High-pressure low-density polyethylene

The method outlined above for characterizing branched polymers will hereafter be referred to as the molecular weight and branching distribution (MWBD) method. In the following sections, its application to the long chain branching in polyvinyl acetate and high pressure low density polyethylene will be demonstrated. 

In order to determine the branching structure factor e, Foster ( ) studied a large qroup of high pressure low density polyethylene resins (HP-LDPE). Using the MWBD method, he calculated the whole polymer number average number of branch points per JOOO carbon atoms from SEC data as a function of e. Then the Xfj values were compared with those obtained by nMR. 

PROPERTY SUMMARY FOR HIGH PRESSURE, LOW DENSITY POLYETHYLENES... 

Experimental data given in Fig. 12 are interesting both from the practical and theoretical point of view. The figure gives tentative flow curves of high-pressure (low-density) polyethylene with MFI = 2.0 g/10 min at a temperature of 170 °C in chan-... 

High pressure low density polyethylene resins are produced in two types of reactors. One is a continuous-flow mechanically stirred autoclave (origi-... 

Theonly important current application of tubular reactors in polymer syntheses is in the production of high pressure, low density polyethylene. In tubular processes, the newer reactors typically have inside diameters about 2.5 cm and lengths of the order of I km. Ethylene, a free-radical initiator, and a chain transfer agent are injected at the tube inlet and sometimes downstream as well. The high heat of polymerization causes nonisothermal conditions with the temperature increasing towards the tube center and away from the inlet. A typical axial temperature profile peaks some distance down the tube where the bulk of the initiator has been consumed. The reactors are operated at 200-300°C and 2000-3000 atm pressure. 

Discovery of High-Pressure (Low-Density) Polyethylene Polyisobutylene... 

Ethylene/carbon monoxide copolymers containing 2 or 3 wt. o carbon monoxide are photo degradable polymers with the same general processing properties as high pressure, low density polyethylene. Exposure to UV radiation causes decomposition. The polymer is essentially a low density polyethylene with an environmental feature. Commercialization of these materials took place in the late 1960s. 

Example 10.8 The production of high-pressure low-density polyethylene is carried out in tubular reactors of typical dimensions 2.5 cm diameter and 1 km long at 250°C and 2500 atm. The conversion per pass is 30% and the flow rate is 40,000 kg/h. Assuming that the polymerization reaction is first order in ethylene concentration, estimate the value of the polymerization rate constant. 

From this brief survey of contemporaneous discoveries on polyolefin polymerization, it is evident that catalysis became a dominant technology factor to consider within 20 years of the discovery of high-pressure (low-density) polyethylene. These various catalysts enabled linear polyethylene of higher density and higher... 

High-pressure, low-density polyethylene, LDPE, was blended with cyclOTubber, to give compounds useful for bonding polyethylene to metal... 

The occurrence of impurities and structural deviations, such as branching and double-bond formation, depend on the method of polymerization. The degree of branching is related to the crystallinity and consequently influences the density of the polyethylene. The more branching the PE has, the more amorphous (i.e., the lower the density vide infra) and the more transparent the PE becomes. Three types of polyethylene are differentiated high-pressure, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE). All three of these PE types are manufactured commercially [30]. 

Kiparissides, C., Krallis, A., and Meimaroglou, D. (2010) From molecular to plant-scale modeling of polymerization processes A digital high-pressure low-density polyethylene production paradigm. Chem. Eng. ej Techn., 33, 1754-1766. 

E/CO is produced commercially by the high-pressure copolymerization of ethylene and carbon monoxide using techniques similar to those used to make high-pressure, low-density polyethylene homopolymer (LDPE). The monomers undergo random copolymerization under well-controlled temperatures and pressures in either tubular or stirred autoclave reactors ... 

Usami, T., Takayama, S. Fine-branching structure in high-pressure, low-density polyethylenes by 50.10-MHz C NMR analysis. Macromol. (1984), 17, pp. 1756-1761... 

---