Tae Lin Pak Choi - 3 Flashcards
X-linking
Difference between step and chaing growth
Step growth:
A-A + B-B → A-AB-BA-A
Chain growth:
A + A-A → AAAAAAAAA
Star polymers
Multi-arm polymers (more than three)
Graft-onto:
4 (polymer with terminal group) + SiCl4 → 4-arm star polymer + 4 Cl
* The branches are synthesized separately before being attached to the core.
* Due to steric hindrance, the density of polymer branches around the core can be limited
Graft from:
* The core is first functionalized with initiator groups capable of initiating polymerization.
* In Situ Polymerization: Monomers are added to the reactive core, and polymerization occurs directly from the attached initiators, allowing polymer chains to grow outward from the core.
Star polymers by ATRP
Arm first approach
Monomer Functionalization
- Start with a monomer that has a functional group (F), e.g., OH.
- The monomer is depicted as F—X.
Polymerization
- Polymerize the monomer to form linear polymer chains with the functional group F at one end.
- Result: F-polymer-X.
Linking phase
- Introduce a divinyl compound, which acts as a multifunctional linker (core).
- Structure: R=CH2—CH2=R.
Star polymer formation
- The functional group F on each polymer chain reacts with the vinyl groups on the divinyl compound.
- Result: Multiple F-polymer-X arms linked to the divinyl core.
Final structure
- The resulting molecule is a star-shaped polymer with a central core (divinyl compound) and several radiating polymer arms (F-polymer-X).
Application of star polymers
Molecular recognition:
* Encapsulation/Release of Dye
Microgel-core catalysis:
* Oxidation of sec-Alcohois
* Reduction of Ketones
* Radical Addition
Dendrimer size comparison
G3 → insulin
G5 → hemoglobin
G7 → histone
Divergent synthesis of dendrimers
defect and mechanism
The bigger the molecules, the less efficient is the coupling
Easy to create defects as the size increases
Initiation: Synthesis begins at what will become the core of the dendrimer. A multifunctional core molecule is used that can undergo multiple reactions.
Growth: Successive layers (generations) of branches are added outward from the core molecule. Each generation involves two steps:
- Activation: The end groups of the existing outermost layer are chemically activated to react with incoming monomers.
- Reaction: Monomer units that contain at least two reactive groups react with the activated ends, expanding the dendrimer’s structure outwardly.
Dendronized & graft polymer synthesis
Extended (via polymer grafting) ← Entangled → (via dendronization) Extended
Stretching of the chain thanks to the steric hindrance of the bulky side groups that have been attached to it.
Convergent Synthesis of Dendrimer
Typically obtain larger dendrimer
Initiation: Synthesis starts at what will be the outer surface of the dendrimer. The process builds the dendrimer’s branches first.
Growth: The branches, called dendrons, are synthesized separately. Each dendron typically grows by:
- Building the outermost segment first, then progressively adding segments towards what will be the core.
- After the dendrons reach the desired number of generations, they are then attached to a central core molecule.
Flexible chain - wormlike chain - molecular object transition
sizes of different Generations
G5 is both more linear than G1, but it is also bigger because you can see that it has more intensity in the AFM
How to detect branches in products of radical polymerization?
Using AFM
if in the crossection there is a constant height, we have branching. If there is a peak, we have entanglement
Cyclic polymers
GPC trace
Efficiency of Cyclization: high dilution techniques to promote cyclization reactions, minimizing intermolecular reactions that lead to linear or branched polymers and favoring the formation of cyclic structures.
Control Over Polymer Architecture: The synthesis approach using sec-BuLi and DDPE for initiating and then cyclizing polystyrene illustrates a method to control polymer topology, transforming linear polymers into cyclic polymers.
Application of Cyclic Polymers: Cyclic polymers, such as those synthesized here, typically exhibit different physical properties compared to their linear counterparts, such as lower viscosity and different thermal behavior.
Grafted cyclic polymers
Linear ABC triblock → (via catalys and high dilution) Macrocyclic polymer
Cyclic polymers by metathesis
“Endless” polymerization
No linear intermediates
MALDI-MS of Cyclic Poly-octenamer
Since it is cyclic, in the diagram you do not see end groups!
Size exclusion chromatography: elution volume of cyclic and linear polymers
A cyclic polymer is smaller than a linear analog of identical molecular weight
Elution Profiles:
The shift in the graph towards higher elution volumes for cyclic polymers as compared to linear ones suggests that cyclic polymers, being more compact, traverse fewer pores within the SEC matrix, thus moving slower through the column.
