Specific Commercial Polymers

About 110 billion pounds of polymers were produced in the United States in 2001. Close to 40 billion pounds of this total are produced by radical chain polymerization. 

Radical chain polymerization of ethylene to polyethylene is carried out at high pressures of 120-300 MPa (17,000-43,000 psi) and at temperatures above the Tm of polyethylene (Fig. 3-18) [Doak, 1986]. Batch processes are not useful since the long residence time gives relatively poor control of product properties. Long-chain branching due to intermolecular chain transfer becomes excessive with deleterious effects on the physical properties. Continuous processes allow better control of the polymerization. 

Tubular reactors are most often used, although autoclave reactors are also employed. Tubular reactors consist of a number of sections, each with an inner diameter of 2-6 cm and length of 0.5-1.5 km, arranged in the shape of an elongated coil. The polymerization mixture has very high linear velocities ( 10m s-1) with short reaction times (0.25-2 min). Trace amounts of oxygen ( 300 ppm) are typically used as the initiator, often in combination 

Autoclave reactors differ from tubular reactors in two respects. Autoclave reactors have much smaller length-to-diameter ratios (2-4 for single-zone and up to 15-18 for multizone reactors) and operate at a much narrower reaction temperature range. 

The polyethylene produced by radical polymerization is referred to as low-density polyethylene (LDPE) or high-pressure polyethylene to distinguish it from the polyethylene synthesized using coordination catalysts (Sec. 8-1 lb). The latter polyethylene is referred to as high-density polyethylene (HDPE) or low-pressure polyethylene. Low-density polyethylene is more highly branched (both short and long branches) than high-density polyethylene and is therefore lower in crystallinity (40-60% vs. 70-90%) and density (0.91-0.93 g cm 3 vs. 0.94-0.96 g cm-3). 

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RADICAL CHAIN POLYMERIZATION 3-14 SPECIFIC COMMERCIAL POLYMERS... 

Solubility parameters can be determined by direct measurements, indirect calculations, or correlations with other physical parameters. The solubility parameters of solvents usually can be determined directly by measuring the energy of vaporization. The solubility parameters of polymers can only be determined indirectly and may be affected by variations in their chemical constitutions, i.e., the number of crosslinks and the distribution of chain branches or substitutive groups along the polymer backbone. The methods presented in this section can be used to develop correlations of solubility parameters with other physical properties for specific commercial polymer products or to estimate the solubility parameters of new polymers. 

The purpose of this monograph, the first to be dedicated exclusively to the analytics of additives in polymers, is to evaluate critically the extensive problemsolving experience in the polymer industry. Although this book is not intended to be a treatise on modem analytical tools in general or on polymer analysis en large, an outline of the principles and characteristics of relevant instrumental techniques (without hands-on details) was deemed necessary to clarify the current state-of-the-art of the analysis of additives in polymers and to accustom the reader to the unavoidable professional nomenclature. The book, which provides an in-depth overview of additive analysis by focusing on a wide array of applications in R D, production, quality control and technical service, reflects the recent explosive development of the field. Rather than being a compendium, cookery book or laboratory manual for qualitative and/or quantitative analysis of specific additives in a variety of commercial polymers, with no limits to impractical academic exoticism (analysis for its own sake), the book focuses on the fundamental characteristics of the arsenal of techniques utilised industrially in direct relation... 

Further, N-methyl dithiocarbamate (MDTC) (.9) and N-metylglycine (sarcosine) (10) were similarly incorporated into PVC matrices resulting in the derivatives usable to chelate forming and introduction of thiol-function as shown in following scheme. Of the two main purpose of modification of commercial polymers 1) improvement of original property of each polymer and 2) incorporation of new function into the polymeric materials, our studies would be served from the viewpoint of the latter as the fundamental design for PVC and PECH with specific functions. 

Each specific protein molecule has a specific chain length, like classical small molecules, and is said to be monodisperse with respect to chain length or molecular weight. However, most synthetic commercial polymers such as HDPE are composed of molecules of different lengths. Thus, the numerical value for the number of repeat units, n, or the degree of... 

While polycarbonate has the desirable qualities as the basic material for information storage, it also has some debits. First, polycarbonate is relatively expensive in comparison with many polymers. Its superior combination of properties and ability for a large cost markup allows it to be an economically feasible material for specific commercial uses. Second, the polar backbone is susceptible to long-term hydrolysis so that water must be ruthlessly purged. The drying process, generally 4 h, is often achieved by placement of polycarbonate chips in an oven at 120°C with a dew point of — 18°C. 

Last but not least, ageing and destruction processes can be monitored in polymers under application, and structural and quantitative analysis of unknown additives (stabilizers etc.) is possible in commercial polymers using UV-vis spectroscopy. Advantage can be taken here of the fact that the position of an electronic absorption in unsaturated systems depends only weakly on the surroimd-ing medium. Even though UV-vis spectroscopy is not very specific in the absorption band, it is highly sensitive and therefore much better than NMR or IR spectroscopy to detect small amounts of chromophors. 

Fifteen years ago, when wood-plastic composites were first introduced many people predicted that this process would solve the problem of wood dimensional stability and great claims were made for its future use. Now that the physical properties of wood-polymer composites are better understood, specific commercial products are being produced which take advantage of the desirable aesthetic appearance, the high compression strength, increased hardness and abrasion resistance and improved dimensional stability. Future use of wood-polymer composites will depend upon the imagination of the producer and the market place. 

On the subject of stabilization and fire-proofing commercial polymers, only one textbook (I) and a few summary articles (2, 3, 4, 5, 6) exist besides specific publications. It is hoped that this book will show the importance of this area to the industry. The trend is to use plastics more and more outdoors and under severe environments. The achievements of the experts and authors of the following chapters are aimed for this target. 

Union of Pure and Applied Chemists (IUPAC) has developed systematic nomenclature rules for polymers. As is the case with many small-molecule organic compounds, the IUPAC names are often complex and cumbersome. Therefore, polymer scientists often use common or abbreviated names, sometimes even product names. Poly[l- methoxycarbonyl)-l-methylethylene] (IUPAC) is almost always referred to as poly(methyl methacrylate), or PMMA, or even Lucite. IUPAC discourages the use of trademarked names, however unless it is importanfto refer to a specific commercial product. The IUPAC Macromolecular Nomenclature Commission recognizes a number of trivial names for common polymers (Metanomski 1999). 

Such polymers are also known as thermosetting resins (or resins). Specific crosslinked polymers, mainly those with physical crosslinking (not with chemical bonds), can be thermoplastic. Both thermoplastic and thermorigid polymers can be called plastics when they are used in the manufacture of objects for commercial or industrial use. 

This is similar to PVC, but made from the monomer 1,1-dichloroethylene (CH, = CC I j. It has a specific gravity of 1.67-1.71 and a degree of polymerisation of over 200. The molecular weight of commercial polymers is about 20 0(X). It is often used in the form of a copolymer with vinyl chloride or ethyl acrylate to improve its properties. Coating formulations are plasticised with highly chlorinated aromatics, as common plasticisers are ineffective. 

Two chapters in the second section contain descriptions of specific commercially available polymers that perform under demanding conditions. Another chapter describes several high-performance plastics and gives general characteristics for each. The final chapter in this section is a comprehensive review of attempts to make polymers that fight back against attack by bioorganisms. 

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