Photografting of unable‐to‐be‐irradiated surfaces. I. Batch vapor‐phase process by one‐step method

Surfaces unable‐to‐be‐irradiated are those that could not be directly exposed to UV irradiation because of their irregular structure or instability under UV irradiation. It is difficult to conduct surface photografting on these kinds of surfaces with conventional photografting methods. Here, a novel one‐step surface photografting method is introduced, by which some monomers were smoothly grafted on the surface of polymer substrates located in a region out of the reach of UV radiation. The mechanism is that the photochemical reaction is separated into three events, absorbing UV light in one place, then transporting light energy to another place, and reacting there; in other words, the conventional photochemical reaction is separated by space and time, and the key point is that the substrate does not need to be exposed to UV irradiation. The occurrence of grafting polymerization was proved by UV–vis, ATR‐IR, SEM, XPS, and water contact angle measurements. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2269–2276, 2006     

Controlled degradation of polylactic acid grafting N‐vinyl pyrrolidone induced by gamma ray radiation

Polylactic acid (PLA) films were surface modified by gamma ray irradiation‐induced grafting of N‐vinyl pyrrolidone (NVP). The in vitro degradation behavior of polylactic acid grafting N‐vinyl pyrrolidone (PLA‐g‐PVP) copolymer was analyzed in terms of weight loss, molecular weight, and thermal properties. Grafting NVP significantly accelerated the degradation of PLA. The mass losses of the copolymers, which were less than that of pure PLA at the beginning of the degradation period, sharply accelerated with increasing degradation time. Moreover, the crystallization temperature decreased with increasing degradation time in the same graft ratio, and the degree of crystallinity increased. Cytotoxicity experiments and animal experiments in vivo were carried out to evaluate the biocompatibility of PLA‐g‐PVP copolymer. Varying graft ratios of PVP could control the degradation rate of copolymers, and thus broadening the applications of this material, such as in tissue engineering scaffolds, drug delivery, and prevention of postsurgical adhesion. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Photodegradation of cellulose acetate film in the presence of benzophenone as a photosensitizer

To study the effectiveness of photosensitizers to accelerate the degradation of cellulose acetate (CA) under ambient environment, CA (degree of substitution = 2.45) films containing benzophenone, which is one of the typical photosensitizers, were prepared and their degradative behavior by photoirradiation was examined. Decrease in molecular weight of CA and generation of carbon dioxide, carbon monoxide, and acetic acid from the CA films were observed by the irradiation of xenon arc lamp light, which was passed through a filter for cutting off the wavelength shorter than 275 nm. With increasing the concentration of benzophenone, the molecular weight of CA decreased and the generation of the degradation products from the CA films increased. These results may suggest that radical reactions of CA films proceed by photoirradiation and lead to oxidation and random cleavage of CA, and that benzophenone is an effective additive to accelerate the degradation of CA under ambient environment. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Effect of gamma‐irradiation on the electret properties of poly(L‐lactide)

Electret stability of poly(L ‐lactide) (PLA) films, gamma‐irradiated up to 100 kGy has been investigated by measuring the surface potential during the storage period. PLA samples—40‐μm thick films—were prepared by the casting method and then irradiated in a ⁶⁰Co radiation facility at a dose rate of 0.25 kGy/h. The structural changes during the irradiation were estimated by viscometric, differential scanning calorimetry and scanning electron microscope measurements. Random chain scission and appearance of end radicals are the most probable results of the irradiation process. After irradiation, the samples were charged in a corona discharge system and surface potential was measured by the method of the vibrating electrode with compensation. The values of the surface potential of the irradiated samples were higher in comparison with the non‐irradiated samples. This effect could be related to the degradation of the macromolecules and changes in the crystal state of PLA during the irradiation. Both of the mentioned factors lead to structural defects that increase the number of discrete trapping levels. The effect of low pressure on the surface potential drop was also investigated. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Degradation of poly(D,L‐lactic acid)‐b‐poly(ethylene glycol)‐b‐poly(D,L‐lactic acid) copolymer by electron beam radiation

