Hyperbranched Polyesters: Synthesis And Curing Epoxy Resin

This work is related to the synthesis and characterization of hyperbranched and dendritic polyesters from the ring opening polymerization of anhydride and multifunctional epoxy compounds. The cure reactions of epoxy resin with carboxyl-functionalized hyperbranched polyesters were studied.Phthalic anhydride(PA), methyltetrahydrophthalic anhydride (MeTHPA), hexahydrophthalic anhydride(HHPA) and Glycidol were used to synthesize hyperbranched polyesters in an one-pot manner. The effects of polymerization temperature, ratio of reactants and the ways of adding reactants on the degree of branching (DB), molecular weight (Mn) and molecular weight distribution of the macromolcules were studied. Due to the special structure of hyperbranched polyester, the branching degree (DB) of the hyperbranched polyesters were determined by ,1H-NMR. Results show that the ratio anhydride/glycidol affects DB and Mn. Addition manner and polymerization temperature also have influence on DB and Mn. Among the resins synthesized, the highest DB reached 0.76 and the lowest one was 0.41, molecular weights of hyperbranched polyesters were from 1000 to 2600 g/mol.The first and second generation of dendritic polyesters have been prepared by divergent synthetic ways using trimethylopropame (TMP) as core and phthalic anhydride (PA), glycidol as branched units. The effects of reaction temperature, ratio of reactants and the ways of adding reactants on reaction conversion, molecular weight and molecular weight distribution of the oligomer were studied. The dendrimers were characterized by GPC, FT-ER, lH-NMR.The cure reaction of epoxy resin with carboxyl-functionalized hyperbranched polyesters, such as HBP-SA, HBP-MeTHPA, HBP-PA and HBP-HHPA etc., were studied. Gel time showed that the reaction rate increasedin the HBPs/epoxy resin systems as comparing with MeTHPA/epoxy resin system. It was also found that volume shrinkage decreased in the HBPs/epoxy resin systems, while mechanical properties and thermal properties of the cured materials in the HBPs/epoxy resin systems decreased .The kinetics of the cure reaction were studied by differential scanning calorimetry (DSC). DSC data indicated that nth-order behavior showed in the stages of the cure. The kinetics parameters were obtained by Ozawa, Kissinger and Crane formula, which includes activation energy (Ea), rate constants and reaction orders.A conventional epoxy resin was cured with the mixture of carboxyl-functionalized hyperbranched polyesters HBP-SA and methyltetrahydrophthalic anhydride (MeTHPA). There is great change in gel time as a result of addition of various HBP-SA contents. HBP-SA showed outstanding performance as toughen-hardeners in epoxy resin. The Tensile strength was increased from 22.57MPa to 64.66MPa using only a 10% HBP-SA, while the Impact strength was increased from 4.99KJ/m2 to 30.63KJ/m2. But then, addition of HBP-SA lead to a decrease in partly in resin properties, including the Bend strength, the Compress strength and the thermal properties.