Chemistry Reference
In-Depth Information
7.2.2 Carboxylic Acid Glycol Polyesters
The production of diacid glycol polyesters employed in food products has
been well recognized since the 1970s.
22,23
Bade
22
generated citric acid esters
from citric acid and partial fatty acids to stabilize fatty emulsions and act as
synergistic agents for anti-oxidants. Since the 1980s, several studies have
been conducted to obtain polyester-type plastics from polyfunctional acids
and glycols (e.g., dicarboxylic or tricarboxylic acid and glycerol) through
polycondensation.
24-45
These polyesters were generated using various pro-
cedures and methods but primarily heating is required to promote ester-
ification, usually followed by a subsequent lower heating process in order to
promote curing and polymerization.
27,28,30-33,36,37,39-46
Glycerol-based poly-
mers have been reported to have potential bio-medical applications because
they are benign and bio-degradable.
24
Citric acid glycerol polyesters or cit-
rate glycerides, see Table 7.1, exhibited high rates of degradation in several
different environments. Interest in the development of bio-degradable
polyesters for drug delivery or temporary surgical prosthesis has been
expressed.
25,34-36
Bio-degradable polymers have uses as bio-medical materials. Absorption
of degradable scaffolds by host tissues may overcome the long-term bio-
compatibility problems associated with persistent implants, as well as
eliminate the high cost of patient morbidity associated with follow-up sur-
gery.
35,47
These new polymers are synthesized by simple catalyst-free poly-
esterification processes using glycol and diol monomers.
35
These polymers
can be further exploited for bio-functionality by attaching biomolecules such
as proteins. Such materials will have applications in tissue engineering.
35
However, to date no commercial utilization of a diacid glycol polymer has
Table 7.1 Response of citrate glyceride polyesters to different
solvent environments. Percentage weight remaining
from polyesters of 1 : 1 molar ratio citric acid to
glycerol in various solvents after a 10-day treatment.
Treatment Foam
a
/% Powder
b
/%
Water 85 75
0.1 M NaOH 74 72
0.5 M NaOH 12 19
1.0 M NaOH 4 6
0.1 M HCl 75 75
0.5 M HCl 63 69
1.0 M HCl 57 62
Chloroform 102 94
Dichloromethane 94 82
Ethanol 96 78
Methanol 94 80
Dimethyl sulfoxide 112 131
a
Foam sample consists of 150 mg, microwave construction.
28
b
Powder is 150 mg obtained by grinding the foam with a Wiley mill
through a 1 mm screen.
