Synthesis of polymers from cyclic diolides

Abstract

Biodegradable polymers with advantageous physical and chemical properties are described, as well as methods for making such polymers. In one embodiment, a new chemical synthesis route to technologically important biodegradable poly(3-hydroxybutyrate) (P3HB) with high isotacticity and molecular weight required for a practical use is described. The new route can utilize racemic eight-membered cyclic diolide (rac-DL), meso-DL, or a rac-DL and meso-DL mixture, derived from bio-sourced dimethyl succinate, and enantiomeric (R,R)-DL and (S,S)-DL, optically resolved by metal-based catalysts. With a stereoselective racemic molecular catalyst, the ROP of rac-DL under ambient conditions produces rapidly P3HB with essentially perfect isotacticity ([mm]>99%), high crystallinity and melting temperature (T m =171° C.), as well as high molecular weight and low dispersity (M n =1.54×10 5 g/mol, Ð=1.01).

What is claimed is: 
     
         1 . A copolymer comprising a polyester of lactone monomers and Formula IA: 
       
         
           
           
               
               
           
         
       
       wherein:
 n is 10 to about 10,000; and 
 R is (C 1 -C 18 )alkyl, (C 1 -C 8 )alkenyl, (C 1 -C 8 )alkynyl, benzyl, or phenyl; and 
 Formula IA comprises at least 95% isotactic triads with respect to the stereocenters of substituents R on the polymer chain, wherein the at least 95% isotactic triads (mm) have consecutive (R) stereochemical configurations or consecutive (S) stereochemical configurations. 
 
     
     
         2 . The copolymer of  claim 1  wherein R is methyl or ethyl. 
     
     
         3 . The copolymer of  claim 1  wherein the molecular weight M n  is at least about 100 kDa. 
     
     
         4 . The copolymer of  claim 1  wherein the dispersity index M w /M n  of the polymers is less than 1.2. 
     
     
         5 . The copolymer of  claim 1  wherein moieties of Formula IA of the copolymer comprise at least 99% isotactic triads with respect to the stereocenters of substituents R. 
     
     
         6 . A method for preparing the copolymer according to  claim 1 , comprising:
 contacting a mixture of meso and racemic diastereomers of Formula V, an effective amount of a yttrium catalyst, and an alcohol initiator, to initiate a ring opening polymerization reaction, wherein:   Formula V is:   
       
         
           
           
               
               
           
         
         wherein R is (C 1 -C 18 )alkyl, (C 1 -C 8 )alkenyl, (C 1 -C 8 )alkynyl, benzyl, or phenyl; to thereby form the copolymer of Formula I. 
       
     
     
         7 . The method of  claim 6  wherein R is methyl or ethyl. 
     
     
         8 . The method of  claim 6  wherein the alcohol initiator is benzyl alcohol or a di-alcohol. 
     
     
         9 . The method of  claim 6  wherein the yttrium catalyst is catalyst 4e: 
       
         
           
           
               
               
           
         
       
     
     
         10 . The method of  claim 6  wherein the yttrium catalyst is a catalyst of Formula X: 
       
         
           
           
               
               
           
         
       
       wherein:
 M is Sc, Y, or a lanthanide(III) metal; 
 Ligand is —OR x , —NR x   2 , or —N(SiR y   3 ) 2 , wherein R x  is alkyl, and each R y  is H or alkyl, wherein at least two R y  groups are alkyl; 
 R a  is H, alkyl, or phenyl; and 
 R b  and R c  are H, alkyl, or phenyl; or 
 R b  and R c  together with the carbon atoms to which they are attached form a 5, 6, 7, or 8 membered cycloalkyl group. 
 
     
     
         11 . A metal complex of Formula X: 
       
         
           
           
               
               
           
         
       
       wherein:
 M is Sc, Y, or a lanthanide(III) metal; 
 Ligand is —OR x , —NR x   2 , or —N(SiR y   3 ) 2 , wherein R x  is alkyl, and each R y  is H or alkyl, wherein at least two R y  groups are alkyl; 
 R a  is H, alkyl, or phenyl; and 
 R b  and R c  are H, alkyl, or phenyl; or 
 R b  and R c  together with the carbon atoms to which they are attached form a 5, 6, 7, or 8 membered cycloalkyl group. 
 
     
     
         12 . The metal complex of  claim 11  wherein the complex is 4d: 
       
         
           
           
               
               
           
         
       
     
     
         13 . The metal complex 4e: 
       
         
           
           
               
               
           
         
       
     
     
         14 . A method for preparing a syndiotactic polymer of Formula I: 
       
         
           
           
               
               
           
         
       
       wherein:
 n is about 10 to about 10,000; and 
 R is (C 1 -C 18 )alkyl, (C 1 -C 8 )alkenyl, (C 1 -C 8 )alkynyl, benzyl, or phenyl; 
 the method comprising, contacting a monomer of Formula V, an effective amount of a metal complex of Formula X, and an alcohol initiator to initiate a ring opening polymerization reaction, wherein Formula V is: 
 
       
         
           
           
               
               
           
         
       
       wherein Formula V is a meso diastereomer and R is as defined for Formula I; and
 Formula X is: 
 
       
         
           
           
               
               
           
         
       
       wherein:
 M is Sc, Y, or a lanthanide metal; 
 Ligand is alkoxy, amide, or —N(SiR x   3 ) 2  wherein each R x  is H or alkyl, and at least two R x  groups are alkyl; 
 R a  is H, alkyl, or phenyl; 
 R b  is alkyl or phenyl; and R c  is alkyl or phenyl; or 
 R b  and R c  together with the carbon atoms to which they are attached form a 5, 6, 7, or 8 membered cycloalkyl group; 
 to thereby form the syndiotactic polymer of Formula I, wherein the probability of racemic linkages between monomers, P r , is greater than 0.94, and the melting temperature, T m , of the polymer formed is greater than 174° C. 
 
     
     
         15 . The method of  claim 14  wherein R is methyl or ethyl. 
     
     
         16 . The method of  claim 14  wherein the alcohol initiator is benzyl alcohol or a di-alcohol.