Polycarbonates development

In the mid-1950s a number of new thermoplastics with some very valuable properties beeame available. High-density polyethylenes produced by the Phillips process and the Ziegler process were marketed and these were shortly followed by the discovery and rapid exploitation of polypropylene. These polyolefins soon became large tonnage thermoplastics. Somewhat more specialised materials were the acetal resins, first introduced by Du Pont, and the polycarbonates, developed simultaneously but independently in the United States and Germany. Further developments in high-impact polystyrenes led to the development of ABS polymers. 

A hospital trolley developed by Bayer and GMP is described. The trolley is equipped with a portable computer for the collection and management of patient information with the aim of reducing medical errors. The main component is a sandwich stracture reaction injection monlded in Bayer s Baydnr 60 PU and consisting of a cellnlar core and a smooth skin. Other components are made of PP, PMMA or polycarbonate. Developments by GMP in the nse of PU foams in refrigerator manufacture are also reviewed, and tnmover fignres are presented for the Company. 

Failure Mechanisms. BPF polycarbonate develops crazes at ascending stresses and fractures in a pseudo-brittle manner similar to polystyrene or PMMA. At room temperature the block polymers develop few separate crazes. As the yield is approached, shear bands grow from the edges. Fracture initiates at an edge from a point where the two shear bands initiated. When a neck forms, the plastic strain in the neck is ca. 80% however fracture occurs shortly after the neck is formed so that the ultimate elongation of the specimen is only 10 or 12%. The shear bands and necks show some stress whitening (Figure 9). 

Fig. 5. Crystallinity of polycarbonate developed in blends with various polyesters. PC crystallization occurs when the polyester Tg is low enough to cause adequate plasticization.

This chapter provides an overview of the properties, synthesis, methods of characterization and production, markets, and uses for polycarbonate and its blends. The chapter focuses primarily on the commercially significant aspects of polycarbonate development, manufacturing, and applications. For more in-depth information, the following excellent resources are recommended Schnell Vemaleken Fox Lapp Serini Clagett and Shafer Freitag et al. LeGrand and Bendler and Brunelle and Korn [2-10, respectively]. 

Usage of phosphoms-based flame retardants for 1994 in the United States has been projected to be 150 million (168). The largest volume use maybe in plasticized vinyl. Other use areas for phosphoms flame retardants are flexible urethane foams, polyester resins and other thermoset resins, adhesives, textiles, polycarbonate—ABS blends, and some other thermoplastics. Development efforts are well advanced to find appHcations for phosphoms flame retardants, especially ammonium polyphosphate combinations, in polyolefins, and red phosphoms in nylons. Interest is strong in finding phosphoms-based alternatives to those halogen-containing systems which have encountered environmental opposition, especially in Europe. 

A method for the fractionation of plasma, allowing albumin, y-globulin, and fibrinogen to become available for clinical use, was developed during World War II (see also Fractionation, blood-plasma fractionation). A stainless steel blood cell separation bowl, developed in the early 1950s, was the earhest blood cell separator. A disposable polycarbonate version of the separation device, now known as the Haemonetics Latham bowl for its inventor, was first used to collect platelets from a blood donor in 1971. Another cell separation rotor was developed to faciUtate white cell collections. This donut-shaped rotor has evolved to the advanced separation chamber of the COBE Spectra apheresis machine. 

The first HFIP-based polycarbonate was synthesi2ed from bisphenol AF with a nonfluorkiated aromatic diol (bisphenol A) and phosgene (121,122). Incorporation of about 2—6% of bisphenol AF and bisphenol A polycarbonate improved the dimensional stabkity and heat-distortion properties over bisphenol A homopolycarbonate. Later developments in this area concern the flame-retardant properties of these polymers (123,124). 

Medical and health-care related appHcations consume about 21,000 t of polycarbonate aimuaHy. Polycarbonate is popular because of its clarity, impact strength, and low level of extractable impurities. Special grades have been developed to maintain clarity and resistance to yeHowing upon gamma radiation sterilization (qv) processes. Leisure and safety appHcations are many and varied, accounting for about 22,000 t of consumption aimuaHy. The... 

