Page 289 - Carrahers_Polymer_Chemistry,_Eighth_Edition

252 Carraher’s Polymer Chemistry

arrangements, equations that allow copolymer composition to be determined from the monomer-
feed ratio are developed.
3. The product of the reactivity ratios can be used to estimate the copolymer structure. When the
product of the reactivity ratios is near one, the copolymer arrangement is random; when the prod-
uct is near zero, the arrangement is alternating; when one of the reactivity ratios is large, blocks
corresponding to that monomer addition will occur.
4. Block and graft copolymers may differ from mixtures by having properties derived from each com-
ponent. Block copolymers can be used as thermoplastic elastomers and graft copolymers with fl ex-
ible backbones can be used for high-impact plastics. Block and graft copolymers can be produced
by step and chain-reaction polymerization. The principle block copolymers are thermoplastic elasto-
mers and elastic fibers such as ABS. Principal graft copolymers are grafted starch and cellulose.

5. Blends are physical mixtures of polymers. Depending on the extent and type of blend, the proper-
ties may be characteristic of each blend member or may be some “blend” of properties. Immiscible
blends are phase separated with the phases sometimes chemically connected. They are generally
composed of a continuous and discontinuous phase. HIPS is an example of an immiscible blend.
Miscible blends occur when the two blended materials are compatible. Often the properties are a
mixture of the two blended materials. The plastic automotive panels and bumpers are generally
made from a miscible blend of polyethylene and a copolymer of polyethylene and polypropylene.
6. Dendrites are complex molecules formed from building up of the dendrite by individual steps
(divergent growth) or from bringing together the units already formed (convergent growth).
7. Ionomers are often referred to as processable thermosets. They are cross-linked through the use
of metal ions such that application of heat and pressure allow them to be reformed.
8. There are a number of applications of copolymers. One of these is the important area of viscos-

ity modifiers that recognizes the influence that small amounts of polymers generally have on

increasing the viscosity of solutions to which they have been added. One of these applications is
to allow the viscosity of motor oils to remain approximately constant over an engine’s tempera-
ture operating range. Here, the polymer additive increases its effective chain distance as temper-
ature increases compensating for the temperature decrease caused by increased temperature.

GLOSSARY
AB: Block copolymer with two separate mers.
ABA: Block copolymer with three sequences of mers in the order shown.
ABS: Three-component copolymer of acrylonitrile, butadiene, and styrene.
Alloy: Rubber-toughened materials in which the matrix can be a mixture of polymer types.
Alternation copolymer: Ordered copolymer in which other building is a different mer.
Azeotropic copolymer: Copolymer in which the feet and composition of the copolymer are
the same.
Blends: Mixtures of different polymers on a molecular level; may exist in one or two phases.
Block copolymer: Copolymer that contains long sequences or runs of one mer or both mers.
Buna-N: Elastomeric copolymer of butadiene and acrylonitrile.
Buna-S: Elastomeric copolymer of butadiene and styrene.
Butyl rubber: Elastomeric copolymer of isobutylene and isoprene.
Charge-transfer complex: Complex consisting of an electron donor (D) and an electron accep-
tor (A) in which an electron has been transferred form D to A resulting in the charge-
−
+
transfer agent D A .
Composites: Mixtures of different polymers, one forming a continuous phase (the matrix) and
one the discontinuous phase (often a fi ber).
Compositional drift: Change in composition of a copolymer that occurs as copolymerization
takes place with monomers of different reactivities.
Copolymer: Macromolecule containing more than one type of mer in the backbone.

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