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Polymer chemistry?

What are the main differences between thermost and thermoplastic polymer materials! any help will be really appreciated! thanks!

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1. A thermoplastic is a material that is plastic or deformable, melts to a liquid when heated and freezes to a brittle, glassy state when cooled sufficiently. Most thermoplastics are high molecular weight polymers whose chains associate through weak van der Waals forces (polyethylene); stronger dipole-dipole interactions and hydrogen bonding (nylon); or even stacking of aromatic rings (polystyrene). Thermoplastic polymers differ from thermosetting polymers (Bakelite; vulcanized rubber) which once formed and cured, can never be remelted and remolded. Many thermoplastic materials are addition polymers; e.g., vinyl chain-growth polymers such as polyethylene and polypropylene. i dont know anything abt. thermost.
2. [quote] An elastomer normally falls into one of two categories: + Thermoplastic + Thermoset A thermoplastic elastomer can repeatedly soften/melt when heated and harden when cooled. Nearly any TPE is soluble in specific solvents and can burn to some degree. A thermoset elastomer undergoes a chemical change during processing to become permanently insoluble and infusible. It is this chemical cross-linking that is the principal difference between a thermoset and a thermoplastic elastomer. A thermoplastic elastomer's capability to repeatedly process is a major benefit over thermoset rubber. Other benefits of a thermoplastic elastomer over its thermoset cousins include: + Design flexibility + Lower fabrication costs + Shorter processing times + Little or no compounding required + Fully recyclable scrap [/quote] source: http://tpe.gls.polysort.com/elastomer_def.htm ================================ [quote] THERMOSET VS. THERMOPLASTIC MATERIALS Polymer properties are linked to heat-induced changes. Though materials may be categorized in many ways (natural versus synthetic, oil-resistant versus non-oil-resistant, etc.), they can also be classified based on the ways in which they respond to heat. Some polymers (large, chainlike molecules) undergo a permanent chemical reaction when heated. Others only undergo a temporary physical change. A clear understanding of why various polymers react the way they do will help you make good decisions when choosing materials. Here’s a closer look: THERMOSET As the name suggests, a thermoset is a material (such as rubber) that cures or hardens (sets) into a given shape, generally through the application of heat (a thermal increase). Curing (also referred to as vulcanizing) is an irreversible chemical reaction in which permanent connections (known as cross-links) are made between the material’s molecular chains. These cross-links (you can think of them as chemical bridges) give the cured polymer a three-dimensional structure, as well as a higher degree of rigidity than it possessed prior to curing. Keep in mind that a cured, thermoset material will not remelt or otherwise regain the processibility it had before being cured. Curing changes the material forever. Thermoset polymers outperform other materials (such as thermoplastics, see below) in a number of areas, including mechanical properties, chemical resistance, thermal stability, and overall durability. For these reasons, thermoset parts tend to make more effective seals. THERMOPLASTIC A thermoplastic material softens (becomes pliable and plastic) when heated, but it does not cure or set. A thermoplastic often begins in pellet form, then becomes softer and more fluid as heat increases. This fluidity allows it to be injected under pressure from a heated cavity into a cool mold. As it cools, the thermoplastic will harden in the shape of the mold, but there is no chemical curing at work. No cross-links are formed as with a thermoset material. The changes seen in the thermoplastic are purely physical and, with the reapplication of heat, wholly reversible. A thermoplastic material can therefore be reprocessed many times, though continual recycling will eventually degrade the polymer. A thermoplastic elastomer (TPE) combines the rubber-like properties of a thermoset elastomer and the processing characteristics of a thermoplastic. The TPE achieves this blend because it is composed of two regions (or phases): soft phases (cured thermoset rubber particles) dispersed within hard phases (the thermoplastic portion). Be aware that the physical, chemical, and thermal limits of both phases will determine the overall limits for the TPE. Because it is a blended material, a TPE is also considerably more expensive than a simpler thermoset material. [/quote] source: http://www.rlhudson.com/tech_thermo.html
3. A plastic material will alter its shape when it melts. If it is then cooled the shape is set when the material is cooled below the melt temp. A thermoset material will keep this shape for ever (or untill it degrades) were as a thermo plastic material can be cycled above and below this temp many times altering its shape each time. A simple as I can put it rather than copying a wipika link out .