1. Indian Institute of Space Science and Technology
SUSTAINABLE MATERIALS BASED ON ALIPHATIC POLYESTERS : TEACHING OLD CHEMISTRY SOME NEW TRICKS
National Conference on Recent Trends in Material Science and Technology
Indian Institute of Space Science and Technology
Thiruvananthapuram
July 10, 2013
DR. S. SIVARAM
A 201, Polymers & Advanced Materials
Laboratory, National Chemical Laboratory, Pune , INDIA Tel : Fax :

2. SUSTAINABLE DEVELOPMENT (CHEMISTRY) Native American Proverb
“ Development (chemistry or chemical industry) that meet the needs of the present without compromising the ability of future generations to meet their own needs”
In other words, each generation must bequeath to its successor at least as large a productive base it inherited from its predecessor
Brundtland Report UN World Commission on Environment and Development, 1987
htm
We do not inherit the earth from our ancestors; we borrow it from our children.
Native American Proverb

3. Exclusive dependence on fossil fuel based resources
ORGANIC CHEMICALS AND MATERIALS
REDUCE
Exclusive dependence on fossil fuel based resources
Generation of wastes that need disposal
REUSE
RECYCLE
Sustainability is the key concern of science, technology, industry and society today
Can the chemical and materials needs
of humankind be based on the concept
of sustainability of both
resources and environment?
RIL, Mumbai

4. Poly( ethylene terephthalate)
Every second we throw away about 1500 bottles
Over 30 billion liters of bottled water is consumed annually
What is the solution ?

5. FROM HYDROCARBONS TO CARBOHYDRATES : FROM NON RENEWABLES TO RENEWABLES
Biomass
Chemicals
Materials
Carbon dioxide
Water
Can a part of the chemicals / materials manufacturing progressively shift to renewable carbohydrate resources (biomass) ?
Is such a virtuous cycle just a dream ?
RIL, Mumbai

6. SUSTAINABLE POLYMERS FROM BIO-DERIVED AND BIO-RENEWABLE RESOURCES
Objectives
Expand the chemistry toolbox with new methods and techniques for next generation products
Materials Platform
Aliphatic Polyesters

7. 60 million tons per annum; One third goes for making bottles !
GENERAL CLASSES OF POLYESTERS
Aliphatic polyesters
Aliphatic-Aromatic polyesters
n : 2 PET
n: 2 PBT
< 200,000 tons per annum !
60 million tons per annum;
One third goes for making bottles !
Fully Aromatic polyesters

8. POLY(LACTIC ACID)S : AN ALIPHATIC POLYESTERS FROM A SIMPLE AB MONOMER
Monomer Lactic acid ( R or S) is produced by fermentation of sugars
PLLA is hydrophobic, impermeable to water, hydrocarbon resistant
Biodegradable and compostable
Clarity and physical properties similar to PET
Requires ~ 49 % less fossil fuel to produce PLLA compared to PET
0.75 kg of CO2 emitted per kg of PLLA produced versus 3.4 kg of CO2 per kg of PET
IF PLLA IS SO ATTRACTIVE FROM A SUSTAINABILITY POINT OF VIEW, WHY IS IT STILL NOT A PART OF OUR EVERY DAY LIFE ?

9. POLY(LACTIC ACID) No. of Patents/Publications Publication Year Patents

10. ALIPHATIC POLYESTERS No. of Patents/Publications Publication Year

11. ALIPHATIC POLYESTERS : PIONEERING CHEMISTRY OF WALLACE HUME CAROTHERS
STUDIES ON POLYMERIZATION AND RING FORMATION
Twenty eight papers from 1929 to 1935
Carothers addressed one important question:
(a) If two bifunctional molecules, e. g., one dibasic acid and one glycol or diamide, react, two possibilities occur. The reaction can result (1) in a chain polymer of lower or higher molecular weight, which still bears either hydroxyl or carboxyl terminal groups or (2) in a smaller or larger ring, which does not contain the reactive group.
Under what conditions does either of these two possibilities take place and what is the molecular weight of the resulting compound?
54 papers
400 pages
Enough for
one lifetime !
Published 1940

12. CAROTHER’S DELINEATION OF POLYMERIZATION OF HYDROXY CARBOXYLIC ACIDS
α-hydroxy acetic acid
(Glycolic acid)
β-Hydroxy Propionic acid
-Hydroxy butyric acid
-Hydroxy pentanoic acid
-Hydroxy Caproic acid
+ Oligomers
+ Oligomers
+ Oligomers
Ref. : Carothers, Chem Rev; (1931)

