Degradation of polymer coating systems studied by positron annihilation spectroscopy. IV. Oxygen effect of UV irradiation

The effect of oxygen on the photodegradation of a polyurethane coating induced by accelerated UV irradiation was studied with two different light sources: 313‐nm UVB and Xe lamps. Doppler‐broadened energy spectra (DBES) and positron annihilation lifetimes were measured as a function of incident positron energy (0–30 keV) and irradiation time (0–100 h). The photodegradation of the coating was characterized in terms of subnanometer defect changes. Significant variations of the S parameter (a defect parameter from DBES) and the ortho‐positronium lifetime and intensity were observed as a function of oxygen concentration during exposure to UV irradiation. These results showed a significant enhancement in photodegradation due to the presence of oxygen, as indicated by a decrease in free volume and holes at the atomic level. Enhanced degradation in the presence of oxygen, as indicated by increased free‐radical production (observed with electron spin resonance spectroscopy), was also observed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2035–2047, 2001     

Degradation of polymer coating systems studied by positron annihilation spectroscopy. II. Correlation with free radical formation

The photo‐degradation of polymer coating systems due to irradiation by UV and Xenon light sources is studied using positron annihilation spectroscopy and electron spin resonance (ESR). Doppler broadened spectra of positron annihilation, as a function of slow positron implantation energy and ESR spectra, are measured in two types of polyurethane which were exposed, ex situ, to UV irradiation for up to 800 h. The UV irradiation systematically decreases the S parameter as a function of exposure duration and increases the ESR signals. Thus, significant S parameter decrease is correlated with the ESR signal increase resulting from photo‐degradation of polymers due to UV irradiation. Parallel in situ positron annihilation and ESR experiments are performed as a function of Xenon light exposure for up to 100 min. These results show that the photo‐degradation of the polyurethane coatings involves initial free‐radical formation, which is correlated with the subnanometer defects detected by positron annihilation spectroscopy. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1289–1305, 1999     

Deterioration of a polyurethane coating studied by positron annihilation spectroscopy: Correlation with surface properties

Deterioration of a polyurethane coating by Florida natural environments as a function of time up to 16 weeks was studied by positron annihilation spectroscopy. Doppler broadening energy spectroscopy (DBES) of annihilation irradiation and positron annihilation lifetime (PAL) were measured as a function of incident positron energy (0–30 keV). A significant decrease in the S‐defect parameter from DBES and the intensity of orthopositronium from PAL was observed as a function of weathering time. This is interpreted as a loss of free volume and holes as a result of the weathering process. The gloss and surface morphology in the same system were measured by glossimetry and atomic force microscopy (AFM), respectively. The gloss decreased and surface roughness increased as a function of weathering time. The AFM images showed a new feature of a spherically coagulated microstructure on the surface after weathering. Direct correlations between the decrease in gloss and the increase in roughness as well as the decrease in the S‐defect parameter from the DBES data and in the free volume from the PAL data were observed. These results were used to discuss the weathering process in terms of chemical and physical changes as a result of photodegradation in protective polymeric systems. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2290–2301, 2001     

Free radical and thermal curing of terpyridine‐modified terpolymers

Terpolymers bearing terpyridine as well as (meth)acrylates as free radical curable groups (UV‐curing) or hydroxyl groups (thermal curing with bis‐isocyanates) were synthesized and characterized using ¹H NMR, IR and UV‐vis spectroscopy as well as GPC. Subsequently, the ability of covalent crosslinking via the UV‐initiated polymerization of the acrylate groups was investigated. Moreover, the thermal covalent crosslinking via the reaction of hydroxyl functionalized terpolymer and bis‐isocyanate compounds could be successfully achieved. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4028–4035, 2004     

Polymers derived from N‐isopropylacrylamide and azobenzene‐containing acrylamides: Photoresponsive affinity to water

