Chemiluminescence kinetic analysis on the oxidative degradation of poly(lactic acid)

The oxidation of polymers is characterized by the generation of free radicals, and the kinetic parameters depicting the progress of oxidation are specific for each material structure and formulation. The durability of materials depends intrinsically on the molecular structure, and degradation mechanism influences the long-term stability of products. The intimate transformations of macromolecules can be reliably characterized by chemiluminescence (CL), which depicts the evolution of oxidation state by the reaction of free radicals with molecular oxygen. The isothermal and nonisothermal CL spectra are complementary proofs for the interpretation of oxidation behavior involving hydroperoxide as the initiators of oxidation. The degradation of PLA takes place by decomposition and fragmentation to lactide. The values of five kinetic parameters (initial CL intensity, CL intensity at the first peak, temperature corresponding to the first peak, oxidation induction time and oxidation rate) obtained for oxidative degradation of PLA lead to the activation energies ranged between 49 and 99 kJ mol^?1. The evolution of thermal degradation for poly(lactic acid) is an excellent example for the explanation of the decay fate of radical intermediates.     

(Photo)oxidative degradation and stabilization of flame retarded polymers

Flame retarded polymer formulations are mainly used in long-term applications whereas antioxidants, light stabilizers and co-additives provide the requested lifetime of plastic materials. However many flame retardants influence the oxidative and photooxidative stability of polymers often in a negative way resulting in early failure and loss in value. Moreover insufficient (photo)oxidative stability of the flame retardant itself may reduce the flame retardance performance over time. Therefore, there is a need to develop adjusted stabilizer systems considering the type of flame retardant, the polymer substrate and the intended application. Therefore, the influence of flame retardants on the (photo)oxidative stability of selected polymers is reviewed and strategies to extend the lifetime of flame retarded polymers are provided. In addition, the specific requirements of the stabilization of nanocomposites as potential flame retardant components are covered.     

Clusteroluminescence: A gauge of molecular interaction

Clusteroluminescence (CL) materials, as an emerging class of luminescent materials with unique photophysical properties, have received increasing attention owing to their great theoretical significance and potential for biological applications. Although much progress has been made in the design, synthesis and application of CL materials, there is still a big challenge in the emission mechanism. So far, through-space interaction has been proposed as the preliminary mechanism of the corresponding clusterization-triggered emission (CTE) effect, but a systematic theory is still needed. This review summarizes the current mechanistic understanding of CL materials including organic/inorganic small molecules, and polymers with/without isolated aromatic structures. In addition, some strategies to achieve high quantum yield, adjustable emission color, and persistent room temperature phosphorescence in CL materials are also summarized. At last, a perspective of the mechanism and application of CL materials are demonstrated, which inspire the researchers working on the development of new kinds of functional materials.     

Grafted poly(1→4-β-glucan) strands on silica: a comparative study of surface reactivity as a function of grafting density

Grafted poly(β-glucan) (β-glu) strands on the surface of silica are synthesized with varying degrees of grafting density, and display an amorphous-like environment via (13)C CP/MAS NMR spectroscopy. Thermal gravimetric analysis of these materials under oxidative conditions shows increased β-glu thermal stability with higher degrees of grafting density. The range of temperature stability between the most and least hydrogen-bound grafted β-glu strands spans 321 to 260 °C. This range is bound by the combustion temperature previously measured for crystalline and amorphous cellulose, with the former having greater oxidative stability, and is likely controlled by the extent of hydrogen bonding of a grafted β-glu strand with the underlying silica surface. When using these materials as reactants for glycosidic bond hydrolysis, the total number of reducing ends formed during reaction is quantified using a BCA colorimetric assay. Results demonstrate that the material with greatest interaction with silica surface silanols undergoes hydrolysis at an initial rate that is 6-fold higher than the material with the lowest degree of such interaction. The role of the surface as a reactive interface that can endow oxidative stability and promote hydrolysis activity has broad implications for surface-catalyzed processes dealing with biomass-derived polymers.     

Selecting polymers for medical devices based on thermal analytical methods

This biomaterials overview for selecting polymers for medical devices focuses on polymer materials, properties and performance. An improved understanding of thermoplastics and thermoset properties is accomplished by thermal analysis for device applications. The medical applications and requirements as well as the oxidative and mechanical stability of currently used polymers in devices are discussed. The tools used to aid the ranking of the thermoplastics and thermosets are differential scanning calorimetry (DSC), thermogravimetry (TG), thermal mechanical analysis (TMA) and dynamic mechanical analysis (DMA) as well as a number of key ASTM polymer tests. This paper will spotlight the thermal and mechanical characterization of the bio-compatible polymers e.g., olefins, nylon, polyacetals, polyvinyl chloride and polyesters.     

