Looking at the two alcohols, both have hydrogen bonding and are singly bonded throughout the molecule. However, propylene glycol has a larger electron cloud which to my knowledge would increase its London dispersion forces and thus its boiling point. I already know both molecules exhibit hydrogen bonding since they're both alcohols. However, it seems that ethylene glycol has a higher boiling point despite propylene glycol seemingly having stronger IMFs. I believe this has something to do with molecular shape but I can't seem to find the definitive answer explaining why ethylene glycol has a higher boiling point. I've used https://pubchem.ncbi.nlm.nih.gov/compound/Propylene-glycol#section=RTECS-Number and https://pubchem.ncbi.nlm.nih.gov/compound/1_2-Ethanediol#section=Odor for comparison of the two alcohols.
This is all about linearity of the molecule and steric hindrance. Consider the linear structure of ethylene glycol versus the branched structure of propylene glycol. EG can "stack" more easily and therefore engage in more intermolecular bonding than PG. More attraction means more energy required to vaporize. On the other hand, 1,3 propane diol, which is the linear isomer of propylene glycol, has a higher boiling boiling point than EG at around 213C. To further illustrate - 1,4 butanediol (linear) has a higher boiling point than 1,3 butanediol (branched).