N‐Isopropylacryamide was copolymerized by free‐radical polymerization with N‐[2‐(4‐phenylazophenoxy)ethyl]acrylamide derivatives that were substituted at their 4′‐position with ethoxy, methoxyethoxy, or isopropyl units, or with N‐{2‐[4‐(pyridin‐2‐ylazo)phenoxy]ethyl}acrylamide. The polymers were soluble in cold water and possessed lower critical solution temperatures (LCSTs). The value of the LCST rose a few degrees after UV irradiation and dropped after irradiation with visible light, reversibly, in processes that corresponded to the isomerization of the azobenzene units. The polymers became increasingly hydrophobic after increasing their azobenzene content. The difference of hydrophobicity correlates with the absorption band height at about 400 nm. The structure of the substituent on the azobenzene unit affected both the transition temperature and the hydrophobicity. A change in photoinduced wettability for water was observed to occur on a prepared film at a temperature different from the LCST determined in water. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5200–5214, 2004     

Photopolymerization of acrylates without photoinitiators with short‐wavelength UV radiation: A study with real‐time fourier transform infrared spectroscopy

This article reports on the UV photopolymerization of acrylates without photoinitiators. Initiation of the reaction was achieved by direct excitation of the acrylates during irradiation with short‐wavelength UV light by use of the 222‐nm emission of a KrCl^* excimer lamp. The reactivity of various acrylates was studied by real‐time Fourier transform infrared–attenuated total reflection spectroscopy. The rate and the extent of the reaction within the layer were strongly dependent on the depth of penetration of UV light, which was determined by the molar extinction coefficient of the acrylate. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 894–901, 2004     

Facile synthesis and responsive behavior of PDMS‐b‐PEG diblock copolymer brushes via photoinitiated “thiol‐ene” click reaction

We present herein a mild and rapid method to create diblock copolymer brushes on a silicon surface via photoinitiated “thiol‐ene” click reaction. The silicon surface was modified with 3‐mercaptopropyltrimethoxysilane (MPTMS) self‐assembled monolayer. Then, a mixture of divinyl‐terminated polydimethylsiloxane (PDMS) and photoinitiator was spin‐coated on the MPTMS surface and exposed to UV‐light. Thereafter, a mixture of thiol‐terminated polyethylene glycol (PEG) and photoinitiator were spin‐coated on the vinyl‐terminated PDMS‐treated surface, and the sequent photopolymerization was carried out under UV‐irradiation. The MPTMS, PDMS, and PEG layers were carefully identified by X‐ray photoelectron spectroscopy, atomic force microscopy, ellipsometry, and water contact angle measurements. The thickness of the polydimethylsiloxane‐block‐poly(ethylene glycol) (PDMS‐b‐PEG) diblock copolymer brush could be controlled by the irradiation time. The responsive behavior of diblock copolymer brushes treated in different solvents was also discussed. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Free radical photopolymerization initiated by UV and LED: Towards UV stabilized,tack free coatings

UV stabilizers (UV absorbers and Hindered Amine Light Stabilizers‐HALS) are added to UV‐curable formulations to provide long‐term durability. The influence of HALS and the filtering effect of UV absorbers are investigated under UV and LED irradiation by using different photoinitiating systems in free radical photopolymerization. The contribution of irradiation conditions and initiating systems on the filtering effect is discussed by performing Real‐Time Fourier Transform Infrared Spectroscopy (RT‐FTIR) and Confocal Raman Microscopy. Additionally, to get quantitative information about the light absorbed by the photoinitiator, without and with the filtering issue arising from UV stabilizers, series of calculations are carried out by taking into account the amount of light absorbed by the compounds and the intensity of the incident light. Finally, formulations are optimized with respect to surface inhibition to obtain tack free coatings in air atmosphere in the presence of UV stabilizers under visible light. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3597–3607     

Polarized light‐induced photoisomerization in glassy poly(methyl methacrylate) and local relaxation processes of the polymer matrix

