Units 1 & 2

Question 1

What gives a polymer its properties?

Answer 1

Chemical structure + Physical structure

Question 2

Polymers differ considerably in what?

Answer 2

amount of crystallinity

Question 3

Crystallinity requires the polymer molecules to be able to….

Answer 3

pack into a regular repeating array

Question 4

Building Block Unit

Answer 4

Mer

Question 5

_____________ can significantly limit potential crystallinity.

Answer 5

Structural irregularities

Question 6

The higher the degree of irregularity, the ____ the polymer is able to crystallize.

Answer 6

less

Question 7

All polymers have a ________ over which they can crystallize.

Answer 7

limited range of temperature

Question 8

A polymer cannot crystallize ____ its melting temperature, or ____ its glass transition temperature.

Answer 8

above

below

Question 9

Why can’t a polymer crystallize above its melting point?

Answer 9

the polymer molecules have too much energy to “settle down”

Question 10

Define melting temperature

Answer 10

the breakup of crystallites

Question 11

Why can’t a polymer crystallize below its glass transtion temperature?

Answer 11

the polymer molecules do not have enough energy to move sufficiently to pack into a crystallite

Question 12

For some plastics, the range for crystallization to occur is ______ than Tm to Tg.

Answer 12

considerably narrower

Question 13

What happens if a plastic is cooled very quickly from the melt to a temperature below its crystallization temperature range? 1

What happens to the same plastic if held within the crystallization temperature range for an extended period of time? 2

Answer 13

1. It will develop little or no crystallinity

2. It may become highly crystalline

Question 14

Chemical Regularity - Branches

Answer 14

at branch points the polymer won’t “fit” into the crystal lattice

Question 15

Chemical Regularity - Cross-links

Answer 15

not only interfere with the fit, but also restrict the ability of molecular segments to move in order to assume a regular order

Question 16

What is the linear homopolymer of ethylene?

Answer 16

HDPE

Question 17

What is the branched homopolymer of ethylene?

Answer 17

LDPE

Question 18

What is the crystallinity of HDPE?

Answer 18

65-90%

Question 19

What is the crystallinity of LDPE?

Answer 19

40-60%

Question 20

HDPE vs LDPE

By decreasing the crystallinity, the presence of the branches results in….

Answer 20

less efficient packing of the molecules into space, decreasing the density of the plastic

Question 21

In the vast majority of materials, the spacing between adjacent molecules is _____ in crystalline areas than in amorphous areas.

Answer 21

smaller (water is an exception)

Question 22

The structure affects how much crystallinity ___ develop. Processing affects how much crystallinity ___ develops.

Answer 22

can

actually

Question 23

For a given polymer, increasing crystallinity increases….

Answer 23

Sealing temperature
Tensile strength
Stiffness

Question 24

For a given polymer, increasing crystallinity decreases…

Answer 24

Elongation
Permability
Impact strength
Tear strength

Question 25

In general, significant structural irregularity will prohibit crystallinity. Why is LDPE an exception?

Answer 25

it has very small side groups (hydrogens only)

Question 26

HDPE, LDPE, and LLDPE are all _____ polymers formed by what?

Answer 26

addition | free radical polymerization reactions from a monomer with a double bond

Question 27

HDPE - Initiation step

Answer 27

formation of the free radical and the addition of the first monomer

Question 28

HDPE Polymerazation - How is the initial generation of a free radical usually accomplished?

Answer 28

by the decompostion of an initiator, which is a relatively unstable compound such as peroxide, hydroperoxide or azo compound

Question 29

Sometimes _____ or _____ are used to generate free radicals.

Answer 29

UV radiation | High temperatures

Question 30

HDPE Polymerazation - What happens after the initiator free radical is formed?

Answer 30

the addition of the first monomer unit occurs

Question 31

How does branching occur?

Answer 31

the free radicals participate in chain transfer reactions

Question 32

Chain transfer reaction are favored by....

Answer 32

high energy states in the free radicals (high temperature)

Question 33

The rate of the propagation reaction generally _____ as temperature increases.

Answer 33

increases

Question 34

How is LDPE made?

Answer 34

under conditions of high temperature and high pressure

Question 35

Why does LDPE have lots of short branches and some long ones?

