An ESR and NMR study of the gamma radiolysis of a bisphenol-A based polycarbonate and a phthalic acid ester

A study of the γ-radiolysis of the commercial polymers U-polymer, UP (Unitake) and polycarbonate, PC, (Aldrich) has been undertaken using ESR spectroscopy. The G-value of radical formation at 77 K has been found to be 0.31±0.01 for UP and 0.5±0.02 for PC. By using thermal annealing and spectral subtraction, the paramagnetic species formed on irradiation has been assigned. The effect of radiation on the chemical structure of UP and PC has been investigated at ambient temperature and at 423 K. The NMR results show that a new phenol type chain end is formed in the polymers on exposure to γ-radiation. The G-value of formation of the new phenol ends was estimated to be 0.7 for PC (423 K) and 0.4 for UP (300 K). © 1998 John Wiley & Sons, Ltd.     

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.     

Radiation-Induced Conductivity of Polymer Composites Filled by Finely Divided Oxides

The radiation-induced conductivity of polymer composites based on polyisoprene rubber filled with finely divided oxides of various chemical natures was studied in the continuous irradiation mode. It was shown that the radiation conductivity is closely related to the molecular mobility of the rubber. It was found that a change in the character of thermal motion of fragments of rubber macromolecules, which is caused by interaction with the filler, could considerably enhance the radiation-induced conductivity of a polymer composite.     

Liquid crystal polymers 23. Steric and polar effects of large substituents in thermotropic aromatic polyesters with decamethylene spacers

A series of thermotropic aromatic polyesters based on a triad ester mesogenic unit containing an arylsulfonyl substituted hydroquinone group and a decamethylene spacer group was prepared. The large arylsulfonyl substituent was substituted in the para-position with either electron donating or accepting groups to study the effect of steric and polar interactions on the thermal transitions of these polymers and on the thermodynamic parameters of their isotropization transitions. All polymers formed nematic melts, and a regular decrease in T₁, ΔH₁ and ΔS₁ was observed with increasing molecular radius of the substituted hydroquinone group. However, a polarity or polarizability effect was superimposed on these relationships. Model compounds containing the same aromatic ester triad were prepared and their thermotropic properties were compared to those of the polymers. Essentially identical effects were observed for both.     

Changes of surface chemical structure and composition of phenolphthalein poly(ether sulfone) in different radiations

To understand the different action mechanisms of space irradiation on polymers, phenolphthalein poly(ether sulfone) (PES‐C) blocks were irradiated by electrons and atomic oxygen. The changes in surface chemical structure and composition of PES‐C in different radiations were studied by attenuated total‐reflection FTIR (FTIR‐ATR) and XPS. It was found that PES‐C was prone to be influenced by space irradiation. Electron and atomic oxygen irradiation can destroy the molecular chain of PES‐C and result in changes of surface chemical composition of the polymer. But due to the different nature of the radiation sources, electron irradiation induced the carbonization of the polymer surface, while atomic oxygen irradiation resulted in the oxidation of the polymer surface. Besides this, the sulfone structure was reduced or oxidized depending on the nature of the radiation sources. So, different radiation sources might influence the surface chemical structure and composition of polymers differently. Copyright © 2008 John Wiley & Sons, Ltd.     

Degradation behavior of poly (l-lactide-co-glycolide) films through gamma-ray irradiation

Gamma-ray irradiation is a very useful tool to improve the physicochemical properties of various biodegradable polymers without the use of a heating and crosslinking agent. The purpose of this study was to investigate the degradation behavior of poly (l-lactide-co-glycolide) (PLGA) depending on the applied gamma-ray irradiation doses. PLGA films prepared through a solvent casting method were irradiated with gamma radiation at various irradiation doses. The irradiation was performed using 60Co gamma-ray doses of 25–500 kGy at a dose rate of 10 kGy/h.The degradation of irradiated films was observed through the main chain scission. Exposure to gamma radiation dropped the average molecular weight (M_n and M_w), and weakened the mechanical strength. Thermograms of irradiated film show various changes of thermal properties in accordance with gamma-ray irradiation doses. Gamma-ray irradiation changes the morphology of the surface, and improves the wettability. In conclusion, gamma-ray irradiation will be a useful tool to control the rate of hydrolytic degradation of these PLGA films.     

Properties and hydrolysis of PLGA and PLLA cross-linked with electron beam radiation

Radiation has been used as a processing tool to modify the properties of polymers. The aim of this study is to understand how electron beam radiation, together with pentaerythritol tetraacrylate (PTTA) as a tetra-functional monomer, can alter the properties (i.e. thermal and mechanical) and hydrolysis rates of PLGA and PLLA. The effects of radiation dose and PFM concentration on the physical properties of the polymers were investigated. The results showed that upon irradiation PLGA and PLLA cross-linked, and an increased in gel content was observed. Glass transition temperature (T_g) and mechanical properties of the polymers also increased. Cross-linked PLGA and PLLA samples were found to retard hydrolytic degradation. The mechanical properties of these polymers were also unaffected by hydrolysis. In summary, PLGA and PLLA cross-linked with PTTA were found to have enhanced mechanical properties and were able to retard hydrolytic degradation.     