Photoisomerization kinetics of trans 4‐methoxystilbene induced by irradiation with linearly polarized light was investigated in the glassy state of poly(methyl methacrylate)(PMMA). The reaction was strongly selected by linearly polarized light as revealed by a large dichroic absorption generated upon irradiation. The optical anisotropy increases with increasing irradiation time and passes through a maximum before approaching an equilibrium value, which strongly depends on the experimental temperatures. From the decay of the total absorbance of the trans‐isomer observed upon irradiation with 313 nm UV light, it was found that the rates of the photoisomerization trans → cis were not significantly changed within the temperature range of the experiments. On the other hand, the reorientational relaxation times of the stilbene, which were directly measured by the annealing‐after‐irradiation techniques, depend strongly on temperature. These relaxation data were compared to the previous results obtained with dopants of the size larger than the stilbene and were discussed in conjunction with the local relaxation processes of the PMMA matrix. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 682–690, 2000     

Surface characterization of untreated and hydro‐thermally pre‐treated Turkey oak woods after UV‐C irradiation

The aim of this study was to determine the effect of UV‐C irradiation on the Turkey oak wood surface (Quercus cerris L.). In order to compare the effect of irradiation, both untreated wood samples and those treated with steam and heat were analyzed. The steam treatments were carried out in an autoclave at 130 °C; samples were then heated in an oven for 2 h at 180 °C. The physical and chemical changes brought about in the untreated and treated wood samples by the UV‐C light were monitored by colorimetry (color changes), X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) (chemical composition) and scanning electron microscopy (SEM) (microstructure and morphology). A detailed analysis of the results indicates that the UV‐C treatment caused irreversible changes in both the chemical composition and morphology of the wood samples via photooxidation and photodegradation processes. Depending on the type of pre‐treatment used, these processes affected the wood samples differently. Copyright © 2014 John Wiley & Sons, Ltd.     

Surface‐confined photopolymerization of single‐ and mixed‐monomer systems to tailor the wettability of poly(L‐lactide) film

The major objective of this research was to modify the surface characteristics of poly(L ‐lactide) (PLA) by grafting a combination of hydrophilic polymers to produce a continuum of hydrophilicity. The PLA film was solvent cast, and the film surfaces were activated by ultra violet (UV) irradiation. A single monomer or combination of two monomers, selected from vinyl acetate (VAc), acrylic acid (AA), and acrylamide (AAm), were then grafted to the PLA film surface using a UV induced photopolymerization process. The film surfaces resulting from each reaction step were analyzed using ATR‐FTIR spectroscopy and contact angle goniometry. Results showed that AAm dominated the hydrophilicity of the film surface when copolymerized with VAc or AA, while the water contact angles for PLA films grafted with poly(vinyl acetate‐co‐acrylic acid) varied more gradually with feed composition. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6534‐6543, 2006     

Visibly observed photocrosslinking reaction in indolyl based pendant liquid crystalline polymers: Synthesis and optical property

Visibly observed photocrosslinkable pendant liquid crystalline polymers containing indolyl based chalcone were synthesized by free‐radical polymerization and characterized spectroscopically. The differential scanning calorimetry and polarized optical microscopy were used to examine liquid crystalline property. The photocrosslinking and luminescence properties were monitored by UV‐Vis spectrophotometer and spectrofluorimeter, respectively. It demonstrates the chalcone unit did not manifest cis ? trans‐isomerization reaction along with 2π+2π photodimerization upon irradiation with UV light like other chalcones hitherto reported. The photocrosslinking was visibly monitored in solution through change of fluorescent color to colorless. The spacer lengths play a key role in the reaction. The fluorescence maximum was blue shifted around 70 nm in chloroform solution upon irradiation with UV light confirms the 2π+2π photodimerization of chalcone unit. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5208–5220, 2009     

Synthesis,characterization and photocatalytic application of TiO2/magnetic graphene for efficient photodegradation of crystal violet

