solvent containing at least an alcohol (particularly, methanol  or the like) or water is preferred as the precipitation or repre› cipitation solvent.  (Mw/Mn, sometimes referred to as "polydispersity") is pref› erably from 1 to 5, more preferably from 1 to 3, still more  preferably from 1 to 2.  As the hydrophobic resin (HR), various commercial prod› ucts may be used, or the resin may be synthesized by a  conventional method (for example, radical polymerization).  For example, the general synthesis method includes a batch  polymerization method of dissolving monomer species and  5  an initiator in a solvent and heating the solution, thereby  effecting the polymerization, and a dropping polymerization  method of adding dropwise a solution containing monomer  species and an initiator to a heated solvent over 1 to 10 hours.  A dropping polymerization method is preferred. The reaction  solvent includes, for example, tetrahydrofuran, 1,4-dioxane,  15  ethers such as diisopropyl ether, ketones such as methyl ethyl  ketone and methyl isobutyl ketone, an ester solvent such as  ethyl acetate, an amide solvent such as dimethylformamide  and dimethylacetamide, and the above-described solvent  capable of dissolving the composition of the present inven- tion, such as propylene glycol monomethyl ether acetate,  propylene glycol monomethyl ether and cyclohexanone. The  polymerization is more preferably performed using the same  solvent as the solvent used in the positive resist composition  of the present invention. By the use of the same solvent, 25  production of particles during storage can be suppressed.  The polymerization reaction is preferably performed in an  inert gas atmosphere such as nitrogen or argon. As for the  polymerization initiator, the polymerization is started using a  commercially available radical initiator (e.g., azo-based ini- tiator, peroxide). The radical initiator is preferably an azo› based initiator, and an azo-based initiator having an ester  group, a cyano group or a carboxyl group is preferred. Pref› erable initiators include azobisisobutyronitrile, azobisdim- ethylvaleronitrile,  dimethyl  2,2’-azobis(2-methylpropi- onate), etc. The concentration in the reaction is from 5 to 50  mass %, preferably from 30 to 50 mass %, and the reaction  temperature is usually from 10 to 150°  C., preferably from 30  to 120°  C., more preferably from 60 to 100°  C.  After the completion of reaction, the reaction solution is  allowed to cool to room temperature and purified. In the  purification, there may be applied a conventional method, for  example, a liquid-liquid extraction method of applying water  washing or combining it with an appropriate solvent to  remove residual monomers or oligomer components; a puri- fication method in a solution sate, such as ultrafiltration of  extracting and removing only polymers having a molecular  weight not more than a specific value; a reprecipitation  method of adding dropwise the resin solution in a poor sol› vent to solidify the resin in the poor solvent and thereby  remove residual monomers and the like; and a purification  method in a solid state, such as washing of a resin slurry with  a poor solvent after separation of the slurry by filtration. For  example, the resin is precipitated as a solid by contacting the  reaction solution with a solvent in which the resin is sparingly  soluble or insoluble (poor solvent) and which is in a volume  amount of 10 times or less, preferably from 10 to 5 times, the  reaction solution.  The solvent used at the operation of precipitation or repre› cipitation from the polymer solution (precipitation or repre› cipitation solvent) may be sufficient if it is a poor solvent for  the polymer, and the solvent which can be used may be  appropriately selected from, for example, a hydrocarbon, a  halogenated hydrocarbon, a nitro compound, an ether, a  ketone, an ester, a carbonate, an alcohol, a carboxylic acid,  water, and a mixed solvent containing such a solvent, accord› ing to the kind of the polymer. Among these solvents, a  Specific examples of the hydrophobic resin (HR) are illus› trated below. Also, the molar ratio of repeating units ( corre› sponding to respective repeating units starting from the left),  weight average molecular weight and polydispersity of each  resin are shown in Table 1 below.  Incidentally, after the resin is once precipitated and sepa› rated, the resin may be again dissolved in a solvent and then  put into contact with a solvent in which the resin is sparingly  soluble or insoluble. That is, there may be used a method  involving, after the completion of radical polymerization  reaction, bringing the polymer into contact with a solvent in  which the polymer is sparingly soluble or insoluble, to pre› cipitate a resin (step a), separating the resin from the solution  (step b ), anew dissolving the resin in a solvent to prepare a  resin solution A ( step c ), bringing the resin solution A into  contact with a solvent in which the resin is sparingly soluble  or insoluble and which is in a volume amount ofless than 10  times (preferably 5 times or less) the resin solution A, to  precipitate a resin solid (step d), and separating the precipi› tated resin ( step e ).  The precipitated or reprecipitated polymer is usually sub› jected to commonly employed solid-liquid separation such as  filtration and centrifugation, then dried and used. The filtra› tion is performed using a solvent-resistant filter element pref› erably under pressure. The drying is performed under atmo› spheric pressure or reduced pressure (preferably under  reduced pressure) at a temperature of approximately from 30  to 100°  C., preferably on the order of 30 to 50°  C.  The temperature at the precipitation or reprecipitation may  be appropriately selected by taking into account the efficiency  or operability but is usually on the order of 0 to 50°  C.,  preferably in the vicinity of room temperature (for example,  approximately from 20 to 35°  C.). The precipitation or repre› cipitation operation may be performed using a commonly  employed mixing vessel such as stirring tank by a known  method such as batch system and continuous system.  The amount of the precipitation or reprecipitation solvent  used may be appropriately selected by taking into account the  efficiency, yield and the like, but in general, the amount used  is from 100 to 10,000 parts by mass, preferably from 200 to  2,000 parts by mass, more preferably from 300 to 1,000 parts  by mass, per 100 parts by mass of the polymer solution.  100  US 9,069,246 B2  99  [Chem. 52]  (HR-1)  CH3  CH3  I  I  ---f CH2 - C-,-- ---fCH2-Cr- OAO  OAO  l  C3F7  (HR-2)  ---fCH2-CH+- o~o  I  CH2  I  -Si-- 0 