Study On The Anionic Graft Polymerization Of ε-caprolactone Onto Substrates Though Hydroxy Groups

Aliphatic polyesters derived from lactic and glycolic acids have been used extecsively as biomaterials and carriers for drug delivery systems. Owing to their low toxicity, excellent biocompatibility and biodegradability, studies on them have resulted in a great interest of many researchers. Polyesters derived from the ring-opening polymerization of a series of lactones such as 3 -lactones , Y -lactones, 5 -lactones and ?-lactones and so on are biodegradable polymers. The extensively studied monomers among them are -caprolactone, lactide, glycolactide buryrolactone. Apart from the polymerization and copolymerization of monomers, the study on the grafting polymerization onto some substrates in order to obtain well defined polymers have gained much interest in recent years.In this paper, a anionic initiator naphthalene sodium was used to initiate the grafting polymerization on the substrates such as starch acetate, polypropylene film having -OH functional groups , EVA film and partially hydrolyzed PVAc film. The reaction conditions of forming -OH and grafting polymerization on every substrates were studied and the graft polymers were characterized by DSC, GPC, FTIR, ATR, NMR, SEM, ESCA.Using pyridine and N,N-dimethylformide (DMF) as an activator, and starch acctatc(St-Ac) with substituting degree (DS) about 0.7-1.9 was obtained. The effect of the solvating time by DMF and quantity of acetic anhydride on DS was studied. Graft polymerization -caprolactone ( -CL) onto starch acetate was carried out through anionic ring-opening polymerization of -CL in diethylene glycol dimethyl ether solution. The graft polymerization was initiated by -ONa groups which were formedthrough the reaction of the remained -OH groups in St-Ac with naphthalene sodium (NS). The grafting reaction was characterized by grafting percentage, monomer conversion, as well as gel permeation chromatography (GPC) through comparison of the Mn, Mw and Mw/Mn of St-Ac with that of the grafted copolymer, starch grafted polycaprolactone (St-g-PCL). The influence of the reaction temperature, monomer and NS concentrations on the grafting percentage and the monomer conversion was discussed. The results showed that the grafting percentage and the monomer conversion vary in a way of S curves as grafting temperature increased from 50'C to 150*C, but increase with the increasing of the monomer concentration and NS concentration. The graft copolymers obtained are also characterized by DSC.NMR and FTIR.This paper also describes the methods to synthesize new graft copolymers such as polypropylene-graft-polycaprolactone(PP-g-PCL), ethylene/vinylacetate-graft-polycaprolactone ( EVA-g-PCL ) and poly(vinyl alcohol)--graft-polycaprolactone (PVA-g-PCL) using commercial polypropylene film, EVA film and PVA film as substrates, on which were introduced some hydroxyl groups Introduction of the hydroxyl groups to the PP, EVA and PVA films is the key step to synthesize PP-g-PCL, EVA-g-PCL and PVA-g-PCL. To introduce the hydroxyl groups onto the PP film, several methods including redox reaction of H202 -NaHSO3, H2O2 -N(CH2CH2OH)3, BPO oxidation and followed saponification, ultraviolet light excited oxidation initiated by BP are taken, the resulted hydroxyled PP film were characterized by FTIR and UV spectra and water-contact angle. The hydroxyl groups onto the EVA film were introduced by the hydroxylation reaction.The graft copolymerization of caprolactone onto the hydroxylated PP and EVA films was carried out using naphthylene-sodium as initiator. The grafting reaction was characterized by grafting percentage, FTIR spectra,. SEM and ATR.