title: Investigating the effect of multi-functional chain extenders on PLA/PEG copolymer properties.
abstract: Biodegradable copolymers polylactic acid-co-poly ethylene glycol (PLA-co-PEG) were synthesized at a specific volume ratio (PLA/PEG) (80/20) using direct melt polycondensation without solvent. The effects of an oligomeric chain extender (CE) on the mechanical, molecular weight, thermal stability, and degradation were evaluated. The copolymers were tailored by introducing classes of CE contents (0.25, 0.5, 0.075, 1.0, 1.25, and 1.5wt%) (styrene- glycidyl acrylate copolymer). Apparently, the mechanical properties of copolymers were enhanced in the presence of CE. A long chain branch structure has led to a slight improvement of tensile strength to reach 70MPa at CE 1.25%, compared with 60MPa for neat PLA. A significant increase of 17% was observed for the elongation at break of copolymers after addition of CE 1.25%. In addition, the impact strength increased to 7.9KJ/m2in the ranges of CE 1-1.25%. Melt flow index dramatically reduces with the addition of CE contents. Gas Permeation Chromatography (GPC) showed that the addition of CE 1.25% has resulted in increasing the PLA molecular weight to 132.569kDa with a broad molecular weight distribution, MWD (2.066), and bimodal distribution. Differential Scanning Calorimetric (DSC) results revealed that the chain extension process improved glass transition temperature (Tg) 62°C, melting temperature (Tm) 161°C, and crystallinity (X%) 34.9% as a result of CE 1.25%. Thermal gravimetric analyses (TGA) results indicated that the CEs have a positive effect on the enhancement of thermal stability. Moreover, Scanning Electron Microscopic (SEM) showed that the compatibility and interfacial adhesion between the PLA and PEG chains were enhanced in the existence of the CE contents. The weight loss of the copolymer during 30days of degradation time was 28%, while the weight loss of CE 1.5% was only 3% during the same time interval.
authors.affiliation: Department of Chemical Engineering, Ryerson University, Toronto, M5B 2K3, Canada.
authors.forename: Mustafa Abu
authors.initials: MA
authors.lastname: Ghalia
authors.affiliation: Department of Chemical Engineering, Ryerson University, Toronto, M5B 2K3, Canada. Electronic address: ydahman@ryerson.ca.
authors.forename: Yaser
authors.initials: Y
authors.lastname: Dahman
mesh_terms: D004355:Drug Stability; D006868:Hydrolysis; D007773:Lactates / Q000737:chemistry*; D055595:Mechanical Phenomena; D008970:Molecular Weight; D011092:Polyethylene Glycols / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*; D013696:Temperature
chemical_list: D007773:Lactates; D011108:Polymers; C088513:poly(lactic acid-ethylene glycol); D011092:Polyethylene Glycols
keywords: Liquid chain extender; Poly (ethylene glycol); Poly (lactic acid); Polycondensation