Title of Invention

"AN IMPROVED PROCESS FOR PREPARING STAR SHAPED BRANCHED POLYISOPRENE"

Abstract

This invention relates to an improved process for preparing star shaped branched polyisoprene characterized by the steps of heating a solvent being cyclohexane in a reaction vessel to a reaction temperature of 40-56°C, adding thereto isoprene premixed with a known catalyst selected from secondary butyl lithium and normal butyl lithium, allowing the temperature to rise due to the presence of the reaction till a steady state temperature is achieved, heating said reaction mixture to a temperature higher than said steady state temperature for completion of the polymerization step, and then reacting the linear polyisoprene with a coupling agent.

Full Text

:2 : SUMMARY OF INVENTION The present invention relates to an improved process for preparing star shaped branched polyisoprene. It is generally recogized in the art that polydienes have useful application as elastomers mainly in the tyre sector and as well as viscosity index improvers or tackiness agents. PRIOR ART Synthesis of polydienes and block copolymers of styrene and dienes by anionic polymerization has been reported by Morton and Fetters (Rubber Chem. & Tech. 1975, 48, 359) and Mc-Grath (Anionic Polymerization Kinetics, Mechanisms and Synthesis 1981; ACS Symposium Series Vol 166) and is known, in the polymer art, to provide precise control over many important properties such as molecular weight and distribution, stereochemistry, end group functionally, topology etc. While synthesizing polymers using bench top method, it has been recognized in the past by many workers from Phillips Petroleum Company (eg. in US Patent 3755273, issued Agu 28, 1973, dutch Patent 7700168 and Shell Oil Company (e.g in US Patent 4116917, issued Sept. 26,1978) that : 3 : deleterious impurities such as protonic: compounds carbonyl compounds, halogen compounds,, oxidizing agents etc. can kill some of the growing chains and thu* broaden the molecular weight distribution. For carrying out polymerization of isoprene in cyclohexane the usual procedure has been to titrate such impurities present in the initial feed comprising of solvent and monomer by butyl lithium (BuLi) at a temperature of about 30~3!:Pc before the addition of required quantity of BuLi. The polymerizations were carried out for 2.5-3 hrs at 50°C. The reaction is extended by 5 hours at 80° C for the synthesis of star polymers. Shell Oil Company in an earlier disclosure US Patent 3553295, dated Jan 5,, .1971), had indicated that cyclohexane could be purified by adopting steps like BuLi scavenging, activated alumina treatment and molecular sieves treatment. Hoover and Me~Brath (Polymer Preprints 1986 Sept, 150-1) have reported purification of cyclohexane by percolation over activated alumina (for deinhibition) and molecular sieves (for dehydration) in pressence of nitrogen which had previously been purified by percolation over molecular sieve. : 4 : Shell Cil Company in its disclosure (US Patent 3553295, issued Jan 5, 1971) had indicated that isoprene could be purified "by treatment with activated alumina to reduce the level of reactive impurities. In a comprehensive procedure for the purification of isoprene required for stereo-specific polymerization purpose, Ceausescu ( in Stereospecific Polymerization of Isoprene Pergamon Press Ltd., 1983), had adopted treatment with maleic anhydride for the steps of ( i.) the removal of eye. 1 open tad iene, (ii) distillation with a 5-TP column under purified nitrogen for removal of oxygen and the inhibitor and (iii) percolation over molecular sieves 5A for the removal of moisture, carbonyl compounds and acetylenic hydrocarbons. Hoover and Me Grath (Polymer Preprints 1986 Sept, 150-1) have adopted purification procedure for isopreru?, similar to the one adopted for cyclohexane but haves cautioned against excessive monomer residence times over molecular s 5 s sieves which might result in inaitu polyroerization and column fouling. Recently, J.E. He Gretth et.el have ^repor ted , 253-4) purification of technical grade divinyl benzene (DVB) by stirring with calcium hydride followed by exposure to neutral alumina and vacuum distillation from dibutyl inagnessiuiB, The prior art methods discussed above have the disadvantage of very long reaction durations of 7—9 hours for the synthesis of star-shaped polyisoprene including 2.5-3 hours for linear polymer. Another limitation of the prior art methods is virtual absence of any description on the process details for regulating the temperature