Synthesis of Biodegradable Poly(Lactic Acid)

268 Pages·2009·4.49 MB·English

Synthesis and Characterization of Biodegradable Polymers

A Thesis Submitted to
The University of Pune
for the degree of

DOCTOR OF PHILOSOPHY
(IN CHEMISTRY)

by

Asutosh Kumar Pandey

Polymer Science and Engineering Division
National Chemical Laboratory
PUNE - 411 008, INDIA.

March 2009
DEDICATED TO MY FAMILY
Acknowledgements
I convey my deep sense of gratitude to my supervisor Dr. (Mrs). Baijayantimala. Garnaik for
her constant guidance and her valuable advices that has enabled me to complete my research
work successfully. I consider myself fortunate for having a chance of working with a person
like her, who is a rare blend of many unique qualities. The tremendous faith on her students
sets her apart from others.
I take this opportunity to thank Dr. (Mrs). B. Garnaik for her tremendous help and
cooperation throughout my research tenure. I have learnt from her the necessity to be hard-
working and sincere, to be honest and critical, and in order to be an accomplished scientist. I
am grateful her for all her contribution towards my research work. I am thankful to all my
lab-mates, Smita, Balaji, Rahul Jadhav, Dnyaneshwar, Taiseen, Edna Joseph, V.K. Rana and
special thanks to lab assistant S .S. Jadhav, Zine, Shelar and Mahesh for their extensive help
and cooperation through the entire period of my research at NCL. I also convey my sincerest
thanks to Dr. R. P Singh, Dr .B. B. Idage, Dr. C. V. Avadhani, Dr. P.P. Wadgaonkar, Dr D.
R. Sani, Mr. Menon and Mrs. D. A. Dhoble for their helpful attitude at all times of need. I
am also thankful to all members of Polymer Science and Engineering Division, NCL, for
maintaining a warm and friendly atmosphere that helped me to overcome the pain of staying
away from all the near and dear ones of my family. My special thanks to Dr. P. Rajmohan for
NMR facility, NCL, for his prompt help, whenever sought for. I thank all my friends, Manish
Singh, Chandrmaulli Jha, Ananad Chubay, Shrikant Singh, Suraj Agrawa, Chitrasen Gupta
and many more, for their friendship, love and cooperation. I am at a loss of words while
expressing my feeling of gratitude towards my family brother (Nishitosh kumar Pandey),
sister (Anupama Pandey), mother (Smt. Usha Pandey), father (Shri.Dinesh kumar Pandey),
son (Yash Pandey) and my wife (Nidhi Pandey) and special thanks to Dr. Gyanandra Prakesh
and Shikhar C. Bapna. The patience and encouragement of my parents has been a major
driving force for me during the last few years of my research career. I am equally indebted to
my wife, who had been a constant source of inspiration for me that gave me the moral boost
to win against odds. I am thankful to all other members of my family for their affection and
faith they have been keeping on me since years. Finally I thank UGC for the junior and
senior research fellowship and the Director (Dr. S. Sivaram) NCL for allowing me to carry
out this in the form of a thesis to the University of Poona, to whom again I am grateful for my
registration towards the eligibility of a dissertation.

(ASUTOSH KUMAR PANDEY)
DECLARATION

Certified that the work incorporated in this thesis “Synthesis and
Characterization of Biodegradable Polymers” submitted by Mr. Asutosh
Kumar Pandey was carried out by the candidate under my supervision. Such
materials as have been obtained from other sources have been duly
acknowledged.

