![Page 1: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/1.jpg)
Chemistry 367L/392N
Macromolecular ChemistryMacromolecular Chemistry
Lecture 14 Lecture 14
Michael Michael SzwarcSzwarc
![Page 2: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/2.jpg)
Chemistry 367L/392N
Midterm ExamMidterm Exam IIII�� Where:Where: Right here….in the lecture room WEL 3.502
�� When:When: Tuesday 3/24/09 at 3:30 – 5PM
�� What:What: Covers lectures through today
�� Bring:Bring: Pencil, eraser, Calculator only…closed book!
�� Do:Do: Study lecture notes, homework, reading assignments, graduate presentations and test I
�� Do not: Do not: Memorize derivations…but do know the principles! Go over homework problems.
�� Please: Please: Do a good job!
![Page 3: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/3.jpg)
Chemistry 367L/392N
F
f
![Page 4: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/4.jpg)
Chemistry 367L/392N
Poly(styrene-alt-maleic anhydride)
OOO
+δ
δ
OOO+
OOO
[ ]n
Charge transfer complex
δ+δ-δ+δ-
![Page 5: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/5.jpg)
Chemistry 367L/392N
![Page 6: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/6.jpg)
Chemistry 367L/392N
I+IV or II+III →
alternating
I+III, II+IV and same →Statistical Copolymers
Χ
Χ I+II or III+IV → Poor Copolymerization
![Page 7: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/7.jpg)
Chemistry 367L/392N
Q and eQ and e
� Generalizations:– This is a purely empirical relationship
– Q and e come from measurements of r1 and r2
– Ideal condition is same Q and e values
– Proceeds poorly if Q1 and Q2 are very different– Tends toward alternating if Q’s are the same and e’s are
large but of opposite sign.
– This assumes that Q and e are not dependent on solvent, temp, etc…..but we know that r1 and r2 are….
– Weak linkage to “linear free energy” relationships…and the Hammet ρ σ
![Page 8: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/8.jpg)
Hammett Equation
� Hammett observed a linear free energy
relationship between the log of the relative rate constants for ester hydrolysis and the log of the relative acid ionization (equilibrium) constants for a series of substituted benzoic esters & acids.
log (kx/kH) = log (Kx/KH) = ρσρσρσρσ
� He arbitrarily assigned ρρρρ, the reaction constant, of the acid ionization of benzoic acid a value of 1.
![Page 9: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/9.jpg)
Definition of Hammett ρρρρ
C
O
OH
X
C
O
O
X
+ H
These σσσσp values are obtained from the best fit line having a slope = 1
Hammett Plot
y = 0.9992x - 4.5305
R2 = 0.9907
-5.3
-5.1
-4.9
-4.7
-4.5
-4.3
-4.1
-3.9
-3.7
-1 -0.5 0 0.5 1
sigma pL
og
K
substituent σσσσp Eq. constant log K
-NH2 -0.66 0.00000554 -5.25649
-OCH3 -0.27 0.000015 -4.82391
-CH3 -0.17 0.000023 -4.63827
-H 0.00 0.000034 -4.46852
-Cl 0.23 0.000055 -4.25964
-COCH3 0.5 0.000088 -4.05552
-CN 0.66 0.000128 -3.89279
-NO2 0.78 0.000166 -3.77989
![Page 10: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/10.jpg)
Hammett Plots
� Aryl substituent constants (σσσσ) were determined by measuring the effect of a substituent on a reaction rate (or Keq). These are listed in tables, and are constant in widely different reactions.
� Reaction constants (ρρρρ) for other reactions may also be determined by comparison of the relative rates (or Keq) of two differently substituted reactants, using the substituent constants described above.
� Some of these values (σσσσ and ρρρρ) are listed on the following slide.
![Page 11: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/11.jpg)
Hammett Rho & Sigma Values
Substituent (Sigma) Values σσσσ (the electronic effect of the substituent;
negative values are electron donating)
p-NH2 -0.66 p-Cl 0.23
p-OCH3 -0.27 p-COCH3 0.50
p-CH3 -0.17 p-CN 0.66
m-CH3 -0.07 p-NO2 0.78
Reaction (Rho) Values ρρρρ
CH2COCH3
O
CH2CO + CH3OH
OOH
ρρρρ = + 2.4
X X
CH3OHC Cl
H
X
φ
C OCH3 + HCl
H
φ
X ρρρρ = - 5.0
![Page 12: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/12.jpg)
Chemistry 367L/392N
Conclusions-radical copolymers
� Co-polymers are important
– Properties depend on composition
� In general, these materials are
heterogeneous
� Mayo equation allows calculation of composition knowing r1 and r2
� Finemann Ross approach allows determination of r1 and r2
� Alfrey – Price allows estimate of r1 and r2
![Page 13: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/13.jpg)
Chemistry 367L/392N
We discussed A B type step growth polymers -ABABABA-
If is the number of A molecules at the beginning of the
polymerization and is the number if B molecules,
We define r, the stoichiometric imbalance as
What about step growth copolymers??
