The reactive modification of polyethylene. I: The effect of low initiator concentrations on molecular properties

Abstract

Commercial samples of high density, linear low density, and low density polyethylene were modified by injection of low concentrations of free radical initiator during extrusion. Molecular properties monitored included molecular weight distribution, degree of unsaturation, and branching. When the polyethylene feed to this reactive extrusion process had similar values of M,, but varying polydispersity, degree of branching and degree of unsaturation, the magnitude of the change in molecular weight distribution was found to be in the following order: HDPE 1 > LDPE2 > LLDPE. In general, terminal vinyls enhanced molecular weight increase, and branching promoted degradation. However, for a second high density polyethylene sample with M , = 154,000 (rather than the previous sample's M , of 85,600). the change in molecular weight distribution was small and located at the lower molecular weight end. This work provided data for the kinetic model develop ment detailed in Part 11.

Microstructural Evolution in Linear Low Density Polyethylene During Peroxide Modification: A Monte Carlo Simulation Study

“…The range of microstructural variations the specific modification method may generate is essential to correlate the evolving micro-scale architecture to processing conditions. [35] The main chemical modification mechanisms proposed are as follows (Scheme 1): 60,61] Considering the above-mentioned mechanism, the reaction scheme suggested by Sarmoria and co-workers [12] is applied for the peroxide-initiated reactive modification of PE in this simulation. In the proposed mechanism, the reactive modification of LLDPE proceeds through the following elementary reaction channels (Scheme 2):…”

Rheological assessment of variable molecular chain structures of linear low‐density polyethylene under reactive modification

“…Any attempt to correlate the evolving molecular architecture to rheology in the course of chemical modification first requires a consideration of the range of structural variation that the specific modifier may generate. 34 In the presence of free radicals, such as the decomposition products of peroxides, PE will undergo many different reactions (Scheme 1). 35 Dominant chemical reactions include the initiator decomposition, radical attack of backbone hydrogen atoms, scission of the chains, and termination by combination.…”

“…The free-radical modification mechanism for PEs implied the formation of a random branch structure consisting of trifunctional and tetrafunctional vertices at the early stages of a crosslink-inducing reactive modification. [33][34][35][36] In this article, the term crosslinking is reserved for tetrafunctional (H-type) LCB resulting from a linkage between two macroradical backbones, and end linking is the trifunctional (T-type) LCB produced when a terminal group of a molecule forms a covalent bond with the backbone of another molecule. In fact, an originally linear chain is partially transformed via free-radical reaction into a star-linear mixture, in which star polymers have two different functionalities (fs 5 3 and 4).…”

Molecular structure evolution in peroxide‐initiated crosslinking of an ethylene vinyl acetate copolymer and a metallocene polyolefin elastomer

“…The molecular structure evolution in the modification of polyolefins has attracted a great deal of interest recently. Suwanda et d, studied the effect of an initiator at low concentrations on the molecular weight distribution of polyethylene (17,18). The initiator concentrations were kept very low (less than 0.1%) so that no crosslinking reaction occurred.…”