Page 696 - Carrahers_Polymer_Chemistry,_Eighth_Edition

Selected Topics 659

O
H C Oleic acid
3
OH

O

OH
Linolenic acid
CH 3

Linoleic acid
CH 3

O

OH

H C O
3
H C
3
Ricinoleic acid
OH

OH

FIGURE 19.11 Vegetable oil derived fatty acids.

Alcaligenes eutrophus is placed in a medium that allows it to rapidly reproduce. After a suffi cient popu-
lation is obtained, the conditions are changed resulting in the production of a range of PHBs with general
structures as shown below. A. eutrophus typically produces so-called short chain PHAs where n = 3–5.
By comparison, Pseudomonas oleovorans produce longer chained PHAs, where n = 6–14.

O R 1
R 1 n x
(19.56)
R O
PHA General structure

PHB has n = 1 and R = methyl. PHB is biocompatible and is a metabolite normally present in
blood. Thus, a wide range of biomaterial uses can be envisioned for it. The copolymer of PHB and
PHV (where R = ethyl and n = 1), poly(-3-hydroxybutyrate-co-3-hydroxyvalerate) is being used as a
packaging material. Compared to PHB, the copolymer is tougher, less rigid, and easier to process.
The general properties can be predicted knowing the values of R and n. As expected, the smaller

the value of n the stiffer the backbone and the larger the R the greater the flexibility because the
ability of the chains to coalesce is less because of the greater steric requirements. Values of “x”
(19.56) generally range from 100 to more than 30,000.

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