Zongjie Du

A study on the properties of epoxy resin toughened by a liquid crystal‐type oligomer

A series of novel reactive toughening agents (LCEUPPG) containing both a flexible spacer and rigid liquid crystalline unit were synthesized to modify the bisphenol epoxy resin/dicyandiamide curing system. The curing reactivity, apparent activation energy, curing mechanism, dynamic mechanical behavior, and impact strength of the modified system were systematically studied. Compared with the unmodified system, the results indicate that LCEUPPG have greatly accelerated the curing reaction between epoxy resin and dicyandiamide, reduced the apparent activation energy of the curing reaction, enhanced the impact strength 3–7 times, and maintained high dynamic modulus and good thermal properties. In addition, SEM observation of the fracture surfaces showed a two-phase microstructure in the modified systems.

Synthesis of well-defined poly(N-isopropylacrylamide)-b-poly(L-glutamic acid) by a versatile approach and micellization.

A novel Fmoc-protected chain transfer agent (CTA) was synthesized and applied in the reversible addition-fragmentation chain transfer (RAFT) polymerization of N-isopropylacrylamide (NIPAAm), resulting in well-defined Fmoc-protected PNIPAAm and the amino-end capped PNIPAAm by the subsequent hydrolysis. Poly(N-isopropylacrylamide)-b-poly(l-glutamic acid) (PNIPAAm-b-PLGA) with controlled molecular weight and narrow molecular weight distribution was synthesized successfully via ring-opening polymerization (ROP) of alpha-amino acid N-carboxyanhydrides (NCAs) by using PNIPAAm-NH2 as the macroinitiator. Both pH- and thermo-responsive micellization behaviors of the block copolymer PNIPAAm55-b-PLGA35 in dilute aqueous solution were investigated by means of the pyrene fluorescence, circular dichroism, 1H NMR, transmission electron microscopy and dynamic and static light scattering. Spherical PLGA-core and rod-like PNIPAAm-core micelles are formed in response to pH and temperature. The reversible transition between the PLGA-core and PNIPAAm-core micelles was observed. This work provides a versatile approach for synthesizing well-defined stimuli-responsive polypeptide-based double hydrophilic diblock copolymers (DHBCs), and is of great potential for generating useful stimuli-responsive materials in biomedical applications.

A study on properties of epoxy resin toughened by functionalized polymer containing rigid, rod-like moiety

Abstract A series of novel reactive toughening agents defined as LCEUPEG containing both flexible chain and rigid, rod-like moiety were synthesized and used to modify the epoxy resin (E-51)/dicyandiamide (dicy) curing system. The curing reactivity, apparent activation energy Ea, curing mechanism, dynamic mechanical behavior, impact strength of E-51/LCEUPEG/dicy systems was studied. The results show that the addition of LCEUPEG to epoxy resin and dicy curing system has apparently accelerated the curing reaction, reduced the apparent activation energy Ea of the curing reaction by about 60 kJ/mol, and decreased the curing temperature by about 50°C. In addition, the high modulus and good thermal properties are maintained, and the impact strength is enhanced by three to seven times compared with that of the unmodified sample.

Application of a series of novel chain-extended ureas as latent-curing agents and toughening modifiers for epoxy resin

A series of novel chain-extended ureas (Ui) containing poly(ethylene glycol) (PEG) spacers with different molecular weights were synthesized and the reactive mechanism, reactive activity, impact strength, dynamic mechanical behavior, morphology, and storage properties of the epoxy resin/chain-extended urea system were studied. Experimental results revealed that the impact strength of the epoxy resin modified with chain-extended urea containing a PEG flexible spacer with molecular weight of 1000 is 9.5 times higher than that of the epoxy resin/dicyandiamide system. Results also show that the molecular weight of PEG in chain-extended ureas hardly has any influence on the reactive activity of the chain-extended ureas. The storage life of the epoxy resin/Ui system can be delayed to 38 h at 50°C.

Modification of epoxy resins by acrylic copolymers with side-chained mesogenic units

A series of acrylic copolymer modifiers with mesogenic side chain (LCGMB) were synthesized and used to modify E-51/DDM system. The dynamic mechanical behavior and impact strength of the modified systems were investigated. The results showed that the impact strength and modulus were influenced by the composition and the amounts of the modifiers. With addition of 10% (wt %) LCGMB (molar ratio of GMA : HEMA : MMA : BA = 4 : 10 : 26 : 60) based on the amount of the epoxy resin, the modified systems obtained 100% increase in impact strength, 10% increase in modulus, and a little increase in Tg. The toughening mechanism of the modified systems was also discussed.