Small-angle x-ray scattering from poly(tetramethyl-p-silphenylene) siloxane (TMPS) fractions

Small-angle x-ray scattering studies were made on bulk-crystallized samples and annealed oriented films of TMPS. The temperature dependence of the small-angle scattering was determined over a range of annealing conditions. The effect of sample molecular weight on the small-angle peaks was also studied. The peak intensity, measured at room temperature after annealing, was strongly dependent on the annealing conditions. The position of the peak gradually moved to smaller angles (larger d spacings) as the annealing temperature was raised. Surface free energies were deduced from the melting point dependence of the crystallite size. This surface energy was found to increase with molecular weight in accord with values deduced for spherulite growth rate-temperature dependence.     

Crystallization of poly(tetramethyl-p-silphenylene)-siloxane (TMPS) polymers. Part II

The crystallization kinetics and morphology of poly(tetramethyl-p-silphenylene)siloxane spherulites have been investigated over a temperature range of 25–130°C. The effect of molecular weight on the spherulitic growth rates, ranging from the monomer to molecular weights about 10⁶, is discussed in terms of conventional rate theory. Surface free energies of crystal growth are computed on the basis of a spherulitic model in which the polymer chains are presumed to be incorporated within the lamellar crystallites which are comprised in the spherulites. Mention is made of the change in mechanical properties with molecular weight.     

In situ SAXS investigations of isothermal crystallization in poly(TMPS) fractions

The isothermal crystallization kinetics of poly(TMPS) has been measured by ISSAXS and results obtained for a molecular weight fraction (21,000) below the critical entanglement molecular weight (25,000) and another one above it (371,000). The SAXS intensity vs. time curves suggest that a single transformation mechanism exists. The SAXS long period is independent of crystallization time for both poly(TMPS) fractions. However the interlamellar thickness contribution to the long period is dependent upon molecular weight and crystallization temperature, increasing with temperature and molecular weight. The crystallite contribution also increases over the range studied. Both fractions exhibit a significant, but reversible decrease in thickness on cooling the sample from the crystallization temperature to room temperature and recyling again. The change is more pronounced for 371,000 specimen in keeping with its lower crystallinity. The path dependence of lamellar dimensions has significant implications in the morphological characterization of polymers annealed or crystallized at one temperature and then measured at another one.Paper presented at the American Physical Society March 25–29, Baltimore, MD (1985).     

Solution Blowing of Poly（dimethylsiloxane）/Nylon 6 Nanofiber Mats for Protective Applications

A new strategy was developed to fabricate superhydrophobic nylon 6 nanofibers, in which the blend solutions of poly(dimethylsiloxane)(PDMS) prepolymer and nylon 6 was spun using an innovative solution blowing process, and then the PDMS prepolymer contianning nanofibers were cured to obtain PDMS/nylon 6 nanofiber mats. Morphology, surface composition, non-wetting property and protective performance were investigated. The results showed that the addition of PDMS prepolymer improved the spinnability of the spinning solutions, and the PDMS/nylon 6 nanofibers had smooth surfaces and diameters from 100 nm to 350 nm. The presence of PDMS effectively enhanced the hydrophobicity of the nanofiber mats, showing water contact angles of 132° to 161° for PDMS contents of 1 wt% to 3 wt%. The PDMS/nylon 6 mats also possessed excellent protective and transport properties. The results indicated the potential application of the novel nanofiber mats in protective clothing.     

Spherulitic crystallization studies of poly(tetramethyl-p-silphenylene)–siloxane (TMPS). Part III

Extensive studies of the kinetics of spherulitic crystallization have been made on fractionated samples of TMPS. An analysis of these results reveals that a two-dimensional growth rate mechanism is a more likely mode of growth than a three-dimensional one. This conclusion is substantiated by experimental evidence from optical microscopy and light scattering from within spherulites. The crystallite end surface energy is found to increase as the molecular weight is raised.     

