PVC heat stabilizers Processing Why do we need

Why do we need PVC heat stabilizers Processing
PVC is the first ideal structure - tail structure-CH2-CHCl-CH2-CHCl-, is quite stable. But so far the PVC synthesis method can not be like synthetic butadiene rubber, as the role of PVC stabilizer for pipe  catalyst in Jigger so there are rules for orientation cis butadiene polymerization. Radical polymerization of vinyl chloride is a random polymerization, in addition to its first stable - tail structure, there are first - the first structure - CH2-CHCl-CHCl-CH-, tail - tail structure-CHCl-CH2-CH2-CHCl -; generating a coupling disproportionation vinyl Results CH2 = CH-CHCl-CH2-structure  polyethylene oxide and allyl chloride-CH2-CH = CH-CHCl-CH2 and so on. Generated in the PVC synthetic allyl chloride, chlorine and tertiary carbon double bond in its molecular chain structure instability, unstable order: PVC within the molecular chain allyl chloride> tertiary carbon Chlorine> allyl end groups chloride> Chung chlorine. PVC is susceptible to degradation during processing because of the structure of PVC molecular chain instability exists, if not modified for  fluorescent brightener stabilization, the decomposition temperature is about 130 ℃, but that the PVC resin processed into useful articles, molding temperature to at above 190 ℃. Therefore, you must add heat stabilizers stabilize its structure improvements.
Pvc in the synthesis process so you need to add PVC heat stabilizers.