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CHG 8187 Introduction to Polymer Reaction Engineering
Part 1: Basic Concepts

1

2

Outline
What is a polymer?
•Nomenclature

Polymer microstructure/properties
•Chemical composition/sequence distribution •Molecular weight and distribution •Polymer architecture •Chain configuration •Morphology •Mechanical properties •Rheological properties •Glass transition temperature •Polymer modification/processing/additives

3

Outline
Polymer classification
•Step vs. Chain Growth

Polymerization techniques
•Bulk •Solution •Suspension •Emulsion •Gas-phase •Slurry

Applications – Main commercial polymers
•Polyolefins •Styrenic polymers •PVC •Waterborne dispersed polymers •Polyesters and polyamides •Thermosets

Polymer history/timeline

CHG 8187 Introduction to Polymer Reaction Engineering
Part 1: Basic Concepts What is a polymer?
4

5

What is a polymer?
 Polymers

are large molecular chains made of many monomers.  Several structural units bound together by covalent bonds.

6

What is a polymer?

7

Nomenclature
1.

Conventional: prefix “poly” followed by monomer name (e.g., poly(styrene), poly(methyl methacrylate)); condensation polymers from two monomers use name of repeat unit (e.g., poly(ethylene terephthalate).

8

Nomenclature
2.

IUPAC* structure-based: similar to conventional but more powerful and general
 

see text by Odian note also rules for copolymers.

3.

Trade names (e.g., nylon, Kevlar, plexiglas, teflon, dacron, neoprene, Spandex), common names, abbreviations


See table next; note that some are not pure polymers but complex materials (e.g., HIPS, ABS).

*IUPAC: International Union of Pure and Applied Chemistry

9

Nomenclature
Abbrev. ABS EPDM Polymer Acrylonitrile-butadienestyrene terpolymer Ethylene-propylene-diene monomer rubber Abbrev. PLA PMMA Polymer Poly(lactic acid) Poly(methyl methacrylate)

HDPE
HIPS LDPE LLDPE

High density polyethylene
High impact polystyrene Low density polyethylene Linear low density polyethylene

PP
PTFE PU PVA

Polypropylene
Poly(tetrafluoroethylene) Polyurethane Poly(vinyl alcohol)

NBR
PAN PEO PET

Acrylonitrile-butadiene rubber
Polyacrylonitrile Poly(ethylene oxide) Poly(ethylene terephthalate)

PVC
PVDF SAN SBR

Poly(vinyl chloride)
Poly(vinylidene fluoride) Styrene acrylonitrile copolymer Styrene-butadiene rubber

10

Nomenclature
 Polymers
 

also sometimes defined by:

Response to heat: Thermoplastics vs. thermosets. Molecular structure: Linear vs. branched vs. network or gel.

CHG 8187 Introduction to Polymer Reaction Engineering
Part 1: Basic Concepts Polymer microstructure/properties
11

12

Polymer microstructure/properties
 Polymers

exhibit high strength, glass transition temperature, rubber elasticity, high viscosity as a melt and solution. Why?
   

High molecular weight Microstructure/architecture: branching, crosslinking, chain entanglement Summation of intermolecular forces Time scale of motion

13

Chemical composition and monomer sequence distribution




Properties of homopolymers largely determined by monomer. Copolymers allow for a broader range of achievable properties.




Blending to be discussed later – but note the differences.

Arrangement or sequence distribution of comonomers also affects properties.

©Dr. Marc A. Dubé, P.Eng., University of Ottawa

14

Name Copolymer Statistical copolymer Random copolymer Alternating copolymer Periodic copolymer Periodic terpolymer Block copolymer Segmented copolymer Gradient copolymer Graft copolymer …a/b…

Structure …aabaaaabbabbbabaaababbba… …aaabaabbabbbabaaababbaab… …ababababababababababababab … …abbabbabbabbabbabbabbabba bb… …abcabcabcabcabcabcabcabcabc … a……….ab………..b (a)n-(b)m-(a)p-(b)q-(a)r-(b)s-(a)t (a)nbaaaaabbaaabbaabbbba(b)m
…a-a-a………a-a-a…..aa | | bm bn

IUPAC designation poly(A-co-B) poly(A-stat-B) poly(A-ran-B) poly(A-alt-B) poly(A-per-B-per-B) poly(A-per-B-per-C) poly(A)-block-poly(B) poly(A)-graft-poly(B)

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Molecular weight and distribution
 An

important measure of commercial polymer product quality and strong influence on polymer properties.  MWD governed by polymerization mechanism, reactor design and operating conditions.  Chain length n represents the number of repeat units in a given polymer molecule.

