Polymers I Flashcards

1
Q

What is a polymer?

A

long chain of molecules made up of a series of repeating units

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2
Q

What is mer

A

repeating unit

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3
Q

What is the backbone of the polymer chain?

A

A series of atoms joined by
strong covalent bonds, most commonly carbon-carbon

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4
Q

What does the random rotation of covalent bonds in the backbone of a polymer chain lead to?

A

Bends,
kinks and coils in the polymer chain

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5
Q

What role do the backbone and addition of side groups play in differentiating polymers?

A

The backbone and addition of side groups distinguish the one polymer
from another

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6
Q

What are plastics?

A

Synthetic or semi-synthetic
polymers

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7
Q

What have plastics been historically generated from?

A

Oil or natural gas

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8
Q

What are common sources that plastics are now generated from?

A

Oil or natural gas
wood fibers
corn
organic materials (banana peels!)

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9
Q

What are natural polymers?

A

Polymers
derived from existing biological
processes

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10
Q

What are examples of natural polymers?

A

-Cellulose
-Sugars and starches (polysaccharides)
-DNA
-Rubber

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11
Q

What is cis-polyisoprene derived from?

A

Sap of some plants and trees

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12
Q

What is unique about cellulose

A

It’s an organic material used for cell walls of plants and trees.

It’s the most abundant organic material on earth

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13
Q

Which chemical is natural rubber?

A

cis-polyisoprene

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14
Q

How are polymers differentiated?

A

By their side groups and/or backbone
chain

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15
Q

What type of impact can small differences in polymers have?

A

Small differences can greatly
impact properties (melting points,
reactivity, brittleness, stiffness)

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16
Q

What are many properties of polymers linked to?

A

the polymer chain length
and molecular weight

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17
Q

What happens to the length of polymer chains during polymerization?

A

Polymer chains grow to different lengths –there is a distribution of chain lengths

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18
Q

What are the 2 ways of defining the molecular weight?

A

Number-average molecular weight
Weight-average molecular weight

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19
Q

How is the number-average molecular weight determined?

A

Determined from a histogram of
the number of chains within a given size interval

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20
Q

How is the weight-average molecular weight determined?

A

Determined from a histogram of
the total mass of the chains within the given size interval

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21
Q

What is true in all cases about the number- vs. weight-average molecular weight?

A

In all cases, the weight-average molecular
weight will be higher than the number-average.

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22
Q

What is the histogram for the weight fraction more heavily weighted towards?

A

The histogram for the weight fraction is more heavily
weighted to the longer, heavier chains.

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23
Q

What is another way of expressing average chain size of a polymer?

A

degree of polymerisation(DP)

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24
Q

What does the degree of polymerization represent?

A

The average # of mer units in a chain

25
How is the degree of polymerization calculated?
DP is typically calculated from the number-average molecular weight.
26
How does the degree of polymerization impact melting points, stiffness, and strength?
Higher DP means: * Higher melting points * Higher stiffness * Higher strength
27
What are linear polymers?
Polymers with mer units joined end to end in single chains
28
What are branched polymers?
Polymers with side-branched chains connected to the main ones
29
How do branched polymers result?
From side reactions that occur during synthesis of polymer
30
How do branched polymers affect the chain packing efficiency and polymer density?
Chain packing efficiency is reduced and lowers polymer density
31
Can polymers with linear structures be branched?
Yes, polymers that form linear structures may also be branched.
32
Describe the branching of high-density polyethylene (HDPE)
Low degree of short-chain branching; primarily a linear polymer.
33
What is the density of HDPE?
The density of greater or equal to 0.941 g/cm^3
34
Describe the properties of HDPE
-Low degree of short-chain branching The mostly linear molecules pack together well, so intermolecular forces are stronger than in highly branched polymers.
35
Describe the commercial applications of HDPE.
Used in products and packaging such as milk jugs, detergent bottles, butter tubs, garbage containers, and water pipes.
36
What proportion of toys are manufactured from HDPE?
One-third of all toys are manufactured from HDPE
37
Describe the branching of low-density polyethylene (LDPE)
High degree of short-chain branching + long-chain branching
38
What is the density range of LDPE?
0.910–0.940 g/cm3
39
Describe the main properties of LDPE?
LDPE has a high degree of short- and long-chain branching, which means that chains pack poorly. It has, therefore, less strong intermolecular forces, resulting in a lower tensile strength and increased ductility.
40
What are the commercial applications of LDPE?
Used for both rigid containers and plastic film applications such as plastic bags and film wrap
41
What happens during crosslinking?
adjacent linear chains strongly joined to one another
42
When is crosslinking achieved?
During synthesis of a polymer or by a nonreversible chemical reaction
43
How is crosslinking often accomplished?
By additive atoms or molecules that are covalently bonded to the chains
44
What is a common property among rubber elastic materials?
Many rubber elastic materials are irreversibly crosslinked (called vulcanization)
45
What is alginate?
A naturally occurring polymer, typically derived from brown algae
46
What are the advantages of alginate?
Low cost, biocompatibility and mild gelation conditions
47
How is hydrogel formed upon cross-linking?
The block copolymer of guluronate and mannuronate residues to create hydrogel. The guluronate cross links with Ca2+ to form an egg box structure.
48
What is the result of guluronate cross-linking with divalent cations (Ex. Ca2+)
An egg-box structure
49
Why does molecular weight or degree of polymerization affect the mechanical properties of polymers? (Written Response)
*Greater van der Waals interactions between polymer chains *Greater thermal energy and stress required to disrupt these bonds *Giving rise to higher melting point and higher strength (lower ductility)
50
What are some defining characteristics of polymers?
*Lightweight (density = 0.9 - 3 g/cm^3) *Low elastic modulus (in bulk form) *Low fracture toughness (in bulk form) *Good ductility and specific toughness (in bulk form) *Highly formable (in bulk form) *Chemistry is well understood and manipulatable
51
Which of these substances are polymers?: Hemaglobin, polylactic acid (PLA), DNA, collagen, and silicone.
All of them are polymers.
52
What is the relationship between the size of a side chain group, bond rotation, and tensile strength?
Larger side groups limit ease of bond rotation (i.e. make it harder), thereby increasing strength
53
What properties of polymers can decrease ductility and increase strength?
-Degree of crosslinking -Number-average molecular weight -Degree of polymerization
54
Why does the polymer strength decrease due to the degree of polymerization decreasing?
Due to reduced secondary bonding between polymer chains.
55
What is the relationship between the average number of monomer units in a chain and the melting point of the chain?
As the average number of monomer units in a chain increases, the melting point of the chain increases.
56
What happens to the ductility when you increase the degree of crosslinking in rubber elastic materials?
The ductility decreases.
57
What is the relationship between temperature, young's modulus, ultimate tensile strength, and ductility?
As temperature increases, the young’s modulus and ultimate tensile strength decreases and ductility increases.
58
How many times can polymers stretch beyond the original length before breaking?
They stretch over ten times the original length before breaking.
59
Is it possible to grind up and reuse phenol formaldehyde and polyethylene polymers?
It's impossible to grind up and reuse phenol formaldehyde since it is a thermoset and not amenable to remolding. It's possible to grind up and reuse polyethylene since it is a thermoplastic and can be remolded