MSE 220 FINAL QUESTIONS WITH VERIFIED
ANSWERS
How do you calculate the repeat unit molecular weight of polypropylene? - Answers -
you take the atomic weight of carbon and multiply it by the number of carbon that are
present on the chain. You do the same thing for hydrogen.
how do you computer the average number of molecular weight for a polypropylene
which has a degree of polymerization of 15000 - Answers - just multiply the repeat unit
molecular weight by the degree of polymerization.
Thermoplast - Answers - linear or branched structures that can be semi crystalline with
covalent bonding within the molecular chains. There is also secondary bonding between
the chains. Note thermoplasts are soft when heated, and the viscosity decreases ass
temperature increases. they are generally recyclable
thermoset - Answers - crosslinked or networked structures. These are amorphous
structures set on initial polymer synthesis. these are all covalent bonding and maintain
properties as high temperature. Thus, they do not soften at higher temperatures. They
are not recyclable and generally stiff with low ductility and relative to their counterparts
elastomers - Answers - long molecular chains in twisted, coiled configurations. chains
are interconnected by crosslinks. crosslink density determines the relative stiffness and
elastic deformation capacity for a given elastomer. all covalent bonding within chains
and crosslinks, amorphous
which sets are not recyclable? - Answers - thermosets
which polymer is likely to crystallize? branched atactic polypropylene or linear
syndiotactic polypropylene - Answers - linear syndiotactic polypropylene
which polymer is likely to crystallize? networked melamine or lightly crosslinked
polyethylene - Answers - lightly crosslinked polyethylene
which polymer is likely to crystallize? heavily crosslinked polyethylene terephthalate or
phenol formaldehyde - Answers - neither crystallize
how does molecular weight influence the tensile or yield strength of semi-crystalline
polymers and why? - Answers - the yield strength increases as molecular weight
increases. Additionally chain entanglement increases as well as secondary bonds as
the molecular weight increases
, how does degree of crystallinity influence the tensile or yield strength of semi-crystalline
polymers and why? - Answers - the yield strength increases as crystallinity increases as
well as enhancing interchain bonding
how does deformation by drawing influence the tensile or yield strength of semi-
crystalline polymers and why? - Answers - the yield strength increases as deformation
by drawing is performed. This is because of chain orientation with load/stress direction
as well as enhanced interchain secondary bonding
how does annealing of an undeformed material influence the tensile or yield strength of
semi-crystalline polymers and why? - Answers - this leads to an increase in crystallinity
which increases the yield strength of a material. it also reduces ductility
what are the stress strain graphical representations of thermosets(A), thermoplasts (B),
and elastomers (C) - Answers - Note that if we are comparing two polymers, the one
with the higher percentages is the highest line but it also breaks sooner
is linear and highly crystalline polyethylene a thermoset, thermoplast, or elastomer? -
Answers - thermoplast
is phenol-formaldehyde a thermoset, thermoplast, or elastomer? - Answers - thermoset
(network structure)
is heavily cross-linked polyisoprene having a glass transition temperature of 50 degrees
C a thermoset, thermoplast, or elastomer? - Answers - since T < Tg its a thermoset
is lightly cross-linked polyisoprene having a glass transition temperature of -60 degrees
C a thermoset, thermoplast, or elastomer? - Answers - elastomer
is linear and amorphous polyvinyl chloride a thermoset, thermoplast, or elastomer? -
Answers - thermoplast
explain on a structural basis the differences in glass transition temperature of
polyethylene (Tg=-140C), polyvinyl-chloride(Tg=87C), and polystyrene (Tg=100C) -
Answers - The first one has the lowest Tg because it is a simple structure with small
side groups. Thus there is very little restriction to inter-chain mobility. The second one
has a chlorine with polar side groups to enhance interchain bonding. This enhanced
inter-chain bonding leads to a restriction on inter-chain mobility. The final one has the
highest Tg because it has large, bulky side groups that restrict inter-chain mobility
For homework 9, what else needs to be reviewed - Answers - The stress strain
diagrams and the average molecular weight ration problem number 4
For a polymer-matrix fiber-reinforced composite, list 3 functions of the matrix phase -
Answers - 1. they find fibers together, applied stresses are thus distributed among the
fibers (think sails)
ANSWERS
How do you calculate the repeat unit molecular weight of polypropylene? - Answers -
you take the atomic weight of carbon and multiply it by the number of carbon that are
present on the chain. You do the same thing for hydrogen.
how do you computer the average number of molecular weight for a polypropylene
which has a degree of polymerization of 15000 - Answers - just multiply the repeat unit
molecular weight by the degree of polymerization.
