Low-density 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. 

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... 

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. 

On a laboratory scale, single site catalysts based on metallocene/MAO are highly useful for the copolymerization of ethene with other olefins. Propene, 1-butene, 1-pentene, 1-hexene, and 1-octene have been studied in their use as comonomers, forming linear low-density polyethene (LLDPE) [188,189]. These copolymers have a great industrial potential and show a higher growth rate than the homopolymer. Due to thee short branching from... 

The main three polyethene classes are low-density polyethene (LDPE), high-density polyethene (HDPE), and linear low-density polyethene (LLDPE) (Scheme 6.20.1). Table 6.20.1 gives an overview of these classes and indicates the differences in density, production processes, and chemical structure. 

PE type Low-density polyethene Linear low-density polyethene (LLDPE) High density polyethene... 

Technical ethylene polymerization leads to three major classes of PE materials low-density polyethene (LDPE), linear low-density polyethene (LLDPE), and high-density polyethene (HOPE). The three classes of PE material differ in the degree and type of branching in the polymer. These differences lead to different physicochemical properties of the polymer, resulting in different application areas of the PE material. 

A LDPE Low-density polyethene Shrink wrap, plastic bags... 

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