Rubbery properties

The solvation by plasticiser also gives celluloid thermoplastic properties owing to the reduction in interchain forces. On the other hand since the cellulose molecule is somewhat rigid the product itself is stiff and does not show rubbery properties at room temperature, cf. plasticised PVC. 

Random copolymers made by copolymerizing equal amounts of ethylene and propylene are highly amorphous, and they have rubbery properties. 

Further evidence for the rubbery properties of high acrylate copolymers is shown in Figure 3, which is a stress vs. strain plot for both... 

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. 

ELASTOMERS. Of natural or synthetic origin, an elastomer is a polymer possessing clastic (rubbery) properties. A polymer is a substance consisting of molecules which are. in the most part, multiples of low-molecular-weight units, or monomers. As an example, isoprcnc (2-methylbutadiene-1,3) is C 2 and normally is from 1,000 to 10.000 for rubbers. Although they differ in composition from natural rubber, many of these high-molecular-weight materials are termed. synthetic lubbers. See also Rubber (Natural). 

In semi-crystalline polymers, crystallites may act as effective crosslinks, which gives rise to rubbery properties above T. In systems with long chains, the presence of crystallites... 

Plasticizers and flexibilizers are incorporated into an adhesive formulation to provide it with flexibility and/or elongation. Plasticizers may also reduce the melt viscosity of hot melt adhesives or lower the elastic modulus of a solidified adhesive. Similar to diluents, plasticizers are nonvolatile solvents for the base resin, and by being incorporated into the formulation, they separate the polymer chains and enable their deformation to be more easily accomplished. Plasticizers generally affect the viscoelastic properties of the base resin whereas diluents simply reduce the viscosity of the system. Whereas diluents result in brittle, hard adhesive systems, plasticizers result in increased flexibility and lower modulus. The temperature at which polymers exhibit rubbery properties (i.e., the glass transition temperature) can also be modified by incorporating plasticizers. 

Although the P(cgTFSI), which showed the highest ionic conductivity among all systems of P(xgTFSI), had ionic conductivity of over 10 S cm at 30°C, the sticky characteristics of this polymer made it difficult to handle. To surmount this problem, the P(cgTFSI) were polymerized with various cross-linkers, as shown in Figure 31.6. First, the CLfs was used as a cross-linker so that the effects of various amounts of the cross-linker on their properties could be examined. The sticky rubbery property of IL polymers was improved by the addition of the cross-linkers. While they were sticky rubbers without cross-linkers, they formed... 

If we look at Figure 21.3, we can see that there is an upper limit to the overall styrene content in the polymer if making a polymer to have rubbery properties is the desired outcome [66]. As the styrene content increases, the stress-strain response changes dramatically for these neat SBS polymers. At 53 and 65% styrene content, the polystyrene endblocks form the continuous phase in the phase-separated block copolymer, and these polymers behave more like polystyrene than a rubber at low strain. This low strain behavior is also shown at 39% styrene content, but a rubbery plateau begins to show at lower stress. 

Extrusion is employed for the composite propellants of plastic properties, and cast technique is used for composite propellants of rubbery properties. 

Replacing the -NH- hydrogen in polyamides by an ether group curtails the intermolec-ular hydrogen bonding. Hence at low degrees of substitution the modulus is reduced and a more elastic fiber is obtained. As the substitution increases, the crystallinity is hompletely destroyed and rubbery property appears. 

The silicone rubbers differ from organic rubbers in that they retain rubbery properties over a much wider temperature span, some having a brittle point of below — 130 F (—90°C) and a useful life above 400 F (210°C). They contain no plasticizers. They show marked resistance to corona discharge. Because of the presence of inorganic filler the heat transfer is good. Different stocks are made for different purposes. 

Conventional rubbers are vulcanized, that is, cross-linked by primary valence bonding. For this reason vulcanized rubbers cannot dissolve or melt unless the network structure is irreversibly destroyed. These products cannot therefore be reprocessed like thermoplastics. Hence, if a polymer could be developed which showed rubbery properties at normal service temperatures but could be reprocessed like thermoplastics, it would be of great interest. 

The choice of maleic anhydride (MAH) as the functionalizing agent is suitable for several reasons. The most important one -- a fact which distinguishes MAH from other unsaturated molecules bearing functional groups - is that MAH, similarly as other 1,2-di-substituted olefins, does not homopolymerize easily. This makes the grafting product, EPM-g-SA, practically unmodified in its rubbery properties and miscible with the parent EPM. 

---