Olefin polymer technologies—History and recent progress at The Dow Chemical Company

A new procedure to fractionate ethylene/α-olefin copolymers using DSC is presented. This procedure allows melt/melt and melt/solid segregation to occur during thermal cycles that promote self-nucleation, crystallization and annealing processes (Successive Self-Nucleation/ Annealing, SSA). The SSA has been compared with the Step-Crystallization (SC) method proposed earlier in the literature to qualitatively characterize chain branching distribution in a faster and easier way than Temperature Rising Elution Fractionation (TREF). In general, SSA produces better fractionation than SC and the DSC derived chain branching distribution by SSA can be qualitatively comparable to that obtained by TREF. The SSA technique could have important applications for the characterization of polymers that crystallize over a broad temperature range.

Successive self-nucleation/annealing (SSA): A novel technique to study molecular segregation during crystallization

The present invention relates to plasticized polyolefin compositions comprising a polyolefin and a non-functionalized hydrocarbon plasticizer.

Plasticized polyolefin compositions

An ethylene polymer extrusion composition having high draw down and substantially reduced neck-in, a process for making such a composition and a process of using such a composition to prepare extrusion coatings, extrusion profiles and extrusion cast films are disclosed. The ethylene polymer extrusion composition is made of 75-95 weight percent of at least one ethylene α-olefin interpolymer and 5-25 weight percent of at least one high pressure ethylene polymer characterized as having high melt strength and a broad, bimodal molecular weight distribution. In profiles, coatings or films, the composition can be used as sealant, adhesive or abuse resistance layers.

Extrusion compositions having high drawdown and substantially reduced neck-in

An outline is given of the development of temperature rising elution fractionation (TREF) technique for polymer separation on the basis of crystallizability. The TREF technique has found application mainly in the area of analysis of semi-crystalline polyolefins and its development has been significantly influenced by the desire to establish the structure of linear low density polyethylenes. These materials exhibit an unusually broad distribution of comonomer which can be readily explored by TREF. Systems have been developed which can provide fractionation on a preparative scale, where recovery of fractions for further analysis is desirable and more recently on a small scale, where rapid analysis using detectors provide refined crystallizability distributions. A description is given of these fractionation systems along with a discussion of the separation mechanism and the significance of controlling the crystallization step to achieve fractionation efficiency.

Temperature rising elution fractionation

A description is given of an analytical temperature-rising elution fractionation (TREF) system for the purpose of determining short-chain branching (SCB) or copolymer distributions in poly-ethylenes and ethylene copolymers. The system achieves fractionation on the basis of crystallizability and is shown to be very little influenced by molecular weight in the normal high polymer range. Sample preparation by slow cooling from relatively dilute solution followed by continuous elution with a simultaneous and fairly rapid rate of temperature rise proves to be an efficient fractionation process. An on-line detector and data system allows application of a calibration curve to give realistic SCB distribution data in a convenient manner. The potential value of the TREF technique for providing structural information is illustrated by examples which include low-density high-pressure resins made by both tubular and autoclave reactors, high- and low-density resins made by low-pressure processes, and copolymers of ethylene with vinyl acetate and ethyl acrylate.

T. R. Ryle

Papers

Determination of branching distributions in polyethylene and ethylene copolymers