Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry, goniometry and electrical measurements were used to investigate repair and capping of porous methylsilsesquioxane (JSR LKD 5109) low-k films using a series of chlorosilanes in the form of R4-nSiXn, where R is a methyl group and X is chlorine (Trimethylchlorosilane-TMCS, dimethyldichlorosilane-DMDCS, and methyltrichlorosilane-MTCS), dissolved in supercritical CO2 (scCO2). All three chemicals deposited methylsilyl (O-Si-CH3) moieties on the surface by reaction with lone and H-bonded silanol (SiO-H) groups on the surface of oxygen ashed porous methylsilsesquioxane (p-MSQ) films. Spectroscopic ellipsometry and goniometry showed that the total film thickness and contact angle are increased in the order TMCS < MTCS < DMDCS. Electrical measurements of the dielectric constant k of capacitors increased in the order TMCS 2.59 +/- 0.05, DMDCS 2.88 +/- 0.13, and MTCS 3.23 +/- 0.11. The bi- or tri-functionality of the molecules with more reactive head groups produced intermolecular linking, but not all of the silanol SiO-H groups in these layers could condense, which mitigated the effect of packing density on k. Ti CVD shows that the mesopores of MSQ were capped after DMDCS and MTCS processes.