A magnetized nano‐photocatalyst based on TiO₂/magnetic graphene was developed for efficient photodegradation of crystal violet (CV). Scanning electron microscopy, X‐ray diffraction, energy‐dispersive X‐ray spectroscopy and elemental mapping were used to characterize the prepared magnetic nano‐photocatalyst. The photocatalytic activity of the synthesized magnetic nano‐photocatalyst was evaluated using the decomposition of CV as a model organic pollutant under UV light irradiation. The obtained results showed that TiO₂/magnetic graphene exhibited much higher photocatalytic performance than bare TiO₂. Incorporation of graphene enhanced the activity of the prepared magnetic nano‐photocatalyst. TiO₂/magnetic graphene can be easily separated from an aqueous solution by applying an external magnetic field. Effects of pH, magnetized nano‐photocatalyst dosage, UV light irradiation time, H₂O₂ amount and initial concentration of dye on the photodegradation efficiency were evaluated and optimized. Efficient photodegradation (>98%) of the selected dye under optimized conditions using the synthesized nano‐photocatalyst under UV light irradiation was achieved in 25 min. The prepared magnetic nano‐photocatalyst can be used in a wide pH range (4–10) for degradation of CV. The effects of scavengers, namely methanol (OH^? scavenger), p‐benzoquinone (O₂^?? scavenger) and disodium ethylenediaminetetraacetate (hole scavenger), on CV photodegradation were investigated.     

Surface modification of polystyrene by blending substituted styrene copolymers

The surface modification of polystyrene (PS) by the blending of 4‐acetoxystyrene polymers and their corresponding hydrolysis products, 4‐hydroxystyrene polymers, was investigated on the basis of X‐ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and contact‐angle measurements. According to XPS and AFM measurements, when polystyrene‐block‐poly(4‐acetoxystyrene) (PS‐b‐PAS) or polystyrene‐block‐poly(4‐hydroxystyrene) (PS‐b‐PHS) was incorporated into PS, the block copolymer was preferentially segregated at the highest surface region of the blend. This segregation increased to a plateau value when more than 5 wt % of either PS‐b‐PHS or PS‐b‐PAS was added. The contact angle of the modified PS by PS‐b‐PAS or PS‐b‐PHS was slightly lower than that of homopolystyrene, but no further decrease was observed with the blend ratio of the diblock copolymer increasing from 5 to 20 wt %. For a PS/PS‐b‐PHS blend, the surface atomic concentration ratio O/C increased linearly with the molecular weight of poly(4‐hydroxystyrene) blocks in diblock copolymer PS‐b‐PHS in the range of our study. The different structures of 4‐acetoxystyrene polymers and their hydrazinolyzed materials may affect the surface compositions of their blends with PS; among these polymers, PS‐b‐PHS and PS‐b‐PAS appeared to be most effective. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1046–1054, 2001     

Large enhancement of the ionic conductivity in an electron‐beam‐irradiated [poly(ethylene glycol)]xLiClO4 solid polymer electrolyte

The effect of electron‐beam (4–8 MeV) irradiation on the ionic conductivity of a solid polymer electrolyte, poly(ethylene glycol) complexed with LiClO₄, was studied. A large enhancement of the conductivity of nearly two orders of magnitude was observed for the highest dose of irradiation (15 kGy) used. The samples were characterized with differential scanning calorimetry, matrix‐assisted laser desorption/ionization, and electron spin resonance spectroscopy. Although no free radicals were present in the irradiated samples, a decrease in the glass‐transition temperature and an increase in the amorphous fraction were observed. Even though pure poly(ethylene glycol) underwent considerable fragmentation, unexpectedly, no significant fragmentation was observed in the polymer–salt complexes. The enhancement of the conductivity was attributed to an increase in the amorphous fraction of the systems and also to an increase in the flexibility of the polymer chains due to the irradiation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1299–1311, 2004     

Monitoring of the shrinkage during the photopolymerization of acrylates using hyphenated photorheometry/near‐infrared spectroscopy

This article describes a new method for the quantitative determination and time‐resolved monitoring of the polymerization shrinkage during ultraviolet (UV) photopolymerization. It is based on rheometry using a modified oscillating rheometer. Shrinkage is determined from the decrease of the gap between the rheometer plates. Moreover, near‐infrared (NIR) spectra can be recorded directly in the rheometer, which allows continuous determination of the conversion at any time of a shrinkage measurement. As both shrinkage and conversion data come from the same experiment, shrinkage can be analyzed in dependence on the current conversion achieved during UV irradiation, which enables direct investigation of correlations between both parameters. Hyphenated photorheometry/FT‐NIR spectroscopy was used for the determination of the polymerization shrinkage of pure acrylate monomers and oligomers as well as acrylate‐based formulations. Quantitative shrinkage values were found to be in excellent correlation with data that were determined by an independent method (via buoyancy measurements) and data from literature. Furthermore, the effect of ambient and irradiation conditions or the content of nanoparticles on the degree of shrinkage was studied. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 729–739     

