Poly [(butadiene-ah-ethene)-co-(butadiene-alf-1-olefin)] terpolymers were synthesized by Ziegler-Natta polymerization using VO(O-ne~pentyl),CVAl(i-Bu)~ catalyst system in toluene. Variation of the 1-olefidethene ratio in the monomer feed produces terpolymers with mixed units of butadiene-alt-ethene and butadiene-alt-1 -olefin. After hydrogenation one obtains model substances for LLDPE with a special distribution of methylene sequences between branching points. Differential scanning calorimetry (DSC) was used to determine the degree of crystallinity and the melting behavior. From the melting temperature region, the thickness distribution of the crystal lamellae, and thus the average number of C-atoms between the alkyl branches, can be determined. From detailed X-ray diffractometry, the mean crystallite size, the lattice distortions and the degree of crystallinity was determined for those products which show distinct reflections. The crystallization behavior can only be described by a three-phase model.
The crystallization behaviour of the series of hydrogenated poly@utadiene-ult-ethene) to poly[butadiene-ult-( 1 -hexadecene)] copolymers was investigated with the aid of differential scanning calorimetry (DSC) and X-ray measurements. Hydrogenated poly(butadiene-ultethene) corresponds to polyethylene and crystallizes in the same way. Hydrogenated copolymers poly@utadiene-ult-propene) through poly [butadiene-ult-( I-decene)] are completely amorphous. In these cases the large branching degree prevents crystallization of the main chains, whereas the side chains are too short to be able to crystallize above the glass transition temperature. The critical length is obviously reached in case of hydrogenated polyputadiene-ult-(1-dodecene)]. The part of the series with large side chains (hydrogenated poly [butadiene-&-( 1 -dodecene)] through poly [butadiene-&-( 1 -hexadecene)]shows the most interesting effects, especially hydrogenated polyputadiene-ult-( 1 -dodecene)], which shows crystallization depending on thermal history. In these substances the side chains are long enough to cause side-chain crystallization, which becomes more pronounced with increasing length of the side chains. The crystal structure is not exactly to be determined, but some data indicate a model, in which the side chains are packed in a manner as in unbranched alkanes, but are also possible orthorhombic. However, the quality of the crystals formed is not very good, so these regions are better described as ordered domains rather than as crystallites.
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