susceptible to thermal degradation during processing, therefore, thermal stabili
ID: 698551 • Letter: S
Question
susceptible to thermal degradation during processing, therefore, thermal stabilizers a igure helow shows dehydrochlorination of PVC and further reaction between HC 11. PVC is needed. The and the polymer to form carbonium salts. According to the following reactions (a) Simply indicate the betw gure below shows de (10 points) e dtferences between molecular A and molecule B shown below (b) why should PVC contain more th stabilizers should have for effectively processing high quality an one type of stabilizers? Please list the functions that those PVC products? CH2 C I CH nCH MM H2Explanation / Answer
Ans a:) molecule A is basically an allylic chlorine containing molecule, which can go dehydrochlorination to form a polyene and molecule B can be considered as stabilizing of polyvinyl chloride towards the dehydrochlorination. Considering the units in {} as the part of infinite polymer chain. We can say that
Molecule A = basically arises because of active labile chlorine present at tertiary or allylic C atom and undergoes the dehydrochlorination and then favors the formation of polyene in propagation step of polymerization.
Molecule B = can be considered as the stabilization of poly vinyl chloride (PVC) to form some stable carbonium salts. So, the degradation of PVC can be stopped. In this case some other group is able to hold the chloride ion release during dehydrochlorination (e.g Metal salts). Hence terminate the degradation step.
b:) List of functions:
Many kind of stabilizers are used and can be categorized;
Primary: Which react with allylic chlorine atoms and prevent the step of dehydrochlorination. (e.g metal salts)
Secondary: Which scavenges the HCl/Cl formed. However primary stabilizers can react with HCl which is important for initiation and propagation of chemical reaction. Hence, they also stabilized the primary stabilizers.
Common example: Alkaline earth metal carboxylate salts for secondary and transition metal carboxylate salts for primary stabilizers.
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