[acs symposium series] polymers from agricultural coproducts volume 575 || synthesis and...

Chapter 4

Synthesis and Characterization of Dodecenyl Succinate Derivatives of Saccharides

Homa Assempour1, M. F. Koenig, and S. J. Huang

Biodegradable Polymer Research Consortium, Institute of Materials Science, University of Connecticut, Storrs, C T 06269-3136

Acid ester derivatives of sucrose, amylose, and corn starch bearing carbon-carbon double bonds were synthesized by reaction of 2-dodecene-1-ylsuccinic anhydride under homogeneous conditions, using a pyridine catalyst. The esters were characterized by FTIR, NMR, elemental analysis, thermal analysis, and solubility tests. The results show that these saccharides can undergo complete or nearly complete substitution in reaction with the anhydride, within the limits of sensitivity of these techniques. The resultant esters posess remarkable solubility in common organic solvents such as THF, methylene chloride, and toluene. Their solubility gradually decreases with time when stored under ambient conditions due to crosslinking through the incorporated double bonds. The esters react wtth aqueous NaOH to give a solution with pH ~8.

A considerable amount of research has been reported in the literature on the development of hydrophobic saccharide esters for a variety of applications (1-5). In the present study, we have synthesized the acid ester derivatives of sucrose, amylose, and corn starch with 2-dodecene-l-ylsuccinic anhydride (DDSA).

The purpose of this work was twofold: (1) to increase the hydrophobicity of the saccharides by incorporation of the DDSA with its long alkyl chain. It was hoped that this group would be long enough to exhibit alkyl chain packing, and hence a low

1Current address: Amir Kabir University of Iran, Tehran, Iran

,CH 2CH=CH(CH 2) 8CH 3

0097-6156/94/0575-0069$08.00/0 © 1994 American Chemical Society

Dow

nloa

ded

by U

NIV

OF

TE

NN

ESS

EE

KN

OX

VIL

LE

on

Dec

embe

r 20

, 201

4 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

May

5, 1

994

| doi

: 10.

1021

/bk-

1994

-057

5.ch

004

In Polymers from Agricultural Coproducts; Fishman, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.

70 POLYMERS FROM AGRICULTURAL COPRODUCTS

melting transition, ease of processing, and enhanced solubility, and (2) to incorporate reactive functional groups which could provide sites for further processing reactions, such as chain extention, crosslinking, or grafting. Sucrose was chosen as a model compound for the reaction of DDSA with polysaccharides.

Alkenyl succinate, as well as other acid ester derivatives of starch, have been patented (6,7), but little has been published on the synthesis and properties of these derivatives, particularly at a high degree of substitution. This paper focusses on the synthesis of these derivatives.

Experiment

Materials. High-amylose corn starch (HA-CS; 70% amylose) and potato amylose (PA) were obtained from Sigma. The potato amylose was used as received. The HA-CS granules were destructured by heating the starch in DMSO at 100 °C for 1 h. Corn amylose (CA) was isolated by precipitating twice with n-butanol from a 10% solution in DMSO. Sucrose used was pure cane confectioners sugar from Domino. It was dried in a vacuum oven at room temperature prior to use. 2-Dodecen-l-yl succinic anhydride (DDSA; 97% purity) was purchased from Aldrich and used without further purification. Pyridine from Aldrich was distilled and stored over 4 Â molecular sieve until use. All solvents used were of high purity (ACS reagent grade or higher) and used as received.

Esterification of sucrose. A solution of 5 g sucrose in 25 ml DMSO was prepared by heating at 50 °C under an argon stream. To the solution was added 2.5 ml pyridine and 34 g DDSA, and the reaction mixture heated for 16 h at 65 °C. (Caution: Pyridine is a known mutagen and a very dangerous fire and explosion hazard; standard laboratory procedures should be carefully followed to limit exposure and prevent mishaps.) The mixture was then poured into 300 ml distilled water and stirred for several minutes to obtain a stable white colloid. On stepwise treatment with an aqueous 0.5 Ν NaOH solution, a sodium salt was precipitated from the colloid. The precipitant was filtered off, washed with 200 ml acetone, and treated with an aqueous solution of 0.5 Ν HC1 to recover the ester at pH -7 as a colloid. Final purification was accomplished by extraction of the ester sample with chloroform (Caution: a CNS poison and carcinogen; avoid inhalation of vapors). After evaporation of the solvent, the ester was dried in a vacuum oven at 40 °C for one week.

