Metallocene polymerized ultralow density polyethylenes (ULDPE) were found t
o be effective impact modifiers for rigid matrices such as polypropylene (P
P). This is mainly due to the very high level of comonomer incorporation wi
th homogeneous short chain branching distributions (SCBD) brought about by
the single site metallocene catalysts. However, a very heterogeneous Ziegle
r Natta copolymer of 0.88 specific gravity was found to be surprisingly eff
ective in impact modification efficiency.
A variety of thermal and morphological techniques were used in this study i
ncluding differential scanning calorimetry (DSC), dynamic mechanical analys
is (DMA), and low voltage scanning electron microscopy (LVSEM). It was foun
d that the modulus difference between the two phases, degree of coupling as
evidenced by morphology at the phase boundaries, and crystallizable fracti
on of the rubber phase all played an important role in impact modification.
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