CH3A4, Polymer Chemistry20022003

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CH3A4, Polymer Chemistry 2002/2003

• www.warwick.ac.uk/polymers

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CH3A4, Polymer Chemistry 2002/2003

• Copolymers
• Ionic Polymerisation
• Statistical Copolymers

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CH3A4, Polymer Chemistry Dave Haddleton 2002/2003
Lecture 1 Introduction
Discussion of polymers in everyday use
structure/property correlation
Brief description of copolymers statistical,
block, graft copolymers
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Books Principles of
Polymerisation
G Odian Polymer Synthesis
P
Rempp and E W Merrill Polymers Chemistry
Physics of Modern Materials J M G Cowie
Polymer Chemistry An Introduction
G Challa Introduction to
Polymers R J Young and P A Lovell

• Mayo Equation

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Need to Know from Year 2

• Viscosity equations
• Mark-Houwink equation
• Scheme for Free radical Polymerisation

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• Plastics
• Paint
• Adhesives
• Fibres/Fabrics
• Tyres

• Mobile phones
• Shampoo
• Cosmetics
• Optics
• CD,s

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Copolymers

• Statistical
• Block
• Graft
• Alternating
• Terpolymers

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When the two monomers are arranged in an
alternating fashion, the polymer is called, of
course, an alternating copolymer
-A-B-A-B-A-B-A-B-A-B-
In a random copolymer, the two monomers
may follow in any order
-A-A-B-A-B-B-B-A-B-A-A-B-
In a block
copolymer, all of one type of monomer are
grouped together, and all of the other are
grouped together. A block copolymer can be
thought of as two homopolymers joined together
at the ends A-A-A-A-A-A-A-B-B-B-B-B-B-B-B-

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Lecture 2 Revision of polymers in
solution viscosity equations, Mark-Houwink
equations Polymers in the solid
state, Tg and Tm, physical meaning of Tg
Tg of copolymers, calculation of Tg
with respect to polymer composition
Revision of free radical homopolymerisation
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Polymers in Solution

• When we add a polymer to a solvent
• A) Polymer swells to a gel
• B) Dissolves to a viscous solution
• Usually into a random coil or sometimes more rod
  like

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Polymers in the solid state

• Crystalline
• Glassy
• Not all polymers can crystallise
• None are 100 crystalline
• (look at USM web page for movie)

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Copolymerisation

• If we have 50 mol MMA and 50 mol Styrene and
  leave the reaction to 50 conversion.
• What is the composition of the polymer?
• What is the composition of the monomer?
• What is the Tg of the polymer produced?

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Statistical Copolymerization

• RM1? M1 ? RM1M1?
• Rate k11RM1?M1
• RM1? M2 ? RM1M2?
• Rate k12RM1?M2
• RM2? M1 ? RM2M1?
• Rate k21RM2?M1
• RM2? M2 ? RM2M2?
• Rate k22RM2?M2

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The rate of monomer disappearance is given
by -dM1/dt k11M1M1
k21M2M1 -dM2/dt k12M1M2
k22M2M2 Steady state approximation k12M1
M2 k21M2M1 M1/ M2 k21M1
k12M2
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The relative rates of comonomer incorporation
then reads dM1/dM2 k11M1M1
k21M2M1 k12M1M2
k22M2M2 divide both by M2 and
rearrange dM1/dM2 M1 k11/ k12 M1
M2 M2 k22/ k21 M2 M1
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• Reactivity ratios
• r1 k11 k12
• r2 k22 k21

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Statistical Copolymerization

• r1 characterizes the reactivity of the 1 radical
  with respect to the two monomers 1 and 2
• If r1 gt 1 then homopolymerization growth is
  preferred
• If r1 0 then only reaction with 2 will occur

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Statistical Copolymerization

• Fa is the amount of monomer A in the POLYMER
• fa is the amount of monomer A in the monomer feed
• Fa Fb 1 fa fb 1

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Mole fraction of monomer A in feed fa
M1/M1 M2
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• Reactivity ratios
• r1 k11 k12
• r2 k22 k21

