Synthesis of Branched Polybutadienes by Anionic Polymerisation with a Divinyl Crosslinker

The facile synthesis of branched polymers in high yields without gelation is a current challenge in polymer chemistry. The ”Strathclyde route” by Sherrington et al. successfully used a divinyl crosslinker during free radical polymerisation in presence of a chain transfer agent and was the inspiration to use the same approach in anionic polymerisation. In this work soluble polybutadienes with a branched architecture were synthesised by anionic copolymerisation of butadiene with divinylbenzene. Potassium tert-butoxide served as an additive to alter the copolymerisation behaviour and to induce chain transfer to toluene in order to avoid gelation. The highest fraction of branched polymer was derived for a sample of a molecular weight of Mn = 23,000 gmol-1, a polydispersity of PDI = 8.5, an estimated content of linear (noncrosslinked) chains of less than 23 wt-% in a high yield of 92% with deliberate termination of the reaction after 20 min. The reaction was carried out as a one-pot batch reaction at 60 C with toluene as the solvent. Lower molecular weight branched polybutadienes (Mn 10,000 gmol-1) were derived with apparently more linear (non-crosslinked) chains in batch reactions. Lower molecular weight branched polybutadienes were also prepared in a controlled feed reactor. Analysis with triple detection (with refractive index, viscosity and light scattering detectors) size exclusion chromatography strongly indicated a branched structured of the samples prepared in presence of the crosslinker compared to a sample prepared in absence of the crosslinker. The vinyl content (1,2-enchainment of polybutadiene backbone) was up to 37% for the most promising reactions and was in good agreement with literature regarding polar additives (potassium tert-butoxide in this work).