Question 1

Which of the following best describes the effect of increasing polymer chain length on the mechanical properties of polyethylene?

Accepted Answer

Mechanical strength increases as chain length increases due to enhanced chain entanglement.

Question 2

A sample contains 15 polymer chains with degrees of polymerization (DPn) from 1 to 5, and each repeat unit has a molar mass $$M_0 = 100$ g/mol. If the number of chains for DPn 1, 2, 3, 4, and 5 are 5, 4, 3, 2, and 1 respectively, what is the number-average molar mass M_n$?

Accepted Answer

$$M_n = \frac{\sum N_i M_i}{\sum N_i} = \frac{3500}{15} = 233 g/$$mol

Question 3

Which equation describes the empirical relationship between glass transition temperature ($$T_g) $$and number-average molar mass ($$M_n) $$for polymers?

Accepted Answer

$$T_g = T_{g,\infty} - \frac{K}{M_n}$$

Question 4

Which technique is most suitable for determining the weight-average molar mass ($$M_w) of a $$polymer sample?

Accepted Answer

Light scattering

Question 5

A polymer sample has $$M_n = 10,000 g/$$mol and $$M_w = 20,000 g/$$mol. What is its dispersity ($$\mathrm{Đ}$$)?

Accepted Answer

$$\mathrm{Đ} = \frac{M_w}{M_n} = 2$$

Question 6

Which of the following statements about size-exclusion chromatography (SEC) is correct?

Accepted Answer

SEC separates polymers based on their hydrodynamic volume.

Question 7

Which property is NOT typically measured by Differential Scanning Calorimetry (DSC)?

Accepted Answer

Decomposition temperature ($$T_d)$$

Question 8

Which of the following best describes the difference between step-growth and chain-growth polymerization?

Accepted Answer

In step-growth polymerization, any two molecular species can react, while in chain-growth, growth occurs only at active chain ends.

Question 9

A MALDI-ToF spectrum of a polystyrene sample shows peaks separated by 104 mass units. What does this spacing represent?

Accepted Answer

The mass of the repeating unit

Question 10

Which of the following is a real-world application where ultra-high molar mass polyethylene is used, as discussed in the study materials?

Accepted Answer

Hip prosthetic acetabular cup

Question 11

Which of the following statements about dispersity ($$\mathrm{Đ}) is $$correct?

Accepted Answer

Dispersity quantifies the heterogeneity of a polymer sample's molar mass distribution.

Question 12

Which of the following best explains why biopolymers such as proteins are typically monodisperse?

Accepted Answer

They are synthesized by highly controlled biological processes.

Question 13

Which of the following is NOT a colligative property used to determine the number-average molar mass ($$M_n) of a $$polymer?

Accepted Answer

Light scattering intensity

Question 14

A polymer sample is analyzed by SEC and shows a broad molar mass distribution. What does this indicate about the sample?

Accepted Answer

The sample has high dispersity.

Question 15

Which of the following is a limitation of MALDI-ToF for polymer analysis?

Accepted Answer

It does not prove the purity of the polymer sample.

Question 16

Which of the following best describes the principle of Size-Exclusion Chromatography (SEC)?

Accepted Answer

Polymers are separated based on their hydrodynamic volume, with larger chains eluting first.

Question 17

Which thermal analysis technique would you use to determine the decomposition temperature ($$T_d) of a $$polymer?

Accepted Answer

Thermogravimetric Analysis (TGA)

Question 18

Which of the following statements about the effect of impurities in step-growth polymerization is correct?

Accepted Answer

Impurities limit the achievable molecular weight by terminating growing chains.

Question 19

Which of the following is a key difference in the time evolution of molecular weight during step-growth versus chain-growth polymerization?

Accepted Answer

In chain-growth, high molecular weight is achieved early, while in step-growth, it is achieved only at high conversion.

Polymer Chemistry: Chain Length, Molar Mass, and Characterization Techniques

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