16

Molecular weight and distribution
 For

high molecular weight polymers,

M

n

 nM

0

molecular weight of polymer molecule

molecular weight of single repeat unit

17

Molecular weight and distribution

18

Molecular weight and distribution
W t  T o ta l w e i g h t o f p o ly m e r




 n 1

Wn

*




M
w

Wn M Wt

*

n





n 1



 n 1

Wn M

n

19

Molecular weight and distribution
Wn  Wn


*

Wt


M
w

Wn M Wt

*

n





n 1



W n 1

n

M

n



w  M

w

M

0



 n 1

nWn

20

Molecular weight and distribution


N n  Wn
*

*

M

n

N

t



 n 1

N

* n



M

n



 n 1

MnN

* n

N

t

21

Molecular weight and distribution


N

n

 N

* n

N

t

 n 1


N

n

 1

M

n



 n 1

M

n

N

n



n  M

n

M

0



 n 1

nN

n

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Molecular weight and distribution (Rudin)


The two most commonly used molecular weight averages are the number- and weight-average molecular weights:
M
n



 

N xM N x x

M

w



 

N xM N xM

2 x

Wx 



N xM

x

x



 

Mx is the molecular weight of a molecule with degree of polymerization x (i.e. consisting of x monomer units of molecular weight M0, thus Mx=xMo). Nx is the total number of molecules of length x. Wx is the total weight of molecules of length x.

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Molecular weight and distribution




The number-average molecular weight is the total weight of all the polymer molecules in a sample, divided by the total number of polymer molecules in that sample. The weight-average molecular weight is based on the fact that a bigger molecule contains more of the total mass of the polymer sample than the smaller molecules do. It is thus, a weighted average.

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Molecular weight and distribution
A


strange, but informative example:
Suppose we have a 10,000 lb elephant with 4 birds each weighing 1 lb on its back. Calculate the molecular weight averages.
M
n



N M N x x

x



 4  1   1  1 0 , 0 0 0   4  1 x x

 2 , 0 0 0 lb s

M

w



 

N xM N xM

2 x



x

W M W x 

 4  1   1 0 , 0 0 0  1 0 , 0 0 0  1 0 , 0 0 4 
 1 0 , 0 0 0 lb s

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Molecular weight and distribution


A more realistic example: We have 10 chains of 100 molecular weight, 20 of 500 mol. wt., 40 of 1,000 mol. wt., and 5 of 10,000 mol. wt. Molecular weight averages = ?
M
n



N M N x x

x



 1 0  1 0 0    2 0  5 0 0    4 0  1, 0 0 0    5  1 0 , 0 0 0  1 0  2 0  4 0  5 

 1, 3 4 7

M

w



 

N xM N xM

2 x

x 2 2 2 2



 1 0  1 0 0    2 0  5 0 0    4 0  1, 0 0 0    5  1 0 , 0 0 0 
 1 0  1 0 0    2 0  5 0 0    4 0  1, 0 0 0    5  1 0 , 0 0 0 

 5, 3 9 0

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Molecular weight and distribution

27

Molecular weight and distribution

28

Molecular weight and distribution

29

Molecular weight and distribution - moments




Average molecular weights are arithmetic means of distributions of molecular weights. An alternative and more useful definition is in terms of moments of the distribution. Concept of moments was adopted in statistics from the science of mechanics:




First moment of a force or weight about an axis is the product of the F and the distance from the axis to the line of action of the force: torque. Second moment of the F about the same axis is the product of the F and the square of the distance between its line of action and the axis: inertia.

30

Molecular weight and distribution - moments
 Moments

in statistics:
N

k  E  X  
 The



k



 x i 1

i

 



k

f

 xi 

first moment about the mean is 0.  The second moment about the mean is the variance.  In polymerization, the moments are not relative to the mean but to the origin, 0. This simplifies the mathematics greatly.

31

Molecular weight and distribution - moments


k 

 n 1

n N

k

n

k  0 ,1 , 2 ,...

w 

2 1

PDI  Q 

w n



20 1
2



M M

w n

Polymer Architecture

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33

Polymer Architecture


Other variations on the same theme…  Comb  Star  Dendrimer and hyperbranched

34

Polymer architecture


Important related concepts:
   



Thermoplastics (linear or branched) vs. thermosets (cross-linked).


