FIELD OF INVENTION The present invention relates to metal salts of amino acids useful for co-polymerization of epoxides and its preparation thereof. More particularly, it describes the preparation of metal salts of amino acids derived from low cost, biodegradable amino acids and corresponding metal precursors and their uses in the synthesis of poly(alkylene carbonate) polymers formed by the copolymerization of carbon dioxide and epoxides. BACKGROUND & PRIOR ART OF INVENTION Carbon dioxide (C02) has seriously been considered as a major environmental pollutant that causes a global warming. Despite many challenges to approach the activation of C02, a lot of explorations have been carried out to transform C02 into useful chemicals. Utilization of carbon dioxide has advantages due to it's readily availability, cheap, non-flammable and non-toxic nature. In this regard, the use of C02 for the synthesis of polymeric material such as poly(alkylene carbonates) is one of most valuable application. Due to their toughness, outstanding thermal stability, outstanding transparency, water resistance, biodegradability and optical clarity, they are widely used for structural parts, impact-resistant glazing, streetlight globes, household appliance parts, and components of electrical/electronic devices, compact |T discs, automotive applications, reusable bottles, food and drink containers, and many other re 2 o CM o O CM being produced from copolymerization of carbon dioxide and an alkylene oxide such as propylene oxide (PO), styrene oxide (SO) and cyclohexene oxide (CHO). In this regard, US patents 3,900,424, 3,953,383 and 3,585,168 described the preparation of poly(alkylene carbonate) by copolymerization of an epoxide, such as propylene oxide, ethylene oxide, styrene oxide, isobutylene oxide or epichlorohydrin, and carbon dioxide under the pressure of carbon dioxide gas and in the presence of organometallic compounds, as a catalyst. However, longer reaction time, poor product yield, lower selectivity and difficult handling of organometallic reagents are certain drawbacks. Japanese patent (JP patent 02,575,199 and 02,575,199) disclosed the use of expensive metal coordination compound of porphyrin as the catalyst for the synthesis of poly(alkylene carbonate). However, the polymer obtained had relatively lower molecular weight (about 5,000), longer reaction time (10 days) and poor polymer yield (103 to 104 grams of polymer per mole of the catalyst). Chinese patent (CN 89,100, 701.6 and CN 91, 109, 459.8) reported the polymer supported anionic ligands bimetallic catalyst system for the synthesis of poly(alkylene carbonate). Catalytic efficiency can be obtained 104 g polymer per mole of the catalyst. But final product separation is difficult from the carrier generated. Hsiang et al. (US patent 4,783,445) disclosed a process for the synthesis of poly(alkylene carbonate) in presence of catalysts, which are soluble in a variety of solvents are prepared by reacting zinc compounds with anhydrides in the presence of an alcohol or by reacting zinc salts with a monoester of a dicarboxylic acid. These catalysts can be added as a solution to a mixture of epoxides and carbon dioxide to prepare poly alkylene carbonates. Disadvantages of this process are low catalytic activity and homogeneous catalyst system. This method includes a 3 reaction of zinc salts with a dicarboxylic acid monoester in an organic solvent, and the yield is 5.1 to 12.4 gram per gram of the catalyst. Motika et al. (US patent 5,026,676) disclosed a process for the synthesis of zinc dicarboxylic acid ester in which zinc oxide reacts with dicarboxylic acid in the presence of an organic solvent. Glutaric acid and adipic acid based catalysts showed higher activity than the known zinc dicarboxylic acid ester catalyst and the catalyst production is about 2 to 26 grams of the aliphatic polycarbonate per gram of catalyst. Coates et al. (US patent 6,133,402 and J. Am. Chem. Soc, 2002, 124, 14284) reported a process for preparing highly active zinc based catalyst having two ligands in which one is propagating group for producing poly(alkylene carbonate) from epoxide and carbon dioxide. Poly carbonate yield was found to be 235 moles per mole of catalyst with the formation of 13-25% of cyclic carbonate as a byproduct. Yuezhong et al. (US patent 6,844,287 B2) disclosed a process for preparing supported zinc dicarboxylate catalysts using silica support with high activity for the copolymerization of carbon dioxide and epoxides. In the present invention, the