Density polyethene

Even more important is the stereoregular catalytic polymerization of ethene and other alkenes to give high-density polyethene ( polythene ) and other plastics. A typical Ziegler-Natta catalyst can be made by mixing TiCU and Al2Eti in heptane partial reduction to Ti " and alkyl transfer occur, and a brown suspension forms which rapidly absorbs and polymerizes ethene even at room temperature and atmospheric pressure. Typical industrial conditions are 50- 150°C and 10 atm. Polyethene... 

High-temperature and -pressure free radical polymerization of ethene, to produce low-density polyethene (LDPE). 

We have studied the alkane and alkene yields from the radiolysis of copolymers of ethylene with small amounts of propylene, butene and hexene. These are examples of linear low density polyethenes (LLDPE) and models for LDPE. Alkanes from Ct to C6 are readily observed after irradiation of all the polymers in vacuum. The distribution of alkanes shows a maximum corresponding to elimination of the short-chain branch. This is illustrated in Figure 8 for the irradiation of poly (ethylene-co-1-butene) containing 0.5 branches per 1,000 carbon atoms at 20 C. 

Reimann, C., U. Siewers, H. Skarphagen, and D. Banks. 1999. Does bottle type and acid-washing influence trace element analyses by ICP-MS on water samples A test covering 62 elements and four bottle types High density polyethene (HDPE), polypropene (PP), fluorinated ethene propene copolymer (FEP) and perfluoroalkoxy polymer (PFA). Sci. Total Environ. 239 111-130. 

Villberg, K., Veijanen, A., Gustafsson, I., and Wickstrom, K. (1997). Analysis of odour and taste problems in high-density polyethene. ]. Chromatogr. 791, 213-219. 

The first polymerizations were free radical reactions. In 1933 researchers at ICI discovered that ethene polymerizes into a branched structure that is now known as low density polyethene (LDPE). In the mid- 50s a series of patents were issued for new processes in which solid catalysts were used to produce polyethene at relatively low pressures. The first was granted to scientists at Standard Oil (Indiana) who applied nickel oxide on activated carbon and molybdenum oxide on alumina. Their research did not lead to commercial processes. In the late 40s Hogan and Banks of Phillips were assigned to study the di- and trimerization of lower olefins. The objective was to produce high octane motor fuels. When they tried a chromium salt as promoter of a certain catalyst (Cr was a known reforming... 

By far the most important industrial coordination polymerization processes are Ziegler-Natta polymerizations of 1-olefins [107-110], most notably the production of high-density polyethene [111] and stereo-specific olefin polymers and copolymers [108], However, these processes employ solid catalysts, and the complex kinetics on their surfaces have no place in a book on homogeneous reactions. 

The earliest Ziegler-Natta catalysts were insoluble bimetallic complexes of titanium and aluminum. Other combinations of transition and Group I-III metals have been used. Most of the current processes for production of high-density polyethene in the United States employ chromium complexes bound to silica supports. Soluble Ziegler-Natta catalysts have been prepared, but have so far not found their way into industrial processes. With respect to stereo-specificity they cannot match their solid counterparts. 

For urine use high density polyethene containers thoroughly cleaned with Suprapur quality nitric acid and bidistilled water 1 + 10. The container must be tested to deliver less than 10% extraneous amounts of cadmium. Test may be performed with a 1% v/v solution of nitric acid (e.g. Suprapur quality) in bidistilled water. Do not use glassware. 

Phillips process A method for the manufacture of high-density polyethene using a catalyst of chromium(III) oxide on a promoter of silica and alumina. The reaction conditions are 150°C and 30 atm pressure. See also Ziegler process. 

Phillips procass A process for making high-density polyethene by polymerizing ethene at high pressure (30 atmospheres) and 150°C. The catalyst is chromium (111) oxide supported on silica and alumina. 

German chemist Karl Ziegler (1896-1973) discovers catalyst for making high-density polyethene. 

Albertsson AC. The shape of the biodegradation curve for low and high density polyethenes in prolonged series of experiments. Eur Polym J 1980 16 623-630. 

For blood cleaned plastic collection tubes with stoppers and for urine high-density polyethene containers thoroughly cleaned with Suprapur (Merck, Germany) quality nitric acid and bidistilled water 1 + 10 must be used. The whole set (tube and stopper, or container) must be tested to deliver less than 10% extraneous amounts of cadmium. Colored stoppers and plastics with a Cd softener should not be used. Before starting the study six test tubes per tube production lot and during the study frequently blank tubes, e.g., for 1% of the total number of samples to study, must be tested. The test may be performed with a 1% v/v solution of nitric acid (e.g., Suprapur quality) in bidistilled water. Preferably vacuum collection tubes must be used. No special type of needle is requested. Needles of stainless steel are adequate. Other needles, e.g., siliconized or... 

While aluminium alkyls on their own convert ethene into oligomers (p. 80), in the presence of traces of nickel termination occurs after only one step, so that the dimer, butene, is produced. This observation ted Ziegler to study the effect of compounds of other transition metals as cocatalysts. With titanium or zirconium compounds in particular, rapid polymerization of ethene occurs at 50°C/10 atm leading to a crystalline, high density polyethene (HOPE) which consists of long... 

Polymers in coexisting phases have different molar-mass distributions which are also different from that of the initial homogeneous system. Obviously, the influence of polydispersity on the LLE is not only of a quantitative nature but of a qualitative nature as well. This demixing behaviour is important for some practical problems, for example, in the high-pressure synthesis of low-density polyethene [polyethylene] or of poly(but-3-enoic acid ethene) [poly(ethylene-co-vinylacetate)]. The polyethene is obtained as a solute in supercritical ethene... 

Synthetic polyolefins were first synthetisized by decomposition of diazomethane [2]. With the exception of polyisobutylene, these polymers were essentially laboratory curiosities. They could not be produced economically. The situation changed with the discovery of the high pressure process by Fawcett and Gibson (ICI) in 1930 ethene was polymerized by radical compounds [3]. To achieve a sufficient polymerization rate, a pressure of more than 100 MPa is necessary. First produced in 1931, the low density polyethene (LDPE) was used as isolation material in cables. 

The widely investigated Phillips catalyst, which is alkyl free, can be prepared by impregnating a silica-alumina (87 13 composition [101-103] or a silica support with an aqueous solution of Cr03). High surface supports with about 400 to 600 g/m are used [104]. After the water is removed, the powdery catalyst is fluidized and activated by a stream of dry air at temperatures of 400 to 800 °C to remove the bound water. The impregnated catalysts contain 1 to 5wt% chromium oxides. When this catalyst is heated in the presence of carbon monoxide, a more active catalyst is obtained [105]. The Phillips catalyst specifically catalyzes the polymerization of ethene to high-density polyethene. To obtain poly ethene of lower crystallinity, copolymers with known amounts of an a-olefin, usually several percent of 1-butene ean be synthesized. The polymerization can be carried out by a solution, slurry, or gas-phase (vapor phase) process. 

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