Copolymers of 1,5‐dioxepan‐2‐one and L‐ or D,L‐dilactide: Hydrolytic degradation behavior

Abstract

SYNOPSISThe degradation of two series of copolymers made of 1,5-dioxepan-2-one (DXO) and Lor D,L-dilactide has been investigated. In uitro degradation of the six copolymers with different ratios of the ingoing components was followed using size exlusion chromatography ( SEC) , nuclear magnetic resonance (NMR) spectrometry, Fourier transform infrared (FTIR) spectroscopy, and differential scanning calorimetry (DSC) . The copolymers with a high content of lactic acid units showed a higher rate of hydrolysis than the DXO-rich copolymers. The copolymer morphology also affects the rate of degradation as seen in the differences between amorphous and semicrystalline samples. The effect of electron beam sterilization was studied as well as the degradation products formed using the gas chromatography-mass spectrometry (GC-MS ) technique. The major degradation products resulted from ester bond cleavage. Kinetics of the in uitro degradation indicate a complex hydrolysis, probably a mixture of an uncatalyzed and catalyzed mechanism.

Novel drug delivery microspheres from poly(1,5-dioxepan-2-one-co-L-lactide)

“…[1][2] We have shown that classical theory of polyester hydrolysis applies to DXO-L-LA copolymers as well. 10 The molecular weight started to decline immediately upon immersion in buffer (Fig. 2).…”

“…This behavior has been confirmed for DXO-rich amorphous copolymers. 10 L-lactide-rich copolymers, on the other hand, became enriched in lactide units because the crystalline lactide material is more resistant to water penetration and bulk erosion than the amorphous DXO units.…”

“…Due to differences in reactivity ratios for the two monomers, a semiblock copolymer structure was obtained, resulting in retention of semicrystallinity. 9 Physical properties are presented in Table I. Copolymer structure and chemical shifts are outlined in Scheme 1.…”

Síntesis, caracterización y aplicaciones biomédicas de redes de copolímeros basados en poliésteres.

“…Dependiendo del iniciador, la polimerización procederá por tres diferentes mecanismos [45]: el catiónico, el aniónico y el de inserción-coordinación [46][47][48]. Existen otros como el mecanismo radical, zwiteriónico [49] o por hidrógenos activos que no son muy utilizados debido a la obtención de polímeros de muy bajo peso molecular.…”

“…La ROP pseudo-aniónica es a menudo llamada ROP de coordinación-inserción, ya que el proceso de propagación se piensa que procede por la coordinación del monómero con las especies activas, seguida por la inserción del monómero entre el enlace metal-oxígeno por la reorganización de los electrones [46,47]. La figura 1.5 muestra la representación esquemática del mecanismo de coordinación-inserción.…”