UV-irradiated Poly Research Articles

On improving the physical properties of poly (urethane urea)s by the inclusion of aromatic amines connected through long aliphatic chains in the hard domain

In order to improve to obtain improved physical properties, new poly (urethane urea)s were obtained by the reaction of the PCL-HDI urethane pre-polymer with poly(1,4-butanediol)bis(4-aminobenzoate (PBBA) or with PBBA and different crosslinkers. The formation of the characteristic groups (i.e. urethane and urea groups) and their non-covalent interactions (such as hydrogen bonding) were analyzed by FTIR spectroscopy. The high thermal stability of the obtained polymers (up to 300–350 °C) is the result of the PBBA structure. The incorporation of PBBA into the polymer backbone generated improved mechanical properties, with a maximum tensile strength of up to 45 MPa and elongation at break of up to 1100 %. These results can be explained by the fact that the inclusion of PBBA increased mobility of the polymer in the area of the hard domain. In addition, this study showed that a higher amount of PBBA does not further increase the mobility of the polymer material. Water contact angles were used to evaluate the hydrophobic performance of the obtained polymer films. The paper also assesses the changes in the structure and morphological appearance, mechanical properties and evolution of the sample surfaces that occurred after different periods of exposure to UV radiation in a UV illumination chamber. The behavior of UV-irradiated poly (urethane urea) films depends on the molecular structure of the hard domains. The new poly (urethane urea) materials offer attractive physical properties for new engineering applications requiring higher mechanical strength and thermal stability.

Photo-directing chemoepitaxy: the versatility of poly(aryl methacrylate) films in tuning block copolymer wetting

UV irradiated poly(aryl methacrylate) films can induce a change in the orientation of the domains of an overlayer of PS-b-PMMA from parallel to perpendicular lamellar structures.

Spectroscopic studies of UV-irradiated poly(vinyl alcohol)/elastin blends

The blends of synthetic and natural polymers are extensively investigated as materials for medical applications. Synthetic component usually ensures appropriate mechanical and physical properties while biopolymer improves biocompatibility of the material. In our work, we decided to use poly(vinyl alcohol) (PVA)—water-soluble, chemically stable, elastic polymer and elastin—a fibrous protein present in the extracellular matrix of connective tissues. The aim of our work was to study the influence of UV light on spectroscopic properties of poly(vinyl alcohol)/elastin hydrolysates blends. PVA is a rather photostable polymer while elastin possesses various chromophores in the structure capable of absorption of light λ > 200 nm. As a result of the blending, some interactions between the synthetic and biological components occur and cause the changes of photochemical stability of the new material. Our study demonstrates that the poly(vinyl alcohol)/elastin mixtures are more sensitive to UV irradiation than both components separately.

Synthesis, Characterization and Photocrosslinkable Studies of Certain Thermotropic Liquid Crystalline Poly(ester-amides)

Five thermotropic liquid crystalline poly(ester-amides) were synthesized by polycondensation method using varying dicarboxylic acids with a common diamine namely 4,4-diaminodiphenyl and a common diol namely 2,6-bis(4-hydroxy-3-methoxybenzylidene)cyclohexanone (CHBV). The solubility data and viscosity measurements of these synthesized poly(ester-amides) were used for qualitative characterization. The spectroscopic techniques such as FT-IR, ¹H NMR, ¹³C NMR were performed for investigating micro structural features. By differential scanning calorimetry (DSC), the thermal phase transition behavior of these poly(ester-amides) was studied. Scanning electron microscopy (SEM) technique was used to investigate the morphology of these poly(ester-amides). By using UV-visible spectroscopic technique, the photocrosslinkability of these poly(ester-amides) were studied by irradiating these poly(ester-amides) under a 160 W medium pressure mercury lamp. SEM analysis of these UV irradiated poly(ester-amides) showed the changes in morphology. Thus, the poly(ester-amides) containing arylidene keto moiety in the main chain exhibited nematic mesophase and were photocrosslinked upon UV irradiation. X-ray diffraction (XRD) patterns of these poly(ester-amides) were taken to assess the degree of crystallinity.<div><br></div>

Methanol-assisted crack healing in UV-irradiated poly(methyl methacrylate)

