QUESTION 39 How would you expect the crystallinity of a poly

QUESTION 39 How would you expect the crystallinity of a polymer to be affected by the addition of a plasticizer? A. Because the plasticizer is a molecule that fits between the main polymer chains, it should reduce the crystallinity B. Because the plasticizer is a molecule designed to be compatible with the main polyme it will not affect the crystallinity at all. C. The plasticizer is a molecule that fits between the polymer chains and helps create folds in the chain which lead to spherulite growth, thus there will be increased crystallinity. D. The plasticizer will tend to crystallize at the same rate as the main polymer. QUESTION 40 What is the difference between configuration and conformation in relation to polymer chains? A. This is a trick question neither term is used to describe polymers B. Configuration refers to the overall chain shape, and Conformation refers to the arrangement of atoms along the chain. Configuration can change above Tg, but conformation cannot change without breaking primary bonds. C. Conformation refers to the overall chain shape, and configuration refers to the arrangement of atoms along the chain. Conformation can change above Tg, but configuration cannot change without breaking primary bonds. D. Conformation and configuration are two different words that basically mean the same thing with regards to polymer chains the overall shape of the chain. This describes how it folds and curves on itself

Solution

The effects of plasticizers (polyethylene glycols [PEG] 400, 1,450, 8,000 and 20,000, glycerol [G] and propylene glycol [PG]), 30% dry basis, on the physical properties of methylcellulose (MC) films were investigated. With the exception of PG, plasticizers with low molecular weights (G and PEG 400) caused the largest increase in the d₁₀₁ spacing of the crystal lattice. All plasticizers significantly (= 0.05) increased oxygen (O₂P) and water vapor permeabilities (WVP) of the films as compared to that of unplasticized MC, with PEG 400 having the greatest effect on O₂P and G having the greatest effect on WVP. With the exception of PG, all plasticizers decreased the tensile strength of MC films, with PEG 400 causing the largest decrease. With the exception of PG and PEG 400, all plasticizers increased percent elongation values of MC films, with PEG 1,450 having the greatest effect. Glycerol and PEG were the most effective plasticizers for MC. the higher molecular weight plasticizers do provide some plasticizing properties and may be more suitable for applications that require a lower permeability to water vapor than can be achieved with glycerol.

That\'s why..ans is A - Because the plasticizer is a molecule that fits between the main polymer chain, its reduce the spacing between the molecules and crystallinity.

Swelling/collapsing would be related to polymer conformation since this is caused by polymer chain segmental motion. When a polymer is added to a suitable solvent, i.e. similar solubility parameters, the solvent molecules diffuse into the polymer creating attraction and dispersion forces between segments of the polymer chain. Since the polymer-solvent interactions are high, chain segments start to absorb solvent molecules which increases the volume of the polymer as the polymer chians un-coil (this is a change in conformation). In a bad solvent, the polymer-polymer attraction forces dominate and the chains maintain their aggregated structure

2. Configuration of polymer chains :

The configuration of a polymer refers to the order of different substituents along the polymer backbone. To change the configuration of a polymer, covalent bonds must be broken and reformed. Common polymer configurations include cis and trans geometries - cis referring to substituent groups on the same side of a carbon-carbon double bond while trans refers to substituent groups on opposite sides of a carbon-carbon double bond. Further examples in polymer chemistry include the steroregularity of a polymer chain. Configurations of a polymer chain can be: (1) Isotactic - substituents on the same side of the polymer chain, (2) Syndiotactic - alternating groups and (3) Atactic - Random placement of substituent groups either side of chain. In contrast, conformation refers to the arrangement of substituents due to rotations about a main chain single bond. As such, the conformation of a polymer may change without the breaking or reforming of covalent bonds. Rotations occur around different sections of the chain therefore, different conformations will have different potential energies due to varying distances between substituent groups. Nuclear Magentic Resonance (NMR) is an effective technique for determining the conformations and configurations of a polymer.

Here , in the answer we have two choices B and C are given same excepts only two words that are conformation and configuration. this is not a trick question ( A) also this both words have their individual meanings that are we know..

That\'s why...From the above discussion..

the ans is C..We can say that, conformation refers to the overall chain shape, and configuration refers to the arrangement of atoms alonf chain.conformation can change above Tg, but configuration cannot change without breaking primary loads.