Crosslink density Swelling index Gel fraction, gelation point Interpenetrating polymer network (IPN)

 

Elastomers: loose networks. Thermoplastic elastomers: processable melt transformed to solid rubber-like object upon cooling.

Thermoplastic melts can lead to crystallinity.

35

Chain configuration vs. conformation


Configuration vs. conformation: some definitions to confuse us from the start!






If we could look at an isolated polymer chain, frozen in space, and specify the position of each of its atoms, then we would have a full description of what is called the conformation of the chain. Except that this is also called a configuration, which can be very confusing because this term is one we use to describe geometric and stereo-isomers. Moreover, local arrangements of groups around a bond are also called conformations, so we have the same word being used to describe a local arrangement as well as the entire shape of a chain.

36

Chain configuration


Configuration: Stereoisomerism






Isomers: molecules composed of identical numbers of corresponding atoms in different arrangements (thus, they may differ in certain properties) Constitutional isomerism: atoms of molecules with equal composition are connected to each other in different sequences Stereoisomers: molecules with the same sequence of atoms but different spatial arrangements. These can originate from two different sources:




Asymmetric carbons (tacticity) Double bonds (a.k.a. geometric isomerism; cis vs. trans, etc.)

37

Chain configuration

38

Chain configuration
 Tacticity:

When polymers have a regular arrangement of their atoms, like we see in isotactic and syndiotactic polystyrene, it is very easy for them to pack together into crystals and fibers. But if there is no order, as is the case with atactic polystyrene, packing can't occur.

Chain configuration

39

40

Chain configuration

41

Chain configuration
 Stereoregularity

or tacticity

42

Chain configuration

43

Chain configuration




Tacticity can be a big problem in some polymers. For example, using free-radical polymerization, one can normally only make atactic polystyrene: a hard plastic, and completely amorphous. However, using metallocene catalysts, syndiotactic polystyrene can be made. It is not only crystalline, but it doesn't melt until 270oC. Another example is polypropylene. At first, there was only atactic polypropylene: soft and sticky, not very strong, and not much good for anything. Then, using Ziegler-Natta polymerization, isotactic polypropylene was possible. This new polypropylene could crystallize, and could be used to make fibers, for things like indoor-outdoor carpeting.

44

Chain configuration
 Geometric

isomerism: Tacticity is also observed for polymers with geometric isomerism of the constitutional repeat units.


Examples: 1,4-poly(isoprene), 1,2poly(isoprene) and 3,4-poly(isoprene)

45

Polymer states
 

Polymers can be thought of as being in two physical states, solid or fluid. Matter, in general is described as a gas or:




 

Low molar mass materials exhibit either ideal elastic OR ideal viscous behaviour. Polymers usually exhibit both at the same time: viscoelastic behaviour. Whether elasticity or viscosity dominates depends on the type of polymer assembly, temperature and pressure.

a solid: small deformations are completely reversible. Behaves elastically, i.e., returns immediately and completely to the initial state if the load is removed. a fluid: deforms completely and irreversibly; exhibits a viscous behaviour.

46

Polymer states
 In
 

the solid state, two ideal types of assemblies are found:
Crystals: completely ordered. Amorphous: completely disordered.

 What


does order mean for polymers?



Recall the typical (relaxed) coil formation of polymers. Order means stretched out straight.

47

Polymer states

48

Polymer states

49

Polymer states

50

Polymer states

51

Polymer states
 Thus,

as shown in the previous pictures, polymers are usually mixtures of amorphous and crystalline material. The crystalline portion being in the lamellae and the amorphous portion outside of the lamellae.

52

Polymer states

53

States

54

Polymer states
 



Crystallinity makes a material strong but also brittle. A completely crystalline polymer would be too brittle to be used as plastic. The amorphous regions give a polymer toughness, that is, the ability to bend without breaking. Many polymers are a mix of amorphous and crystalline regions, but some are highly crystalline and some are highly amorphous:
 

Highly crystalline polymers: polypropylene, syndiotactic polystyrene, nylon, Kevlar and Nomex, polyketones Highly amorphous polymers: poly(methyl methacrylate), atactic polystyrene, polycarbonate, polyisoprene, polybutadiene

55

Polymer states


For making fibers, we like our polymers to be as crystalline as possible. This is because a fiber is really a long crystal.



Polymeric fiber: a polymer whose chains are stretched out straight (or close to straight) and lined up next to each other, all along the same axis.