etc. during the polymerization. Another disadvantage of the prior art methods is lack of adequate details for developing a complete purification methodology for solvent, taonomer and coupling agent. Prior art methods have also not reported the methods a* storage of purified solvent and monomers and subsequent handling i-f any, without any loss to their purity levels. While the above are the major disadvantages of the prior art methods, there are various other related aspects regarding the monitoring of quality/purity levels of solvent and monomers, activation of deinhibitors and dehydrants, purification of inert gas and regeneration of oxygen removing catalysts, which have not been described. OBJECT AND DESCRIPTION QF THE PRESENT INVENTION It is therefore, an object of this invention to propose an improved polymerization process for the preparation of hamopolymers and star polymers of i&oprerte with narrow molecular weight distribution. Another object of this invention is to propose a polymerization process for the preparation of homopolymers and star polymers of isoprene which is completed within short period of time say 2 hr- Still a further abject af this invention is to propose a polymerization process for the preparation of homopolymers and star polymers of isoprene having included therein an improved method for the purification of solvent, monomer and coupling agent. A still further object of this invention is to propose a polymerization process for the preparation of homopolymers and star polymers of isoprene and having included therein an improved method : 7 : of storage of purified solvent and manomers without any loss to their purity levels. Further objects and advantages of this invention will be more apparent from the ensuing description. According to this invention there is provided an improved process for preparing star shaped branched polyisoprene characterized by the steps of heating a solvent being cyclohexane in a reaction vessel to a reaction temperature of 40-56°C, adding thereto isoprene premixed with a known catalyst selected from secondary butyl lithium and normal butyl lithium, allowing the temperature to rise due to the presence of the reaction till a steady state temperature is achieved, heating said reaction mixture to a temperature higher than said steady state temperature for completion of the polymerization step, and then reacting the linear polyisoprene with a coupling agent. It has not been found that isoprene manomer can be polymerized using Butyl Lithium catalyst within half an hour of the start of the reaction. Additional one hour is required for converting the linear homopolyisoprene into star branched polyisoprene as a result of coupling reaction, with divinyl benzene. In accordance with the present invention, the entire polymerization is completed within a period of 25-30 minutes with quantitative conversion and molecular weight close to the oretical molecular weights with narrow molecular ! 8 S weight distribution. The polymerization process is a multistep process comprising in the addition o-f monower premixed with defined catalyst quantity to a solvent in a reaction vessel at a given temperature and regulation o-f the temperature for polymerisation. Addition of DVB, at this stage is carrried out for the synthesis of star branched polyisoprene which takes an hour more. The reaction is otherwise terminated : 9 : The present invention involves regeneration of oxygen removing catalysts, activation of deinhibitors and dahydrants, proper cleaning, purification and drying of glasswares, purification of solvent, monomer and coupling agent, storage and handling of purified solvent, monomer and coupling agent and storage, assay and handling of n-butyllithium. The inert gas such as nitrogen or argon is required to be absolutely free from oxygen and moisture. Conseguently, inert gas belonging to analytical reagents grade was further purified by passing through oxygen removal tower, packed with BASF catalyst R3-11 duly regemsratecl and gas drying tower packed with any powerful dehydrant such as activated molecular sieves 5A. The inert gas so purified is used in all the purification, transfer and polymerisation operations. The alumina was activated at 180-200 C°for 3- 4 hrs under a purified stream of inert gas. Similarly, the molecular sieves 5A was activated at 300-350°C for 6-8 hrs under the purified stream of inert gas. The activated alumina/sieves were preserved by storage either in an electric oven maintained at 120-130 C°or in > a glove box. : 10 : The air-less-wares and equivalent