The important characteristics of hyperbranched polymers (HBP) are the extremely high degree of branching of its branched repeating units and the large number of functional end groups on the surface of the polymer core-shell structure. Because the highly branched structure prevents the occurrence of chain entanglement, hyperbranched polymers usually show lower viscosity in the molten state or in solution. The performance of hyperbranched polymers is mainly affected by a large number of end groups, so end group modification can obtain hyperbranched polymers for different purposes. Recently, the industry has carried out experiments on toughening epoxy resins with reactive core-shell hyperbranched block copolyethers. The purpose is to use the anionic ring-opening copolymerization of glycidol and propylene oxide to prepare nano-new onion-type hyperbranched polyethers. As a new softener and toughening agent for thermosetting resins. In order to obtain good compatibility, lower viscosity, better interfacial adhesion, phase separation and other properties, the focus is on the polarity and activity design of hyperbranched polyethers. In this experiment, the preparation of raw materials is very critical,
After the raw materials are in place, the end groups are modified first. The first step is to prepare 36P21 and 35P26: 200g (12.0mmol; 1.03 mol hydroxyg) of hyperbranched block copolymer and 83g (0.50mol) of ethyl p-hydroxybenzoate are mixed and heated to 160° C., reacting at constant temperature for 14 days. Continuously pass nitrogen gas to take away the ethanol produced in the reaction; the amount of ethyl hydroxybenzoate can convert 49% of the terminal hydroxyl groups into phenolic groups. Add 2.0mL dibutyltin dilaurate (DBTDL.2.1g, 0.5% mass fraction) as a catalyst; the obtained high-viscosity product 36P21 is degassed under reduced pressure, and then 57g (2.6mmol; 0.24 mol hydroxyl) is taken to functionalize the phenolic group HBP 36P21 reacted with 16.4g (0.055mol) methyl stearate and 0.3mL catalyst DBTDL (0.3g, 0.4% mass fraction) at 160℃ for 6 days. The stoichiometry is used to control the end group conversion rate of 24.2%. In theory, 21 alkyl chains are finally introduced on the end groups of the hyperbranched block copolymer; a heterogeneous mixture is formed at the initial stage, and the heterogeneous mixture becomes a single Phase system. The obtained yellow high-viscosity liquid product 35P26 was degassed under reduced pressure.
Step 1 Preparation of 22E22 and 6E40: In order to introduce primary active epoxy end groups, 139g (8.05mmol; 0.10mol phenolic group) phenolic functionalized block copolymer 36P21 was dissolved in 1.5L DMF, and then 194g (1.4mol ) Anhydrous K2C03 and 110mL (130g, 1.4mol) epichlorohydrin; the active mixture is reacted at 60°C for 10h under mechanical stirring and nitrogen atmosphere. The inorganic salt in the reaction product is filtered out, and then it is removed by distillation under reduced pressure. The solvent was removed, the residue was dissolved with dichloromethane and washed 3 times with water; the organic phase was dried with anhydrous MgS04, and the solvent was removed by vacuum to obtain a viscous light yellow oily product 22E22. The third step is to prepare PPO 6E4: For comparison experiments, the terminal hydroxyl groups of the six-arm star polyoxypropylene/ethylene oxide block copolymer Baygal are completely converted into phenolic groups, and then the same as the above-mentioned synthetic hyperbranched block copolymer is used. Method, these phenolic groups are epoxidized, and finally epoxy functionalized six-arm star PPO 6E4 is obtained, which is a viscous yellow liquid product.
In the fourth step, 18E31 was prepared, 130g (7.6 mmol; O.67mol hydroxyl) hyperbranched block copolymer, 66g (0.22mol) methyl stearate, 1.4g catalyst DBTDL (O.5%), kept at 160℃ Reaction for 8d; continuous nitrogen gas to take away the methanol generated in the reaction. The amount of methyl stearate can modify 33% of the terminal hydroxyl groups on the hyperbranched block copolymer. The viscous product obtained was vacuum degassed, and then further modified with 47g (0.28mol) ethyl p-hydroxybenzoate, the method used is the same as the modification method for 36P21 above; the amount of ethyl p-hydroxybenzoate 42% of the initial hydroxyl groups of the hyperbranched block copolymer can be modified; in the end, the modified hyperbranched polymer is epoxidized with epichlorohydrin in the same way as the previous method to obtain a viscous orange liquid product "18E31".
After completing the above steps, proceed to the preparation of the epoxy blend. Take 22.5g of each polymer modifier and 240g of bisphenol A diglycidyl ether (Araladite CY225) in a Moheni Planimax high-speed shear mixer under the conditions of 1000Pa and 80℃, stir and mix for 45min to make the polymer fully dissolved And reduce residual moisture. Then, 190 g of hexahydrophthalic anhydride (Hardener HY 925) was added to obtain 450 g of mixture. Stir for another 30 min under the conditions of 1000 Pa and 80°C. The obtained resin was poured into a 200mm×200mm×4mm mold, cured at 120°C for 2h, and then dried in a ventilated drying oven at 140°C for 8h. Finally, a ring containing 5% mass fraction of polymer modifier was obtained. Oxygen blend. All blends containing 2.5% or 5% by mass of polymer modifier are prepared in this way. The blend containing HBP 35P26 was pre-gelled at 80°C for 18 hours before curing in the mold. For each polymer modifier, the actual amount of resin and curing agent is calculated based on the number of active end groups of the functionalized modifier used. The stoichiometric ratio between the epoxy group (on the BADGE or modifier) and the functional group (anhydride group or phenol group) with which it reacts remains constant. The epoxy blends were characterized by TEM and mechanical tests widely used in the literature. '