Thermal crosslinking of hydrophilic polymers using polyperoxidesPart of:
Tissue engineering and regenerative medicine have attracted significant scientific interest  in recent years and material development in this area remains an important aspect. We require suitable materials and techniques which can help to create materials that can mimic mechanical properties and functions of the biological tissue. Hydrogels appear particularly suited as promising material class to deal with this difficult task [1-3]. New approaches to obtain hydrogels from new, simple and readily available building blocks are interesting to increase the molecular toolkit available to the materials engineer.
Here, we propose the possibility to crosslink functionalized as well as unfunctionalized hydrophilic polymers using polyperoxide copolymers . This process is solvent free, can be carried out over a large range of temperatures, and allows to crosslink a large variety of different polymers.
To this end, novel copolymers, that contain peroxide groups in their side chains were synthesized and utilized to crosslink hydrophilic polymers with different molecular weight via recombination reaction of thermally activated free radicals of peroxide groups (Fig.1).
Figure 1. Simplified schematic illustration of peroxide containing copolymer induced cross-linking: (a) thermal decomposition of peroxide copolymer into two radicals when exposed to heat and then hydrogen abstraction from polymer chain by primary radical (b) and recombination reaction of polymer radicals (c).
We investigated the influence of crosslinker concentration, temperature as well as crosslinking time on swelling degree (SD) of the resulting hydrogels. The resulting SD is markedly depended mostly on polyperoxide concentration and temperature, while the curing time has only a minor effect on crosslinking process (Fig.2).
Figure 2. Influence of the peroxide containing copolymer concentration (10 - 20 wt.%), temperature (120-200 °C) and crosslinking time 10 – 40 min, on the swelling degree (SD) of PEtOx hydrogels. (A) - P[PM-co-MA] and (B) - P[PM-co-BA-co-MA].
In summary, we successfully crosslinked non-functionalized hydrophilic polymers and investigated the influence of crosslinking concentration, temperature and time on SD of resulting hydrogels. Variation parameters of the process can allow us to control the mechanical properties of an obtained materials.