We describe a method for determining the thermal and elastic properties of the noncrystalline phase of semicrystalline polymers (the "interphase") by Monte Carlo simulations. The method is applied to an interphase composed of freely rotating polyethylene-like chains, studied previously by Balijepalli and Rutledge (J. Chem. Phys. 1998, 109, 6523). The isochoric and isobaric heat capacities, Gruneisen coefficients, thermal expansion coefficients, and elastic stiffnesses are reported. The interphase exhibits material properties comparable to that of the corresponding melt, with significant contributions of both enthalpic and entropic origins. Through judicious selection of Monte Carlo moves, we approximate the rate sensitivity of the stiffness normal to the crystal surface, C-33, on time scales that are long and short, respectively, relative to the characteristic time scale of the crystalline alpha(c) relaxation.