Crosslinked fabrics

From the point of view of technology, it is convenient to classify polymers as thermosetting and thermoplastic. The former set by chemical crosslinks introduced during fabrication and hence do not change appreciably in their deformability with changes in temperature. Thermoplastics, on the other hand, soften and/or melt on heating and can therefore be altered in shape by heating... 

The ease of hydrolysis of a DMEU-treated fabric has been used to produce bicolored cotton fabrics. This was accompHshed by applying a thickened DMEU solution in a print configuration to the pile of fabric, curing the resin, and dyeing the fabric. The DMEU-treated areas resisted dyeing because of the cross-links. Subsequendy, the DMEU-crosslinks were removed via an acid hydrolysis and the entire fabric was overdyed to achieve the desired bicolored effect (69). 

TPEs are materials that possess, at normal temperatures, the characteristic resilience and recovery from the extension of crosslinked elastomers and exhibit plastic flow at elevated temperatures. They can be fabricated by the usual techniques such as blow molding, extrusion, injection molding, etc. This effect is associated with certain interchain secondary valence forces of attraction, which have the effect of typical conventional covalent crosslinks, but at elevated temperatures, the secondary... 

Collagen, because of its unique structural properties, has been fabricated into a wide variety of forms including crosslinked films, meshes, fibers, and sponges. Solid ocular inserts have also been prepared from purified animal tissues. 

The collagen shield, fabricated from procine scleral tissue, is a spherical contact lens-shaped film whose thickness can be made to vary from 0.027 to 0,071 mm. It has a diameter of 14.5 mm and a base curve of 9 mm. Once the shield is hydrated by tear fluid and begins to dissolve, it softens and conforms to the corneal surface. Dissolution rates can be varied from 2 to as long as 72 hr by exposing the shields to ultraviolet radiation in order to achieve varying degrees of crosslinking. 

Foly(dimethylsiloxane) (silicone rubber) membranes are fabricated by hydrolysis of alkox-ysilyl terminal groups of silicone-rubber precursors [oligo(dimethylsiloxane) derivatives and crosslinking agents], followed by condensation. Covalent bonding of neutral carriers carrying an alkoxysilyl group to silicone rubber is, therefore, feasible by simple reaction of the silicone-rubber precursor with alkoxysilylated neutral carriers, as schematically shown in Scheme 1 [44]. 

The design of bioeompatible (blood compatible) potentiometric ion sensors was described in this chapter. Sensing membranes fabricated by crosslinked poly(dimethylsiloxane) (silicone rubber) and sol gel-derived materials are excellent for potentiometric ion sensors. Their sensor membrane properties are comparable to conventional plasticized-PVC membranes, and their thrombogenic properties are superior to the PVC-based membranes. Specifically, membranes modified chemically by neutral carriers and anion excluders are very promising, because the toxicity is alleviated drastically. The sensor properties are still excellent in spite of the chemical bonding of neutral carriers on membranes. 

The choice of metal ion in this work is interesting since it has been known for a considerable time that Ag+ is a rare example of a d-block metal ion that does not disrupt the duplex DNA structure (172,173). Rationalization of this effect has tended to focus on the possible base-pair crosslinking due to the preferred linear coordination geometry of Ag1 ions (174). The importance of Ag+ DNA coordination chemistry to the procedure described is not clear. However, reports that other metal ions, e.g., Pdri (175), can be plated to DNA to fabricate metallic wires (Fig. 51) suggests that this may not be essential. 

A difference between microcrystallite-based ultrastructure and covalently-crosslinked systems is that microcrystallites melt at specific temperatures, allowing the polymer to be fabricated by heating at modest temperatures. Subsequent cooling of the system below the crystallization temperature allows the physical property advantages of the solid state to become manifest. Liquid crystallinity is also possible if some order is retained in the molten state. Crystalline order not only adds mechanical strength, it also provides opportunities for the appearance of other properties that depend on solid state order—such as electronic conductivity. 

Thermosets differ molecularly from thermoplastics in that their individual chains are anchored to one another through crosslinks. The resulting network creates cohesive materials that demonstrate better thermal stability, rigidity, and dimensional stability than thermoplastics. Some examples of traditional thermosets are melamine-formaldehyde resins, which are used to treat fabrics to make them wrinkle-free, and Bakelite (a phenol-formaldehyde resin), a historically important polymer used in many applications, such as costume jewelry, electrical switches, and radio casings. 

Essentially nonionic soil-release agents comprise polyesters, polyamides, polyurethanes, polyepoxides and polyacetals. These have been used mainly on polyester and polyester/ cellulosic fabrics, either crosslinked to effect insolubilisation (if necessary) or by surface adsorption at relatively low temperature. Polyester soil-release finishes have been most important, particularly for polyester fibres and their blends with cellulosic fibres. These finishes, however, have much lower relative molecular mass (1000 to 100 000) than polyester fibres and hence contain a greater proportion of hydrophilic hydroxy groups. They have been particularly useful for application in laundering processes. These essentially nonionic polymers may be given anionic character by copolymerising with, for example, the carboxylated polymers mentioned earlier these hybrid types are generally applied with durable press finishes. 

Chemical Crosslinking. Only linear polymers are produced from bifunctional monomers. The reaction system must include a polyfunctional monomer, i.e., a monomer containing 3 or more functional groups per molecule, in order to produce a crosslinked polymer. However, the polyfunctional reactant and/or reaction conditions must be chosen such that crosslinking does not occur during polymerization but is delayed until the fabrication step. This objective is met differently depending on whether the synthesis involves a chain or step polymerization. In the typical... 

The first resist used to fabricate solid-state devices was a negative resist based on cyclized poly(cis-1,4-isoprene) which is crosslinked using a photoactive bis-... 

Radiation-sensitive polymers are used to define pattern images for the fabrication of microelectronic devices and circuits. These polymers, called resists, respond to radiation by either chain scission (positive resists) or by crosslinking (negative resists). In positive resists, the exposed areas dissolve selectively by chemical developers in negative resists, the exposed areas are insoluble and remain after development. 

Moreover, in-situ copolymerization approaches of polymerizable chiral cin-chonan carbamate selectors have also been shown to be viable straightforward routes to enantioselective separation media. In one approach, polymethacrylate-type monoliths have been fabricated by copolymerization of functional monomers and crosslinker in presence of porogenic solvents [80-85]. They have been utilized mainly for CEC (and will be described in detail later) while they turned out to be less suitable for HPLC application because of a low crosslinking degree. 

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