Homework 2 Flashcards
How many Carbons and Hydrogen atoms does the aromatic ring have
6C & 5H
How do you find Mn from table? Eq.14.5a?
average of molecular weight range x Xi. add them all up after.
On equation 14.7. what does the Fj mean?
This is the fraction given to you in the problem. Example Fja=0.25 then Fjb=1-0.25
Explain briefly why the tendency of a polymer to crystallize decreases with increasing molecular weight
chains become longer it is more difficult for all regions along adjacent chains to align so as to produce the ordered atomic array
For equation 14.8 what do the densities mean? And how do you manipulate them when given 2 densities in problem?
Ps1 and Ps2 are given densities. C1 & C2 are % given in decimal form. you have to solve for P(amorphous) & P(crystalline).
For equation 14.9, what is Pm?
Permiability coefficient, usually given in a table. Or you are given an equation to solve.
Contrast the manner in which stress relaxation and viscoelastic creep tests are conducted.
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
experimental parameter of interest for stress relaxation?
relaxation modulus
experimental parameter of interest for viscoelastic creep?
creep modulus
how does molecular weight influence the tensile modulus of a semicrystalline polymer
tensile modulus is not directly influenced
how does degree of crystallinity influence the tensile modulus of a semicrystalline polymer
Tensile modulus increases with increasing degree of crystallinity
how does deformation by drawing influence the tensile modulus of a semicrystalline polymer
increases the tensile modulus. drawing produces a highly oriented molecular structure
how does annealing of an undeformed material influence the tensile modulus of a semicrystalline polymer
When an undeformed semicrystalline polymer is annealed below its melting temperature, the tensile modulus increases
how does annealing of a drawn material influence the tensile modulus of a semicrystalline polymer
decrease in tensile modulus as a result of a reduction in chain-induced crystallinity
how does molecular weight influence the tensile or yield strength of a semicrystalline polymer and why
tensile strength of a semicrystalline polymer increases with increasing molecular weight
how does degree of crystallinity influence the tensile or yield strength of a semicrystalline polymer and why
enhancement of the tensile strength
how does deformation by drawing influence the tensile or yield strength of a semicrystalline polymer and why
drawing increases the tensile strength
how does annealing of an undeformed material influence the tensile or yield strength of a semicrystalline polymer and why
increase in its tensile strength.
for Equation 15.3 you are given Mn and TS. How do you find TSinfinity and A?
Make two equations to solve for two variables
Is linear more likely to crystallize than branched polymers? T or F?
True
Do block copolymers have higher crystallinity than random copolymers? T or F
True
Do branch polymers crystallize?
No
Do atactic polymers crystallize?
No
two molecular characteristics that are essential for elastomers
Amorphous (with coil and kinks)
Crosslinking
difference in molecular chemistry between silicone polymers and other polymeric materials
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
four factors that determine what fabrication technique is used to form polymeric materials
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.
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?
one that was formed by extrusion and then rolled would have the higher strength
