The free radical polymerization of methyl methacrylate in bulk at 0 °C initiated by photochemical decay of azobis(cyclohexanenitrile) (ACN) is tested over the full range of conversion up to the glassy state. Rate constants of propagation, kp, and termination, kt, are evaluated by the rotating sector technique and after effect. Instantaneous degree of polymerization and efficiencies, /, are given for all conversions. The conversion dependence of f can be expressed by the self-diffusion of small molecules in a polymer matrix.Both rate constants depend on the conversion; kt for conversions near and beyond the onset of entanglement also depends on the chain length of the polymer radicals but becomes independent of this length at about 45% conversion. The diffusion processes describing the different stages of conversion are discussed.

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Average configuration-dependent properties (mean-square radius of gyration, mean-square end-to-end distance, helical content, helix probability profile, and average number of amino acid residues in a helical segment) have been evaluated for unperturbed partially helical polypeptides by using two weighting schemes. The weighting schemes differ with regard to whether end effects in a helical segment are assigned in like manner to amino acid residues at each end or are instead associated with only one amino acid residue. Molecules considered are block copolypeptides and specific sequence copolypeptides with amino acid sequences corresponding to those found in 44 proteins. Without exception, helix formation in the proteins is found to exhibit greater cooperativity if amino acid residues at each end of a helical segment contribute to the end effects. The helix probability profile for proteins is also found to be much smoother with this weighting scheme. Block copolypeptides show more dramatic changes in helicity, helix probability profile, and average number of amino acid residues in a helical segment. Unperturbed dimensions for both proteins and block copolypeptides are nearly independent of the weighting scheme adopted. Modification of the statistical weights used for arginyl, histidyl, and lysyl residues can produce helicities and unperturbed dimensions in reasonable agreement with helicities and dimensions deduced from circular dichroism spectra and viscosity measurements of complexes formed by reduced bovine serum albumin and sodium dodecyl sulfate.

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