ISSN:
0449-2951
Schlagwort(e):
Chemistry
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Physik
Notizen:
A study was made of the effect of polymerization temperature on the syndiotacticity of polyvinyl formate. Vinyl formate was polymerized with ultraviolet light initiation in the temperature range from -20 to +30°C. The value of (Ep - Et)/2 obtained, 4.5 kcal./mole, is characteristic of those values obtained by other workers for the free radical-initiated polymerization of vinyl acetate. A linear relationship was found to exist between the viscosities of the polyvinyl formates and those of the derived polyvinyl alcohols. The degree of polymerization of polyvinyl formate may be calculated from the equation: [η] = 4.42 × 10-3 DP0.63. The low temperature polymerization of vinyl for- mate results in more syndiotactic polymer, as shown by x-ray diffraction. Polyvinyl for-mate obtained at more elevated polymerization temperatures did not demonstrate the same degree of order. No difference was found between the infrared spectra of the polyvinyl formates. The polyvinyl alcohol derived from polyvinyl formate polymerized at low temperatures (0 to -35°C.) exhibits water resistance and forms a colored iodine complex similar to that obtained with the syndioactic polyvinyl alcohol derived from polyvinyl trifluoroacetate. Conventional polyvinyl alcohol and that derived from polyvinyl acetate polymerized at -30°C. do not exhibit the same properties. Minor differences in the 1,2-glycol content in the various polyvinyl alcohols do not account for the differences in the observations. The amount of head-to-head addition in various vinyl aliphatic esters seems to be related to the inductive strength of the acid portion of the ester. No difference was found between the crystallinities of the various polyvinyl alcohols, as measured by film density. Heat treatment increases the crystallinities about the same amount, but the water resistance of the stereoregular materials remains higher. From the good correlation between the observations made on polyvinyl formate and the derived polyvinyl alcohol, it is concluded that syndiotactic polyvinyl formate, and hence syndiotactic polyvinyl alcohol, is obtained by the low temperature free radical-initiated polymerization of vinyl formate. Increased syndiotacticity is more readily obtained in polyvinyl formate than in polyvinyl acetate, indicating the greater influence of inductive effect compared with the steric effect in controlling stereoregularity during free-radical propagation.
Zusätzliches Material:
5 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/pol.1963.100010310
Permalink
