Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4....
Transcript of Macromolecular Chemistrywillson.cm.utexas.edu/Teaching/Chem367L392N/Files/Lecture... · 2015. 4....
Chemistry 367L/392N
Macromolecular ChemistryMacromolecular Chemistry
Lecture 14 Lecture 14
Michael Michael SzwarcSzwarc
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!
Chemistry 367L/392N
F
f
Chemistry 367L/392N
Poly(styrene-alt-maleic anhydride)
OOO
+δ
δ
OOO+
OOO
[ ]n
Charge transfer complex
δ+δ-δ+δ-
Chemistry 367L/392N
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
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
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.
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
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.
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
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
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 =
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
−+
+=
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
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
+=
Chemistry 367L/392N
This illustrates the high precision required to
achieve high molecular weights
!!!
DP
DP
r
rDP
−
+=
1
1
Chemistry 367L/392N
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”
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
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
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
Conjugated dienes
CH2
CHCH
2C
CH3
CH2
CH CH CH2
CH2
CH C CH2
CH3
styrene αααα-Me-styrene
butadiene isoprene
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
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
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
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
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
-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:
Living test
Szwarc’s Experiment