Effect of copper (II) chelate on photodegradation of poly (1-butene)

Photo-oxidative degradation of isotactic poly(1-butene) in the presence and absence of copper (II) bis-(1,3-diphenyl triazine-N-oxide) chelate has been studied, by measuring the weight average molecular weight, measuring changes in the carbonyl groups and by measuring changes in the hydroperoxide contents in the temperature range of 267 to 313 K using monochromatic light of wavelength 253.7 nm. The mechanism leading to the stabilization observed, resulting from the addition of chelate, is discussed.     

Structural changes during photodegradation of poly(ethylene terephthalate)

An investigation has been conducted into the effects of photodegradation on the structure of poly(ethylene terephthalate) (PET). Films, with and without ultraviolet absorbers and prepared by biaxial orientation after extrusion, have been exposed in the laboratory for periods of up to 1020 hours. The samples were investigated by differential scanning calorimetry (DSC), X-ray diffraction and size exclusion chromatography. The appearance of a cold crystallization peak during DSC heating scans was noted for exposed samples and this was considered to be a result of released molecules in the amorphous region that could rearrange into a crystalline phase. From X-ray analysis, a loss of crystalline orientation was observed after degradation and an interpretation was given based on relaxation in the mesophase region. In samples containing the photostabilizer additive the magnitude of changes in structure was lower, possibly due to segregation effects during film production making the non-crystalline region relatively immune to degradation effects.     

退火温度对聚氯代对二甲苯膜性能的影响

采用化学气相沉积聚合法制备了厚度为0.082mm的聚氯代对二甲苯膜,并将其置于80～220℃Ar气气氛中恒温2h退火.采用X-射线结构衍射仪(XRD)、扫描电子显微镜(SEM)表征了其结晶度变化和表面显微结构,并对退火前后膜的拉伸强度、透气率、透明度及雾度进行了测试.结果表明,随着退火温度升高,聚氯代对二甲苯薄膜的结晶度,拉伸强度和雾度增大,并在200℃达到最高;其断裂延伸率、透明度、气体渗透率则随之降低.     

Effect of the molecular weight of poly(ethylene glycol) on the plasticization of green sheets composed of ultrafine BaTiO3 particles and poly(vinyl butyral)

The effect of the molecular weight (MW) of poly(ethylene glycol) (PEG) on the plasticization of poly(vinyl butyral) (PVB) binder in green BaTiO₃ sheets prepared with PEG with MW values of 400 and 1530 was investigated. The MW of PEG had a profound effect on the rheological properties of the suspension as well as the physical properties of the green sheet. The suspension viscosity decreased with decreasing MW of PEG for shear rates above 4 s⁻¹. PEG 400 gave rise to a higher degree of plasticization of the green sheet than PEG 1530. This was due to the reduction in hydrogen bonding between the vinyl alcohol units in the PVB binder in the green BaTiO₃ sheet, as identified by FT-IR spectroscopy. As the MW of the PEG decreased, the green BaTiO₃ sheets exhibited a lower glass transition temperature, and a noticeably more ductile behavior. These results indicate that the green sheets became more flexible due to a higher plasticizing effect. However, laminated green BaTiO₃ sheets prepared with PEG 1530 showed delamination defects that were observed at a cut surface, which arose because of the low plasticization. This suggests that PEG 1530 has limited utilization as a plasticizer for the BaTiO₃/PVB binder system.     

Effect of supporting electrolyte on the polymerization of electrochemically deposited poly(o-anisidine) films

Poly(o-anisidine) films deposited galvanostatically exhibit the formation of different oxidation states of the polymer with varying pH of the solution. The influence of supporting electrolyte on the extent of formation of the conducting phase at pH 2.1 has been investigated with the help of optical, thermal and potential cycling techniques. The optical spectra of the films reveal the proportionate increase in the fraction of the conducting emeraldine salt phase with the amount of supporting electrolyte (NaCl) added to the solution. Similarly, clarity in the decomposition steps of the thermal patterns and redox peaks in the cyclic voltammograms are found to increase as a function of NaCl concentration. This revised version was published online in November 2006 with corrections to the Cover Date.     

Degradation and miscibility of poly(DL-lactic acid)/poly(glycolic acid) composite films: Effect of poly(DL-lactic-co-glycolic acid)

The in vitro degradation behaviour of poly(glycolic acid) (PGA) and its composite films containing poly(DL-lactic acid) (PDLLA) and poly(DL-lactic-co-glycolic acid) (PDLGA) were investigated via mass loss, scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). All the films were prepared by solution casting, using 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as the solvent. Since the degradation rate of PDLLA is lower than that of PGA, those of the PDLLA/PGA composite films decreased. As a compatibilizer, PDLGA improved the compatibility and hydrolytic stability of PDLLA/PGA composite films. Changes in the composite films indicate that this kind of PGA-based composite biomaterial may be applicable to device design for clinical application in the future.     