This article investigates the effects of electron beam (EB) radiation on poly(D ,L ‐lactic acid)‐b‐poly (ethylene glycol) copolymer (PLA‐b‐PEG‐b‐PLA). The copolymer films were EB irradiated at doses from 0 to 100 kGy. The degradation of these films was studied by measuring the changes in their molecular weight, mechanical and thermal properties. The dominant effect of EB radiation on PLA‐b‐PEG‐b‐PLA is chain‐scission. With increasing irradiation dose, recombination reactions or partial crosslinking may occur in addition to chain scission. The degree of chain scission G_s and crosslinking G_x of sample are calculated to be 0.213 and 0.043, respectively. A linear relationship is also established between the decreases in molecular weight with increasing irradiation dose. Elongation at break of the irradiated sample decreases significantly, whereas its tensile strength decreases slightly. The glass transition temperature (T_g) is basically invariant as a function of irradiation dose. Thermogravimetric analysis shows that its thermal stability decreases with increasing dose. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

锐钛矿结构TiO_2/glass膜光催化作用的研究.紫外灯照射下水中苯酚的光催化降解

以溶胶 -凝胶法制得锐钛矿型结构的 Ti O2 /glass膜。在紫外灯照射下研究了膜对水中苯酚的光催化降解作用 ,研究证明 ,灯距控温反应器 1 0 cm时的液外照射 ,可使苯酚降解率达 70 %以上 ;在 H2 O2 存在下效果更佳 ;若通入空气可使苯酚降解几近完全     

Surface hydrophilic–hydrophobic property on transparent mesoporous silica thin films containing chromium oxide single-site photocatalyst

Using a sol–gel/spin-coating method with organic template, the transparent mesoporous silica thin films containing chromium oxide moieties can be prepared on quartz plate. The spectroscopic characterization has revealed that these thin films contain isolated and tetrahedrally coordinated chromium oxide moieties (single-site photocatalyst) in their frameworks. Even before UV light irradiation these Cr-containing mesoporous silica (CrMS) thin films have demonstrated a hydrophilic surface property more strongly than Cr-containing non-porous silica films and mesoporous silica thin films without chromium oxide. Furthermore, the Cr-containing mesoporous silica thin films showed the super-hydrophilic property not only under UV light irradiation but also even under visible light irradiation from a fluorescent lamp. In the presence of ethylene gas, the polyethylene was successfully formed on the surface of the CrMS thin film under UV light irradiation. After the formation of polyethylene the surface property of the CrMS thin film was converted into hydrophobic while keeping its transparency. The isolated and tetrahedrally coordinated chromium oxide moieties are responsible for these photo-induced surface reactions.     

Surface functionalization of poly(lactic acid) film by UV‐photografting of N‐vinylpyrrolidone

The photoinitiated grafting of N‐vinylpyrrolidone (NVP) onto poly(lactic acid) (PLA) film with the use of benzophenone (BP) as the initiator, modified the natural hydrophobic PLA behavior to an hydrophilic film with desirable wettability. The surface photografting parameters‐percent conversion of monomer to overall photopolymerization (Cp), percent conversion of monomer to the photograft polymerization (Cg), and grafting efficiency (Eg) were calculated. The resulting film surface was analyzed using ATR‐FTIR and UV spectroscopy, derivative spectroscopy and water contact angle. Besides, we demonstrated that the grafted polyvinylpyrrolidone chains could easily react with iodine to form a complex as the homopolymer does with antibacterial activity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Gloss and degradation of hydroxyl polyacrylic resin/hexamethylene‐1,6‐diisocyanate coatings under ultraviolet and natural‐exposure aging

