ISSN:0959-8103    

DOI:10.1002/pi.4990270302

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractTwo series of thermotropic liquid crystalline polymers were prepared from hydroquinone, methylhydroquinone, 2,5‐dichloroterephthaloyl chloride and four terephthalates with varying length substituents. Some of the properties of the terephthalates and polymers were characterized by IR, elementary analysis, differential scanning calorimetry (DSC), X‐ray diffraction and polarized hot‐stage micro

ISSN:0959-8103    

DOI:10.1002/pi.4990270303

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe preparation of pure microgels in high yield was investigated by a new method which restricts the intermolecular crosslinking reaction between second‐stage crosslinked products by steric hindrance of the first‐stage crosslinked products. This is followed by ultrasonic degradation of the first‐stage crosslinked products. The first‐stage crosslinked products were prepared by copolymerization of styrene and divinylbenzene monomer in dioxane. with α,α′‐azobisisobutyronitrile as initiator. The second‐stage crosslinked products were prepared by copolymerization of acrylic acid and divinylbenzene monomer in first‐stage crosslinked products highly swollen in dioxane, using α,α′‐azobisisobutyronitrile as initiator. Degradation of first‐ and second‐stage crosslinked products was carried out using an ultrasonic vibrator.The characteristics of the crosslinked products synthesized were investigated by gel permeation chromatography, dynamic laser light scattering and electron microscopy. It was found that the styrene‐divinylbenzene gel of high molecular weight was scissioned preferentially with increasing ultrasonic degradation time and that ultrasonic degradation of compact and small size crosslinked products was very difficult. The crosslinked poly(acrylic acid)s are small compact microgels having a very narrow size distribution of 20‐30 nm diameter.A pure microgel at nearly 100% conversion was obtained by the new preparation

ISSN:0959-8103    

DOI:10.1002/pi.4990270304

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractPolyvinylidene fluoride and its copolymers with trifluoroethylene and tetrafluoroethylene are ferroelectric. Reversal of polarization in these polymers is known to occur by a rotation of the polar molecular chains, in response to an externally applied electric field. Recent evidence suggests that the dynamics of polarization reversal can be affected by movement of space charges in the amorphous phase of the polymers. If a 75/25 mol.% vinylidene fluoride/trifluoro‐ethylene (VF2/VF3) copolymer is poled at elevated temperature, the subsequent polarization reversal currents show large asymmetry and significant shifts in successive reversals. The field required to reverse the polarization in such high‐temperature poled material is significantly larger than the normal coercive field. The asymmetry in the reversal currents is consistent with the presence of local fields within the polymer, generated by space charge which accumulates during the poling process. The subsequent movement of this space charge causes the shift in successive reversal currents. The variation of reversal current with temperature indicates that the movement of space charge within the copolymer is a thermally activated proc

ISSN:0959-8103    

DOI:10.1002/pi.4990270305

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractPolypyrrole films containing a variety of dopants were synthesised. Special attention was given to ensuring that all films were morphologically similar so that differences in the electronic properties of the films were more strongly associated with the intrinsic character of the dopants, in particular their electron affinity. To achieve this, dopant exchange was performed by an electrochemical process and a strong correlation was found between dopant electron affinity (X) and film electrical conductivity.

ISSN:0959-8103    

DOI:10.1002/pi.4990270306

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractPreparation of photoreactive Langmuir‐Blodgett (LB) films was carried out using polymers/oligomers prepared from long‐chain dialkyl esters of di‐and tetra‐olefins and having cyclobutane rings in the main chain. These polymers/oligomers formed stable monolayers on a water surface when mixed with arachidic acid. These monolayers could be deposited onto a substrate successfully forming Y‐type films. The oligomer LB films were polymerized on irradiation. The polymer LB films showed a photo‐reversible process between polymers and oligomers, depending on wavelength of the irradiating light. On the basis of spectral data and molecular weight change, this behaviour was found to be caused by cleavage and formation of cyclob

ISSN:0959-8103    

DOI:10.1002/pi.4990270307

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractPoly(2‐hydroxyethyl methacrylate) was prepared by bulk polymerization and then exposed to ablation by 193‐nm pulsed radiation provided by an ArF excimer laser. The etch curve, i.e. ablation rate versus radiation fluence, presents two changes in the slope, which are consistent with a presumably characteristic behaviour of addition polymers with a strong tendency towards thermal depolymerization. Samples exposed to two fluences, each in the vicinity of one of the inflection points, were analysed by X‐ray photoelectron spectra (XPS) at two different take‐off angles. The results suggest that the ablation mechanism may vary when the fluence changes. At the higher fluence (280mJ/cm2), depolymerization is the dominant process and the material left after etching displays almost no change in the O/C atomic ratio. At the lower fluence (80mJ/cm2), cleavage of the pendant group is dominant and the O/C ratio decreases significantly, especially on the polymer

ISSN:0959-8103    

DOI:10.1002/pi.4990270308

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractErasable memory devices are fabricated by the combination of a conducting polymer and solid polymer electrolyte. The former is used as a memory channel and the latter as an electrolyte medium. The channel conductivity can be controlled over 3‐4 orders of magnitude by electrochemical doping through a writing electrode. The response time, depending on the writing voltage, is several seconds. The characteristics of the memory device are discusse

ISSN:0959-8103    

DOI:10.1002/pi.4990270309

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe influence of several variables on the rate of oxidation of heterocycles to form conductive, electroactive polymers has been considered. It has been shown that the extent to which variables such as electrode size, monomer/counterion concentrations and applied potential influence the rate depends on the monomer and counterion being employed.

ISSN:0959-8103    

DOI:10.1002/pi.4990270310

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractTernary polymer solutions [polystyrene and poly(methylvinylether) dissolved in a single solvent] have been studied to investigate the thermodynamic compatibility of the polymers and the solvents, and also to facilitate the investigation of the self‐diffusion of polystyrene to greater polymer concentration. Both good and poor quality solvents have been used in this study. The self‐diffusion coefficient of the polystyrene has been measured by dynamic light scattering and by pulsed field gradient NMR where appropriate. The self‐diffusion data are also used to critically examine the recent theoretical developments in this field. Important confirmation of theory has been demonstrated for good solvent solutions and intriguing discrepancies have been discovered for poor solvent solu

ISSN:0959-8103    

DOI:10.1002/pi.4990270311

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY