Amorphous polycarbonate, thermal properties

Polycarbonates are tough, amorphous, and transparent polymers made by reacting bisphenol A and diphenyl carbonate. It is noted for its excellent mechanical and thermal properties (high Tgi 150°C), hydrophobicity, and antioxidative properties. 

The data in Fig. 2.84 indicate that an amorphous polycarbonate sample as small as 50 pg could be heated at 400 C/min and yield a glass transition that is as discernible as that shown in Fig. 2.84 for the 1-mg sample of polycarbonate scanned at 20 C/min. These results indicate that it is now possible to determine thermal properties on polymeric samples that were previously deemed too small to analyze. 

PROPERTIES OF SPECIAL INTEREST Polycarbonate engineering thermoplastics are amorphous, clear polymers that exhibit superior dimensional stability, good electrical properties, good thermal stability, and outstanding impact strength. They... 

Polycarbonate (PC) is the fourth largest volume material. It is an amorphous engineering thermoplastic with good thermal stability, transparency, impact resistance and the ability to be processed on conventional machinery. Its surface properties are important for many applications, including medical, optics and so on. Table 2.10 illustrates the properties of PC. 

Homopolymers derived from MDI and azelaic acid are semicrystalline engineering plastics with a Tg of 135°C and a Tm of 290°C (88). Copoljrmers of MDI with azelaic acid, containing 20-30 mol% of adipic acid show a eutectic Tm of approximately 240°C. These amorphous or slightly crystalline copolymers have mechanical properties comparable to transparent nylons or polycarbonates. Although injection molded samples are transparent, they will crystallize and turn opaque. Copolyamides derived from MDI and aromatic dicarboxylic acids are more difficult to prepare. Because of the very high Tm (420°C) of the isophthalic acid/MDI block it was necessary to prevent the formation of any appreciable ciystalline blocks, which was accomplished by prereacting a portion of the isophthalic acid (15-20 mol%) with 2,4-TDI. In this manner crystallization of the isophthalic acid/MDI blocks was surpressed (89). Thus, copolyamides containing IPA/azelaic acid (50 50) are obtained with thermal and mechanical properties similar to poly-sulfone. 

Thermal transitions other than Tg and are sometimes observed in polymers. Some polymers possess more than one crystal form, so there will be an equilibrium temperature of transition from one to another. Similarly, second-order transitions below Tg occur in some materials Tg is then termed the a transition, the next lower is the /3 transition, and so forth). These are attributed to motions of groups of atoms smaller than those necessary to produce Tg (type 3 motions, Section 6.2). These transitions may strongly influence properties. For example, tough amorphous plastics (e.g., polycarbonate) have such a transition well below room temperature, while brittle amorphous plastics (e.g., PS and PMMA) do not. 

PBT pol Tner blends combine the properties of partially crystalline PBT with those of amorphous thermoplastics such as ABS and polycarbonate. The amorphous partner improves the warpage behaviour (low thermal expansion, higher impact strength, and an improved surface quality), while PBT ensures the temperature and chemical resistance of the blend. These properties in general and the low warpage in particular, makes PBT blends a perfect choice for use on housings for electronic systems which require maximum imperviousness to all weathering conditions. 

Polycarbonate resins are amorphous engineering thermoplastics with an excelient balance of toughness, strength, optical properties, and heat resistance properties. Bisphenol A (BPA) polycarbonate (BPA-PC), the industry standard, is used in such diverse applications as CDs, DVDs, commercial and automotive lighting, instrument panels, water bottles and ophthalmic lens. However, many new applications require thermal capabilities greater than that of BPA-PC, which has a glass transition temperature (Tg) of 150°C and heat deflection temperature (HDT) ofl32°C at 1.8 MPa. 

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