glass wares were scrupluously and meti culously cleaned with the help of a good quality detergent solution for the removal of any physical and chemical contaminants. The cleaned glasswars were dried in an electric: oven at 120- 130 t for a period not less than 12 hrs. The dried glassares were assembled hot and cooled under a stream of purified inert gas till they attained room temperature. For the purpose of storage of BuLi solutions, the catalyst solutions were packaged using sure/seal system and storing the bottles containing the BuLi solution, in a refrigerated storage cabinet. The synthesis of polyisoprenes and starbranched polyisoprene were carried out in eyelohexane. Accordingly, in accordance with the objectives of this invention suitable purification methods for eyelohexane, followed by subsequent storage methods with a view to obtain solvent ready for anionic polymerisation, were adopted. Quality checks for the purity levels in terms of moisture content, were made s 11 The solvent generally contains 4C*-5fiJ ppm moisture though higher moisture levels are not uncommon. The gross moisture front the solvent is removed by having the solvent re-fluxed over sodium wire in presence of the benzophenene -followed by distillation. This etep results in reduction of moisture level to 15-20 ppm. The next step in purification of solvent is scavenging of catalytic poisons by refluK from isoprenyl l i t h i um or a combination of 1.1-diphenyi ethyl ene and BuLi , followed by distillation over vigruew column. The storage of the solvent between two consecutive steps is an important aspect. Many methods like storage over a bed of activated molecular sieve* or under inert gas can be adopted. However, the best results are obtained by storing the solvent in glove box. The last step for the purif i cation comprises of percolation over alumina and molecular sieves 5A packed in a column (70cm x 2.5cm ) in a Is2 wt. ratio at a preferred rate of '299 *l/hr. This step ensures complete removal of inhibitors and moisture present at trace level. ! 12 : It is observed that no systematic account of the puri.ficat*cm method for isoprene has been presented in the 1iterature. Accordingly, in accordance with the objectives of this invention, purification methods for isoprene, followed by subsequent storage methods with a view to obtain monomer ready for anionic polymerization, were developed. Like for cyclohexane, rnoisutre levels of the monomer was also measured at various steps of purification. In the -first step of the purification of isoprene, monomer was purified by stirring with freshly sublimed maieic anhydride at i7. loading at hrs for the removal of cyclopentadiene and dicyclopentadiene inhibitors. In the second step, the monomer was stirred over BuLi and distilled over vigruex column. Storage of isoprene between two consecutive steps was carried out by covering the fiask containing : 13 : the? monomer with plastic sheets and storing in freezer. In the next step of the purification of monomer, the monomer was percolated over alumina and molecular sieves 5A using a set up similar to that adopted for the solvent. This step ensures complete removal of inhibitors and moisture present, at trace level. The monomer thus purified has moisture level less than 1C ppm and is quite suitable for anionic polymerization purposes. The coupling agent used for the synthesis of star-branched polyisoprene, is DVB. Method for the purification of DVB followed by subsequent storage methods with a view to obtain the coupling agent ready for carrying out coupling reactions, was developed. Like for cyclohexane and isoprene, moisture levels of the coupling agent was also monitore^d. The technical grade DVB, inhibited with antioxidant. „ is supplied as its solution in ethyl styrene isomers (55%). As their boiling points are very close to each other and as the isomers do not. 14 s participate in the coupling reactions their separation from DVB has not been considered necessary. For the removal of inhibitors, two methods were employed. According to the -first method, the DVB Mas utashed with saturaed solution of sodium hydroxide or potassium hydroxide, followed by washing with water for the removal of alkali and storage over fused CsCl-> in freezer. In the second method, the divinyl benzene was percolated over activated alumina. Both the methods give DVB of required purity level, In the second step, catalytic poisons and moisture were removed by scavenging DVB by divinyl benzyl lithium anion, formed by DVB, cyclobexane and BuLi f prior to distillation at