Molecular weight data for a polymer is tabulated here. (a) Compute the number-av
ID: 942131 • Letter: M
Question
Molecular weight data for a polymer is tabulated here.
(a) Compute the number-average molecular weight
(b) Compute the weight-average molecular weight
(c) If it is known that this material's degree of polymerization is 710, which one of the polymers listed in Table 4.3 is this polymer? Why?
(d) After you do the calculations, consider whether you would consider this material a high molecular weight polymer and why or why not.
(e) Give one property that tends to increase with increasing molecular weight.
Molecular Weight
Range g/mol
xi
wi
15,000–30,000
0.04
0.01
30,000–45,000
0.07
0.04
45,000–60,000
0.16
0.11
60,000–75,000
0.26
0.24
75,000–90,000
0.24
0.27
90,000–105,000
0.12
0.16
105,000–120,000
0.08
0.12
120,000–135,000
0.03
0.05
Molecular Weight
Range g/mol
xi
wi
15,000–30,000
0.04
0.01
30,000–45,000
0.07
0.04
45,000–60,000
0.16
0.11
60,000–75,000
0.26
0.24
75,000–90,000
0.24
0.27
90,000–105,000
0.12
0.16
105,000–120,000
0.08
0.12
120,000–135,000
0.03
0.05
Explanation / Answer
a and b
c) Degree of polymerisation = Number average molecular weight / Molecular weight of monomer
Molecular weight of monomer = 73800 / 710 = 103.94
So you can match with the said table
d) we can calculate the polydispersity index as
PDI = weight average molecular weight / Number average molecular weight = 1.1
So this is average molecular weight
e) the strength of polymer increases with increase in molecular weight.
Molecular Weight xi wi Range g/mol Mean Mi xiMi wiMi 15,000–30,000 0.04 0.01 22500 900 225 30,000–45,000 0.07 0.04 37500 2625 1500 45,000–60,000 0.16 0.11 52500 8400 5775 60,000–75,000 0.26 0.24 67500 17550 16200 75,000–90,000 0.24 0.27 82500 19800 22275 90,000–105,000 0.12 0.16 97500 11700 15600 105,000–120,000 0.08 0.12 112500 9000 13500 120,000–135,000 0.03 0.05 127500 3825 6375 Number average molecular weight = sum of xiMi = 73800 Weight average molecular weight = Sum of wiMi = 81450Related Questions
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