Polyethylene networks crosslinked in solution: Preparation, elastic behavior, and oriented crystallization. I. Crosslinking in solution

Abstract

A study has been made of the crosslinking of linear polyethylene in solution. Networks containing a low number of trapped entanglements and elastically ineffective chain ends were prepared by crosslinking high molecular weight linear polyethylene in 1,2,4‐trichlorobenzene solutions with dicumyl peroxide at 120°C. No syneresis was observed during crosslinking except at high peroxide concentrations. The networks were characterized by swelling measurements, infrared spectroscopy, and differential scanning calorimetry. The crosslinking efficiency, calculated from swelling, was found to be proportional to the square of the polymer volume fraction. The proportionality constant was 0.8, indicating close to unit efficiency for undiluted polymer. Chemical modification of the polyethylene chains by attachment of peroxide and solvent fragments was of the order of one foreign unit per elastically active network chain, depending on peroxide and polymer concentration. Sol–gel analysis indicated that no chain scission occurred. These results are shown to be consistent with a “cage” mechanism for crosslinking. The possible topological consequence of this mechanism, preferential crosslinking of entanglements, is discussed. The concentration of trapped entanglements was also found to be proportional to the square of the polymer volume fraction. The proportionality constant corresponds to a molecular weight between entanglements of 4000 for the undiluted polymer, which is close to the value of 4200 found for networks prepared from the undiluted polymer. Since the results obtained are based mainly on the use of the swelling equation, different aspects of the applicability of this equation for the evaluation of the crosslinking process are discussed. As regards the reference dimensions, which should be known for a quantitative application of the elastic theory, the results strongly support the use of the dimensions of the network chains after completion of crosslinking.

Preparation of granular crosslinkable medium‐density polyethylene

“…MDPE (3840 UA, Tabriz Petrochemical, Iran, MFI 1908C, 3.8-4.5 gr/10min, density: 0.938 g/cm 3 ) was mixed with a sufficient amount of [2, 5-Dimethyl-2, 5-di-(t-butyl-peroxy) hexyne-3 (DYBP; Inter chem. GMBH with half-life of 57 s at 2008C, 85% in white oil)] by a mixer at room temperature.…”

Deformation behavior of poly(dimethyl siloxane) networks. I. Applicability of various theories to modulus prediction

“…5 ) ] 4 ( 7 ) where p = extent of reaction and r = reactant stoichiometric ratio. ( 8 ) where the assumption is made that all incomplete reactions led to sol fraction and that there are no side reactions that lead to sol fraction.…”

Lamellar crystallization of pendant chains in radiation-crosslinked polyethylene fibres

“…In the latter, the mass of pendant chains is relatively low, which implies that practically all chains should remain extended during constrained melting of such networks. Densely crosslinked fibre networks were produced by vulcanizing as-spun polyethylene fibres in the oriented state with dicumylperoxide [17], which is known to crosslink polyethylene without chain fracture [29]. Fig.…”