Two‐dimensional polymer synthesis through the topochemical polymerization of alkylenediammonium muconate as a multifunctional monomer

Here we demonstrate a unique two‐dimensional polymer synthesis through topochemical polymerization via polymer crystal engineering, which is useful for controlling and designing the polymerization reactivity as well as the polymer chain and crystal structures. We have succeeded in the synthesis of a sheet polymer through the polymerization of alkylenediammonium (Z,Z)‐muconate as a multifunctional 1,3‐diene monomer in the crystalline state under the irradiation of UV and γ‐rays or upon heating in the dark. The photopolymerization reactivity of several muconates and the structural control of the obtained polymer are described. The stereochemical structure of the polymer and the polymerization mechanism are discussed on the basis of the results of IR and NMR spectroscopy, thermogravimetric measurements, and solid‐state hydrolysis for the transformation into poly(muconic acid). © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3922–3929, 2004     

Photocatalytic degradation of polyhydroxybutyrate films using titanium dioxide nanoparticles as a photocatalyst

Photocatalytic degradation of polyhydroxybutyrate (PHB) polymeric films (30 μm thickness) containing different concentrations of titanium dioxide (TiO₂) nanoparticles under ultraviolet (UV) irradiation (λ_max = 313 nm) has been studied. The activity of TiO₂ (0.001-0.005%) as a photocatalyst was determined by monitoring various functional group indices, weight loss in polymeric films and photodegradation rate constant (k _d) with irradiation time. Photodegradation was found to be highly dependent on the TiO₂ nanoparticles concentration and the UV irradiation time. The rate of PHB sample photodegradation was highest when the concentration of TiO₂ was 0.005% (by weight) and lowest when its concentration was 0.001%.

     

Synthesis of organic–inorganic chiral block poly(methylphenylsilane) functional polymers,and study of their optical and chiroptical properties

Polysilanes upon UV irradiation give rise to silyl macroradicals which are capable to initiate radical polymerization. Hence, chiral block functional polysilanes were synthesized by UV irradiation of poly(methylphenylsilane) (PMPS) with a vinyl chiral monomer, (R)‐N‐(1‐phenylethyl)methacrylamide (R‐NPEMAM). The synthesized copolymer samples were characterized by FTIR, NMR, and UV–vis spectroscopy. The number and weight average molecular weights of PMPS and synthesized chiral‐block‐PMPS were measured by GPC analysis. Two glass transition temperatures (T_g) of the synthesized materials clearly indicate the formation of chiral‐block‐PMPS copolymers. SEM analysis also indicated the synthesized organic–inorganic block copolymers. The optical and chiroptical properties of the synthesized materials were studied. The cotton effect is observed not only at 276 nm due to aromatic ring of the chiral monomer units but also at 325 nm which is associated with the Si–Si conjugation of PMPS block of synthesized functional polysilanes. Such tunable chirality may find potential application in optoelectronics. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3626–3634     

The influence of UV light on collagen/poly(ethylene glycol) blends

The photodegradation behaviour of the collagen and poly(ethylene glycol) PEG blends has been studied by Fourier transform infrared spectroscopy (FTIR), UV-Vis spectroscopy and viscometry. Surface properties before and after UV irradiation were observed using optical microscope.Collagen and PEG were immiscible and the films obtained from the mixture were fragile with poor mechanical properties. The photochemical stability of the collagen and PEG blend was different from that of the single components. In general collagen/PEG blends are less stable under UV irradiation than pure collagen. The influence of PEG on the photochemical stability of collagen depends on its concentration in the blend. Microscope photographs showed that the surface characteristics of collagen and collagen/PEG blends in film form are not drastically altered after UV irradiation.