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Copolymer equation

• Incorporate reactivity ratios and use mole
  fractions
• F1 r1f12 f1f2
• r1f12 r2f22 2f1f2

Reactivity ratios are monomer pair dependant I.e.
they are always the same for each monomer pair
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Assumptions

• Long Chain assumption i.e. initiation and
  termination reactions can be ignored in the
  calculation of copolymer composition
• Equal reactivity i.e rate is independent of chain
  size
• Reactivity ratios are independent of dilution
• Reactivity ratios are independent of rate and
  conversion

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Assumptions continued

• Reactivity ratios are independent of inhibitors,
  retarder CTAs and solvents

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We now need to look at the effect of
the reactivity ratios on the copolymerisation proc
ess. We plot the composition of the polymer as a
function of the composition of the monomer feed.
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Ideal Copolymerization

• ra rb 1
• A and B exhibit the same relative reactivity
  towards B
• equation becomes
• Fa rafa
• rafa fb

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Ideal Copolymerization

• Plot is around the diagonal

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Alternating copolymer

• rb 0

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Ideal copolymer
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Alternating Copolymer
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Rich in one monomer
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Quite typical copolymerisation
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Determination of reactivity ratios

• Copolymerise at different monomer feed ratios
• Obtain Fa vs fa data (E.g. 0.2, 0.4, 0.6)
• Interpret data by a lineraization method
• Kelen-Tudos
• Fineman-Ross

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Linearization method

• Fineman Ross
• (see transparency)
• ra and rb not treated symmetrically
• Kelen-Tudos method probably most common

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Factors that affect copolymer reactivites

• Steric Factors
• Resonance stabilization of radical
• Polarity of the double bond

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Qe scheme

• Attempt to predict the reactivity of a monomer
  towards a radical
• Use resonance and polarization parameters
• Similar to Hammett plots
• Rather Qualitiative

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Penultimate effects
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Living/Ionic Polymerisation

• Anionic Polymerisation
• Cationic Polymerisation
• Ring Opening Polymerisation
• Living Radical Polymerisation
• Group transfer Polymerisation

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Living Polymerisation

• Method to prepare polymers with predetermined Mn
• DP Monomer/Initiator
• Narrow PDi (lt1.20)
• Controlled functionality
• Block copolymers by various strategies
• No termination
• No Chain Transfer

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Anionic Polymerisation

• More selective than radical polymerisation
• Need electron withdrawing group attached to vinyl
  group
• e.g. -CO2R, -CN, -Ph, -vinyl
• Invented in 1956 by Swarzc (Nobel Prize)
• Industrial use limited
• Blocks, stars, grafts
• Usually an organometallic initiator

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Anionic Polymerisation of Styrene
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Anionic Polymerisation of dienes
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Aggregation of Butyl Lithium
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Ion-Pair formation
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Solvents

• Aprotic to prevent transfer to solvent and
  termination
• Free of electrophilic impurities which will react
  with ionic sites
• Dissolve both monomer and polymer allowing
  heterogeneous polymerisation

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Solvents can vary in polarity

• e.g.
• alkanes
• cyclohexane
• benzene
• toluene
• thf, dimethoxyethane

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Additives can be used to increase polarity
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Anionic Polymerisation of Acrylics
E.g.
Initiation
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Anionic Polymerisation of MMA
Propagating end is an enol
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Problems with Propagation
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Calculate Mn for Psty with BuLi
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Calculate PDi
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Propagation

• Dependant on ion-pair
• Anion
• Cation (or Gegen-ion)
• Solvent polarity

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Effect of solvent polarity on stereochemistry
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Termination
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Termination with protic impurities
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Termination to functioanl polymers
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Block copolymers

• Sequential Monomer Addition
• Multi-functional Initiators

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Calculate Mn for Block Copolymer
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GTP

• Initiator

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Group Transfer Polymerisation