reduced pressure 910 mm Hg). The use of this scavenging mixture leads to instantaneous polymerization in many cases and accordingly DVB has to be distilled at reduced pressure against anionic polymerization. The use of divinyl benzyl lithium as a scavenging agent has accordingly, turned cH.it to be not a very satisfactory proposition and « t *=* - il Aw * consequently, in a later development the scavenging mixture comprising of cyclohewane, 1,1 diphenylethylene and BuLi were used, which provided to be quite satisfacotry. DVB thus puri-fied has a moisture level of less than 10 ppm and is quite suitable -for- carrying out coupling reactions. The solvents, monomer and coupling agent are quite suitable, if the polymerizations are taken instantaneously. If it is desired to carry out polymerization on subsequent days, then in instant invention, the solvent, monomer and coupling agent have been stored by two methods successfully. According to the first method, the solvent is stared in the flask either over a bed of activated molecular sieves 5A, or under inert gas. The monomer iBoprene is once again stirred over BuLi and distilled over a vigruex column, in order to rule out the possibility of pressure and future growth of any polyi.soprene nuclei as a result of percolation over mole cul ar sieves, and the flask duly covered with plastic sheets is stored in a freezer, LVB is similarly 16 : stored after the removal of inhibitor. On the day of carrying out. polymerization, required quantity of solvent, monomer or coupling agent can be respectively treated with scaventing mixture and distilled into the reaction flask or addition funnel with pressure equilizer type or a flask, as the case may be. In the second method, the solvent, monomer and coupling agent are transferred sure-seal way directly inside the glove box, except that the solvent is stored at room temperature and the monomer and DVB are stored in a refrigerated storage cabinet maintained at -20°C to - 30°C. On the day of carrying out the reaction, required quantity of solvent, monomer or coupling agent is transferred out sure-seal way, without any need of terminal purification steps. The polymerization process involves multisteps. In the first step, transfer of solvent to the reaction vessel is carried out either by distillation or sureseal way. The reaction vessel comprises of an inert gas inlet, a thermo well pocket and a s 17 s te-f Ion-coated magnet. Th« reaction vessel containing the solvent is placed in an oil bath mounted on to a magnetic starrer. The temperature of the bath is achieved by an immersion heater and regulated by & contact thermometer—jumo relay assembly. The inert gas inlet is connected to the purified inert gas stream with outlet provided through a double walled condenser mounted onto the reaction vessel. Ice cold water circulation is commenced through the condenser to arrest the escape of monomer during its addition and pol yrner i 2 at i on. The next step of the process comprises °^ addition of monomer prefixed with required catalyst quantity to the reaction vessel maintained at set temperature of the solvent. In the instant invention, it has been experienced that this set temperature is 40°C and above if the catalyst selected for the polymerization is sec—BuL.i . If the catalyst chasers for the polymerization is n-BuLi, then this set temperature is 5O°C and above. With the commencement of addition of ButLi mixed isoprene to the solvent maintained at the set temperature, the- temperature of the feed starts rising due to the rapid initiation of polymerization. s 18 t In fact, such rapid initiation steps are responsible for a narrow molecular weight, distribution and any attempt at. this juncture? to disturb this rise in temperature by way of attempting to iow-jr the temperature o-f the oil bath, by replacing the hot oil by cold 01 i is likely to result in .immature termination of growing polymeric chain. Accordingly, in the third step of processT when an estotherroicity by about 15-26°C has been attained in a period of 8-18 minutes o-f the completion of addition o-f monomer and the temperature of the feed no longer rises, the temperature of the bath is quickly raised to a temperature higher than the maximum of the temperature attained. Under this condition, the reaction is allowed to run for 15 minutes. In the instant invention, a time of 15 minutes has been found to be sufficient for attaining quantitative conversion. For preparing the star branched polymer, the reaction is continued further in presence of DVB, Appearance of blood red colour