The UV irradiation can cause structural degradation of polymer and limit the applications of polymer as structural materials. In this work, the effects of UV irradiation on the mass transport and crack healing in poly(methyl methacrylate) (PMMA) are studied. The transport behavior of methanol in the PMMA plates with and without the irradiation of UV can be described by anomalous transport. Both activation energies for the case I transport and for the velocity of the case II transport decrease with the increase of the UV-dose for the UV-irradiation on either one side or both sides of the PMMA plates. The UV irradiation reduces the fracture stress of the cracked PMMA plates and retards the recovery of the mechanical strength of the UV-damaged PMMA plates in methanol due to the UV-induced structural degradation. For the methanol-assisted healing of the irradiated, cracked PMMA plates, the recovery of fracture stress is proportional to a power function of the healing time.

Surface studies of UV-irradiated poly(vinyl chloride)/poly(methyl methacrylate) blends

Surface properties of poly(vinyl chloride) (PVC), poly(methyl methacrylate) (PMMA) and their blends have been studied using FTIR-ATR spectroscopy, AFM and contact angle measurements. It was found that the surfaces of PVC/PMMA blends were enriched in PMMA, the lower surface free energy component. The results also revealed the existence of weak interactions between the blend components resulting in partial miscibility of system observed for the blends containing below 40% of PMMA.UV-irradiation made the sample surfaces more polar and rough owing to photochemical processes such as oxidation, degradation, dehydrochlorination, depolymerization or etching. The oxidation was more efficient for PVC compared to PMMA. In the case of PVC/PMMA blends, the efficiency of oxidation reactions increased with increasing PVC content and this process was approximately the average of the changes in the pure polymers. The photooxidation reactions were accompanied by degradation reactions leading to formation of low molecular weight oxidized products.AFM studies of UV-irradiated sample surfaces revealed cone-like and globular objects which were easily removed from the surfaces after washing the samples. These objects were made of low molecular weight oxidized material and/or methyl methacrylate. Only neat PMMA surface behaved contrary to all samples. It seemed that irradiation did not yield any changes in surface morphology of PMMA but washed surface of this polymer revealed presence of cone-like structures. It suggests that the mechanism of photooxidative degradation of pure PMMA and PMMA in the blends was different. Probably the presence of chlorine radicals from PVC modifies the route of PMMA photochemical processes in PVC/PMMA blends.

Effects of UV light-irradiated buffer layer on the performance of polymer solar cells

We investigate the effect of a UV-irradiated poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) buffer layer on the performance of polymer photovoltaic cells based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blends. It was found that UV irradiation can reduce the bulk and contact resistance of PEDOT:PSS films, improving the power conversion efficiency from (3.05 ± 0.04)% to (3.50 ± 0.03)% due to the lower device series resistance under an illumination of AM1.5G, 100 mW/cm 2. The work function change after UV irradiation and negligible surface morphology change was noticed.

AFM and XPS study of UV-irradiated poly(methyl methacrylate) films on glass and aluminum support

Thin poly(methyl methacrylate) (PMMA) films were obtained by casting a polymer solution in chloroform on a glass plate or aluminum foil and solvent evaporation. Next, the PMMA samples on those supports were UV-irradiated using low-pressure mercury vapor lamp emitting 254 nm radiation. The changes in chemical structure of PMMA were monitored by X-ray photoelectron spectroscopy (XPS). Photoinduced changes of the surface morphology were observed using atomic force microscopy (AFM). It was found that the support type and its surface quality has significant influence on the photochemical transformations in the investigated polymer. The high damage of polymeric surface accompanying by the efficient photochemical reactions in macromolecules were found in the case of PMMA placed on an aluminum foil, whereas the glass support exhibited lower effect on the PMMA photodestruction. The different interaction of macromolecules with the support influences indirectly the surface morphology of the UV-irradiated PMMA.

Surface properties of UV-irradiated poly(vinyl alcohol) films containing small amount of collagen

The surface properties of poly(vinyl alcohol) (PVA) films in the presence of 1%, 3% and 5% of collagen before and after UV-irradiation have been studied by atomic force microscopy (AFM) and by contact angle measurements. PVA films have been obtained by solvent evaporation from water solution of PVA and PVA containing small amount of collagen. After drying, the samples were irradiated with UV light wavelength λ = 254 nm in air. Surface properties before and after UV-irradiation were observed using AFM. Contact angles of two liquids: diiodomethane (D) and glycerol (G) on polymeric films were measured at constant temperature using goniometer. The results have shown that the contact angle and the surface free energy for PVA films were altered by UV-irradiation. These alterations indicate photooxidation and an increase of polarity of the surface. The comparison of surface properties of PVA films and PVA containing collagen points out that collagen is more sensitive to photooxidation than PVA and PVA/collagen blends. PVA films containing collagen easier undergo photooxidation process with formation of new polar groups than pure PVA films.