Reactive coatings of hydroxyl polyacrylic resin (HPAR) with hexamethylene‐1,6‐diisocyanate were carried out under accelerated 313‐nm ultraviolet (UV) aging for 2000 h and under natural exposure in Lhasa, Tibet, for 24 months. With UV irradiation and exposure time, the gloss changes in coatings with HPAR containing 3.0% or less hydroxyl groups decreased exponentially, whereas the gloss decay of coatings with HPAR containing over 4.5% hydroxyl groups decreased linearly. During 254‐nm UV aging, the gloss changes in coatings with HPAR containing 1.4% or less hydroxyl groups decreased as a Gaussian function. The weather resistance of a coating was correlated to the HPAR, UV irradiation, temperature, and humidity. Scanning electron microscopy indicated that there were degradation reactions and that some substance was lost in the matrix polymer during accelerated UV aging; then, uneven surfaces appeared and caused decreased gloss. Accelerated UV aging was faster than natural‐exposure aging, and the aging velocity of 254‐nm UV was 3–5 times faster than that of 313‐nm UV. Through the changes in the gloss, the aging tolerance of a coating could be monitored, and its aging resistance could also be predicted. The dynamic mechanical thermal analysis results showed that the coatings had good properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1271–1278, 2007     

Synthesis and degradation of PLA–PCL–PLA triblock copolymer prepared by successive polymerization of ε-caprolactone and DL-lactide

A PLA–PCL–PLA triblock copolymer was synthesized by ring-opening polymerization of successively added ε-caprolactone and DL-lactide in the presence of ethylene glycol, using zinc powder as catalyst. The resulting copolymer was compression molded to yield circular films from which 10×10×0.4 mm³ square samples were cut. These samples were allowed to degrade in isoosmolar 0.13 M, pH 7.4 phosphate buffer at 37 °C. Various analytical techniques such as weighing, SEC, ¹H NMR, IR, DSC, X-ray, ESEM and CZE were used to monitor property changes during degradation such as water absorption, weight loss, molecular weight distribution, composition, bulk and surface morphologies, thermal behavior, and release of water-soluble oligomers into the aqueous phase. Comparison is made with a PCL homopolymer under similar ageing conditions. The presence of PLA sequences did not alter the ability of PCL segments to crystallize during degradation, in agreement with the microphase separation between PLA and PCL blocks. Large amounts of lactic acid-rich soluble degradation by-products were released into the solution between 18 and 25 weeks. Copolymer films cracked down under drying beyond 25 weeks' degradation, while the surface remained smooth. The copolymer exhibited faster degradation as compared with PCL homopolymer, a feature which is of great interest for temporary therapeutic applications.     

聚碳酸亚丙酯/聚乳酸共混物光照条件下的降解行为研究

研究了聚碳酸亚丙酯（PPC）/聚乳酸（PLA）共混物在光照条件下的降解性能,通过力学实验、质量变化、扫描电子显微镜（SEM）、衰减全反射红外光谱技术（ATR-FTIR）、高温凝胶渗透色谱（GPC）和热重分析（TG）分别研究了共混物力学性能、质量损失、表面微观形貌、化学结构、相对分子质量和热稳定性的变化规律。结果表明,100/0、70/30、50/50、30/70、0/100（质量比,下同）的PPC/PLA共混物光照56d时质量损失率为34.89%、40.50%、39.38%、29.6%和6.24%,共混物在14d时几乎损失所有的力学性能;光照56d后PPC和50/50的PPC/PLA共混物表面有明显的裂纹和孔洞,而PLA表面没有变化,光照时间越长,共混物表面越粗糙,降解程度越大;共混物的羟基指数（HI）和羰基指数（CI）在前21d不断增大,其中前14d比较明显;共混物在光照56d后相对分子质量降低,多分散性指数减小,分子量分布变窄;共混物失重5%的热分解温度（T-5%）和最大速率失重温度（TP）提高,而PPC的TP却降低。     

Synthesis and photoinduced surface‐relief grating of well‐defined azo‐containing polymethacrylates via atom transfer radical polymerization