56

Polymer states
 

Polymers arranged in fibers can be spun into threads and used as textiles. Examples of polymers which can be drawn into fibers:



   




Polyethylene Polypropylene Nylon Polyester Kevlar and Nomex Polyacrylonitrile Cellulose Polyurethanes

57

Polymer states

58

Polymer states
 What


influences the degree of crystallinity?
Polymer structure:
 Tacticity

(see previous polystyrene examples)  Degree of branching (e.g., polyethylene)


Intermolecular forces (see nylon-6,6) example)

59

Polymer states


What does crystallinity influence?
   

Strength: Generally increases with degree of crystallinity Stiffness: Generally increases with degree of crystallinity Toughness: Generally decreases with degree of crystallinity Optical Clarity: Generally decreases with increasing degree of crystallinity. Semi-crystalline polymers usually appear opaque because of the difference in refractive index of the amorphous and crystalline domains, which leads to scattering. Will depend upon crystallite size.

60

Polymer states


What does crystallinity influence?




Barrier Properties: Small molecules usually cannot penetrate or diffuse through the crystalline domains, hence “barrier properties”, which make a polymer useful for things like food wrap, increase with degree of crystallinity Solubility: Similarly, solvent molecules cannot penetrate the crystalline domains, which must be melted before the polymer will dissolve. Solvent resistance increases with degree of crystallinity

61

Polymer states


Examples of crystallinity values:
       

polyethylene, high density (HDPE) 50- 90% teflon 95% poly(vinyl chloride) (PVC) 5% trans-poly(1,4-butadiene) 80% cis-poly(1,4-butadiene) 0% Linear polyethylene can be as high as 90% crystalline Isotactic polypropylene can be as high as 90% crystalline Linear random poly(ethylene-co-propylene) has 0% relative crystallinity. Thus, the random copolymerization of two monomers which produce highly crystalline homopolymers produces an amorphous copolymer.

62

Liquid crystals
 Liquid
  

crystal materials generally have several common characteristics: rod-like molecular structure, rigidness of the long axis, strong dipoles and/or easily polarizable substituents.

63

Liquid crystals
 Two


types of liquid crystals:



Thermotropic: liquid-crystalline in the temperature range between a melt and solid. Lyotropic: form liquid crystals in concentrated solutions

64

Liquid crystals
 Mesogens


form three classes of mesophases:
Nematic

65

Liquid crystals
 Mesogens


form three classes of mesophases:
Smectic

66

Liquid crystals
 Mesogens


form three classes of mesophases:
Cholesteric

67

Polymer liquid crystals


Polymer liquid crystals (PLCs) are a class of materials that combine the properties of polymers with those of liquid crystals. These "hybrids" show the same mesophases characteristic of ordinary liquid crystals, yet retain many of the useful and versatile properties of polymers.

68

Polymer liquid crystals
 Main

chain liquid crystal polymers (MCLCP)

69

Polymer liquid crystals
 MCLCPs

often cannot show mesogenic behavior over a wide temperature range  Side chain liquid crystal polymers (SCLCPs), however, are able to expand this scale because these structures can be varied in a number of ways.

70

Polymer liquid crystals
 Side

chain liquid crystal polymers

71

Polymer liquid crystal applications


High-strength fibres: Kevlar (e.g., in helmets and bulletproof vests) is just one example of the use of PLCs in applications calling for strong, light weight materials. Ordinary polymers have never been able to demonstrate the stiffness necessary to compete against traditional materials like steel. It has been observed that polymers with long straight chains are significantly stronger than their tangled counterparts. Main chain liquid crystal polymers are well-suited to ordering processes. For example, the polymer can be oriented in the desired liquid crystal phase and then quenched to create a highly ordered, strong solid. As these technologies continue to develop, an increasing variety of new materials with strong and lightweight properties will become available.

72

Polymer liquid crystal applications


Optical Applications: The use of polymer liquid crystals in the display industry is an exciting area of research. At this time, PLC's demonstrate relatively slow "response times" to electric fields. That is, when a field is applied, the molecules take a long time to align along it. This is not a good property for use in displays where the screen must be able to change rapidly from one view to another. Researchers are working to overcome this problem because the manipulation of polymers is often much easier than traditional liquid crystals.

73

Morphology - polymer blends
 Polymer


blends: physical mixture of two or more polymers using extruders (usually). compatibility issues: introduce functional groups such as carboxylic or sulfonate groups

74

Morphology – polymer blends
 Most

polymers are immiscible with each other and phase separate.

