Amorphous thermoplastics polymer classes

Polycarbonate was developed by the chemist Hermann Schnell in 1953 for Bayer AG. It is a basic polymer for a whole class of polymers with a widespread field of application. Polycarbonate is a mainly amorphous thermoplastic polymer with a very high optical transparency in the visible spectrum. Its crystalline portion is mostly less than 5%. Polycarbonates are resistant against weather and radiation, they are flammable but self-extinguishing if the ignition source is removed. They can be colored and are good electrical insulators. 

Polycarbonates are an unusual and extremely useful class of polymers. The vast majority of polycarbonates are based on bisphenol A [80-05-7] (BPA) and sold under the trade names Lexan (GE), Makrolon (Bayer), CaUbre (Dow), and Panlite (Idemitsu). BPA polycarbonates [25037-45-0] having glass-transition temperatures in the range of 145—155°C, are widely regarded for optical clarity and exceptional impact resistance and ductiUty at room temperature and below. Other properties, such as modulus, dielectric strength, or tensile strength are comparable to other amorphous thermoplastics at similar temperatures below their respective glass-transition temperatures, T. Whereas below their Ts most amorphous polymers are stiff and britde, polycarbonates retain their ductiUty. 

Imide-based polymers are another class of amorphous thermoplastics. 

Polyetherimides (PEI) are a newer class of amorphous thermoplastics with high-temperature resistance, impact strength, creep resistance, and rigidity. They are transparent with an amber color. The polymer is sold under the trade name of Ultem (General Electric) and has the stracture shown in Eig. 2.20. It is prepared from the condensation polymerization of diamines and dianhydrides. ... 

In this class of amorphous polymers, there are many biomedical polymers such as phenolic resins (adopted for production of surgical instruments), unsaturated polyester resins (used in bone repair) (Kharas et al., 1997), polystyrene (e.g. Petri dishes for cell culture) and polymethyl methacrylate (PMMA, used in bone cements, intraocular lens, and dental fillings) (Stuart, 2002). These are highly crosslinked polymers (resins in particular) or linear thermoplastic polymers that do not show structural macromolecular regularity. 

The polymers used in injection moulding can be divided into three main classes, depending on their structure and properties. These classes are amorphous thermoplastics semi-crystalline thermoplastics rubbers. 

There are four main polymer classes (thermoplastics, thermosets, elastomers and thermoplastic elastomers) but thermoplastics fall into two distinct classes as amorphous thermoplastics and semi-crystalline thermoplastics (Figure 2.1). 

As discussed earlier, amorphous thermoplastics have polymer chains arranged in a random, haphazard state. They have no distinct melting temperature, but instead soften when heated above their glass transition temperature. As a class, their properties differ from the properties of semicrystalline thermoplastics in some general ways (lower strength, less chemical resistance, etc.). These differences are well documented and frequently discussed, but I believe these differences are over exaggerated. 

This class of polyesters consists of four major commercial polymers and their copolymers, namely PET, PTT, PBT, and PEN (see Table 2.1). They compete for engineering thermoplastics, films, and fibers markets with other semicrystalline polymers, such as aliphatic polyamides, and for some other applications with amorphous engineering plastics such as polycarbonate. The syntheses of PET and PBT, detailed in numerous reviews and books,2-5 are described in Sections 23.2.2 and 2.3.2.1. 

Another remarkable character of this class of Ni complexes is their tendency to promote living polymerization of a-oleftns at low temperatmes and with low concentrations of the monomer. Thus, the low-temperatme polymerization of propylene leads to a material whose number average molecular weight (Mn) increases almost linearly as a function of time and propylene consumption, reaching values ofM = 160 000 Daltons and polydispersities of ca. 1.13. This character allows these Ni catalysts to produce A-B-A type block copolymers composed of semicrystalline and amorphous segments, which is used to prepare thermoplastic elastomeric polymers. The Ni catalysts can also polymerize internal cyclic... 

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