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LWBK575-20-Stud-Prob LWW-Sinko-educational March 16, P1: Trim: 8.375in × 10.875in LWBK575-20-Stud-Prob LWW-Sinko-educational March 16, 2010 11:2 2 STUDENT PRACTICE PROBLEMS: CH. 20

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  • P1: Trim: 8.375in × 10.875in LWBK575-20-Stud-Prob LWW-Sinko-educational March 16, 2010 11:2

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

    CHAPTER 20: PHARMACEUTICAL POLYMERS

    20–1 There are three monomers: M1, M2, and M3; M1 contains one double bond and no functional group, M2 contains one reactive functional group and no double bond, and M3 contains two reactive func- tional groups and no double bond. Which statement is true? (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 via condensation.

    (c) M1 can be polymerized via addition, and both M2 and M3 can be polymerized via condensation.

    (d) None of the monomers are polymerizable.

    20–2 Which statement is true regarding polymer molecular weight? (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 is true? (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 a given 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 of polymers? (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 with a minimum amount of the following polymers, which polymer 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 action would 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.

    1

  • P1: Trim: 8.375in × 10.875in LWBK575-20-Stud-Prob LWW-Sinko-educational March 16, 2010 11:2

    2 S T U D E N T P R A C T I C E P R O B L E M S : C H . 2 0

    20–10 Which of the following polymers can be used as an enteric 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 would you 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 and chain 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 asked to coat your tablet with these polymers, which one would 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 being a tough polymer, the tougher the better. After test- ing different polymers using a mechanical tester, you select (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 of the entire sample is 23,000, calculate the molecular weight of fraction B.

    20–17 A sample of polyvinyl chloride was fractionated from its solution in tetrahydrofuran. The weight percent (based on the weight of the entire sample) and the molecular weight (g/mole) of successive fractions were as follows:

    Data for Problem 20–17

    Fraction Number 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 essentially monodisperse, calculate Mz, Mw, Mn, and Mw/Mn of the polyvinyl chloride sample.

    20–18 Will the intrinsic viscosity of polyethylene oxide increase, 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 from E to F to G.

  • P1: Trim: 8.375in × 10.875in LWBK575-20-Stud-Prob LWW-Sinko-educational March 16, 2010 11:2

    S T U D E N T P R A C T I C E P R O B L E M S : C H . 2 0 3

    20–20 Drugs targeted for colon diseases may be formulated into a material (a polymer) which can protect them from the harsh low pH environment of the gastric medium. The material selected for such application should 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 precipitating the polymer in solution. If the drug is sensitive to heat and acid, which option would be least attrac- tive for precipitating the polymer from its aqueous solution? (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 sensitive to temperature, that material displays thermogelling property. Which of the following materials less likely displays 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 of the following areas? (a) Superdisintegrants, which are used in tablets and

    capsules to help the dosage form to disintegrate properly.

    (b) Osmotic tablets (Oros technology), which can deliver the drug at a constant rate over a 24-hr period.

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

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

    (e) All of the above.

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