A well‐defined photoresponsive polymethacrylate containing azo chromophores, poly[6‐(4‐phenylazophenoxy)hexylmethacrylate] [Poly(PPHM)], was prepared with azo‐based monofunctional and difunctional initiators via atom transfer radical polymerization in the presence of CuCl/1,1,4,7,10,10‐hexamethyltriethylenetetramine. The polymerizations with first‐order kinetics were well controlled with theoretical expected molecular weight and narrow molecular weight distributions in two initiation systems. The UV absorption intensities of the poly (PPHM)s increased with increasing molecular weight of the poly(PPHM)s in all cases. The 80‐nm surface‐relief gratings with 2.7% efficient diffraction formed on the poly (PPHM) film surface were obtained with a linearly polarized krypton laser with 10 min of irradiation at a recording beam intensity of 188 mW/cm² with a wavelength of 413.1 nm. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Uniform high‐molecular‐weight polylactide nanofibers electrospun from a solution below its entanglement concentration

In this article, we report the effects of the molecular weight on the electrospinnability of polylactide (PLA) solutions under identical conditions. Only above the entanglement concentration could uniform fibers be generated for PLA with a low molecular weight. However, electrospinning from a solution below its entanglement concentration produced uniform nanofibers when a high‐molecular‐weight PLA was adopted. The slow relaxation of high‐molecular‐weight PLA was expected to preserve chain interconnectivity in the highly stretched liquid jets during electrospinning. Correspondingly, rapid cold crystallization and a high modulus were exhibited by the resulting PLA nanofibers because of their remarkable molecular alignment.© 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44853.     

Functionalization of industrial polypropylene films via the swift‐heavy‐ion‐induced grafting of glycidyl methacrylate

Swift‐silver‐ion irradiation was explored as a means of forming chemically active sites on the surface of biaxially oriented polypropylene films. The active species, formed in air, was used to induce the graft copolymerization of glycidyl methacrylate in an aqueous solution. The surface structure, crystallinity, morphology, and hydrophilicity of the grafted samples were characterized with Fourier transform infrared, UV, wide‐angle X‐ray diffraction, scanning electron microscopy, and contact‐angle measurements. Glycidyl methacrylate could be grafted onto biaxially oriented polypropylene after swift‐heavy‐ion irradiation without an additional initiator. The contact angle of the modified films decreased with the grafting percentage of glycidyl methacrylate on the polypropylene. The swift silver ions induced significant grafting only in small regions (i.e., the latent tracks) of the polymer. Furthermore, as the fluence of swift heavy ions increased beyond an optimum value, the overlapping of the latent tracks reduced the grafting yield. The observed findings could be very useful in developing an initiator‐free grafting system. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Photoactivity of Poly(lactic acid) nanocomposites modulated by TiO2 nanofillers

Photoactivity of poly(lactic acid) (PLA) nanocomposites is of great interest for rational design of products for either short‐term/single‐use or long‐term/durable applications. We prepared PLA/TiO₂ nanocomposite films through a solution mixing/film casting method. Results showed that photodegradability/photostability of PLA could be well modulated by selecting appropriate TiO₂ nanofillers. TiO₂ nanoparticles and nanowires were characterized using X‐ray diffraction, UV–Vis–NIR spectrophotometer, and scanning electron microscopy. Changes in color, weight, structure, thermal stability, and phase transitions of PLA and nanocomposite films before and after UV irradiation were evaluated to study photoactivity characteristics. Pure PLA exhibited moderate photodegradability, but the photodegradability and photostability of PLA nanocomposites (PNA) were significantly enhanced by NanoActive (NA) TiO₂ nanoparticles and A type TiO₂ nanowires, respectively. Pure PLA had a weight loss of 27% after 38 days of UV irradiation. The weight loss of photodegradable (PD) PNA (PNA = PLA with 1% NA TiO₂) reached 38%, whereas that of photostable (PS) nanocomposites (P3AW) (P3AW = PLA with 3% A type TiO₂ nanowire) was only 5%. PD PLA exhibited characteristic peaks of carboxylic acid OH stretching and C?C double bond after UV irradiation in Fourier‐transform infrared spectra, whereas spectra of PS PLA remained almost the same. Thermal decomposition temperatures, glass transition temperatures, and melting temperatures of PD PLAs decreased dramatically after UV irradiation, but no obvious changes were observed for those of PS PLAs. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40241.     