75

Mechanical properties
 Polymers


exhibit different mechanical behaviour:
Rigid (teflon, polystyrene blocks, polyurethane chair) Plastic (polyethylene bags, cellophane wrap) Elastomeric (rubber bands) Non-Newtonian (liquid crystals, paints) Combinations of the above







76

Mechanical properties
 Polymer


mechanical behaviour is predetermined by:
Chemical structure (composition, configuration, conformation, MW & MWD…) Physical state (crystalline, amorphous, liquid crystals…) Testing conditions (technique, load and its rate, temperature, frequency…)




77

Rheological properties
 Response

of polymer solids to deformation (e.g., rubber elasticity)  Rheology of polymeric liquids, polymer melts  Viscoelastic behaviour

78

Viscoelastic effects ?

79

Glass transition temperature
  

Unique to polymers Below Tg, polymer is hard and brittle (like glass), whereas above Tg, polymer is soft and flexible (rubbery state). The glass transition is not the same thing as melting. Melting is a transition which occurs in crystalline polymers. Melting happens when the polymer chains fall out of their crystal structures, and become a disordered liquid. The glass transition is a transition which happens to amorphous polymers. Recall, however, that even crystalline polymers will have an amorphous portion. This portion usually makes up 40-70% of the polymer sample. This is why the same sample of a polymer can have both a glass transition temperature (for the amorphous portion) and a melting temperature (for the crystalline portion).

80

Glass transition temperature
 

Why does it happen? The snake analogy. Polymers: at warm temperatures, the polymer chains can move around easily. So, when you take a piece of the polymer and bend it, the molecules, being in motion already, have no trouble moving into new positions to relieve the stress you have placed on them. But if you try to bend a sample of a polymer below its Tg, the polymer chains won't be able to move into new positions to relieve the stress which you have placed on them. So, one of two things will happen. Either (A) the chains are strong enough to resist the force you apply, and the sample won't bend; or (B) the force you apply will be too much for the motionless polymer chains to resist, and being unable to move around to relieve the stress, the polymer sample will break or shatter in your hands.

81

Glass transition temperature
 What
 

affects Tg? Four categories of motion: translational motion of entire molecule; long cooperative wriggling of 40 to 50 C-C bonds of the molecule, permitting flexing and uncoiling; short cooperative motion of 5 to 6 C-C bonds of the molecule; vibration of carbon atoms in the molecule.

 

82

Glass transition temperature


What affects Tg? Chain flexibility:  -C-C- or -C-O- bonds are flexible;  presence of phenyl rings or double bonds has a stiffening effect;  flexibility is dependent on free space available for rotation (VF);  reduction in flexibility = reduction in VF = increase in Tg.

83

Glass transition temperature
 What

affects Tg? Plasticizer

84

Glass transition temperature
 What


affects Tg?

Pendant groups

85

Glass transition temperature
 What


affects Tg?

Pendant groups

86

Glass transition temperature
 What


affects Tg?



Interaction between polymers: secondary bonding between molecules due to dipole forces, induction forces, and/or hydrogen bonds which increases Tg. Molecular weight of polymers:

Tg  Tg 



K M n 87

Glass transition temperature
 What


affects Tg?

Copolymers:

1 Tg



w1 Tg 1



1  w 
1

Tg 2

88

Glass transition temperature


Glass transition vs. melting temperature


It's tempting to think of the glass transition as a kind of melting of the polymer. But this is an inaccurate way of looking at things. There are a lot of important differences between the glass transition and melting. First of all, melting is something that happens to a crystalline polymer, while the glass transition happens only to polymers in the amorphous state. A given polymer will often have both amorphous and crystalline domains within it, so the same sample can often show a melting point and a Tg. But the chains that melt are not the chains that undergo the glass transition.

89

Glass transition temperature
 Amorphous

polymers

90

Glass transition temperature
 Crystalline

polymers

91

Glass transition temperature


Glass transition vs. melting temperature




There is another big difference between melting and the glass transition. When you heat a crystalline polymer at a constant rate, the temperature will increase at a constant rate. The amount of heat required to raise the temperature of one gram of the polymer one degree Celsius is called the heat capacity. The temperature will continue to increase until the polymer reaches its melting point. When this happens, the temperature will hold steady for awhile, even though you're adding heat to the polymer. It will hold steady until the polymer has completely melted. Then the temperature of the polymer will begin to increase once again. The temperature rising stops because melting requires energy. All the energy you add to a crystalline polymer at its melting point goes into melting, and none of it goes into raising the temperature. This heat is called the latent heat of melting.

