13 Polymer Physicals Properties

Question 1

Structure: Polymer architecture

Answer 1

Properties: Crystallinity, viscosity,
mechanical properties

Question 2

Structure: Molecular weight and
distributions

Answer 2

Properties: Melting point, viscosity,
solubility

Question 3

Structure: Additives (Plasticizers)

Answer 3

Properties: Mechanical properties

Question 4

Structure: Stereoregularity

Answer 4

properties: Crystallinity, solubility

Question 5

Polymer architecture

Answer 5

• linear
• Comp
• Branched
• Star
• Dendritic
• Crosslinked

Question 6

High vs low density

Answer 6

Linear=high
branched = low

Question 7

Molecular weight affects

Answer 7

affect solubility, strength, viscosity, among other
properties.

Question 8

Number average molecular weight (𝑴𝒏)

Answer 8

sum( number of polymer chains of a given mass (Ni) *molecular weigh (Mi)/sum

use colligative properties (i.e. osmotic
pressure) to determine MW we obtain a
number-average molar mass.

Question 9

Weight average molecular weight (𝑴𝒘)

Answer 9

=sum(NiMi^2)/sum(NiMi)

If light scattering measurements are used to
determine MW, a weight average (Mw
) is
obtained. Mw
is biased towards higher
molecular weight polymers.

Question 10

Mv

Answer 10

viscosity average molecular weight. Useful
to compare viscosity of polymer chains.

Question 11

Mz

Answer 11

centrifugation average molecular weight.
Useful for describing mechanical properties.

Question 12

Rank all the M

Answer 12

Mz > Mw > Mv > Mn.

number of molecules is opposite

Question 13

What is PDI

Answer 13

Polydispersity = Mw/Mn

Provides a measure of the heterogeneity of
polymer lengths.

Question 14

Degree of poymerization

Answer 14

DPn = Xn = Mn/M0

Number average number of repeat units in chain

Question 15

what is M0

Answer 15

MW monomer

Question 16

MW and mechanical strength

Answer 16

MW below certain point poly no mechanical strength

MW increases
beyond that point, mechanical strength
increases rapidly

At a given chain length,
the increase in MW does not significantly
change the mechanical strength of the material

Question 17

Mw and processing

Answer 17

• Large MW increases mechanical
  strength/viscosity. (Increased viscosity undesirable for melt extrusion/injection molding
  .
  – Broad MW favor low
  softening point.

– Narrow MW distribution favors crystallization.

Question 18

Crystalline vs. amorphous domains polymers

Answer 18

• Polymers have
  crystalline and amorphous
  domains.
• # domains impactsmechanical strength

Question 19

Glass transition temperature (Tg)

Answer 19

• Temperature below which a material has
  properties similar to that of a glass (rigid,
  brittle).
• Above Tg
  the material is elastic.

Question 20

Tuning Tg

Answer 20

Plasticizers interfere with intermolecular
interactions between the chains,

• plasticizers reduce theTg

Question 21

Tg vs Tm

Answer 21

Tm involves change in latent
heat where Tg does not.

Question 22

Thermoplastics

Answer 22

amorphous polymer with a
Tg
above room temperature. Polymer can be
reversibly shaped by heating while applying a
stress before cooling.

Question 23

Elastomer

Answer 23

An amorphous polymer with a Tg
below room temperature

Question 24

Thermosets

Answer 24

Soft solid or liquid that crosslinks
upon heating (a process known as curing). After
curing the shape of the polymer is irreversibly
se

Question 25

machine that measures stress-strain

Answer 25

Instron Machine

Question 26

Stress-strain plots

Answer 26

Stress (N cm-2, MPa) vs. elongation or strain (ΔL/L)

Question 27

Modulus:
Ultimate strength or Tensile strength:
Ultimate elongation:
Elastic elongation:

Answer 27

• The initial slope of the stress-strain curve.
• The stress
  required to rupture a sample.
• The maximum elongation
  before the sample ruptures.
• The maximum elongation in the
  elastic region

Question 28

Stress-Strain Curves and Deformation

Answer 28

When a stress is applied,
the material will
experience a reversible
change shape (strain)
until the elastic limit.
If the stress increases,
the change of shape is
irreversible.

Question 29

Tacticity

Answer 29

Defines stereoregularity of neighboring C centers
isotactic, syndiotactic, and atactic.

Question 30

Other structure – property relationship backbone

Answer 30

• C-C: High torsional flexibility (low Tg)
• C=C: Restricted rotation; chemical sensibility; electrical conductivity.
  Ring: Restricted rotation (high Tg); chemical resistance.
• ring w/ alkene: Restricted rotation; colored; electrical conductivity.
  -C-O- High chain flexibility; stable.
• S: Chain flexibility; sensitive to oxidation.
  -Si-O: Very high chain flexibility (very low Tg); stable to heat and oxidation

Question 31

Other structure – property relationship side groups

Answer 31

Side groups affect solubility, flammability,
hydrophobicity or reactivity.
– Bulky side groups (i.e. biphenyl) raise Tg
and
make the material stiff.

Crosslinking:
– Decreases solubility.
– Enhances thermal stability.

Question 32

Strength and extensibility

Answer 32

High strength and low extensibility is obtained
by combinations of high crystallinity,
crosslinking, or polymer structure (rigid chains)
Low strength and high extensibility is obtained
from polymers with low crystallinity, limited or
no crosslinking, and low Tg

Strength decreases and is eventually lost near Tg