Answer 35

the free radical is most likely to collide with a nearby part of the same molecule

Question 36

How is HDPE made?

Answer 36

under milder conditions than LDPE, where chain transfer reactions are much less likely to occur *requires a catalyst

Question 37

In most cases, two different monomeric units _____ into the same crystalline arrangment.

Answer 37

will not fit

Question 38

The presence of a comonomer ______ crystallinity.

Answer 38

disrupts

Question 39

Isomorphous

Answer 39

when 2 different structures will fit into the same crystalline latice

Question 40

LLDPE is a _______ copolymer, with comonomers of ______

Answer 40

linear polyethylene | butene, hexene or octene

Question 41

How is LLDPE made?

Answer 41

essentially the same conditions as HDPE | using a catalyst to provide a lower energy route for polymerization

Question 42

How are HDPE and LLDPE different?

Answer 42

differences in crystallinity

Question 43

How are LLDPE and LDPE similar?

Answer 43

equal density | equal percent crystallinity

Question 44

How are LDPE and LLDPE different?

Answer 44

molecular weight and molecular weight distribution

Question 45

What is required for molecules to pack into a crystal lattice?

Answer 45

Stereochemical regularity and structural regularity

Question 46

What does stereochemistry refer to?

Answer 46

the arrangement of molecules in space

Question 47

Chiral Carbon

Answer 47

a carbon attached to 4 different groups, therefore it can exist in two mirror image forms, which cannot be interconverted without breaking primary bonds

Question 48

What are the different stereochemical forms?

Answer 48

Isotactic Syndiotactic Atactic

Question 49

What refers to the pattern of bonding within the molecule - what atoms are attached to what, and in what position?

Answer 49

Configuration

Question 50

What refers to the current arrangement in space?

Answer 50

Conformation

Question 51

_____ changes every time there is rotation about a bond.

Answer 51

Conformation

Question 52

______ cannot be changed without disrupting and reforming primary chemical bonds.

Answer 52

Configuration

Question 53

In ______ PP, when the PP molecule is laid out in its fully-extended-chain conformation, the position of the methyl group alternates from one side of the chain to the other.

Answer 53

Syndiotactic

Question 54

In ______ PP, when the PP molecule is laid out in its fully-extended-chain conformation, all the methyl groups are on the same side of the chain.

Answer 54

Isotactic

Question 55

In ______ PP, when the PP molecule is laid out in its fully-extended-chain conformation, the position of the methyl group is random

Answer 55

Atactic

Question 56

______ polymers are generally amorphous.

Answer 56

Atactic

Question 57

What is the PP we use in packaging?

Answer 57

linear isotactic

Question 58

_____ PP is a soft, weak material which is not useful to us as a packaging material.

Answer 58

Atactic

Question 59

Sources of structural irregularity:

Answer 59

- branching (or, even worse, cross-linking) - departure from the "normal" head-to-tail pattern of monomer addition - presence of comonomers (except if we have an alternating copolymer)

Question 60

_____ may be present if we have chiral carbons in our polymer, even if the polymer is chemically (structurally) regular.

Answer 60

Stereochemical irregularity

Question 61

A chiral carbon in a polymer molecule can be recognized as one that has _____ side groups attached to it.

Answer 61

2 different

Question 62

How does crystallinity affect polymer properties?

Answer 62

Increases tensile strength, stiffness, and barrier

Question 63

The coordinated crankshaft-type motion of 10-50 atoms.

Answer 63

Segmental mobility

Question 64

What is the basic requirement for segmental mobility?

Answer 64

that there be rotation around single bonds in the polymer backbone

Question 65

Which conformation has the lowest energy state?

Answer 65

Staggered conformation, where all the side groups are, on average, farthest apart

Question 66

Why is the eclipsed conformation at a higher energy level than the staggared conformation?

Answer 66

As there is rotation around the single C-C bound causes side groups to move closer to each other

Question 67

Polymers with double bonds in the backbone - | If we look at rotation about the single bond adjacent to the double bond, there is ________ with rotation

Answer 67

less interference

Question 68

Polymers with double bonds in the main chain tend to have ____ Tg's, and are _______.

Answer 68

low | soft and flexible

Question 69

What group are elastomers usually found?

Answer 69

polymers with double bonds

Question 70

The presence of a double bond means that the material ...

