Rheological Properties of Metallocene-Catalyzed Polyolefins in the Melt and Solid States and Comparison with Conventional Polyolefins

LIDIA MARÍA QUINZANI; JOSÉ CARELLA

Metallo­cene-based Polyolefins. Preparation, Properties and Technology

John Wiley & Sons

Lugar: Londres; Año: 1999; p. 381 - 397

Since the discovery by Ziegler and Natta,during the 1950?s, of the powerful catalyst used in the low pressure polymerizationsof ethylene and propylene, remarkable progress has been made in polyolefinstechnology.  Continuing efforts have beenmade to design and produce new generations of highly active and stereoselectivecatalysts, to achieve a better tailoring of the macromolecular structuredistributions, therefore allowing a better control of melt and solid staterheological properties of polyolefins. Novel types of polyolefins are produced nowadays with the introductionof metallocene catalysts, like very low density polyethylenes, polyethyleneswith controlled type and amount of short-chain branching sequences,sindiotactic polypropylenes, or polypropylenes with controlled tacticitysequences. The topic that is presented with moreemphasis in this Chapter is that of Linear Viscoelasticity.  This is a very important subject that hasbeen extensively studied in the past.  Abrief analysis of the current phenomenological and molecular theories permitsto interpret the response of polymeric materials to a restricted class of flow,and relate it to the molecular structure of the polymers.  We begin by presenting the necessarybackground followed by the discussion of experimental and theoretical resultsof the linear viscoelasticity of polyolefins.