Collagen fibrils in UV irradiated poly(vinyl pyrrolidone) films

The surface properties of poly(vinyl pyrrolidone) (PVP) films and PVP films containing 1, 3 and 5% of collagen before and after UV irradiation ( λ = 254 nm) were investigated using atomic force microscopy (AFM) and monitored by contact angle measurements. Measurements of the contact angle for diiodomethane (D) and glycerol (G) on PVP films were made before and after UV irradiation of the films. AFM images show the fibrils formation in PVP films containing collagen. The amount of collagen in PVP matrix has an important effect on the structure and size of collagen fibril formed. The size of collagen fibrils in irradiated PVP films is bigger than in non irradiated ones. The values of polar and dispersive components of surface free energy show that PVP films are more polar when collagen was added.

Surface Ionization State and Nanoscale Chemical Composition of UV-Irradiated Poly(dimethylsiloxane) Probed by Chemical Force Microscopy, Force Titration, and Electrokinetic Measurements

The surface chemistry and ionization state of cross-linked poly(dimethylsiloxane) (PDMS) exposed to UV/ozone were studied as a function of treatment time. Various complementary and independent experimental techniques were utilized, which yielded information on the macroscopic as well as the nanometric scale. The average chemical composition of the PDMS surface was quantitatively investigated by time-of-flight secondary ion mass spectrometry (ToF-SIMS). It was found that the top 1-2 nm surface layer was dominated by silanol groups (-SiOH) for which the concentration increased with increasing treatment dose. The lateral distributions of the silanol groups were analyzed on the nanometer scale by means of atomic force microscopy (AFM) with chemically functionalized tip probes in aqueous buffer solutions at varying pHs. Spatially dependent pull-off force curves (also called "force volume" imaging) indicated the presence of strong chemical heterogeneity of the probed surface. This heterogeneity took the form of patches of silanol functionalities with high local concentration surrounded by a matrix of predominantly hydrophobic domains at low pH. The average pull-off forces for the entire surface scanned were significantly reduced for pH values larger than a characteristic pK(a) constant (in the range between 4.5 and 5.5). The extent of the decrease in the pull-off force and the particular value of pK(a) were found to be a function of treatment time and to differ from the commonly reported values for silanol functional groups on a homogeneous silica surface. These dependences were ascribed to the evoking of a protonation/deprotonation process of the surface silanol groups which was sensitive to the hydrophobic/hydrophilic balance of their close molecular environment. Intermolecular hydrogen bonding may also account for the shifts in the surface pK(a). Furthermore, depending on the nature of the electrolyte, a third effect related to double layer composition, as determined by specific ion adsorption, was quantitatively analyzed by streaming potential measurements in the presence of sodium chloride and phosphate electrolytes.

Changes of surface morphology in UV-irradiated poly(acrylic acid)/poly(ethylene oxide) blends

Thin polymer films of PAA, PEO and PAA/PEO blends with different components ratio were obtained by means of casting their aqueous solutions and water evaporation. All samples were then exposed to short-wavelength UV-radiation ( λ=254 nm). The morphology of samples, as observed in polarized light of optical microscope, exhibited the existence of spherulitic structures. Surface properties were studied using the SEM technique and contact angle measurements. It was found that UV-irradiation changes the size of spherulites in pure PEO and in blends containing its major amount. The contact angle measurements indicate that UV-radiation induces some changes of hydrophilicity of samples.

