What is the reasoning for higher pH values in this scene? In this article regarding low-boiling point amine-catalyzed biodiesel transesterification reactions, it is stated that, 


  "From Table 1, we can also see that, for the isomers, the
  branched amines always showed higher yields of methyl acetate
  than the normal amines. For example, the yields of methyl
  acetate for n-dipropylamine, n-butylamine, and n-propylamine
  were 25.3%, 46.1%, and 48.2%, respectively, while those for
  diisopropylamine, tert-butylamine, and isopropylamine were
  42.1%, 49.6%, and 50.7%, respectively. This was probably due
  to the high pH values of the branched amines than the normal
  amines."


Why is this the case? Why do high pH values correlate to higher yields? Does the geometry (branched or linear) of the amine play a role in this?
Branched amines are more basic than their linear counterparts because inductive effect of alkanes places more electron density in the adjacent carbon atom. The higher the electron density near/at the amine group, the higher its pH will be.