and its stability are indicative of the start and continuance of the coupling reaction. In the instant invention, a time of 1 hourhas been found to be 5 19 ! sufficient for obtaining maximum star content. The last step is the recovery of the polymer from the polymer solution. This comprises of precipitation into a large excess of methanol, which has been predoped with 0.5"/. antioxidant such as ditert-butyl paracresol. The step avoids the degradation of polymer during storage. The polymer so precipitated is dried in vacuum oven at 50--6 Specific Example of the Invention Under mentioned examples illustrated the process for the synthesis of polyisoprenes and starbranched polyisoprenes at 20-50g batch size levels, following the philosophy as contained in the detailed description section of the instant invention. These examples should be considered only as illustrative in nature and in no case, should be considered to limit the scope of this invention. Moisture levels of the solvent, monomer and DVB were measured by Karl Fischer moisture titrator. The average molecular weights Mw,Mn and molecular : 20 s weight, distribution (Hw/fln) and star content were determined by GPC using linear polyisoprene standards. Example 1.5 liter eyelohexane was taken in a solvent repurification still and 15g sodium wire was pressed into it. The solvent was refluxed for 8 hours and stored under purified Ar. The solvent was subsequently distilled into 3-neck 2-L RB flask. The distilled solvent was scavenged by refluxing from isoprenyl lithium (formed by iml isoprene., 10 ml eye lohexane and 10 mmol n-BuLi) with the appearance of deep crange colour for 2 hours and distilled over a vigruex column into single neck 2™L flask. The solvent, contained in the flask was stored under purified Ar. The solvent was dried by percolation over activated alumina and molecular sieves 5A. The purified solvent was stored under purified Ar till use. On the date of carrying out reaction 600 ml of cyclahexane was transferred into a 3 neck RB flask and scavenged by refluxing from iaoprenyl lithium (formed by 0.5 ml isoprene, 5 ml eyelohexane s 21 : and 5 atttoi n— BuLi with the appearance of deep orange colour -for 2 hr and distilled 230 r»l over a vigruex column into 4 -neck 500 ml reaction -flask. The moisture level of the solvent was 7 ppm. 2, 1.5 liter cycl. ohex ane was taken in a solvent repurif ication still and 15 g. sodium wire was pressed into it. ©.5 g. benzophenene was also added. The solvent was re-fluxed -for 8 hrs. and stored under purified Ar. The solvent was subsequently distilled into 3-**eck 2L RB 11 ask. The distilled solvent was scavenged by re-fluxing -from 2 mmoi 1,1 diphenyl ethyl ane and 10 MMBol n— BuLi for 2 hours and distilled over a vigruex column into single neck 2-L -flask. The solvent contained in the -flask was stored inside the glove box. The solvent was dried by percolation over activated alumina and molecular sieves 5A. The purified and dried solvent had a moisture level o-f & ppm. The solvent was, there-fore, transferred into a 1L sure— seal bottle for storage inside the glove box, till use. On the date of reaction, solvent was : 22 : transferred from the sure-seal bottle to the reaction flask. Example g.. 1.5 litre isoprene was taken in a single neck 2-L RB flask and 10 g. freshly sublimed maleic anhydride in powere^d from was added to it. The contents were allowed to stir for 4 hours at 5°C under purified Ar. The monomer was filtered into a 3 neck 2-L flask and subsequently scavenged by stirring from 5 mmol n~ BuLi for 3 hrs and distilled over vigruex column into single neck 2--L flask. The isoprene contained in the •flask duly covered with plastic sheets was stored in freezer. The monomer was dried by percolation over activated alumina and molecular sieves 5A, followed by stirring from 2 mmol n-BuLi for 2 hours and distilled over a vigruex column into single neck 2-L flask. The purified monomer contained in flask duly covered with plastic was stored in freezer. On the date of carrying out reaction 180 ml of isoprene was transferred into a 3 neck 500 ml RB flask and scavenged by stirring from 1.5 mmol n-BuLi for i hour and distilled 68 «*1 over a vigruex column into a graduated addition funnel, pressure equalizer type. The moisture level of the monomer was 5 ppau Example 4 1. 