13. What is the importance of general acid catalysis in these reactions?
IX. Polymerization*
TABLE OF CONTENTS
I. Definitions
1. Current definitions
2. Proposed definitions
3. Linear and non-linear polymers
4. Types of compounds capable of polymerizing
5. Types of polymerization
6. Condensation polymerizations and bi functional reactions
II. Condensation polymerization
1. Polyesters
a. The self- esterification of hydroxy acids
b. Polyesters from dibasic acids and glycols
* Wallace H. Carothers; Chemical Reviews 8, (1931); Communication No. 55 from the Experimental Station of the E. I. du Pont de Nemours and Company.
Received March 21, Published June 1931.
Key questions
On what factors do the relative rates k1 and k2 depend ? Are there conditions where k1 >>> k2
What is the importance of general acid catalysis in these reactions?
Can larger oligomers undergo thermolysis to large rings?
If ring formation limits chain growth reaction, is there an alternative chemistry to make high molecular weight linear aliphatic polyesters ?

14. DIRECT CATALYTIC POLYCONDENSATION OF L(+)- LACTIC ACID (90 % aqueous solution)
Water tolerant Lewis acid catalyst;
Water removal is rate limiting
Reversible ester hydrolysis of polymer
Competing lactide and macrocycle formation : Loss of reactive end groups
Water Tolerant Lewis Acid

15. Mixtures of linear and cyclics
DIRECT CATALYTIC POLYCONDENSATION OF L(+)- LACTIC ACID
solvent
Temp. C
Conv.,%
Lactide,%
Mn,VPO
Mw/Mn
Xylene
143 96
Nil
800
2.0
Mesitylene
165 76 27
1800
4.0
Decalin
190 82 15
5500
4.7
Oligomer structures established by 13 C NMR and MALDI TOF MS
Mixtures of linear and cyclics
Exclusively cyclics !
Shyamroy, Garnaik and Sivaram, J. Polymer Science: Part A: Polymer Chemistry, 43,2164 (2005)

16. SYNTHESIS OF PBA BY POLYCONDENSATION OF DIMETHYL ADIPATE (DMA) AND 1,4-BUTANEDIOL (BD)
All these reactions result in loss of end groups needed for chain growth reaction

17. EFFECT OF REACTION TEMPERATURE ON POLYCONDENSATION REACTION
No.
Temp. (0C)
Conv.a (%mol)
Conv.b (%)
Yield c (% wt.)
THF d (%mol)
Mne (VPO)
Mw/Mne
Tme (0C)
Tce (0C) 1
125 88 95 27
3.0
3980
1.6 58 22 2
150 92 97 75
3.7
7060
1.5 60 25 3
180 94 98 85
9010 61 20 4
200 86
4.4
7720 21 5
220 93
3.8
8120
a : conversions based on moles of methanol formed as determined by GC
b : % conversion calculated using the Carothers equation Xn = 1/1-p
c: yield of methanol insoluble fraction calculated based on the total weight of polymer obtained
d :THF calculated based on moles of BD from GC; e- Mn , Mw/Mn , Tm & Tc of methanol insoluble fraction
Neeta Kulkarni, PhD Thesis, 2007

18. MALDI-TOF MS of PBA, 1250C MeOH Insoluble MeOH soluble Peak End group
Structure a
hydroxy-ester b
hydroxy-hydroxy c
ester-ester d
No end group e
carboxy –hydroxy
MALDI-ToF MS analysis shows formation of varying amounts of cyclic oligomers and carboxylic end groups which result in loss of end groups and thereby limiting further step growth polymerization
Cyclics of DP : 2 were detected even at 1250C whereas cyclics of DP 2 to 12 were detected at C
Structure of the oligomers changes from linear oligomers with hydroxy-ester end groups to cyclics with no end groups

19. RING OPENING POLYMERIZATION (ROP) OF CYCLIC ESTERS
Only Low molecular weight oligomers can be obtained by polymerization of Lactic acid as monomer at temperatures < 150 0C . Only practical way to polymerize glycolic or lactic acid to high molecular weight polymers is via ROP of their corresponding cyclic esters

20. GENERAL ACID CATALYZED SELF POLYMERIZATION OF LACTIC ACID
General Acid Catalysis
Commercial 90 % lactic acid in water contains : HL = 60 % HL2+ oligomers = 27 % and LL = 13 %
pH of 0.1 N Lactic acid solution : 2.3 ; pka : 3.86; !
10x stronger than acetic acid due to intramolecular hydrogen bond
Purification by crystallization possible only via Lactide; however processes for purification expensive.
Lactide has a mp 96 0C and sublimes
Difficult to copolymerize Lactide by any other mechanism except ROP
Methyl Lactate is a volatile liquid with a bp of C
Need
An AB monomer, which has a bp above 250 0C, high vapor pressure, easily purified, hydrophobic , neutral, preferably a methyl ester

21. SYNTHESIS OF A LINEAR DIMER FROM L(+)-LACTIC ACID AND METHYL-L-LACTATE
bp : 107 0C at 5 mm
Can be purified by distillation
60 %
1 M solution in methylene chloride obtained by L-L extraction
Reaction under anhydrous conditions

22. TRANS-ESTERIFICATION OF LINEAR DIMER
No intramolecular hydrogen bonded aggregate formation
No free acidity; general acid catalysed self oligomerization not possible
Shelf stable
Simple purification by distillation
Removal of methanol is easier
Negligible Cyclization ! k2 k1
Titanium Isopropoxide
Two stage polymerization C
Is k1 >>>> k2 ?
Nevare and sivaram, research in progress

23. SYNTHESIS OF HIGH MOLECULAR WEIGHT LINEAR ALIPHATIC POLYESTERS
Problem
Beyond 150 °C , aliphatic polyester forming polycondensation reactions result in variable quantities of macrocycles; hence high molecular weight polymers cannot be realized. Alternative chemistries are needed
Coupling of preformed oligomer chains with suitably disposed end groups at temperatures less than 150C
Converting a reversible chain growth reaction into an irreversible reaction; avoid removal of volatile by products from a melt to drive conversion
Use of conformationally constrained cyclo-aliphatic diacid or diol monomers

24. However, chain termination vis N-acyl urea formation
HOMO COUPLING OF POLY(ACTIC ACID)S OLIGOMERS ACTIVATED POLYCONDENSATION
Mn increases from 1500 to 50,000 !
However, chain termination vis N-acyl urea formation
Shyamroy, Garnaik and Sivaram, Polymer Chemistry , 2013

25. CHAIN TERMINATION VIA N-ACYL UREA FORMATION
M = (CH3)2N-C5H10NH+ -O-(CO-CH-(CH3)-O)n-H-----Na+
= 72n
Also 72n found (K+ )
M = (CH3)2CH-NH-CO-N(CH(CH3)2)-(CO-CH(CH3)-O)n-H-----Na+
= 72n
Also 72n found (K+ )

26. SYNTHESIS AND CHARACTERIZATION OF HYDROXYL TERMINATED POLY(BUTYLENE ADIPATE)
ηinh in chloroform at 250C (dL/g)
Mn (VPO) Mn
(31P NMR)
Mn (GPC)
Mw (GPC)
Mw/Mn
Tm (0C)
0.211
2700
2430
7600
11,900
1.57 55
Concentration of hydroxyl end groups as determined by 31P NMR was found to be x 10-4 mol / g, corresponding to 1.9 hydroxyl groups per molecule
The telechelic oligomer was found to be thermally stable up to 2000C by TGA.

27. END GROUP ANALYSIS OF PBA TELECHELIC BY MALDI-TOF MS
Repeat unit structure
Sum of end groups (observed)
Structure of end groups
Series
89-91
1114,1314,1513,…Na+ adduct
1130,1329,1530,…K+ adduct
33-34
1056,1456,1656,…Na+ adduct
Poly(butylene adipate) oligomers contain mainly chains with hydroxyl end groups along with small amounts of hydroxy ester end groups

28. CHAIN EXTENSION WITH DIVINYL ADIPATE : FIRST EXAMPLE OF IRREVERSIBLE POLYCONDENSATION
Mn : 2700
Mn : 36,500, Tm: 59 C
The reaction by product cannot react with the growing polymer chain !
GPC of telechelic and the polyester chain extended
with divinyl adipate (DVA)
Neeta Kulkarni and Sivaram, Macromol. Chem, 2013

