Radical polymerization is a method of choice for polymer synthesis. Easy to implement and compatible — Biochemistry Chemistry Question
Radical polymerization
Radical polymerization is a method of choice for polymer synthesis. Easy to implement and compatible with a wide range of functional monomers, this process can be carried out under various experimental conditions, including in the presence of water. Typically, radical polymerization is composed of three steps: (i) initiation, (ii) propagation, and (iii) termination.
Identify the initiator and the monomer used for styrene polymerization. [Reconstructed from solution]
Model Answer
The initiator is benzoyl peroxide. The monomer used is styrene.
The table below gives the evolution of A2 concentration over time at 82 °C in chlorobenzene. Determine graphically the value of t½ for the initiator A2 at 82 °C in chlorobenzene.
[VISUAL]
Model Answer
The half-life is the time required to consume 50% of the reactants (approximately 1.0 h).
Give the chemical structure of the alkoxyamine that will be written ALK1 and is used to obtain the polymer P2.
In the figure below, assign the state (P4 or P5) of the PHEA-b-P4VP block copolymer in aqueous solution according to the pH values.
[VISUAL]
Model Answer
State A (pH > 6, where poly(4-vinylpyridine) is insoluble, forming micelles with insoluble P4VP core and hydrophilic PHEA corona) corresponds to P5, and State B (pH < 6, where the block copolymer is soluble/dispersed) corresponds to P4.
Give the expected number of 1H NMR signals with their splitting pattern for the C(=O)OCH2CH2OH side chains of the copolymer P4 dissolved in deuterated tetrahydrofuran. In this solvent, the copolymer P4 is perfectly soluble. (Note: No coupling will be considered with the terminal OH group).
Model Answer
2 signals (triplet) for the two non-equivalent CH2 groups, 1 signal (singlet) for OH.
Assign on the following chromatogram obtained by Size Exclusion Chromatography (SEC, see question 12 in problem 14) which curve corresponds to a polystyrene sample prepared by conventional free radical polymerization (P6) and which one corresponds to polystyrene prepared by NMP (P7).
[VISUAL]
Model Answer
Curve C (broader peak) corresponds to P6 (prepared by conventional free radical polymerization, which has a broad molecular weight distribution), and Curve D (narrower peak) corresponds to P7 (prepared by NMP, which has a narrow molecular weight distribution due to controlled/living radical polymerization).