"Sorry big J, but you've got it backwards. Phenyl-prop. is LONGER than prop., half-life is closer to 4-5 days, not 3 like regular prop. Trust me, just look up the chemical formula, the molecular chain of phenyl-prop weighs almost twice what prop. does. But both are still fast-acting -PhatD"
PHAT, you may be correct in the half-life of phenyl-propionate, but do not mistake ester length, or weight, as being the determinant for half-life. The phenolic group is going to change the chemical nature of the ester, as compared to the propionate alkane.