29. ALIPHATIC POLYESTERS BASED ON CONFORMATIONALLY CONSTRAINED MONOMERS
DIACIDS
DIOLS

30. ALIPHATIC POLYESTERS: SYNTHESIS
Aliphatic polyesters were syntheised from cyclohexane cyclopentane and norbornane diesters
by melt condensation
Catalyst : Titanium Isopropoxide
(i) Transesterification °C/6-10h
(ii) Polycondensation °C/10-12 h/0.02 mbar
Sandhya, Ramesh and Sivaram, Macromolecules, 40, 6906 (2007)

31. STRUCTURE –PROPERTY RELATIONSHIPS IN ALIPHATIC POLYESTERS
ee: ae Mn
Tm, ºC
Tg, ºC
IDT, ºC
100
20,000
163 31
403
70:30
16,500 56
-10
400
cis: trans Mn
Tm, ºC
Tg, ºC
IDT, ºC
100
57,000 -
-44
400
50:50
36,000
-15
408
cis: trans Mn
Tm, ºC
Tg, ºC
IDT, ºC
100
36,000 -
-24
500 Mn
Tm, ºC
Tg, ºC
IDT, ºC
exo-endo
37,000 -
-56
480

32. PLLA : MAJOR PROPERTY DEFICITS AND METHODS FOR IMPROVEMENT
Slow rate of crystallization ( t1/2 : 2.5 hours)
Annealing and cold crystallization
Nucleation
Very brittle material ; Poor Toughness and Elongation
Plasticization
Copolymerization
Poor heat stability ( Tm : 180 ºC ; Tg : 60 ºC )
Stereo-complexation
Poor chain entanglement in melt state leading to poor melt viscosities
Crosslinking
Branching and chain end aggregation
CSIR Proprietary

33. ISOSORBIDE: A BIO DERIVED RENEWABLE MONOMER
Hydrogenation
Acid catalyzed dehydration

34. L(+) LA- ISOSORBIDE COPOLYMER : SYNTHESIS
Mn : 80,000
Tm: 165 o C; Tg : 50 o C
Melt or solution
70 to 150 o C
Mn : 39,000
Solid State Polymerization (SSP)
Mn : 70,000

35. 1H NMR SPECTRA OF PLA-ISOSORBIDE COPOLYMER IN CDCL3Mn
Tm,˚C
Tg, ˚C
Before SSP
39,000
140 40
After SSP
69,000
185 60 2
Isosorbide Content : 9 % 1
3,8
7,4
6,5
 ppm

36. SYNTHESIS OF STAR BRANCHED POLY( LACTIC ACID)S IONOMER
Sn(Oct)2
1800C, 1 h +
Mn : 18,000
Mw / Mn; 1.13
mol ratio : 170 : 1
DCM , 12h, 25˚C +
NaH, THF, 25 ˚C

37. j.j’ k c f
Acid
Two regions in 13C spectras of acid and ionomer where we see the shifts are shown, left one is from the end groups and right one is from methyl of succinic anhydride c f
j.j’ k
Ionomer

38. MOLECULAR WEIGHT DISTRIBUTION, STORAGE MODULUS AND COMPLEX VISCOSITY OF STAR BRANCHED PLLA IONOMERS-
-CO2- Na
-CO2H
-OH
Amruta, Sivaram and Lele, research in progress

39. Click reaction on D(+)-Glucose propargyl ether
using azido-terminated PLGA
Reaction control : Excellent
Homogeneous, low temp.
reaction
Well defined structure

40. Poly(DL-Lactide-co-glycolide)-glucose
FTIR : cast-film on KBR salt-plate in transmission mode.
GPC analysis Poly(D,L)Lactic - Glycolic Acid - Star glucose copolymer in DCM using Polystyrene standards)
Polymer
Mn (GPC)
Mw (GPC)
PDI
PLGA-Glucose
13635
19942
1.46
1H-NMR (500 MHz) Spectrum of Poly(D,L)Lactic-glycolic
Acid - Star glucose (Mw ~30kDa) polymer in CDCl3 (55% Lactide/ 45% Glycolide mole ratio)

41. Acknowledgments Colleagues
Students
Dr. Sandhya Shankar
Dr S. Shyamroy
Dr Neeta Kulkarni
Mr Yogesh Nevare
Ms Amruta Kulkarni
Ms Megha Deorkar
Ms Maithili Dumbre
Ms Dipti Lai
Acknowledgments
Colleagues
Dr B.B.Idage
Dr Ms. B. Garnaik
Dr.Ashish Lele
Financial Support
J.C.Bose Fellowship (DST)
S.S.Bhatnagar Fellowship (CSIR)
CSIR’s TAPSUN Programme

42. THANK YOU