摘要:

The polymerization of alkyl vinyl ethers initiated by hydrogen iodide and iodine catalyst has been studied in detail. The polymerization showed living behavior in nonpolar solvents at low (-15°) temperatures as reported earlier by others. The observed rate of polymerization under the reaction conditions was linearly dependent on the initial concentration of hydrogen iodide and iodine, respectively. However, the monomer concentration did not influence the rate of polymerization (apparent zero order). From the observed rate equation, two possible reaction schemes were proposed and attempts were made to distinguish them by using UV/visible spectroscopy and13C-NMR spectroscopy. In both schemes a reversible interaction between monomer and an iodine molecule was postulated as a necessary elemental reaction to fit the observed expression for rate of polymerization. From the spectroscopic analysis results, the interaction between the iodide compound (chain end) and the iodine molecule seems to be very weak compared to the interaction between monomer and the iodine molecule.

ISSN:0022-233X    

DOI:10.1080/00222338808053381

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The synthesis of polymers characterized by a preferred helical screw sense (macromolecular asymmetry) is a subject of considerable experimental interest. Here, we summarize our efforts toward the preparation of optically active polychloral in which asymmetry at the macromolecular level is the only factor contributing to the polymer's chiroptical properties. Through the use of chiral initiating species, we have prepared optically active polychloral with specific rotations reaching 4500° at the sodium D-line. The results of this work and the prospects for further investigation are outlined.

ISSN:0022-233X    

DOI:10.1080/00222338808053382

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Radical polymerization of fumaric acid derivatives, such as dialkyl fumarates, gave polymers consisting of a less-or nonflexible substituted polymethylene structure. The yield and molecular weight of the polymers produced increased as the bulkiness of the ester substituents increased. For example, when di-t-butyl fumarate was polymerized in bulk with azocyclohexanecarbonitrile (20 mmol/L) at 80°C for 6 h, polymer withMnof more than 100 000 was produced in more than 80% yield. The polymers obtained were colorless powders and did not melt before degradation at ∼250°C, but they were soluble in such organic solvents as benzene, carbon tetrachloride, tetrahydrofuran, and dioxane. A transparent brittle film or fiber was obtained from toluene solution. Some properties and possibilities for application of these polymers are described and discussed.

ISSN:0022-233X    

DOI:10.1080/00222338808053383

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

For one of the approaches to antithrombogenic materials, the combination of synthetic polymers with physiologically active substances seems to be promising. One of these ways involves crosslinked urokinase (HM-UK), in which urokinases are linked with side chains of poly(2-hydroxyethyl methacrylate) (PHEMA) by 4,4′-diisocyanatodiphenyl-methane, and encapsulated urokinase (HMe-UK), in which urokinases are encapsulated in the network of crosslinked PHEMA. The HMe-UK with a low degree of crosslinking was found to be highly antithrombogenic. For another way, Val-Pro-Arg-immobilized polyetherurethaneurea (PEUU) was synthesized. The tripeptide, Val-Pro-Arg, is a substrate of thrombin. The tripeptide-immobilized PEUU was found to complex specifically with thrombin and inactivate it, and hence to prolong the thrombin time and the active partial thromboplastin time. For a further approach to antithrombogenic materials, the design of materials which are covered with a living tissue formed by cell proliferation seems to be promising. For one of the ways in this approach, Arg-Gly-Asp-Ser-immobilized silicone films were synthesized. The tetrapeptide constitutes the active site of cell-adhesion proteins. A number of fibroblast cells were found to grow on the tetrapeptide-immobilized silicone film more resistant to changes of temperature and pH than proteins. Third, novel functions such as cell separation are expected, according to the nature of the carrier macromolecule.

ISSN:0022-233X    

DOI:10.1080/00222338808053384

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Aluminum porphyrin is an excellent initiator for the living polymerizations of a wide variety of monomers such as epoxide, β-lactone, δ-lactone, ε-lactone, and lactide, and also for the alternating copolymerization of epoxide and cyclic acid anhydride or carbon dioxide, to give polymers and copolymers with narrow molecular weight distribution. Aluminum porphyrin was recently found to initiate also the living polymerization of methacrylic ester. In the polymerizations of epoxides and lactones initiated with aluminum porphyrin in the presence of an appropriate protic compound, polymers with narrow molecular weight can be obtained with the number of the polymer molecules more than those of the initiator. This fact demonstrates the “immortal” nature of the polymerization due to unusual reactivities of aluminum prophyrin.

