摘要:

Benzocyclobutenes are a family of thermally polymerizable monomers which can be classified into two groups: 1) monomers which contain only benzocyclobutene moieties and 2) monomers which contain sites of unsaturation in addition to benzocyclobutene moieties. The monomers can be partially polymerized (B-staged) by heating to form oligomers having processing advantages for various composite fabrication techniques. The polymerization proceeds through the thermally initiated cyclobutene ring opening to yield an o-quinodimethane intermediate (calculated to be a ground state singlet). Preliminary characterization of the network structures indicates that monomers which contained multiple benzocyclobutene moieties, optionally with sites of unsaturation, were transformed into multifunctional network junctions when the thermosets were fully cured. The 3-maleimidobenzocyclobutenes thermally polymerize to yield substantially linear, high glass transition temperature (Tg) polymers. Thus benzocyclobutene polymers encompass materials which have properties ranging from high Tg, thermosets to those of substantially linear thermoplastics. Some polymers exhibit an excellent retention of their room temperature mechanical properties to at least 200-250°C, making them useful as high performance polymers for applications in the aerospace industry. Other polymers have outstanding electrical properties including very low dielectric constant and water pickup, making them useful in electronic applications.

ISSN:0022-233X    

DOI:10.1080/00222339108054087

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A new class of photosensitive aromatic polymers containing disilane units was successfully synthesized from new disilane-based monomers such as 1,2-bis(diethylamino)tetramethyldisilane and 1,2-bis(p-aminophenyl)tetrarnethyldisilane. The disilane-contain-ing aramids and polyimides had glass transition temperatures above 190°C, and all the polymers were thermally stable up to 300°C in air. The polymers were photosensitive; their molecular weight decreased rapidly upon ultraviolet light irradiation. The photosensitive polymers, especially the soluble polyimides having diphenyl sulfone units, were potential candidates for positive working photoresist materials. New highly branched polysiloxane star-burst polymers were synthesized by a siloxane synthetic reaction starting from tris[(phenyldimethylsiloxy)dimethylsiloxy]methylsilane and bis[(phenyldimethylsiloxy)methylsiloxy]dimethylsilanol as the initial core (G0-Ph) and the building block, respectively. Thus, the first generation polymer G1-Ph, second generation polymer G2-Ph, and third generation polymer G3-Ph had 6, 12, and 24 phenylsilyl groups in their exterior layers. The formation of the siloxane-based starburst polymers were confirmed by means of1H-,13C-, and29Si-NMR spectroscopy. These polysiloxane starburst polymers were suggested to have spherical structure. Some functionalized starburst polymers were further synthesized by the introduction of functional groups in their exterior layers. New silica-polyimide hybrid materials were prepared by the sol-gel process through the hydrolysis-condensation reactions of tetraethoxysilane in the presence of the polyamic acid (polyimide precursor) in dimethylacetamide, followed by heating at 270°C. The hybrid system having silica content up to 70 wt% had good quality films. The spherical silica particles were dispersed homogeneously in the polyimide matrix. With increasing silica content, the glass transition temperature and decomposition temperature, as well as the modulus of the hybrid films, increased, while the coefficient of thermal expansion decreased.

ISSN:0022-233X    

DOI:10.1080/00222339108054088

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A novel polymer membrane having a transmembrane permeation pathway (channel) was prepared from a polyvinyl-polypeptide graft copolymer. The transmembrane continuous phases of the hydrophilic polypeptide were found to be formed in the stable matrix from vinyl polymer and to function as a permeation pathway for polar substances; the polypeptide domain is regarded as a membrane protein model. The infrared and circular dichroism spectra of the membrane showed the pH-dependent conformational change of the polypeptide segment. Regulation of permeability and permselectivity was performed by pH based on the conformational transition of the channel-composing polypeptide. In addition, the membrane has been found to respond to divalent cations, cationic surfactants, urea, and organic solvents in terms of membrane permeability as well as conformational status of polypeptide.

