Study On Thermoset Acrylate Liquid Crystalline Resin

Thermoset liquid crystalline resin (TLCR) is a new material which has properties of both thermoset and liquid crystalline (LC). Its high mechanical strength and heat resistance, good dimensional stability and processability, excellent optical and electrical properties make it be promisingly used as a high-performance resin matrix. As a member of the family of TLCR, thermoset acrylate liquid crystalline resin (TALCR) has drawn much attentions compared to other TLCRs because of its low thermotropic transition temperature, good solubility in common solvents.Although studies on TALCRs have been conducting relatively longer, investigation on their mechanical properties remains a fewer. Some TALCRs also show low heat resistance due to the presence of long spacer. Besides, the present synthesis routes are involved in too much acryloylchloride and chloro-nol, which are either poisonous or expensive. With these considerations, four novel TALCRs are firstly designed and synthesized. Two of them are TALCRs without spacer, and the other two are TALCRs with short spacer. The latter are synthesized with a new route, which relies on the esterification of epoxy and acrylic acid. All TALCRs possess desired structure and good solubility in common solvents such as acetone. Most of them have mesogenic phase, which is proved with POM and DSC. At the same time, the factors influencing mesogenic phase are also discussed. Furthermore, mechanical properties and heat resistance of the cured resins are characterized with DMA, DTA, TGA and other related methods. Compared with the cured resins of common vinyl ester, the cured TALCRs have good performances with higher 'impact and bend strength, higher modulus and glass transition temperatures. It is the mesogenic phase in the cured TALCRs that contribute to these advantages over the common resins, and the presence of the mesogenic phase is characterized with SEM and WAXD.In'addition, thermosets often show low impact strength and poor fracture toughness, so it is desirable to improve their toughness. However, the present approaches to toughen thermosets such as incorporating reactive rubbers or thermoplastics to thermosets usually result in decrease of other properties, such as heat resistance, modulus and processability. For the first time, the TALCRs are used to toughen diallyl isophthalate (DAIP), and the factors influencing the properties such as type and content of modifier, curing procedure are discussed. With a great improvement of impact strength, the modified DAIPs also show the increase in bend strength, .modulus and heat resistance. Moreover, the toughness mechanism of the modified systems is studied with DMA, SEM and WAXD.Modification of vinyl ester (VE) and poly(methylmethacrylate) (PMMA) with TALCRs is also studied. Same as modified DAIP systems, these two modified systems are also characterized with above methods. It is found that good compatibility, high copolymerziation of modified systems and low content of modifiers can influence the phase-separation and the appearance of mesogenic phase, which may reduce the modifying effect.