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P R A C T I C E P R O B L E M S F O RS T U D E N T U S E

CHAPTER 20: PHARMACEUTICAL POLYMERS

20–1 There are three monomers: M1, M2, and M3; M1contains one double bond and no functional group,M2 contains one reactive functional group and nodouble bond, and M3 contains two reactive func-tional groups and no double bond. Which statement istrue?(a) All three monomers can be polymerized via addi-

tion and condensation polymerization.(b) M1 can be polymerized via addition, M2 cannot

be polymerized, and M3 can be polymerized viacondensation.

(c) M1 can be polymerized via addition, and both M2and M3 can be polymerized via condensation.

(d) None of the monomers are polymerizable.

20–2 Which statement is true regarding polymer molecularweight?(a) Number average molecular weight is related to

the size of the polymer chains.(b) Weight average molecular weight is related to the

number of polymer chains.(c) Polydispersity is related to the number and the

size of the polymer chains.(d) Number average molecular weight is always big-

ger than the weight average molecular weight.

20–3 The Tg values of the two polymers P1 and P2 are−20◦C and 100◦C, respectively. Which statement istrue?(a) At room temperature of 25◦C, both P1 and P2 are

rubber.(b) At room temperature of 25◦C, P1 is rubber but P2

is glass.(c) At room temperature of 25◦C, both P1 and P2 are

glass.(d) At room temperature of 25◦C, P1 is glass but P2

is rubber.

20–4 Which statement is false regarding the Tg and Tm of agiven polymer?(a) Tm is a first-order thermal transition but Tg is a

second-order one.(b) Tg and Tm are related to the amorphous and crys-

talline parts of the polymer chain, respectively.(c) Tg has a broader temperature range than does Tm.(d) For a given polymer, Tg is always higher than Tm.

20–5 Which statement is true for the elastic properties ofpolymers?(a) A low modulus polymer is stiffer than a high mod-

ulus polymer.(b) A high modulus polymer is tougher than a low

modulus polymer.(c) Stiffness is the ratio of strain to stress.(d) Toughness is the area under stress and strain

curve; energy to break.

20–6 If you are asked to increase the viscosity of water witha minimum amount of the following polymers, whichpolymer would be your choice?(a) A very hydrophilic and low-molecular-weight

polymer.(b) A very hydrophilic and high-molecular-weight

polymer.(c) A very hydrophobic and low-molecular-weight

polymer.(d) A very hydrophobic and high-molecular-weight

polymer.

20–7 In preparing a water-soluble polymer, which actionwould be wrong?(a) Using a water-soluble monomer(b) Utilizing emulsion technique(c) Utilizing inverse-emulsion technique(d) Utilizing inverse-suspension technique

20–8 Pseudo latex is a(a) Dispersion of a monomer in water.(b) Dispersion of a water-soluble polymer in water.(c) Dispersion of a water-insoluble polymer in water

using high HLB surfactant(s).(d) Dispersion of a water-insoluble polymer in water

using low HLB surfactant(s).

20–9 Which of the following statements is true for a dis-persion system?(a) In a W/O system, the dispersed phase is water,

and the continuous phase is oil.(b) In an O/W system, the dispersed phase is oil, and

the continuous phase is water.(c) Surfactant should be more soluble in the contin-

uous phase.(d) Surfactant concentration determines the size of

the dispersed phase.(e) All of the above are true.

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20–10 Which of the following polymers can be used as anenteric coating material?(a) An anionic polymer.(b) A cationic polymer.(c) An amphoteric polymer.(d) Both anionic and cationic polymers.

20–11 For taste-masking application, what polymer wouldyou not recommend to use?(a) A polymer which is soluble in water at neutral

pH.(b) A polymer which is soluble in water at low pH.(c) A polymer which is insoluble in water at all pHs.(d) An oil-soluble polymer.

20–12 Which statement is false about polydispersity andchain length?(a) A monodispersed polymer contains similar

chains.(b) A polydispersed polymer contains different

chains.(c) Polydispersity�1 means polymer chains are very

different in size.(d) Polydispersity is always lower than 1.

20–13 You have two polymers with different Tg values: poly-mer 1 (−90◦C) and polymer 2 (90◦C). If you are askedto coat your tablet with these polymers, which onewould you select?(a) Polymer 1.(b) Polymer 2.