Surface photografting polymerization of vinyl acetate,maleic anhydride,and their charge‐transfer complex. IV. Maleic anhydride

In general, it has been accepted that maleic anhydride (MAH) cannot be homopolymerized under normal conditions. However, MAH can be grafted onto substrates under UV irradiation rather easily. In this study, the photografting polymerization of MAH was examined with low‐density polyethylene (LDPE) film as a substrate. The initiating performances of different photoinitiators, including benzophenone (BP), Irgacure 651, and benzoyl peroxide (BPO), were examined. The effects of some principal factors, such as the temperature, solvent, and UV intensity, on the grafting polymerization of MAH were also investigated. The results show that MAH can be smoothly grafted onto LDPE film by UV radiation. Enhancing the intensity of UV radiation and elevating the irradiation temperature facilitate the grafting polymerization of MAH. Among BP, Irgacure 651, and BPO, Irgacure 651 can initiate the polymerization of more MAH, but BP is more effective for the initiation of surface grafting polymerization. Solvents of MAH also have a great influence on the grafting polymerization; some of them even seem to take part in the reaction. The occurrence of photografting polymerization was verified with Fourier transform infrared and electron spectroscopy for chemical analysis spectra. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2318–2325, 2003     

Comparison of the effect of ethylene oxide and γ-irradiation on selected tyrosine-derived polycarbonates and poly(L-lactic acid)

Tyrosine-derived polycarbonates are a new class of degradable polymers that have possible biomedical applications. In this study, the effect of the two most common sterilization techniques, ethylene oxide and γ-irradiation (0.3, 1.1, 3.9, 6.4, 10.6 Mrad), was evaluated for a family of four structurally related tyrosine-derived polycarbonates and for poly(L-lactic acid) (PLLA). The four polycarbonates were poly(DTE carbonate), poly(DTB carbonate), poly(DTH carbonate), and poly(DTO carbonate) and differed only in the length of the pendent chain. Ethylene oxide exposure had little effect on molecular weight, surface composition, mechanical properties, or degradation rate of all test polymers except for poly(DTO carbonate). Poly(DTO carbonate) was unique since following ethylene oxide exposure it degraded faster than did the nonsterilized control. γ-Irradiated tyrosine-derived polycarbonates retained over 81% of their initial molecular weight when exposed to a clinically relevant dose of 3.9 Mrad and retained still 58% of the initial molecular weight when exposed to the highest test dose of 10.6 Mrad. No changes in surface composition and only slight changes in yield strength and the Young's modulus were detected for any of the tyrosine-derived polycarbonates following γ-irradiation. In vitro, irradiated films of poly(DTE carbonate), poly(DTB carbonate), and poly(DTH carbonate) degraded at approximately the same rate as did the nonsterilized films regardless of irradiation dose. Only poly(DTO carbonate), irradiated at high doses, degraded faster than did the control. Medical-grade PLLA was tested under identical conditions. Ethylene oxide exposure of PLLA did not affect the molecular weight, surface composition, mechanical properties, or in vitro degradation rate. However, upon irradiation at 10.6 Mrad, PLLA retained only 29% of its initial molecular weight; a dose of 3.9 Mrad resulted in retention of 49% of the initial molecular weight. In correspondence with earlier publications, irradiation of PLLA induced significant losses in the Young's modulus, % strain at break, and changes in the postirradiation rate of degradation in some specimens. Compared to PLLA, tyrosine-derived polycarbonates are significantly more stable to γ-irradiation and can be sterilized by conventional γ-sterilization techniques. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1499–1510, 1997     

TiO2‐kaolin‐PE composite film: A study based on photocatalytic degradation and biodegradation