Radiothermoluminescence of tetiamethylene sulfoxide

Radiothermoluminescence (RTL) and ESR spectra of tetramethylene sulfoxide (TMSO) irradiated by X-ray and⁶⁰Co γ-ray radiation have been studied at 77 K. The temperatures of RTL maxima were correlated with the changes in color of specimens and the shape of the ESR spectral lines. The temperatures at which maxima or inflections are observed (depending on the kind of irradiation, dose, and introduced additives) were determined: 90, 115, 125, 133, 145, and 155 K. A signal of the TMSO radical cation was observed in the ESR spectrum (a singfet with g = 2.008±0.001 and δH = 12 Oc); it completely disappeared after the cessation of luminescence at the maximum at 133 K. An analogous result is achieved by illumination of the specimen with maximum effect in the yellow-green region of the spectrum. Activation of RTL by the UO₂ ²⁺ and Tb³⁺ ions was studied. Their thermal deactivation was correlated with molecular mobility manifested in RTL.     

Vinyl acetate polymerization by ionizing radiation

For this work an irradiation system to be used in the polymerization of the vinyl acetate in methylethylketone and in ethyl alcohol solution using the gamma radiation as initiator was projected and built. The molecular weights of the polymers obtained by irradiation with gamma rays in methylethylketone and in ethyl alcohol solution were 33,000 and 44,000 g/mol, respectively. From the characterization by infrared spectroscopy it was possible to verify that the polymers obtained in two studied cases actually correspond to poly(vinyl acetate).     

Effect of gamma radiation on fluoropolymers

A series of fluoropolymer films were synthesized by reacting several bisphenol monomers with 1,3‐bis(1,1,1,3,3,3‐hexafluoro‐2‐pentafluorophenyl methoxy‐2‐propyl)benzene via a nucleophilic aromatic substitution to form polyethers. The bisphenols used included two diphenol‐substituted spirodilactams (SDL; aliphatic and aromatic), biphenol, bisphenol A, bisphenol AF, bisphenol O, and bisphenol F to form seven different polymers. Polymers were irradiated by a Gamma beam 651‐PT at a dose rate of 10.5 kGy/h; the absorbed dose in each film was varied between 300 and 1000 kGy. The effect on the chemical structure upon radiation was studied by DSC, TGA, FTIR‐ATR, and NMR after and before irradiation. Thermal analysis showed a lessened thermal stability and a lower T_g after irradiation. Further, irradiation caused a decrease in molecular weight as a result of cleavage of sp³ bonds. These data allowed calculation of the radiochemical yield scission (G_s) for each of these polymers. The SDL aromatic system proved the most radiation‐resistant. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1617–1626, 2009     

Effect of Supermolecular Structure Changes on the Glass Transition of Polymer

The idea of two miscellaneous amorphous fractions in one polymeric system is under consideration. A new factor influencing the glass transition and a relaxation observed in polymers exhibiting different supermolecular structures is discussed. In order to clarify the specific arrangement of backbone chains two types of polymers were taken under investigation: semicrystalline poly(4-methyl-1-pentene) and a liquid-crystalline poly(norbornene) derivative. In both cases,it was possible to find two well separated glass transitions. Differential scanning calorimetry and dynamic mechanical thermal analysis were used to study the effect of thermal history on the assignment of the glass transition event associated with two miscellaneous amorphous phases. The problem of molecular arrangement in the amorphous phases is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal expansion of irradiated polyoxymethylene

The thermal expansion coefficient of gamma irradiated polyoxymethylene has been measured in the temperature range 80–340 K by using a three terminal capacitance technique. The radiation induced changes are measured by recording the i.r. spectra of the irradiated samples. The change in crystallinity caused by irradiation is measured by an X-ray technique. The thermal expansion coefficient increases with radiation dose below 170 K due to the predominant effect of degradation. Above 170 K, this trend reverses and the expansion coefficient decreases with radiation dose due to the increased crystallinity caused by irradiation.     

Viscoelastic Behavior of Amorphous Polymers near the Glass Temperature

Lack of thermorheological simplicity and possible effects of the molecular weight distribution in the softening dispersion of linear amorphous polymers are demonstrated with viscoelastic data on polymethylacrylate PMA and polyvinylacetate PVAc. Superposition of the short time portion of the softening transitions of the retardation spectra of PMA, PVAc, polystyrene, and amorphous polypropylene APP indicates that the local molecular mobility is a constant at T_g within experimental uncertainty. The general features of the retardation spectra of linear amorphous polymers are discussed.     

