SYNTHESIS AND CHARACTERIZATION OF …

1 CHAPTER-2 SYNTHESIS AND CHARACTERIZATION OF UNSATURATED POLYESTER RESINS Introduction Unsaturated polyesters are condensation polymers formed by the reaction of polyols and polycarboxylic acids with olcfinic un saturation being contributed by one of the reactants, usually acid. The polyols and polycarboxylic acids used are usually difunctional alcohols (glycols), and difunctional acid such as phthalic and maleic acid. Water is produced as by-product of the esterification reaction and is removed from the reaction mass as soon as it is formed to drive the polyesterification reaction to completion. In the last stages of the reaction, the decrease in carboxyl group concentration is slow and the increase in viscosity is fast. These last stages are usually followed under vacuum. However, in order to avoid loss of volatile reactants an azeotropic distillation of water in the presence of added organic solvents, such as toluene or xylene may be usedl.

2 The main drawbacks of this process are longer reaction time and difficulty in removing the last traces of solvent. has enumerated that polyesterification is the most important reaction in the preparation of unsaturated polyesters and side reaction also take place like (a) Isomerization of maleate to fumarate (b) Addition of glycol to maleate and fumarate double bonds. (c) Oxidative destruction of double bonds (d) Loss of glycol. Some of the earliest vinyl estcr resms resulted from efforts by the Commerce Department to find a better dental adhesive with which to bond acrylic dental prostheses to teeth. Bowen esterified glycidyl 46 methacrylate and acrylate with Bisphenol -A m these efforts. Unfortunately, these resins were too reactive to afford a practical working life and only further vinyl ester development succeeded in providing commercially useful dental bonding resins. Other workers, such as Fekete and his associates, worked on resins intended for use in electrical insulation and chemically resistant composites.

3 Vinyl esters are the reaction products of epoxy resms with ethylenically unsaturated carboxylic acids. The most common vinyl esters are made by esterifying a diepoxide resin with a monocaboxylic unsaturated acid such as methacrylic acid or acrylic acids. Such epoxymethacrylates or epoxy acrylates can be used in free radical curing reactions alone or can be dissolved in unsaturated monomers such as styrene to give liquid resins which can be used very much like styrenated unsaturated polyester resms. Methacrylic acid is most commonly used for vinyl ester resins intended for composites applications while acrylic acid is favored for resins intended for application in coatings. The uses of other unsaturated acids such as crotonic and cinnamic acids have been reported. Before going to the synthetic methods adopted in the present case, it is worthwhile to have a glance on some of the important research work reported in literature pertaining to the SYNTHESIS of polyester resins.

4 A. Abdeen and coauthors2 synthesized polyester resin taking different proportions of phthalic anhydride and maleic anhydride for esterification 47 with propylene glycol. Polyester based on unsaturated diols were prepared by and coworkers 3 by trans-esterification of di-ethyl adipate and diols: cis-2-butene-l, 4-diol and trans-2-butane-I ,4-diol having molecular weight 500-2000. A Michiaki and coworkers4 synthesized polyester by heating propylene glycol, phthalic anhydride, maleic anhydride and fumaric acid in molar ratio at 205 C to acid value 60 and vacuumed to 5 torr for 2 hrs to acid value 18. Dicyclopentadiene, maleic anhydride and propylene glycol were heated at 210 C for 10 hrs by and coauthorss. Maleic anhydride, phthalic anhydride, ethylene glycol and (C6Hs0)3P were heated at 160 C for 5 hrs by Dabholkar and coworkers6 to give polyester having acid number 45. The SYNTHESIS of unsaturated polyesters involving two step reaction based on phthalic anhydride, maleic anhydride and propylene glycol was studied by Korbar.

5 The first step involves a reaction of an anhydride with glycol producing monoester followed by a step growth polymerization reaction producing polymer. Resin having light colour was obtained by Frietag on heating dicyclopentadiene , maleic anhydride, water and 25% hydrophosphorus acid at 130 C and then reacting with diethylene glycol at 210 C. prepared polyester using maleic anhydride, phthalic anhydride and diethylene synthesized polyester by heating a mixture of terphthalic acid, propylene glycol, neopentyl glycol and ethylene glycol at 230 C adding triphenyl phosphate and maleic anhydride at 220 C and continued the reaction for 5 hrs at 215 C. 48 Experiments The work reported in the present chapter deals with the preparation of various unsaturated polyesters by melt polycondensation process. Materials Phthalic anhydride, maleic anhydride, isophthalic acid, propylene glycol, Diglycidyl ether of bisphenol A, Glacial methacrylic acid Sodium Hdroxide which were obtained from Chiti-Chem Corporation Ltd.