Miscibility, optical and dielectric properties of UV-irradiated poly(vinylacetate)/poly(methylmethacrylate) blends

Films of PVAc/PMMA blend with different contents were prepared using the casting technique. The results obtained by DSC indicate the miscibility between the two components at any content. Also, PMMA could be blended with PVAc to improve its impact strength. The electronic spectra results reveal that pure PMMA is a photo-stable polymer. Moreover UV-irradiation causes degradation of PVAc and formation of ketonic and aldehyde carbonyl groups according to a suggested scheme. Irradiation of PVAc/PMMA blends causes a higher degree of degradation as compared to the PVAc alone although the PMMA is photo-stable. It was found that all studied samples prior to UV-irradiation have one optical absorption edge. The UV-irradiation leads to the appearance of a second edge at a lower photon energy due to the formation of induced energy states. Both the intensity of the absorption band for PVAc film at 273 nm and the calculated values of energy gaps are linearly dependent on the content of blends and irradiation time. The results suggest the possible use of PVAc film as a dosimeter for absorbed doses. The ε ́ and tan δ values were investigated over a range of temperatures (40–140°C) at various frequencies (1×10 3, 1×10 4, and 1×10 5 Hz). The obtained data seem to confirm the DSC and electronic spectra results.

A positron lifetime study of structural relaxation in UV irradiated poly (ethylene terephthalate)

Structural relaxation in UV irradiated poly (ethylene terephthalate) (PET-UV) has been investigated using positron lifetime techniques. Positron lifetime results show that the structural relaxation processes in PET-UV encompass three different time regimes, unlike the unirradiated poly (ethylene terephthalate) (PET) where only two relaxation times were observed. The relaxation functions constructed from the measured ortho positronium intensity, I 3, exhibit non-exponential character that can be best fitted with two additive exponentials. To determine the extent of deviation from exponential relaxation, we have used the Narayanaswamy model (KWW function) and evaluated the stretching parameter β. From the relaxation times derived from the exponential decay curves, the activation energies have been calculated and from these activation energies it seems possible to label the different kinetic units of the UV irradiated poly (ethylene terephthalate) structure participating in the relaxation processes.

Gas sorption and transport in UV-irradiated poly(2,6-dimethyl-1,4-phenylene oxide) films

Gas sorption and transport properties at 35°C have been reported for a series of UV-irradiated films of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO). UV irradiation induced crosslinking in all films. The gas permeability was reduced upon crosslinking while significant increases in gas permselectivity were observed. The addition of benzophenone to the PPO films did not result in marked improvements in crosslinking or the resulting gas transport properties of the film. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:875–883, 1998

Liquid Crystalline Polymer Stabilized FLCDs with Conventional Rubbed Polyimide Films or with Photo Alignment Films of Poly(vinyl Cinnamate)

Polymer stabilized SSFLCDs have been successfully fabricated. A liquid crystalline polymer network in a device cell is formed by the photo-cure of UV photo-currable liquid crystalline monomers that are doped in an FLC, where both the rubbed polyimide (PI) and non-rubbed but linearly polarized UV irradiated poly(vinyl cinnamate) (PVCi) films are utilized as surface FLC molecular alignment. The actual monomers adopted is acrylate with a mesogenic side chain. The PVCi is one of the photo alignment polymer. The fabrication process of these SSFLC cells is as follows; first the photo-cure is done on a monomers and initiators doped LC medium at the temperature where this material takes SmA phase and then the cell is cooled down to room temperature, at which the medium takes SmC* phase. The layer structure of the liquid crystalline polymer stabilized (LC-PS) FLC cells has been investigated by X-ray diffraction measurement. As the experimental results, it is found that the formed polymer network suppresses the formation of a chevron layer structure, resulting in the formation of a quasi-bookshelf layer structure; the only C1-uniform state is spontaneously formed without giving a high surface pretilt angle; and a fairly good memory state with an excellent contrast ratio and a low threshold voltage are obtained for a low concentration of doped monomers (2 ∼ 3 wt%) in particular with photo-alignment layers of PVCi; and furthermore, in a cell with a higher concentration of doped monomers (4 wt%) an excellent electroclinic like behavior (called the quasi-electroclinic effect) is obtained.

