| Aliphatic polyesters, with outstanding biodegradability, bioabsorbability and biocompatibility, have attracted great interest of researchers in recent decades. A series of aliphatic polyesters and copolyesters have been synthesized successfully from the lactone monomers such as glycolide (GA), lactide (LA), and s-caprolatone (CL). Most of them have been applied to produce biodegradable products, especially surgical devices such as surgical suture, anchors, staples, tacks, clips, plates, screws and bone fixation devices.Comparing with other aliphatic polyesters, 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 also endue it with good flexibility. 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 in recent years. Furthermore, PPDO also has great potential for general uses such as films, molded products, laminates, foams, nonwoven materials, adhesives, and coatings. However, PPDO did not become the focus of polyesters in quite a long period since the activity of the PDO monomer is comparatively low, and most catalysts that have been mentioned in available information are not effective enough, and they could only be used to produce the PPDO with low reaction rate, low monomer conversion and wide molecular weight distribution. Consequently, PPDO can only beobtained in very high cost, which become an obstacle for the completed and deep research of the properties of PPDO. In this present work, three catalysts have been employed to synthesize PPDO and a thorough investigation of the properties of PPDO has been conducted.PPDO has been synthesized by ring-opening polymerization (ROP) of p-dioxanone (PDO). Several instruments such as IR, NMR, MS, DSC, WAXD, PM, TG, DMA and Capillary Rheometer have been employed to investigate the structures and properties of PPDO. Furthermore, block copolymers of PDO/LA and PDO/CL have been synthesized.Several catalysts such as stannous octoate (SnOct2), triethylaluminum (AlEts) and lanthanum isopropoxide (La(0'Pr)3) have been utilized to catalyze the ROP of PDO. The investigation shows that the reaction rate of polymerization, monomer conversion, molecular weight of PPDO were influenced dominantly by the mole ratio of monomer and catalyst, reaction temperature and reaction time. SnOcta is a mild catalyst for ROP of PDO, nevertheless, high molecular weight of PPDO can been produced by it. Comparing with SnOct2 and AlEt3, La(0'Pr)3 exhibits a high catalytic efficiency. As a result, the high reaction rate, high monomer conversion and narrow molecular weight distribution can been achieved. MS, IR and NMR have been used to characterize the structures of PDO and PPDO. In addition, the mechanism of each catalyzing process has also been discussed and a coordination mechanism has been found.. PM, DSC and WAXD have been utilized to investigate the crystallization and morphology of PPDO. PPDO can develop well-defined spherulites with a clear Maltese cross and bands while cooling from melt. The spherulitic morphology changed as a function of crystallization temperature. Molecular weight of PPDO is also one of the key factors, which not only governed kinetic parameters of crystallization, the crystal thickness, crystalline morphology, and degree of crystallinity, but also influenced melt point (Tm) and glass transition temperature (Tg) of PPDO during the dynamic crystallization process. The Avrami equation has been used to analyze the overall isothermal crystallization of PPDO. Avrami exponentsranging from 2 to 3 were obtained with good fits (correlation coefficients were greater than 0.999 in all cases) at Tc ranged from 55-75 . Although no significant influence of molecular weight on Avrami exponent has been found, the molecular weight of PPDO acts domi...
|
PDF Full Text Request