S e r i e s o f C h e m i s t r y 1 9 ( 4 ) ( 2 0 1 0 ) 1 9 -26 T A I L O R E D ST A R -SHAPE B I O D E G R A D A B L E P O L Y ( L A C T I C A C I D ) G. polycondensation method, using as catalyst tin chloride, and phosphorus oxychloride or 2-amino-2-methyl-1,3-propandiol as core. The influence of molar ration and concentration of catalyst on molar masses was studied. Moderately high molecular weight and inherent viscosities values up to 0.60 dl/g were obtained

Adriana Popa

Aurelia Visa

G Ilia

Lavinia Macarie

Nicoleta Pleş

Smaranda Iliescu

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Annals of West University of Timisoara 
Ser ies  o f  Chemis t r y  19  (4 )  (2010)  19-26  
 
 19 
 
 
TAILORED STAR-SHAPE BIODEGRADABLE 
POLY(LACTIC ACID) 
G .  I l i a a , b ,  S m a r a n d a  I l i e s c u a ,  A d r i a n a  P o p a a ,  N i c o l e t a  P l eşu a ,                 
L a v i n i a  M a c a r i e a ,  A u r e l i a  V i s a a  
aInstitute of Chemistry Timisoara, 24 Mihai Viteazul Str., 300224-Timisoara, 
ROMANIA, ilia@acad-icht.tm.edu.ro 
bWest University, Faculty of Chemistry-Biology and Geography, 116 Pestalozzi  Str.,  
300115 Timisoara, ROMANIA 
Received: 16 November 2010 Modified: 23 November 2010 Accepted: 23 November 2010 
 
SUMMARY 
 
Three-arm star-shaped poly(lactic acid)s were prepared by direct 
polycondensation method, using as catalyst tin chloride, and phosphorus oxychloride or 2-
amino-2-methyl-1,3-propandiol as core. The influence of molar ration and concentration of 
catalyst on molar masses was studied. Moderately high molecular weight and inherent 
viscosities values up to 0.60 dl/g were obtained. 
Keywords: star-shape; poly(lactic acid); phosphorus oxychloride: 2-amino-2-
methyl-1,3-propandiol 
 
INTRODUCTION  
 
Polymers such as polyethylene and polypropylene persist for many years after 
disposal. These polymers seem inappropriate for applications in which plastics are used for 
short time periods and then disposed. In contrast, biodegradable polymers are designed to 
degrade upon disposal by the action of living organisms. Markets for biodegradable 
 I L I A  G . ,  I L I E S C U  S .  E T  A L .  
 
