Question

2. During the acid catalyzed polymerization of terephthalic acid and ethylene glycol, some fraction of methanol (CH-OH) is incorporated, but no more ester bonds can be formed. a. Based on the above, what is the extent of reaction, p? b. How does fav determine whether a linear or network polymer is formed as p nears 1? c. Why do you believe the polymer in this reaction will be a gel-network or linear chains? d. What is fivg, the average number of functional groups per monomer, if the molar ratio of ethylene glycol to methanol to terephthalic acid is 11:1:10? e. Why is it more feasible to remove methanol than ethylene glycol from the reaction? f. If you were to remove all the methanol present based on the stoichiometry given in 2.c, what would the theoretical chain length be? g. If the final X, is 1,000: i. What is r, the final monomer stoichiometry? ii. From the repeat unit shown on the formula sheet, estimate the molecular weight. High transparency is typically associated with a completely amorphous structure, as in polystyrene and acrylic (polymethylmethacrylate or PMMA). Despite this general rule", PET possesses significant crystallinity, though it is optically transparent to the eye. h. Based on the above statement, does crystallinity in a polymer always mean that the polymer will not be transparent? i. What aspects of the PET molecular structure could enhance crystallinity? j. What aspects of the PET molecular structure could reduce crystallinity? Beyond optical transparency, gas permeability is a very important property for carbonated beverages, such as soda pop, where CO2 binds with water in the form of carbonic acid H2CO3. k. Is the density of amorphous or crystalline regions (or domains) higher in general? 1. Would you expect diffusion of CO2 molecules to be higher or lower in amorphous or crystalline regions? Why? On the other hand, milk jugs/bottles are often composed of high density polyethylene, and polyethylene is arguably the lowest cost polymer available. Unfortunately, it not transparent m. Low-density polyethylene (LDPE), however is transparent. What reduces crystallinity in the case of LDPE? What properties might make it unsuitable for carbonated beverage use?

Answer 1

a) The extent of reaction 'p" indicates the degree of polymerisation (in this case number averaged x_n) of the given monomers.

p = 1 - (1/x_n)

b) It is a well known fact that the polymerization of monomers containing two functional groups would generally result in linear polymer where as the monomer containing three functional groups generally resulted in polymer having network structure.

c) Polyethylene terephthalate (PET) is formed when these two monomers are reacted together. PET is a linear polymer having better mechanical and thermal properties.

d) f_avg is around two