A-For a polyethylene chain with a degree of polymerization of 100,000, what is t
ID: 498712 • Letter: A
Question
A-For a polyethylene chain with a degree of polymerization of 100,000, what is the effect of the root mean square end-to-end distance of this chain in a good solvent compared to in the polymer melt. Assume the projected length of one ethylene unit is 1.78 Angstroms. Show your calculations to support your answer. Is root mean square end-to-end distance the same? Larger? Smaller? By how much if larger or smaller? B- Discuss briefly the effect of increasing the degree of on the following properties (include a short explanation), a) Density b) Modulus (stiffness) c) Transparency explain your answer. Which of the following polymers would you expect to have the best barrier properties (i.e., provide the best barrier to diffusion of a gas and hence prove most effective as a beverage container)? In your answer include an explanation of the polymer morphology of your selection that supports your answer. 1-Atactic polystyrene 2-A random ethylene/propylene copolymer (50/50) composition. 3-Low density polyethylene 4-High density polyethylene Ataxic polystyrene (~ 100 degree C) is quenched (i.e., cooled very quickly) from 120 degree C to room temperature. Reviewing the states of matter for a polymer (page 207 in textbook), what will be the morphology of the resulting polymer solid? In your answer Include an explanation of what is happening microscopically to the polymer chains of this particular polymer due to Its chemical structure that supports your conclusion.Explanation / Answer
A. Degree of polymerization, N = 100000, Length of the segment, L = 1.78 Ao
Root-mean-square end-to-end distance = N1/2 L = (100000)1/2 X 1.78 = 562.89 Ao
For Root-mean-square end-to-end distance will be higher in a good solvent compared to the polymer melt as expansion is more in a good solvent compared to the polymer melt.
Good solvent, Root-mean-square end-to-end distance = N3/5 L = (100000)3/5 X 1.78 = 1780 Ao
B. a) Increase in degree of crystallinity increases the density of the material as increase in degree of crystallinity increases the orderliness of the arrangement of the atoms/molecules in the material. So, the maximum space is occupied by the atoms/molecules in the material, which in turn increases the density of the material
b) Increase in degree of crystallinity increases the modulus(stiffness) of the material as it reduces the amorphous nature of the material which in turn reduces the modulus(stiffness) of the material.
c) Increase in degree of crystallinity reduces the transparency of the material as it reduces the amorphous nature of the material & leads to close packing of the material which in turn will not allow light to pass through the material and as a result the transparency reduces.
c. 4. High density polyethylene (HDPE) has the best barrier properties due to the high crystallinity of the material (Crystalline materials are more closely packed compared to the amorphous material which does not allow the gas or chemicals to pass through the crystalline materials, which results best barrier properties). Hence HDPE is used in beverage containers like milk containers and also automotive fuel tank application.
Atactic polystryrene, A rondom ethylene-propylene copolymer & Low density polyethylene are amorphous compared to HDPE, which results in poor barrier properties compared to HDPE.
D. Atactic polystyrene is amorphous polymer as the bulky pendant group (phenyl) is arranged randomly along the polymer chain. When this polymer is quenched i.e., rapidly cooled from a high temperature of 120°C to room temperature, the resultant polymer will be highly amorphous, which results in the morphology of randomly coiled structure i.e., the molecules are oriented in a highly random manner.