• Polar Solvent
• eg thf, glymes
• (Will not work in non polar solvents eg toluene,
  MWD is 2)
• Catalysts
• Nucleophiles
• eg F-, HF2-, AcO-, CN-
• Gegen-ions
• large eg Bu4N, Et4N

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Mechanism of GTP

• Associative
• Dissociative

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GTP Associative Mechanism
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GTP Irreversible Dissociative Mechanism
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Cationic Polymerisation

• Over 20 yrs old
• Industrial use in butyl rubber manafacture
• Copolymer of
• Active sites are carbenium or oxonium

Need electron donating groups to stabilise the
cation
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Cationic polymerisation

• Usually reactive enough to make polymers at very
  low temperatures
• However, inherently unstable, side reactions
• in particular ?-proton elimination from active end

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Monomers for Cationic Polymerisation
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Cationic polymerisation

• Usually no real molecular weight control
• Living cationic polymerisation would yield
  controlled polymer geometries not available from
  other methods.

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Cationic Initiation
Protonic acids with bulky anions e.g. H2SO4,
HClO4, FSO3H, etc, etc
Lewis Acids e.g SnCl4, AlCl3, BF3 when reacted
with a nucleophile
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Cationic Propagation
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Termination in Cationic Polymerisation
See http//www.psrc.usm.edu/macrog/index.htm
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Living cationic polymerisation

• 1980's Sawamoto and Higahimura theorised that if
  the charge on the cation could be decreased by a
  specific nucleophilic interaction it may be
  stabilised towards ?-proton elimination.
• 1984 1st example of living cationic polymerisation

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Living cationic polymerisation

• using HI/I2
• shortly afterwards HI/ZnX2 X I, Br, Cl
• Mn ? M/I
• Block copolymer by sequential addition
• Mn increases linearly with conversion

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Ring Opening Metathesis
Metathesis of alkenes
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Ring Opening Metathesis
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Ring Opening Metathesis
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Ring Opening MetathesisCatalysts

• Normally made in-situ
• WCl6/AlEt3
• MoCl5/AlEt3

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Ring Opening Metathesis
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Living ROMP
Good ROMP catalyst W or Mo Bulky ligands M-O and
MN ligands
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Living ROMP

• Metal needs to be in high oxidation state
• 4-coordinate alkylidene with bulky ligands
• this allows small substrates to attack
• change alkoxide to (CF3)2MeC.O increase turnover
  for pentene from 2 to 1000 turnovers per minute

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Commercial use of ROMP

• Poly(norbornene)
• MoO3/alumina
• production for 20 years
• PDCP
• Reaction injection moulding
• 2 reactant streams
• high density of crosslinks

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ROMP in water
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Overview of course

• Radical Copolymerization
• Living Polymerization
• Anionic Polymerization
• Cationic Polymerization
• ROMP

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Control of Polymer Structure

• Block copolymers
• Telechelic polymers
• Graft copolymers
• Star copolymers
• Narrow PDi polymers

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When the two monomers are arranged in an
alternating fashion, the polymer is called, of
course, an alternating copolymer
-A-B-A-B-A-B-A-B-A-B-
In a random copolymer, the two monomers
may follow in any order
-A-A-B-A-B-B-B-A-B-A-A-B-
In a block
copolymer, all of one type of monomer are
grouped together, and all of the other are
grouped together. A block copolymer can be
thought of as two homopolymers joined together
at the ends A-A-A-A-A-A-A-B-B-B-B-B-B-B-B-

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Equations

• Instantaneous copolymer equation
• Fa vs fa plots
• Mn in living polymerisation
• PDi in living polymerisation
• Mn for block copolymers
• Molecular weight equations
• Viscosity equations
• Tg for copolymers

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Copolymer equation

• Incorporate reactivity ratios and use mole
  fractions
• F1 r1f12 f1f2
• r1f12 r2f22 2f1f2

Reactivity ratios are monomer pair dependant I.e.
they are always the same for each monomer pair
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Characterisation methods

• GPC
• NMR
• FTIR
• DSC
• MALDI MS
• Gravimetry