During the eady development of polycarbonates, many bisphenols were investigated for potential useftil products. Some of these monomers and polymers are hsted in Table 3. Despite this intensive search, however, no homopolycarbonates other than that of BPA have been produced. Copolymers and blends, on the other hand, have been quite successhil. Blends of polycarbonate with ABS and with poly(butylene terephthalate) (PBT in particular have shown significant growth since the mid-1980s. 

Multilayered structures play an important role in the production of, e.g., biomaterials, catalysts, corrosion protectors, detectors/diodes, gas and humidity sensors, integral circuits, optical parts, solar cells, and wear protection materials. One of the most sophisticated developments is a head-up-display (HUD) for cars, consisting of a polycarbonate substrate and a series of the layers Cr (25 nm), A1 (150 nm), SiO, (55 nm), TiO, (31 nm), and SiO, (8 nm). Such systems should be characterized by non-destructive analytical methods. 

Today about 75% of the market is held by General Electric and Bayer with their products Lexan and Makrolon respectively. Other manufacturers are ANIC (Italy), Taijin Chemical Co., Mitsubishi Edogawa and Idemitsu Kasei in Japan and, since 1985, Dow (USA) and Policarbonatos do Brasil (Brazil). Whilst this market is dominated by bis-phenol A polycarbonates, recent important developments include alloys with other thermoplastics, polyester carbonates and silicone-polycarbonate block copolymers. 

A more recent development of interest with this material is that scratch-resistant coatings may be stoved on at temperatures not feasible with conventional bisphenol A polycarbonates to give products with a scratch resistance comparable to glass. 

Another recent development is the preparation of a polyester-polycarbonate copolymer. The polymers involve a polyester component based on the reaction between bis-phenol A and iso- or terephthalic acid with the carbonate component arising from the reactions described in Section 20.3 (see Section 20.9). 

Although moulded polycarbonate parts are substantially amorphous, crystallisation will develop in environments which enable the molecules to move into an ordered pattern. Thus a liquid that is capable of dissolving amorphous polymer may provide a solution from which polymer may precipitate out in a crystalline form because of the favourable free energy conditions. 

One recent development is rotational moulding. This process has enabled large mouldings of polycarbonate to be made using reasonably simple and inexpensive equipment. 

Yet another recent development has been the alloying of polycarbonates with liquid crystal polymers such as Vectra (see Section 25.8.1). These alloys are notable for their very good flow properties and higher strength and rigidity than conventional bisphenol A polycarbonates. 

JOHNSON, K., Polycarbonates—Recent Developments (Patent Review), Noyes Data Corporation, New Jersey (1970)... 

The successful development of polyfethylene terephthalate) fibres such as Dacron and Terylene stimulated extensive research into other polymers containing p-phenylene groups in the main chain. This led to not only the now well-established polycarbonates (see Chapter 20) but also to a wide range of other materials. These include the aromatic polyamides (already considered in Chapter 18), the polyphenylene ethers, the polyphenylene sulphides, the polysulphones and a range of linear aromatic polyesters. 

It has already been shown (e.g. Chapters 20 and 21) that the insertion of a p-phenylene into the main chain of a linear polymer increased the chain stiffness and raised the heat distortion temperature. In many instances it also improved the resistance to thermal degradation. One of the first polymers to exploit this concept commercially was poly(ethylene terephthalate) but it was developed more with the polycarbonates, polysulphone, poly(phenylene sulphides) and aromatic polyketones. 

The RIM process was originally developed for the car industry for the production of bumpers, front ends, rear ends, fascia panels and instrument housings. At least one mass-produced American car has RIM body panels. For many of these products, however, a number of injection moulding products are competitive, including such diverse materials as polycarbonate/PBT blends and polypropylene/EPDM blends. In the shoe industry the RIM process has been used to make soling materials from semi-flexible polyurethane foams. 

To overcome the disadvantages of nylon as an engineering material-high water absorption and poor creep strength at elevated temperatures—many newer polymers were developed. Table 3.47 lists polymers that are among the most commercially important acetal, polycarbonate, polyphenylene oxide and polysulfone. 

The process was originally developed in the 1940s for use with vinyl plas-tisols in liquid form. It was not until the 1950s that polyethylene powders were successfully moulded in this way. Nowadays a range of materials such as nylon, polycarbonate, ABS, high impact polystyrene and polypropylene can be moulded but by far the most common material is polyethylene. 

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