The following dependence of Tg on M for poly(dimethylsiloxane) was determined: M
ID: 510890 • Letter: T
Question
The following dependence of Tg on M for poly(dimethylsiloxane) was determined:
Mn
Tg (K)
240
123.4
310
129.1
530
137.4
630
139.4
810
141.2
990
143.3
1290
144.8
1630
146.1
2260
147.5
2460
148
2920
148.3
4080
149.2
4880
148.8
6330
149.3
7720
149.5
10060
149.5
12290
149.4
14750
149.7
18250
149.8
21390
149.8
25460
149.7
(a) What is the value of Tg for this polymer at infinite molecular weight?
(b) Using the sol-gel reaction shown in the notes for step-growth polymerization, and using the appropriate end-groups, what is the value of Tg for a poly(dimethylsiloxane) with a degree of polymerization = 47?
(d) An unkown polymer was investigated and the molecular weight values, intrinsic viscosity and zero-shear melt-viscosity (h0) determined. The following numbers were obtained:
Sample
Mn
Mw
[h]
h0
1
17800
19000
0.126
1.70 x103
2
58300
61800
0.289
6.18 x104
3
164400
171000
0.626
1.06 x106
4
339100
393400
1.148
8.51 x106
5
985500
1015000
2.291
1.04 x109
Determine the Mark-Houwink-Sakurada constants for this polymer.
(e) Was the polymer entangled in the melt?
This is all the information given in the question.
Mn
Tg (K)
240
123.4
310
129.1
530
137.4
630
139.4
810
141.2
990
143.3
1290
144.8
1630
146.1
2260
147.5
2460
148
2920
148.3
4080
149.2
4880
148.8
6330
149.3
7720
149.5
10060
149.5
12290
149.4
14750
149.7
18250
149.8
21390
149.8
25460
149.7
Explanation / Answer
a) the value of Tg for this polymer at infinite molecular weight is 149.8
b) the value of Tg for a poly(dimethylsiloxane) with a degree of polymerization 47 is 101.2
d) the polymer was not entangled in the melt
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