Cyclosilazanes and borazines: polymer precursors to silicon‐ and boron‐containing ceramics

The chemistry of cyclosilazanes and borazines is a topic of current interest in view of preceramic polymers which yield on pyrolysis various useful ceramic materials, e.g. silicon and boron carbide, silicon and boron nitride, and ternary or quaternary mixtures of these materials. These materials are hard and have high oxidative and thermal stability. Other useful properties are resistance to corrosion, thermal shock and creep, low electrical conductivity and low coefficient of thermal expansion. One of the best application prospects is the use of the preceramic polymers as protective coating material for carbon fibres. Copyright © 2000 John Wiley & Sons, Ltd.     

NIR Clusteroluminescence of Non-conjugated Phenolic Resins Enabled by Through-Space Interactions

Clusteroluminescence (CL) and through-space interactions (TSIs) of non-conjugated molecules have drawn more attention due to their unique photophysical behaviors that are different from largely conjugated luminogens. However, achieving red and even near-infrared (NIR) emission from such systems is still challenging due to the intrinsic drawbacks of non-conjugated molecules and the lack of theories for structure–property relationships. In this work, six phenolic resins are designed and synthesized based on two molecule-engineering strategies: increasing the number of TSIs units and introducing electron-donating/-withdrawing groups. All phenolic resins are verified as luminogens with CL property (CLgens), and the first example of CLgens with NIR emission (maximum emission wavelength ≥680 nm) and high absolute quantum yield (47 %) is reported. Experiments and theoretical analysis reveal that two TSIs types, through-space locally excited state and through-space charge transfer state, play essential roles in achieving CL from these non-conjugated polymers, which could be manipulated via changing structural conformation and electron density or altering electron transition behaviors. This work not only provides an approach to manipulate TSIs and CL of non-conjugated polymers but also endows commercially available phenolic resins with high practical value as luminescence materials.     

PREPARATION AND CHARACTERIZATION OF INCLUSION COMPLEXES OF TWO-ARM LINEAR AND FOUR-ARM STAR-SHAPED POLY（ε-CAPROLACTONE）S WITH α-CYCLODEXTRIN

Both four-ann star-shaped poly（ε-caprolactone） （4sPCL） and two-ann linear PCL （2LPCL） were synthesized and their inclusion complexation with α-cyclodextrin （α-CD） were studied. The inclusion complexes （ICs） formed between the PCL polymers and α-CD were characterized by ^1H-NMR, DSC, TGA, WAXD, and FT-1R, respectively. Both branch ann number and molecular weight of the PCL polymers have apparent effect on the stoichiometry （CL：CD, mol：mol） of these ICs. All these analytical results indicate that the branch arms of the PCL polymers are incorporated into the hydrophobic α-CD cavities and their original crystalline properties are completely suppressed. Moreover, the inclusion complexation between two-ann linear or four-ann star-shaped PCL polymers and α-CD not only enhances the thermal stability of the guest PCL polymers but also improves that of α-CD.     

Evaluation of n-valeraldehyde modified chitosan as a matrix for hydrophobic interaction chromatography

The n-valeraldehyde modified Chitosan (pentyl-Chitosan CL) was prepared by Schiff-base formation and hydrogenation. By studying the IR spectra of Chitosan and pentyl-Chitosan CL, it is suggested that a pentyl group is linked to 2'-NH, by a C-N bond. The influence of temperature and ionic strength on the adsorption of protein on pentyl-Chitosan CL were studied, and it was found that the behavior of adsorption met with the theory of hydrophobic interaction. The storage stability of these packing materials was also investigated, the results show storage in 20% ethanol at 4 degrees C is the most suitable condition. Alpha-amylase was purified successfully by hydrophobic interaction chromatography, using pentyl-Chitosan CL as hydrophobic matrix. The purification factor is about 2.5 and the recovery is over 82%.     

SYNTHESIS OF POLYMERS CONTAINING N-N LINKAGES

The N-N linkage in hydrazine is thermally stable when it is tetrasubstituted and there are electron-withdrawinggroups attached to the nitrogen atoms. Our research on the synthesis of polymers contaning N--N linkages is reviewed. TheN,N-bisimide structure has been introduced in the backbone of polymers as well as a pendant group in poly(aryl ether)s togive very thermoxidatively stable polymers with very high glass transition temperatures. Most of the polymers form tough,flexible films. N-Aminotriazoles also form stable imides by reaction with anhydrides and these N-imidotriazole groups havebeen introduced as pendent groups on poly(aryl ether)s. The polymers are highly fluorescent materials. Three methods for thesynthesis of polymers containing the tetrasubstituted-azine structure will be discussed: (1) oxidative coupling of bisimines;(2) condensation of bishydrazones with diketones; (3) poly(aryl ether azines) from the azine formed from 4-fluorobenzo-phenone by reaction with salts of bisphenols.     