Thermoplast - Answers - linear or branched structures that can be semi crystalline with
covalent bonding within the molecular chains. There is also secondary bonding between
the chains. Note thermoplasts are soft when heated, and the viscosity decreases ass
temperature increases. they are generally recyclable
thermoset - Answers - crosslinked or networked structures. These are amorphous
structures set on initial polymer synthesis. these are all covalent bonding and maintain
properties as high temperature. Thus, they do not soften at higher temperatures. They
are not recyclable and generally stiff with low ductility and relative to their counterparts
elastomers - Answers - long molecular chains in twisted, coiled configurations. chains
are interconnected by crosslinks. crosslink density determines the relative stiffness and
elastic deformation capacity for a given elastomer. all covalent bonding within chains
and crosslinks, amorphous
which sets are not recyclable? - Answers - thermosets
which polymer is likely to crystallize? branched atactic polypropylene or linear
syndiotactic polypropylene - Answers - linear syndiotactic polypropylene
which polymer is likely to crystallize? networked melamine or lightly crosslinked
polyethylene - Answers - lightly crosslinked polyethylene
which polymer is likely to crystallize? heavily crosslinked polyethylene terephthalate or
phenol formaldehyde - Answers - neither crystallize
how does molecular weight influence the tensile or yield strength of semi-crystalline
polymers and why? - Answers - the yield strength increases as molecular weight
increases. Additionally chain entanglement increases as well as secondary bonds as
the molecular weight increases
, how does degree of crystallinity influence the tensile or yield strength of semi-crystalline
polymers and why? - Answers - the yield strength increases as crystallinity increases as
well as enhancing interchain bonding
how does deformation by drawing influence the tensile or yield strength of semi-
crystalline polymers and why? - Answers - the yield strength increases as deformation
by drawing is performed. This is because of chain orientation with load/stress direction
as well as enhanced interchain secondary bonding
how does annealing of an undeformed material influence the tensile or yield strength of
semi-crystalline polymers and why? - Answers - this leads to an increase in crystallinity
which increases the yield strength of a material. it also reduces ductility
what are the stress strain graphical representations of thermosets(A), thermoplasts (B),
and elastomers (C) - Answers - Note that if we are comparing two polymers, the one
with the higher percentages is the highest line but it also breaks sooner
is linear and highly crystalline polyethylene a thermoset, thermoplast, or elastomer? -
Answers - thermoplast
is phenol-formaldehyde a thermoset, thermoplast, or elastomer? - Answers - thermoset
(network structure)
is heavily cross-linked polyisoprene having a glass transition temperature of 50 degrees
C a thermoset, thermoplast, or elastomer? - Answers - since T < Tg its a thermoset
is lightly cross-linked polyisoprene having a glass transition temperature of -60 degrees
C a thermoset, thermoplast, or elastomer? - Answers - elastomer
is linear and amorphous polyvinyl chloride a thermoset, thermoplast, or elastomer? -
Answers - thermoplast
explain on a structural basis the differences in glass transition temperature of
polyethylene (Tg=-140C), polyvinyl-chloride(Tg=87C), and polystyrene (Tg=100C) -
Answers - The first one has the lowest Tg because it is a simple structure with small
side groups. Thus there is very little restriction to inter-chain mobility. The second one
has a chlorine with polar side groups to enhance interchain bonding. This enhanced
inter-chain bonding leads to a restriction on inter-chain mobility. The final one has the
highest Tg because it has large, bulky side groups that restrict inter-chain mobility
For homework 9, what else needs to be reviewed - Answers - The stress strain
diagrams and the average molecular weight ration problem number 4
For a polymer-matrix fiber-reinforced composite, list 3 functions of the matrix phase -
Answers - 1. they find fibers together, applied stresses are thus distributed among the
fibers (think sails)
