Noncrystalline polymers

Below their glass transition temperatures Tg, noncrystalline polymers (without fillers) usually exhibit high tensile strengths, although lower than those of typical crystalline polymers if the strength is referred to the cross section at rupture in both cases. A brittle type of fracture occurs, which probably is initiated by a different mechanism... 

A similar comparison can be made with cis-poly(isoprene), natural rubber, by taking advantage of the fact that the polymer is very slow to crystallize [164], Consequently, the comparison can be made between the supercooled, noncrystalline polymers at 0°C and the semi-crystalline polymer (31% crystalline) at the same temperature. The Tlc values for each of the five carbons involved were again found to be the same for the completely disordered polymer and the semicrystalline one, so that a similar conclusion can be made with regard to their chain structure. 

There are two major experimental techniques that can be used to analyze hydrogen bonding in noncrystalline polymer systems. The first is based on thermodynamic measurements which can be related to molecular properties by using statistical mechanics. The second, and much more powerful, way to elucidate the presence and nature of hydrogen bonds in amorphous polymers is by using spectroscopy (Coleman et al., 1991). From the present repertoire of spectroscopic techniques which includes IR, Raman, electronic absorption, fluorescence, and magnetic resonance spectroscopy, the IR is by far the most sensitive to the presence of hydrogen bonds (Coleman et al., 1991). 

Packing efficiency can also be described by the extent of short-range order in the amorphous state. Mitchell has shown through X-ray scattering studies that, while the local molecular organization of noncrystalline polymers is random, in many cases, there are additional correlations that do not perturb the chain trajectory but will impact polymer properties.15 These correlations have a limited spatial range (<50A) but will have a particular impact on bulk properties... 

Noncrystalline polymers, 9 554 Noncyanide baths, 9 804-805 Noncyclic maleyl chloride, 15 485—486 Noncyclopentadienyl compounds, covalent, 25 105-109... 

The Amorphous Phase and Ts. Not all polymers crystallize, and even those that do are not completely crystalline. Noncrystalline polymer is termed amorphous. Four types of molecular motion have been identified in amoiphous polymers. Listed in order of decreasing activation energy-, they... 

New heterocyclic polymers designed especially for service at elevated temperatures have intriguing properties, some of which are in contrast to properties usually associated with linear noncrystalline polymers. These polymers have sometimes been described as stiff chains because of the long inflexible repeat units of which they are comprised. Relatively few quantitative studies have yet appeared in the dilute solution properties or the viscoelastic behavior of the new heterocyclic polymers—partly because of the difficulties inherent in working with the poorly soluble materials. Some studies on the polyimide with the (idealized) structure ... 

A sufficient amount of strong interchain complex formation occurs in the solid state to give the linear, noncrystalline polymer some of the physical properties of a highly crosslinked network polymer. 

The glassy state of materials refers to a nonequilibrium, solid state, such as is typical of inorganic glasses, synthetic noncrystalline polymers and food components. Characteristics of the glassy state include transparency, solid appearance and brittleness (White and Cakebread 1966 Sperling 1992). In such systems, molecules have no ordered structure and the volume of the system is larger than that of crystalline systems with the same composition. These systems are often referred to as amorphous (i.e., disordered) solids (e.g., glass) or supercooled liquids (e.g., rubber, leather, syrup) (Slade and Levine 1991 Roos 1995 Slade and Levine 1995). 

In region FG the polymer is completely amorphous and the properties of the polymer-solute solution can be investigated. Care must be taken to ensure that any contribution from surface adsoption is taken into account. Usually for thick polymer films contributions from surface adsorption will be small. For noncrystalline polymers, liquid-like behavior is observed from point C onwards. The location of point C on the temperature axis depends both on the polymer-solute system considered and on experimental conditions, film thickness and flow rate. For most polymers, equilibrium bulk sorption is achieved at temperatures in excess of about Tg + 50°. 

A is the fraction of noncrystalline polymer, i.e., elastically effective My is the molecular weight of the repeating unit of the polymer A//f is the heat of fusion of the polymer Tin is melting temperature of the crystalline phase... 

The ease of rotation of chain segments has a great influence on the properties of a polymer structure. As previously discussed, this is a function of polymer structure and temperature. The glass transition temperature of a polymer is that temperature at which backbone segments begin to rotate. An ideal noncrystalline polymer is a glass below the transition temperature and a non-Newtonian viscous liquid at temperatures above Tg. Thus, normally, plastics have Tg values above the use temperature, while elastomers have Tg values below the use temperature. 

The synthesis of dimeric fatty acids is based on the reaction between a fatty acid with one double bond (oleic acid) and a fatty acid with two double bonds (linoleic acid) or three double bonds (linolenic acid), at higher temperatures in the presence of solid acidic catalysts (for example montmorillonite acidic treated clays). Dimerised fatty acids (C36) and trimerised fatty acids (C54) are formed. The dimer acid is separated from the trimeric acid by high vacuum distillation. By using fatty dimeric acids and dimeric alcohols in the synthesis of polyesters and of polyester polyurethanes, products are obtained with an exceptional resistance to hydrolysis, noncrystalline polymers with a very flexible structure and an excellent resistance to heat and oxygen (Chapter 12.5). Utilisation of hydrophobic dicarboxylic acids, such as sebacic acid and azelaic acid in polyesterification reactions leads to hydrolysis resistant polyurethanes. 

PVC), a polymer with extremely low crystallinity. These two are contrasted with atactic polystyrene (PS), a typical noncrystalline polymer. 

In previous sections we have shown that the redistribution of additives at the spherulite boundaries during polymer crystallization leads to the additives uneven distribution, whose form is determined by the kinetics of the growth rejection process. In time, this initial dynamic distribution should relax to an equilibrium form in which the noncrystalline polymer is uniformly permeated by the additive, whose distribution reflects that of the noncrystalline polymer. The relevanoe of these observations to oxidative degradation processes in semi-crystalline polyolefins is discussed in this section. 

The two common forms of phosphorus are white, which is made up of P4 molecules, containing font atoms of phosphorus arranged in a regular tetrahedral formation, and red, which is a noncrystalline polymer. White phosphorus glows in the dark and bnrsts into flame in air. Red phosphorus does not react rapidly with air. 

In most cases, free-radical polymerization of a monomer containing a C>C double bond results in a noncrystalline polymer. Explain. Give three examples of monomers that yield crystalline polymers by free-radical polymerization. 

MAJOR APPLICATIONS Poly(vdf-hfp) is a synthetic, noncrystalline polymer that exhibits elastomeric properties when cross-linked. Known to be chemically inert, it is designed for demanding service applications in hostile environments and commonly used as a sealmt in hot and corrosive environments. 

Polyether-imides are noncrystalline polymers made up of alternating aromatic ether and imide imits. The molecular structure has rigidity, strength, and impact resistance in fabricated parts over a wide range of temperatures. PEI is one of the strongest thermoplasts even without reinforcement. 

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