Polymer of commercial importance

As is usually characteristic of crosslinked polymers of commercial importance, epoxy resins are prepared in two stages, with the initial reaction leading to a linear prepolymer and the subsequent reaction introducing the crosslinks between the molecules. The prepolymers from which epoxy resins are prepared are diglycidyl ethers with the structure shown in Figure 4.2. 

The IUPAC nomenclature will be used in this book with some exceptions. One exception is the use of well-established, non-IUPAC names for most of the commonly encountered polymers of commercial importance. Another exception will be in not following rule 2 for writing the constitutional repeating unit (although the correct IUPAC name will be employed). Using the IUPAC choice of the CRU leads in some cases to structures that are longer and appear more complicated. Thus the IUPAC structure for the polymer in Eq. 1-3 is... 

Among the fluorine-containing polymers of commercial importance, our polymer of choice was PCTFE, the homopolymer of chlorotrifluoroethylene. The reason for choosing this polymer was the assumption that the chloride group would have sufficient reactivity to allow chemical modifications (Equation 1), but, in the most likely case that such modifications were incomplete, would be inert toward the ultimate reagents and substrates when the functionalized polymers were applied in their subsequent uses in carrying out organic reactions. 

However, there are a few synthetic polymers of commercial importance that are biodegradable (see Table 9.2). 

Syndiotactic polymers, as we have seen above, are stereoregular and so are crystallizable. They, however, do not have the same mechanical properties as isotactic polymers, because the different configurations affect the crystal structures of the polymers. Most highly stereoregular polymers of commercial importance are isotactic, and relatively few syndiotactic polymers are made. Atactic polymers, on the other hand, are usually completely amorphous unless the side group is so small or so polar as to permit some crystallinity. Thus, while atactic poly(vinyl acetate) has never been crystallized, poly(vinyl alcohol), which is derived from it and is also atactic, has been found to crystallize. 

Aminoresins or aminoplastics cover a range of resinous polymers produced by reaction of amines or amides with aldehydes [14,46,47]. Two such polymers of commercial importance in the field of plastics are the urea-formaldehyde and melamine-formaldehyde resins. Formaldehyde reacts with the amino groups to form aminomethylol derivatives which undergo further condensation to form resinous products. In contras to phenolic resins, products derived from urea and melamine are colorless. 

Various P-FRs are used in major polymers of commercial importance. For POs and other polymers, the char-initiating component is aided by synergists that promote foaming and cross-linking. The following three critical functionalities are typically required in each P-FR package ... 

Isobutylene has been of interest since the early days of synthetic polymer research when Friedel Crafts catalysts were used to prepare elastic materials. Isobutylene polymers of commercial importance include homopolymers and copolymers containing small amounts of isoprene or p-methylstyrene. Currently, chlorinated and brominated derivatives of butyl(poly[isobutylene-co-isoprene]) have the highest sales volume. 

Amorphous polymers of commercial importance include polymers which are glassy or rubbery at room temperature. Many amorphous thermoplastics, such as atactic polystyrene and poly (methyl methacrylate), form brittle glasses when cooled from the melt. The glass transition temperature, Tg or glass-rubber transition, is the temperature above which the polymer is rubbery and can be elongated and below which the polymer behaves as a glass. Thermal analysis of amorphous polymers shows only a glass transition temperature whereas crystalline poly-... 

The isotactic form is the only polymer of commercial importance. An unusual feature is that bulk polymer is transparent because the molecular chain is only very slightly birefringent. A second unusual feature is that the crystalline density and the amorphous density are very similar. The transparency is further enhanced by nucleation giving finer texture, and by balancing crystalline and amorphous densities even more closely, by copolymerization. The monomer is obtained by the dimerization of propylene. 

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