Synthesis and Characterization of Co-Polymer (Styrene / Allyl 2,3,4,6-tetra-O-acetyl-β-D-glucopyranoside) and Studying some of its thermal properties

: In this research, a Co-polymer (Styrene / Allyl-2.3.4.6-tetra-O-acetyl-β-D-glucopyranoside) was synthesized from glucose in four steps using Addition Polymerization according to the radical mechanism using Benzoyl Peroxide (BP) as initiator. Initially, Allyl-2.3.4.6-tetra-O-acetyl-β-D-glucopyranoside monomer was prepared in three steps and the reaction was followed by (HPLC, FT-IR, TLC), in the fourth step the monomer was polymerized with Styrene and the structure was determined by FT-IR and NMR spectroscopy. The reaction conditions (temperature, reaction time, material ratios) were also studied to obtain the highest yield, the relative, specific and reduced viscosity of the prepared polymer was determined, from which the viscosity average molecular weight was calculated, which amounted to about (63,000 g/mol). Thermal properties of the polymer were studied by Differential Scanning Calorimeter (DSC) and determining the Oxidation Induction Time (OIT).


Introduction:
Various carbohydrates of natural origin with all their simple and complex types are among the most widespread and abundant compounds in nature and serve as the main source of energy in living organisms. Recently, the trend has increased towards organic synthesis using carbohydrates as building blocks of a renewable natural source to obtain monomers that can enter into polymerization reactions, also many sugar-based polymers have been discovered and used as biodegradable materials for drug delivery Systems within living organisms 1-2 . Some polymers prepared from carbohydrates show anti-corrosion properties, which encouraged using them instead of toxic and high cost chemicals as they are biodegradable, chemically stable and ecofriendly materials at low cost. Bonds with the metal surface, and the inhibition activity of these polymers is due to their ability to form complexes with metal ions on the surface of the metals through the functional groups of those polymers and thus the polymer forms a cover on the metal surface due to the large specific surface area of the polymer molecules and thus protect the metal from corrosion 3 .
In the last few years, using of plastic which is made of fossil materials has increased in several applications including food preservants, canned foods, and others, which negatively affects the environment as a result of the non-decomposition of these consumables after they are used, Therefore, it was necessary to search for a better alternative. Polymers derived from glucose and galactose is one of the best alternatives because it is widely available, eco-friendly and non-toxic new polymers have been prepared starting from monomers in which glucose and galactose have a terminal alkene using addition polymerization with sugar ring opening. High molecular weights were obtained (reaching about 135 KDa) degradability of these polymers were studied in order to use them as an eco-friendly alternative instead of fossil polymers 4 . Because of carbohydrates have eco-friendly and non-toxic properties and their high abundance in nature, many studies reported on introducing carbohydrates in preparing polycarbonates in order to improve the thermal properties of these polymers and the using of materials from natural renewable sources, so both sugar d-mannose and carbon dioxide were used in preparing polycarbonate containing six-membered ring and comparing it with aliphatic polycarbonate. The cyclic polycarbonate showed higher glass transition temperatures than the aliphatic ones and possibility of modifying the polymer structure after the polymerization which leads to the possibility of using this type of polymers in multiple applications, especially in the biological and medical fields 5 .
Carbohydrate co-polymers that contain glucose in their structure showed special properties in the field of plastics and adhesives, where a co-polymer was prepared from monomers (6-acrylo-1,2,3,4-tetraglucose acetate) and (n-butyl acrylate) to obtain a new polymer including environmentally friendly materials, the polymer possessed flexibility and rubbery structure which enables it to be used in making sustainable commodity products at low cost and less harmful to the environment. The mechanical properties and adhesive properties of the resulting polymer have also been studied to determine the areas of use 6 .
Therefore, based on the importance of carbohydrate polymers as environmentally friendly and biodegradable materials and the possibility of using them in various applications, we have seen that it is appropriate to synthesize this type of polymers, a glucose-Styrene Co-polymer was prepared in this research, characterized and studied some of its thermal properties.

