SynopsisElectron spectroscopy for chemical analysis (ESCA) was used to study the surface composition of several radiation-grafted polymers in both the dry and hydrated (frozen at 160'K) states. Poly(2-hydroxyethyl methacrylate) (HEMA) and polyacrylamide, both hydrophilic polymers, were readily detected in the hydrated or dehydrated states when grafted to polyethylene substrates. For silicone rubber substrates, both grafts were observed on the hydrated surface but were significantly decreased in surface concentration upon dehydration. For grafts on a polyester-urethane, acrylamide was not a major constituent of either the dry or hydrated surface, while HEMA appeared to increase in abundance upon drying. The amount of the hydrophobic poly(ethy1 methacrylate) found on the graft surface depended upon the substrate polymer used, but the surface abundance of poly(ethy1 methacrylate) was not affected by drying. These results were considered in terms of polar group orientation, polymer chain mobility, substrate permeability, and the limitations of the ESCA technique. The implications of these results with respect to the use of radiation-grafted hydrophilic polymers for biomedical applications are also discussed.

The microwave spectrum of cyclobutanone in the ground state and the first 10 excited states of the ring-puckering vibration has been assigned. Most features of the observed variation of rotational constants with ring-puckering state and of the far-infrared spectrum are accounted for with the ring-puckering potential function V(Z) = ν0[12Z2 + 0.4918Z4 + 1.598 exp(−1.0Z2)], with ν0 = 29.85 cm−1. Z is a dimensionless coordinate for the ring-puckering motion. A barrier of 7.6 ± 2 cm− exists at the planar ring conformation; with the υ = 0 level lying 9.2 cm−1 above the top of the barrier. A perturbation of the υ = 8 state is discussed. The ground-state rotational spectra of the three 13C monosubstituted species have also been assigned and the structure of the ring determined. With the carbonyl carbon labeled C1 and other carbons numbered sequentially around the ring, the ring structural parameters are r(C1C2) = 1.527 + 0.003 Å, r(C2C3) = 1.556 ± 0.001 Å, ∠C2C1C2′ = 93.1 ± 0.3°, ∠C1C2C3 = 88.0 ± 0.3°, ∠C2C3C2′ = 90.9 ± 0.2°. Stark-effect measurements have yielded a value of 2.89 ± 0.03 D for the dipole moment of the common isotopic species in the ground vibrational state.

The microwave spectra of cyclohexene, cyclohexene-d10, and 3,3,6,6-cyclohexene-d4 have been assigned. Subject to certain assumptions, the nine moments of inertia were least-squares fitted to obtain the structural parameters ∢C1–C2–C3 = 123.3°, ∢C2–C3–C4 = 111.6°, ∢C3–C4–C5 = 110.3°, ∢C–C–H (methylene) = 109.9°, ∢C–C–H (ethylene) = 119.5°, and θ=30.1°, where θ is the angle between the C1–us;C2 and C4–C5 bonds projected on the a–c principal axis plane. θ measures the deviation of the ring from planarity. The assumptions related to symmetry were (1) the molecular point group is C2; (2) the methylene groups are symmetric with equal C–C–H angles; and (3) the ethylene group and two adjacent carbons lie in a plane. The bond lengths were taken to be r(C1 –C2) = 1.34 Å, r(C2–C3) = 1.51 Å, r(C3–C4) = 1.53 Å, r(C4–C5) = 1.53 Å, r(C–H) (ethylene) = 1.09 Å, and r(C–H) (methylene) = 1.10 Å. Stark effect measurements yielded μb = 0.331 D for the common isotopic species and showed that μb is unchanged (within the experimental uncertainty) in the deuterated species. The Stark effect also confirmed the haclf-chair conformation and C2 symmetry by requiring μc to be less than 0.003 D.

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Very accurate Stark effect measurements were made on rotational transitions of nitrous oxide and propyne-d3. Measurements were made with a microwave spectrometer incorporating a special parallel-plate absorption cell capable of sustaining large magnitude electric fields and of producing very homogeneous fields in the absorption region. Analysis of the data gives an electric polarizability anisotropy of 3.222 ± 0.046 Å3 for nitrous oxide and of 2.7 ± 0.6 Å3 for propyne-d3. The dipole moment of nitrous oxide was determined to be 0.160830 ± 0.000016 D. For propyne-d3, there is evidence for a K dependence of the dipole moment. The determined values for the J = 3 → 4 transition are 0.78780 ± 0.00013 D (K = 0), 0.78765 ± 0.00021 D (K = 2), and 0.78741 ± 0.00014 D (K = 3). Stark effect data reported previously for OCS were reanalyzed using a refined method of statistical analysis and the new molecular beam value for the OCS dipole moment to determine the revised OCS polarizability anisotropy of 4.67 ± 0.16 Å3. In each case, the error limit represents the 95% confidence level calculated in the least-squares analysis, but does not include the uncertainty in the dipole moment value for OCS which was used as a standard in the data reduction.