first step involves the formation of zinc catalyst from zinc oxide and dicarboxylic acid such as succinic acid, glutaric acid, adipic acid, pimelic acid and suberic acid followed by immobilization to silica support (weight ratio from 1/1 to 1/15). The silica support can be selected from the group consisting of aerosil, silica gel for chromatography or reagent grade silicon dioxide. Chinese patent (CN 200410021316.5) disclosed a two component catalyst system involving tetra dentate-Schiff-base-metal-eomplex-and-quaternary-ammonium-orphosphohium saltsTCatalytic efficiency was found to be about 105 g polymer per mole of catalyst. Kim et al (WO -patent 2015005616 Al 20150115) disclosed a preparation for cobalt (III) complexes with salen-type ligands as catalyst for preparation of poly (alkylene carbonate). Brym et al (US patent 2014/0200328 Al) disclosed a process for preparing a zinc dicarboxylate from a zinc compound and a C4-C,0 dicarboxylic acid in the presence of a cationic emulsifier and a solvent. In the present invention cationic emulsifier was used to prepare zinc dicarboxylate crystallize rods with different morphologies. Jeong et al (US patent 8,785,592 B2) disclosed a method for preparation of poly(alkylene carbonate) having cross-linked high molecular weight chains by introducing a di epoxide compound to alternating copolymerization of an epoxide compound and carbon dioxide using a metal(III) complex prepared with a salen-type ligand containing quaternary ammonium salts as a catalyst. Thus, the drawbacks such as mostly homogeneous catalyst system, low activity catalyst, long reaction times, difficult handling of organometallic catalysts and formation of cyclic carbonates as byproduct makes the hitherto known processes of less practical utility. Reference may be made to the article Progress in Chemistry 23 (2011) 614 by Xianhong et al where they developed y-Al203 supported rare earth ternary catalyst with high activity for. the copolymerization of carbon dioxide and propylene oxide. The designed catalyst was prepared either by reacting ZnEt2 with Y (CCl3COO)3-glycerin impregnated support (in situ supported oT catalyst) or by initial synthesis of the rare earth ternary catalyst followed by dispersion on the G) CO _2 support (independent supported catalyst). ?T Reference may also be made to the article J. App. Polym. Sci. 123 (2012) 977-985 by Zhang et tt : al-where-t-hey-used-douW^^ CO o CO o 99 % without any side product. DETAILED DESCRIPTION OF INVENTION According to the present invention, metal salts of amino acids were prepared by reaction of biocompatible amino acids selected from the group of glycine, aspartic acid, glutamic acid, cysteine and lysine with metal salt precursors selected from group zinc chloride, zinc acetate, copper chloride, copper acetate, copper sulfate, nickel acetate, chromium chloride, cobalt acetate and cobalt chloride in the ratio of 1:1 to 5:1 in a polar protic medium at temperature in the range 50-70 °C and atmospheric pressure for duration in the range of 2-5 h. The prepared amino acid salt of metal was used as heterogeneous catalyst for copolymerization of epoxides such as propylene oxide, styrene oxide, glycidyl methacrylate, cyclohexene oxide and other synthetic epoxides etc. with carbon dioxide to synthesize poly(alkylene carbonate) in a solvent-less medium. The copolymerization experiments were carried but in a 100 ml autoclave reactor containing amino acid salt of metal catalyst in the range of 0.02 to 0.5 wt % with carbon dioxide gasheld specific pressure (20-50 bar) at specific temperature (60-130 °C) under stirring for specific time (5-50 h). After the certain period of time the heater and stirrer were turned off, the system was cooled down to room temperature and the pressure was slowly released. The _ polymer was collected and the catalyst was easily separated by simple filtration or centrifngatjon aT m « Following are the examples given Q . to further illustrate the invention and should not be construed CD CN E o to limit the scope of the present invention. Example 1-5 CO o CO o was solid, white in color and having melting point in the range of 300-310 °C. Elemental analysis of the synthesized zinc glycenato {Zn(gly)2}, % obtained (calculated), C% 23.32 (22.51), H% (3.65 (3.75), N% 13.82 (13.19). In the FTIR, the characteristic vibrational frequencies related to Vas (Coo") and Vs (Coo") in glycine was found to be 1680 and 1391 cm"1, respectively (Fig. 1). The synthesized catalysts were tested for copolymerization of propylene