Rubbery polymeric materials

Three factors affect the essential nature of a polymeric material and determine whether it is glassy, rubbery, or fibre-forming under a given set of conditions. These are ... 

The relative magnitudes of these two moduli, Gj and G2, vary according to the state of the polymeric material. In the glassy state, where good elasticity is shown, Gj is high in the rubbery state, where there is a greater contribution from the viscous element, G is low. 

Polymeric material whose impact resistance and toughness have been increased by the incorporation of phase microdomains of a rubbery material. 

Among various rubbery polymeric materials, a special polyester resin has been developed as a binder in view of its curing at ambient temperature, low viscosity (as a result of addition of vinyl monomers) without appreciable sedimentation of explosives. In addition, polyester resin has the greatest advantage of having an oxygen moiety in the skeleton which increases oxygen balance of the final sheet,... 

Composite rocket propellants are two-phase mixtures comprising a crystalline oxidizer in a polymeric fuel/binder matrix. The oxidizer is a finely-dispersed powder of ammonium perchlorate which is suspended in a fuel. The fuel is a plasticized polymeric material which may have rubbery properties (i.e. hydroxy-terminated polybutadiene crosslinked with a diisocyanate) or plastic properties (i.e. polycaprolactone). Composite rocket propellants can be either extruded or cast depending on the type of fuel employed. For composite propellants which are plastic in nature, the technique of extrusion is employed, whereas for composite propellants which are rubbery, cast or extruded techniques are used. 

Another type of geometric arrangement arises with polymers that have a double bond between carbon atoms. Double bonds restrict the rotation of the carbon atoms about the backbone axis. These polymers are sometimes referred to as geometric isomers. The X-groups may be on the same side (cis-) or on opposite sides (trans-) of the chain as schematically shown for polybutadiene in Fig. 1.12. The arrangement in a cis-1,4-polybutadiene results in a very elastic rubbery material, whereas the structure of the trans-1,4-polybutadiene results in a leathery and tough material. Branching of the polymer chains also influences the final structure, crystallinity and properties of the polymeric material. 

The physics of sorption and diffusion through polymeric materials in the rigid and rubbery states is discussed thoroughly in several outstanding reviews [14-18],... 

Thin films of many polymeric materials exhibit good adhesive i operties and are easily applied to most substrates. In addition, relatively rapid diffusion and a high capacity for organic solutes make amorphous rubbery polymers attractive as sensor coatings. An example of this rapid and sensitive detection is shown in Figure 5.17, the response of a polyisobutylene-coated SAW device to trichlraoeth-... 

Polymeric materials show a wide range of stress-strain characteristics. One characteristic of polymers that is markedly different from metals and ceramics is that their mechanical properties are highly time- and temperature-dependent. An elastomer or a rubbery polymer shows a stress-strain curve that is nonlinear. 

For example, Song et al [209] described three methods for predicting the long-term mechanical behavior and lifetime of polymeric materials based on the detailed analysis and interpretation of experimental data. They used semicrystalline, glassy amorphous and rubbery polymers as examples in validating these methods. The three methods are the following ... 

DSC defines the glass transition as a change in the heat capacity as the polymer matrix goes from the glassy state to the rubbery state. This is a second-order endothermic transition (requires heat to go through the transition), and so in DSC the transition appears as a step transition and not a peak such as might be seen with a melt transition. DSC is the classic and official way to determine even though in some cases there are polymeric materials that do not exhibit a sharp by DSC this has been the case of chitin and CS as well as cellulose [12, 39]. 

Although metallic and ceramic materials are used as membranes, polymeric materials account for the vast majority of commercial products. Polymer selection depends on a number of factors including intrinsic transport properties, mechanical properties, thermal stability, chemical stability (e.g., chemical resistance and biocompatibility), membrane manufacturability, cost, and patentability. The two most common types of polymers are glassy engineering thermoplastics and rubbery polysiloxanes. 

To surpass Robeson s upper bound, materials are emerging that rely on transport mechanisms other than solution-diffusion through glassy or rubbery polymeric materials. In particular, a number of materials have been developed that possess fixed microporosity (2 nm or less) in contrast to the activated, transient molecular gaps that give rise to diffusion in most polymers. These materials include amorphous and crystalline (zeolite) ceramics [68-69], molecular sieve carbons [70], polymers that possess intrinsic microporosity [71-72], and carbon nanotube membranes [73-76]. Transport in such materials is determined primarily by the average size and size distribution of the microporosity - the porosity can be tuned to allow discrimination between species that differ by less than one Angstrom in size. However, surface... 

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