The Achilles heel of the parylene polymers is their oxidative stability at room temperature with UV exposure and at elevated temperature >115 °C in air. This weakness is attributed to the aliphatic carbon-carbon single bond in the main-chain backbone. Fluorinating this chemistry helps the oxidation substantially, but the precursor then becomes nearly prohibitive to use due to cost of the precursor and the processing cost. Another option is to explore the methylation of this benzyl position. Poly(α,α′-dimethyl-p-xylylene) and poly(α,α,α′,α′-tetramethyl-p-xylylene)-co-poly(p-xylylene) are deposited on the parylene platform via alkoxy precursors. Their oxidation as a function of temperature to 300 °C; and time at 150 °C is explored via variable angle spectroscopic ellipsometry (VASE) and infrared spectroscopy (IRS). Results show very little difference between the two polymers as a function of oxidation temperature, and better results compared to what was previously observed with the poly(p-xylylene) homopolymer, however the oxidation of poly(α,α′-dimethyl-p-xylylene) at 150 °C as a function of time is less positive with 16% thickness loss over 1000 h with the post-deposition annealed sample.