Polyethylene dilatometry

Figure 4.18 illustrates volumedilatometry of an extended-chain, high-crystaUinity polyethylene sample (see also Chap. 6). A close to equiUbrium melting is observed by such slow dilatometry with equipment illustrated on the left of Fig. 4.15. 

From Fig. 6.20, the limits of molecular nucleation of Fig. 3.75, and the phase diagram evaluated from dilatometry, a separation of the various contributions to the reversible melting is possible. The polyethylene of Fig. 7.18 has 3% of its molar-mass... 

A sununary comparison of the melting behavior of all samples discussed above is shown in Graph E of Fig 6.15. The lower the molecular mass, the broader is the melting region, and the lower is the maximum melting temperature. All four of these samples can be compared to a polyethylene sample produced by polymerization of diazomethane and hence labeled polymethylene. This is a pressure-crystallized sample of very high molecular mass whose dilatometry curve is shown in Fig. 6.13. This sample has no molecular... 

Dilatometry. DTA extrapolated to zero heating rate. Rapid heating on hot stage. Table 5 Extrapolated for Linear Polyethylene... 

Dilatometry can be used to follow the slow crystalhzation of polyethylene at high temperatures or secondary crystallization over extended periods of time. It can also be used to investigate density changes as a function of temperature. The sensitivity of dilatometry is such that changes in density of less than 0.0001 g/cm can readily be detected. Measurements may be made over a period of days, weeks, months, or even years, providing that the oil bath in which a dilatometer is immersed is adequately thermostated. 

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