Comparison of the Effects of UV Irradiation on 5-Methyl-Substituted and Unsubstituted Pyrimidines in Alternating Pyrimidine-Purine Sequences in DNA

We previously demonstrated the UV-induced formation of cytosine hydrate in DNA and its deamination product, uracil hydrate, via their release from the DNA backbone by the DNA glycosylase activity of Escherichia coli endonuclease III. Subsequently, endonuclease III-mediated release of thymine hydrate from UV-irradiated poly(dA-dT) was reported. Therefore, we asked whether 5-methylcytosine residues in DNA underwent photohydration and deamination to thymine hydrate in analogy to UV-induced deamination of cytosine. An alternating DNA copolymer containing 5-methylcytosine was irradiated with UVC and incubated with endonuclease III. No 5-methylcytosine hydrate was released. Instead, UV-induced nonenzymatic release of 5-methylcytosine occurred. Similarly, incubation of UV-irradiated poly(dA-dT) with endonuclease III did not release thymine hydrate; nonenzymatic release of thymine occurred. Nonenzymatic release of 5-methylpyrimidines was oxygen dependent, enhanced by ferric ion and inhibited by free radical scavengers. In contrast, photohydration of cytosine was oxygen independent, and only small amounts of cytosine were nonenzymatically released. Thus, 5-methylpyrimidine residues within alternating Pu-Py sequences in DNA do not undergo photohydration, but instead undergo cleavage of their N-glycosyl bonds yielding abasic (AP) sites. The inability to repair such AP sites may explain the UV sensitivity of E. coli xthnfo mutants, which lack AP endonuclease activity. We suggest that N-glycosyl bond cleavage is mediated by radical species formed via transfer of an electron from UV-excited triplet 5-methylpyrimidines to ground state oxygen and/or ferric ions.

Replacing tryptophan-128 of T4 endonuclease V with a serine residue results in decreased enzymatic activity in vitro and in vivo.

Endonuclease V of bacteriophage T4 possesses two enzymatic activities, a DNA N-glycosylase specific for cyclobutane pyrimidine dimers (CBPD) and an associated apurinic/apyrimidinic (AP) lyase. Extensive structural and functional studies of endonuclease V have revealed that specific amino acids are associated with these two activities. Controversy still exists regarding the role of the aromatic amino acid stretch close to the carboxyl terminus, in particular the tryptophan at position 128. We have expressed wild-type and mutant W128S endonuclease V in Escherichia coli from an inducible tac promoter. Purified W128S endonuclease V demonstrated substantially decreased N-glycosylase (approximately 5-fold) and AP lyase (10- to 20-fold) activities in vitro compared to the wild-type enzyme when a UV-irradiated poly(dA)-poly(dT) substrate was used. However, a much smaller difference in AP lyase activity between the two forms was observed with a site-specific abasic oligonucleotide. The difference in enzymatic activity was qualitatively, but not quantitatively, reflected in the survival of UV-irradiated bacteria, that is the W128S cells were slightly less UV resistant than wild-type cells. No difference was observed in the complementation of UV repair using UV-damaged denV- T4 phage. A more pronounced difference between the wild-type and W128S proteins was observed in human xeroderma pigmentosum group A cells by host-cell reactivation of a UV-irradiated reporter gene. The relatively large discrepancy between the in vitro and in vivo results observed with bacteria may be because saturated levels of DNA repair are obtained in vivo with relatively low levels of endonuclease V. However, under limiting in vitro conditions and in human cells in vivo a considerable difference between the W128S mutant and wild-type endonuclease V activities can be detected. Our results demonstrate that tryptophan-128 is important for endonuclease V activity.

Photodegradation of Polysilanes Studied by Far-Infrared Spectroscopy

The photodegradation of polysilanes was investigated by far-infrared spectroscopy. The band intensity of asymmetric and symmetric Si–Si stretching vibration of poly(methylphenylsilylene) was decreased by UV-irradiation. The formation of the Si-branching structure in the UV-irradiated poly(methylphenylsilylene) was suggested. Poly(phenylsilyne) showed stability of the Si rings during the photodegradation.

Immunochemical detection of sequence-specific modifications to DNA induced by UV light.

Sequence specificity of antibodies to UV-damaged DNA has not been described previously. The antisera investigated here were specific for UV-modified DNA and were absolutely dependent upon the presence of thymine residues. Using a series of oligonucleotides in competition ELISA, increased inhibition was observed with increasing chain length of UV-polythymidylate. A minimum of three adjacent thymines was required for effective inhibition; alone, dimers of thymine were poor antigens. Although UV-irradiated poly(dC) was not antigenic, cytosines could partially replace thymines within the smallest effective epitope (T-T-T) with a high degree of sequence specificity, not previously described. The main epitope induced by UV was formed from adjacent thymines and either a 3' or a 5' pyrimidine.