Esterifîcation of amylose. A solution of 5 g CA or PA in 25 or 45 ml DMSO, respectively, was prepared by heating the solution to 110 °C under Ar. The solution was cooled to about 50 °C. Both 2.5 ml pyridine and 24 g DDSA were then added with constant stirring, after which the reaction mixture was heated to 65 °C for 16 h. The mixture was then poured into 300 ml distilled water and shaken. The crude product was separated as a doughy mass from the water by décantation. The product was rinsed in this manner several times with distilled water, after which it was dissolved in 200 ml methanol at 40 °C with stirring. (Caution: Methanol has a high cumulative toxicity, and can be absorbed through the skin. It is also a potential fire hazard.) The product was precipitated by cooling in an ice water bath, filtered, and dried in a vacuum oven at room temperature. Final purification was accomplished by twice dissolving in 200 ml acetone, precipitating in distilled water, filtering, and drying in a vacuum oven at 40 °C for one week.

Dow

nloa

ded

by U

NIV

OF

TE

NN

ESS

EE

KN

OX

VIL

LE

on

Dec

embe

r 20

, 201

4 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

May

5, 1

994

| doi

: 10.

1021

/bk-

1994

-057

5.ch

004


4. ASSEMPOUR ET AL. Dodecenyl Succinate Derivatives of Saccharides 71

Esterification of HA-CS. One gram of déstructurée HA-CS, 8 g DDSA, and 10 ml DMSO were combined in a 60 ml test tube. The mixture was then stirred thoroughly with a glass stirring rod. After adding a magnetic stir bar, the test tube was closed with a rubber septum, flushed with argon, and vented with a small needle. The tube was heated in an oil bath to 130 °C and held at that temperature for 6 h. The product was precipitated in 200 ml distilled water. The excess DDSA was suspended in the water by vigorous stirring, causing it to turn milky white. The water was then decanted. The precipitant was rinsed several more times with 50 ml aliquots of distilled water until the water remained clear. The product was then twice dissolved in 100 ml acetone and precipitated in 200 ml distilled water, followed by filtration with a fritted glass funnel. The product was dried in a vacuum oven at 40 °C overnight.

Methods of Characterization. A 270 MHz Bruker NMR spectrometer was used for recording proton decoupled 1 3 C spectra. CH2Cl2/DMSOd6 was used as solvent, and TMS was added for an internal stardard. The FTIR spectrometer used in these studies was a Nicolet 60 SX. The specimens were prepared by casting thin films on NaCl plates from CHCI3 solutions. Elemental analysis was performed by Galbraith Laboratories. Size-Exclusion Chromatography (SEC) was carried out using a Waters 150C system equipped with two 103Â and two 105Â Ultrastyragel columns. The mobile phase used was tetrahydrofuran (THF) at a flow rate of 1 ml/min at 30 °C. Differential Scanning Calorimetry (DSC) thermograms were recorded using a Perkin-Elmer DSC-7 at a heating rate of 15 °C/min. A dry nitrogen purge gas was used, and sample sizes of about 10 mg. Thermogravimetric Analysis (TGA) was performed using a Perkin-Elmer TGA-7 at a heating rate of 10 °C/min in a nitrogen atmosphere.

Results and Discussion

Degree of substitution. The extent of substitution of the prepared acid/esters was studied by NMR, elemental analysis, and FTIR. These methods are also useful for detecting impurities in the isolated products. Of special concern was the removal of the pyridine catalyst from the derivatives. Size-exclusion chromatography (SEC) was also performed on the amylose derivatives to determine the extent of degradation of the amylose macromolecules during the esterification reaction.

