Preparation And Encapsulation Of Amphiphilic Copolymers

During recent years, self-assembly and applied studies of amphiphilic copolymers have attracted greater attention from academia and industry member. So far most studies on self-assembly have focus on block copolymers. Because of their complex synthesis, it is different to mass produce. Compared to block copolymers, random and alternating copolymers are much easy to synthesis, so they have potential applicable prospects. Additionally, random and alternating copolymers self-assemble micelles can be used as particulate emulsifier, but corresponding research reports are few. Block copolymers self-assemble into core-shell structure, while the surface of random copolymer micelles are enriched hydrophilic segment and partial hydrophobic segment, so the micelles have amphiphilicity and can be used as emulsifier. The oil phase of O/W emulsion could be took as microencapsulate of oil-soluble actives.In this paper, photosensitive random amphiphilic copolymer and alternating amphiphilic copolymer were synthesized respectively. Their self-assemble behavior were studied. We attempt to use self-assemble micelles as particular emulsifier to study their emulsification and encapsulation, wish to expand the research domain of copolymer micelles. Additionally, we try to research the effect of aliphatic chains in the alternating copolymer which simultaneous self-assemble with dye on their micellar encapsulation. The actives could be encapsulated into emulsions which were stabilized by random copolymer micelles. To the best of our knowledge, no attempt has been reported so far. My paper divides three parts.1. A photosensitive random copolymer P(St/VM-co-MA) was synthesized from styrene (St), a styrene-containing photosensitive monomer 7-(4-vinylbenzyloxy)-4-methyl coumarin (VM) and maleic anhydride (MA) by free radical copolymerization. Its structure was characterized by FT-IR, ¹H-NMR, GPC and DSC. P(St/VM-co-MA) self-assembled into micelles in the selective solvent DMF/H₂O. The morphologies, sizes, and size distributions of the micelles were characterized by TEM and DLS. The micelles were photo-crosslinked by the photodimerization of the coumarin groups under UV irradiation to form crosslinked micelles. The photosensitivity, fluorescence and structural stability of micelles were studied by UV-Vis, fluorospectro photometer and DLS. The results showed that micellar photosensitivity increased with increasing pH, and decreased with increasing salt concentration. The fluorescence intensity of non-crosslinked micelles was higher than those of crosslinked in pH 1-12 scope, and the intensity reached maximum when pH was neutral. The micellar structure was strengthened when it was photo-crosslinked.2. The O/W emulsion was prepared by homogenizing with Solvent Yellow 98 dye solution as oil phase, and P(St/VM-co-MA) micelle as particulate emulsifier. The effects of micellar concentration, oil/water ratio, photo-crosslinked, pH, salt concentration and oil solidified on emulsification and encapsulation were studied. Results showed that when micellar concentration was bigger than 2 mg/mL and oil/water ratio less than 2:1, the micelles could stabilize emulsion. During emulsification, the oil-soluble dye was encapsulated into emulsion. When use the crosslinked micelles as emulsifier, they could expand the range pH, salt concentration of micelles stabilized emulsion and the emulsification and encapsulation were both improved. Solidified droplets were obtained by polymerizing the oil phase of styrene-dye containing the initiator AIBN to enhance encapsulation, which is an innovation of this paper.3. A alternating copolymer P(St-alt-MAA₈) with long anhydride chains was obtained by aminolysis between maleic group of P(St-alt-MA) and aliphatic amine. Its structure was characterized by FT-IR, ¹H-NMR and GPC. The self-assembly behavior of P(St-alt-MAA₈) was studied by UV-Vis, TEM and ZS. P(St-alt-MA)/dye and P(St-alt-MAA₈)/dye complex micelles were obtained by simultaneous self-assembly of dye and copolymer. The results indicated that copolymer concentration, self-assemble methods, pH, salt concentration influenced the micellar sizes greatly, while ultrasonic treatment was less influential. The complex micelles sizes were smaller than those of polymeric micelles. When the alternating copolymer has anhydride chains, their encapsulation could be improved.