(Baijayantimala Garnaik)
Research Supervisor
A B S T R A C T
The thesis highlights the results of dehydropolycondensation of L-lactic acid in to poly
(L-lactic acid) (PLA oligomers) followed by post polymerization in presence of various
zeolites i.e. ZSM-5, ZSM-12 and β-zeolites. The dehydropolycondensation was achieved
under various reaction conditions of temperature, solvents and using various Lewis acid
catalysts. The oligomeric product of such dehydropolycondensation were characterized
for their thermal and crystalline properties as well as for molecular weight and end
groups, using SEC, DSC, powder XRD, NMR and MALDI-ToF spectroscopy. It has
been observed that properties of PLA oligomers as well as molecular weights can be
controlled by varying these reaction parameters. The analysis of end groups is of
importance for the successes of any post polymerization process.
Formation of macrocyclic oligomers was identified by MALDI-ToF at higher
temperature. The probability of macrocyclic compounds formation were found to
increase with increasing temperature and with the use of solvent in performing the
dehydropolycondensation reaction temperature and the use of solvent in performing
dehydropolycondensation reaction. The reaction done at temperature ~ 145 0C or at high
temperature but with out solvent were found to result in linear oligomers with both
hydroxyl and carboxyl end groups. PLA oligomers which posses both hydroxyl and
carboxylic end groups and which are semicrystalline were subjected to post
polymerization using dehydropolycondensation techniques.
The post polycondensation was carried out under different reaction condition such as
temperature, solvents and using different Lewis acid catalysts. It was found that the
molecular weight increased thirteen folds using decaline as a solvent and SnCl .2H O as
2 2
a catalyst in 5h. The results obtained using β-zeolite was promising in comparison with
other zeolites such as ZSM-5 and ZSM-12.
The sequence determination of resulting polymers showed hexad using 13C quantitative
NMR (125 MHz). The sequence results obtained from carbonyl (C=O) and methine
regions conform the presence of recemization and transesterification reactions
respectively.
Poly (aleuritic acid) and L-lactic acid-co-aleuritic acid were prepared by
dehydropolycondensation using protection and deprotection method. A linear poly
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(aleuritic acid) with ⎯M =12,000 was prepared. Aggregation behavior of PAA showed
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micelle type structure in various solvents. The copolymers of L-lactic acid and aleuritic
acid are soluble in organic and also mixed solvents. The copolymers also assembled
micelle like structure in various organic solvents and combination of two solvents at
various compositions.
The grafting reaction of L-lactic acid, PLA oligomers and L-lactic acid-co-12-hydroxy
stearic acid copolymer were on the surface of functionalized MWCNTs using
dehydropolycondensation in presence of Lewis acid catalyst. Thermal studies revel that
the PLA-g-MWCNTS has the effect of plasticizing the PLA matrix and also suggest the
formation of new crystalline domains, which is likely to be induced in the proximity of
functionalized MWCNTs. The homogeneous distribution of MWCNTs was observed by
AFM and ultimately improves the mechanical and electrical properties of PLA polymers.
PLA oligomers with ⎯M 2900-5100 were obtained using ring opening polymerization
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in presence of zinc L-prolinate catalyst. A series of linear copolymers of L, L-lactide
with ε-caprolactone with ⎯M 9000 to 30,000 were also obtained by ROP using the same
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catalyst. Block copolymer of L, L-lactide with ε-caprolactone was prepared by
sequential addition of ε-caprolactone and L, L-lactide and ⎯M was found to be 52,000.
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13C NMR results also proved the nature of copolymers were random as well as blocky
depending on the comonomer addition during copolymerization reaction.

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GLOSSARY

LA Lactic acid
L-LA L-Lactic acid
PLA Poly (L-lactic acid)
TPT Tetraphenyltin
ROP Ring opening polymerization
AL Aleuritic acid
proAL Protected aleuritic acid
PAL Protected poly (aleuritic acid)
PAA poly (aleuritic acid)
PTSA p-Toluene sulphonic acid
CNTs Carbon nanotubes
MWCNTs Multiwalled Carbon nanotubes
12-HSA 12-Hydroxystearic acid
CL ε-Caprolactone
PCL Poly (ε-caprolactone)
M Number average molecular weight
n
M Weight average molecular weight
w
M Viscosity average molecular weight
v
MWD Molecular weight distribution
[η] Intrinsic viscosity
T Glass transition temperature
g
T Melting point
m
m.p. Melting point (of an organic compound)
b.p. Boiling point