 20
polymers include packaging materials (trash bags, wrappings, loose-fill foam, food 
containers, film wrapping, laminated paper), disposable nonwovens (engineered fabrics) 
and hygiene products (diaper back sheets, cotton swabs), consumer goods (fast-food 
tableware, containers, egg cartons, razor handles, toys), and agricultural tools (mulch films, 
planters). [1]   
Biodegradable polymers can be either natural or synthetic. In general, synthetic 
polymers offer greater advantages than natural materials in that they can be tailored to give 
a wider range of properties and more predictable lot-to-lot uniformity than can materials 
from natural sources. Synthetic polymers also represent a more reliable source of raw 
materials, one free from concerns of immunogenicity. 
Poly(lactic acid) (PLA) belongs to the family of aliphatic polyesters commonly 
made from a -hydroxy acids, which include polyglycolic acid or polymandelic acid, and are 
considered biodegradable and compostable. PLA is a thermoplastic, high-strength, high-
modulus polymer that can be made from annually renewable resources to yield articles for 
use in either the industrial packaging field or the biocompatible/bioabsorbable medical 
device market. [2] Various methods of synthesizing polycondensation and ring opening 
polymerization and modifying properties of polylactic acid (PLA), which may be used as 
biomaterials, such as a drug carrier in a drug delivery system, as a cell scaffold and suture in 
tissue engineering, and as packaging materials in packaging engineering field are known.  
Copolymerization of lactide with other monomers or polymers such as malic acid, 
polyethylene glycol (PEG), polyglycolic acid (PGA), or dextran, as well as blending 
polylactide with natural derivatives and other methods of modification are presented in 
literature. Surface modifications of PLA-type copolymers, such as surface coating, chemical 
modification, and plasma treatment are also described in the literature. [3] In recent times, 
several PLA-based technologies have emerged with an emphasis on achieving chemical, 
mechanical, and biological properties equivalent or superior to conventional polymers. The 
frequent need for a chemical or physical modification of PLA to achieve suitable properties 
for its intended consumer and biomedical applications, however, has demanded significant 
attention in the last decade. [4]  
Star-shaped polymers consist of at least three linear polymeric chains of 
comparable lengths radiating from one single multifunctional branched point, usually called 
the core or the central nodule, and which can itself be polymeric The main feature of star-
shaped polymers, differing them from the linear analogues of identical molar masses (Mn), 
is their compact structure (smaller hydrodynamic volume and radius of gyration, and 
therefore lower viscosity) and the multiple functionality that is useful in some of their 
applications. [5]  
In this work the synthesis of star-shaped PLA starting from phosphorus 
oxychloride or 2-amino-2-methyl-1,3-propandiol is described. 
TAILORED STAR-SHAPE BIODEGRADABLE POLY(LACTIC ACID) 
 
 21 
 
MATERIALS AND METHODS  
 
D,L-lactic acid, SnCl2, tetrahydrofuran, methylene chloride, potassium 
phosphate(K3PO4), 2-amino-2-methyl-1,3-propandiol (AMPD) were purchased from 
Aldrich and were used without purification. Phosphorus oxychloride was also purchased 
from Aldrich and was freshly distilled prior use. 
Viscosity measurements  
Viscosity measurements were performed in chloroform at a temperature of 25C in 
an Ubbelohde viscometer. Inherent viscosity was calculated according to the following 
equation:  
inh = ln rel / c 
where: rel - relative viscosity, c - concentration of polymer, g/dl.  
Determination of molar masses by GPC method
The molar masses of polymers were determined by gel permeation 
chromatography, using an Evaporative Light Scattering Detector, PL-EMD 950 (2x PL gel 
MIXEDC 300 x 7.5 mm columns; T=35C; chloroform as solvent; Flow 1 ml/min; 
calibration with KIT polystyrene as standard). 
FT-IR analysis 
The obtained compounds were characterized by Fourier Transform Infrared 
Spectroscopy with a Jasco 430 spectrometer (spectral range 4000-400 cm-1, 256 scans, and 
resolution 2 cm-1) using KBr pellets.  
Synthesis of star shape AMPD - PLA
Copolymerization of (D,L)-lactic acid and 2-amino-2-methyl-1,3-propandiol was 
carried out in a 100 ml round bottom three-necked flask, containing a water-cooling 
condenser. The reaction temperature was set by adjusting a heating mantle equipped with a 
temperature regulator and the suitable thermocouple. The appropriate capillary inlet for dry 
nitrogen gas was fitted in one of the side necks. (D,L)-lactic acid solution was placed in the 
reaction flask, at amounts varying from 25–50 ml then 2-amino-2-methyl-1,3-propandiol (5 
mol%) and SnCl2 as catalyst were added. The solution was heated in a first stage up to 
100C, in order to expel the free water then to a programmed temperature in the range 140-
200C. In order to better remove polycondensation by-products and thus, achieve a higher 
degree of polymerization, the reaction was performed at reduced pressure by connecting a 
vacuum pump with the condenser. Nitrogen gas flow was applied to the above reaction flask 
in order to safely perform polymerization at high temperature. 
 I L I A  G . ,  I L I E S C U  S .  E T  A L .  
 
