Biomedical Engineering Reference
In-Depth Information
TABLE 3.1
Requirements for Biomedical Polymers
Properties
Description
Biocompatibility
Noncarcinogenesis, nonpyrogenicity, nontoxicity, and nonallergic response
Sterilizability
Autoclave, dry heating, ethyleneoxide gas, and radiation
Physical property
Strength, elasticity, and durability
Manufacturability
Machining, molding, extruding, and fiber forming
Source:
Modified from Lewin, M. and Preston, J. Eds. 1989.
Handbook of Fiber Science and Technology
Volume III: High Technology Fibers, Part B
, 332 pp, Marcel Dekker, Inc., New York. With permission.
3.2.1.1 Condensation or Step Reaction Polymerization
During
condensation polymerization
, a small molecule such as water will be condensed out by the chem-
ical reaction. For example,
R-NH
+
RCOOH
′
→
RCONHR
′
+
HO
(3.1)
2
2
(
carboxylic acid
)
(
amide
)
densed molecule)
(
amine
)
(
con
This particular process is used to make polyamides (Nylons). Nylon was the first commercial poly-
mer, made in the 1930s.
Some typical condensation polymers and their interunit linkages are given in Table 3.2. One major
drawback of condensation polymerization is the tendency for the reaction to cease before the chains
grow to a sufficient length. This is due to the decreased mobility of the chains and reactant chemical
species as polymerization progresses. This results in short chains. However, in the case of Nylon, the
chains are polymerized to a sufficiently large extent before this occurs and the physical properties of the
polymer are preserved.
Natural polymers such as polysaccharides and proteins are also made by condensation polymeriza-
tion. The condensing molecule is always water (H
2
O).
TABLE 3.2
Typical Condensation Polymers
Typ e
Interunit Linkage
Polyester
O
CO
Polyamide
OH
CN
Polyurea
HOH
NCN
Polyurethane
OH
OCN
Polysiloxane
R
Si O
R
Protein
OH
CN
