The effect of multiwalled carbon nanotube (MWCNT) dimensions and surface modification on the morphology, mechanical reinforcement, and electrical properties of PP-based composites, prepared by melt mixing, has been studied. The MWCNTs of small (d < 10 nm) and large (d ¼ 40-60 nm) diameters with various intrinsic aspect ratios (L/d) have been used as filler. Transmission electron microscopy and very cold neutrons (VCN) scattering showed that both as-received and surface modified small diameter MWCNT(1)s exhibit a strong tendency to bundle or cluster together in melt compared to both long MWCNT(3)s and short MWCNT(2)s large diameter nanotubes. The fractions of isolated nanotubes are higher and the mass-fractal dimensions are lower for thick MWCNTbased nanocomposites. The nanotubes of all types are heterogeneous nucleation sites for PP crystallization. The tensile and DMA testing results revealed that both long thick MWCNT(3)s with L/d % 300 and thin MWCNT(1)s with highest intrinsic L/d > 1000 exhibit similar reinforcing effects, because drastically decreasing the effective aspect ratio (L/d) eff of the thin flexibly nanotubes within polymer matrix. The nanocomposites based on the long large diameter MWCNT(3)s demonstrated the lowest percolation threshold equal to 1.5 vol % loading, highest dielectric and electromagnetic waves shielding properties. It was concluded that the choice of optimal diameter and length of MWCNTs is right approach to the improvement in the dispersion state and straightness of multiwelled carbon nanotubes in polymer melt as well as to enhancement of their efficiency as reinforcing and conductive nanosized filler.

Amorphous atactic polypropylene (PP) with an average molecular weight of 50,000-100,000 is produced by polymerizing propylene with a ternary Ti(Oiso-Pr) 4 -AlEt 2 Cl/MgBu 2 catalyst at 30-50. Main advantages of this catalyst compared with other catalysts capable of nearly exclusively producing atactic PP (such as some heterogeneous Ziegler-Natta, metallocene and postmetallocene catalysts) are high activity, low cost and the ease of use: the catalyst is prepared in situ from three commercially available compounds readily soluble in aliphatic and aromatic hydrocarbons.

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The polymerization of ethylene and propylene and the copolymerization of ethylene and hexene-1 with a Ti(O-iso-Pr) 4 -AlR 2 Cl/MgBu 2 catalyst system have been studied. The advantages of this system over metallocene and postmetallocene catalysts are high activity, low cost, and ease of synthesis. The resulting polymers and copolymers are characterized by a broad molecular-mass distribution, which reflects the heterogeneity of the active sites with respect to kinetic parameters. As a consequence, the ethylene/hexene-1 copolymers exhibit compositional heterogeneity. The active sites of the system produce copolymers with a pronounced tendency toward alternation of monomer units. The propylene polymerization product is mostly amorphous atactic polypropylene.

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