The synthesis of mesogenic polymers provoked by molecular mobility. polysiloxanarylenes

An approach to the synthesis of potentially thermotropic liquid crystalline polymers based on parallel investigation of their molecular mobility was realized. The initial idea was provoked by the observation that there exists some correspondence of molecular mobility data and the ability of a polymer to form a liquid crystalline phase. Previously this phenomenon was demonstrated on the example of a series of thermotropic main chain polymers with flexible dimethylsiloxane spacers of variable length. The relation between the structure of the main chain and local molecular mobility of different fragments was investigated in a series of regular polysiloxane-silarylenes containing rigid aromatic sequences. Molecular mobility was studied by dielectric spectroscopy in solution and in solid state. The structure of the main chain has been changed by variation of the repeated fragments' length, substituents and joint groups. The data of molecular mobility and their conformity with the chain structure were used for directed synthetic search of desired mesogenic polymers.     

含离子聚合物体系的动力学

离子作用的可逆性赋予了含离子聚合物丰富的力学和电学性能,使其广泛应用在高抗冲材料、记忆材料、自修复材料和智能响应材料等新兴领域.本专论结合作者近年的研究工作,介绍了含离子聚合物体系的构效关系和分子流变学,从3个方面展开:第1部分介绍了对于含离子聚合物的离子聚集状态的调控,和离聚物与聚电解质的相互转化;第2部分介绍了离子高度聚集的无规离聚物丰富的线性黏弹性,重点介绍了非缠结体系在链均一个离子浓度附近区域的溶胶凝胶转变以及缠结体系在平均每个缠结链段一个离子浓度附近区域的单平台到双平台模量的转变;第3部分介绍了如何进行分子设计,使得含离子聚合物成为有效的离子传输介质.最后总结了该研究领域的科学问题和面临的挑战.     

Combining X-ray scattering with dielectric and calorimetric experiments for monitoring polymer crystallization

In order to understand nucleation; crystallization and other phase transitions in polymers, polymer based composites, or in liquid crystals simultaneous experiments with a combination of different methods are useful. Due to different sample geometry, contact faces with the sample holder, and thermal conditions it is usually difficult to compare the results of several individual experiments. As an important supplement to the classical techniques for studying crystallization like X-ray scattering, or differential scanning calorimetry, measurements which test molecular mobility like dielectric or mechanical spectroscopy are of interest during isothermal and non-isothermal crystallization. From such simultaneous experiments one can learn about the existence of pre-ordered structures before formation of crystals, as detected by DSC or X-ray scattering.In this contribution we present the development of a device for simultaneous measurements of electrical properties and X-ray scattering intensities, which was extended to a microcalorimeter and allows measuring thermal properties like heat capacity and thermal conductivity additionally at the same time and at the same sample volume.     

Broad line NMR study of molecular motion in uniaxially stretched polymers

Capability of NMR technique to study fracture and elementary destruction acts in polymers is discussed. Tensile stress influences macromolecular mobility As a rule mobility of macromolecules decreases under deformation. So far deformation remains reversible, this effect is reversible, too. As a result of chain micro-Brownian motion hindering under stress the amorphous layers can pass from high-elastic to solid state even at temperatures rather higher than T_g measured under initial conditions. It is mechanical vitrification (not structure changes) that is regarded as the general causes of draw process interruption (destruction of polymer). Deformation-induced electron emission was detected. It is caused by ionization of stressed chains and tunnel transitions of electrons into deep traps. Influence of molecular mobility on the traps and their destroying under stress are considered.     

Radiation luminescence of polymers—Emission behavior of aromatic compounds incorporated in synthetic rubbers

For a deep understanding of a radiation protection mechanism of some aromatic compounds on synthetic polymers, their optical emission behavior under electron irradiation was studied. The fluorescence light was led out of an irradiation room through a wave guide and detected by a photomultiplier so that less noisy spectrum was obtained. Acenaphthene or acenaphthylene was added to the synthetic rubbers such as ethylene propylene diene terpolymer, styrene butadiene rubber and cis-1,4-polybutadiene. The intensities of optical emission induced by electron beams changed from polymer to polymer, while those by ultraviolet lights were independent of the kind of polymers. The dependence of emission intensity on polymers under electron irradiation was estimated to show the fact that the radiation excited energy transfers occur from the polymer matrix to the additives and that an efficiency of the energy transfer is dependent on kinds of polymers.     

A possible effect of quantum characteristics of vibrational dynamics on the conformational dynamics in polymers

Dielectric losses in poly(vinyl acetate) and poly(ethyleneterephthalate) polar polymers are measured in wide ranges of frequencies and temperatures. The temperature dependences of the frequency of activation transitions of two types, small-scale and conformational, are derived. For conformational transitions, it is revealed that the temperature dependence of their frequency exhibits nonlinear behavior (in Arrhenius coordinates); it determines the temperature dependence of barriers to transitions and the defreezing temperature of conformational dynamics (∼300 K for poly(vinyl acetate) and ∼370 K for poly(ethyleneterephthalate)). This temperature is found to be close to the temperatures of the quantum defreezing of the molecular dynamics of poly(vinyl acetate) and poly(ethyleneterephthalate) (∼300 and 400 K) according to IR spectroscopy data. It is assumed that a decrease in the barrier to the conformational transitions that provide defreezing of the conformational dynamics is caused by a decrease that occurs in the rigidity of polymer molecules owing to quantum defreezing of the vibrational molecular dynamics of the polymers.