Homework 2

Question 1

How many Carbons and Hydrogen atoms does the aromatic ring have

Answer 1

6C & 5H

Question 2

How do you find Mn from table? Eq.14.5a?

Answer 2

average of molecular weight range x Xi. add them all up after.

Question 3

On equation 14.7. what does the Fj mean?

Answer 3

This is the fraction given to you in the problem. Example Fja=0.25 then Fjb=1-0.25

Question 4

Explain briefly why the tendency of a polymer to crystallize decreases with increasing molecular weight

Answer 4

chains become longer it is more difficult for all regions along adjacent chains to align so as to produce the ordered atomic array

Question 5

For equation 14.8 what do the densities mean? And how do you manipulate them when given 2 densities in problem?

Answer 5

Ps1 and Ps2 are given densities. C1 & C2 are % given in decimal form. you have to solve for P(amorphous) & P(crystalline).

Question 6

For equation 14.9, what is Pm?

Answer 6

Permiability coefficient, usually given in a table. Or you are given an equation to solve.

Question 7

Contrast the manner in which stress relaxation and viscoelastic creep tests are conducted.

Answer 7

Stress relaxation- rapidly straining the material elastically in tension, holding the strain level constant, and then measuring the stress as a function of time
Viscoelastic creep, a stress (usually tensile) is applied instantaneously and maintained constant while strain is measured as a function of time

Question 8

experimental parameter of interest for stress relaxation?

Answer 8

relaxation modulus

Question 9

experimental parameter of interest for viscoelastic creep?

Answer 9

creep modulus

Question 10

how does molecular weight influence the tensile modulus of a semicrystalline polymer

Answer 10

tensile modulus is not directly influenced

Question 11

how does degree of crystallinity influence the tensile modulus of a semicrystalline polymer

Answer 11

Tensile modulus increases with increasing degree of crystallinity

Question 12

how does deformation by drawing influence the tensile modulus of a semicrystalline polymer

Answer 12

increases the tensile modulus. drawing produces a highly oriented molecular structure

Question 13

how does annealing of an undeformed material influence the tensile modulus of a semicrystalline polymer

Answer 13

When an undeformed semicrystalline polymer is annealed below its melting temperature, the tensile modulus increases

Question 14

how does annealing of a drawn material influence the tensile modulus of a semicrystalline polymer

Answer 14

decrease in tensile modulus as a result of a reduction in chain-induced crystallinity

Question 15

how does molecular weight influence the tensile or yield strength of a semicrystalline polymer and why

Answer 15

tensile strength of a semicrystalline polymer increases with increasing molecular weight

Question 16

how does degree of crystallinity influence the tensile or yield strength of a semicrystalline polymer and why

Answer 16

enhancement of the tensile strength

Question 17

how does deformation by drawing influence the tensile or yield strength of a semicrystalline polymer and why

Answer 17

drawing increases the tensile strength

Question 18

how does annealing of an undeformed material influence the tensile or yield strength of a semicrystalline polymer and why

Answer 18

increase in its tensile strength.

Question 19

for Equation 15.3 you are given Mn and TS. How do you find TSinfinity and A?

Answer 19

Make two equations to solve for two variables

Question 20

Is linear more likely to crystallize than branched polymers? T or F?

Answer 20

True

Question 21

Do block copolymers have higher crystallinity than random copolymers? T or F

Answer 21

True

Question 22

Do branch polymers crystallize?

Answer 22

No

Question 23

Do atactic polymers crystallize?

Answer 23

No

Question 24

two molecular characteristics that are essential for elastomers

Answer 24

Amorphous (with coil and kinks)

Crosslinking

Question 25

difference in molecular chemistry between silicone polymers and other polymeric materials

Answer 25

The backbone chain of most polymers consists of carbon atoms that are linked together. For the silicone polymers, this backbone chain is composed of silicon and oxygen atoms that alternate positions

Question 26

four factors that determine what fabrication technique is used to form polymeric materials

Answer 26

whether the polymer is thermoplastic or thermosetting; (2) if thermoplastic, the softening temperature; (3) atmospheric stability; and (4) the geometry and size of the finished product.

Question 27

Which of the following polyethylene thin films would have the better mechanical characteristics? (1) Those formed by blowing. (2) Those formed by extrusion and then rolled. Why?

Answer 27

one that was formed by extrusion and then rolled would have the higher strength