Photoluminescence and Raman spectroscopy studies of the photodegradation of poly(3-octylthiophene)

This work examines the photodegradation of poly(3-octylthiophene) (P3OT) by UV-irradiation at 405 nm under vacuum and as a function of temperature (300 and 10 K). Two different P3OT films were studied. The first one was electrochemically synthesized on platinum plate and chemically reduced in a basic medium (P3OT-E) whereas the second one, chemically synthesized was spread out on glass by casting process from polymer previously dissolved in chloroform (P3OT-Q). After 200 s under UV illumination, the photoluminescence (PL) spectra observed on the P3OT-E samples showed an unexpected increase of some eight times in the emission intensity. In contrast, the PL spectra of P3OT-Q, subjected to the same temperature, pressure and photoirradiation time, showed a drop of to around half the initial signal intensity. Similarly experiments were performed at low temperature 10 K. In this temperature condition, PL spectra of P3OT-E and P3OT-Q obtained under photoirradiation, presented similar decreases of the intensity of their fluorescence. In order to explain these different results, Raman spectroscopy studies had been performed, and it was been possible to follow the formation of C=O group on the side alkyl chain after 200 min of irradiation. From the results obtained, we proposed a mechanism to explain the unexpected intensification of the PL emission signal for P3OT-E at 300 K. This mechanism was based on the destabilization of the charge transfer complex between the radical cations in P3OT-E and the residual dioxygen.     

Effects of plasticization on the piezoelectric properties of nylon 11 films

Nylon 11 films (-form) were plasticized by immersion in 2-ethyl 1,3 hexanediol. Two different kinds of studies were performed. In the first study, poled nylon 11 films were plasticized by immersion in the plasticizer for different lengths of time. The piezoelectric strain constant,d ₃₁, initially increased up to a plasticizer content of 14% (by weight) and then decreased. The values of piezoelectric stress constant,e ₃₁, however, decreased with increase in dipping time. In the second study, the films were initially plasticized and then poled. Bothd ₃₁ ande ₃₁ were higher for plasticized films compared to unplasticized films under identical poling conditions. X-ray diffraction studies showed some conversion of -phase to -phase during the process of plasticization.     

Electrosyntheses of free-standing poly (dibenzofuran) films

High quality free-standing poly (dibenzofuran) (PDBF) films with conductivity of 10⁰ S cm^− 1 were synthesized electrochemically by direct anodic oxidation of dibenzofuran in mixed electrolytes of boron trifluoride diethyl etherate (BFEE) containing 30% trifluoroacetic acid (TFA) (by volume). The structure analysis of PDBF was performed using UV–vis and FTIR spectroscopy. To the best of our knowledge, this is the first report on the electrodeposition of free-standing PDBF films.     

Morphological, crystallization and plasticization studies on isomorphic blends of poly (vinyl fluoride) (PVF) and poly (vinylidene difluoride) (PVDF): using microhardness, XRD and SEM techniques

Property modification by blending of polymers has been the area of immense interest. In this paper, the isomorphic blends of two polymers poly (vinyl fluoride) (PVF) and poly (vinylidene difluoride) (PVDF) with different ratios were prepared using solution cast technique. The microhardness studies have been carried out on pure and polyblend specimens at various loads to test the plasticization and hardening effects using Vickers microhardness testing. The X-ray diffraction (XRD) study has been utilized to detect the crystalline and amorphous characteristics of specimens. Thus PVDF acts as plasticizer in the polyblend when the content of PVDF is relatively high as compare to PVF. When the PVF is major component in the polyblend, the microhardness of the blend specimen increases and the isomorphic blend specimens with 50:50 proportion of two polymers exhibit the maximum value of microhardness. Scanning electron microscopy (SEM) micrographs indicate complete chain formation with uniform texture, when the two polymers are blended in equal proportions. The findings of XRD and SEM have been correlated with the microhardness values.     

Atmospheric effects on the photosensitive response of poly(methylphenylsilane) thin films

Agile ready-when-needed patterning of refractive index structures in photosensitive materials requires an understanding of the impact of local application environment on mechanisms contributing to the desired photoinduced index change. The present work examines the impact of atmosphere on the photosensitive response of poly(methylphenylsilane) (PMPS) thin films whose high photoinduced index change under low incident optical fluence make them attractive candidates for such applications. Changes in optical absorption and refractive index are investigated after exposure to ultraviolet (UV) light resonant with the lowest energy transition exhibited by the Si–Si backbone structure in the material. A comparison between photoinduced absorption changes for thin films exposed in an air atmosphere versus those observed for samples subjected to a nitrogen environment during photoexposure is made for the first time. The study reveals that the anaerobic conditions of the nitrogen atmosphere significantly reduce the photosensitive response of the material to light. These results are discussed in terms of photooxidation processes within the polysilane structure and in the context of the need for predictable photosensitive refractive index change in varied photoimprinting environments.     

The electrical conductivity of poly(divinylbenzene) films

Conductivity measurements reported previously for thin films of poly(divinylbenzene) have been interpreted in terms of a quantum mechanical tunneling conductivity mechanism. Quantum mechanical tunneling of carriers through thin spots (5–45 Å) in films having dielectric thickness of a few hundred Å is more consistent with the reported current-voltage-temperature characteristics than the previously suggested Richardson-Schottky mechanism.     

