The Study Of Binary Crystalline Polymer Blends: Polypropylene/Polybutene-1

Polymer blending provides a simple and effective approach for the preparation of materials with new desirable properties aswell as reducing the basic costs and improving the processability. The properties of polymer blends depend not only on the constituents* individual properties but also on their aggregation Structure. Recently, the crystalline/crystalline polymer blends have received much attention, as they canproduce a wide variety of superstructures, which is more helpful in tailoring the properties. As most polymer pairs are thermodynamically immiscible or partially miscible, two typesof phase transitions, liquid-liquid phase separation (LLPS) and crystallization may occur simultaneously upon cooling the blend melt. The final morphology and property of the polymer blends are controlled by the pathways determined by the competition and interaction between these phase transitions. However, up to now, the complexity of the interplay between LLPS and crystallization remains largely unexplored.Isotactic poly-propylene (iPP) and isotactic poly(1-butene) (iPB-1) are widely used polymer materials, with many attractive properties, however, may have shortcomings in some aspects. Blending them together can complement each other’s advantages. As two kinds of crystalline poly-a-olefin, the similarities of iPP and iPB-lin chemical structure and helical conformation ensure the miscibility of iPP/iPB-1 blends to some extent, which can be a model system of crystalline/crystalline polymer blends. In this thesis, the miscibility of iPP/iPB-1 blends, the effects of blending on the crystallization behavior and morphology, the interplay between LLPS and crystallization and its influence on LLPS and crystallization behavior of each component have been systematically studied. The major work and conclusions are summarized as follows:(1) The evolution of phase morphology of blends melt with different compositions were studied by optical microscope (OM). LLPS take place with different mechanisms, depending on the compositions. Results show that iPP/iPB-1 blends are partially miscible with an UCST type of phase diagram.(2) The effects of blending on the crystal morphology and crystallization behavior of each component were studied by combining OM, DSC and FTIR. The morphology of crystals became regular with the increase of the corresponding content; Mixing with iPP always promotes the crystallization kinetics of iPB-1. while the addition of iPB-1 introduces two opposite effects:the crystallization of iPP may suppressed since iPB-1 may acting as one kind of high viscosity polymeric diluent may also be assisted by the LLPS in blends system.(3) The influence of initial state before cooling on LLPS and the interplay of LLPS and iPP crystallization were studied by OM and FTIR. The initial state of blends melt play an important role in the relative rate of LLPS and iPP crystallization. The higher the mixing degree of the melt state, the easier the LLPS occurs. If LLPS and iPP crystallization take place simultaneously, the crystallization kinetics of iPP can be accelerated to a large extent, which depends on the strength of LLPS.(4) A two-step crystallization experiment was performed. iPP component crystalized first at different temperatures which were too high for iPB-1 to crystallization. The competition of LLPS and iPP crystallization in the first crystallization procedure at different temperatures produce blends state with different phase structure. The effect of phase structure on the crystallization of iPB-1 was studied. The crystallization of iPB-1 is enhance with the increase of iPP crystallization temperature; while when iPP is crystalized at a moderate temperature, two types of iPB-1 crystallization occurs which is due to the distribution and concentration of iPB-1 component.(5) The influence of thermal processes on the polymorphism of iPB-1 was studied. Form 1’crystal can be generated directly at atmospheric pressure when cooling the iPP/iPB-1 blend melt. The formation of form I’is promoted by increasing the mixing degree of blends melt, while is suppresses by raising the quenching temperature. Results indicate that crystallization pathway can be altered by the interplay between LLPS and crystallization.