92

Glass transition temperature


Glass transition vs. melting temperature




Once the polymer has melted, the temperature begins to rise again, but now it rises at a slower rate. The molten polymer has a higher heat capacity than the solid crystalline polymer, so it can absorb more heat with a smaller increase in temperature. But when you heat an amorphous polymer to its Tg, something different happens. First you heat it, and the temperature goes up. It goes up at a rate determined by the polymer's heat capacity, just like before. Only when we reach the Tg, the temperature doesn't stop rising. There is no latent heat of glass transition. But the temperature doesn't go up at the same rate above the Tg as below it. The polymer does undergo an increase in its heat capacity when it undergoes the glass transition.

93

Glass transition temperature
 Glass

transition vs. melting temperature

94

Polymer modification
 Processing
 Functionalization  Grafting

 Blending/compounding
 

Composite materials Nanocomposites

 Additives

©Dr. Marc A. Dubé, P.Eng., FCIC, FEIC

95

Polymer modification – polymer processing
 Polymer

processing: conversion of polymer (& additives!) to final product.  Methods: extrusion, injection molding, blow molding, thermoforming, reacting techniques (e.g., RIM).  Processing  orientation of macromolecules, accompanied by modification of properties with additives.

96

Polymer modification – additives
 Polymer
    

property retention:

Antioxidants Processing stabilizers Heat stabilizers Lubricants Acid scavengers

97

Polymer modification – additives


Polymer property extension:

   

Service life/extended applications
UV/light stabilizers Antioxidants Flame retardants Pigments Optical brighteners Biocides/antimicrobials Scavengers (Anti)odorants Conductive additives Repellants Markers Foaming agents


   


 

98

Polymer modification – additives
 Polymer


property extension:

Modifying bulk/surface properties
 Antistatic

agents  Nucleating agents  Clarifiers  Plasticizers  Surface modifiers  Slip/antiblocking  Antifogging

99

Polymer modification – additives
 Polymer


property extension:

Modifying polymer structure
 Chain

extenders  Crosslinking/coupling agents  Chain transfer agents  Compatibilizers  Prodegradants

100

Polymer modification – additives
 Plasticizers:

high-boiling liquids (and solids) mixed with polymer to give softer more flexible material; e.g., dioctyl phthalate (with PVC).  Fillers: solid additives to modify physical (usually mechanical) properties; e.g., calcium carbonate, titanium dioxide, carbon black.

101

Polymer modification – additives
 Coupling

agents: chemicals used to treat the surface of fillers. Usually in two parts: one compatible with polymer and the other with the filler; e.g., stearic acid, silanes.  Antioxidants and stabilizers: protection against light, heat and oxygen in the air.

102

Polymer modification – additives

103

Polymer modification – additives
 Antioxidants


and stabilizers:

 

peroxide decomposers: mercaptans, sulfonic acids, zinc alkyl thiophosphate, et al.; chelating agents: N-tetrasalicylidene tetra (aminomethyl) methane, EDTA; UV light absorbers: phenyl salicylate, resorcinol monobenzoate, 2-hydroxyl-4methoxybenzophenone.

104

Polymer modification – additives


Fire retardants may:
   



chemically interfere with the propagation of flame; produce large volumes of inert gases that dilute the air supply; decompose or react endothermally; form an impervious fire-resistant coating to prevent contact of oxygen with the polymer. examples: ammonium polyphosphate, chlorinated n-alkanes, tritolyl phosphate.

CHG 8187 Introduction to Polymer Reaction Engineering
Part 1: Basic Concepts Polymer classification
105

106

Classification of polymers
 Modern

polymer classification is based on the polymerization mechanism: chain growth vs. step growth polymerization.  Here we discuss the differences in the two mechanism “classes”.

107

Classification of polymers
 Chain

growth polymerization

Pn  M  Pn 1

(formerly known as addition polymerization)

Classification of polymers
 Chain

growth polymerization

108

109

Chain-growth polymerization


Coordination polymerization:






Carried out on a catalyst by an insertion mechanism. Insertion controlled by catalyst and results in highly stereoregular polymers. Catalysts: ZieglerNatta, transition metal, metallocenes.