Polypyrrole coating of inorganic and organic materials by chemical oxidative polymerisation

Polypyrrole is one of the most frequently studied conducting polymers, having high electrical conductivity and stability, suitable for multi-functionalised applications. Coatings of chemically synthesised polypyrrole applied onto various organic and inorganic materials, such as polymer particles and films, nanoparticles of metal oxides, clay minerals, and carbon nanotubes are reviewed in this paper. Its primary subject is the formation of new materials and their application in which chemical oxidative polymerisation of pyrrole was used. These combined materials are used in antistatic applications, such as anti-corrosion coating, radiation-shielding, but also as new categories of sensors, batteries, and components for organic electronics are created by coating substrates with conducting polymer layers or imprinting technologies.     

燃料电池质子交换膜用新型磺化聚芳醚酮的合成和性能表征

报道了一种新型磺化聚芳醚酮材料的合成方法, 通过引入取代基对聚芳醚主链进行保护，用氯磺酸直接磺化方法在聚芳醚酮高分子侧基上引入磺酸功能基, 实现了聚合物磺化结构的可控定位合成, 得到了稳定性较好的磺化聚芳醚酮. 通过核磁共振(NMR)、 热重(TG)和凝胶渗透色谱(GPC)等分析方法对其结构及性能进行了表征. 用溶液浇膜法制备了质子交换膜, 考察了膜的各种性能, 并与商用Nafion膜进行了比较, 其导电性、 热稳定性和吸水性远优于Nafion膜, 抗氧化性、抗水解性和机械强度也达到了较高的指标.     

Effect of metal-free porphyrins on the thermal–oxidative breakdown of biocompatible polymers

The inhibitory effect of metal-free porphyrins on the thermal–oxidative breakdown of several biocompatible polymers is observed for the first time. Differential thermal analysis shows that the thermal stability of poly(ethylene oxide) and triblock copolymers of ethylene oxide and propylene oxide increases by 80–100 K, compared to the initial breakdown temperatures of these polymers in the presence of metal-free porphyrins (up to 3 wt %).     

含硫甲基的芴-苯结构化合物的合成、结构和性能

通过双Suzuki偶联反应一步合成了2种含硫甲基的芴-苯结构化合物2,7-二(4-硫甲基苯基)-9,9-二己基-芴(a)和2,7-二(2,6-二甲基-4-硫甲基苯基)-9,9-二己基-芴(b).紫外-可见和荧光光谱以及分子轨道理论计算表明,位阻较小的化合物a具有更好的共轭性能,其最大紫外-可见吸收波长达到351nm,比两端苯基含4个邻位取代基的化合物b红移了38nm;化合物a的最大荧光发射波长达到410nm,为典型的蓝光化合物,比化合物b红移了43nm.化合物a和b都具有较高的荧光量子产率,分别为59%和65%,在光电材料方面具有潜在的应用前景.     

Design and synthesis of interpenetrating polymer networks for second-order nonlinear optics

There has been a tremendous recent interest in the development of second-order nonlinear optical (NLO) polymeric materials for photonic applications. However, a major drawback of second-order NLO polymers that prevents them from being used in device applications is the instability of their electric field induced dipolar alignment. The randomization of the dipole orientation leads to the decay of second-order optical nonlinearities. Numerous efforts have been made to increase the stability of the second-order NLO properties of polymers. The search for new approaches to develop NLO polymers with optimal properties has been an active research area since the past decade. A novel approach, combining the hybrid properties of high glass transition temperatures, extensively extensively crosslinked networks and permanent entanglements, based on interpenetrating polymer networks (IPN) is introduced to develop stable second-order NLO materials. Two types of IPN systems are prepared and their properties are investigated. The designing criteria and the rationale for the selection of polymers are discussed. The IPN samples show excellent temporal stability at elevated temperatures. Long-term stability of the optical nonlinearity at 100°C has been observed in these materials. Temporal stability of the NLO properties of these IPNs is synergistically enhanced. Relaxation behavior of the optical nonlinearity of an IPN system has been studied and compared with that of a typical guest/host system. The improved temporal stability of the second-order NLO properties of this IPN system is a result of the combination of the high rigidity of the polymer backbones, crosslinked matrices and permanent entanglements of the polymer networks. A slight modification of the chemical structure resulted in an improvement of the optical quality of the sample.     

