北京理工大学829高分子物理2006年真题

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2006 年攻读博士学位研究生入学考试试题
科目代码： 374 科目名称： 高分子物理
一、Choice questions (20 points)
1. Consider the properties of the following two polyethylene samples. Sample 1
was produced by a high pressure process while sample 2 was synthesized using a
catalyst.
Polyethylene 1 Polyethylene 2
Mol wt. 200,000 200,000
Density (g/cm3) 0.92 0.96
Crystalline melting pt. 108°C 133°C
Stiffness (lb/in2x103) 25 125
Hardness (Shore D) 45 65
Which of the following statements is true?
a. Sample 2 is more branched than sample 1
b. Sample 1 is more branched than sample 2
c. Sample 1 is more atactic
d. Sample 1 is more isotactic
e. Painter shouldn't set such easy gift questions
2. Atactic polystyrene (Tg - 100°C) quenched (i.e., cooled very quickly) from 120°C
to room temperature
a. Is a rubbery material.
b. Crystallizes.
c. Is a glassy material.
3. High density polyethylene cooled slowly from 160°C to room temperature
a. Is still amorphous.
b. Crystallizes.
c. Is a glass.
d. Is a mixture where some regions are rubbery and some regions are glassy.
4. Which of the following polymers would you expect to be most suitable for
theproduction of a rubber car bumper guard?
a. Atactic polystyrene (Tg ~ 100°C)
b. A random ethylene/propylene copolymer (50/50 composition) Tg ~ 40°C).
c. Low density polyethylene.
d. High density polyethylene.
5. What is the root mean square end-to-end distance of a chain of 100 freely
hinged and jointed monomer units, each of which has a length of 4 Å?

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