The 1 3 C NMR results for sucrose, amylose, and their derivatives are shown in Figures 1 and 2. From the results for sucrose, Figure 1, it appears that complete substitution of both the primary and secondary hydroxyl groups has occurred. This is evidenced by the fact that the peaks due to the various carbon atoms of the glucose and fructose subunits, between 60 and 110 ppm, have shifted position. This indicates a change in the chemical environment of the atoms. These peaks also have appeared to have broadened, which may be due to the low signal intensity. This broadening causes some difficulty in comparing the shifts of the individual peaks with the theoretical shifts, because of peak overlap. Peaks from the DDSA component can be clearly seen at 10-40,120-140, and 170-180 ppm, which are due to the alkyl, alkenyl, and carbonyl carbons, respectively. The splitting of the acid carbonyl peaks at 176.06 and 175.14 ppm and ester carbonyl peaks at 173.97 and 171.92 ppm can be attributed to the incorporation of two environmentally-different acids and esters. This is a consequence of the two different ways that the cyclic anhydride can open, resulting in either the C2 or C5 carbonyl carbon of the anhydride being bonded through oxygen to sucrose. The absence of a peak at 150 ppm indicates that the pyridine catalyst has been removed successfully by the purification procedure.

Dow

nloa

ded

by U

NIV

OF

TE

NN

ESS

EE

KN

OX

VIL

LE

on

Dec

embe

r 20

, 201

4 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

May

5, 1

994

| doi

: 10.

1021

/bk-

1994

-057

5.ch

004



I I ' I ' I • I I I I I ' I

200 160 120 80 40 0

Field strength (ppm)

an

(b)

—ι 1 1 ' 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 r 200 160 120 80 40 0


Figure 1. 1 3 C NMR spectra of (a) SU/DDSA and (b) sucrose.

Dow

nloa

ded

by U

NIV

OF

TE

NN

ESS

EE

KN

OX

VIL

LE

on

Dec

embe

r 20

, 201

4 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

May

5, 1

994

| doi

: 10.

1021

/bk-

1994

-057

5.ch

004



A comparison of the amylose spectra, Figure 2, shows similar features as the sucrose spectra: a shifting of the six amylose carbon peaks, the presence of the DDSA peaks, and the absence of peaks due to pyridine. The peak positions, both measured and calculated, for the amylose carbon peaks are listed in Table I. The shift factors used for these calculations are from ref. 8. Although there are some differences betwen the calculated and measured values, the peak assignments are believed to be accurate. The changes in measured peak positons due to esterification of the C2, C3, and C6 hydroxyl groups show the same trends as those calculated. From these observations, it can be concluded that the PA/DDSA sample has undergone complete substitution, within the detection limits of this technique. The presence of a small CI peak at 100.8 ppm for the CA/DDSA sample reflects incomplete substitution at the C2 position.

Table Π shows the results of the elemental analysis for these derivatives. They are in good agreement with the calculated values and with the NMR results presented above.

The FT-IR spectra of SU/DDSA and PA/DDSA are shown in Figure 3. Both spectra show similar features. Characteristic bands due to carbonyl stretching are visible for both the acid at 1712-1713 cm"1 and the ester at 1737-1739 cm"1. The peaks at 1152-1160 cm*1 are assigned to C-0 stretching of the ester. The absorption bands at 2932 cm-1,2854 cnr1, and 721 cm-1, due to stretching andbending vibrations of the CH2 groups, and the peak at 969 cnr1, due to out-of-plane bending of the =C-H bond, are also clearly visible. All of these bands indicate the incorporation of DDSA. The broad band from 3100-3500 cm"1 can be attributed to the inter- and intramolecular hydrogen bonding of the carboxylic acid groups.

The SEC data shown in Figure 4 for the two amylose derivatives show that both samples have single peak molecular weight distributions. This implies that the starting materials also have unimodal molecular weight distributions and that the derivatization reaction was homogeneous, with similar conversions for all molecules in the reaction mixtures. It also indicates that not much degradation of the polymer chains occurred during the derivatization reaction, or that any degradation that occurred was uniform throughout the reaction mixture. The calculated molecular weights (M n = number average, M w = weight average molecular weights) and polydispersities (M w /M n ) for these two samples are listed in Table ΠΙ.