0
AN0
BN
0
0
B
A
N
Nr =
![Page 14: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/14.jpg)
Chemistry 367L/392N
DP is the number of monomer units divided by number of chains
−+
+
==
pr
N
r
rN
N
NDP
A
A
r
21
12
1
20
0
Which luckily reduces to…rpr
rDP
21
1
−+
+=
![Page 15: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/15.jpg)
Chemistry 367L/392N
rpr
rDP
21
1
−+
+=
Note that if there is no stoichiometric imbalance, r =1 and we get…..
This is nice!!!
pDP
−=
1
1 The Carothers Equation!!
When A is totally consumed (p =1) then….
r
rDP
−
+=
1
1
![Page 16: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/16.jpg)
Chemistry 367L/392N
rpr
rDP
21
1
−+
+= “A” is A-□-A and and B is really B-□-B…..
B’-□A-□-B
B’-□Monofunctional
A-□-A + B-□-BEquimolar
B-□-BA-□-B
B-□-BA-□-A + B-□-B0
0
B
A
N
Nr =
0
0
B
A
N
Nr =
0
'
0
0
2 BA
A
NN
Nr
+=
0
'
0
0
2 BA
A
NN
Nr
+=
![Page 17: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/17.jpg)
Chemistry 367L/392N
This illustrates the high precision required to
achieve high molecular weights
!!!
DP
DP
r
rDP
−
+=
1
1
![Page 18: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/18.jpg)
Chemistry 367L/392N
![Page 19: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/19.jpg)
Chemistry 367L/392N
Capping TrickOften wise to use a capping agent than to
use excess of one monomer
CH2CH2OH + CH2CH2O C
O
CH2CH2O C
O
C
O
OH
CH2CH2O C
O
Ph
Ph
+~
~ ~ ~
~ ~
“molecular weight stabilization”
![Page 20: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/20.jpg)
Chemistry 367L/392N
Conclusions
� A tiny amount of monofunctional monomer has a big effect�You will see this in the homework
�We can now calculate the copolymer composition for both radical chain growth and step growth polymerizations.
�We need to know
� the Copolymer equations� Mayo Plot,
� Finemann Ross Plot
� Implications of r1 and r2
� Implications of Q and e
![Page 21: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/21.jpg)
Anionic polymerization
1914, Schlenk reacts Na with butadiene and styrene
1929, Ziegler proposes a mechanism
1952 Higginson, styrene, KNH2, kinetic study
1956 Szwarc, sodium naphthalene, Styrene,
living polymerization conception
60's, commercial products were available
90‘s, study on the living polymerization of polar
monomers
History
![Page 22: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/22.jpg)
Monomers
Alkenes with polar substituents
CH2
C H
C N
CH2
C H
NO O
CH2
C
C O
CH3
O CH3
Acrylonitrile Nitroethene Methyl methacrylate
For example
![Page 23: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/23.jpg)
Conjugated dienes
CH2
CHCH
2C
CH3
CH2
CH CH CH2
CH2
CH C CH2
CH3
styrene αααα-Me-styrene
butadiene isoprene
![Page 24: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/24.jpg)
Reactivity of monomers
Group A:
Group B:
Group C:
Group D:CH
2CH CH CH
2
CH2
C(CN)2 CH 2 C
CN
COOC 2H 5CH
2CH
NO 2
> >
CH 2 CHCN CH 2 C
CN
CH 3 CH 2 CH C
O
CH 3> >
CH 2 CH
CO OCH 3
CH 2 C CH 3
COO CH 3
>
CH2 CH CH2 C
CH3
![Page 25: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/25.jpg)
Group A
Group B and group C
Group D
R
R R ,
R R R+
, ,
>>
>>
Initiator should be
stronger
Stronger or
weaker
only
Reactivity Type of polymerization
![Page 26: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/26.jpg)
Initiator and initiation
(1) alkali metal Lithium (Li)
Sodium (Na)
Potassium (K)
-Na CH
2CH
electron
transferCHCH
2Na ++ .
e
-Na
-CH CH
2Na CHCH2
++dimerize
radical couple
Szwarc’s
favorite
![Page 27: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/27.jpg)
K: soluble in ethers
Li and Na dispersion:
insoluble in hydrocarbon
Solubility of alkali metals
homogeneous or heterogeneous
Organic reaction is on the surface
adsorbtion
reaction
desorption
![Page 28: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/28.jpg)
Alkali metal complex
-Na Na +
+ [ ]
complex (greenish blue color)e
.
preparation
initiator
a. Species
b. Initiation
c. Solubility
Aromatic radical-anions:
Sodium naphthalene
Lithium naphthalene
Alkali metal Aromatic compound
![Page 29: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/29.jpg)
-Na CH
2CH
+[ ].
+Initiation:
-electron
transferCHCH
2Na +. +
-Na
-CH CH
2Na CHCH
2++
dimerize
radical couple
soluble in polar solvents only
( such as: ether)
Solubility:
![Page 30: Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4. 2. · Hammett Equation Hammett observed a linear free energy relationship between](https://reader036.vdocuments.us/reader036/viewer/2022071411/6107d5675553ff1a2d0d2803/html5/thumbnails/30.jpg)
Living test
Szwarc’s Experiment