5 liter isoprene was taken in a single neck 2-L RB flask and i anhydride in powdered form was added to it. The contents were allowed to stir for 4 hrs at 5°C under purifed ftr. The monomer was filtered into a 3 neck 2-L flask and subsequently scavenged by stirring from 5 mnol n~-BuLi for 3 hours and distilled over a vigruex column into a single neck 2-L flask. The isoprnee contained in the flask duly covered with plastic sheets was stored in freezer. The monomer was dried by percolation over activated alumina and molecular sieves 5A, followed by stirring from 2 fltmol n—BuLi for 2 hours and distilled over a vigruex column into a single neck 2-1. flask. The purified and dried monomer- had a moisture level of 5 ppm. The monomer was, therefore, transferred into a L sure seal bottle for storage in a refrigerated storage cabinet maintained at 26°C inside the glove box, s 24 s till use. On the date of reaction, monomer is transferred from sure seal bottle to the additin funnel f pressure equalizer type. Example §. 30® ml DVB was deinhibited by percolation over activated alumina, followed by its storage in freezer. 40 ml of DVB taken in 2 neck 250 ml RB flask Mas purified by scavenging by stirring fro* di vinyl benzyl lithium anion (formed by 0.5 »«1 DVB* 5 ml cyclohexane and 2 romol n— BuLi under purified Ar and distillation at reduced pressure (10mm Fg) for immediate use. The «toisutre level of DVB was 8 ppm. 100 ml DVB was deinhibited by percolation over activated alumina followed by scavenging by stirring front scavenging mixture comprising of 0.5 mmole it i diphenyl ethylene, 5 ml cyclohexane and 2 mmol n- BuLi under purified Ar and distillation at reduced pressure level of 8 ppm. The DVB was, therefore transferred into a 1(9 ml sure seal battle for storage in a refrigerated storage cabinet maintained at — 26°C inside the glove box, till use. : 25 s Example 7 The reaction flask containing 230 ml solvent was placed in an oil bath mounted onto a magnetic stirrer. A thermometer was placed in the thermo well pocket. The intert gas inlet was connected to the purified inert gas stream with outlet provided through a double walled condenser mounted onto the reaction vessel. Ice? cold water circulation was commenced through the condenser. The temperature of the bath of 50°C was achieved by an inmersion heater and regulated by a contact thermometer junto relay assembly. As soon as the solvent attained the temperature of 50° C, .1.25 mmole of n-Bul_i was added to 60 ml isoprene contained in the addition funnel and the addition funnel was placed onto the remaining neck of the reaction vessel. The isoprene alongwith the catalyst was added slowly into the reaction flask. With the addition, the temperature of the flask started rising and within 13 minutes reached a maximum of 70°C. The temperature of the oil bath was immediately raised to 80°C and reaction allowed to run for 20 minutes. After completion of the reaction, the reaction mixture was poured into a large excess of methane] , which had been previously doped with 0.57. di tert butyl para cresol. The polymer was isolated s 26 i redissoived in toluene and reprecipitated into methanol. The polym«r so obtained was dried in vacuum oven at 50°C giving a yield of 40.8 g (100%) with a mol wt. of Mw 47000, Hn 39000 and Mw/fin 1.19. Example g The reaction -flask containing 115 ml solvent was placed in an oil bath in an experimental set up similar to that described in Example 7. As soon as the solvent attained a temperature of 56°C, 0.3125 mmole of BuLi was added to 30 ml isoprene and the reaction mixture attained a maximum temperature of 76°Cf in a period o4 12 minutes. The temperature of the oil bath was raised to 80°C and reaction allowed to run for 15 minutes. At th« end o-f reaction, the poly«»er was processed in an exactly similar manner as mentioned in Example 7. The yield of the polymer was 100% with «w 75000, Mn 6500® and Mw/Hn of 1,15. Example 2 The reaction flask containing 115 ml solvent was placed in an oil bath in an experimental set up similar to that described in Example 7. s 27 i fts soon as the solvent attained a temperature of 56°C, 0.1563 mmole of n-BuLi was added to 30 ml isoprene and the reaction mixture attained a maximum temperature of 75°Cf in a period o-f 13 minutes. The temperature o-f the oil bath was raised to 80°C and reaction allowed to run for 15 minutes. At the end o-f reaction, the polymer was processed in an exactly similar manner as mentioned in Example 7. The yield of the polymer was 100£ molecular weights o-f MM 131009, Mnl0a000 and Hw/Sn of 1.21- Example JJ| The reaction flask containing 230 ml. solvent was placed in the oil bath in an experimental set up similar to that, described in Example 7. As soon as the solvent attained a temperature of 50°C, 1.875 romole of n-BuLi was added