Synthesis of amino acid-derived bioerodible polymers

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the preparation of the polycarbonates of the present invention, amino acid-derived diphenol compounds are employed as the starting materials.
Useful amino acid-derived diphenol compounds include those disclosed in U.
S.
Pat.
application Ser.
No.
219,290.
The disclosure of amino acid-derived diphenol compounds useful to form polycarbonates in said U.
S.
Pat.
No.
4,980,449 is hereby incorporated herein by reference thereto.
The amino acid-derived diphenol compounds can be used in any conventional polymerization process using diphenol monomers, including those processes that synthesize polymers traditionally considered hydrolytically stable and non-biodegradable.
Accordingly, the amino acid-derived diphenol compounds of the present invention can not only be used in the preparation of amino acid-derived polycarbonates, they can also be used in the preparation of amino acid-derived polythiocarbonates, polyiminocarbonates and polyethers, as well.
As stated above, the amino acid-derived polymers demonstrate hydrolytic instability without sacrificing thermal stability or mechanical properties compared to their counterpart polymers not derived from amino acids.
Preferred amino acid-derived diphenol starting materials for the preparation of the amino acid-derived polycarbonates of the present invention are the amino acid-derived diphenol compounds of Formula II discussed above, with R.
sub.
1 being an alkyl group up to 18 carbon atoms in length.
The particularly preferred amino acid-derived diphenol compound starting materials for the preparation of amino acid-derived polycarbonates according to the present invention are derived from the naturally occurring amino acid L-tyrosine and its analog desaminotyrosine (Dat), which occurs naturally in plants.
In this preferred group, the diphenol starting material can be regarded as a pseudodipeptide, properly referred to as a desaminotyrosyl-tyrosine alkyl ester.
The most preferred member of the group of desaminotyrosyl-tyrosine alkyl esters is the hexyl ester, referred to as desaminotyrosyl-tyrosine hexyl ester, or DTH