Research On Migration And Compatibilization Of Block Copolymers In Polymer Blends

Polymer blending is an important processing method for the application of polymer materials.It can obtain low-cost and convenient materials and facilitate the recycling of waste polymer materials.However,most of the polymer materials are incompatible and have two-phase morphology,and the phase morphology is unstable,which is exhibit poor mechanical properties.Thus,amphiphilic block copolymers are added during processing to solve the incompatible issue.After adding a small amount of amphiphilic block copolymers,the interfacial tension and the size of the dispersed phase are effectively reduced while the interactions across the phase boundaries are strengthen.In our previous studies,we have found that different mixing sequences lead to different phase morphology.In this paper,we studied how the asymmetric block copolymers PS-PMMA migrate and enhance the compatibilization in PCHMA/PMMA under different mixing sequences.Phase morphology and distribution of block copolymers were observed by transmission electron microscope(TEM),Based on the above studies,the mechanism of block copolymer migration and compatibilization are discussed.Morphology of asymmetric block copolymers/homopolymers blends was observed by TEM.Normally,when asymmetric block copolymer add to homopolymer,the asymmetric block copolymer form micelle structure that the outer is compatible chain segment with homopolymer while the inner is incompatible chain segment.In our study of the PS-PMMA/PCHMA blend,we found that the micelles changed to vesicle by decreasing the molecular weight of block copolymer.While asymmetric PS-PMMA blend with PMMA,the micelles took place coalescence with increasing block polymer molecular weight.There is no significant effect on the phase morphology by increasing the volume percent of asymmetric copolymer.The phenomenon of migration and diffusion limitation of asymmetric block copolymers was discussed under different blending sequences: I)PS-PMMA premixing with PMMA and then mixing with PCHMA;II)PS-PMMA premixing with PCHMA and then mixing with PMMA.Comparing the phase morphologies of the polymer blend under the two blending sequences,we find that the morphology of the polymer blend is quite different.under different blending sequences,the migration of the block copolymers in the polymer blends is affected by the disentanglement and thermodynamics of the micelles,making it different for the block copolymers to migrate to the blending interface.Different trends have led to different morphologies of polymer blend.In a blending sequence I,block polymer prone to diffusing into another phase,the reason for affecting the compatibilization efficiency of the asymmetric copolymer is that the diffusion of the block copolymer from one phase to the other is limited.The diffusion limitation was related with critical micelle concentration of block copolymer.The diffusion process of block polymer was limited below the maximum transport limitation concentration(MTCL).The MTCL will be lower when the molecular weight of block copolymer was increasing.This process also affects the distribution of the block copolymer in the polymer blend,thus influences the phase size and the stability of the morphology of the polymer blend.