Process for the post-modification of homo and copolymers prepared by controlled free radical polymerization processes

Abstract

The instant invention pertains to the preparation of polymers or copolymers wherein in a first step a controlled free radical polymerization process is carried out and in a second step the resulting polymer is modified by transesterification reactions. The final modified polymer or copolymer is useful as a dispersant for pigments. Further aspects of the invention are the thus prepared polymers or copolymers, a pigment concentrate containing the polymer or copolymer and a coating material containing the pigment concentrate.

1 . A process for the preparation of a modified polymer or copolymer comprising the steps
 a1) polymerizing in a first step one or more ethylenically unsaturated monomers in the presence of at least one nitroxylether having the structural element   
       
         
           
           
               
               
           
         
          wherein X represents a group having at least one carbon atom and is such that the free radical X. derived from X is capable of initiating polymerization; or 
         a2) polymerizing in a first step one or more ethylenically unsaturated monomers in the presence of at least one stable free nitroxyl radical 
       
       
         
           
           
               
               
           
         
          and a free radical initiator;
 wherein at least one monomer used in the steps a1) or a2) is a C 1 -C 6  alkyl or hydroxy C 1 -C 6  alkyl ester of acrylic or methacrylic acid; 
 
         and a second step 
         b) comprising the modification of the polymer or copolymer prepared under a1) or a2) by a transesterification reaction with an alcohol which alcohol is an unsubstituted linear or branched C 8 -C 36 alkyl mono alcohol or a mono alcohol derived from ethylenoxide, propylenoxide or mixtures thereof with up to 100 C atoms 
         wherein step a1 or a2 is a controlled free radical polymerization which produces a polymer with a polydispersity index of 1.1-1.5. 
       
     
     
         2 . A process according to  claim 1  wherein the first polymerization step is carried out according to a1). 
     
     
         3 . A process according to  claim 1  wherein step a1 or a2 is carried out twice to form a block copolymer and in the first polymerization step the monomer or monomer mixture contains from 50 to 100% by weight based on total monomers of a C 1 -C 6  alkyl ester of acrylic or methacrylic acid and in the second polymerization step the ethylenically unsaturated monomer or monomer mixture comprises 4-vinyl-pyridine or pyridinium-ion, 2-vinyl-pyridine or pyridinium-ion, vinyl-imidazole or imidazolinium-ion, dimethylacrylamide, 3-dimethylaminopropylmethacrylamide, styrene, α-methyl styrene, p-methyl styrene or p-tert-butyl-styrene. 
     
     
         4 . A process according to  claim 1  wherein the polymer or copolymer is a gradient copolymer. 
     
     
         5 . A process according to  claim 1  wherein the structural element 
       
         
           
           
               
               
           
         
       
       is a structural element of formula (I) 
       
         
           
           
               
               
           
         
       
       wherein
 G 1 , G 2 , G 3 , G 4  are independently C 1 -C 6 alkyl or G 1  and G 2  or G 3  and G 4 , or G 1  and G 2  and G 3  and G 4  together form a C 5 -C 12 cycloalkyl group; 
 G 5 , G 6  independently are H, C 1 -C 18 alkyl, phenyl, naphthyl or a group COOC 1 -C 18 alkyl; 
 X is selected from the group consisting of —CH 2 -phenyl, CH 3 CH-phenyl, (CH 3 ) 2 C-phenyl, (C 5 -C 6 cycloalkyl) 2 CCN, (CH 3 ) 2 CCN, 
 
       
         
           
           
               
               
           
         
          —CH 2 CH═CH 2 , CH 3 CH—CH═CH 2  (C 1 -C 4 alkyl)CR 20 —C(O)-phenyl, (C 1 -C 4 )alkyl-CR 20 —C(O)—(C 1 -C 4 )alkoxy, (C 1 -C 4 )alkyl-CR 20 —C(O)—(C 1 -C 4 )alkyl, (C 1 -C 4 )alkyl-CR 20 —C(O)—N-di(C 1 -C 4 )alkyl, (C 1 -C 4 )alkyl-CR 20 —C(O)—NH(C 1 -C 4 )alkyl and (C 1 -C 4 )alkyl-CR 20 —C(O)—NH 2 , wherein R 20  is hydrogen or (C 1 -C 4 )alkyl and 
         * denotes a valence. 
       
     
     
         6 . A process according to  claim 1  wherein the structural element 
       
         
           
           
               
               
           
         
       
       is a structural element of formula (II) 
       
         
           
           
               
               
           
         
       
       wherein
 G 1 , G 2 , G 3 , G 4  are independently C 1 -C 6 alkyl or G 1  and G 2  or G 3  and G 4 , or G 1  and G 2  and G 3  and G 4  together form a C 6 -C 12 cycloalkyl group; 
 G 5 , G 6  independently are H, C 1 -C 18 alkyl, phenyl, naphthyl or a group COOC 1 -C 18 alkyl and 
 * denotes a valence. 
 
     
     
         7 . A process according to  claim 5  wherein the structural element of formula (I) is a compound of formula (O1) 
       
         
           
           
               
               
           
         
       
     
     
         8 . A process according to  claim 1  wherein the monomer in step a1 or a2 is selected from isoprene, 1,3-butadiene, α-C 5 -C 18 alkene, 4-vinyl-pyridine, 4-vinyl-pyridinium-ion, 2-vinylpyridine, 2-vinyl-pyridinium-ion, vinyl-imidazole, vinyl-imidazolinium-ion, dimethylacrylamide, 3-dimethylaminopropylmethacrylamide, styrene, α-methyl styrene, p-methyl styrene, p-tert-butyl-styrene and a compound of formula CH 2 ═C(R a )—(C═Z)—R b , wherein R a  is hydrogen or methyl, R b  is NH 2 , O − (Me + ), unsubstituted C 1 -C 18 alkoxy, C 2 -C 100 alkoxy interrupted by at least one N and/or O atom, or hydroxy-substituted C 1 -C 18 alkoxy, unsubstituted C 1 -C 18 alkylamino, di(C 1 -C 18 alkyl)amino, hydroxy-substituted C 1 -C 18 alkylamino, —O—CH 2 —CH 2 —N(CH 3 ) 2  or —O—CH 2 —CH 2 —N + H(CH 3 ) 2 An − ;
 An −  is a anion of a monovalent organic or inorganic acid; 
 Me is a monovalent metal atom or the ammonium ion and 
 Z is oxygen or sulfur. 
 
     
     
         9 . A process according to  claim 1  wherein in step b the alcohol is an ethoxylate of formula
   (A)R A —[O—CH 2 —CH 2 —] n —OH  (A)
 
 
       wherein R A  is saturated or unsaturated, linear or branched chain alkyl with 1-22 carbon atoms, or alkylaryl or dialkylaryl with up to 24 carbon atoms and n is 1 to 150. 
     
     
         10 . A process according to  claim 1 , wherein the alcohol is an unsubstituted linear or branched C 8 -C 36 alkyl mono alcohol. 
     
     
         11 . A process according to  claim 1  wherein step b comprises transesterification with an alcohol which alcohol is a polydimethylsilicone oligomer of formula (B) 
       
         
           
           
               
               
           
         
       
       wherein R B  is C 1 -C 18 alkyl, phenyl or C 7 -C 15 aralkyl; n is 1 to 50 and R′ is a linking group with 1 to 20 carbon atoms. 
     
     
         12 . A process according to  claim 1  wherein step b comprises transesterification with an alcohol which alcohol is a partly or fully fluorinated primary alcohol. 
     
     
         13 . A polymer or copolymer obtained by a process according to  claim 1 .