It has been shown that the use of the industrial S-1 thermostabilizer in the synthesis of polyethylene terephthalate aids in obtaining high molecular polymer with an improved thermal stability and an increased degree of crystallinity.

A process for preparation of modified Lavsan fibre using caprolactam as the modifier has been proposed and has been checked out on the pilot plant of the Mogilevsk “Khimvolokno” Industrial Association.