| A systematic study of linear random copolymers of ethene with 1-butene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene and 1-octadecene has been made. Most copolymers were synthesized in a range of compositions, using dicyclopentadienyl zirconocene dichloride (in hexane solution polymerization) or titanium tetrachloride (in bulk polymerization) as catalysts. Copolymers of ethene with 1-butene, and some of the copolymers of ethene with 1-octene were commercial samples prepared via metallocene chemistry. All copolymers were characterized by solution viscometry, Fourier-transform infrared spectroscopy-FTIR, and differential scanning calorimetry-DSC. Films of the copolymers had their permeability to water vapor, carbon dioxide and oxygen measured. In agreement with previous studies, the melting point of random ethene copolymers was shown to depend only on the molar content of comonomer, being mostly independent of the type of branch. However, it was found that the permeability coefficients to oxygen and carbon dioxide not only are affected by the comonomer content, as established by previous knowledge, but that they also depend on the type of branch. In addition, highly branched copolymers, which develop side-chain crystallinity, exhibited permeation properties that are much more sensitive to temperature than their unbranched counterparts. Exploration of the temperature and branch-dependence of the permeability of these olefin-based materials is proposed for the manufacturing of films used in the packaging of fresh produce, which need controlled atmosphere and adjusted gas permeation rates for extended preservation. |
