Crosslinked polymers elastomers

The use of lightly crosslinked polymers did result in hydrophilic surfaces (contact angle 50°, c-PI, 0.2 M PhTD). However, the surfaces displayed severe cracking after 5 days. Although qualitatively they appeared to remain hydrophilic, reliable contact angle measurements on these surfaces were impossible. Also, the use of a styrene-butadiene-styrene triblock copolymer thermoplastic elastomer did not show improved permanence of the hydrophilicity over other polydienes treated with PhTD. The block copolymer film was cast from toluene, and transmission electron microscopy showed that the continuous phase was the polybutadiene portion of the copolymer. Both polystyrene and polybutadiene domains are present at the surface. This would probably limit the maximum hydrophilicity obtainable since the RTD reagents are not expected to modify the polystyrene domains. 

The next breakthrough came with the discovery of how to make almost linear polymers with just a few crosslinked connections between molecules. These materials will not flow after crosslinking, and they become elastomers. A final type is the heavily crosslinked polymers such as epoxy and urea-formaldehyde, which are processed as monomers and then crosslinked at a suitable time and rate to make paints, adhesives, and very hard and durable plastic materials. 

Crosslinked LC elastomers (Figure 19d) are very promising for piezoelectric and ferroelectric applications, and also as non-linear optic materials. The first synthetic step to such materials is the preparation of usual side chain or combined LC copolymers doped with a small part of side chains containing a polymerizable >C=C< double bond at the end (Figure 23 shows a particular example of a crosslinkable LC polymer64). The copolymer can be further photocrosslinked, giving an elastic polymer film which reveals... 

The synthesis of PU can be carried out by the reaction described in Eq. (2.24). If the functionality of the hydroxy-containing compounds or the isocyanate is increased beyond 2, branched and possibly crosslinked polymers are produced. Because the nature of the polyol (polyether, polyester, polybutadiene, etc.) and isocyanate components can vary widely, PU are among the most versatile polymers, producing a wide variety of materials such as elastomers, foams, coatings, adhesives, or fibers. 

This plastic includes a large group of polyaddition polymers which are formed through the reaction of bifunctional or trifunctional alcohols with di- or polyisocyanates. By varying the starting materials, linear as well as crosslinked macromolecules with correspondingly different properties are formed. Alcohols with three functional groups and/or triisocyanate are used to make crosslinked polyurethane elastomers (PUR). 

Gagnon, K. D., Lenz, R. W., Farris, R. J., and Fuller, R. C. 1994a. Chemical modification of bacterial elastomers. 1. Peroxide crosslinking. Polymer, 35,4358-4367. 

Thermosets are polymeric materials which when heated form permanent network structures via the formation of intermolecular crosslinks. Whether the final product has a glass transition temperature, Tg, above or below room temperature, and therefore normally exists as an elastomer or a glass, it is, strictly speaking, a thermo-set. In practice, however, thermosets are identified as highly crosslinked polymers that are glassy and brittle at room temperature. These materials typically exhibit high moduli, near linear elastic stress-strain behavior, and poor resistance to fracture. 

The hydroxytelechelic acrylic polymers can be synthesized by a free-radical polymerization. They can be crosslinked as elastomers, generally with alcohols, esters, anhydrides, and isocyanates 2 6). 

Polystyrene alone or with photosensitizer was unaffected under photolysis conditions, apart from some yellowing, and polystyrene-blsmaleimlde solutions appear to be stable Indefinitely in the dark. Blsmalelmldes have beat used previously in peroxide-Induced crosslinking of polymers l however, polystyrene was reported to be unreactlve under these conditions. Thus, the crosslinking reactions described here are not free radical in nature and are best formulated according to Reaction 3. Blsmalelmldes have also been reported to accelerate the radlolysls-induced crosslinking of elastomers.—... 

ZAGORSKI, Z.P., EB — crosslinking of elastomers, how does it compare with radiation crosslinking of other polymers , International Meeting on Radiation Processing Chicago 2003, Sept. 7-12, Book of Abstracts. 

Liquid crystalline polymers can be crosslinked to form a network, or an elastomer, while retaining liquid crystallinity. This section is devoted to both the liquid crystallinity and the rubber elasticity of the crosslinked polymers. 

Luperox. [Atochem N. Am.] Organic peroxide compds. initiator for poly-meiizaticHi, polymer modification, dier-moplastic crosslinking, curing elastomers, high-tenq>. cure ci polyester resins. 

Polysiloxanes, [-O-Si(RR )-], are linear resins that can be branched or crosslinked into elastomers. They have high compressibility, permeability to gases, low T and viscosity, exceptional weather-ability, low surface tension coefficient and are relatively expensive. Siloxane polymers or copolymers have been incorporated into engineering or specialty resins to improve processability, toughness, HDT, solvent and weather resistance. 

Characterization of the chemical structure of highly cross-linked polymers, and of the chemical changes that accompany degradation processes, relies on spectroscopic methods. Solid-state nuclear magnetic resonance techniques have the potential to allow a more detailed characterization than before possible of the chemical environment and structure of chemical crosslinks in elastomers and thermoset epoxies. Degradation processes in cross-linked systems have been studied by using infrared spectroscopy, solid-state NMR, and electron spin resonance. 

Three urethane-crosslinked polybutadiene elastomers (TB-1, TB-2, and TB-3) of varying crosslinking levels, along with a similarly crosslinked styrene-butadiene copolymer (HTSBR) and two polybutadiene polymers randomly crosslinked with dicumyl peroxide (PB-1 and PB-2), have been investigated to determine their viscoelastic behavior. Elsewhere, TB-1, TB-2, and TB-3 have been designated as HTPB-1, HTPB-2, and HTPB-3, respectively. 

Chang, W. V., Bloch, R.,Tscho l, N. W. A New Measure of Strain to Describethe Mechanical Response of Elastomer Networks, in Chemistry and Properties of Crosslinked Polymers (S. S. Labana ed.). Academic Press, New York 1977... 

Uses Monomer for polyester resins (surface coatings) intermediate silane intemrediate crosslinker, polymer modifier for high impact plastics, adhesives, acrylic elastomers, optical polymers Manuf/Distrib. Aldrich Atofina CPS Ciba Spec. ChemsTWater Treatment Eastech Fluka Mitsubishi Gas Monomer-Polymer Dajac Labs Nippon Nyukazai Polysciences Rhodia HPCII Richman Rohm Tech Rohm Am. San Esters Trade Names SR 201... 

In the past 4-5 years, quite a number of relevant review articles and books have appeared. These included general reviews on NMR of polymers (1 10), reviews on solid state NMR (11-15), solid state multidimensional techniques (16-19), spatially resolved techniques (20), solid state NMR studies of polymer dynamics and structure (21), hydrated polymers (22), vulcanized elastomers (23), crosslinked polymers (24), and polymer networks (25), Reviews have also been written on polymer gels (26-28), polymer colloids (29), polymer-surfactant systems (30), and polymers on surfaces (31). 

An elastomer may be defined as a crosslinked polymer network whose temperature is above its glass transition temperature. The molecular mechanism responsible for rubber elasticity is based on changes in chain conformation brought about by the overall strain (see Figure 1.13). Clearly, the number of possible chain conformations must be fewer in case (c) than in case (a), resulting in a reduction of entropy (Flory, 1953, Chapter 11). Statistically all possible chain conformations are equally likely, assuming negligible... 

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