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LIST OF TABLES

Table 1.1 Lactic acid production: Global Scenario 4
Table 1.2 PLA vs. other polymers: intrinsic properties 32
Table 3.1 Number average molecular weights of the PLA oligomers 93
synthesized by ROP of L-lactide with water as co-initiator
and Sn (Oct) as initiator
2
Table 3.2 Thermal characterization and crystallinity values of PLA 93
oligomers synthesized by ROP of L-lactide
Table 4.1 Effect of L-lactic acid polymerization time on various type 101
zeolites
Table 4.2 Dehydropolycondensation of L- lactic acid prepolymers 102
using various catalyst concentrations
Table 4.3 Effect of catalyst concentration on the 104
dehydropolycondensation of L-lactic acid
Table 4.4 Effect of solvent (polar and nonpolar) on the 105
dehydropolycondensation of L- lactic acid
Table 4.5 Effect of reaction time on the dehydropolycondensation of 109
L-lactic acid in decaline
Table 4.6 13C NMR carbonyl assignments of poly (L-lactic acid) 114
prepared from L-lactic acid in xylene
Table 4.7 13C NMR carbonyl assignments of poly (L-lactic acid) 121
prepared from L-lactic acid in decaline
Table 4.8 13C NMR carbonyls assignments of poly (L-lactic acid) 125
prepared from L-lactic acid using various solvents
Table 4.9 Percentage of transesterification in polymer samples 125
Table 4.10 Experimental relative intensities of various regions in the 129
C=O 13C pattern of PLA stereocopolymers shown in
Figure 4.14 to Figure 4.18
Table 5.1 Effect of reaction time on polymerization reactions of 144
proAL
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Table 5.2 Effect of catalyst concentrations on polymerization 148
reactions of proAL
Table 5.3 Effect of temperature on polymerization reactions of 150
proAL
Table 5.4 Comparison results of PAA and PAL polymers 150
Table 5.5 Properties of L-lactic acid protected aleuritic acid 155
copolymers
Table 5.6 Properties of L-lactic acid- protected and deprotected 155
aleuritic acid copolymers
Table 7.1 Effect of temperature on ROP of L, L-lactide. 198
Table 7.2 Effect of [M]/[C] ratio on the polymerization (ROP) 199
reaction of L, L-lactide
Table 7.3 Effect of reaction time on polymerization (ROP) of lactide 202
Table 7.4 Zinc (L-prolinate) catalyzed homopolymerization and 214
2
copolymerization of L, L-lactide and ε-caprolactone
Table 7.5 Comonomer sequence distribution by using 1H NMR 219

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LIST OF FIGURES

Figure.1.1 Stereoisomers of lactide. 12
Figure.1.2 Structure of aleuritic acid. 18
Figure.1.3 Different stereo types of poly lactides. 29
Figure.1.4 PLA stereo complexes and stereo blocks. 33
Figure.1.5 A few comonomers that have been polymerized 40
with lactide.
Figure.3.1 Coordination-insertion mechanism of ROP of L- 90
lactide.
Figure.3.2 13C-NMR spectrum of PLA oligomer 3.1 91
synthesized by ROP of L-lactide: inset showing
ester carbonyl region (ester as well as carboxylic
acid) as enlarged.
Figure.3.3 Thermal characterization (DSC) first and second 92
heating showing T and T , respectively of PLA
m g
oligomers: (a) 3.1, first heating; (b) 3.2, first
heating; (c) 3.1, second heating and (d) 3.2, second
heating.
Figure.3.4 Powder X ray Diffraction (XRD) patterns of PLA 92
oligomers: (a) 3.1 and (b) 3.2.
Figure.4.1 Structure of catalysts (A) tin chloridedihydrate, (B) 98
tetraphenyl tin and (C) dichloride distannoxane.
Figure.4.2 Size Exclusion Chromatography (SEC) elugrams of 106
PLA oligomers (a) PLA-29, (b) PLA-30, (c) PLA-
31, (d) PLA-32, (e) PLA-33 and (f) PLA-34.
Figure.4.3 Differential Scanning Calorimetry (DSC) 107
thermograms showing melting temperature of PLA
oligomers (a) PLA-29, (b) PLA-30, (c) PLA-31, (d)
PLA-32, (e) PLA-33 and (f) PLA-34.
Figure.4.4 DSC thermogram showing glass temperature of 108
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