 22
Synthesis of star shape Phosphate- PLA 
To o solution of 0.5 mol lactic acid and 0.3 mol potassium phosphate in 50 ml 
methylene chloride is added drop wise, under stirring, a solution of 0.1 mol phosphorus 
oxychloride in 10 ml methylene chloride. Temperature of mixture was kept below 10oC 
during the addition of phosphorus oxycloride. Then the temperature was raised to reflux and 
maintained at this temperature 10 hours. After the mixture is cooled to room temperature the 
mixture of KCl and K2HPO4 [6] is filtered, and the solvent removed by distillation. To the 
crude intermediate is added D, L lactic acid, that the concentration of phosphoester to be 5 
mol %, and the mixture is polymerized as in the case of star shape AMPD – PLA. 
 
RESULTS AND DISCUSSIONS 
 
Two types of three-arm star-shaped polylactic acid were synthesized starting from 
phosphorus oxychloride (Scheme 1) having carboxylic-terminated group, or from 2-amino-
2-methyl-1,3-propandiol (Scheme 2) when the end group is hydroxyl group. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Scheme 1. Structure of star-shape poly(lactic acid) starting from phosphorus oxychloride. 
n
C
H
+
n
3
TAILORED STAR-SHAPE BIODEGRADABLE POLY(LACTIC ACID) 
 
 23 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Scheme 2. Structure of star-shape poly(lactic acid) starting from 2-amino-2-methyl-1,3-propandiol 
 
The IR spectra of the Phosphate-PLA copolymers showed that the most important 
and characteristic peaks were P=O appearing at 1273 cm-1 and P-O-C at 1046 and 999 cm-1. 
The peak at 1755 cm-1 was assigned to C=O from the PLA segment. Polymers gave a broad 
absorption at 2530-3100 cm-1 due to terminal acid group. The most important peaks for 
AMPD - PLA copolymers were at 1670 cm-1(C=O amide), 3230 cm-1 (N-H). 
The main feature of star-shaped polymers, differing from the linear analogues of 
identical molar masses (Mn), is their compact structure (smaller hydrodynamic volume and 
radius of gyration, and therefore lower viscosity) and the multiple functionality, which is 
useful in some of their applications.  
Star-shaped polymers are called homostars when all arms have the same chemical 
structure. Arms may be built of homo-, co-, or even terpolymers, therefore the final 
properties of the resulting star-shaped polymers (e.g., star-block and heterostar copolymers) 
may be adjusted by choosing the respective chemical structure of an arm and core, 
depending on the required application. In general, the polycondensation of lactic acid 
 
 I L I A  G . ,  I L I E S C U  S .  E T  A L .  
 
 24
proceeds stepwise in similar manner to the esterification of a diacid with a diol.  
The molecular weight of the resulting polymer increases in proportion to the 
reaction time. During the polycondensation, an amount of wather is produced as by-product, 
which hydrolyzes the resulting polymer, and thus decreasing the molecular weight of the 
polymer. 
Therefore, it was attempted to synthesize PLA by polycondensation of  lactic acid 
without any solvent, focusing on the following parameters: 
1. Stirring the reaction mixture, which allows easier removal of by-products 
2. Prevention of the thermal degradation during polymerization 
In order to respond to the above mentioned requirements and achieve a higher 
conversion of polycondensation of lactic acid the reaction was run at higher temperatures in 
the absence of azeotropic solvent whose boiling point controls the temperature and under 
nitrogen atmosphere as prevention of the thermal degradation and as mixing agent. 
The influence of temperature was first studied. In Table 1 the obtained results are 
presented. 
 
