The infrared identification of short-chain branches in polyolefins

Abstract

A series of polymers have been prepared that contain ethyl, n-propyl, n-butyl, n-pentyl, and n-hexyl branches. We have determined the rocking vibrations of the branches and have shown that branches in solid polymers have their rocking vibrations at frequencies comparable with those shown by liquid hydrocarbons. The ethyl branches in seven different polymers have infrared absorption bands in the 785–760 cm. −1 (12.74–13.18 μ) region. The terminal n-propyl group absorbs at 740 cm.−1 (13.51 μ) and the n-propyl branch at 735 cm.−1 (13.61 μ). The n-butyl, n-pentyl, and n-hexyl branches in polymers have their infrared absorption at 724 cm.−1 (13.81 μ), 723 cm.−1 (13.83 μ) and 722 cm.−1 (13.85 μ), respectively. The above data have been used to identify ethyl, n-propyl, and n-butyl branches in polymers produced by the cationic polymerization of propylene and l-butene.