18 Questions
The end-to-end distance for a poly(isobutylene) chain of molecular weight 105 will be the same for fully extended chain and statistical coil at 25 °C.
False
For flexible chains without long-range interactions, the value of n is 0.5-0.6.
False
The average quadratic distance between ends for a monodispersed polyethylene sample is directly proportional to its molecular weight.
False
The radial distribution function, W(r), expresses the probability of finding the end on the surface of a spherical cap of radius r, having a minimum.
False
In the context of short-range interactions, an excluded volume of 0 indicates perfect solvation.
False
A distorted propeller chain with n = 0.9 is more flexible than a chain with n = 0.6.
True
Short-range interactions occur between units that are in close proximity to each other.
False
The excluded volume depends on the molecular weight, the degree of solvation, and the temperature.
False
In the case of synthetic polymers and denatured natural macromolecules, intramolecular forces are often strong.
False
Random coil conformations have a specific and defined structure due to strong intramolecular forces.
False
Short-range interactions are a consequence of the steric impediment imposed by the effective volume occupied by each unit.
False
Statistical coil dimensions include mean end-to-end distance and average radius of gyration.
True
In the concept of statistical coil, the rigid conformation is the exclusive conformation adopted by the macromolecule.
False
Short-range interactions occur intermolecularly between distant units, i + l, i + 2, etc.
False
Short-range interactions are not influenced by factors like bond angles and steric impediments.
False
Steric impediments play a role in causing short-range interactions between molecules.
True
In the statistical coil concept, the molecular state is highly ordered and predictable.
False
The short-range interactions primarily involve long-distance electrostatic interactions between molecules.
False
Study Notes
Proportionality of Distance between Extremes and Molecular Weight
- The distance between extremes has a proportionality with molecular weight, influenced by favorable solvation, excluded volume, and unfavorable solvation.
- Excluded volume = 0 corresponds to a non-perturbed state (T = Θ).
Excluded Volume and Molecular Weight
- For flexible chains without long-range interactions, n = 0.5.
- For flexible chains with interactions, n = 0.5-0.6.
- For distorted propellers, n = 0.6-0.9.
- For rigid chains or helixes, n = 1.
Distribution Function
- The end-to-end distance follows a Gaussian distribution defined by the probability density function W(r).
- The radial distribution function W(r) 4πr2 expresses the probability of finding the end on the surface of a spherical cap of radius r.
Statistical Coil Dimensions
- For synthetic polymers and denatured natural macromolecules, intramolecular forces are very weak.
- Many possible conformations have the same energy and are equally likely.
- Statistical coil dimensions include mean end-to-end distance and average radius of gyration.
Random Coil Model
- The random coil model is constructed using links with a length equivalent to the bond.
- Each link joins the previous one adopting a random orientation, except for the restrictions imposed by the chemical bonds.
- The result is a random coil conformation.
Molecular Interactions
- Short-range interactions occur intramolecularly between nearby units and are caused by bond angles, rotational barriers, steric impediments, and electrostatic interactions.
- Long-range interactions occur between units separated from each other and are a consequence of the steric impediment imposed by the effective volume occupied by each molecule (excluded volume).
Test your knowledge on polymer conformations and the proportionality of distance between extremes with molecular weight. This quiz covers concepts such as solvation, excluded volume, distribution functions, and conformation characteristics for flexible and rigid chains.
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