changes of poly(butylene terephthalate) (PBT) specimens treated with an alkali solution at room temperature were investigated with the grazing incidence X-ray diffraction (GIXRD) analysis method. A new phenomenon was found: the aqueous alkali solution induced the crystallization of the PBT polymer. Under the GIXRD analysis condition of an incidence angle of 1°, the penetration depth of the X-ray in PBT was less than 80 μm, and this agreed well with the rough theoretical estimation. The alkali solution adopted in this study was an aqueous sodium hydroxide solution, which had a concentration of 2.5 N. Dissolved quantities of the surface layers during the alkaline treatment were found to be small. No appreciable intrinsic viscosity change due to the alkaline treatment was detected. Possible factors that might contribute to the crystallization, such as water absorption and a chemical reagent effect, were examined, and a plausible explanation for the phenomenon was developed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1938–1948, 2004     

Synthesis, characterization and hydrolytic stability of poly (amic acid) ammonium salt

A series of new poly (amic acid) ammonium salt (PAAS) precursors were prepared by incorporating different amounts of triethylamine (TEA) into terpolymer polyamic acid (PAA), which was synthesized by pyromellitic dianhydride (PMDA), 4,4’-oxydianiline (ODA) and p-phenylenediamine (PDA) in dimethylacetamide (DMAc). Then, the PAAS films were made by casting their solutions onto glass plates followed by the evaporation of the solvent. The chemical structure of PAAS films was confirmed by ¹H NMR and FTIR spectroscopy. Mechanical properties, intrinsic viscosities and solubility of PAAS precursors were examined, respectively. It was found that the intrinsic viscosity of PAA solution obviously decreased with storage time during 30 days, while no distinct changes were observed in the intrinsic viscosity of the PAAS (the mole ratio of TEA/repeating unit of PAA = 2/1) solution after 90 days. The results suggested that hydrolytic stability of the PAAS films was significantly improved as compared with that of PAA film due to the polyelectrolyte structure of PAAS. Moreover, the thermal and mechanical properties of polyimide (PI) films prepared from PAAS precursors were also investigated, respectively.