20–14 Which statement is false?(a) Polymers do not exist as gas.(b) Monomers containing double bond may be poly-

merized via free radicals.(c) Polymers containing high concentrations of resid-

ual monomers may not be suitable for pharmaceu-tical use.

(d) Different isomers of a polymer have same physic-ochemical and mechanical properties.

20–15 A pharmaceutical packaging material requires beinga tough polymer, the tougher the better. After test-ing different polymers using a mechanical tester, youselect(a) A polymer which shows high modulus.(b) A polymer which deforms less at its failure or

breaking point.(c) A polymer which shows high stiffness.(d) A polymer whose force-deformation curve has the

largest area.

20–16 A polymer sample was fractionated into three homo-geneous or monodisperse fractions as follows:

Data for Problem 20–16

Fraction Weight, Grams Molecular Weight

A 10 100,000

B 20

C 100 10,000

Given that the weight-average molecular weight ofthe entire sample is 23,000, calculate the molecularweight of fraction B.

20–17 A sample of polyvinyl chloride was fractionated fromits solution in tetrahydrofuran. The weight percent(based on the weight of the entire sample) and themolecular weight (g/mole) of successive fractionswere as follows:

Data for Problem 20–17

FractionNumber Weight (%) Molecular Weight

1 6 7 × 103

2 9 1.7 × 104

3 15 3.8 × 104

4 20 7.5 × 104

5 23 1.4 × 105

6 16 2.5 × 105

7 8 4.5 × 105

8 3 1.05 × 106

Assuming that the fractions are essentiallymonodisperse, calculate Mz, Mw, Mn, and Mw/Mn

of the polyvinyl chloride sample.

20–18 Will the intrinsic viscosity of polyethylene oxideincrease, decrease, or remain unaffected as the tem-perature of its aqueous solution is increased?

Hint: Express your answer in terms of hydration.

20–19 The melting points of some isotactic polyolefins[ CH2 CH ] are as follows:

R

R Melting Point, ◦C

E CH3 165

F C2H5 125

G CH2 CH2 CH3 75

Explain the trend in melting point when going fromE to F to G.

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20–20 Drugs targeted for colon diseases may be formulatedinto a material (a polymer) which can protect themfrom the harsh low pH environment of the gastricmedium. The material selected for such applicationshould have(a) High solubility or complete solubility at low

pH.(b) No solubility or low solubility at low pH.

20–21 Coacervation is a process by which a drug is encap-sulated inside a polymeric matrix by precipitatingthe polymer in solution. If the drug is sensitive toheat and acid, which option would be least attrac-tive for precipitating the polymer from its aqueoussolution?(a) Increasing the temperature of the polymer solu-

tion.(b) Adding an effective but permitted amount of alco-

hol to the polymer solution.(c) Increasing the pH of the polymer solution.(d) Increasing the ionic strength of the polymer solu-

tion by adding reasonable amounts of salts.

20–22 Which of the following materials displays thermo-gelling at a higher temperature?(a) Cellulose (has no solubility in water).(b) Cellulose with methyl substitution (it is soluble

in cold water).(c) Thermogelling is not dependent on the number

and nature of substituents.

(d) Cellulose with methyl and hydroxypropyl substi-tution (it is soluble in water over a wider temper-ature range).

20–23 If the solution property of a material is sensitiveto temperature, that material displays thermogellingproperty. Which of the following materials less likelydisplays a thermogelling property?(a) A material containing both hydrophilic and hy-

drophobic groups.(b) A material with ionizable hydrophilic groups.(c) A material whose chains can aggregate if temper-

ature changes.(d) A material whose hydrophobic groups associate

if temperature rises.

20–24 Swelling concept has found applications in which ofthe following areas?(a) Superdisintegrants, which are used in tablets and

capsules to help the dosage form to disintegrateproperly.

(b) Osmotic tablets (Oros technology), which candeliver the drug at a constant rate over a 24-hrperiod.

(c) Implantable osmotic pumps (Duros technology),which can deliver the drug over a few months toa 1-year period.

(d) Superabsorbent polymers, which are used in ultra-thin baby diapers to absorb baby’s urine.

(e) All of the above.