Photo- and Radiation Creep and Durability of Polymers

The creep behavior of polycarbonate, polycaproamide, and polystyrene samples upon simultaneous and successive irradiation by fast electrons and optical-frequency radiation (photo- and radiation impact) was studied. The action of visible light in conjunction with electrons or immediately after electron irradiation leads to a dramatic increase in the creep rate. The absorbed doses of the onset of polymer degradation upon photo- and radiation impact are about an order of magnitude lower than those for electron irradiation alone. Macroradicals and stable radiolytic products absorbing light in a longer wavelength spectral region as compared with the initial polymers are assumed to be responsible for the photo- and radiation creep and durability of the polymers.     

Radiation degradation of poly(arylene ether ketone)s

The resistance of five poly(arylene ether ketone)s with related chemical structures to degradation by ionizing radiation has been studied by ESR spectroscopy and yields of volatile products. All of the polymers showed high resistance to radiation with low yields of radicals after irradiation in vacuum at 77 K (when up to 84% of the radicals were identified as radical anions) and much lower yields at 300 K. The yields of volatile products were much less than reported for poly(arylene sulfone)s [1, 2]. Methyl substitution on a main-chain aromatic ring decreased the radiation resistance, but methane only comprised 10% of the volatile products from the methyl-substituted polymers. A polymer containing an isopropylidene group in the main chain and a substituent aromatic carbonyl showed significantly decreased radiation resistance. Extremely low radical yields were obtained after irradiation in air at 300 K, contrary to many polymers. XPS analysis showed an increase in C–O bonds on the surface after irradiation in air.     

Conjugated Molecules and Polymers in Secondary Batteries: A Perspective

Intrinsically conducting polymers constituting a subclass of macromolecules, as well as a still growing family of large, conjugated molecules, oligomers, and polymers, have attracted research interest for the recent decades. Closely corresponding to the fascination of these materials, combining typical properties of organic polymers and metallic materials, numerous applications have been suggested, explored, and sometimes transferred into products. In electrochemistry, they have been used in various functions beyond the initially proposed and obvious application as active masses in devices for electrochemical energy conversion and storage. This perspective contribution wraps up basic facts that are necessary to understand the behavior and properties of the oligo and polymers and their behavior in electrochemical cells for energy conversion by electrode reactions and associated energy storage. Representative examples are presented and discussed, and an overview of the state of research and development is provided. Particular attention is paid to stability and related aspects of practical importance. Future trends and perspectives are indicated.     

Radiation processing of natural polymers: The IAEA contribution

Radiation processing offers a clean and additive-free method for preparation of value-added novel materials based on renewable, non-toxic, and biodegradable natural polymers. Crosslinked natural polymers can be used as hydrogel wound dressings, face cleaning cosmetic masks, adsorbents of toxins, and non-bedsore mats; while low molecular weight products show antibiotic, antioxidant, and plant-growth promoting properties. Recognizing the potential benefits that radiation technology can offer for processing of natural polymers into useful products, the IAEA implemented a coordinated research project (CRP) on “Development of Radiation-processed products of Natural Polymers for application in Agriculture, Healthcare, Industry and Environment”. This CRP was launched at the end of 2007 with participation of 16 MS to help connecting radiation technology and end-users to derive enhanced benefits from these new value-added products of radiation-processed natural materials. In this paper the results of activities in participating MS related to this work will be presented.     

Effect of gamma radiation on dilute aqueous solutions and thin films of N-succinyl chitosan

N-Succinyl chitosan (N-SC) products with various degrees of substitution were synthesized by a direct reaction between chitosan and succinic anhydride. The susceptibility of the as-synthesized polymers to degradation upon their exposure to γ-ray radiation was investigated. The results were compared with the as-received chitosan. The size exclusion chromatographic results showed that chitosan and N-SC products in their dilute aqueous solution state were more subservient to degradation by γ-ray radiation than in their solid film state, despite the much less exposure to the radiation (i.e., 5-30 kGy for the solutions versus 20-100 kGy for the films). Increasing the radiation dose resulted in the rather monotonous decrease in the molecular weights of the polymers. Structural analyses of the irradiated polymers by Fourier-transformed infrared spectroscopy (FT-IR) and UV-visible spectrophotometry indicated the increase in the amount of carbonyl groups with the radiation dose. The formation of the carbonyl groups suggested that the radiolysis of chitosan and N-SC products occurred at the glycosidic linkages. In addition, FT-IR, elemental analysis and proton nuclear magnetic resonance spectroscopy (¹H NMR) results suggested that γ-ray radiation affected both the N-acetyl and N-substituted groups on the polymer chains.     