6 ,Vadodara and all the chemicals were of analytical grade. SYNTHESIS Polyester resins were prepared in the present work by the technique reported by 11. A 500ml three necked flask equipped with a stirrer, thermometer and condenser was charged with the monomers. The mix. was heated till acid no. falls to 135. Then temp. was raised, not allowing the vapour temp. to exceed 105 oC at any time. The reaction continued until the acid no. had fallen to less than 45 and then ( ) hydroquinone added as inhibitor to prevent polymerization during storage. The mixture is cooled as rapidly as possible and stored below The details about the variations m molar ratio of acids/Anhydrides to glycols and reaction temp. for the SYNTHESIS of the resins are as follows: 49 Composition and reaction temp. for unsaturated polyester resins (UPEG) Reactants Used: Maleic anhydride (MA) Phthalic anhydride (PA) Propylene glycol (PO) Molar ratio Reaction temperature : 98 gms 148 gms 160 gms MA: PA: PO: : 175 -190 C Reaction mechanism: as shown in scheme: Composition and reaction temp.

7 For unsaturated polyester resin (UPEI) Reactants used: Maleic anhydride (MA) IsophthaIic acid (IPA) Propylene glycol (PO) Molar ratio Reaction temperature 196 gms 166 gms 235 gms : MA:IPA: PO: : 2000 -2250C Reaction mechanism: as shown in scheme: All the unsaturated polyester resins were viscous liquid, light yellow in colour and soluble in common organic solvents like acetone, methanol, chloroform and OMF'. SYNTHESIS of Vinyl Ester Resins (UPEV) Vinyl ester resins coded as (UPEV) were prepared in the present work by esterifying diglycidyl ether of bisphenol A epoxy resin and methacrylic acid at 130 -140 C. The details about the variations in molar ratio of monomers and reaction temp. for the SYNTHESIS of the resins are as follows: 50 Composition and reaction temp. for unsaturated polyester resin (UPEV) Reactants Used: Diglycidyl ether of Bis Phenol A: 185 gms Glacial methacrylic acid : 86 gms Catalyst : benzyl trimethyl ammonium chloride.

8 Molar Ratio : 1: 1 Reaction temperature Reaction mechanism: as shown in scheme: CHARACTERIZATION of Resins All the unsaturated polyester resms were characterized by vanous techniques as shown below: Functional group analysis Brook field viscosity Infrared spectroscopy Molecular weight determination Functional Group Analysis Acid Value Acid value of unsaturated polyester resin was determined according to the process reported by mantel About one gram (exactly weighed) of the sample was dissolved in 50ml of acetone in 250ml conical flask. After standing for a few minutes, the solution was titrated with N alcoholic potassium hydroxide solution, using phenolphthalein as an indicator. Blank determination was made at the same time without a sample. 51 The acid value is reported as the no. of milligrams of potassium hydroxide required to neutralize one gram of resin sample. Calculation: Acid value ~ (A -B) X N W Where, A ~ Consumption of KOH solution by the sample (ml) B = Consumption of KOH solution by the blank reading (ml) N = Normality of KOH solution W = Weight of sample (gm) Acid value of unsaturated polyester resins is reported in table Iodine Value Unsaturation in the polyester resin was determined in terms of Iodine value by the standard method reported in the literature 13 About 1 gram (exactly weighed) of the sample was dissolved in 50 ml chloroform in a 250 ml Iodine flask.

9 After adding 25ml Wij's reagent, the flask was sealed with a stopper and allowed to stand in the dark for 30 minutes with occasional shaking. At the end of the reaction period, 20 ml of potassium Iodide solution (10%) and 100 ml of water were added and the contents immediately titrated against sodium thiosulphate solution with vigorous shaking to ensure the extraction of all the Iodine from the organic layer until the liquid becomes light yellow. 2% starch solution (-2 ml) was added and the titration was completed till the end point of the liquid is aehived from blue to colourless. 52 The blank determination of 25 ml of the iodine monochloride solution (Wij's reagent) was carried out in a similar fashion omitting the sample. Where, Iodine value was calculated by using the formula: Iodine Value = (Vl-V2) X N W V I = vol.(ml) of thiosulphate solution used for blank reading. V 2 vol.(ml) of thiosulphate solution used for sample reading.

10 N Normality of sodium thiosulphate solution. W = Weight (gm) of the resin sample. Iodine Value of unsaturated polyester resins is reported in Table Brook field viscosity of the resin: Viscosity by Brookfield viscometer Method: ASTM 0-1824 Apparatus: Brookfield viscometer model RVT Conditioning :The reSIn sample is conditioned at 23 10C and 50 5% relative humidity throughout the period of viscosity determination. The viscosity defines the flow behaviour of a resins under low shear. The spindle is selected so that it will read in the middle or upper portion of the viscometer dial at the highest rotational speed to be used. The spindle is inserted into the sample at approximately 450 angle. The spindle is withdrawn and attached to the viscometer. Taking care not to entrap any air bubble,the viscometer is lowered to immerse the spindle near the edge of the sample. The sample adjusted so as to center the spindle and the depth is adjusted to the immersion mark.