polyethylene glycol MW 400

wt%		log P (dynes/cm^2)

2.5		6.30
5.0		6.55
10.0		6.93
15.0		7.14
20.0		7.33
25.0		7.50
30.0		7.65
	
An equation that fits this data is the following.

log P = a + b * (wt%) ^ c

where a = 5.29, b = 0.73 and c = 0.34

Note that it should be applied only over the range of pressures measured.