RAFT Dispersion Polymerization of 2-Hydroxyethyl Methacrylate in Non-polar Media

Area of Science:

• Polymer Chemistry
• Materials Science
• Nanotechnology

Background:

• Reversible Addition-Fragmentation chain Transfer (RAFT) polymerization is a controlled radical polymerization technique.
• Polymerization-Induced Self-Assembly (PISA) enables the synthesis of well-defined nanostructures in situ.
• Synthesizing polar polymers in non-polar solvents via PISA presents unique challenges.

Purpose of the Study:

• To investigate the RAFT dispersion polymerization of 2-hydroxyethyl methacrylate (HEMA) in n-dodecane using a poly(lauryl methacrylate) (PLMA) precursor.
• To characterize the formation and stability of PLMA-PHEMA nanoparticles synthesized via PISA.
• To address challenges related to particle size distribution and colloidal stability in this specific PISA system.

Main Methods:

• RAFT dispersion polymerization at 90 °C in n-dodecane.
• Polymerization-induced self-assembly (PISA) to form spherical nanoparticles.
• Characterization using Gel Permeation Chromatography (GPC) with derivatization, Dynamic Light Scattering (DLS), Transmission Electron Microscopy (TEM), 1H Nuclear Magnetic Resonance (NMR) spectroscopy, and time-resolved Small-Angle X-ray Scattering (SAXS).

Main Results:

• Formation of spherical PLMA-PHEMA nanoparticles at 10-20% w/w solids via PISA.
• Transient formation of unstable aggregates at ~50% conversion, followed by immediate breakup into stable nanoparticles.
• Bimodal particle size distributions observed in one-shot batch protocols, attributed to a side reaction, which were mitigated by monomer-starved conditions or multi-batch addition.
• Optimized formulation produced monomodal nanoparticles with a PHEMA degree of polymerization up to 1000.

Conclusions:

• The PLMA-PHEMA PISA system in n-dodecane successfully produces well-defined nanoparticles.
• Strategies like monomer-starved conditions or multi-batch addition are crucial for achieving monomodal particle size distributions.
• This optimized PISA formulation allows for controlled synthesis of nanoparticles with high polymer content and tunable block lengths.