to 60 ml isoprene and the reaction temperature attained a maximum temperature of 71°C within 15 minutes. The temperature o-f the oil bath was immediately raised to 80°C and reaction allowed to run for 17 minutes. At the end of 17 minutes, 13.85 matoi DVB was injected into the reaction flask gradually. This resulted in an appearance of the dark red colourf which remained stable for rest of the : 28 s reaction duration of 1 hour. At the end of the reaction, the polymer was processed in an exactly similar manner as metioned in Example 7. The yield of the polymer was 100% with molecular weights of Nw 31900, Mn28900 and Mw/lin of 1.10 for the arm and Mw 564800, Mn 444000 and Mw/Mn of 1.27 for the star, the star content was 93% with 18 arms. Example 11 The reaction flask containing 115ml solvent was placed in an oil bath in an experimental set up similar to that described in Example 7. As soon as the solvent attained a temperature of 53^, 0.3125 mmole of n-BuLi was added to 30 ml isoprene and the reaction mixture attained a maximum tetnperture of 73°C in a period of 12 minutes. The temperature of the oil bath was raised to S0°C and reaction allowed to run for 20 minutes. At the end of 20 minutes, 0.3125 mmole of DVB was injected into the reaction flask gradually. This resulted in an appearance of dark red colour, which remained stable for rest of the duration of « 29 s 1 hour. At the end of reaction* the polymer processed in an exactly similar manner, as mentioned in Example 7. The yield of the polymer was 104BX with 88% star content having molecular weights of Mw 46880B, Mn430000 and Mw/Mn of t.09 and those of th* arm da having Mv* 78000, Mn75000 and Mw/Mrt of 1.04. The number of arms obtained was 6. Example 12. The reaction flask containing 115 ml solvent «*as placed in an oil bath in an experimental set. up similar to that described in Example 7. As soon as the solvent attained a temperature of 55°C. 0.15&3 mmuJe of n-BuLi was added to 30 ml isoprene and the reaction mixture attained a maximum temperature of A7°Cf in a period of 12 minutes. The temperature of the oil bath was raised to 8 reaction allowed to run for 20 minutes. At the end of 20 minutes, 0.469 mmole of DVB was injected into th* reaction flask gradually. This resulted in an appearance of dark red colour, which remained stable for rest of the duration of 1 hour. At the end of reaction, the : 30 t polymer was processed in an exactly similar manner as mentioned in Example 7. The yield of the polymer was 100% with 89% star content having molecular Heights of Mw 701000, Mn 559000 and Mw/Mn of 1.25 and those of the arm as having MM 132000, Mn102000 and Mw/Mn of 1.29. The number of arms obtained was &. WE CLAIM; 1. An improved process for preparing star shaped branched polyisoprene characterized by the steps of heating a solvent being cyclohexane in a reaction vessel to a reaction temperature of 40-56°C, adding thereto isoprene premixed with a known catalyst selected from secondary butyl lithium and normal butyl lithium, allowing the temperature to rise due to the presence of the reaction till a steady state temperature is achieved, heating said reaction mixture to a temperature higher than said steady state temperature for completion of the polymerization step, and then reacting the linear polyisoprene with a coupling agent. 2. An improved process as claimed in claim 1 wherein said coupling agent comprises divinyl benzene. 3. A process as claimed in claim 1 wherein the reaction temperature is atleast 40°C for secondary butyl lithium. 4. A process as claimed in claim 1 wherein the reaction temperature is atleast 50°C for normal butyl lithium. 5. A process as claimed in claim 1 and 2 wherein said steady state temperature is preferably in the range of 67 to 76°C. 6. A process as claimed in claim 1 wherein the said polymerization is completed within 30 to 40 mins. 7. A process as claimed in any of the preceding claims wherein said solvent and monomer treated with alumina and molecular sieve 5A° prior to its use having a purity/level of moisture of less than 10 ppm. 8. An improved process for preparing star shaped branched polyisoprene substantially as herein described and illustrated in the examples.

Documents:

798-del-1999-abstract.pdf

798-del-1999-assignment.pdf

798-del-1999-claims.pdf

798-del-1999-correspondence-others.pdf

798-del-1999-correspondence-po.pdf

798-del-1999-description (complete).pdf

798-del-1999-form-1.pdf

798-del-1999-form-10.pdf

798-del-1999-form-19.pdf

798-del-1999-form-2.pdf

798-del-1999-form-3.pdf

798-del-1999-petition-138.pdf