Vacuum-ultraviolet induced oxidation of the polymers polyethylene and polypropylene

The emission from low-pressure microwave plasmas in the vacuum-ultraviolet (VUV) region (λ < 200 nm) was investigated in order to use these plasmas as light sources for the study of the VUV photochemistry of polyethylene (PE) and polypropylene (PP) as part of the study of plasma-polymer interaction. These polymers, immersed in low-presure oxygen, were exposed to radiation with wavelengths down to 112 nm, the cut off of magnesium fluoride used as a window to separate the polymer specimen from the plasma light source. Total oxygen incorporation in the surface [O], and the formation of hydroxyl, carbonyl, and carboxyl groups were measured using XPS in combination with chemical derivatizations, particularly their dependence upon the radiation spectrum and the oxygen pressure around the sample. In most experiments the surface oxygen concentration [O] attained a constant value that appears to be related to the initial oxidation rate; this suggests a competition between oxygen incorporation and chain scission reactions, followed by the removal of volatile oxidation products. PE is usually oxidized to a higher level than PP, the latter appearing to be more susceptible to reaction with atomic oxygen than PE. A general initiation mechanism for the VUV experiments is proposed that allows us to explain the observed differences in behavior between PE and PP, and the results obtained under different irradiation conditions. The nature of oxidation products is in both cases very similar to what is observed after direct plasma treatment of the polymers. We conclude that short wavelength radiation contributes very appreciably to the observed surface modification effects during plasma treatment of PE and PP. © 1995 John Wiley & Sons, Inc.     

Effects of solar radiation on collagen and chitosan films

Photo-aging and photo-degradation are the deleterious effect of chronic exposure to sun light of many materials made of natural polymers. The resistance of the products on the action of solar radiation is very important for material scientists. The effect of solar radiation on two natural polymers: collagen and chitosan as well as collagen/chitosan blends in the form of thin films has been studied by UV-Vis and FTIR spectroscopy. It was found that UV-Vis spectra, which characterise collagen and collagen/chitosan films, were significantly altered by solar radiation. FTIR spectra of collagen and collagen/chitosan films showed that after solar irradiation the positions of amide A and amide I bands were shifted to lower wavenumbers. There was not any significant alteration of chitosan UV-Vis and FTIR spectra after solar radiation. In the condition of the experiment chitosan films were resistant to the action of solar radiation. The effect of solar UV radiation in comparison to artificial UV radiation has been discussed.     

天然植物高分子药用胶囊的研究与发展

讨论了天然植物高分子药用胶囊的最新研究与发展,介绍了目前的主要研究成果并提出展望.不仅从化学结构、流变和相变等基础理论方面探讨了各类植物药用胶囊的特性和研制中所遇到的问题,同时对各种胶囊制备设备与工艺的发展及应用中的技术改进进行了综述分析.传统明胶胶囊生产工艺的应用已有160多年的历史,目前植物胶囊生产设备和工艺多是建立在传统明胶胶囊生产的基础上.研究植物胶囊材料的流变和凝胶性能以尽量满足传统明胶的设备与工艺是当今急需解决的难题之一.近年来,随着人们对淀粉结构和改性方法的深入研究(尤其是将淀粉基可生物降解材料的制备技术与传统食品科学的研究成果有效结合),应用高分子科学理论和方法提高淀粉基材料的加工性能,力学性能与稳定性的研究有了突破性进展,为淀粉胶囊的研制提供了理论和技术上的有力支持.使用传统塑料加工的挤出加工法制备植物胶囊,是植物胶囊研究中的重大突破和创新.从原材料来源的充足性和价格上考虑,淀粉是最有潜力替代传统胶囊的原料之一.     

