Generally speaking, the polarity of adhesive molecules and adherend molecules affects the bonding strength, but this does not mean that an increase in the polarity of these molecules will necessarily improve the bonding strength.
From the perspective of polarity, in order to improve the bonding strength, it is better to change the polarity of the surface in the interface area rather than changing the polarity of all molecules of the adhesive and the adherend. For example, after plasma surface treatment of polyethylene, polypropylene, and polytetrafluoroethylene, many polar groups such as hydroxyl groups, carbonyl groups, or carboxyl groups are generated on the surface, thereby significantly improving the bondability.