Thermal oxidative stability and effect of water on gas transport and mechanical properties in PA6‐EVOH films

The thermal oxidative stability and the effect of water on gas transport and mechanical properties of blends of polyamide 6 (PA6) with ethylene‐co‐vinyl alcohol (EVOH) and EVOH modified with carboxyl groups (EVOH‐COOH) have been investigated. The presence of EVOH reduces water vapor and oxygen gas permeability of polyamide, as well as small amounts of EVOH‐COOH further improve barrier properties, especially to oxygen. This has been explained in terms of improved interactions of the blend constituents in the amorphous phase, due to ionic linkages between the polyamide amino groups and the carboxyls of modified EVOH. The permeation to gases was found to increase with the amount of sorbed water. The morphology of the samples was found to have an effect on barrier properties, as the presence of EVOH causes the PA6 α crystalline form to increase, lowering the permeability to oxygen and water vapor. Mechanical properties are strongly affected by water sorption, as tensile modulus and strength decrease with increasing water content. Chemiluminescence (CL), infrared spectroscopy (FTIR), and tensile test were employed in order to assess the correlation between chemical composition and the thermal oxidative stability of the films aged at 110 °C in air. CL experiments suggest that the presence of EVOH and EVOH‐COOH efficiently inhibits the formation of peroxidized species during the processing, and increases the thermal oxidative stability of the films. Infrared spectroscopy showed a build‐up of carbonyl absorption in the range 1700–1780 cm^?1, due to the formation of oxidation products, which is greater in the case of the pure polymer. Tensile tests on films revealed a reduction in ductility as a result of ageing for neat PA6, whereas in comparison the blends exhibit a far better long‐term stability. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 840–849, 2007     

对可见光有良好吸收的新型烷基芴共聚物的合成、表征与性质

以芴为起始原料, 合成了两种主链含有芴酮及二腈基亚甲基芴结构单元的聚烷基芴光伏材料, 通过红外光谱和核磁共振谱对其进行了表征. 目标共聚物P1和P2的热分解温度分别为461.2和448.1 ℃, 玻璃化转变温度(Tg)分别为122.4和146.6 ℃, 具有良好的热稳定性. 在300~700 nm范围内, 该种材料对太阳光的吸收基本覆盖了整个可见光区域, 电化学分析得出其具有较好的氧化还原可逆性, 并且具有1.94和1.86 eV的相对较窄的能带宽度.     

含二乙炔类共轭聚合物的合成及性能研究

在以CuCl和四甲基乙二胺(TMEDA)作为催化剂和邻二氯苯作溶剂条件下,以二-(4-乙炔苯基)-4-辛氧基苯胺(M1)和3, 6-双(乙炔基)-N-辛基咔唑(M2)作为单体,通过Glaser-Hay氧化偶联反应合成了含有咔唑和三苯胺结构单元的聚芳烃二乙炔共轭聚合物.采用红外光谱、核磁共振谱、热失重分析、紫外吸收光谱和荧光光谱等方法对聚合物进行结构表征与性能测试.所得到的聚合物都溶于普通的有机溶剂(如四氢呋喃、二氯甲烷、氯仿、甲苯等).结果表明,聚合物具有优异的热稳定性,热失重5 %时,分解温度在400℃以上;在光激发的条件下,聚合物在二氯甲烷溶液中发射蓝光.     

Unexpected selective enhancement of the thermal stability of aromatic polyimide materials by cerium dioxide nanoparticles

The unusual effect of selective enhancement of the thermal stability of aromatic polyimide materials was established through the introduction of cerium dioxide nanoparticles into these polymers as nanofiller. Depending on the chemical structure of the polymers, a marked increase or a substantial decrease in the thermal stability of the nanocomposite material was registered by thermal analysis, as compared with that of unfilled polymer material. The positive effect was registered only for the composite materials based on the matrix polyimides containing the sulfur atoms located in the sulfonic groups arranged in the elementary units. The results of the thermogravimetric examination are compared with the data obtained during the mechanical tests of the same samples. The possible reasons for the alteration of the thermal stability of polymers by ceria nanoparticles are discussed. The effect above can be of substantial practical interest providing new options for the design of polyimide nanocomposite materials with enhanced thermal stability.     

表面活性剂稳定高内相乳液的研究进展

具有较高孔隙率和较高比表面积的多孔聚合物材料在能源、化工、生物和功能性材料等领域应用广泛。目前越来越多的研究是以高内相乳液为模板来制备多孔聚合物材料,其中高内相乳液的稳定对多孔聚合物材料的制备十分重要。本文主要介绍了近年来发展的多种用于高内相乳液滴稳定的表面活性剂,以及以高内相乳液为模板制备得到的多孔聚合物材料在多个领域中的应用。