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Copolymerizations and grafted copolymers of poly(lactide-co-glycolide) macromers and poly(vinyl alcohol)

Macromonomers bearing a functional polymerizable chain and capable of undergoing copolymerization provide a facile route of synthesis of various graft copolymers of well-defined structure. In this study, poly(D, L-lactide) (PLA) or poly(lactide-co-glycolide) (PLG) macromers were grafted onto hydrophilic macromolecular backbone of poly(vinyl alcohol) (PVA). Such a copolymer shows a hydrogel properties and act as potential biomaterial. The aim was the manipulation of physico-chemical properties and increase of hydrophilicity by changing: the length of grafted aside chains (4, 8, 16 repeating units), the ratio D, L-LA : GL (100:0 ; 75:25 ; 50:50 mol/mol), percent of grafting on PVA backbone chain (10, 15, 20 mol. %). The synthesis was performed in steps, first of which was a ring-opening polymerization of cyclic dimers of D, L-lactide or/and glycolide in presence of 2-hydroxyethyl methacrylate (HEMA) as an initiator and stannous octoate as a catalyst. The next step was transformation of hydroxyl end groups into acid groups using succinc anhydride, in presence of pyridine and 4-dimethylamino-pyridine (DMAP). The fallowing step of synthesis was coupling of PLA or PLG aside chains onto PVA backbone in DMSO solution using dicyclohexyl carbodiimide (DCC) as coupling agent. The last step of synthesis was crosslinking of resulting grafted copolymer into hydrogel. The single steps of synthesis were characterized by 1H-NMR, 13C-NMR and IR methods. The hydrolytic degradation of the obtained hydrogels was investigated by performing mechanical test and by means of water uptake measurements. Both of them show a big influence of the polymer structure. Mechanical tests have shown that by increasing the length of aside PLA/ PLG chains from 4 to 16 repeating units there is increase of Young modulus from 0.5 MPa to 40 MPa, at the same time keeping all the other parameters constant. Water uptake values show that by increasing the length of aside PLA/PLG chains from 4 to 16 there is decrease of water uptake from 80 wt. % to 20 wt. % for the period of time e.g. 4 weeks. Contribution of the other parameters (D, L-LA : GL ratio ; degree of grafting, dilution of crosslinking polymer solution) were shown to be important as well.

Graft-copolymers ; Poly(vinyl alcohol) ; Poly(lactide-co-glycolide)

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