110

Chain-growth polymerization


Free-radical polymerization:
 


 



Active centre is a free-radical (highly reactive, unpaired electron) from an initiator. Polymerization via addition of monomer to active chain ends. Bimolecular termination between two radicals vs. transfer reactions. Huge number of monomers available, robust to impurities. Results in mostly amorphous polymer. Highly exothermic: reactor temperature control is important

111

Chain-growth polymerization
 Free-radical

polymerization:

112

Chain-growth polymerization
 Controlled
  

radical polymerization (CRP):



Bimolecular termination is minimized. Uses free-radical mechanism to prepare almost any kind of architecture. Establish rapid equilibrium between tiny concentration of growing free-radicals and large majority of dormant polymer chains. NMP, ATRP, RAFT

113

Chain-growth polymerization


Controlled radical polymerization (e.g., ATRP)

114

Chain-growth polymerization
 Anionic


polymerization




Initiators with anions, thus requires monomers whose electrons can be moved such that a monomer anion results. Limited monomers. No termination – referred to as “living polymerization” – very narrow MWD.

115

Chain-growth polymerization
 Anionic

polymerization

116

Chain-growth polymerization
 Cationic
  

polymerization

Cationic initiators from carbenium salts, Bronsted acids or Lewis acids. Monomers require electron donating groups. More cationically polymerizable monomers vs. anionic but few industrial systems (e.g., butyl rubber) because macrocations are highly reactive and prone to termination and chain transfer.

Classification of polymers
 Step

growth polymerization

Pm  Pn

Pm  n  W

(formerly known as condensation polymerization)
117

118

Step Growth Polymerization

119

Chain vs. Step Growth Polymerization
 Monomers:
 

Chain Growth: Should contain at least a double bond Step Growth: Should contain at least two functional groups

120

Chain vs. Step Growth Polymerization
 Growing


principle:



Chain Growth: Reaction of monomer with active centre. Chain activity initiated by a catalyst or an initiator. Step Growth: Reactions of functional groups of either monomers or growing chains. No initiator required. Catalyst used to accelerate reactions.

121

Chain vs. Step Growth Polymerization


Reacting species:
 

Chain Growth: Growing chain + mononer. Step Growth: Two different functional groups. Any two molecules (polymeric or monomers) in the reaction mass may react. Chain Growth (only for coordination & free radical): Small (10-8 – 10-7 mol/L). Step Growth: All the macromolecules in the reaction mixture.



Number of growing chains:
 

122

Chain vs. Step Growth Polymerization


Growing chain life time:
 

Chain Growth (exception – living systems): Very short (0.5 – 10 s). Step Growth: Chains grow during the whole process. Chain Growth: Steadily throughout the reaction. Monomer present up to high conversions. Step Growth: Faster than in chain-growth. Monomer disappears early in the reaction.



Monomer consumption:
 

123

Chain vs. Step Growth Polymerization
 Termination:




Chain Growth (living systems do not include termination): Chain-termination event involved. Step Growth: No termination involved. Chains remain active.

 Side


reactions:



Chain Growth: not usually a major issue. Step Growth: Critical for achieving high molecular weights.

124

Chain vs. Step Growth Polymerization


Molecular weight:




Chain Growth: Very high from the beginning of the polymerization. No big changes during the polymerization. Exception: ionic and controlled FRP: molecular weight continuously increases during the process but starts relatively small. Step Growth: Smaller than in chain-growth. Continuous increase during the process. Commercial chain lengths are only attained at very high monomer conversions (99%+).

125

Chain vs. Step Growth Polymerization
 Thermodynamics:
 

Chain Growth: Exothermic – mostly irreversible. Step Growth: Exothermic – reversible (polycondensation). Equilibrium constant decreases with temperature.

126

Chain vs. Step Growth Polymerization
 Stoichiometry:
 

Chain Growth: N/A. Step Growth: Critical for achieving high molecular weight (in AA + BB reactions).

 Viscosity
 

of reaction media (bulk):

Chain Growth: Severe increase because of high molecular weights. Step Growth: Moderate during most of the process because of the low molecular weights.

127

Chain vs. Step Growth Polymerization
 Temperature
 

control (bulk):

Chain Growth: Challenging due to large heat of reaction and high viscosity. Step Growth: Easier than for chain-growth because viscosity only increases significantly during last stages of process when only a limited amount of heat is generated.

