Light-Induced In Situ Chain Extension and Critical Gelation of Benzophenone End-Functionalized Telechelic Associative Polymers in Aqueous Solution

Telechelic associative polymers (TAPs) can form a dynamic physical network in water and exhibit interesting solution viscoelastic behavior. In this work, we designed and prepared two benzophenone (BP) end-functionalized poly(ethylene glycol) TAPs (BPC(n)TAPs, n = 6, 10) by the efficient CuAAC click reaction of alkyne-modified BP and azide end-capped poly(ethylene glycol). BP moieties in the two TAPs can perform typical hydrogen abstraction reactions and consequent radical recombination under UV light irradiation in the core of micelles. Such a light-induced BP radical recombination has significant influence on the structure and solution dynamics of TAPs. When the polymer concentration exceeds the percolation concentration, only BPC(10)TAP can undergo in situ chain extension and even crosslinking reactions in the core of micelles under light irradiation by the self-assembly-assisted recombination strategy due to the slower escaping rate of stickers from micelles. Meanwhile, the association of extended chains (high-frequency plateau) coupling with the critical gelation behavior (low-frequency plateau) and a sol-gel transition were observed in the BPC(10)TAP solution also. The chain extension and consequent gelation behavior in bulk are usually based on the different reactivities of functional groups, whereas the present case is based on the topology of the dynamic network in consideration of only end-capped BP groups in the chain. This is the first report about such a chain extension and subsequent vulcanization-like critical gelation behavior of TAPs in aqueous solution. The work not only provides a new approach to understand the influence of chain topology on rheological behavior of TAP aqueous solution but also brings new insights into the sol-gel transition of TAPs.

Automated summary

Telechelic associative polymers (TAPs) can form a dynamic physical network in water and exhibit interesting solution viscoelastic behavior. In this work, two benzophenone (BP) end-functionalized poly(ethylene glycol) TAPs (BPC(n)TAPs, n = 6, 10) were designed and prepared, with BP moieties performing typical hydrogen abstraction reactions and consequent radical recombination under UV light irradiation. Particularly, BPC(10)TAP shows in situ chain extension and even crosslinking reactions in the core of micelles under light irradiation, leading to critical gelation behavior and a sol-gel transition.