Synthesis of hydroxypropyl cellulose derivatives modified with amphiphilic diblock copolymer side-chains for the slow release of volatile molecules

Hydroxypropyl cellulose (HPC) was used as carrier material to prepare comb-like grafted block copolymers having an amphiphilic core–shell structure. The hydroxyl groups of HPC were partially protected with trimethylsilyl groups and the free OH groups used to initiate the ring opening polymerisation (ROP) of L-lactide. The end-chain of the grafted hydrophobic poly(L-lactide) (PLLA) chain was then functionalised with 2-bromopropionyl bromide which was used to polymerise the tert-butyl acrylate (tBA) monomer by atom transfer radical polymerisation (ATRP). The hydrophobic PtBA block was then hydrolysed to a hydrophilic poly(acrylic acid) (PAA) block. The resulting amphiphilic grafted copolymer HPC-g-(PLLA-b-PAA) was dissolved in an ethanol/water mixture (9 : 1), such as a typical Eau de Toilette (EdT) formulation. Atomic force microscopy (AFM) and size measurements confirmed the presence of core–shell structures in solution. A significant swelling of HPC-g-(PLLA-b-PAA) in the presence of a volatile bioactive molecule, methyl 2,2-dimethyl-6-methylene-1-cyclohexanecarboxylate (Romascone®), was observed by dynamic light scattering (DLS). Furthermore, the presence of HPC-g-(PLLA-b-PAA) significantly decreased the evaporation rate of Romascone®, thus serving as an efficient fragrance delivery system in formulations with high ethanol content.