oxide with C02 into a 100 ml stainless steel autoclave reactor equipped with probes for temperature, pressure, . and heat demand. The reactor was charged with 0.75 g of the catalyst (1-5) and propylene oxide (0.25 mol, 12 ml). The reactor was then charged with 30 bar of C02 and the mixture was heated and maintained at 110 °C. After the certain period (8 h) of time the heater and stirrer were turned off, the system was cooled down to room temperature (20-35 °C) and the pressure was slowly released. The polymer was collected and the catalyst was easily separated from the polymer by ^ diluted with acetone and centrifugation. The yield was determined on the basis of the weight of the residue left after evaporation of diluted polymer. Polymer was then analyzed by 'H NMR. The results and yield of obtained poly propylene carbonate using zinc salts of different amino CD D OS Q. CD £ o CO o CO o 99 % without observing any by-product. • The developed catalyst is very cost effective and can be easily synthesized and therefore the present invention has a great potential for development of commercial process for synthesizing polycarbonates from epoxides and C02. We Claim: 1. Metal salts of amino acids useful for copolymerization of epoxides with CO2, consisting of: metal salt precursors and biocompatible amino acids in a molar ratio in the range of 1:1 to 1:5 possessing vibrational frequencies related to Vas (Coo") and Vs (Coo") in glycine to be 1680 and 1391 cm'1, respectively. 2. The metal salt of amino acids as claimed in claim 1, wherein amino acids are selected from the group of glycine, aspartic acid, glutamic acid, cysteine and lysine. 3. The metal salt of amino acids as claimed in claim 1, wherein metal salt precursors are selected from the group of zinc chloride, zinc acetate, copper chloride, copper acetate, copper sulfate, nickel acetate, chromium chloride, cobalt acetate and cobalt chloride. 4. A process for the preparation of metal salts of amino acids as claimed in claim 1, comprising the process steps of: i)reacting biocompatible amino acids with metal salt precursors in a ratio in the range of 1:1 to 5:1 in a polar protic medium at a temperature in the range of 50-70 ° C at atmospheric pressure for a period in the range of 2-5 hrs to obtain a clear solution, ii) adding drop-wise hydroxide solution in clear solution of step i) to adjust pH in the range of 6-10 to obtain precipitate, iii) separating the metal salts of amino acids from precipitate by centrifugation, washing and drying. ^^^he-proeess-as-elaimed4n-eM 6. The process-as claimed in claim 1, wherein polar protie medium is hot distilled water, ethanol, methanol, butanol, isopropanol, preferably water. 7. A process for copolymerization of propylene oxide with carbon dioxide using metal salts of amino acids (catalyst) as obtained in claim 1, comprising steps of: i) copolymerizing epoxides with carbon dioxide in a autoclave batch reactor containing the metal salt of amino acids in the range of 0.02 to 0.5 wt %, epoxides to catalyst weight ratio in the range of 10:1 to 100:1, at temperature in the range of 50-150 °C and pressure of C02 in the range for 10-60 bar for time period in the range of 5-30 h with stirring under solvent less conditions, ii) cooling the reactor contents of step i) to temperature in the range of 20 to 35 °C and separating polymer, poly(alkylene carbonate) from the reaction mixture by extraction with polar aprotic solvent, iii) recovering the catalyst by filtration or centrifugation for reuse. 8. The process as claimed in claim 7, wherein epoxides used for the copolymerization with CO2 were selected from the group consisting of propylene oxide, styrene oxide, cyclohexene oxide and glycidyl methacrylate. 9. The process as claimed in claim 7, wherein the copolymerization of epoxides with carbon dioxide is carried out in the temperature range,, preferably 100-120 °C. 10. The process as claimed in claim 7, wherein the copolymerization of epoxides with carbon dioxide is carried out under the pressure, preferably in the range of 20-40 bar. —1-1-—The-proeess-as~claimed-in-claim-7—wherein^the_copo1ym"erizatton~of epoxKJes~~witlT carbon dioxide is carried out for the preferable duration of 5-18 h. 12. The process as claimed in claim 7, wherein, the conversion of epoxide to corresponding poly(alkenyl)carbonate is in the range of 40-80 %. 13. The process as claimed in claim 7, wherein the selectivity of poly(alkylene carbonate) in the copolymerization of epoxide and carbon dioxide is 100 % without any side product.