Stepwise annealing of poly(butylene terephthalate)

Annealing of poly(butylene terephthalate) (PBT) was studied by differential scanning calorimetry (DSC) and small angle X‐ray scattering (SAXS) measurement. A PBT sample was annealed at a recrystallization temperature where recrystallization occurs with a maximum rate in the heating process of the sample. In the subsequent annealing steps, the annealed sample was annealed repeatedly at the recrystallization temperatures, and the stepwise annealing sample was obtained. Peak melting temperature (T_m) and sharpness of DSC peak of the stepwise annealing sample increased with the annealing step. A high melting‐temperature sample was obtained in a short time, and T_m increased up to 238.5°C which is higher than all the T_m values that appear in the literature. The long period calculated from SAXS curves of the stepwise annealing sample increased with the annealing step. The increase of crystallite size and perfection of the crystal in the stepwise annealing process is suggested. Annealing experiment indicated that T^°_m should be higher than about 235°C. T_m increased linearly with the annealing temperature of the final step in the stepwise annealing (T_a). The equilibrium melting temperature (T^°_m) for PBT was estimated to be 247°C by the application of a Hoffman–Weeks plot to the relation between T_m vs. T_a. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2420–2429, 1999     

Study on morphology of electrospun poly(vinyl alcohol) mats

Submicron poly(vinyl alcohol) (PVA) fiber mats were prepared by electrospinning of aqueous PVA solutions in 6-8% concentration. Fiber morphology was observed under a scanning electron microscope and effects of instrument parameters including electric voltage, tip-target distance, flow rate and solution parameters such as concentration on the morphology of electrospun PVA fibers were evaluated. Results showed that, when PVA with higher degree of hydrolysis (DH) of 98% was used, tip-target distance exhibited no significant effect on the fiber morphology, however the morphological structure can be slightly changed by changing the solution flow rate. At high voltages above 10 kV, electrospun PVA fibers exhibited a broad diameter distribution. With increasing solution concentration, the morphology was changed from beaded fiber to uniform fiber and the average fiber diameter could be increased from 87 ± 14 nm to 246 ± 50 nm. It was also found that additions of sodium chloride and ethanol had significant effects on the fiber diameter and the morphology of electrospun PVA fibers because of the different solution conductivity, surface tension and viscosity. When the DH value of PVA was increased from 80% to 99%, the morphology electrospun PVA fibers was changed from ribbon-like fibers to uniform fibers and then to beaded fibers. The addition of aspirin and bovine serum albumin also resulted in the appearance of beads.     

Processing and characterization of oriented electrospun poly(vinylidene fluoride) mats

Mats of highly oriented poly(vinylidene fluoride) nanofibers were electrospun by means of a conventional electrospinning equipment; the orientation, however, was obtained using a disk collector rotating at a speed of 4000 rpm and a device that reduced the influence of air displacement during nanofiber orientation. Thermal transitions of the mats were determined by differential scanning calorimetry, the predominant crystalline phase by Fourier transform infrared spectroscopy and wide‐angle X‐ray scattering and the nanofiber orientation and morphology by scanning electron microscopy. Relative permittivity, loss index, stable remnant polarization, and coercive field of the mats were also determined and compared with those obtained for a mat electrospun at 2000 rpm and an oriented commercial film. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 000: 000–000, 2012     

Characterization of poly(methyl methacrylate) nanofiber mats by electrospinning process

In this study, the aim is to describe the influence of electrospinning parameters on the morphology, the water wetting property and dye adsorption property of poly(methyl methacrylate) nanofiber mats. Specifically, the effects of solution concentration, solvent type, applied voltage, distance between the electrodes and particulate reinforcement on the diameter and shape of the nanofibers were investigated. All poly(methyl methacrylate) nanofiber mats contained beaded nanofiber structures. With increasing the polymer solution concentration, the average fiber diameter also increased. Poly(methyl methacrylate) nanofiber mat electrospun from dimethylformamide solution resulted in thicker fibers when compared with the mat electrospun from acetone solution. Increasing the electric potential difference between the collector and the syringe tip did not increase the average fiber diameter. Besides increasing the distance between the electrodes resulted in a decrease in the average fiber diameter. When compared with PMMA nanofiber mat, thicker fibers were obtained with silica nanoparticles reinforced nanofiber mat. According to the water contact angle measurements, all poly(methyl methacrylate) nanofiber mats revealed hydrophobic surface property. PMMA nanofiber mat with the highest water contact angle gave rise to the highest dye adsorption capacity.     

