AbstractFilms of low‐density polyethylene, polypropylene, and rigid poly(vinyl chloride) were exposed for 1700 h to artificial aging in a Weather‐O‐Meter. Photochemical aging was characterized by tensile measurements. We noted that only ultimate properties are affected, whereas properties defined in the low strain range remain unchanged. The kinetics of strain and stress at break depend as much on the polymer's initial rheological characteristics as on the rate of the chemical degradation. The results show that aging results in localized chain breaking leading to defects at the supermolecular level. The average decrease of molecular weight does not seem to influence the mechanical beh