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

New alternating poly(amide-ester)s derived from β-hydroxy acids and α-amino acids 3a,b or ϵ-aminocaproic acid 4a-c were prepared. Two approaches were considered: (i) polycondensation of N-(β-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)-ϵ-aminocaproic acid lactone [c(3HB-ϵAC); 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-(3-hydroxypropionyl)-ϵ-aminocaproic acid lactone [c(3HP-ϵAC); 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, semi-crystalline polymers were obtained (T_m = 145.9°C). Polymerization of N-(hydroxypivaloyl)-ϵ-aminocaproic acid lactone [c(HPv-ϵAC); 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°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 β-hydroxy acids and α-aminoacids could not be polymerized.     

Ring-Opening Polymerization of the Cyclic Ester Amide Derived from Adipic Anhydride and 1-Amino-6-hexanol in Melt and in Solution

The ring-opening polymerization (ROP) of the cyclic ester amide (cEA) 5 (systematic name, 1-oxa-8-aza-cyclotetradecane-9,14-dione) - prepared from adipic anhydride and 1-amino-6-hexanol - in the melt at 165 °C and in solution at 100 °C and 120 °C with Bu₂Sn(OMe)₂ or Ti(OBu)₄ as initiator yields the alternating poly(ester amide) (PEA) 4 (systematic name, poly(5-(6-oxyhexylcarbamoyl)-pentanoate) with regular microstructure. Kinetic studies for different monomer-to-initiator ratios, different reaction media, initiators and temperatures reveal that the ROP is a first-order reaction with respect to the monomer. Under suitable polymerization conditions termination and transfer reactions are suppressed. The elementary chain growth reaction proceeds by a coordination insertion mechanism in analogy to the polymerization of lactones. By using monohydroxy- and bishydroxy-functional telechelic poly(ethylene oxide) and Sn(octoate)₂ as the initiating system poly(ethylene oxide)-block-poly(ester amide)s and poly(ester amide)-block-poly(ethylene oxide)-block-poly(ester amide)s are obtained. The poly(ester amide) 4 is a semicrystalline material with a melting point of 140 °C, the block copolymers are phase separated systems showing two melting points characteristic for the respective homopolymers.