title: Polylactide stereocomplexation leads to higher hydrolytic stability but more acidic hydrolysis product pattern.
abstract: Poly-l-lactide/poly-d-lactide (PLLA/PDLA) stereocomplex had much higher hydrolytic stability compared to plain PLLA, but at the same time shorter and more acidic degradation products were formed. Both materials were subjected to hydrolytic degradation in water and in phosphate buffer at 37 and 60 degrees C, and the degradation processes were monitored by following mass loss, water uptake, thermal properties, surface changes, and pH of the aging medium. The degradation product patterns were determined by electrospray ionization-mass spectrometry (ESI-MS). The high crystallinity and strong secondary interactions in the stereocomplex prevented water uptake and resulted in lower mass loss and degradation rate. However, somewhat surprisingly, the pH of the aging medium decreased much faster in the case of PLLA/PDLA stereocomplex. In accordance, the ESI-MS results showed that hydrolysis of PLLA/PDLA resulted in shorter and more acidic degradation products. This could be explained by the increased intermolecular crystallization due to stereocomplexation, which results in an increased number of tie chains. Because mainly these short tie chains are susceptible to hydrolysis this leads to formation of shorter oligomers compared to hydrolysis of regular PLLA.
authors.affiliation: Department of Fibre and Polymer Technology, School of Chemical Science and Engineering, Royal Institute of Technology (KTH), S-100 44, Stockholm, Sweden, and Tate & Lyle Finland Oy, Tykistokatu 4D, 20520 Turku, Finland.
authors.forename: Sofia Regnell
authors.initials: SR
authors.lastname: Andersson
authors.forename: Minna
authors.initials: M
authors.lastname: Hakkarainen
authors.forename: Saara
authors.initials: S
authors.lastname: Inkinen
authors.forename: Anders
authors.initials: A
authors.lastname: Södergård
authors.forename: Ann-Christine
authors.initials: AC
authors.lastname: Albertsson
mesh_terms: D000143:Acids / Q000378:metabolism*; D001672:Biocompatible Materials / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D003460:Crystallization; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D011091:Polyesters / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D013237:Stereoisomerism; D013499:Surface Properties; D014867:Water / Q000378:metabolism*
chemical_list: D000143:Acids; D001672:Biocompatible Materials; D011091:Polyesters; D014867:Water; C033616:poly(lactide)