Doctor of Philosophy (Ph.D.)
William H Starnes, Jr
Unlike vinyl chloride, 1,2-dichloroethylene (DCE) experienced dimerization under free-radical conditions. Chain transfer to DCE by beta-Cl elimination was shown to be the major reason for its nonpolymerization.;During the chlorination of alkyl chlorides with molecular chlorine, the involvement of a bridged intermediate led to the formation of vicinal chlorides as the major products. The yields of geminal chlorides increased significantly in the presence of solvents that form complexes with chlorine atoms, but such solvents also decreased the reactivity of the chlorination. Thus the chlorination of poly(vinyl chloride) (PVC) in the presence of complexing solvents was not a useful method for the synthesis of poly(1,2-dichloroethylene).;Polyacetylene (PA) was prepared by the methods of both Shirakawa and Luttinger. The PA's were chlorinated with Cl2 to form white polymers that were, however, not chlorinated completely, in that double bonds were invariably left in the polymer backbone. The chlorinated PA's had a much higher glass transition temperature than PVC but were much less thermally stable, apparently owing to the presence of allylic chloride groups.;Ring-opening metathesis polymerization (ROMP) followed by addition chlorination with Cl2 provided an approach to the preparation of a series of new polymers that could be interesting technologically. However, experiments with model compounds showed that the addition chlorination of conjugated double bonds or the double bonds of allylic dichlorides is frequently slow and incomplete. The chlorination of ROMP polymers made from cyclopentadiene, 1,3-cyclooctadiene, and 1,3,5-cyclooctatriene also did not proceed to completion, and the chlorination of the -(CH=CHCHClCHCl)n- polymer made from cis-3,4-dichlorocyclobutene did not occur at all.;Polyene sequences formed during the thermal degradation of PVC were found to interact with HCl in order to form an ion pairs whose thermal excitation produces triplet cation diradicals. These diradicals abstract methylene hydrogen atoms from PVC, and the ensuing beta-Cl scission forms internal allylic chloride structural defects that quickly lose HCl. as a result, the autoacceleration of thermal dehydrochlorination occurs.;A "Plasticizer thiol", 2-ethylhexyl 3-mercaptobenzoate, was confirmed to be an excellent thermal stabilizer for PVC and was suggested by preliminary experiments to function via a mechanism involving both the nucleophilic displacement of labile chloride and addition to double bonds.
© The Author
Ge, Xianlong, "Synthetic and mechanistic studies of poly(vinyl chloride) and some other chlorinated polymers" (2003). Dissertations, Theses, and Masters Projects. Paper 1539623417.