Nanocomposites of Poly(n-butyl acrylate) with Cellulose Nanocrystals: Surface-Initiated RAFT Polymerization, Cross-Linking through Exchange of Hindered Amines, and Reprocessing Properties.

In this contribution, we report a new approach to achieve a fine dispersion of cellulose nanocrystals (CNCs) in poly(n-butyl acrylate) (PBA); i.e., the nanocomposites of PBA with CNCs were obtained. First, CNCs were surface-functionalized with trithiocarbonate groups, and then the modified CNCs were exploited to mediate the radical polymerization of n-butyl acrylate (BA). To endow the PBA-grafted CNCs with a post-cross-linking capability, an acrylate monomer bearing a single hindered urea bond [i.e., 2-((tert-butylmethylcarbamoyl)amino)ethyl acrylate (BMAE)] was synthesized and utilized as a comonomer. The P(BA-stat-BMAE)-grafted CNCs can be post-cross-linked with a hindered diamine [viz., 1,2-bis(tert-butyl) ethylenediamine] through the exchange of hindered amines. As a result of the exchange of hindered amines, the interchain HUBs were generated. It was found that the kinetics of the exchange reaction was quite contingent on the compositions of the P(BA-stat-BMAE)-grafted CNCs. Transmission electron microscopy showed that in the nanocomposites, CNCs were finely dispersed. By taking control of the compositions, the nanocomposites can be regulated, displaying variable thermomechanical properties. Most importantly, the nanocomposites displayed excellent reprocessing (or recycling) properties, which can be attributed to the dynamic exchange of the HUBs integrated with the networks. Benefiting from the cross-linking with HUBs, the nanocomposites displayed shape memory properties, featuring reconfigurability under mild conditions.