Polymerization-Induced Self-Assembly for the Synthesis of Polyisoprene-Polystyrene Block and Random Copolymers:...

Area of Science:

• Polymer Chemistry
• Materials Science

Background:

• Isoprene polymerization faces challenges like cross-linking and Diels-Alder reactions, limiting polymer molecular weight and conversion.
• Developing controlled polymerization techniques is crucial for synthesizing well-defined polymers.

Purpose of the Study:

• To synthesize polyisoprene (PI)-based block and random copolymers with polystyrene (PS) using RAFT and PISA.
• To optimize polymerization conditions to achieve high molecular weight and monomer conversion, overcoming existing limitations in isoprene polymerization.

Main Methods:

• Utilized reversible addition-fragmentation chain-transfer (RAFT) polymerization combined with polymerization-induced self-assembly (PISA).
• Employed a poly(methacrylic acid) (PMAA) macroRAFT agent synthesized in ethanol.
• Conducted polymerization in water-emulsion under optimized conditions.

Main Results:

• Achieved high molecular weight (target 50,000 g/mol) and high monomer conversion (≈80%) for PS-PI copolymers.
• ¹H NMR confirmed successful synthesis and high 1,4 microstructure content in PI.
• Differential scanning calorimetry showed distinct glass transitions for block copolymers and a single transition for random copolymers, indicating microphase separation in block copolymers.
• Dynamic light scattering and transmission electron microscopy revealed self-assembled emulsion nanoparticles with sizes ranging from 70 to 130 nm.

Conclusions:

• Optimized RAFT-PISA conditions successfully synthesized PS-PI block and random copolymers with high molecular weight and conversion.
• The method effectively addresses challenges associated with isoprene polymerization.
• Characterization confirmed polymer structure, self-assembly into nanoparticles, and distinct properties of block versus random copolymers.