Page 242 - Academic Press Encyclopedia of Physical Science and Technology 3rd Polymer

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Encyclopedia of Physical Science and Technology EN012B-596 July 27, 2001 18:18

Polymers, Synthesis

Timothy E. Long
James E. McGrath
Virginia Polytechnic Institute and State University

S. Richard Turner
Eastman Chemical Co., Kingsport, TN

I. Review of Fundamental Definitions
II. Basic Considerations
III. Linear Step-Growth Polymerizations
IV. Linear Chain-Growth Polymerizations

GLOSSARY single repeating unit, which is called a homopolymer,
or more than one chemical repeating unit in the chain
Chain-grown (addition) polymerization Transforma- structure.
tion of a reactive small molecule (often containing an Degree of polymerization (molecular weight) Number
alkene group) via radical or ionic intermediates into a of repeating units in the macromolecule or polymeric
macromolecule by a series of addition reactions which chain structure. The molecular weight of the chain is
may involve several distinct kinetic chain-growth then a simple product of the degree of polymeriza-
steps such as initiation, propagation, and possibly tion multiplied by the molecular weight of the structure
termination. within the repeating unit.
Chain isomerism Geometric (cis, trans, etc.), stereo- Living and controlled polymerization Polymerization
chemical (isotactic, syndiotactic, heterotactic), or reaction wherein the terminal unit of the growing chain
regio (head-to-tail, head-to-chain configurations) species has an indefinitely long lifetime and will essen-
isomerisms. tially react only with the monomer.
Composition Characteristic of a material defining Step-growth (polycondensation) polymerization
whether it will have, for example, weak intermolecular Process by which a macromolecule is built up via
forces, as illustrated by a hydrocarbon elastomer (e.g., a series of reactions between functional groups,
polybutadiene), or be strongly hydrogen bonded, as in for example, the hydroxyl–carboxyl reaction, to
the case of a fiber-forming polyamide. The term is also produce a macromolecule at very high conversions
related to the question of whether one is dealing with a (>99.9%).

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