200 JOURNAL OF COSMETIC SCIENCE laboratory, we were prepared to detect the utility of rosin-based polymers as a cream base. The rosin-based polymers were prepared by the esterification of rosin with glycerol and pentaerythritol at 220-240øC in the presence of sodium sulphide and sodium bisulphate as catalysts. The primary aim of the present work is to evaluate polymer 2 as a cream base. The cream-containing polymer 2 (R2) was also studied for its stability and the release profile of diclofenac diethylammonium. The prepared cream was compared with a standard cream containing Tween 60 (RT) and a marketed preparation (RM). EXPERIMENTAL MATERIALS The procured materials along with their sources are as follows: rosin N grade (Tayebai Ebrahimji Pettodwala, Mumbai), glycerol (Qualigen), sorbitol (Qualigen), Tween 60 (S.D. Fine), maleic anhydride (Qualigen), pthaleic anhydride (Qualigen), castor oil (P.J. Chemicals, Nagpur), glycerin (Qualigen), isopropyl myristate (Qualigen), cetyl alcohol (S.D. Fine), stearyl alcohol (S. D. Fine), propylene glycol (Qualigen), and diclofenac diethylammonium (Crossland Laboratories Ltd., Pune). Distilled water was used when collected fresh. The polymers based on rosin were prepared in the Laboratory of Phar- maceutical Sciences, Nagpur University, Nagpur. PREPARATION AND DETERMINATION OF THE PHYSICOCHEMICAL PROPERTIES OF ROSIN-BASED POLYMERS Preparation of rosin-basedpolymers. The reaction of polymer synthesis was conducted in a four-neck two-liter glass reactor. This reactor was fitted with a condenser, stirrer, and temperature control arrangement. The reaction temperature was maintained within +2øC with the help of an accurate thermometer. As a first step, rosin, part of the maleic anhydride, castor oil, and sodium sulphide and sodium bisulphate (catalysts) were added to the reactor and the temperature was slowly raised to 160øC. The reaction was maintained at this temperature for one hour. After this, the temperature was lowered to 120øC and glycerol and sorbitol were added slowly after about 15 minutes. The cooling was continued for three to four hours at 210-250øC. At the end of this period, the calculated solvent, part of the maleic anhydride, and pthaleic anhydride were slowly added after about 15 minutes. Further cooling was done at a lower temperature for three to four hours until the desired acid value was reached. Finally, xylene was stripped off totally by heating at a slightly higher temperature (150øC) using a vacuum. The sample was finally strained through a fine mesh and stored carefully. During the process, the acid value of the product was determined intermittently as reported previously (13). Determination ofphysicochemicalproperties of rosin-basedpo/ymer. The acid value is the num- ber that expresses in milligrams the amount of KOH necessary to neutralize the free acids present in one gram of the substance. The acid value of the polymers was deter- mined by using the test described in the Indian Pharmacopoeia (Pharmacopoeia of India, 1996). The maximum acid value for rosin-based polymer should not exceed more than 10. Two grams of rosin-based polymer was dissolved in 50 ml of a mixture of equal volumes of ethanol (95%) and ether previously neutralized with 0.1 M KOH to phenolphthalein

ROSIN-BASED POLYMER AS CREAM BASE 201 solution. One milliliter of phenolphthalein was added to the above mixture and titrated with 0.1 M KOH until the solution remained faintly pink after shaking for 30 seconds. The average of three readings was reported. The acid value = 5.61 N/W, where N is the number of milliliters of 0.1 molar KOH required, and W is the weight of the substance in grams. The specific gravity was determined using a simple displacement method using a gravity bottle as described in the Pharmacopoeia of India, 1996. The saponification value is the number of milligrams of KOH required to neutralize the free acid and to saponify the ester present in one gram of sample. It is determined as per the procedure described in the Pharmacopoeia of India, 1996. Four grams of rosin-based polymer was introduced into a 200-ml borosilicate glass fitted with a reflux condenser. To it 25 ml of ethanolic KOH was added along with a little pumice powder, and it was refluxed on a water bath for 30 minutes. One milliliter of phenolphthalein was added to it and titrated with 0.5 ml of HCL (a). The experiment was repeated omitting the rosin-based polymer (b). The saponification value = 28.05 (b - a)/w, where w is the weight of the substance taken. The HLB of the prepared rosin-based polymers for the present experiment was deter- mined by following a formula described by Griffin: HLB = 20 (1 - S/A), where S is the saponification number and A is the acid number of the acid. The viscosity of the prepared polymers was determined by using a Brookfield synchro- lectic viscometer, model RVT. The sample was taken in suitable size glass bottles, and the spindle was inserted in it up to the mark. Spindle number 1 was used in all the cases. The dial reading thus obtained was multiplied by the factor given in the chart supplied by the manufacturer. The composition of the polymers used to prepare the creams and their physicochemical properties are given in Tables I and II, respectively. PREPARATION OF THE CREAMS The ingredients used to prepare cream bases are listed in Table III. The cream bases were formulated using a regular fusion method: The surfactants (Tween 80/rosin-based) were added to water to which diclofenac diethylammonium was dissolved with constant stirring at 70øC in a glass beaker. Cetyl alcohol and stearyl alcohol were melted by heating at 70øC. The mixture ofpropylene glycol, isopropyl myristate, and glycerol was preheated to 70øC and added to the melted cetyl alcohol and stearyl alcohol. To this Table I Composition of Polymer 2 Composition Weight in grams Rosin 50 Castor oil 35 Glycerol 2.2 Sorbitol 14.7 Maleic anhydride 6 Pthaleic anhydride 2 Pentaerythritol