Materials and Methods:
All reagents were commercially available. HPLC experiment were acquired using LC-Prominence from Shimadzu. IR spectra were acquired using potassium bromide within the 400-4000 cm -1 range using an IR Affinity-1S spectrometer from Shimadzu. The 1 H-NMR 400 MHz spectra were run in CDCl3 using Bruker spectrometers.

Glucose pentaacetate I Scheme 1. protection of the Hydroxyl groups in Glucose
Place 100 mL in a flask equipped with a magnetic stirrer, (0.105 mol) of acetic anhydride, then (0.0111 mol = 2.001 g) of pure d-glucose is added with stirring where a suspension is formed, then the specified amount of iodine as catalyst is added on four experiments to study the effect of catalyst concentration on reaction time as mentioned in Table1: the end of the reaction was determined by two indicators, the first one is the complete reaction of glucose and transformation of the suspension into a transparent liquid with a reddish-brown colour, and the second one is the Thin Layer Chromatography test (TLC) with mobile phase hexane:ethyl acetate 1:1. After the reaction was finished, the product was purified by extraction with CHCl3 and washed with sodium thiosulfate to get rid of iodine, separate the organic layer with separation funnel, dried with anhydrous sodium sulfate, the solvent was expelled by drying under vacuum to give white crystals with a pungent smell with yield 99%, mp 132 ºC, TLC Rf 0.75 silica gel, hexane:ethyl acetate 1:1. IR: (cm -1 ) 1750, 1242 as shown in Fig.1. By comparing FT-IR with glucose as shown in Fig.2 we notice the disappearance of the absorption band at 3200-3500 cm -1 belongs to the OH groups, and the appearance of a sharp and strong absorption band at 1750 cm -1 belongs to the stretch of the new carbonyl group in the product.

2,3,4,6-tetra-O-acetyl-β-D-glucopyranoside II Scheme 2. Anomeric group deprotection
In 250 mL flask equipped by a Heater with magnetic stirrer, and a glass condenser (10 mmol = 3.9093 g) of glucose pentaacetate was added with 100 mL of methanol, the mixture heated to 55 ºC and then (1 mmol = 0.22 g) of zinc acetate added as catalyst, the reaction was followed with me by TLC. Stirring was continued until TLC Showed 3 rd spot indicates to deprotection of another hydroxyl group which is undesirable product.
The reaction took 5 hours, after which the mixture was dried from the solvent under vacuum to get a white precipitate, extracted with H2O:CHCl3 1:1, the organic layer was separated, the solvent was expelled, the product was purified by column chromatography to give yellowish-white precipitate, mp 118 ºC, TLC and column chromatography (1m, SiO2 mesh 400) Rf 0.527 silica gel, hexane:ethyl acetate 1:1 . IR: (cm -1 ) 3476, 1750, 1242 as shown in Fig.3.

Figure 3. FT-IR Spectrum of II
By comparing FT-IR between the raw material and the product as shown in fig.4 we note reappearance of the absorption band at 3476 cm -1 belongs to the hydroxyl group, while the sharp and strong absorption band remained at 1750 cm -1 due to the stretching of the carbonyl group in the remaining protective groups.

Figure 4. Comparison of FT-IR spectrums of I and II
• Third stage: producing the double bond in the sugar ring (Scheme 3):

