Study Of The Ring-opening Polymerization Of Cyclic Monomers Catalyzed By Immobilized PPL Nanoparticles

Biodegradable polymer has attracted much attention and got rapid development since the past two decades. Among these studies, the application of immobilized enzyme in the preparation of biodegradable polymer is still in the preliminary stage. Immobilized enzyme has shown many advantages such as preservation of catalytic activity of free enzyme, higher stability to reaction temperature and pH, lower sensitivity to inhibitor, higher stability for storage and non-toxic, it is convenient to recover and can be repeatedly use without much loss of its catalytic activity. So it is expected to gain more and more attention and applications in the catalytic preparation of biodegradable polymers.Nanotechnology has developed rapidly since 1980s. The application of nanotechnology the in preparation of immobilized enzymes has been a new route in recent years. By the use of nanometer materials as carriers for the immobilization of enzymes will endowed the immobilized enzymes with higher specific surface area and more enzyme loading and thus to obtain higher catalytic activity. In these studies, porcine pancreas lipase (PPL) immobilized on silica nanoparticles (10 run) was prepared. It was used as catalyst for the ring-opening polymerization of 2, 2-dimethyltrimethylene carbonate (DTC), trimethylene carbonate (TMC), D, L-Lactide, L, L-Lactide and 1,4-dioxan-2-one to evaluate its catalytic activity.Biodegradable polycarbonate is one of the most important biomedical materials, which has good biocompatiblity and biodegradablity. It has been extensively used as bioabsorable suture, bone fixing materials and drug controlled-release carriers. In chapter 2 and 3, the ring-opening polymerization of 2, 2-dimethyl-trimethylene carbonate (DTC) and trimethylene carbonate (TMC) catalyzed by IMPPL were explored. Influences of IMPPL concentration, reaction temperature and reaction time on the molecular weight and yield of corresponding polymers were studied. IMPPL exhibited much higher catalytic activity compared with free PPL. The recycling IMPPL showed even higher catalytic activity and higher molecular weight of polycarbonate could be achieved. It was also found that polycarbonates chains were grafted onto the surface of IMPPL. That would both improve the dispersibility and miscibility of the IMPPL in the polymerization system and increase obstruction of the substrates to makecontact with the poly carbonates-grafted silica catalysts. The two factors determined the catalytic activity of the recovered IMPPL. In chapter 3, enzymatic degradation of PTMC was conducted at different temperatures. The experimental data showed that enzymatic degradation would be accelerated at high temperature.Polylactide (PLA) is one kind of biomaterials for pharmaceutical and medical application. In chapter 4, the ring-opening polymerization of D, L-Lactide and L, L-Lactide catalyzed by IMPPL was studied. Influences of different experimental parameters on the molecular weight and yield of polymers were also studied. It was found that in the same reaction condition, the polymer molecular weight and yield of poly (D, L-Lactide) were higher than that of poly (L, L-Lactide).Poly (1,4-dioxan-2-one) (PDON) is used to make monofilament sutures and knotting and other surgical devices for its good tenacity. It was usually prepared by the ring-opening polymerization of 1, 4-dioxan-2-one (DON). In chapter 5, the ring-opening polymerization of DON was performed using IMPPL as catalyst. The reaction products were composed of linear PDON and cyclic oligomers. Most of cyclic oligomers were hexamer to octamer. The yield of cyclic oligomers was influenced by reation time, IMPPL concentration and reaction temperature. The molecular weight of linear PDON ranged from 1000 to 4000. It was also found that the ring-opening polymerization of DON catalyzed by IMPPL could take place at room temperature.1, 4-dioxan-2-one (DON) is an important monomer for the preparation of PDON, however the functional derivatives were scarely reported. It was known that the polymer with functional side group will have new physical, mechanical and other properties for new application. In chapter 6 and 7, two derivatives of DON, 6-hydroxymethyl -1,4-dioxan-2-one (HDON) and 6-methyl -1, 4-dioxan-2-one (MDON), were prepared. Hyperbranched aliphatic polyester, poly (6-hydroxymethyl-1, 4-Dioxan-2-one) (PHDON), was prepared by ring-opening polymerization of HDON in bulk. The branching degree of obtained polymers was calculated to be about 0.4. This hyperbranched polyester can allow further surface modification and facilitates prodrug attachment. It may find promising application in biomedical field. The ring-openning polymerization of MDON catalyzed by Sn(Oct)2, Al(OⁱBu)₃, Al(OⁱPr)₃, PPL and IMPPL was failed. Perhaps the stability of the monomer was increased due to the methyl substituent at the monomer ring.