Synthesis And Modification Of Hyperbranched Polyester And Its Application In Dental Restorative Resin

The conventional dental restorative resin system is bisphenol A glycerolatedimethacrylate (Bis-GMA) and triethylene glycol dimethacrylate (TEGDMA). However, they induces obvious volumetric shrinkage in the process of light-cure polymerization. The polymerization shrinkage leads to microleakage between resin restoration and tooth interface, causing secondary caries. Hyperbranched polymer has the potential to reduce shrinkage because of its highly branched three-dimensional structure. In this study, the end hydroxyl of hyperbranched polyester was further modified and adding modified hyperbranched polyester to the system of Bis-GMA and TEGDMA to prepare dental restoration resin of low volumetric shrinkage. At last, its influence on volumetric shrinkage and other properties of the resin system was investigated.Firstly, the second generation Boltorn-type aliphatic hyperbranched polyester (HBP) with 16 hydroxyl at the end was synthesized. It was based on pentaerythritol (B4) as a core molecule and 2,2-dimethylolpropionic acid (AB2) as monomer and p-toluenesulfonic acid as catalysis. And it was characterized by Fourier Transform Infrared Spectrometer (FT-IR) and Nuclear Magnetic Resonance(1H-NMR). The degree of branched (DB) is an important parameter of the hyperbranched polymer, and it was determined by C-NMR. The DB of HBP synthesized by one-step and pseudo one-pot procedure were compared. Then the methacryloyl chloride and propionyl chloride were synthesized. To form four different modified hyperbranched polyesters, namely GHBP1,GHBP2,GHBP3 and GHBP4, the 16 hydroxyl of HBP was modified in different degree according to the four proportions of methacryloyl chloride, propionyl chloride and residual hydroxyl. The proportions are 16:0:0, 13:0:3,7:6:3 and 5:10:1. All or part of the double bond were introduced at the end of HBP. The products were characterized by FT-IR and 1H-NMR.The conventional dental restorative resin system of Bis-GMA and TEGDMA was modified by adding different proportions of modified hyperbranched polyester. Then the system was cured by visible light used commonly in dental restoration. In order to evaluate the system comprehensively, the volumetric shrinkage, the conversion of double bond and water absorption were investigated. The results indicated that modification with GHBP lead to an obvious decrease in the volumetric shrinkage, even down to 2.97%, but a slightly change in the degree of conversion. The reduction of contact angle meant better hydrophilicity. Water absorption increased but in the controllable range(≤40μg/mm3). The TG results showed that the modified hyperbranched polyesters had little effect on the thermal stability of the resin system. The mechanical properties of the resin material was investigated preliminarily. The results indicated that hardness of the system modified by GHBP1, GHBP2, GHBP3 decreased slightly and hardness of the system modified by GHBP4 decreased obviously.According to the mechanism of radical initiated photopolymerization, the effects of initiator and co-initiator content and illuminating time on the extent of polymerization was investigated. The results showed that the conversion of double bond increased at first but later decreased with the increase of initiator.In a certain range, the conversion increased with the increase of co-initiator. With the increase of illuminating time, the rate of polymerization of resin system was fast at first and slowed down later until the conversion reached stable.