Question

(a) Any polymeric material will have a distribution of molecular weights, and therefore an average molecular weight is used to characters the material. Is it possible to have a polyethylene homopolymer with the following molecular weight distribution data and a weight average degree of polymerization of 2090? Why or why not? The polyethylene mer is shown below. (b) Based on the mer structure shown for poly(methyl methacrylate) (PMMA) and polyethylene (PE). Which has potential for greater crystallinity? Provide a brief explanation of your answer that demonstrates a good understanding of the crystallinity in polymers.

Answer 1

2. (a) Average molecular weight of the polymer is calculated using the molecular weight ranges given as below.

Molecular weight range | | 8000 24000 40000 56000 24000 40000 56000 72000 Average Molecular weight ( 16000 32000 48000 64000 40000 w 0.08 0.36 0.42 0.14 | MiXWi 1280 11520 20160 8960 41920 Average MW of Polymer

Given average degree of polymerization (n₁) = 2090

Average molecular weight of polymer (M_P) = 40000 g/mol

Moleular weight of monomer or Ethylene (M_M) = 28 g/mol

Calculated average degree of polymerization (n₂) = M_P / M_M = 41920 g/mol / 28 g/mol = 1497

Calculated average degree of polymerization (1497) is less than the given average degree of polymerization (2090).

So, it is not possible to have the given molecular weight distribution data and the average degree of polymerization.

(b) PE has more potential for greater cystallinity than PMMA as the PE has only H as substited group which will arrange in ordered fashion to form crystalline polymer but PMMA has bulky group -COOCH₃ which will arrange in random fashion to form amorphous polymer.