An Assessment of the Role of Quenched Randomness in the Stereochemical Sequences of Atactic Vinyl Polymers
| Autor: | Wayne L. Mattice, Numan Waheed |
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| Rok vydání: | 2006 |
| Předmět: | |
| Zdroj: | Macromolecules. 39:2380-2387 |
| ISSN: | 1520-5835 0024-9297 |
| DOI: | 10.1021/ma052434q |
| Popis: | The influence of the quenched randomness in the stereochemical sequences of atactic chains on the mean-square unperturbed end-to-end distance, 〈r2〉0, is assessed. The method uses a rotational isomeric state (RIS) model based on virtual bonds between the centers of mass of the C6 rings in polystyrene. This virtual bond model is derived from a conventional RIS model expressed in terms of the C−C bonds in the main chain. The zeroth-approximation virtual bond model, which retains only the most probable conformations of each tetrad, correctly finds 〈r2〉0 ∼ n in the limit as n → ∞ if the probability for a meso diad, pm, is 0 < pm < 1, although the same zeroth-approximation model yields 〈r2〉0 ∼ n2 if pm is either 0 or 1. The values of 〈r2〉0 at intermediate pm are surprisingly close to the ones deduced from a full, C−C bond based RIS model. This achievement of the zeroth-approximation model demonstrates the important role of the quenched randomness of the stereochemical sequences in determining the unperturbed di... |
| Databáze: | OpenAIRE |
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