Functional nanocomposites for energy storage: chemistry and new horizons

Energy storage devices are one of the hot spots in recent years due to the environmental problems caused by the large consumption of unsustainable energy such as petroleum or coal. Capacitors are a common device for energy storage, especially electrical energy. A variety of types including electrolytic capacitors, mica capacitors, paper capacitors, ceramic capacitors, film capacitors, and non-polarized capacitors have been proposed. Their specific applications depend on their intrinsic properties. Dielectric capacitors have reasonable energy storage density, with current research focusing on the enhancement of energy density and making the materials more flexible as well as lightweight. Improvement strategies are based on the premise that use of two or more different materials (e.g. polymers and ceramics/metals) at an optimal formulation can result in properties that combine the advantages of the precursor materials. Different polymers especially fluoropolymers (e.g. PVDF and PVDF based co-polymer) are the main components in dielectric nanocomposites for capacitors with high energy storage performance. In this article, we have briefly summarized the recent advances in functional polymers nanocomposites for energy storage applications with a primary focus on polymers, surface engineering, functional groups and novel synthesis/manufacturing concepts applied to new materials. The article presents a unique integrated structure and approaches providing key knowledge for the design and development of novel, low-cost, multifunctional next-generation energy storage materials with improved efficiency.     

微孔配位聚合物作为新型储氢材料的研究

微孔配位聚合物性质独特、结构多样,具有广泛的应用前景,它已成为近几年来一个热门的研究领域。本文简要介绍该类化合物作为一种新型的储氢材料,在合成、结构和储氢性能方面的研究进展。     

Highly efficient and well‐controlled ambient temperature RAFT polymerization of glycidyl methacrylate under visible light radiation

A range of well‐defined poly(glycidyl methacrylate) (PGMA) polymers and their corresponding block copolymers were synthesized via 2‐cyanoprop‐2‐yl(4‐fluoro) dithiobenzoate or CPFDB‐mediated ambient temperature reversible addition fragmentation chain transfer radical polymerization or RAFT polymerization under environmentally friendly visible light radiation (λ = 405–577 nm), using a (2,4,6‐trimethylbenzoyl) diphenylphosphine oxide photoinitiator. As comparison, CPFDB‐mediated ambient temperature RAFT polymerizations of glycidyl methacrylate (GMA) under both full‐wave radiation (λ = 254–577 nm) and long‐wave radiation (λ = 365–577 nm) were also studied in this article. The results indicated that CPFDB moieties were significantly photolyzed under either full‐wave radiation or long‐wave radiation, thus undermining the controlled behavior of these RAFT processes. Whereas this photolysis was significantly suppressed under visible light radiation, thus CPFDB functionalities exerted well control over RAFT process, leading to a remarkably living behavior up to 90% GMA monomer conversions. This strategy facilitates the facile synthesis of well‐defined PGMA polymers. More importantly, under visible light radiation, a relatively high initial molar ratio of GMA to CPFDB and TPO led to shortening initialization period of RAFT process and accelerating overall polymerization rate. These effects are remarkably in favor of the facile synthesis of well‐defined PGMA polymers and PGMA‐based copolymers with high molecular weights. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5091–5102, 2007     

Effects of ionizing radiation on linear aromatic polyesters

The influence of chemical structure on the response of aromatic polyesters to high-energy ionizing radiation was studied. Systematic variations of polymers related to poly(ethylene terephthalate) were subjected to γ radiation, and the competitive chain scission and crosslinking reactions were determined by measuring changes in intrinsic viscosity and molecular weights. It was found that an increase in the paraffinic glycol segment of polyterephthalates facilitated crosslinking, while the protective nature of aromatic groups was demonstrated by modifying the dibasic acid segments. The influence of substituents on the terephthalate moiety was mixed: electronegative groups led to chain scission (as evidenced by decreased viscosities), but electropositive substituents exerted a stabilizing effect on polymer viscosity. In almost all cases, number-average molecular weights were decreased by exposure to γ radiation, regardless of viscosity behavior. Crystalline melting temperatures of the polymers generally were decreased by the combined radiation effects of chain scission and crosslinking.     

