Properties Of Aliphatic Polyesters Of Short Carbon-Chain Dicarboxylic Acid And Diols

From an environmental perspective, biodegradable polymers produce an attractive alternative to conventional non-biodegradable products. There are much research has been done on the syntheses, physicochemical properties, and degradations of biodegradable polymers over the past few decades. Among those polymers, one of the successfully developed polymers is aliphatic polyester, such as poly(glycolic acid) (PGA), poly(lactic acid) (PLA), and poly(ε-caprolactone) (PCL), have been diffusely applied in medical and pharmaceutical areas, due to their excellent biocompatibility and biodegradability. The biodegradability of polyesters depends mainly on its chemical structure and especially on the hydrolysable ester bond in the main chain. Other factors such as molecular weight, crystallinity, stereoregularity, morphology, temperature, pH value, enzyme and microorganism also affect the biodegradation of polymers. The researches mainly focused on the synthesis, the structure of the polymers and polymer modification over the past few decades. The biodegradable mechanism is weak and could not produce the controlled biodegradable polymers. Therefore, according to the requirement and the environment, it needs to exploit the controlled biodegradation polymers through molecular design in the near future.There are biological method and chemical method to prepare the aliphatic polyesters. The aliphatic polyesters obtained from biological synthesis are usually brittle. The molecular-weight of aliphatic polyesters obtained from chemical synthesis is low, which is not fit to be plastic products. So it is important to research on the prepared method or polymer modification.As the length of the carbon-chain could affect the biodegradability of the aliphatic polyesters, in the present research, we use the short carbon-chain dicarboxylic acid and diols as the materials to prepare the aliphatic polyesters.In the present research, the aliphatic polyesters and co-polyesters were prepared from fumaric acid (FA), succinic acid (SA), diethylene glycol (DEG) and 1,4-butanediol (BD) by melt polycondensation method. The biodegradability and the controlled biodegradability were investigated in phosphate buffer solution with porcine pancreas lipase. In the present research, cyclic dimer of poly(succinic acid-co-butanediol) (CDBS) was purified from the crude oligomers of poly(butylene succinate). The purified CDBS was subjected to ring-opening polymerization (ROP) to obtain poly(succinic acid-co-butanediol) (poly(SA-co-BD)), and compared with the poly(SA-co-BD) obtained from succinic acid (SA) and 1,4-butanediol (BD) by melt polycondensation method. In the present research, the biodegradability and other properties of the aliphatic polyesters after copolymerization, blending, and chain-extension were also investigated.Firstly, hydroxyl terminated aliphatic polyesters and co-polyesters were prepared from fumaric acid (FA), succinic acid (SA), diethylene glycol (DEG) and 1,4-butanediol (BD) by melt polycondensation method. The effects of mole ratio of diacid to diols, reactive temperature, reactive time, the kind of catalyst, and the air pressure on polyesters were discussed. The resultant aliphatic polyester was characterized by Fourier transform infrared (FTIR) spectroscopy and 1H NMR spectrum. The results showed that, to obtain the hydroxyl terminated aliphatic polyesters, the mole ratio of diacid to diols is 6:5, SnCl2 as catalyst, esterification temperature is 150℃, polycondensation temperature is 190～200℃under low air pressure (3.3 KPa).Secondly, the enzymatic degradation was performed in phosphate buffer solution with porcine pancreas lipase. The biodegradability of unsaturated aliphatic polyesters poly(FA-co-DEG),poly(FA-co-BD) was compared with the saturated aliphatic polyesters poly(SA-co-DEG) and poly(SA-co-BD). Effects of structures, compositions and cross-linking degrees of carbon-carbon double bonds of polyesters on the biodegradability were discussed. The results indicated that, the molecular weights, Tm value, and the polyester structure affect the biodegradability of aliphatic polyesters. The results also indicated that, the C=C double bonds in unsaturated aliphatic polyesters poly(FA-co-DEG) have been opened partially after heat-treatment under high temperature in air, and the higher the cross-linking degree, the slower the enzymatic degradation of poly(FA-co-DEG).Thirdly, chain-extended polymer was prepared by the reaction of poly(FA-co-DEG),2, 4-toluene diisocyanate (TDI) and 1,4-butanediol (BD). The effects of mole ratio of polyester to TDI, mole ratio of polyester to BD, reactive temperature, reactive time, and catalyst on chain-extension reaction were discussed. And the biodegradability of chain-extended polymer was also investigated. It was found that the biodegradation of the obtained chain-extended polymer was slower than that of the original unsaturated aliphatic polyester poly(FA-co-DEG). Accordingly, the degradability of the chain-extended polymer after cross-linked was slower than that of the uncross-linked polymer.In order to investigate the peeling strength of the resulting chain-extended polymer, the effects of laminating pressure, temperature and time on peeling strength were measured. The results show that, the peeling strength of the chain-extended polymer revealed good adhesion of the polymer to fabrics. The adhesion property was affected by laminating pressure, time and temperature, because the C=C bonds were allowed to cross-link to increase the cohesive interaction of the chain-extended polymer.Fourthly, cyclic dimer of poly(succinic acid-co-butanediol) (CDBS) was purified from the crude oligomers of poly(butylene succinate). The purified CDBS was subjected to ring-opening polymerization (ROP) to obtain poly(succinic acid-co-butanediol) (poly(SA-co-BD)) with 1-dodecanol as the initiator and tin octoate as the catalyst. Compared with the poly(SA-co-BD) obtained from succinic acid (SA) and 1,4-butanediol (BD) by melt polycondensation method. The resultant aliphatic polyester was characterized by Fourier transform infrared (FTIR) spectroscopy and 1H NMR spectrum. The results show that, ROP can obtain high-molecular-weight poly(SA-co-BD), the highest number-average molecular weight (Mn) reached about 63.3 kDa in 3 h at 220℃. The enzymatic degradation of the resultant poly(SA-co-BD) was performed in phosphate buffer solution with porcine pancreas lipase. The results show that, the higher the molecular-weight, the slower the biodegradation.Finally, a novel polymer blend system consisting of poly(succinic acid-co-butanediol) (poly(SA-co-BD)) and a thermotropic liquid crystalline polymer (LCP:an aromatic polyester comprising poly(4-hydroxybenzoate) sequences) was investigated in the presence and absence of a polycabodiimide (PCD) or 1, 1'-carbonyl biscaprolactam (CBC) which worked as chain extender. The properties of the resultant blend samples were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), scanning electron micrographs (SEM), wide-angle X-ray diffraction (WAXD) and tensile test. It was found that, the blend specimens containing LCP in 10-30 wt% were found to hold high dynamic storage-moduli (E'), and those containing 30 wt% of LCP showed E'reaching 9.6 GPa at room temperature. Scanning electron micrograph (SEM) of the polymer blends revealed the fibrous structure of LCP in the poly(SA-co-BD) matrix by which efficient toughning of the injection-molded polymer blends was supported. These polymer blends can replace the conventional oil-based engineering plastics having superior mechanical properties.