| Shape memory epoxy (SMEP), a new type of smart material attracts more attentions in recent years because of its outstanding shape memory performance and excellent mechanical property as well as broad application prospects. Toughening research is important for the basic study and practical application of SMEP. Hyperbranched polymer (HBP) is another recent emerging research hotspot. HBP modified epoxy can be effectively toughened along with slight impact on the strength and thermal properties. Moreover, the reactivity between HBP and epoxy matrix can easily be adjusted. In this thesis, hyperbranched polymer “poly-3-ethyl-3-(hydroxymethyl)oxetane (HBPO)” with different degree of branching and HBPO with different proportion of carboxyl grafting were synthesized and used for toughening SMEP. The effects of HBPO content, curing method, degree of branching and proportion of carboxyl grafting on properties of SMEP systems were investigated. The curing mechanism and toughening mechanism were studied.First, HBPO with high degree of branching was synthesized and characterized by1H-NMR, quantitative13C-NMR and GPC methods. The curing mechanism of HBPO/SMEP-AA system was studied through variable-temperature FT-IR method. Two curing methods were chosen for preparation of HBPO/SMEP-AA systems. Then, the effects of HBPO content and curing method on mechanical property, Tg and shape memory property of SMEP system were investigated. The system10%-HBPO-1-GX prepared with the second curing method the best toughening performance with elongation at break, work of fracture and tensile strength increased by70%,147%and40%respectively. Tg value slightly decreased compared with the unmodified SMEP system. Incorporation of HBPO had no effect on SMEP’s shape retention ratio and shape recovery ratio, whereas improved the shape recovery rate. Thus, good toughness, high strength and good heat resistance were concomitantly achieved. It was revealed that HBPO/SMEP-AA was a homogeneous system with higher extent of reaction, smaller free volume size and lower free volume content. Microstructural analysis revealed a toughening mechanism of HBPO/SMEP-AA system which well explained the observed simultaneous improved toughness and strength, and the difference between HBPO/SMEP-AA and other HBP modified epoxy systems. With this toughening mechanism, three-dimensional staggered fields centered in HBPO formed in the modified system. A series of HBPO with different degree of branching were synthesized and characterized. The effects of HBPO’s degree of branching on curing mechanism and properties of HBPO/SMEP-AA system were investigated. The results showed that, with lower HBPO’s degree of branching, toughness, strength and modulus of the modified system all reduced, Tg slightly decreased, shape retention ratio and shape recovery ratio unaffected, but the shape recovery temperature lowered, temperature range during recovery process became larger, and the recovery rate reduced. The microstructural analysis revealed, with lower HBPO’s degree of branching for HBPO/SMEP-AA system, poorer compatibility, slightly reduced extent of reaction, larger free volume size, higher free volume content and weaker interfacial interaction. Three-dimensional staggered fields were hard to form and to function effectively in HBPO/SMEP-AA system modified by HBPO with low degree of branching, and that’s what made properties reduced.A series of HBPOS with different proportion of carboxyl grafting were synthesized and characterized in detail. The effects of carboxyl grafting on curing of HBPOS/SMEP-AA and HBPOS’s proportion of carboxyl grafting on properties of this system were investigated. The results showed that, with increased HBPOS’s proportion of carboxyl grafting, toughness and strength of the modified system both reduced, Tg value first increased and then slightly decreased, shape retention ratio and shape recovery ratio of modified system unaffected, but temperature range during recovery process larger, and the shape recovery rate reduced. The microstructure analysis revealed that, with increased HBPOS’s proportion of carboxyl grafting, HBPOS/SMEP-AA system got poorer compatibility, slightly improved extent of reaction, larger free volume size, higher free volume content, weaker interfacial interaction and a gradually changed fractograph. Three-dimensional staggered fields were hard to form in HBPOS/SMEP-AA system because of intense steric effect of HBPOS.HBPO was used for toughening SMEP-AM system. The curing mechanism of HBPO/SMEP-AM system was studied through variable-temperature FT-IR. Then the effect of HBPO content on properties of HBPO/SMEP-AM system was investigated. The results showed that, with increased HBPO content, toughness and strength of the modified system first increased and then decreased. The modified system with5wt.%HBPO content achieved the best toughening performance, with elongation at break, work of fracture, tensile strength and Tg value increased by38%,77%,29%and3℃respectively. The shape retention ratio and shape recovery ratio of modified system were unaffected, and the shape recovery rate of SMEP could be improved at an appropriate HBPO content. The microstructural analysis revealed that HBPO/SMEP-AM was a heterogeneous system and its extent of reaction was highly improved after incorporation of HBPO. The toughening mechanism of HBPO/SMEP-AM system was found to be cavitation and matrix shear deformation. |
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