Study On Poly (L-lactide) Modified With Poly (Vinyl Alcohol)

PVA-g-PLLA copolymers were synthesized by solution-grafting and three-step method respectively to modify the PLLA, and PVA/PLLA/PVA-g-PLLA blend system was also studied to improve the properties of the PLLA.In the solution-grafting method, a series of PVA-g-PLLA was synthesized under nitrogen, 90℃, 20h, by using DMSO as cosolovent with different ratio of PVA to lactone. The PVA-g-PLLA copolymers were characterized by FTIR, ~1HNMR, GPC and DSC etc. The result show that PVA-g-PLLA copolymers were synthesized by solution-grafting method and the molecular weight, T_g of the copolymers were increased with the content of lactone.To observe the effect of average grafting number on the PVA-g-PLLA copolymers, three-step method was proposed. In the three-step method, hydroxyl terminated PLLA was first synthesized by using hexadecanol as chain transfer agent. The effect of concentration of chain transfer agent and reaction conditions on the relative molecular mass of PLA were studied. The result indicate that the M_η decreases with increasing the content of hexadecanol, while under the same content of chain transfer agent the optimum reaction condition for higher molecular weight of PLLA-OH was as follows: mass fraction of stannous octoate 0.14%, polymerization temperature 140℃ and polymerization time 20 hours. Then in the second step PLLA-OH was caboxylated by succinic anhydride. In the third step, PLLA-COOH was grafted onto the PVA backbone using DCC as coupling agent. The structures, molecular weight, thermal properties of the PVA-g-PLLA were observed by FTIR, HNMR, GPC and DSC. The average grafting number was calculated, and the effect of the average grafting number on the thermal properties, hydrophilicity and degradation properties of PVA-g-PLLA were studied. T_g of graft copolymers PVA-g-PLLA was decreased with the reduction of average grafting number. While the water adsorption properties and the degradation ratio of PVA-g-PLLA increased with decreasing average grafting number. Therefore the properties of the PVA-g-PLLA can be simply modulated by changing the average grafting numbers.In addition, in the PVA/PLLA/PVA-g-PLLA blend system, the effect of PVA-g-PLLA on the compatibility of PLLA and PVA, hydrophilicity and degradation properties of...