Thermal Degradation Of PVC Research Articles

Sur la dégradation thermique du polychlorure de vinyle. IV. Influence de la régularité structurale des polymères sur leur stabilité thermique sous atmosphère inerte

The kinetics of the dehydrochlorination and the other effects of the thermal degradation of PVC in an inert atmosphere have been studied between 140 and 250°C., special attention being paid to the initial steps of the process. The polymers studied are either pure PVC polymerized by free radicals at 60, 0, −12, or −35°C. or derivatives obtained by the partial substitution of the chlorine by diphenylmethyl groups. It is possible to explain the observed results by assuming the existence of two processes. The first is dehydrochlorination, a radical chain reaction made up of an initiation reaction, a fairly short sequence of fast dehydrochlorination steps, and a termination reaction; the second process is an intermolecular condensation with HCl elimination causing both the crosslinking of the polymer and the formation of secondary sites for the initiation of the radical process which is thereby accelerated. The irregular structures initially present in the PVC provide the primary initiation sites and act especially at the beginning of the degradation. These sites are less numerous when the polymerization temperature is lower. The termination occurs by the mutual destruction of two radicals. A higher degree of polymer crystallinity favors intermolecular condensation and therefore the acceleration of the dehydrochlorination. The substitution of chlorine atoms by diphenylmethyl groups leads to a marked stabilization of the polymer as a result of the neutralization of the primary initiation sites.

ポリ塩化ビニルの熱分解と酸素の吸収

を空気中で熱劣化させると, 脱塩酸と酸化によるカーボニル基や水酸基の生成とがみられる。赤外吸収だけでは結合酸素の絶対量がわからないので, 酸素を直接に微量分析によって定量した。元素分析の結果, C1が1個とれた場合Hは約2個とれ, 酸素が約1/2個ついた。180℃ 熱劣化の場合, 1725cm-1の赤外吸収と酸素分析値はほぼ直線関係であった。685cm-1付近の吸収と塩素分析値とは直線にならなかった。劣化試料の紫外部の吸収, 粘度と溶解性, 比重, X線回折などを測定した。熱劣化により比重は増大するが, X線による変化は認められなかった。