The Ring-Opening Polymerization Of P-Dioxanone Prepared With Various Catalyst Systems

Poly(p-dioxanone) (PPDO) has its own special characters. Except of its ultimate biodegradability due to the existence of ester bonds in polymer chains, the unique ether bonds endue it with good flexibility. The high molecular weight of PPDO also has received the approval of the Food and Drug Administration (FDA) to be used as suture material in gynecology. The more applications in medical, such as bone or tissue fixation device and drug delivery system, have also been reported frequently in recent years. Furthermore, PPDO also has great potential for general uses such as films, molded products, laminates, foams, nonwoven materials, adhesives, and coatings. But low molecular weight of PPDO has no applications at all.However, PPDO doesn't become the focus of polyesters in quite a long period. The activity of the PDO monomer is comparatively low, and most catalysts that have been mentioned in available information are not effective enough, which produce the PPDO with low reaction rate, low monomer conversion and wide molecular weight distribution.In order to find some new catalysts to systhesis of PPDO with high molecular weight, high monomer conversion and high reaction rate, various catalysts or initiators for the ring-opening polymerization of PDO have been developed in the recent decades . However, most of them are centered on heavy metals such as Ti, Zr, Sn, Ld, La, Yb, and Hg, which are not acceptable as "by products" when a pharmaceutical or medical application of PPDO is taking into account. Thereafter, the catalysts including Stannous octotate, Aluminum isoproposxide, Zinc (II) L-lactate, enzymes have been used most frequently in the ring-opening polymerization of PDO, even though the long reaction time and the quite low conversion of monomer make them to be less effective catalysts.For example,in 1977,Doddi et al synthesized the PPDO whose inherent viscosity was about 0.7dl/g by using zinc diethyl as catalyst after 72 hours reaction.However,zinc diethyl is an inconvenient catalyst because it is a self-inflammable liquid and unstable on storage. in 1997,Forchner et al synthesized the PPDO whose molecular weight could reach 81,000 but the monomer conversion could only reach 67% by using stannous octoate as catalyst and dodecanol as co-initiator. in 1998, zinc(â…¡)L-lactate(ZnLac2) has been first used in ring-opening polymerization of PDO by Kricheldorf et al ,the PPDO with an inherent viscosity can be achieved though it needs a rather long reaction time about 14 days and results in low conversion of about 62%. in 2000, Nishida et al synthesized the PPDO whose molecular weight could reach 142,000 but the monomer conversion could only reach 79.4% by using stannous octoate as catalyst with co-initiator under conditions that T = 100oC, M/I = 4900, t = 20 h, in 2000, the enzymatic polymerization of PDO was carried out at 100oC for 15 hours using 5wt% immobilized lipase CA by Nishida et al.The results show that the lipase CA,derived from candida antarctica exhibited especially high catalytic activity. The highest weight-average molecular (MW=41,000) was obtained even though the quite low conversion of monomer makes it unlikely to be an industrialized method in a short period.From above, there were no mature methods to sythesize PPDO with high molecular weight ,high conversion of monomer and high reaction rate.In this paper, various catalyst systems such as HClSO3,AlEt3, AlEt3-H2O, AlEt3-M(ACAC)3-H2O, AlEt3-H3PO4-H2O have been used to produce PPDO.and new catalyst systems such as HClSO3,AlEt3-H2O, AlEt3-M(ACAC)3-H2O AlEt3-H3PO4-H2O, were successfully used for synthesizing poly (1,4-dioxan-2-one) (PPDO) in bulk via the ring-opening polymerization (ROP) of 1,4-dioxan-2-one (PDO) for the first time . The effects of the molar ratio of monomer to catalyst, the polymerization temperature, the reaction time and the water content of monomer PDO were studied systematically. Several instruments such as IR, NMR, have been employed to investigate the structure of PPDO. It was found that only low molecular wei...