摘要:

Acrylic fibers are among the most important man-made fibers. They rank third after polyesters and nylons [1]. The first commercially available acrylic fiber was orlon, introduced by DuPont in 1943. Soon thereafter, other companies introduced new acrylic fibers, such as Acrilan, Dralon, and so forth. During the 1950s, the acrylic fiber industry experienced a rapid growth, with 18 companies introducing acrylic fiber products into the market. In 1970 21% of the synthetic fibers produced were acrylic fiber, whereas this figure fell to about 14% in 1992. In the corresponding period, the actual production of acrylic fibers increased from 809,890 tons to 2,410,520 tons. However, the overall production of synthetic fibers increased from 4.809 million tons to 17.218 million tons (Fig. 1). Interestingly, in 1970 only 12% of the acrylic fibers were produced in Third World countries (countries other than the United States, Japan, and western Europe) whereas this figure increased to 46% in 1989 and was expected to go still higher by 1995 [2–4] indicating a remarkable growth in the expansion of the acrylic fiber industry especially in the developing countries (Fig. 2). In India also there has been a considerable increase in the production of acrylic fibers as three new companies -Pasupati Acrylon Ltd., Indian Acrylics, and Consolidated Fibres—have started producing acrylic fibers of different denier range. In China, the acrylic fiber industry has made rapid progress. The total production of acrylic fiber in 1970 was about 5100 tons, whereas the production had increased to more than 140,000 tons in 1993.

ISSN:1532-1797    

DOI:10.1080/15321799608009642

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The term “model polymers” has long been utilized to designate linear macromolecules of controlled size and low dimensional fluctuation. Interest in these polymers was mainly motivated by the need for samples of well-controlled length, useful for the calibration of characterization techniques such as viscometry and size exclusion chromatography. Methods based on “living” polymerizations—so called because of the absence of transfer and termination reactions-proved to be the best suited for this objective. The first example of such a process was given by Szwarc [1, 2], who demonstrated that the anionic polymerization of styrene is free of the above-cited side reactions, when carried out in aprotic solvents. From the observation made while carrying on this study, Szwarc invented the concept of “living” polymerization. Since this pioneering work, many other unsaturated and heterocylic monomers have been shown to undergo “living” polymerizations through one of these five processes: anionic [3–6], cationic [7–9], metathesis [10–12], group transfer [13, 14], and even free radical [15–17]. This has led to a noticeable diversification of tailor-made linear polymers.

ISSN:1532-1797    

DOI:10.1080/15321799608009643

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

High-performance polymers are used in applications demanding service at enhanced temperature while maintaining their structural integrity and an excellent combination of chemical, physical, and mechanical properties. Some of the important polymers in this respect are polyimides, polyamides, and polybenzazoles. However, all of these polymers have a common problem of processing difficulty due to their infusibility and poor solubility in organic solvents. The reasons are strong interchain forces, inherent macromolecular rigidity, or semicrystallinity. A great amount of work has been directed to making polymers more tractable, soluble, and processable without sacrificing their high-performance characteristics. Thus, the last two decades have witnessed the spectacular growth of research in a new polymer type, the one containing hexafluoroisopropylidene (6F) groups. Incorporation of 6F units into the macromolecular chain increases the solubility, thermal stability, flame resistance, glass transition temperature, oxidation resistance, adhesion, optical transparency, and environmental stability, while decreasing the crystallinity, dielectric constant, water absorption, and color [1].

ISSN:1532-1797    

DOI:10.1080/15321799608009644

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The ability to predict the key physical and chemical properties of polymers from their molecular structures prior to synthesis is of great value in the design of polymers. The performance criteria that must be satisfied for the technological applications of polymers have become increasingly more stringent with the recent rapid advances in many areas of technology. At the same time, the applications of most of the familiar polymers with relatively simple repeat unit structures have reached their limits. The chemical structures of polymers suitable for advanced applications have therefore increased in complexity. Consequently, the development of predictive computational schemes to evaluate candidates for specific applications has gained urgency.

ISSN:1532-1797    

DOI:10.1080/15321799608009645

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor