Crosslinking of polyimides via spirodilactone unit in polymer backbone

A new approach for the crosslinking of polyimides via the lactamization of spirodilactone unit in polyimide backbone was studied by two means: model reaction and the comparison of the properties of the polyimide precursors to those of the crosslinking polymers. Polyimides 4 and 5 were soluble in N,N'dimethylacetamide (DMAc), dimethylformamide (DMF), dimethylsulfoxide (DMSO), N'-methylpyrrolidone (NMP), and other common organic solvents, whereas their corresponding crosslinking polymers were insoluble in these solvents. The glass transition temperatures for polyimide 5 and its crosslinking polymer were 262 degrees C and 291 degrees C, whereas those for polyimide 4 and its crosslinking polymer were 265 degrees C and 360 degrees C. The weight-loss rate of the crosslinling polymers was apparently slower than that of the precursors when the temperature was >400 degrees C. The 10% weight-loss temperature for the polyimides 4 and 5 was <500 degrees C, whereas that for the crosslinking polymers was close to or above 600 degrees C. The results indicate that this type of crosslinking polymer has good thermal properties. The temperature for the formation of lactam was above 180 degrees C. (C) 1999 John Wiley & Sons, Inc.

Synthesis and characterization of novel crosslinkable side-chain liquid crystalline polyesters

Crosslinkable side-chain liquid crystalline polyesters PCn from N-[n-(4-(4-nitrophenylazo)phenyloxy)alkyl]diethanolamine (Cn, n = 3, 5, 6, 10) as mesogenic monomers and maleic anhydride were synthesized and characterized. The thermal properties of PCn's were studied by means of DSC, polarized optical microscopy (POM) and wide angle X-ray diffraction (WAXD), and the results showed that all the polymers studied exhibit enantiotropic liquid crystallinity. In the molar mass independent region, the relatively high content of cis -CH=CH- groups in the polymer backbone of PC3 causes an increase of the melting temperature (T-m) and a decrease of T-g and isotropisation temperature (T-i). The crosslinking of PCn in the radical polymerization with styrene was confirmed by FTIR spectroscopy. The absorption band at 1300 cm(-1) attributed to the in-plane C-H-bending vibration of trans -CH=CH- in the polymer backbone disappeared after crosslinking, indicating that the trans -CH=CH- functions are consumed in the crosslinking polymerization of styrene.

Enzymatic degradation of poly(epsilon-caprolactone)/poly(DL-lactide) blends in phosphate buffer solution

Blend films of poly(epsilon-caprolactone) (PCL) and poly(DL-lactide) (PDLLA) with 0.5 weight fraction of PCL were prepared by means of solution casting and their degradation behavior was studied in phosphate buffer solution containing Pseudomonas (PS) lipase. Enzymatic degradation of the blend films occurred continuously within the first 6 days and finally stopped when the film weight loss reached 50%, showing that only PCL in the blends degraded under the action of PS lipase in the buffer solution. These results indicate the selectivity of PS lipase on the promotion of degradation for PCL and PDLLA. The thermal properties and morphology of the blend films were investigated by differential scanning calorimetry, wide-angle X-ray diffraction and scanning electron microscopy (SEM). The morphology resulting from aggregate structures of PCL in the blends was destroyed in the enzymatic degradation process, as observed by SEM. These results confirm again the enzymatic degradation of PCL in the blends in the presence of PS lipase. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.

A comparative study of insoluble and soluble polyimide thin films

Physical properties of thin films of soluble and insoluble aromatic polyimides were compared by d.s.c., u.v.-visible and fluorescence spectroscopy, and prism coupler technique. D.s.c. results showed that the thermal properties of insoluble polyimides are superior to those of soluble ones, owing to the specific molecular interactions of insoluble polyimides, revealed by fluorescence spectroscopy. However, the specific molecular interactions sacrifice the transparency in their thin films, shown by u.v.-visible transmission spectra. Negative birefringence of thin films, not only for soluble polimides but also for polyamic acids of insoluble polyimides, was confirmed by prism coupler, while thin films of insoluble polyimides thermally imidized lack high levels of negative birefringence. It is regarded that thin films of insoluble polyimides thermally imidized are likely to be isotropic because of molecular relaxation above their glass transition temperatures (T-g) in the course of thermal imidization, according to Flory's principle. On the contrary, thin films of insoluble poyimide chemically imidized keep the same levels of negative birefringence as those of the relevant polyamic acid thin films. Judging from the opposite cases, it is recognized that molecular relaxation above T-g weakens the optical anisotropy of polyimide thin films. (C) 1998 Elsevier Science Ltd. All rights reserved.

Crystallization behavior of poly(propylene)/polyamide 1010 blends using poly(propylene)-graft glycidyl methacrylate as compatibilizer

Polyamide 1010/poly(propylene) (PA1010/PP) blends were investigated with and without the addition of poly(propylene)-graft-glycidyl methacrylate (PP-g-GMA). The effect of the compatibilizer on the thermal properties and crystallization behavior was determined by differential scanning calorimetry and wide-angle X-ray diffraction. From the results it is found that the crystallization of PA 1010 is significantly affected by the presence of PP-g-GMA. PP/PA 1010 (75/25) blends containing higher amounts of PP-g-GMA show concurrent crystallization at the crystallization temperature of PP. Isothermal crystallization kinetics also were performed in order to investigate the influence of the compatibilized process on the nucleation and growth mechanism. In the PP/PA 1010 (25/75) blends, concurrent crystallization behavior was not observed, even though the amount of PPg-GMA was high.

SYNTHESIS AND CHARACTERIZATION OF POLYACRYLATES CONTAINING CHARGE-TRANSFER GROUPS

Polyacrylates containing para-nitro azobenzene have been synthesized by free radical polymerization. The influence of the length of the spacer of the homopolyacrylates (HPn, n=3,4,6), content of methyl acrylate in the copolyacrylates (CP6) with para-nitro azobenzene groups on the thermal properties, such as liquid crystallinity, Tg and Tm, was studied by DSC, WAXD and polarized optical microscopy. Among the polymers studied, only the homopolyacrylate (HP6)with six carbon atoms in the spacer exhibited a nematic phase. The second-harmonic generation (SHG) signal of the poled HP6 film was detected qualitatively by Maker-fringer method.

STUDIES ON THE SULFONATION OF POLY(PHENYLENE OXIDE) (PPO) AND PERMEATION BEHAVIOR OF CASES AND WATER-VAPOR THROUGH SULFONATED PPO MEMBRANES .1. SULFONATION OF PPO AND CHARACTERIZATION OF THE PRODUCTS

Poly(2,6-dimethylphenylene oxide) (PPO) was sulfonated to varying degrees using different sulfonating agents. Physical properties such as solubility, density, and thermal properties were studied for both PPO and sulfonated PPO (SPPO) with different degree

南海北部陆缘深水区构造－热演化与烃源岩成熟度史研究

Abstract In order to provide basic data for evaluation of the petroleum potential in the deep water area of the northern margin of the South China Sea (SCS), present-day thermal regime and basin tectonothermal evolution are reconstructed and the maturation history of the Cenozoic major source rocks in the study area is derived. The present-day geothermal regime in the deep water area of the northern margin of SCS is defined according to the geothermal gradient, thermal properties and heat flow data. Tectonic subsidence history is reconstructed based on borehole and seismic data, and accordingly the stretching episodes are determined from the subsidence pattern. Heat flow history in the deep water area of the northern margin of SCS is estimated on a finite time, laterally non-uniform and multi-episode stretching model. Maturation history of the main source rocks in the study area is estimated through EASYRo% kinetic model and thermal history, and the potential of petroleum in the deep water area of the northern margin of SCS is evaluated based on the data above. The results show that the present-day geothermal regime in the deep water area of the northern margin of SCS is characterized by “hot basin” with high geothermal gradient (39.1±7.4℃/km) and high heat flow (77.5±14.8 mW/m2), and that the Qiongdongnan Basin (QDNB) underwent three stretching episodes and consequently suffered three heating episodes (Eocene, Oligocene and Pliocene time) with highest paleo-heat flow of 65～90 mW/m2 at the end of the Pliocene, that the Pearl River Mouth Basin (PRMB) two stretching and two heating episodes (Eocene, Oligocene time) with highest paleo-heat flow of 60～70 mW/m2 at the end of the Oligocene, and that the source rocks matured drastically responding to the heating episodes. There are four hydrocarbon generation kitchens in the deep water area of the northern margin of SCS which are favor of its bright petroleum perspective. Tectonothermal analysis indicates that the present-day geothermal regime which is characterized with “hot basin” in the deep water area of the PRMB resulted mainly from the Cenozoic stretching as well as faulting and magmatic activities during the Neotectonic period, and that the Pliocene heating episode of the QDNB is coupled with the transition from sinistral to dextral gliding of the Red Rive fault, and that the deep water basins in the northern margin of SCS are typical of multiple rifting which caused multi-episode heating process.

单（多）井抽灌对浅部地温场的影响研究

The technique of energy extraction using groundwater source heat pumps, as a sustainable way of low-grade thermal energy utilization, has widely been used since mid-1990's. Based on the basic theories of groundwater flow and heat transfer and by employing two analytic models, the relationship of the thermal breakthrough time for a production well with the effect factors involved is analyzed and the impact of heat transfer by means of conduction and convection, under different groundwater velocity conditions, on geo-temperature field is discussed.A mathematical model, coupling the equations for groundwater flow with those for heat transfer, was developed. The impact of energy mining using a single well system of supplying and returning water on geo-temperature field under different hydrogeological conditions, well structures, withdraw-and-reinjection rates, and natural groundwater flow velocities was quantitatively simulated using the finite difference simulator HST3D. Theoretical analyses of the simulated results were also made. The simulated results of the single well system indicate that neither the permeability nor the porosity of a homogeneous aquifer has significant effect on the temperature of the production segment provided that the production and injection capability of each well in the aquifers involved can meet the designed value. If there exists a lower permeable interlayer, compared with the main aquifer, between the production and injection segments, the temperature changes of the production segment will decrease. The thicker the interlayer and the lower the interlayer permeability, the longer the thermal breakthrough time of the production segment and the smaller the temperature changes of the production segment. According to the above modeling, it can also be found that with the increase of the aquifer thickness, the distance between the production and injection screens, and/or the regional groundwater flow velocity, and/or the decrease of the production-and-reinjection rate, the temperature changes of the production segment decline. For an aquifer of a constant thickness, continuously increase the screen lengths of production and injection segments may lead to the decrease of the distance between the production and injection screens, and the temperature changes of the production segment will increase, consequently.According to the simulation results of the single well system, the parameters, that can cause significant influence on heat transfer as well as geo-temperature field, were chosen for doublet system simulation. It is indicated that the temperature changes of the pumping well will decrease as the aquifer thickness, the distance between the well pair and/or the screen lengths of the doublet increase. In the case of a low permeable interlayer embedding in the main aquifer, if the screens of the pumping and the injection wells are installed respectively below and above the interlayer, the temperature changes of the pumping well will be smaller than that without the interlay. The lower the permeability of the interlayer, the smaller the temperature changes. The simulation results also indicate that the lower the pumping-and-reinjection rate, the greater the temperature changes of the pumping well. It can also be found that if the producer and the injector are chosen reasonably, the temperature changes of the pumping well will decline as the regional groundwater flow velocity increases. Compared with the case that the groundwater flow direction is perpendicular to the well pair, if the regional flow is directed from the pumping well to the injection well, the temperature changes of the pumping well is relatively smaller.Based on the above simulation study, a case history was conducted using the data from an operating system in Beijing. By means of the conceptual model and the mathematical model, a 3-D simulation model was developed and the hydrogeological parameters and the thermal properties were calibrated. The calibrated model was used to predict the evolution of the geo-temperature field for the next five years. The simulation results indicate that the calibrated model can represent the hydrogeological conditions and the nature of the aquifers. It can also be found that the temperature fronts in high permeable aquifers move very fast and the radiuses of temperature influence are large. Comparatively, the temperature changes in clay layers are smaller and there is an obvious lag of the temperature changes. According to the current energy mining load, the temperature of the pumping wells will increase by 0.7°C at the end of the next five years. The above case study may provide reliable base for the scientific management of the operating system studied.

Precursor chemistry for oxide related materials

This thesis describes modelling, synthesis, spectroscopic and physical characterisation, as well as application of Magnesium, Calcium and Copper β-diketonate, β-ketoiminate, β-diiminate, Schiff base, amide and fluorenyl compounds. The selected compounds could potentially find application in materials deposition using Atomic Layer Deposition (ALD), MOCVD, CVD and Sol-Gel techniques. Quantum chemical modelling was used as a tool to perform the comprehensive and rapid study of magnesium and calcium precursor molecules in order to predict which of them would be more successful in ALD of metal oxides. Precursor chemistry plays a key role in ALD, since precursors must be volatile, thermally stable, chemisorb on the surface and react rapidly with existing surface groups. This Thesis describes one aspect of this, surface reactivity between ligands and hydroxyl groups, via a gas-phase model with energetics computed at the level of Density Functional Theory (DFT). A number of different synthetic strategies, both aerobic and anaerobic, were investigated for the synthesis of the described metal complexes. These included the use of different metal starting reagents such as, anhydrous and hydrated inorganic metal salts, metal alkyls and Grignard reagents. Some of previously unreported metal complexes of homoleptic and heteroleptic magnesium, calcium and copper β-diketonates, β-ketoiminates, β-diiminates, amides and Schiff base type were synthesised and characterised: [Mg(hfpd)2(DipPa)], [Mg(hfpd)2(MapH)2], [Mg(hf-ebp)(THF)2], [Mg(tf-Pap)Cl(THF)2], [Ca(PhNacnac)2], [Cu(tf-Pap)2], [Cu(PhNacnac)2], [Cu(hf-ebp)], [Cu(DipPa)] and [Cu(DipPa)2(4,4’-bypy)]. A comprehensive study on the thermal properties of magnesium, calcium and copper β-diketonates, β-ketoiminates, β-diiminates, Schiff base, amide and fluorenyl complexes was performed using TGA and sublimation of selected compounds. Atomic Layer Deposition of MgO using magnesium β-ketoiminate – [bis{(4-N-phenyl)-2-pentonato} magnesium] and β-diketonate - [bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionato)(THF)magnesium hydrate] was performed on Si(100) substrates at 180°C and 0.2 Torr using O2 plasma.

Structure of phytoplankton (Continuous Plankton Recorder and SeaWiFS) and impact of climate in the Northwest Atlantic Shelves

All marine organisms are affected to some extent by the movement and thermal properties of oceanic currents. However phytoplankton, because of its small size is most directly coupled to the physical environment. The intense hydrodynamic activity observed in the Northwest Atlantic Shelves Province makes this region especially intriguing from the point of view of physical-biological interactions. In the present work, remote sensed data of Sea Surface Height (SSH) anomalies, Sea-surface chlorophyll a concentrations (SeaWiFS), and Sea Surface Temperature (SST) are used to complement the Continuous Plankton Recorder (CPR) survey that continuously sampled a route between Norfolk (Virginia, USA; 39° N, 71° W) and Argentia (Newfoundland; 47° N, 54° W) over the period 1995–1998. Over this period, we examined physical structures (i.e. SST and SSH) and climatic forcing associated with space-time phytoplankton structure. Along this route, the phytoplankton structures were mainly impacted by the changes in surface flow along the Scotian Shelf rather than significantly influenced by the mesoscale features of the Gulf Stream. These changes in water mass circulation caused a drop in temperature and salinity along the Scotian Shelf that induced changes in phytoplankton and zooplankton abundance.