Radiation effects on polymer materials in radiation sterilization of medical supplies

Radiation degradations of polypropylene were studied by measuring chemiluminescence of the irradiated samples. The chemiluminescence emitted by recombination of peroxy radicals were found to increase with increasing dose, reflecting degree of oxidation of polymers. The degradation of PP may be attributed mainly to the oxidation, since the degradation of PP irradiated in air were markedly larger than that in vacuo. It was found that degree of oxidation of EB-irradiated PP was only one-half that for γ-ray-irradiated one. And also the degree of oxidation was found to be very high at the surface area of the film where oxygen can diffuse during irradiation and decrease sharply with increasing depth from the surface.The degradation during storage after irradiation were estimated by the decay curves of chemiluminescence. The degradation during storage occurred at earlier stage up to three months, while in later stage, it hardly proceeded. The degradation of EB-irradiated samples during storage was much smaller than that found in gamma rays irradiation. Irradiation of 2.5 Mrad with EB caused degradation only during storage. It was suggested that the degradation during storage depends on the degree of radiation oxidation. Both degradations, during irradiation and during storage after irradiation, caused by EB irradiation were also found to be smaller than those by γ-rays. The relationship between radiation degradation and degree of crystallinity of polypropylene was also discussed in this paper.     

Chemical structure of poly(ethylene terephthalate)–styrene and nylon–styrene graft copolymers prepared by radiation techniques

The graft copolymerizations of styrene onto poly(ethylene terephthalate) (PET) and nylon fibers were carried out by the mutual irradiation and preirradiation methods. True graft copolymers were isolated from the products by extraction and characterized by hydrolysis and osmometry. Among the swelling agents employed, methanol was most effective for increasing the extent of grafting onto PET. In both methods of the grafting, the molecular weight of polystyrene formed in the substrate matrix was higher than one million if no chain-transfer agent was added to the monomer solution. Similar to the case of radiation grafting onto poly(vinyl alcohol) and cellulose, the isolated graft copolymer carried only one branch per copolymer molecule in both cases. Of great interest is the particularly low extent of grafting in the case of PET–styrene. This should be attributed to the low sensitivity of PET to radiation. The grafting site on the mother polymer molecule is discussed on the basis of the solution behavior of the branch polymers separated from the backbone.     

含偶氮苯生色团的环氧树脂型光动力高分子的合成

1995年 ,Ｎａｔａｎｓｏｈｎ等和Ｔｒｉｐａｔｈｙ等分别同时报道了在干涉的偏振激光照射下 ,聚合物膜表面分子可发生宏观质量迁移的现象[1 ,2 ] .这种现象一经发现就得到了科技界和工业部门的广泛关注 .利用此效应可以在聚合物表面形成表面起伏光栅 (Ｓｕｒｆａｃｅｒｅｌｉｅｆｇｒａｔｉｎｇｓ)等复杂结构 ,并可用热或光的方法不留痕迹地进行擦除[3 ,4] .这类新型材料和有关的表面可逆光加工技术在光电子通讯和信息存储等领域具有很大的发展潜力和应用价值[5 ,6] .具有上述特性的聚合物也被称为光动力高分子 (Ｐｈｏｔｏｄｙｎａｍｉｃｐ…     

Vacuum Ultraviolet Irradiation of Polymers

The interest in incoherent sources for wavelength-selective photochemistry has increased lately, but little is still known about the behavior of polymers when exposed to far UV and vacuum UV (VUV) radiation. The same dearth of information exists regarding UV (VUV) radiation emitted by low-pressure plasmas during polymer treatment. In order to study VUV-UV effects on several polymers (polyethylene - PE, polystyrene - PS, hexatriacontane - HTC, and poly(methyl methacrylate) - PMMA), we have used the well-characterized emissions from hydrogen (broad-band emission) and hydrogen/argon mixture (near-monochromatic radiation) plasmas as light sources. During irradiation, samples were kept under vacuum or in a flow of pure oxygen at low pressure; in both cases the radiation fluxes at the sample position have been precisely determined by careful spectroscopic calibration experiments. We have employed a quartz crystal microbalance (QCM) to measure in-situ any possible mass change of the various polymers. Following irradiation, samples were analysed by ellipsometry (for thickness and refractive index), X-ray photoelectron spectroscopy (XPS, to evaluate the near-surface composition and content of various functional groups), and atomic force microscopy (AFM, for surface topography and roughness measurements).     