Table 1. The influence of temperature on molecular weight and 
viscosity, (reaction time 20h, 0.1% catalyst) 
 
Run Temp. C  Mw Mw/Mn , dl/g 
1 140 Phosphate-PLA 8600 1.45 0.50 
2 AMPD - PLA 9350 1.57 0.54 
3 180 Phosphate-PLA 15700 1.75 0.65 
4 AMPD - PLA 16200 1.86 0.61 
5 200 Phosphate-PLA 20600 1.78 0.69 
6 AMPD - PLA 26300 1.82 0.73 
 
As can be seen from the Table 1 the molecular weights of both polymers increase 
with the increasing temperature.  The best results were obtained at 200C when molecular 
weights reached to 20600 for Phosphate- PLA and to 26300 for AMPD - PLA. 
Also reaction time has influence on molecular weights and viscosity. The obtained 
results are presented in Table 2.  
 
 
 
 
 
TAILORED STAR-SHAPE BIODEGRADABLE POLY(LACTIC ACID) 
 
 25 
 
Table 2. The influence of reaction time on molecular weight and 
viscosity (temperature 200C, 0.1% catalyst) 
 
Run Reaction time, h  Mw Mw/Mn , dl/g 
1 25 Phosphate- PLA 25250 1.65 0.78 
2 AMPD - PLA 28300 1.73 0.73 
3 30 Phosphate- PLA 27600 1.75 0.72 
4 AMPD - PLA 29800 1.69 0.81 
5 35 Phosphate- PLA 29000 1.45 0.85 
6 AMPD - PLA 31400 1.42 0.83 
7 40 Phosphate- PLA 32700 1.50 0.87 
8 Phosphate- PLA 34600 1.62 0.91 
 
When reaction time was 40 hours the best results were obtained, the molecular 
weight increased from 25250 to 34600, the inherent viscosity vary between 0.72 dl/g and 
0.91 dl/g. 
Also the influence of catalyst concentration was studied and the results are 
presented in Table 3. 
 
Table 3. Results of polymerization using various amount of 
catalyst temperature 200C, reaction time 40h) 
 
Run Catalyst, %  Mw Mw/Mn , dl/g 
1 0.2 Phosphate- PLA 35300 1.56 0.90 
2 AMPD - PLA 36200 1.68 0.95 
5 0.3 Phosphate- PLA 33600 1.40 0.82 
6 AMPD - PLA 34400 1.42 0.75 
 
Increasing the concentration from 0.1% to 0.3% did not increase significantly 
neither molecular weight nor viscosity, and technologically is not recommended because 
the remove of catalyst from the polymer is difficult and the cost of product increases. 
 
 
 
 
 
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 26
 
CONCLUSION  
 
Two three-arm star-shaped polylactic acids were synthesized one starting from 
phosphorus oxychloride. 
For both compounds the influence of temperature, reaction time and concentration 
of catalyst was studied. The best results were obtained at 200C, when reaction time was 40 
hours and concentration of catalyst 0.2%. 
 
REFERENCES  
 
1. Gross R.A. and Kalra B., “Biodegradable Polymers for the Environment”, Science, 297 (2002) 803-
807. 
2. Garlotta D., “A Literature Review of Poly(Lactic Acid)”, J. Polym. Environ., 9 (2001) 63-84. 
3. Cheng Y., Deng S., Chen P., Ruan R., “Polylactic acid (PLA) synthesis and modifications: a 
review”, Front. Chem. China, 4 (2009) 259–264. 
4. Rasal R.M., Janorkar A.V., Hirt D.E., “Poly(lactic acid) modifications”, Prog. Polym. Sci., 35 (2010) 
338–356. 
5. Lapienis G., “Star-shaped polymers having PEO arms”, Prog. Polym. Sci., 34 (2009) 852–892. 
6. Ilia G., Iliescu S., Macarie L., Popa A., “Synthesis of tervalent phosphorus esters in biphasic system 
using potassium phosphate as unique solid base”, Heteroatom Chem., 19 (2008) 360-364. 
 
 


T A I L O R E D ST A R -SHAPE B I O D E G R A D A B L E P O L Y ( L A C T I C A C I D )

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T A I L O R E D ST A R -SHAPE B I O D E G R A D A B L E P O L Y ( L A C T I C A C I D )

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