title: gamma-irradiation of PEGd,lPLA and PEG-PLGA multiblock copolymers: II. effect of oxygen and EPR investigation.
abstract: The purpose of this research was to evaluate how the presence of oxygen can affect irradiation-induced degradation reactions of PEGd,lPLA and PEG-PLGA multiblock copolymers submitted to gamma irradiation and to investigate the radiolytic behavior of the polymers. PEGd,lPLA, PEG-PLGA, PLA, and PLGA were irradiated by using a (60)Co irradiation source in air and under vacuum at 25 kGy total dose. Mw and Mn were evaluated by gel permeation chromatography. The stability study was carried out on three samples sets: (a) polymer samples irradiated and stored in air, (b) polymer samples irradiated and stored under vacuum, and (c) polymer samples irradiated under vacuum and stored in air. The thermal and radiolytic behavior was investigated by differential scanning calorimetry and electron paramagnetic resonance (EPR), respectively. Samples irradiated in air showed remarkable Mw and Mn reduction and Tg value reduction due to radiation-induced chain scission reactions. Higher stability was observed for samples irradiated and stored under vacuum. EPR spectra showed that the presence of PEG units in multiblock copolymer chains leads to: (a) decrease of the radiolytic yield of radicals and (b) decrease of the radical trapping efficiency and faster radical decay rates. It can be concluded that the presence of oxygen during the irradiation process and the storage phase significantly increases the entity of irradiation-induced damage.
authors.affiliation: Department of Pharmaceutical Chemistry, University of Pavia, V.le Taramelli 12, 27100 Pavia, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Dorati
authors.forename: C
authors.initials: C
authors.lastname: Colonna
authors.forename: C
authors.initials: C
authors.lastname: Tomasi
authors.forename: I
authors.initials: I
authors.lastname: Genta
authors.forename: T
authors.initials: T
authors.lastname: Modena
authors.forename: A
authors.initials: A
authors.lastname: Faucitano
authors.forename: A
authors.initials: A
authors.lastname: Buttafava
authors.forename: B
authors.initials: B
authors.lastname: Conti
mesh_terms: D002152:Calorimetry, Differential Scanning; D002850:Chromatography, Gel; D004578:Electron Spin Resonance Spectroscopy; D005720:Gamma Rays; D019344:Lactic Acid / Q000737:chemistry*; D008970:Molecular Weight; D010100:Oxygen / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry*; D011100:Polyglycolic Acid / Q000737:chemistry*; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer
chemical_list: D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; D019344:Lactic Acid; D011092:Polyethylene Glycols; D010100:Oxygen