Elastomeric thermoset

For non-elastomeric thermosets, Carrasco [13] described the use of DSC to follow the conversion during cure of a trifunctional aminoepoxy resin. Here, the conversion was determined versus a non-cured sample. Sauerbrunn [14] also described the use of DSC to follow fiiermoset curing amongst other applications. Stephan [15] utilized dielectric analysis (DEA) as well as DSC, viscosity measurements and insolubles analysis to follow the curing, cure state and... 

A siloxane-diacetylene ferrocene polymer with carborane groups in its backbone (116) was heated to 350°C imder an inert atmosphere, resulting in the formation of an elastomeric thermoset. CrossUnking of the butadiyne groups was confirmed... 

Polymeric Ma.teria.Is, The single-ply membranes are made from a wide variety of polymers. The following is a brief description of those polymers and their characteristics. There are three thermosetting-type elastomeric membranes as of this writing (1996) neoprene, CSPE, and EPDM. Neoprene is stiU used where oil resistance is needed. Eor instance. Hydrotech uses neoprene flashings, the base of which is hot-set in mbberized asphalt (see ElASTOL RS, SYNTHETIC-POLYCm.OROPRENE). 

The use of elastomeric modifiers for toughening thermoset resias generally results ia lowering the glass transition temperature, modulus, and strength of the modified system. More recendy, ductile engineering thermoplastics and functional thermoplastic oligomers have been used as modifiers for epoxy matrix resias and other thermosets (12). 

A number of BMI resias based on this chemistry became commercially available through Rhc ne Poulenc for appHcation ia priated circuit boards and mol ding compounds and Rhc ne Poulenc recognized the potential of bismaleimides as building blocks for temperature-resistant thermoset systems. The basic chemistry, however, was not new, because the Michael addition reaction had been employed by Du Pont to obtain elastomeric reaction products from bismaleimides and Hquid polymeric organic diamines (15). 

When a thermoplastic polyurethane elastomer is heated above the melting point of its hard blocks, the chains can flow and the polymer can be molded to a new shape. When the polymer cools, new hard blocks form, recreating the physical crosslinks. We take advantage of these properties to mold elastomeric items that do not need to be cured like conventional rubbers. Scrap moldings, sprues, etc. can be recycled directly back to the extruder, which increases the efficiency of this process. In contrast, chemically crosslinked elastomers, which are thermosetting polymers, cannot be reprocessed after they have been cured. 

Tne effectiveness of inorganic tin compounds as flame and smoke retardants, both alone and in combination with inorganic fillers, in several halogen-free thermoplastic, thermosetting and elastomeric substrates, is currently under investigation at the ITRI. 

Several high-performance or engineering polymers, such as the polyfluo-rocarbons, acetals, ABS, nylons, polyurethanes (PUs), silicones, and phos-phazenes, have been described in previous chapters. Several elastomers, such as butyl rubber, EPDM (elastomeric terpolymer from ethylene, propylene, and a nonconjugated diene), and Neoprene, which play a vital role in engineering, and a host of classic thermosets should also be considered high-performance polymers. The properties of other high-performance polymers are described in this chapter. 

The contribution of Babu and Naskar gives a comprehensive overview on the recent developments of the thermoplastic vulcanizates (TPVs) with special reference to the technological advancement. TPVs combine high volume molding capability of thermoplastic with elastomeric properties of thermoset rubber. Therefore, they land themselves to broad area of applications in various fields. 

Core-shell polymers were commercially introduced as impact modifiers for poly(vinyl chloride) PVC, in the 1960s. They are produced by a two-stage latex emulsion polymerization technique (Cruz-Ramos, 2000). The core is a graftable elastomeric material, usually crosslinked, that is insoluble in the thermoset precursors. Typical elastomers used for these purposes are crosslinked poly(butadiene), random copolymers of styrene and butadiene,... 

Conductive adhesives are generally formulated from base polymers that are low-viscosity, thermosetting resins such as epoxies. Where elastomeric properties are required, silver-filled flexible epoxy and silver-filled silicone rubber systems are commercially available. 

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