Polymerization reactions and modifications of polymers by ionizing radiation

Ionizing radiation has become the most effective way to modify natural and synthetic polymers through crosslinking, degradation, and graft polymerization. This review will include an in-depth analysis of radiation chemistry mechanisms and the kinetics of the radiation-induced C-centered free radical, anion, and cation polymerization, and grafting. It also presents sections on radiation modifications of synthetic and natural polymers. For decades, low linear energy transfer (LLET) ionizing radiation, such as gamma rays, X-rays, and up to 10 MeV electron beams, has been the primary tool to produce many products through polymerization reactions. Photons and electrons interaction with polymers display various mechanisms. While the interactions of gamma ray and X-ray photons are mainly through the photoelectric effect, Compton scattering, and pair-production, the interactions of the high-energy electrons take place through coulombic interactions. Despite the type of radiation used on materials, photons or high energy electrons, in both cases ions and electrons are produced. The interactions between electrons and monomers takes place within less than a nanosecond. Depending on the dose rate (dose is defined as the absorbed radiation energy per unit mass), the kinetic chain length of the propagation can be controlled, hence allowing for some control over the degree of polymerization. When polymers are submitted to high-energy radiation in the bulk, contrasting behaviors are observed with a dominant effect of cross-linking or chain scission, depending on the chemical nature and physical characteristics of the material. Polymers in solution are subject to indirect effects resulting from the radiolysis of the medium. Likewise, for radiation-induced polymerization, depending on the dose rate, the free radicals generated on polymer chains can undergo various reactions, such as inter/intramolecular combination or inter/intramolecular disproportionation, b-scission. These reactions lead to structural or functional polymer modifications. In the presence of oxygen, playing on irradiation dose-rates, one can favor crosslinking reactions or promotes degradations through oxidations. The competition between the crosslinking reactions of C-centered free radicals and their reactions with oxygen is described through fundamental mechanism formalisms. The fundamentals of polymerization reactions are herein presented to meet industrial needs for various polymer materials produced or degraded by irradiation. Notably, the medical and industrial applications of polymers are endless and thus it is vital to investigate the effects of sterilization dose and dose rate on various polymers and copolymers with different molecular structures and morphologies. The presence or absence of various functional groups, degree of crystallinity, irradiation temperature, etc. all greatly affect the radiation chemistry of the irradiated polymers. Over the past decade, grafting new chemical functionalities on solid polymers by radiation-induced polymerization (also called RIG for Radiation-Induced Grafting) has been widely exploited to develop innovative materials in coherence with actual societal expectations. These novel materials respond not only to health emergencies but also to carbon-free energy needs (e.g., hydrogen fuel cells, piezoelectricity, etc.) and environmental concerns with the development of numerous specific adsorbents of chemical hazards and pollutants. The modification of polymers through RIG is durable as it covalently bonds the functional monomers. As radiation penetration depths can be varied, this technique can be used to modify polymer surface or bulk. The many parameters influencing RIG that control the yield of the grafting process are discussed in this review. These include monomer reactivity, irradiation dose, solvent, presence of inhibitor of homopolymerization, grafting temperature, etc. Today, the general knowledge of RIG can be applied to any solid polymer and may predict, to some extent, the grafting location. A special focus is on how ionizing radiation sources (ion and electron beams, UVs) may be chosen or mixed to combine both solid polymer nanostructuration and RIG. LLET ionizing radiation has also been extensively used to synthesize hydrogel and nanogel for drug delivery systems and other advanced applications. In particular, nanogels can either be produced by radiation-induced polymerization and simultaneous crosslinking of hydrophilic monomers in “nanocompartments”, i.e., within the aqueous phase of inverse micelles, or by intramolecular crosslinking of suitable water-soluble polymers. The radiolytically produced oxidizing species from water, •OH radicals, can easily abstract H-atoms from the backbone of the dissolved polymers (or can add to the unsaturated bonds) leading to the formation of C-centered radicals. These C-centered free radicals can undergo two main competitive reactions; intramolecular and intermolecular crosslinking. When produced by electron beam irradiation, higher temperatures, dose rates within the pulse, and pulse repetition rates favour intramolecular crosslinking over intermolecular crosslinking, thus enabling a better control of particle size and size distribution. For other water-soluble biopolymers such as polysaccharides, proteins, DNA and RNA, the abstraction of H atoms or the addition to the unsaturation by •OH can lead to the direct scission of the backbone, double, or single strand breaks of these polymers

On the nature of macroradicals formed upon radiolysis of aqueous poly(N-vinylpyrrolidone) solutions

In this work we have explored the nature of macroradicals formed upon radiolysis of aqueous poly(N-vinylpyrrolidone) (PVP) solutions using pulse radiolysis, density functional theory (DFT) and literature data. On the basis of literature data on site-specific kinetics of hydrogen abstraction from simple amides and spectra corresponding to specific radical sites on the same amides we have assessed the distribution of H-atom abstraction by \u2022OH radicals from different positions on the pyrrolidone ring and the polymer backbone. Pulse radiolysis experiments performed at different doses per pulse and different PVP concentrations demonstrate that the H-abstracting radiolysis products are not quantitatively scavenged by the polymer when the dose per pulse exceeds 4840 Gy. The implications of this are discussed in the context of radical-initiated crosslinking reactions. At a mass fraction of 0.1% PVP and doses per pulse ranging from 7 Gy to 117 Gy, the overall radical decay observed at 390 nm follows second order kinetics with rate constants on the order of 109 dm3 mol-1 s-1

Phylogeography of the smooth-coated otter (Lutrogale perspicillata): distinct evolutionary lineages and hybridization with the Asian small clawed otter (Aonyx cinereus)

We investigated the phylogeography of the smooth-coated otter (Lutrogale perspicillata) to determine its spatial genetic structure for aiding an adaptive conservation management of the species. Fifty eight modern and 11 archival (dated 1882–1970) otters sampled from Iraq to Malaysian Borneo were genotyped (mtDNA Cytochrome-b, 10 microsatellite DNA loci). Moreover, 16 Aonyx cinereus (Asian small-clawed otter) and seven Lutra lutra (Eurasian otter) were sequenced to increase information available for phylogenetic reconstructions. As reported in previous studies, we found that L. perspicillata, A. cinereus and A. capensis (African clawless otter) grouped in a clade sister to the genus Lutra, with L. perspicillata and A. cinereus being reciprocally monophyletic. Within L. perspicillata, we uncovered three Evolutionarily Significant Units and proved that L. p. maxwelli is not only endemic to Iraq but also the most recent subspecies. We suggest a revision of the distribution range limits of easternmost L. perspicillata subspecies. We show that smooth-coated otters in Singapore are L. perspicillata x A. cinereus hybrids with A. cinereus mtDNA, the first reported case of hybridization in the wild among otters. This result also provides evidence supporting the inclusion of L. perspicillata and A. cinereus in the genus Amblonyx, thus avoiding the paraphyly of the genus Aonyx

Molecular phylogeography of the smooth-­‐coated otter (Lutrogale perspicillata, Mustelidae) for its conservation in the Mesopotamian marshes of Iraq

The smooth-coated otter (Lutrogale perspicillata) (SCO) includes perspicillata (SE Asia), sindica (SE Pakistan, W India) and endemic-to-Iraq maxwelli morphological subspecies. Classified as vulnerable by IUCN, the SCO is threatened by habitat transformation, illegal trade and poaching. Non-invasively collected samples in Iraq (10), central and E Asia (nine countries, 46) were sequenced at the entire mtDNA Cytochrome-b gene and genotyped (ongoing) at the microsatellite DNA. We also obtained 307 bp-long gene fragments from 16 SCOs resident to US and European museums. We used 19 Lutrinae GenBank entries. In Iraq, we provided genetic evidence for endemicity of maxwelli to Mesopotamia (private haplotype, mostly from Al-Hawizeh Marsh, S Iraq), while we could not confirm the occurrence of the SCO in N Iraq (Kurdistan).We found reciprocally monophyletic mtDNA lineages across the SCO range each corresponding to a subspecies. Preliminary microsatellite DNA results confirmed this mtDNA picture, overall pointing to three Evolutionarily Significant Units. Looking-like SCOs from Singapore showed oriental small-clawed otter (Aonyx cinerea) mtDNA. We will investigate A. cinerea-mtDNA introgressed SCOs at the microsatellite DNA to assess if they are descendant of L. perspicillata x A. cinerea otters (i.e., first hybrid record in the wild for Lutrinae). Several museum specimens were genetically identified as other than the SCO (even an African otter),indicating that morphology can be not sufficient to reliably catalogue otter study skins. In Iraq, genetic and fieldwork (not shown) data will help establishing a National Single Species Action Plan for the SCO. [National Geographic Society Conservation

Unravelling the biogeography of secretive taxa by museum collections: the untold story of the black francolin (Francolinus francolinus, Phasianidae) in the Mediterranean

The black francolin (Francolinus francolinus) (BF) comprises six morphological subspecies distributed from Cyprus and Turkey across Asia to India. In spite of being renowned as courtly gamebird since the Classic Age, this species suffers from paucity of demographic and molecular studies. In order to update the BF biogeographic pattern by pursuing a thorough sampling across the unsafe and remote areas representing most of the specie’s range, tissues from museum specimens (76, XVIIIth c.-­‐1954) hosted in US and European ornithological collections were genotyped at a 185 bp-­‐long fragment of the mtDNA Control Region gene along with modern birds (205) sequenced at the entire gene. The access to ornithological collections opened the unforeseen opportunity to elucidate the genetic affinity of the extinct populations once residing in the western Mediterranean (Italy, Spain), thus settling the debate about autochthony versus allochthony in that region. Three well-­‐defined haplogroups -­‐ each one including a pair of morphological subspecies and matching the phylogeographical pattern inferred with the whole gene -­‐ were found to reflect a westward adaptive radiation, a more complex scenario being nonetheless disclosed in the Indian sub-­‐continent. The nonnative status of the western Mediterranean BFs was ultimately assessed, a tight genetic affinity with conspecifics from Cyprus and southern Asia being found. This finding, which partly confirmed the invoked importation during the Crusades, pointed to the major human impact on Mediterranean biodiversity through long-­‐distance trade across Asia to satisfy the high demand for exotic species by the European aristocracy during the Medieval times and the Renaissance