Investigation on the homogeneity of PMMA gels synthesized via RAFT polymerization

- PMMA gels made by RAFT polymerization are compared with gels made by FRP.
- Cross-linking efficiency is lower for the RAFT gels.
- Cross-linking efficiency increases markedly with rising concentration for both types.
- Gels with similar modulus have similar homogeneity despite different preparation.

PMMA gels synthesized by RAFT polymerization and corresponding gels made by free radical polymerization (FRP) were characterized macroscopically by determining the shear moduli and the swelling ratios, and microscopically by dynamic light scattering (DLS) with particular emphasis on inhomogeneity. The gels were prepared in the solvent γ-butyrolactone at concentrations ranging from 13 to 20 wt% (15-22.5 vol%).The cross-linking efficiency attained in RAFT polymerizations was significantly smaller than that obtained in corresponding FRPs. This means that in RAFT polymerizations more cross-links were wasted in network imperfections. The static fraction of the total ensemble-averaged scattering intensity determined by DLS was used as a measure of inhomogeneity. This quantity decreased with rising amount of RAFT agent and when going from FRP to RAFT polymerization. However, since the effective network density decreased concurrently, the influence of the polymerization mechanism on homogeneity is just an apparent one. The RAFT gels are not more homogeneous than the FRP gels when the comparison is based on systems having the same effective network density. On the contrary, RAFT gels prepared with a high content of RAFT agent appear slightly less homogeneous than those made with a lower content of RAFT agent or via FRP, provided gels having identical moduli are compared.