Properties. PA/DDSA and CA/DDSA are opague white solids and SU/DDSA is a light-brown waxy solid. Solubility tests in various ordinary polar and nonpolar solvents showed these acid/esters to be easily dissolved in methylene chloride, chloroform, toluene, THF, and acetone, and partially soluble in ethanol, methanol, hexane, benzene, and carbon tetrachloride. The derivatives are insoluble in distilled water or dilute aqueous acid solutions. On mixing with dilute aqueous NaOH solutions, these acid/esters produce a solution with pH of ~8.

TGA results, Figure 5, show that the derivatives have moderate thermal stability, their onset of decomposition occurring at -200 °C. DSC thermograms, shown in Figure 6, detect a broad melting transition at about 65 °C. After annealing at 80 °C., a small melting transition was seen at about 90 °C., and a small endotherm at about 112 °C. FT-IR revealed that this endotherm is probably due to the crosslinking reaction of the alkenyl group of the DDSA. This was supported by monitoring the alkenyl absorption band at 969 cm-1 for PA/DDSA while heating at 112 °C. Figure 7 shows the reduction of intensity of this band with time over the course of 12 h.

Dow

nloa

ded

by U

NIV

OF

TE

NN

ESS

EE

KN

OX

VIL

LE

on

Dec

embe

r 20

, 201

4 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

May

5, 1

994

| doi

: 10.

1021

/bk-

1994

-057

5.ch

004



Figure 2. NMR spectra of (a) PA/DDSA, (b) CA/DDSA, and (c) potato amylose.

Dow

nloa

ded

by U

NIV

OF

TE

NN

ESS

EE

KN

OX

VIL

LE

on

Dec

embe

r 20

, 201

4 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

May

5, 1

994

| doi

: 10.

1021

/bk-

1994

-057

5.ch

004


4. ASSEMPOUR ET AL. Dodecenyl Succinate Derivatives of Saccharides

(O u 200 160 120 80


Figure 2. Continued

40

Table I. Selected 1 3 C NMR chemical shifts of the amylose derivatives Peak Assignments

Sample CI C4 C5 C2 C3 C6 (ppm) (ppm) (ppm) (ppm) (ppm) (ppm)

PA 100.05 78.71 73.23 71.92 71.60 60.39 (calc.) 121.5 84.7 81.5 77.7 72.9 62.8

PA/DDSA 96.18 75.5 69.7 73.6 71.9 62.96 CA/DDSA 100.8;96.4 75.5 69.7 _a _a 62.81 ave. shift -3.78 -3.21 -3.53 +1.68 +0.3 +2.50

(calc.) -2 -1 -2 +1 +1 +4 Peak positions uncertain because of peak overlap.

Table II. Composition data obtained from elemental analysis Calculated Experimental

Sample C Η C Η (wt%) (wt%) (wt%) (wt%)

Sucrose 42.10 6.47 SU/DDSA 67.98 9.37 67.39 9.43

PA 44.44 6.21 PA/DDSA 67.47 9.15 66.04 9.02 CA/DDSA 67.47 9.15 66.30 9.28

Dow

nloa

ded

by U

NIV

OF

TE

NN

ESS

EE

KN

OX

VIL

LE

on

Dec

embe

r 20

, 201

4 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

May

5, 1

994

| doi

: 10.

1021

/bk-

1994

-057

5.ch

004


POLYMERS FROM AGRICULTURAL COPRODUCTS

π—«—ι—«—ι—»—ι—«—ι—'—ι—1—ι—1—ι—1—ι—«—h 3600 2800 2000 1200 400

Wavenumber (cm"1)

igure 3. FTIR spectra of (a) PA/DDSA and (b) SU/DDSA.

Dow

nloa

ded

by U

NIV

OF

TE

NN

ESS

EE

KN

OX

VIL

LE

on

Dec

embe

r 20

, 201

4 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

May

5, 1

994

| doi

: 10.

1021

/bk-

1994

-057

5.ch

004



J I ι I ι I ι I ι I u

(b)

"1 1 I 1 I 1 I 1 I 1 ~T 1 Γ

0 10 20 30 40 50 60

Retention volume (ml)

Figure 4. SEC chromatographs of (a) PA/DDSA and (b) CA/DDSA.

