פולימרים

Discuss, Learn and be Happy דיון בשאלות

• «
• 1
• 2
• 3
• 4
• 5
• 6
• »

If a condensation polymerization is carried out with equal molar quantities of carboxyl and hydroxyl groups from a difunctional carboxylic acid monomer (two carboxylic groups), and from a tetra functional polyhydroxy monomer (four hydroxy groups), such that a crosslinked gel forms at a given point of monomer conversion what will be the approximate reaction conversion, p, of monomers into polymer at the gelation point.

-

1

+

שאלה #38964

		0.92
		0.57
		0.32
done		0.66

• gavel
• mood_bad
• share

הגב

מיין לפי דירוג חדש ישן

Amylose and cellulose are both polymers of glucose but have very different physical and mechanical properties. Cellulose is mechanically strong and insoluble in water and many other solvents. Amylose starch is water soluble and mechanically weaker compared to cellulose. Of the following which is the best explanation for these properties: (Choose from the following 4 possibilities)

-

1

+

שאלה #38965

		In cellulose the glucose monomer is in α configuration but in amylose the connection between the monomers is a β glucose configuration.
done		Differences in the cellulose chain configuration compares to amylose results in very different inter hydrogen bonding characteristics.
		Cellulose has a higher molecular weight than amylose hence more hydrogen bonding interactions between the chains.
		Cellulose is bound together by lignin which gives it different properties than amylose.

• gavel
• mood_bad
• share

הגב

מיין לפי דירוג חדש ישן

If a free radical polymerization is carried out with vinyl monomer 1 (H2C=CHR1) and vinyl monomer 2 (H2C=CHR2) where R1 can resonance stabilized a forming radical and R2 cannot resonance stabilize a radical what would you expect reactivity ratio r1=k11/k12 to be?

-

1

+

שאלה #38966

done		r1 > 1.0
		r1 = 1.0
		r1 < 1.0
		r1 = 0

• gavel
• mood_bad
• share

הגב

מיין לפי דירוג חדש ישן

Atom transfer polymerization is similar to which of the following polymerization processes with respect to the ratio of number average molecular weight to weight average molecular weight (Mn/Mw) it can achieve?

-

1

+

שאלה #38967

		Free radical polymerization with benzoyl peroxide.
done		Anionic polymerization without chain termination.
		Cationic polymerization with BF3/H20
		Friedel-Crafts polymerization used in condensation polymerization reactions

• gavel
• mood_bad
• share

הגב

מיין לפי דירוג חדש ישן

If i have a polymer with a solubility parameter of 11.6 and in one case I want to make blend 1 with another polymer where the final mixture has two different glass transition points (Tg) and in the second case I want to make 2 with another polymer where the blend has only one Tg's what should be the solubility parameters of the second polymer in each case.

-

1

+

שאלה #38968

		For blend 1 the second polymer should have a solubility parameters as close to 11.6, and for blend 2 as far as possible from 11.6
		For blend 1 the second polymer should have a solubility parameters much lower than 11.6 and for blend 2 as far as possible from 11.6
done		For blend 1 the second polymer should be much higher than 11.6 and for blend 2 as close as possible to 11.6
		In both blends the solubility parameters can be the same but the preparation of the blend with the single Tg includes a heat treatment step

• gavel
• mood_bad
• share

הגב

מיין לפי דירוג חדש ישן

Both liquid crystalline aromatic polyamides and linear high molecular weight polyethylene can be extrudes into fibers with tensile strengths higher than steel. The reason for this is (Choose from the following four possibilities)

-

1

+

שאלה #38969

		Both polymers are linear and have similar secondary forces which hold the individual polymer molecules in place.
		In the process of fiber formation the linear PE undergoes crosslinking while the polyamides interact through hydrogen bonding
done		In the process of fiber formation both polymers can be highly aligned with ordered crystalline domains.
		In fiber formation both the polyamide and PE are chosen with very high molecular weights.

• gavel
• mood_bad
• share

הגב

מיין לפי דירוג חדש ישן

Characteristics of tensile stress-strain behavior for fibers, plastics & elastomers - distinction between. Which of the following statements is not correct? (Choose from the following four possibilities)

-

1

+

שאלה #38970

		Both the brittle plastic and fibers exhibit a steep slope (high modulus), but fibers cangenerally sustain greater stress before breaking.
		Non brittle plastics can have a yield point beyond which the molecules begin to untangleand flow over one another, and further elongation beyond the yield point is irreversible.
		Highly crystalline polymers exhibit little change in morphology on drawing (stretching)and break soon after the yield point.
sentiment_very_satisfied		Elastomers have a low modulus initially, but once in the stretched state the modulusincreases sharply due induced chemical crosslinks by oxygen in the air.

• gavel
• mood_bad
• share

הגב

מיין לפי דירוג חדש ישן

Choose the secondary interactions in the polymers I) polyethylene, II) polyamide, III) Polyester, IV) Polyacrylic acid sodium salt: (Choose from the following four possibilities)

-

1

+

שאלה #38972

		I) Hydrogen bonding, II) Ionic bonding, III) Dipole-dipole IV) London forces
		I) London forces, II) Dipole-dipole, III) Hydrogen bonding IV) Ionic bonding
done		I) London forces, II) Hydrogen bonding III) Dipole-dipole IV) Ionic bonding
		I) Dipole-dipole, IT) Ionic bonding, III) Hydrogen bonding IV) London forces

• gavel
• mood_bad
• share

הגב

מיין לפי דירוג חדש ישן

condensation polymerization reactions such as polyamide or polyester polymerization are classified as stepwise reaction processes because (Choose from the following four possibilities)

-

1

+

שאלה #38973

		There is a termination by coupling and not disproportionation
		There is a release of side products in each reaction step
		The reactions are related to polymerization kinetics where the chains grow rapidly to high molecular weight with a large fraction of the monomer still present.
done		None of the above

• gavel
• mood_bad
• share

הגב

מיין לפי דירוג חדש ישן

condensation polymerization reactions are classified as stepwise reaction processes because (Choose from the following four possibilities)

-

1

+

שאלה #38974

		There are steps of initiation, propagation and termination, and each step has different kinetics
done		There is slow build up of polymer chains from monomer, dimers and trimers with equal reactivity regardless of molecular weight of each of the reacting molecules.
		There is a release of side products in each reaction step
		The reactions are related to radical growth kinetics where the chains grow rapidly to high molecular weight with a large fraction of the monomer still present..

• gavel
• mood_bad
• share

הגב

מיין לפי דירוג חדש ישן

• «
• 1
• 2
• 3
• 4
• 5
• 6
• »