Structural studies of poly(p-phenylene benzbisthiazole) films

Poly(p-phenylene benzbisthiazole) (PBT) is one member of a new class of highly-rigid, linear, thermally-stable aromatic heterocyclic polymers. The role of heat-treatment in the improvement of the perfection of crystallinity and mechanical properties of oriented films is discussed. Part of the heat-treatment process seems to be to increase the conjugation length of the polymer chain by increasing the planarity of the molecule, as revealed by visual colour changes and by differential scanning calorimetry. This may in turn account for the improved quality of crystallinity. Considerable detail can be seen in the electron diffraction patterns of heat-treated films. With the exception of the equatorial diffraction peaks this scatter can be accounted for by the detailed molecular transform of the PBT polymer, suitably cylindrically averaged, indicating that the crystal structure is essentially two-dimensional, that is the chains while closely and regularly packed lack longitudinal register. A two-dimensional unit cell with the corresponding molecular packing is proposed which can satisfactorily account for the observed density and for the equatorial diffraction peaks.     

Effect of annealing on phase transition in poly(vinylidene fluoride) films prepared using polar solvent

The γ-phase poly (vinylidene fluoride) (PVDF) films are usually prepared using dimethyl sulfoxide (DMSO) solvent, regardless of preparation temperature. Here we report the crystallization of both α and γ-phase PVDF films by varying preparation temperature using DMSO solvent. The γ-phase PVDF films were annealed at 70, 90, 110, 130 and 160°C for five hours. The changes in the phase contents in the PVDF at different annealing conditions have been described. When thin films were annealed at 90°C for 5 h, maximum percentage of β-phase appears in PVDF thin films. The γ-phase PVDF films completely converted to α-phase when they were annealed at 160°C for 5 h. From X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), differential scanning calorimetry (DSC) and Raman studies, it is confirmed that the PVDF thin films, cast from solution and annealed at 90°C for 5 h, have maximum percentage of β-phase. The β-phase PVDF shows a remnant polarization of 4.9 μC/cm² at 1400 kV/cm at 1 Hz.     

Further insights into the photodegradation of poly(3-hexylthiophene) by means of X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) was used to monitor the chemical changes resulting from irradiation (> 295 nm) in air of poly(3-hexylthiophene) (P3HT), polymer which is a good candidate for photovoltaic applications. The formation of carbonyl moieties and the stepwise oxidation of sulphur atoms were characterised. The oxidation and the cleavage of the hexyl side-chain was monitored. It is also shown that sulfur was first converted into sulfoxides, then into sulfones and finally into sulfinate esters. The formation of these ultimate degradation products provoked a disruption of π-conjugation in P3HT, leading to diminished visible absorbance. Based on these results, a mechanism of P3HT photooxidation is proposed. Comparison of XPS data with previously reported infrared and UV-visible spectral analysis showed that the information provided by these techniques is completely consistent.     

Biocompatibility and biodegradation of poly(hydroxybutyrate)/poly(ethylene glycol) blend films

Using chloroform as co-solvent, a series of poly(3-hydroxybutyrate) (PHB) and polyethylene glycol (PEG) blend materials with different ratio ranging from 80 : 20 (wt %) to 20 : 80 (wt %) were prepared by solution blend. The blood-compatibility was evaluated by means of platelet clotting time test and exploring its morphological changes. The results showed that PEG played an important role in resisting platelet adhesion. With the increased addition of PEG, the clotting times became longer and the number of platelet adhesion decreased apparently. All platelets were in discrete state, no pseudopodium had been found and no collective phenomenon had been happened. The cell-compatibility was evaluated via Chinese Hamster Lung (CHL) fibroblast cultivation in vitro. The cells cultured on the matrix spread and proliferated well. With the increase of PEG content in the blend films, the number of live cells became more and more. These results indicated that PHB exhibited satisfying cell-compatibility and the addition of PEG also could improve the cell-compatibility of PHB. The biodegradation experiment indicated that the degradation of PHB/PEG was accelerated by enzyme in vitro and the blending of PEG was favorable to degradation.     

Characterization of smooth muscle cells on poly(ε-caprolactone) films

Bioresorbable vascular grafts can be used for direct implantation. Over time, the grafts will degrade and be replaced by natural tissue. In this study, the potential application of biaxially drawn poly(ε-caprolactone) (PCL) films for the design of vascular grafts was examined. PCL films were first modified to enhance cell physiological response to the surface. Two methods of surface modification were studied: surface hydrolysis by immersion in sodium hydroxide, and immobilization of collagen onto PCL film surface. Tensile tests indicate that immersion in sodium hydroxide results in a significant drop in ultimate tensile strength, whereas collagen-immobilized films remained uncompromised. Human coronary artery smooth muscle cells were cultured on the different surfaces, and it was demonstrated that collagen-immobilized films elicited the most favorable response from the cultured cells. This indicates the potential for collagen-immobilized PCL films for vascular tissue engineering applications.