ISSN:0022-233X    

DOI:10.1080/00222339108054089

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Polysilanes are polymers with a linear Si-Si catenation in the main chain and with two organic substituents at each silicon atom:

ISSN:0022-233X    

DOI:10.1080/00222339108054090

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Synthesis and magnetic properties of π-conjugated stable polyradicals bearing a polyacetylene backbone are described. 2,6-Di-tert-butyl-4-ethynylphenol (8) and 4-ethynylphenylhydrogalvinoxyl (9) are polymerized with W, Mo chloride or Rh complex to yield their polyacetylene derivatives with molecular weight of ca. 104, while 2-ethynylphenalenone (10) gives only its oligomer. The polymers are soluble in common solvents and converted to the corresponding conjugated polyradicals via heterogeneous chemical oxidation using PbO2or alkaline K3Fe(CN)6. The polyradicals with extremely high spin concentration (up to 4.8 × 1023spins/monomer mol) are obtained by regulating the oxidative conditions. The polyradicals are quite stable in solution and even in the solid state because of resonance stabilization and/or a steric effect of the substituents. Magnetic interactions between the unpaired spins in the conjugated stable polyradicals are discussed.

ISSN:0022-233X    

DOI:10.1080/00222339108054091

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

When a water-swollen polyelectrolyte gel is interposed between a pair of electrodes and dc is applied, the gel undergoes electrochem-omechanical contraction and concomitant water exudation. Micro-particles of crosslinked poly(acrylic acid) also undergoes reversible shrinkage by the electric field. The contraction was associated with the electrohydrodynamic transport of hydrated ions, and an equation expressing the rate of size change was derived as a function of voltage, charge density, and degree of swelling. Applications of this phenomenon to drug delivery systems, artificial muscles lifting and lowering a load, and some gel actuators walking in water are introduced.

ISSN:0022-233X    

DOI:10.1080/00222339108054092

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A number of useful functionalized polystyrenes have been prepared. Studies on fluoroalkyl ketone, fluoroalkyl carbinol, and hydroxy-contain polystyrenes, as well as polystyryl pyridine-based polymers, in regard to a variety of properties were made. These are discussed individually in regard to their reactions with alcohols to form hemiketals, miscibilization by hydrogen bonding, improvements in the thermostability of blends, and char formation at elevated temperature, respectively. In addition, enhancements of polystyrene and copolymers of modified polymers in regard to the oxidative stabilization of blends are discussed.

ISSN:0022-233X    

DOI:10.1080/00222339108054093

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Several polyimides were prepared by the palladium-catalyzed carbonylation and condensation of tetraiodoaromatic compounds and diamines. This new reaction for preparing polyimides was verified in model compound work to be an efficient, high yield route to cyclic imides. Since fully imidized groups are formed during the polymerization, it was necessary to limit the diamines to those that would impart solubility to the polymer. In contrast to the model compound work, the polymerization reaction yielded an appreciable concentration of amide functional groups due to incomplete cyclization and/or branching reactions. Thermal characterization of the polyimides formed by this process is reported.

ISSN:0022-233X    

DOI:10.1080/00222339108054094

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Homogeneous Ziegler-Natta catalysts are stereoselective cyclopolymerization catalysts for non-conjugated dienes. Cyclopolymerization of 1,5-hexadiene affords poly(methylene-l,3-cyclopentane) (PMCP), a polymer for which four structures of maximum order are possible. A variety of metallocene catalyst precursors have been investigated; the molecular weight and microstructure of the polymers are sensitive to the structure of the catalyst precursor as well as the reaction conditions. The selectivity for cyclization depends on reaction conditions; decreasing the olefin concentration and increasing the temperature of the reaction favor cyclization. The stereochemistry of cyclopolymers can also be controlled with appropriate choice of catalyst precursor. Diastereoselective cyclopolymerization of 1,5-hexadiene with achiral catalysts yields atactictrans-PMCPandcis-PMCP, depending on the catalyst precursor. Enantioselective cyclopolymerization with optically active catalysts yields optically active poly(methylenecyclopentane), a novel example of a polymer which is chiral by virtue of its main-chain stereochemistry.

ISSN:0022-233X    

DOI:10.1080/00222339108054095

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

This paper reviews the synthesis and fluid properties of several associating polymer systems. Both hydrocarbon-soluble and water-soluble associating polymers are described. The hydrocarbon-soluble associating polymers are based upon functional poly-octene copolymers. The water-soluble associating polymers are based upon polyacrylamide polymers containing hydrophobic groups.

ISSN:0022-233X    

DOI:10.1080/00222339108054096

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor