Below, molecular weight data for a polytetrafluorocethyllene (C_2F_4) material a

Question

Below, molecular weight data for a polytetrafluorocethyllene (C_2F_4) material are tabulated. Compute (a) the number-average molecular weight, the degree of polymerization. M^overbar_n = sigma x_i M_i, DP = M^overbar_x/m Where: represent the mean (Middle) molecular weight of the range I x_r: is the fraction of the total of chains within the corresponding size ranges. m: is the repeat unit molecular weight. Molecular Weight Hange (g/mol) x_i 10,000-20,000 0.03 20,000-30,000 0.09 30,000-40,000 0.15 40,000-50,000 0.25 50,000-60,000 0.22 60,000-70,000 0.14 70,000-80,000 0.08 80,000-90,000 0.04

Explanation / Answer

so Number average molecular weight = Sum of xiMi / sum of xi = 49800 / 1 = 49800

2) Degree of polymerisation = Number average mol wt of polymer / Mol wt of monomer

Mol wt of monomer = 2 X At wt of Carbon + 4 X at wt of F = 2 X 12.011 + 4 X 18.998 = 100.014

So DP = 49800 / 100.014 = 497.93

molecular weight mol wt (Mi) fraction (xi) xiMi 10000-20000 15000 0.03 450 20000-30000 25000 0.09 2250 30000-40000 35000 0.15 5250 40000-50000 45000 0.25 11250 50000-60000 55000 0.22 12100 60000-70000 65000 0.14 9100 70000-80000 75000 0.08 6000 80000-90000 85000 0.04 3400 sum of fraction 1 sum of xiMi 49800

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