Superhydrophobic fiber mats by electrodeposition of fluorinated poly(3,4-ethyleneoxythiathiophene)

The control of surface morphology and wettability is crucial in the development of superhydrophobic surfaces, which implies new strategy and molecular design. In this Article, we report the synthesis, characterization, and electrochemical properties of original 3,4-ethyleneoxythiathiophenes (EOTT) as platform molecules and its derivatives bearing a semifluorinated chain of various length (F-octyl, F-hexyl, F-butyl, and F-ethyl). We report the influence of the fluorinated chain length as well as the presence of sulfur atoms in the monomer on the surface construction and nonwetting properties of the corresponding electrodeposited polymer films. Surprisingly, these films exhibit the possibility to obtain extremely long polymer fibers with a possible control of their length by a careful choice in the monomer structure. We show that the presence of sulfur atoms in the monomer structure seems to be necessary to modulate the formation of extremely long polymer fibers by aggregation of smaller polymer fibrils. In this Article, the formation of superhydrophobic material (contact angle above 150°) for four, six, and eight fluoromethylene units but also highly hydrophobic surfaces (contact angle above 125°) from extremely short chains (two fluoromethylene units) is also demonstrated.     

Solution properties of poly(thiocarbonates)

For a series of poly(thiocarbonates) derived from bisphenol A several conformational and thermodynamic solution properties (partial specific volume, refractive index increment, effective dipole moment and characteristic ratio) were summarized. The effect of the structure, size and polarity of the different poly(thiocarbonates) side chains on these properties were analyzed. The high rotational freedom of the poly(thiocarbonate) chains, obtained from theoretical calculations, justifies the variation of the different properties experimentally obtained in the studied polymers.     

Solution properties of poly(methacrylamide)

Poly(methacrylamide) samples obtained by radical polymerization were fractionated by isothermal precipitation (formamide-methanol). Molecular weights were determined by light scattering and the Archibald approach-to-equilibrium method (in 0.4 M aqueous magnesium perchlorate), and the [η] M correlation was constructed. The characteristic ratio (C₁ = 6.1). Its temperature coefficient (dln C₁ dT ? 0) and the interaction parameters of the polymer in aqueous solutions of urea (2–8 M) and magnesium perchlorate (0.4–1.2 M) at 10–50°C were determined using analysis of the viscometric data ([η], dln [η]/dT). The data thus obtained are used to discuss the behaviour of the polymer in water.     

Effect of Solvent Annealing Temperature on Crystal Modifications and Phase Transition Behavior of Regioregular Poly（3-octylthiophene）

In present study, the effect of the solvent annealing temperature on the crystal modifications and the phase transition behavior of the subsequently dried poly（3-octylthiophene） （P3OT） film has been investigated by the combination of DSC, WAXD and FTIR techniques. When chloroform is employed as the solvent, it is unexpectedly found that form I and form II crystal modifications of P3OT could be respectively obtained by room temperature and low temperature annealing. Comparing to the mostly used solvent reported for preparing form II, i.e. carbon disulfide （CS2） which is toxic and corrosive, chloroform is less toxic and corrosive and more suitable for solution processing of P3OT. Therefore, this finding provides an alternative way to obtain form II. By temperature dependent IR spectroscopy, the structural evolution of P3OT during the form II to form I phase transition process has also been studied in detail.     

Stabilization of electrospun poly(vinyl alcohol) nanofibrous mats in aqueous solutions

<正>The stability ofpoly(vinyl alcohol)(PVA) nanofibrous mats in water media was improved by post-electrospinning treatments.Bifunctional glutaraldehyde(GA) in methanol was used as a crosslinking agent to stabilize PVA nanofiber,but fiber twinning was observed frequently,and the highly porous structure of PVA nanofibrous mats was destroyed when the crosslinked fiber was soaked in water.To overcome this shortcoming,chitosan(CS) was introduced into the PVA spinning solution to prepare PVA/CS composite nanofibers.Their treatment in GA/methanol solution could retain the fiber morphology of PVA/CS nanofibers and porous structure of PVA/CS nanofibrous mats even if they were soaked in aqueous solutions for 1 month.Scanning electron microscopy(SEM),X-ray diffraction(XRD),thermal gravimetric analysis(TGA) and differential scanning calorimetry(DSC) were applied to characterize the physicochemical structure and thermal properties of PVA nanofibers.It was found that the water resistance of PVA nanofibrous mats was enhanced because of the improvement of the degree of crosslinking and crystallinity in the electrospun PVA fibers after soaking in GA/methanol solution.     