A novel photodegradable and biodegradable polyethylene (PE) film was prepared through a melt blending technique, where nano‐TiO₂ and common kaolin were used as the photocatalyst and biodegradable promoter showing improved degradable efficiency of the waste PE. The photo‐degradation of the composite film was investigated by weight loss monitoring, attenuated total reflection–fourier transformed infrared spectroscopy (ATR–FTIR), and scanning electron microscopy. The aerobic biodegradation of the residue films after photodegradation was investigated by analysis of evolved carbon dioxide of films in aquatic test systems according to the international standards (ISO 14852, 1999). The results showed that the weight loss of as‐prepared photo‐ and biodegradable composite film reached 26.8% after 240 h of UV light irradiation. The big cavities formed not only on the film surface but also inside the bulk film, together with the chalking phenomenon taking place. The biodegradation results revealed that the addition of kaolin enhanced the degradation of UV‐light treated TiO₂‐PE films. The prepared PE based composite films showed promising application as novel photo‐biodegradable environment‐harmless materials. In addition, a degradation mechanism for this composite film was also discussed. POLYM. COMPOS., 37:2353–2359, 2016. © 2015 Society of Plastics Engineers     

Polymerization of methacryl and triethoxysilane functionalized stearate ester: Titanium dioxide composite films and their photocatalytic degradations

Stearoyl chloride was reacted with 3‐(acryloyloxy)‐2‐hydroxypropyl methacrylate (AHM). Then the resulting product (SAHM) was reacted with 3‐amino propyl ethoxysilane (APTES) by Michael addition on the acrylate. The product (SAHMA) is a specialized coupling agent containing an oleophilic 18 carbon alkyl chain, a radically polymerizable methacrylate and an alkoxysilane group capable of coupling to inorganic surfaces, analyzed by FT‐IR, NMR, and UV techniques. Photopolymerization and free radical homo and copolymerization of SAHMA with styrene were examined. SAHMA was coupled to powdered titanium dioxide (P25‐Degussa) and polymerized. TiO₂ filled materials were analyzed by SEM, UV and TGA techniques. Glass transiton temperatures (T_g) of the polymers were determined by differential scanning calorimeter (DSC). Interfacial compatibility between SAHMA and TiO₂ was demonstrated by FT‐IR spectroscopy. The photocatalytic degradation of the TiO₂‐SAHMA polymer films was also investigated under medium pressure mercury lamp illumination in air. SAHMA based film containing 2 wt % TiO₂ showed the highest degradation and the highest loss in weight. The weight of the polymer was reduced by 25% of its initial value after irradiation for 40 h. To examine the surface morphology of the irradiated polymer films, SEM analysis was carried out and cavities were detected around TiO₂ particles. The photocatalytic and thermomechanical properties of SAHMA and styrene (STY) based copolymers were also investigated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Preparation and drug‐release behavior of 5‐fluorouracil‐loaded poly(lactic acid–4‐hydroxyproline–polyethylene glycol) amphipathic copolymer nanoparticles

Poly(lactic acid–4‐hydroxyproline–polyethylene glycol) (PLA–Hpr–PEG) was synthesized via melt copolymerization with stannous chloride as a catalyst activated by a proton acid. Copolymers with different poly(ethylene glycol) (PEG) concentrations (0.1, 0.5, 1, and 5 wt %) were synthesized and exhibited moderate molecular weights (weight‐average molecular weight = 9705–13,600 g/mol) and reasonable molecular weight distributions (weight‐average molecular weight/number‐average molecular weight = 1.35– 1.66). The structure of the polymers was verified with infrared spectroscopy and proton nuclear magnetic resonance spectroscopy. The nanoparticles were made by the nanoprecipitation method with PLA–Hpr–PEG. The size and size distribution of the nanoparticles were investigated with laser light scattering, and the surface morphology of the nanoparticles was investigated with transmission electron microscopy. The drug encapsulation efficiency and drug loading content were measured with ultraviolet absorption spectroscopy. The effects of various formulation parameters were evaluated. The prepared nanoparticles were spherical and greater than 100 nm in size. The drug loading content and encapsulation efficiency were greatly influenced by the amount of the copolymer and the volume of the solvent. The PEG content in the polymer could affect the release of drugs from the PLA–Hpr–PEG nanoparticles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2654–2659, 2007