Degradation of poly-L-lactide. Part 1: in vitro and in vivo physiological temperature degradation

Poly-L-Lactide is a bioresorbable polymer which degrades through hydrolysis of its ester linkage influenced by initial molecular weight and degree of crystallinity. Polymers belonging to the aliphatic polyester family currently represent the most attractive group of polymers that meet the medical and physical demands for safe clinical applications. Compression moulded PLLA pellets were produced as rods, sterilized and degraded both in vitro and in vivo (sub-dermal implantation model). The material molecular weight, crystallinity, mechanical strength and thermal properties were evaluated. In both in vitro and in vivo environments, degradation proceeded at the same rate and followed the general sequence of aliphatic polyester degradation, ruling out enzymes accelerating the degradation rate in vivo. By 44 weeks duration of implantation the PLLA rods were still biocompatible, before any mass loss was observed.

Degradation of poly-L-lactide. Part2 : increased temperature accelerated degradation

Poly-L-lactide (PLLA) is one of the most significant members of a group of polymers regarded as bioresorbable. The degradation of PLLA proceeds through hydrolysis of the ester linkages in the polymer's backbone; however, the time for the complete resorption of orthopaedic devices manufactured from PLLA is known to be in excess of five years in a normal physiological environment. To evaluate the degradation of PLLA in an accelerated time period, PLLA pellets were processed by compression moulding into tensile test specimens, prior to being sterilized by ethylene oxide gas (EtO) and degraded in a phosphate-buffered solution (PBS) at both 50°C and 70°C. On retrieval, at predetermined time intervals, procedures were used to evaluate the material's molecular weight, crystallinity, mechanical strength, and thermal properties. The results from this study suggest that at both 50°C and 70°C, degradation proceeds by a very similar mechanism to that observed at 37°C in vitro and in vivo. The degradation models developed also confirmed the dependence of mass loss, melting temperature, and glass transition temperature (Tg) on the polymer's molecular weight throughout degradation. Although increased temperature appears to be a suitable method for accelerating the degradation of PLLA, relative to its physiological degradation rate, concerns still remain over the validity of testing above the polymer's Tg and the significance of autocatalysis at increased temperatures.

The role of plug design in determining wall thickness distribution in thermoforming

An experimental investigation has been carried out into the effects of changes in plug design on the wall thickness distribution of thermoformed products. Plugs were machined with a series of geometrical variations and their effects on the process were measured. The overall results show that the plug has a crucial role in controlling the wall thickness distribution in thermoforming. Larger plugs tend to distribute more material to the base of the product, but the introduction of a small sidewall taper, base radius, or a reduction in plug diameter tend to lead to more balanced distributions. However, larger changes in any of the variables tend to destroy these benefits. It has also been demonstrated that the frictional and thermal properties of the plug are important in determining the deformation response of the sheet material. There is a clear evidence of slip in the sheet during plug contact and, although the cooling effect of the plug appears to be minimal, cooling in the highly deformed regions away from the plug appears to be a significant factor.

Anti-infective photodynamic biomaterials for the prevention of intraocular lens-associated infectious endophthalmitis

Bacterial attachment onto intraocular lenses (IOLs) during cataract extraction and IOL implantation is a prominent aetiological factor in the pathogenesis of infectious endophthalmitis. Photodynamic therapy (PDT) and photodynamic antimicrobial chemotherapy (PACT) have shown that photosensitizers are effective treatments for cancer, and in the photoinactivation of bacteria, viruses, fungi and parasites, in the presence of light. To date, no method of localizing the photocytotoxic effect of a photosensitizer at a biomaterial surface has been demonstrated. Here we show a method for concentrating this effect at a material surface to prevent bacterial colonization by attaching a porphyrin photosensitizer at, or near to, that surface, and demonstrate the principle using IOL biomaterials. Anionic hydrogel copolymers were shown to permanently bind a cationic porphyrin through electrostatic interactions as a thin surface layer. The mechanical and thermal properties of the materials showed that the porphyrin acts as a surface cross-linking agent, and renders surfaces more hydrophilic. Importantly, Staphylococcus epidermidis adherence was reduced by up to 99.0 ± 0.42% relative to the control in intense light conditions and 91.7± 5.99% in the dark. The ability to concentrate the photocytotoxic effect at a surface, together with a significant dark effect, provides a platform for a range of light-activated anti-infective biomaterial technologies.