Solution properties of poly(dialkyl-cyclohexyl) itaconates

Di(methyl-), di(ethyl-) and di(propylcyclohexyl) esters of itaconic acid were polymerized radically in bulk. The products were characterized in solution, then fractionated and the limiting viscosity number/molecular weight relations established for toluene at 25°. From extrapolations to θ-conditions, a set of σ-values from 2.75 to about 2.90 was obtained and compared with published results for poly(dicyclohexyl itaconate) [1], the first member of this polymer homologous series. The non-uniform change of unperturbed dimensions and other thermodynamic parameters are discussed in terms of chemical composition and constitution of the monomer residues.     

Solution properties of poly(dimethyl siloxane)

The solution properties of poly(dimethyl siloxane) (PDMS) were studied with light scattering (LS), gel permeation chromatography/light scattering (GPC/LS), and viscometry methods. PDMS samples were fractionated, and the weight‐average molecular weights, second virial coefficient, and the z‐average radius of gyration of each fraction were found according to the Zimm method with the LS technique. In this work, the molecular weight range studied was 7.5 × 10⁴ to 8.0 × 10⁵. Molecular weights and molecular weight distributions were determined by GPC/LS. The intrinsic viscosities of these fractions were studied in toluene at 30 °C, in methyl ethyl ketone (MEK) at 20 °C, and in bromocyclohexane (BCH) at 26 °C and 28 °C. The Mark–Houwink–Sakurada relationship showed that toluene was a good solvent, and MEK at 20 °C and BCH at 28 °C were θ solvents for PDMS. The unperturbed dimensions were calculated with LS and intrinsic viscosity data. The unperturbed dimensions, expressed in terms of the characteristic ratio, were found to be 6.66 with different extrapolation methods in toluene at 30 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2678–2686, 2000     

Lamellar thickening in nascent poly(acrylonitrile) upon annealing

No systematic study has been reported on the lamellar thickening in atactic poly(acrylonitrile) (PAN) upon annealing because PAN, in the form of solution‐cast films or their drawn products, generally shows no small‐angle X‐ray scattering (SAXS) maximum corresponding to the lamellar thickness. In this work, PAN crystals were precipitated during the thermal polymerization of acrylonitrile in solution. The nascent PAN film, obtained by the filtration of the crystal suspension, exhibited a clear SAXS maximum revealing the lamellar structure. The lamellar thickening upon annealing of the nascent PAN films was studied in the temperature range 100–180 °C, where the degradation was minimal, as confirmed by the absence of an IR absorption band at 1605 cm⁻¹ ascribed to the cyclized nitrile groups. Above 190 °C, the degradation of the samples was significant, and the SAXS became too broad to determine the scattering maximum. The long period was significantly affected by the annealing time (t_a) and the temperature (T_a). Depending on t_a, three stages were observed for the lamellar thickening behavior. The lamellar thickness stayed constant in stage I (t_a = 0.5–3 min, depending on T_a), rapidly increased in stage II (t_a = 0.5–8 min), and stayed at a constant value characteristic for each T_a at yet longer t_a's in stage III. The lamellar thickness characteristic for T_a increased rapidly with increasing T_a at 165 °C (or higher), which was 152 °C lower than the estimated melting temperature of PAN (T_m = 317 °C). A possible mechanism for such lamellar thickening in PAN far below the T_m is discussed on the basis of the enhanced chain mobility in the crystalline phase above the crystal/crystal reversible transition at 165–170 °C detected by differential scanning calorimetry and wide‐angle X‐ray diffraction. The structural changes associated with annealing are also discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2571–2579, 2000     

The crystal structure of poly(tetramethylene terephthalate)

The unit cell of poly(tetramethylene terephthalate) is triclinic with parameters a = 5.96 Å, b = 4.83 Å, c (fiber axis) = 11.62 Å, α = 115.2. β = 99.9, and γ = 111.3°; space group P1 , calculated crystalline density 1.41 g/cc. The plane of the benzene ring is found to be inclined by about 15° from the fiber axis, contributing to a shortening of the fiber period as compared to the period expected on the basis of analogy with other members of the terephthalate ester series. The remaining shortening of the fiber period occurs in the ? O? °CH₂? °CH₂? segment of the chain. No abnormally short distances among neighboring chain atoms were observed. A typical texture pattern was found in specimens of this polymer that were cold rolled and subsequently annealed. In this texture the c axis of the unit cell is highly oriented in the rolling direction; the a and b axes of the unit cell are oriented preferentially so that the terephthalate residue lies as close as possible to the plane of rolling.