The Average Molecular Weight Determination of Polysulfide Polymers by Using Ir Spectroscopy

Abstract

IR spectroscopy method has been designed in order to determine the average molecular weight of polysulfide polymers of the general formula:

where: the symbol End denotes the fragment H₃C - CH(C₆H₅) or SH functionality; x = 1 - 4, m = 1 - 40 and n = 1 - 40.

The average molecular weight was determined, according to the formula:

where L₁ represented the number of H₃C - CH(C₆H₅) fragments; L₂ corresponded to the number of polysulfide bonds; the parameter x was the number of sulfur atoms per one polysulfide bond; L₃ was the number of CH₂ - CH(C₆H₅) fragments bound along the polymer chain; L₄ represented the number of the ethylene fragments involved; L₅ denoted the number of - SH end groups and M₁ M₂, M₃, M₄, M₅ corresponded to the molecular masses of the various structural fragments indicated above.

To determine the content of ethylene fragments in the copolymers₁ the characteristic absorption band at 1104 cm⁻¹ was selected, whereas the band at 1600 cm⁻¹ was used for the evaluation of the fragments containing benzene rings. The content of the end methyl groups was, in turn, calculated by employing the band at 1380 cm⁻¹. The class of polysulfidity x was determined by using both the elemental analysis method and IR spectroscopy₁ particularly₁ the absorption band at 492 cm⁻¹. The results obtained from the spectroscopic determination of the average molecular weight were compared to those obtained by using the cryoscopic method. The relative analytical error for the determination of the average molecular weight did not exceed 5.9%.