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MATERIALS 1

Tutorial B1

Question 1On the basis of the structures presented in this chapter, sketch repeat unit structures for the following polymers: (a) polychlorotrifluoroethylene, and (b) poly(vinyl alcohol).

(2 marks)

Question 2(a) Compute the repeat unit molecular weight of polypropylene. (b) Compute the number-average molecular weight for a polypropylene for which the degree of polymerization is 15,000.

(2 marks)

Question 3 Is it possible to have a poly(vinyl chloride) homopolymer with the following molecular weight data, and a degree of polymerization of 1120? Why or why not?

Molecular Weight Range (g/mol) wi xi 8,00020,000 0.02 0.0520,00032,000 0.08 0.1532,00044,000 0.17 0.2144,00056,000 0.29 0.2856,00068,000 0.23 0.1868,00080,000 0.16 0.180,00092,000 0.05 0.03

(4 marks)

Question 4Sketch portions of a linear polypropylene molecule that are (a) syndiotactic, (b) atactic, and (c) isotactic.

(3 marks)

Question 5Calculate the number-average molecular weight of a random poly(isobutylene-isoprene) copolymer in which the fraction of isobutylene repeat units is 0.25; assume that this concentration corresponds to a degree of polymerization of 1500.

(4 marks)

2Reference Solutions:

Question 1 (total 2 marks)

Question 2 (total 2 marks)

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3Question 3 (total 4 marks)

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4Question 4 (total 2 marks)

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5Question 5 (total 5 marks)

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1Material 1

Assignment B2 (Total Mark of 25)

Q1 (5 Marks)

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2Q2 (4 marks)

2 Marks

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1 Mark

3Q 3 (6 marks)

3 Marks

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2 Marks

4Q 4 (4 marks)

From the figure, the elastic modulus is the slope in the elastic region of the 20 oC curve, which is

GPa3.303109

MPa0MPa30strainstress

E

We are able to find the value cited in the table ranges from 2.24-3.24 GPa. As such, our estimation of the elastic modulus is a little higher than the literature value. (Since both stress and strain values are read from the figure, there should be some reading error. While you mark the assignment, please pay attention to above equation rather than the absolute value of 3.3 MPa. Thanks)

The tensile strength is related to the stress at which the curve ends, which is about 52 MPa or 7500 psi. This value is within the literature range in the table (48.3 to 72.4 MPa)

Q 5 (6 marks)The first part of this question is to determine the valu es of a and n. From the raw data and equation provided, we can plot the log(creep rate) vs, log(applied stress). The plot is linear and we can solve both constants by either selecting any two points from the graph or least squa re fitting in this log-log plot. The second part is just to determine the stress at creep rate of 2 % per year. (Since the data of a and n are obtained from fitting, all results within +/- 10% of error are acceptable. Thanks.)

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