Neutron scattering studies on solution-grown crystals of polyethylene: a statistical preference for adjacent re-entry

Neutron scattering studies of solution-grown polyethylene crystals demonstrate a strong statistical preference for adjacent re-entry, with 75% of stems occupying adjacent lattice sites. The number of sheets of stems for one molecule increases with molecular weight, with an average molecular weight per sheet of 21 000. These are the main features of computer models which give the best agreement with scattering data obtained over an angular range ($\text{q</1}\text{A}\text{?}{}^{\mathrm{?1}}$). Scattering in this q range is directly sensitive to typical stem separations. Any preference for alternate re-entry would result in a peak at $\text{q=0.7}\text{A}\text{?}{}^{\mathrm{?1}}$, which was not observed. The results are discussed in terms of possible crystallization mechanisms.