Preparation And Properties Of PP/mEOC In-reactor Alloy

A new process that combines the excellent morphology control of Ti-based catalysts with the unique features of polyolefm from metallocenes has been developed. First, Functional polypropylene was prepared with the copolymerization of propylene and polar comonomer (trimethyl-(1,1,5-trimethyl-hept-6-enyloxy)-silane) catalyzed by MgCl₂-supported TiCl₄ catalyst, which, upon being hydrolyzed, resulted in polypropylene granules containing hydroxyl functionality. The copolymerization conditions( such as comonomer concentration, polymerization temperature, pressure, polymerization time) were studied. Immobilization of rac-Et(Ind)₂ZrCl₂/MAO was then conducted in toluene solution at a elevated temperature following the procedure of treating the hydroxyl-containing polymers sequentially with MAO and rac-Et(Ind)₂ZrCl₂. Then, the ethylene-octene copolymerization, catalyzed by the metallocene supported PP particles, is carried out in slurry environment. A noticeable increase in activity is seen as the concentration of 1-octene in the reaction medium increases. ¹³C NMR analysis shows higher incorporation of comonomer at the higher 1-octene concentration in the feed used here. The melting temperature of the copolymers shows a decrease with increasing comonomer content. Under appropriate reaction conditions, well separated spherical particles of i-PP/m-EOC reactor alloy containing up to about 39% m-EOC were obtained, which is indicative of the stable immobilization of the homogeneous catalyst on functional PP granulas.The isothermal crystallization behavior of polypropylene (PP) in-reactor alloys was studied by using differential scanning calorimetry (DSC) and polarized optical microscopy in this dissertation. In the isothermal crystallization experiments, it was found that the Avrami exponent n of PP and PP in-reactor alloy are nearly the same, which suggested that they shared the same heterogeneous nucleation mode. Crystallization half-time t_1/2 showed that the crystallization rate of PP in-reactor alloy faster than that of both PP homopolymer and mechnical blends, indicating that the in-situ formed ethylene-octene copolymer component increased the nucleation rate and therefore the crystallization rate. By using polarized optical microscopy, we found that the spherulites of PP in-reactor alloy showed smmller crystalline size. The phase morphology studies prove that the m-EOC could be finely in-situ formed inside the PP granules with average size below 2μm. The DMA analysis shows that E' value of in- reactor alloy is higher than that of mechanical alloy; loss modulus E" peaks corresponding to the glass transition of EOC in reactor blends is obviously lower than that in mechanical one. On the other hand, the loss modulus E" peaks relevant to the glass transition of PP in mechanical blends is much lower than that of reactor ones. These findings are due to chemical absorption of metallocene to improve the adhesion between PP matrix and dispersed phase and increase the interfacial thickness. With the improvement of interaction between EOC and PP, the segmental motion of EOC chains in reactor blends will be further restricted. And when the PP segments begin to move, the EOC chain in turn will restrict its motion because of chain interaction. The higher E' of in-reactor alloy can also be explained by the well phase adhesion between PP and EOC.