production of selected secondary metabolites in transformed ...

CHARACTERIZATION AND DEGRADATION BEHAVIOUR OF
TRIBLOCK COPOLYMER
Ing. Ludmila Nová
Supervisor: Prof. RNDr. Milada Vávrová, CSc.
Consultant: Ing. Lucy Vojtová, PhD.
Institute of Chemistry and Technology of Environmental Protection, Faculty of Chemistry,
Brno University of Technology, Purkyňova 118, 612 00 Brno
E-mail:nova@fch.vutbr.cz
ABSTRACT
This work is focused on the studying of the thermoreversible behaviors of two copolymers,
PLGA-PEG-PLGA and the same but modified with itaconic acid (ITA-PLGA-PEG-
PLGA-ITA). The critical gel concentrations (CGC) and the critical gel temperatures (CGT)
were determined. As for PLGA-PEG-PLGA the CGC and CGT equal to 19,2 w% and 34,5
°C, respectively, was observed. Second polymer of ITA-PLGA-PEG-PLGA indicated the
shift of the sol-gel transition curve down to the lower values of both CGC (15,3 w%) and
CGT (25 °C). The degradation behaviors of PLGA-PEG-PLGA in a phosphate buffer (pH
7.4) at 37 °C were investigated. A significant decrease in the molecular weight and increase in
the polydispersity within 10 days (until the samples have dissolved) was observed.
INTRODUCTION
Poly(lactic acid) and poly(glycolic acid) have been under extensive study since they were
introduced as biodegradable polymers having hydrolytically unstable backbones. Therefore,
these biopolymers can be used for a certain type of biomedical application such as injectable
polymer drug delivery systems, tissue implants or resorbable bone adhesives. The prevailing
mechanism for the biopolymer degradation is a simple random chemical hydrolysis [1]. The
most common explanation for this heterogeneous degradation process comes from the
absorption of water, followed by a hydrolytic cleavage of ester bonds, which generates chain
fragments with the acidic groups (Fig. 1). This process is characterized by a decrease in
molecular weight, an increase in polydispersity (PD = Mw/Mn) and polymer mass loss
accompanied by an increase in low molecular chain compound concentration in the
surrounding medium [2 – 7].
H
CH 3
O
O
CH 3
O
O
x
O
poly(lactic-co-glycolic acid)
O
O
y
OH
CH
H 3
OH
HO
O
lactic acid
Fig. 1: Scheme of the PLGA degradation.
+
2x 2y
H
HO
H
O
OH
glycolic acid
The injectable biodegradable thermosensitive ABA triblock copolymers consisting of
hydrophobic biodegradable copolymer of poly(lactic acid-co-glycolic acid) (PLGA) and
hydrophilic poly(ethylene glycol) (PEG) acting as A and B block, respectively, were
synthesized via ring-opening polymerization method in a bulk at 155 °C. The ABA
Sborník soutěže Studentské tvůrčí činnosti Student 2006 a doktorské soutěže O cenu děkana 2005 a 2006
Sekce DSP 2006, strana 218