10.569 Synthesis of Polymers
Prof. Paula Hammond
Lecture 5: Interfacial Polymerizations, Application example: Polyamides
Biologically Relevant Polymer Presentation
Definitions of Biologically Relevant Polymers:
• Enzymatically degradable – Polymer degrades through enzymatic
breakdown in a biological (or ecological) environment (hydrolysis or oxidation
catalyzed by enzyme).
•
Hydrolytically degradable – Polymer undergoes hydrolytic degradation
without assistance from enzyme under biologic conditions – often accelerated
by pH or pH/temperature.
•
Bioresobable or absorbable or resorbable – Polymer breaks down into
remnants that are natural products readily absorbed into the body, resulting
in complete loss of original mass.
•
Biocompatible – Polymer (degradable or not) does not cause a negative
reaction or induce toxicity in the presence of or in contact with tissue, blood
or organs
Erdmann, L and K. E. Uhrich. “Synthesis and Degradation Characteristics of Salicylic
Acid-derived Poly(anhydride-esters).” Biomaterials 21, no. 19 (2000): 1941-1946.
Ikada, Y. and H. Tsuji. “Biodegradable Polyesters for Medical and Ecological
Applications.” Macromolecular Rapid Communications 21, no. 3 (2000): 117-132.
Poly α-hydroxyacids are hydrolytically degradable (PLLA, PDLA, PGA, PLGA)
Poly(hydroxyalkanoates), poly(alkylene dicarboxylates) are enzymatically degradable
Polycondensation of traditional monomer yields low molecular weight oligomer
Polycondensation of cyclic monomer yields high molecular weight material
Hydrophobic, hydrophilic nature determined by R groups
For example, -CH2- groups affect hydrophobicity and make the polymer more difficult
to degrade in water
Stereochemistry affects crystallinity.
Enzymatic breakdown dependent on ability of enzyme to adsorb to the PE
macromolecule at appropriate sites.
Aliphatic polyesters typically undergo enzymatic breakdown via esterases such as
lipase (used in body to break down triacylglycerols to fatty acid and glycerol)
Aromatic polyesters are too hydrophobic and too rigid to allow binding by enzyme.
Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 course materials, MIT OpenCourseWare
(http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, Date
Lipases often ineffective on PEs with optically active center (PHB, PLLA, etc.) – PHA
depolymerase effective in some cases, others require hydrolytic degradation or other
enzymes.
Factors in degradation rate: hydrophobicity, stereochemistry, bulkiness of side
groups, and crystallinity.
Manipulate with primary monomer structure, copolymerization.
PGA, PLLA, PDLLA, and PCL have moderate glass transition temperature.
Can create libraries of molecules:
Anderson, D. G., D. M. Lynn, and R. Langer. “Semi-Automated Synthesis and
Screening of a Large Library of Degradable Cationic Polymers for Gene Delivery.”
Angew. Chem. Int. Ed. 42 (2003): 3153-3158.
Polyamides (Nylons)
Coin phrase by Dupont
- Most common nylons:
Nylon 6,6:
O
H2
C
H
N
6
O
H2
C
H
N C
4
C
n
- aliphatic polyamides
⇒diamines + diacids
O
NH2
+
Keq ∼ 10 – 100 (high rate of rxn)
HOC
Commercial Syntheses
1)
O
O
n H2N
H2
C
6
NH3 +
pKa ∼ 9.0
basic
HOC
H2
C
pKa ∼ 5.0
acidic
OC
4
COH
conc'd
H2O
H3N
O
H2
C
4
CO
NH3
C
H2 6
“Nylon Salt”
Not nylon but precursor
10.569, Synthesis of Polymers, Fall 2006
Prof. Paula Hammond
Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 course materials, MIT OpenCourseWare
(http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, Date
Lecture 5
Page 2 of 4
proton exchange
salt
- 50% wt concentration in H2O
- Adjust pH of solution by titrating acid/base monomer
⇒ pH = 7.0 → stoichiometry r = 1.0
- If MW control desired, add monofunctional acid or amine
2) Salt solution concentration to a slurry
- a concentrated solution containing particles (concentrated suspension)
Raise T to ∼ 210oC, P = 250 psi (steam)
Rxn proceeds at moderate rates (water → steam → …)
3) As pn ↑, go to next stage:
T ↑ to 275oC (above Tm of Nylons)
P ↓ to 1 atm → reduces H2O
⇒ High MW with time/conversion
** One way to make a polyamide
Nylon6,6
- 50% crystallinity
- form flexible fibers: crystalline structures are strong
good H-bonding
- solvent resistance (Patagonia – clothing, carpets)
Differences in Reactivity
1.
O
HO
O
O
R
OH
diacids
R
O
O
acid anhydride
O
Cl
O
O
R
Cl
diacid chlorides
(very reactive)
Cl
Cl
phosgene
(extremely reactive
→ poisonous)
2. Also very reactive
10.569, Synthesis of Polymers, Fall 2006
Prof. Paula Hammond
Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 course materials, MIT OpenCourseWare
(http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, Date
Lecture 5
Page 3 of 4
O
N
C
O
urethane
R
ROH
N C O
isocyanate
group
O
RNH2
H
N
C
H
N
urethane
urea
3.
HO
R
OH
HO
OH
R'HN
R
NHR
H2N
R
NH2
R = alkyl
For highly reactive species:
Ex: diacid chloride + diamine
Keq = 105 ∼ 108
+ diol
can treat these as irreversible
→ different reaction profiles and times
-
Kinetics can become diffusion controlled (stirring becomes more important)
Highly exothermic (high ΔH)
Need to consider heat transfer
Short reaction times (relative to diol + diacid)
Most common:
O
C
O
Cl
+
H2N
CNH
O
C
+
HCl
+
HCl
O
Cl
+
OH
CO
O
N
C
OH +
OH
H
N
CO
no byproduct
10.569, Synthesis of Polymers, Fall 2006
Prof. Paula Hammond
Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 course materials, MIT OpenCourseWare
(http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, Date
Lecture 5
Page 4 of 4