Answer 70

retains some reactivity, permitting subsequent cross-linking and other modification, if desired.

Question 71

What do ring structures in the backbone of a polymer do?

Answer 71

put rigid links but provide no appreciable effect of easing rotation around adjacent single bonds like double bonds do

Question 72

Polymers containing _____tend to be quite stiff, and have high Tg and Tm.

Answer 72

backbone rings

Question 73

What does the presence of O or N in the main chain tend to do?

Answer 73

increase the flexibility of a polymer structure, lowering its Tg (and Tm, if applicable)

Question 74

What must we consider whenever we have atoms other than C and H in the polymer?

Answer 74

the effects of the magnitude of secondary forces on properties

Question 75

Below Tg, there is ______ mobility of the polymer molecules.

Answer 75

no significant

Question 76

What happens to the polymer above Tm?

Answer 76

we have mobility everywhere (liquid flow)

Question 77

Large side groups ______ the mobility (conformational flexibility) of the molecule.

Answer 77

decrease

Question 78

What are the 3 main types of primary bonds?

Answer 78

covalent, ionic and metalic

Question 79

Which type of bonds involve sharing of electrons between the 2 atoms being bonded.

Answer 79

covalent

Question 80

Which type of bonds involve the transfer of electrons from one atom to another?

Answer 80

ionic (the molecular fragments are then joined together by electrostatic attraction)

Question 81

_____ bonds occur when electrons are very loosely held, and are therefore relatively free to wander away from their originating atom.

Answer 81

metallic

Question 82

Covalent bonds can be further subdivided into...

Answer 82

non-polar and polar bonds

Question 83

Non-polar Bonds

Answer 83

electron sharing is equal

Question 84

Polar Bonds

Answer 84

electron sharing is unequal

Question 85

Bonds involving _______ are generally polar.

Answer 85

C and O, N, Cl and F

Question 86

What is the prime determinant of the chemical reactivity of the polymer?

Answer 86

the strength of the primary bonds

Question 87

What determines the basic spacing of the atoms in the molecule?

Answer 87

the bond length

Question 88

If a substance had no secondary bonds....

Answer 88

it would behave like an ideal gas

Question 89

Types of secondary bonds

Answer 89

dispersion forces induction forces dipole forces hydrogen bonds

Question 90

Forces due to electostatic attractions between atoms with equal and opposite electric charges.

Answer 90

Dipole

Question 91

_______ forces occur when a polar molecule induces dipoles in surrounding nonpolar molecules.

Answer 91

Induction

Question 92

_______ forces are the attraction between neighboring molecules that results from instantaneous configurations of electrons and nuclei.

Answer 92

Dispersion

Question 93

Intermolecular attractions are proportional to ____

Answer 93

r^-6, where r is the distance between the atoms

Question 94

One of the ways in which crystallinity influences polymer properties is by achieving a _______ packaging of the atoms, and hence _____.

Answer 94

tighter | increasing intermolecular forces

Question 95

In order for segmental mobility to occur, not only must we have enough energy for ______, we must also have enough energy to ______.

Answer 95

rotation within the polymer backbone | disrupt the secondary bonds

Question 96

In general, lower conformational flexibility, for instance, associated with side groups, would tend to ____.

Answer 96

increase Tm

Question 97

Increasing the spacing (in the crystal framework) acts to _______ the strength of secondary bonds in the cystallite, which acts to _____ Tm.

Answer 97

decrease | lower

Question 98

_______ is a measure of the strength of secondary forces.

Answer 98

cohesive energy density

Question 99

Polymers which have intermolecular hydrogen bonds are often ________ by the presence of water.

Answer 99

strongly affected | example: PVOH, which interacts so strongly that it is soluble in water

Question 100

Polymers with significant hydrogen bonding are usually ________ when dry than in high moisture conditions.

Answer 100

better barriers | ex: nylon and ethylene vinyl alcohol

Question 101

Primary bonds are inportant in determining properties such as ___________ and _________.

Answer 101

thermal stability | chemical reactivity

Question 102

Most of the performance properties that we care about are determined predominantly or exclusively by the ______.

Answer 102

secondary bonds | primary bonds can have an important indirect effect

Question 103

The more polar groups we have (or the more polar the groups are), the _________ the resulting intermolecular forces.

Answer 103

stronger