ISSN:0022-233X    

DOI:10.1080/00222338808053385

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Ultrathin membranes of a polymer/(liquid crystal) mixture were prepared by spreading a single drop of a casting solution on the water surface. The thickness and the aggregation state of the water-cast membrane can be controlled by the kind of solvent and the concentration of the solution. In the case of a liquid crystalline state above the crystal-nematic phase transition temperature,TKN, the polymer (liquid crystal) composite membrane follows Henry's law for the sorption isotherm of hydrocarbon gases and, also, Fickian sorption for the sorption-desorption kinetics. These results indicate that hydrocarbon gases permeate through a homogeneous medium composed of liquid crystalline molecules. Therefore, the permeability coefficients of hydrocarbon gases can be controlled by the dimensions of the channels through which the gas molecules diffuse. The channel for diffusion is generated by thermal or fluctuating molecular motion which opens up the intermolecular distance between liquid crystalline molecules. In the case of a self-supported liquid crystalline membrane, the channel dimension can be controlled in the range of several Å by both the intermolecular distance and the degree of thermal molecular motion of the liquid crystalline molecules. Separation of hydrocarbon isomers was investigated by use of composite membranes composed of a polymer matrix and self-supported liquid crystalline molecules.

ISSN:0022-233X    

DOI:10.1080/00222338808053386

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A unique polyconjugated systems having longitudinal π-electron overlaps was synthesized by using a metacyclophane monomer, 8, 16-dihydroxy-[2,2]-metacyclophane. The monomer was synthesized according to Tashiro's method and was converted to two types of polycyclophanes. One was obtained as a quinoid-type polymer from FeCI3-catalyzed oxidative coupling of the 2,5-disubstituted phenols. The polymer obtained was composed of [2,2,] -metacyclophane units polymerized via a diphenoquinone linkage. Amorphous, bright reddish-orange powders were obtained quantitatively under mild reaction condition. Another one was a phenol-type polymer that contained [2,2] -metacyclophane units linked with a 4,4′-dihydroxybiphenyl skeleton. This polymer was obtained by way of a unique polycondensation reaction characteristic of cyclophane compounds. The polymer obtained had a fine whisker form with a golden luster and partial crystallinity. The structures of these polymers were confirmed by various spectroscopic methods and elemental analysis. The electrical conductivity of both polymers was of almost the same order of magnitude (10−8S/cm). When doped with sulfuric acid (H2SO4) vapor, the phenol-type polymer exhibited a conductivity of 0.25 S/cm, which was much higher than that of the quinoidtype polymer (10−4S/cm).

ISSN:0022-233X    

DOI:10.1080/00222338808053387

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A negative photoresist has been developed by partial esterification of poly(p-hydroxystyrene) withp-azidobenzenesulfonyl chloride. About 10% of esterification is sufficient to sensitize the polymer to light in the wavelength region between 240 and 300 nm. The dose required to insolubilize the polymer was 80 mJ/cm2. The resolution capability is not as high as expected because of the swelling of photoinsolubilized resist films in an aqueous alkaline developer.

ISSN:0022-233X    

DOI:10.1080/00222338808053388

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The present paper describes a new type of polymerization of 2-vinyl-2-oxazoline and 2-vinyl-5,6-dihydro-4H-1,3-oxazine and their salts. When these two imino ether monomers are allowed to react with Meerwein reagents or super acid esters,N-alkylation takes place first, followed by polymerization through the opening of vinyl groups to give poly [(2-oxazolinium-2-yl)ethylene] and poly [(5,6-dihydro-4H-1,3-oxazinium-2-yl)ethylene], respectively. With the corresponding 2-isopropenyl homologs, 2-isopropenyl-2-oxazoline and 2-isopropenyl-5,6-dihydro-4H-1,3-oxazine, stableN-alkylated salts are obtained, which were subjected to radical and base-catalyzed polymerizations. From the above results the reactivities of the salts are considered in terms of their ring size and the substituents on the olefinic functions.

ISSN:0022-233X    

DOI:10.1080/00222338808053389

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Highly aligned polyacetylene films are synthesized by three different methods in which nematic liquid crystals are used as an ordered matrix solvent: Method 1, polymerization of acetylene is carried out in a quiescent nematic solution in which a Ti(OBu)4-AlEt3Ziegler-Natta catalyst is dissolved homogeneously; Method 2, macroscopic alignment is attained by gravity flow of the nematic liquid crystal-catalyst system; and Method 3, the nematic liquid crystal-catalyst solution is aligned under a magnetic field. Characterization of these films is carried out through SEM observation and measurements of polarized visible and infrared absorption spectra. Results indicate that as-prepared films have highly aligned fibrils. Upon doping by I2and AsF5, these films exhibit high electrical condactivity of the order of 104S/cm.

ISSN:0022-233X    

DOI:10.1080/00222338808053390

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor