New alternating poly(amide-ester)s:: Synthesis and properties

New alternating poly(amide-ester)s derived from beta-hydroxy acids and alpha-amino acids 3a,b or epsilon-aminocaproic acid 4a-c were prepared. Two approaches were considered: (i) polycondensation of N-(beta-hydroxyacyl)-amino acids 1a,b and 2b,c and (ii) ring-opening polymerization of cyclic amide-esters 5a-c and 6a-c. For all the linear precursors polycondensation reactions result in oligomers with number average molecular weights lower than 5000. The ring-opening polymerization of the cyclic precursors is substrate specific and is sensitive to changes in the polymerization conditions. For N-(3-hydroxybutyroyl)-epsilon-aminocaproic acid lactone [c(3HB-epsilon AC); 5b] (IUPAC nomenclature: 2-methyl-5-aza-1-oxa-cycloundecan-4-11-dione) bulk and solution polymerizations result in oligomers with an alternating ester amide microstructure. Polymerization of N-(3hydroxypropionyl)-epsilon-aminocaproic acid lactone [c(3HP-epsilon AC); 5a] (IUPAC nomenclature: 5-aza-1-oxa-cycloundecan-4-11-dione) in dimethylformamide solution and with Bu2Sn(OMe)(2) as initiator high molecular weight linear, semicrystalline polymers were obtained (T-m = 145.9 degrees C). Polymerization of N-(hydroxypivaloyl)-epsilon-aminocaproic acid lactone [c(HPv-epsilon AC); 5c] (IUPAC nomenclature: 3,3-dimethyl-5-aza-1-oxa-cycloundecan-4-11-dione) in bulk results in amorphous alternating poly(amide-ester)s with cyclic structure (T-g = 6.8 degrees C). The fourteen membered cyclo(diamide-diester)s 6a-c (IUPAC nomenclatures:: 4, 11-diaza-1,8-dioxa-cyclotetradecan-2,5,9, 12-tetraone (6a), 7,14 dimethyl-4,11-diaza-1,8-dioxa-cyclotetradecan-2,5,9, 12-tetraone (6b), 3, 10-dimethyl-4, 11-diaza-1,8-dioxa-cyclotetradecan-2, 5,9,12-tetraone (6c) based on beta-hydroxy acids and alpha-aminoacids could not be polymerized.