Waterborne RAFT polymers

Abstract

A recently invented novel family of RAFT ( Reversible Addition- Fragmentation chain Transfer) agents having a common formula Z–C( S)–S–CR 2COOR 1 where Z = –SR, –NR 2, or –OR, and R 1 represents H or a variety of functional groups allows for tailoring their hydrophilicity–hydrophobicity balance. A limited hydrophilicity of the RAFT agents can be achieved which is sufficient for their diffusion through water, yet the agents are hydrophobic enough to phase-separate out of water. Thus, the limited hydrophilicity of otherwise hydrophobic agents allows them to be at the loci of polymerization making them suitable for the emulsion polymerization mechanism. With several RAFT agents, good control over molecular weight was demonstrated for a broad variety of ab initio acrylic emulsion polymers. For methyl methacrylate, a portion of RAFT did not engage, resulting in less than the theoretical number of polymer chains. It was found, however, that as little as ∼10 wt% of an acrylic monomer slowed down polymerization enough to engage all RAFT agent molecules and yield predicted molecular weights. A broad variety of colorless and odorless telechelic acrylic and methacrylic emulsion polymers were synthesized. Microemulsion and solution-dispersion techniques produced clean colloidally stable RAFT dispersions. These two techniques did not require RAFT agents with tailored hydrophilicity–hydrophobicity. The UV spectra and photooxidative stability of the RAFT polymers were studied. The RAFT fragment in polymers appeared to have no impact on their photooxidative stability.