ISSN:
0021-8995
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
A number of fluorinated polyesters have been prepared by condensing hexafluoropentanediol with one or more dibasic acid chlorides, and melting and glass transition temperatures and rates of crystallization have been determined, largely by means of volume dilatometry. The relation between [η] in chloroform at 30° and M̄n for hexafluoropentylene adipate (HFPA) was found to be [η] = 3.20 × 10-5 M̄n. The melting point Tm was found to increase from 34.5° to 104° as the isophthalate content in a series of adipate copolyesters increased from 0 to 100 mole-%. The glass transition Tg increases from -57° to -31° as isophthalate content increases from 0 to 50 mole-%. Tg is raised about 6° by the crosslinking of the polyesters. Rates of crystallization were determined for two HFPA samples with M̄n's of 13,000 and 19,500. Maxima in these rates occurred at about -13° and -15°, respectively. Respective t½ values for (linear) HFPA, vulcanized HFPA, and a copolyester containing 20 mole-% isophthalate are 48, 1140, and 27,200 min., respectively, at -10°. All the crystallization isotherms conform to Avrami's equation, (Vt - V∞)/(Vt - V∞) = exp {-αt″} for n = 6 over the initial stages of the process. At 1° both HFPA isotherms agree with the above equation over a large part of the process; however, as the isotherm temperature decreases, the equilibrium degree of crystallinity, as judged by the overall specific volume change, decreases and the isotherms diverge from Avrami's equation over progressively larger portions of the process. The product of the maximum rate of crystallization for each isotherm with either t½ or τi, the “induction time,” decreases with decreasing temperature, as would be expected in view of Avrami's equation. The value of 6 observed for n, a constant determined by the nucleation and growth mechanisms, is anomalous since only values of 1 to 4 are theoretically predictable. Values over the range of 1 to 4 have been observed experimentally by other workers for a variety of polymers.
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/app.1959.070010315
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