Isotactic polypropylene(iPP) is a versatile semicrystalline polymer of considerable commercial importance. Its properties are greatly affected by isotacticity of itself. In this work, thermal and rheological behaviors of iPP were investigated in a view of tacticity effect. In addition, thermal and rheological behaviors of blend of iPP and sPP ,chemically same but having different tacticity, were also studied in a view of the their miscibility. To obtain highly isotactic polypropylene, commercial iPP was fractionated by conventional soxhlet extractor using xylene. The isotacticity of iPPs were measured using FT-IR spectroscopy. Insoluble fractions obtained from fractionation had higher IR-indices compared with unfractionated iPPs.
Melting and crystallization behaviors of each samples obtained by fractionation were examined using DSC measurement. Melting point ($T_m$) and enthalpy of fusion ($ΔH_f$) of insoluble fractions, having higher IR-indices, were higher than those of unfractionated samples. Futhermore cystallization temperature ($T_c$) and enthalpy of cystallization ($ΔH_c$) were increased in insoluble fractions. These implied that the isotacticity of iPP was increased by fractionation using solvent.
In non-isothermal crystallization experiment ozawa constant, n, obtained using ozawa equation, was increased as isotacticity increased, but fractionated iPPs had lower ozawa constants than unfractionated samples.
To investigate the tacticity effects on the rheological properties of iPPs, LogG'-LogG"plots of unfractionated samples and insoluble fractions were compared. Slops of insoluble fractions were slightly lower than those of unfractionated samples in low frequency region. Modulus curves of all samples were well superposed by horizental shifting on frequency axis. Using the shifting factor, aT, flow activation energy($E_a$) was obtained by using the Arrhenius-like equation. Flow activation energy of insoluble fractions (12~13 kcal/mol) had higher values than those of unfractionated samples (9~10 kcal/mol). This higher activation energy was due to the rotational hidrance of more regular isotactic chains.
In iPP/sPP blend, crystallization temperature of iPP component were lower than pure iPP and those of sPP component were higher than pure sPP. This behaviors were due to the dilution and nucleation effects of each component. But these temperature did not changed with blend compositions. This trends were same in melting behaviors. The enthalpy of melting and crystallization were followed the mixing rule. This results showed that each component in blend did not affect on the melting and crystallization behaviors of counter components.
Morphologies of iPP/sPP blend showed that two components were separated in molten state. Slops of LogG'-LogG" plot of blends were decreased in the lower frequency region. Thus iPP and sPP, having different tacticity, were immisicble in melt state due to their tacticity.
