Structure and Rheology of Molten Polymers

Frontmatter

1. Introduction

Abstract

Our subject is how molecular structure affects melt flow and how rheological behavior can provide information about structure. Rheology has been used as a semiquantitative tool in polymer science and engineering for many years, for example for quality control, but quantitative relationships between structure and measurable properties were elusive, particularly in the case of commercial polymers.

John M. Dealy, Daniel J. Read, Ronald G. Larson

2. Structure of Polymers

Abstract

The features that distinguish one polymer molecule from another are the monomer or monomers involved, the molecular size, and the molecular architecture. This chapter presents ways of describing molecular size and architecture and explains how these can be determined using analytical methods. A much more thorough treatment of polymer structure can be found in the monograph of Graessley [1]. The development of many new polymer analysis techniques over the last decade has led to the introduction of a bewildering array of abbreviations, and to help the reader deal with these, they are listed at the end of this chapter.

John M. Dealy, Daniel J. Read, Ronald G. Larson

3. Polymerization Reactions and Processes

Abstract

The objective of this chapter is to demonstrate how molecular structure, also called architecture, is governed by the polymer synthesis reaction mechanism and how this, in turn, depends on polymerization conditions. This information is essential for establishing relationships between molecular structure and rheological properties. It is only from knowing the reaction process that we can have a priori knowledge of the molecular structure.

John M. Dealy, Daniel J. Read, Ronald G. Larson

4. Linear Viscoelasticity-Fundamentals

Abstract

The treatment of linear viscoelasticity presented in this chapter is sufficient for a full understanding of the models described in subsequent chapters. However, readers wishing to delve more deeply into this subject may wish to consult the monographs by Ferry [1] and Tschoegl [2]. Ferry treats the rheological properties of polymers, while Tschoegl's book is a compendium of empirical models and relationships between various linear material functions.

John M. Dealy, Daniel J. Read, Ronald G. Larson

5. Linear Viscoelasticity—Behavior of Molten Polymers

Abstract

In this chapter, we review what is known about how molecular structure affects linear viscoelastic properties such as the zero-shear viscosity, the steady-state compliance, and the storage and loss moduli. For linear polymers, linear properties are a rich source of information about molecular structure, rivaling more elaborate techniques such as GPC and NMR. Experiments in the linear regime can also provide information about long-chain branching but are insufficient by themselves and must be supplemented by nonlinear properties, particularly those describing the response to extensional flow. The experimental techniques and material functions of nonlinear viscoelasticity are described in Chapter 10.

John M. Dealy, Daniel J. Read, Ronald G. Larson

6. Tube Models for Linear Polymers—Fundamentals

Abstract

The polymer industry has found two practical uses for polymer melt rheology. The first is to characterize molecular structure, e.g., the molecular weight distribution (MWD) and the long-chain branching (LCB) structure. The second is to characterize the processing behavior of the melt. When used to characterize structure, melt rheology can supplement (or even replace) GPC, NMR, light scattering, and other probes of molecular weight distribution and branching structure.

John M. Dealy, Daniel J. Read, Ronald G. Larson

7. Tube Models for Linear Polymers—Advanced Topics

Abstract

In Chapter 6, polymer deformation and relaxation in entangled melts were discussed using the "tube" model. Chapter 6 culminated with a discussion of the "double reptation" model, which can predict reasonably well the orientation and stress in the linear viscoelastic regime for some polydisperse linear polymers; i.e., polymers without long side branches.

John M. Dealy, Daniel J. Read, Ronald G. Larson

8. Determination of Molecular Weight Distribution Using Rheology

Abstract

In Chapter 2 it was pointed out that the primary tool for determination of molecular weight distribution (MWD) is gel permeation chromatography (GPC), also called size exclusion chromatography (SEC). But sometimes GPC is not an option, as some polymers of commercial importance dissolve either with difficulty or not at all in a solvent so that the chromatography column must be operated at high temperature or is not an option at all.

John M. Dealy, Daniel J. Read, Ronald G. Larson

9. Tube Models for Branched Polymers

Abstract

In Chapter 6, various versions of the “tube” model were presented, which can predict the linear viscoelasticity of monodisperse and polydisperse linear polymers, i.e., polymers without long-chain branching (LCB).

John M. Dealy, Daniel J. Read, Ronald G. Larson

10. Nonlinear Viscoelasticity

Abstract

In Chapter 4, it was noted that linear viscoelastic behavior is observed only in deformations that are very small or very slow. The response of a polymer to large, rapid deformations is nonlinear, which means that the stress depends on the magnitude, rate and kinematics of the deformation. The Boltzmann superposition principle is no longer valid, and nonlinear viscoelastic behavior cannot be predicted from linear properties.

John M. Dealy, Daniel J. Read, Ronald G. Larson

11. Tube Models for Nonlinear Viscoelasticity of Linear and Branched Polymers

Abstract

This chapter presents tube-based theories of nonlinear rheology. In principle, a successful theory for the nonlinear rheology of polymer melts must incorporate all the effects described in Chapters 6 to 9 for linear rheology, as well as the relaxation and flow phenomena peculiar to the nonlinear regime described in Chapter 10. The difficulty of the task of developing theories for nonlinear rheology is such that no completely general molecular theory is available at present.

John M. Dealy, Ronald G. Larson

12. State of the Art and Challenges for the Future

Abstract

In this brief chapter, we give a birds-eye view of the topics we have covered and end with our impression of where the field of polymer rheology and characterization is going, or should go, to achieve its full impact on the advancement of polymer physics and the development, production, and processing of commercial polymers.

John M. Dealy, Ronald G. Larson

Backmatter