Chemical Modification of Poly(Vinyl Chloride): Improved Thermal Stability by Partial Reduction with Organoboron Reagents

The thermal degradation of poly(vinyl chloride) (PVC) by a zipperlike dehydrochlorination is believed to initiate at abnormal structures present in the resin backbone. The allylic chlorines are major contributors to instability of the polymer. A selective replacement of the allylic chlorines with hydrogen on the PVC chain is accomplished by the use of organoboron reagents. Treatment of PVC with lithium triethylborohydride resulted in the reduction of chloroethyl chain ends, as well as the allylic chlorines. A considerable improvement in the static and dynamic thermal stabilities of PVC, treated with organoboron reagents, is observed. It is also demonstrated that the removal of chain end chlorines further enhances the stabilization effect. The reaction of certain model compounds, representing the defect structures present in PVC, with organoboron reagents was studied. The evidence for an addition—elimination mechanism in the reactions with substrates, containing allylic chlorines, is presented.