固化剂对环氧树脂/聚砜共混物层状结构形成的影响

不同含量的聚砜(PSF)对环氧树脂(EP)/PSF共混物相结构有重要影响,通过对反应分相后的样品进行断面观察,发现一定PSF含量时,体系形成了层状结构.这种层状结构通常为3层,包括上下2个外层、由聚砜和环氧树脂的颗粒-基体结构组成,以及1个双连续结构形成的中间层.研究表明,这种层状结构由反应诱导相分离开始之初形成的双连续结构发展而来,由于反应和相分离的进一步发展热塑性树脂富集相的体积分数逐渐减小、以及组分间的动力学不对称而最终形成的.在一定PSF浓度范围内,不同温度固化样品时均得到了这种层状结构.改变固化剂类型,层状结构的形貌受到影响,当固化剂活性较高时,外层变薄中间层增厚.当组分间的相容性较好时,双连续结构甚至不能演化发展到层状结构.

CURING AGENT INFLUENCE ON THE LAYERED-STRUCTURE FORMATION IN THE EPOXY/POLYSULFONE BLENDS

Epoxy/thermoplastic blends have been extensively studied because of the importance in toughening application and the fundamental academic interests.Morphological structure formation through reaction-induced phase separation in the diglycidyl ether of bisphenol A(DGEBA) and polysulfone(PSF) blends are investigated with various amounts of PSF and different kinds of curing agents.The fractured surfaces are studied with the scanning electron microscope,on the cross section or normal to the film surface of the sample film.Several morphological structures are observed at different PSF concentrations.Sea-island and inter-connected nodular structures are respectively obtained at lower and higher PSF concentrations.At appropriately middle PSF compositions,usually around 0.15 weight fractions for the samples,an unusual three-layered structure is formed.The upper and lower layers are similar,with PSF-rich particles sparsely dispersing in the epoxy-rich matrix;most of the PSF-rich domains are located in the middle layer,where bicontinuous structure is formed.It is found that the three-layered structure is developed from an initially bicontinuous structure,which will retract(PSF-rich network shrink) toward the middle region of the sample film with the proceeding of reaction and phase separation.Driving force for this phenomenon is the change of the Gibbs free energy,shift of the coexistence curve,volume fraction decrease of the PSF-rich network and the dynamic asymmetry between the components.At middle PSF compositions,the layered structure can be formed at various curing temperatures.When different curing agents are used,reaction rate will change,however,the reaction rate is not an essential cause for the formation of the layered structure.When the curing agent has a higher reactivity with the epoxy(for the DGEBA,2-ethyl-4-methylimidazole(2E4MZ) and PSF system),reaction kinetics may be better competitive with the phase separation kinetics,and the thickness ratio of the middle layer will increase,compared with the DGEBA,4,4′-diaminodiphenyl sulfone(DDS) and PSF system.However,better compatibility on the molecular level is introduced when the medium reactive curing agent,4,4′-diaminodiphenyl methane(DDM) is used to react with the DGEBA.The consequence is that the components are more dynamically symmetric during the phase separation,and the bicontinuous structure may not(or need not) develop to become a layered structure.