Table III, SEC results for the amylose derivatives* Samples M n M w M w / M n

PA/DDSA 22,700 70,800 3.11 CA/DDSA 14,300 30,600 2.14

a Molecular weights calculated relative to polystyrene standards. Dow

nloa

ded

by U

NIV

OF

TE

NN

ESS

EE

KN

OX

VIL

LE

on

Dec

embe

r 20

, 201

4 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

May

5, 1

994

| doi

: 10.

1021

/bk-

1994

-057

5.ch

004



0 -j 1 1 1 1 1 1 1 1 1 h

0 100 200 300 400 500

Temperature (eC) Figure 5. TGA thermograms of (a) PA/DDSA and (b) CA/DDSA.

Dow

nloa

ded

by U

NIV

OF

TE

NN

ESS

EE

KN

OX

VIL

LE

on

Dec

embe

r 20

, 201

4 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

May

5, 1

994

| doi

: 10.

1021

/bk-

1994

-057

5.ch

004


Figu

re 6

. D

SC th

erm

ogra

ms

of P

A/D

DSA

(a) f

irst h

eatin

g an

d (b

) se

cond

he

atin

g.

Dow

nloa

ded

by U

NIV

OF

TE

NN

ESS

EE

KN

OX

VIL

LE

on

Dec

embe

r 20

, 201

4 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

May

5, 1

994

| doi

: 10.

1021

/bk-

1994

-057

5.ch

004



Dow

nloa

ded

by U

NIV

OF

TE

NN

ESS

EE

KN

OX

VIL

LE

on

Dec

embe

r 20

, 201

4 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

May

5, 1

994

| doi

: 10.

1021

/bk-

1994

-057

5.ch

004



Conclusions

Sucrose, amylose, and starch derivatives of DDSA were successfully made by reacting with an excess of the anhydride, both with and without a pyridine catalyst. It was shown that all of the primary and secondary hydroxy groups in these saccharides are susceptible to substitution, and under the conditions described here, can lead to complete substitution. These derivatives have a high solubility in several common organic solvents. The low melting temperature and reactivity of the alkenyl group makes these materials easy to crosslink at moderate temperatures. The properties of these acid/esters are being further investigated toward their application in designing novel coatings and thermoset polymers, as well as their biodegradability.

Acknowledgments

The authors would like to thank Dr. Levant Cimecioglu for the 1 3 C NMR data and for helpful discussions. One of the authors (H.A.) thanks The Amir Kabir University of Iran for awarding her a Senior Research Fellowship.

Literature Cited

1. Starch: Chemistry and Technology,; Whistler, R. L . , Bemiller, J. N. & Paschall, E. F., Eds.; ,Academic Press: New York, NY, 1984.

2. Industrial Polysaccharides: Genetic Engineering,Structure/Property Relations and Applications; Yalpani, M . , Ed.; Elsevier: Amsterdam, 1987.

3. Kawaguchi, T., Nakahara, H. & Fukuda, K. J. Colloid Interface Sci., 1985, 104, 290-293.

4. Malm, C. J., Mench, J. W., Kendall, D. L. & Hiatt, G. D. Ind. Eng. Chem., 1951, 43, 684-688.

5. Malm, C. J., Mench, J. W., Kendall, D. L. & Hiatt, G. D. Ind. Eng. Chem., 1951, 43, 688-691.

6. Caldwell, C. G. , U. S. Patent 2 613 206 (1952). 7. Jane, J., Gelina, R. J., Nikolov, Z. & Evangelista, R. L . , U . S. Patent 5 059 642

(1991). 8. Silverstein, R. M . , Bassler, G. C. & Morrill, T. C. Spectrometric Identification of

Organic Compounds, John Wiley & Sons: New York, NY, 1981.

RECEIVED July 26, 1994

Dow

nloa

ded

by U

NIV

OF

TE

NN

ESS

EE

KN

OX

VIL

LE

on

Dec

embe

r 20

, 201

4 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate:

May

5, 1

994

| doi

: 10.

1021

/bk-

1994

-057

5.ch

004


[acs symposium series] polymers from agricultural coproducts volume 575 || synthesis and...

Documents