Modification,degradation and stabilization of polymers in view of the classification of radiation spurs

Classification of spurs according to their size dominated early developments of aqueous radiation chemistry and still applies to polymers dissolved in water. The energy of ionizing radiation is absorbed proportionally to the participation of electrons in the system and therefore in diluted aqueous solutions in polymer is attacked by products of radiolysis of water and the direct interaction of radiation with polymer is negligible. Pure polymers also absorb the ionizing radiation energy heterogeneously with the resulting variety of spur sizes. A full theoretical approach, already difficult and not fully understood in the case of water, is practically impossible for polymers at the time being, but there are sufficient experimental facts, showing that, even with low LET radiation, there is a full spectrum from single-ionization to multi-ionization spurs. The paper promotes the idea that single-ionization spurs do not cause the chain scission, but are responsible for energy transfer, protection effect (in aliphatic–aromatic copolymers and blends) and grafting. Large spurs with their high concentration of energy cause chain-scission and low MW debris. Depending on the type of polymer, all sizes of spurs can contribute to radiation-induced crosslinking.     

“Living” free radical graft copolymers I: Preparation and properties

Polymers substituted with thio groups are useful for the photochemical synthesis of graft copolymers. Such copolymers have been prepared by the initial conversion of backbone polymers containing chlorinated substituents into polymers containing diethyldithiocarbamate (TC), isopropyl xanthate (IX) or mercaptobenzothiazole (BT) functionality. The photochemical reaction of monomers with these products produced graft copolymers. A variety of halogenated polymers were investigated as starting materials for these syntheses, including poly(vinyl chloride), chlorinated polyvinyl chloride), chlorinated polyethylene, chlorobutyl rubber and neoprene. Characteristics of the grafting reactions, including “pseudo-living” behavior and tandem grafting aspects, were investigated. Glass transitions of the grafted polymers were found to vary uniformly with composition for most of the grafted products.     

Polymerization behavior of N-(p-vinyl)phenylacrylamide

The polymerization behavior of N-(p-vinyl)phenylacrylamide, synthesized from p-aminostyrene and acryloyl chloride by means of the Schotten-Baumann reaction was studied. Due to a marked difference in electron density between the two double bonds, this monomer provided soluble polymers by both cationic and anionic polymerization procedures, the cationic and anionic polymers mainly carrying, as side chains, the acrylamide and styrene moieties, respectively. The polymerization behavior of the residual double bonds was also investigated for both polymers, leading to crosslinked, insoluble products.     

Excitation Frequency Dependence of the Surface Properties and Composition of Plasma Polymers from Aldehyde Monomers

The effect was investigated of varying the plasma excitation frequency in the range 125 to 375 kHz upon the air/water contact angles of plasma polymers prepared from the monomers ethylbutyraldehyde (EBA), acetaldehyde (AA), capronaldehyde (CA), and nonyl aldehyde (NA). The surfaces of EBA, CA, and AA plasma films were more hydrophilic when deposited at lower excitation frequencies whereas little frequency dependence was observed in the case of NA plasma polymers. Lower contact angles correlated with increased amounts of C=O and O–C=O groups measured by FTIR and XPS analyses. The effects of storage (aging) in air at room temperature upon the properties of the plasma polymers were also studied. Contact angles of EBA plasma polymers decreased during aging. The contact angles of NA plasma polymers were stable over a 3 months storage period. In the case of CA plasma polymers, the contact angles decreased on aging for films deposited at higher frequencies, whereas CA films deposited at lower frequencies showed increasing contact angles on storage. This aging behavior is interpreted as a result of competition between post-deposition oxidative reactions with atmospheric oxygen and reorientation of polar polymer segments away from the air interface.