The polymer used in the LCMS compatible vials consists only of repeating hydrocarbon monomer units that have no polar or ionizable groups, so the polypropylene vials are hydrophobic.
A primary reason one might use these vials is to avoid undesirable properties of hydrophilic silanols on conventional borosilicate glass vials is their hydrophobicity. The silanolic groups of glass can bind with basic functional groups, especially with proteins, where they cause low recovery and quantitative accuracy issues. The purity of the plastic and extremely low extractables including ions makes these vials LCMS compatible. They represent a solution to these common problems as they may be more inert in this respect especially compared with other plastic vials.