Origin of the molecular structure and properties of low density polyethylene

Abstract

It is generally accepted that the origin of the structural features of low density polyethylene (branching, unsaturation, molar mass and its distribution) can be explained by various isomerisation and decomposition reactions of the macroradicals and by various chain transfer processes. On the other hand, it is known that ethylene molecules under high pressure are organised in various supermolecular particles. There are several phases in compressed ethylene (a, 0 and y) depending on the pressure and temperature. The purpose of the present work was to determine the effects of the phase state of ethylene on the structure and properties of polyethylene. The authors have compiled published data about the effects of the synthesis pressure and temperature on the structure and properties of polyethylene. The entropy of ethylene under sythesis conditions for those published experiments was determined from the available information on pressure and temperature. The effects of ethylene entropy on the number and type of short chain branches, long chain branches, unsaturated bonds, molar mass and its distribution, chain flexibility, density and the melting point of polyethylene are demonstrated. It was found that under given ethylene entropy conditions, the same structure and properties of polyethylene are obtained.

Importance of Boscovich's theory of natural philosophy for polymer science

“…8) and amount 127.6, 63.8 and 40 cm 3 /mole for the molecular pair, the bimolecule and the oligomolecule, respectively. These values are very [18][19][20][21][22][23] close to the empirical values for these particles: 127.6, 57.1 and 37.8 cm 3 /mole, respectively. The existence of these particles and the higher order phase transitions in compressed ethylene have been confirmed by the thermodynamic, physical and spectroscopic methods.…”

“…The existence of these particles and the higher order phase transitions in compressed ethylene have been confirmed by the thermodynamic, physical and spectroscopic methods. The effects of the supra-molecular particles on the mechanism and kinetics of polymerization as well as on the structure and properties of polyethylene have been published by us in [18][19][20][21][22][23].…”

Free Radical Polymerization of Ethylene

“…The transformation of one kind of species to other ones could be the reaction rate limiting step. On this base, in each ethylene phase the theoretical values of the energy and volume of activation of polymerization were calculated and a good agreement with the experimental data was obtained [12,13,29,30,38].…”

“…Philosophical considerations [3,4,20,21,38] were preceded by our works on ethylene polymerization about which we have published several dozen articles in journals and conference proceedings: the mechanism [12,39] and kinetics of polymerization [13,29,30], origin of polyethylene structure formation (short and long branches [28][29][30][39][40][41], unsaturated bonds [29,30,41], molecular mass [13,29,30] and its distribution [29,30]), effects of polymerization conditions on polyethylene density [29,30,41] and melting [29,30], importance of ethylene phase state for industrial process operation [42,43]. Here, we shall emphasize the main conclusions published in our articles where the details are extensively elaborated.…”

Supermolecular organization and polymerization of compressed ethylene

“…The period of rapid growth arises when a macroradical begins to connect ethylene molecules within a supermolecular particle. This rule was proved on the following structural characteristics of polyethylene: molecular mass [19], short chain branching [ I I , 251, long chain branching [32], and unsaturated bonds [25]. During the period of stagnation, a macroradical can isomerize or collide with other particles present in the system (impurities, chain transfer agent, comonomer, polymer, nonreactive supermolecular particles of ethylene, etc.).…”