Allyl-2,3,4,6-tetra-O-acetyl-β-D-glucopyranoside (III) Scheme 3. Alkylation using Allyl Bromide
(1 mmol = 0.35 g) of 2.3.4.6-tetra-O-acetyl-β-Dglucopyranoside with 20 mL of acetonitrile (as solvent) added to a flask equipped with a heater, magnetic stirrer, and a glass condenser then (0.06 mmol = 14 mg) of silver oxide added to the flask as catalyst with stirring and heating up to 50 ºC and then excess amount of Allyl bromide was added, the reaction was monitored by TLC. After 12 hours the reaction was stopped and the silver oxide was removed by simple filtration, the solvent was expelled, followed by extraction with water and CHCl3, dried the organic layer, the excess amount of the unreacted Allyl bromide was removed by heating to the boiling point of the Allyl, and its disposal was ensured by using high-performance liquid chromatography HPLC, a standard of the Allyl and the reaction mixture prepared and injected into the HPLC, note the disappearance of the Allyl from the reaction mixture as shown in Fig.5. To separate the resulting material, thin-layer glass chromatography sheets were used with the same mobile phase, the product was obtained and extracted from silica gel with chloroform, evaporate solvent and dried to obtain white crystals 32.27%, mp 91.2 ºC, TLC R f 0.704 silica gel, hexane:ethyl acetate 1:1 . IR: (cm -1 ) 3086, 1750, 1420, 1110. FT-IR spectrum Fig.6 Showed disappearance of the band at 3450 cm -1 belongs to the hydroxyl group,

The Co-Polymer IV Scheme 4. Polymerization with Styrene
After (10 mmol = 3.888 g) of Allyl-2.3.4.6-tetra-O-acetyl-β-D-glucopyranoside with (0.02 mmol = 48.3 mg) of Benzoyl Peroxide as initiator and 20 mL of acetonitrile (as a solvent) have been added to a Two-neck round bottom flask equipped with a magnetic stirrer and vacuumed by passing Nitrogen gas, the reaction mixture was heated to 70 ºC, then (10 mmol = 1.039 g) of Styrene was added. The reaction was followed by TLC with the same conditions. The viscosity of the mixture increased after 8 hours, where the reaction took 9.5 hours, after which the polymer was purified by extraction with water and CHCl3, taking the organic layer, the solvent was expelled, re-extracted with CHCl3, evaporate solvent to get a solid, plastic texture with a very light orange colour, mp 144.2-146.8, IR: (cm -1 ), Fig.7: 3028, 2920, 1753, 1226, 758-700. 1  By taking the integration ratio of the two signals (a) at 0.86 and (a') at 1.04 as shown in Eq.1 we can find the ratio of each monomer within the copolymer structure: 1 Therefore, the co-polymer consists of 60.15% Styrene and 39.85% of Allyl-2.3.4.6-tetra-O-acetylβ-D-glucopyranoside.

3-3-Viscosity Average Molecular Weight calculation Mv:
Viscosity is usually measured using the Ostwald scale U form by measuring the time required for the solvent and the polymer solutions with known concentrations through the tube and recording them (t0, t) respectively, then calculating the relative viscosity (ƞ rel ( from the law ƞ rel = and the specific viscosity (ƞ ) from the Eq. 2:

2
Then the reduced viscosity (ƞ red ) was determined (ƞ re = ƞ ) where C is the concentration of the polymer solution in g/mL as shown in Table 2, and to determine the rate of molecular weight we measure the flow time for standard solutions of the polymer and draw a graph expresses the reduced viscosity changes (ƞ red ) in terms of concentration as shown in Fig.9, then we extend the Line to C = 0 to get the real viscosity [ƞ], the average molecular weight can be calculated using the following Mark-Houwink equation :

3
Where: K, a are constants that depends on the type of polymer, the solution, and temperature of the solution and they are reference values.    By comparing the (O.I.T) values of the polymers, we note that the Co-polymer can decompose by heat more than Polystyrene, which makes it more biodegradable and environmentally friendly than polystyrene with the same physical structure. Thus, it is possible to study the use of the new polymer in industries as an alternative to Polystyrene such as plastic.

Conclusion:
The monomer (Allyl-2,3,4,6-tetra-O-acetyl-β-Dglucopyranoside) was synthesized from glucose in three stages, then polymerized with Styrene according to the radical addition mechanism. The structure of the Co-polymer was confirmed by using FT-IR and 1 H-NMR. The average molecular weight was calculated by using Mark-Houwink equation.
(DSC) spectrum of the polymer was recorded and the Oxidation Induction Time O.I.T was determined and compared with PolyStyrene prepared with the same conditions, it was found that the new polymer is more degradable than Polystyrene which makes it more eco-friendly with the same physical structure.