CHG 8187 Introduction to Polymer Reaction Engineering
Part 1: Basic Concepts Polymerization techniques
128

129

Key steps in polymer production
Process variables

Processing compounding
Molecular and morphological characteristics of the polymer

Reactor

Polymeric material microstructure

End-use properties

Formulation • • • • • • Chemical composition Monomer sequence distribution Molecular weight distribution Polymer architecture (branching, grafting, crosslinking, gel) Chain configuration (tacticity) Morphology

130

Polymerization techniques
 Bulk,

solution, gas-phase, slurry, suspension, emulsion  Impact on kinetics, mixing, heat transfer, and ultimately microstructural and enduse properties

131

Polymerization techniques
 Bulk
   

polymerization:

Components: monomers and initiator Typically homogeneous (polymer soluble in monomer) Main advantage: very pure polymer, high production rate Disadvantage: removal of heat is difficult due to high viscosity (worse for free radical than step-growth)

132

Polymerization techniques
 Solution
 

polymerization:



Components: monomers, initiator and solution Main advantage: lower viscosity and higher heat removal rate, reflux cooling is very effective Disadvantage: toxicity of solvents, solvent recovery

133

Polymerization techniques
 Suspension
   

polymerization:

Monomer droplets containing initiator are suspended in water. Droplets act as small, individual bulk polymerization reactors. Main advantage: good heat transfer Disadvantage: use of suspending agent

134

Polymerization techniques
 Emulsion
  

polymerization:

Fine dispersion of polymer particles (usually in water) = latex Components: monomer, emulsifiers, water and water-soluble initiator Very good heat transfer.

135

Polymerization techniques
 Gas-phase


polymerization:

A process primarily for ethylene using a heterogeneous coordination catalyst.

 Slurry


polymerization:

Often used in manufacture of polyolefins such as HDPE and PP.

CHG 8187 Introduction to Polymer Reaction Engineering
Part 1: Basic Concepts Polymer applications
136

137

Main commercial polymers
 Polyolefins
 Styrenic

polymers  Poly(vinyl chloride)  Waterborne dispersed polymers  Polyesters and polyamides  Thermosets

138

Main commercial polymers


Polyolefins
  

½ of world production of synthetic polymers Polypropylene: fibres, films, automotive parts, appliances, rigid packaging, etc. Polyethylene:


HDPE – linear, no branches (crystallizable)  LLDPE – linear, short branches  LDPE – branched polymer  LLDPE, LDPE: film applications, wire/film insulation  HDPE: blow-molded containers for liquids, films, pipes, extruded and injection molded items.

139

Main commercial polymers
 Styrenic
   

polymers

PS, HIPS, expandable PS, SAN, ABS Expandable PS: packaging, insulation, floatation SAN: heat and chemical resistance due to AN; used in ABS… ABS: electrical and electronic equipment, house and office appliances, automotive

140

Main commercial polymers
 Poly(vinyl
 

chloride)



Produced by suspension polymerization PVC is heavily compounded with heat stabilizers, lubricants, processing aids, plasticizers, impact modifiers and fillers due to its inherent instability Extensive use in construction, domestic goods, packaging and clothing

141

Main commercial polymers
 Waterborne
   

dispersed polymers

Synthetic polymer dispersions and rubber Produced by emulsion polymerization SBR, acrylic latexes, vinyl acetate… Paints and coatings, paper coating, adhesives, carpet backing.

142

Main commercial polymers


Polyesters and polyamides
 

  

Polyesters: PET, PBT PET: fibres, gastight bottles, highly stressed technical molded parts (e.g., gear teeth, bolts, screws, washers) PBT: automotive parts, domestic appliances Polyamides: Nylon 6 and nylon 6,6 Nylons resistant to oils and solvents: transportation, electrical and electronic applications, consumer products, appliances, power tools

143

Main commercial polymers
 Thermosets
  



Polyurethanes, phenol-formaldehyde resins, epoxy resins Densely crosslinked polymers that do not melt upon heating PUs: foams (rigid and elastic), moldings, films, hoses, etc. The rest used largely in coatings, adhesives

144

Main commercial polymers

145

Main commercial polymers

146

Main commercial polymers

147

Main commercial polymers

CHG 8187 Introduction to Polymer Reaction Engineering
Part 1: Basic Concepts A brief history of polymer production technology
148

149

Various historical perspectives
 Very

good virtual polymer museum with details on the inventors: http://www.plastiquarian.com/  Plastipedia with chronological details of inventions: http://www.bpf.co.uk/plastipedia/plastics _history/default.aspx  http://inventors.about.com/od/pstartinve ntions/a/plastics.htm

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