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Occurrence of head‐to‐head arrangements of structural units in polyvinyl alcohol

1948; Wiley; Volume: 3; Issue: 6 Linguagem: Inglês

10.1002/pol.1948.120030608

1542-6238

Paul J. Flory, Fred S. Leutner,

biodegradable polymer synthesis and properties

Abstract Polyvinyl alcohol prepared by hydrolyzing polymerized vinyl acetate is partially degraded within a few minutes by reagents known to attack 1,2‐glycol structures. The degree of degradation is limited, however, the final molecular weights of the degraded products being in the range of 3700 to 6500 (viscosity averages). The extent of degradation seems to depend solely on the temperature at which the vinyl acetate was polymerized. Mole percentages (based on the structural unit CH 2 CHOH) of 1,2‐glycol structures, corresponding to head‐to‐head unit arrangements, have been computed from the degree of degradation with periodic acid. They increase from about 1.23% for polymerization at 25°C. to 1.95% at 110°C. The occurrence of head‐to‐head structures is attributed to occasional “abnormal” addition of monomer in the chain‐growth phase of the polymerization. The activation energy for the abnormal addition reaction is 1250 calories higher than for the normal (preferred) addition; the steric factor for the abnormal addition is about one‐tenth that for the normal addition.