Well-defined gels prepared by radical addition-coupling polymerization

A novel radical addition-coupling polymerization method is applied to prepare gels with controlled chain structure and length between branch points. Structure of the chains was varied between rigid or flexible ones by synthesizing different tribromide and dibromide monomers and reacting them with 2-methyl-2-nitrosopropane (MNP) under catalysis of Cu/N,N,N ',N '',N ''-pentamethyldiethylene-triamine. The carbon radical generated by single electron transfer from the bromides can be efficiently captured by MNP, forming nitroxide radical. The in situ formed nitroxide radical immediately undergoes cross-coupling reaction with another carbon radical, generating gel bridged with alkoxyaime moiety via step-growth mechanism. The tribromide and dibromide monomers were synthesized from different saturated and unsaturated compounds, or by bulk atom transfer radical polymerization of styrene using small bromide as initiator. The rigid gel has better controlled chains between branch points than the flexible ones. Selective dissociation of the ester group in the backbone of chains has been realized, which reserved the weak of NO-C. Flory-Huggins interaction parameter chi of the gels with fixed length between branch points were measured, which solved the difficulty that chi of insoluble polymer cannot be determined by common methods used for soluble polymers.