# Synthesis of Covalently Cross-Linked Colloidosomes from Peroxidized Pickering Emulsions
## 3 Results and Discussion
### Synthesis and Characterization of Pervidized Latexes  
An amphiphilic PM-1-MA copolymer used as an inisurf was synthesized through a free-radical copolymerization of a peroxide monomer 2-_tert_-butylperoxy-2-methyl-5-hexen-3-ine (PM-1) with maleic anhydride (Scheme 1). The subsequent hydrolysis of the synthesized PM-1-MA copolymer leads to the formation of a surface active initiator (inisurf) with carboxyl groups (at pH \(<\) 7) or carboxylate (salt) groups (at pH \(>\) 7) (Scheme 2). Figure 1: Synthesis of PM-1-MA containing peroxide and anhydride groups. In a similar way, an amphiphilic PM-2-MA copolymer was synthesized through a free-radical copolymerization of a peroxide monomer N-(_tert_-butylperoxymethyl)acrylamide (PM-2) with maleic anhydride (Scheme 3). The capability of the peroxide groups in the PM-2-MA copolymer to undergo thermal decomposition was demonstrated by a thermogravimetric analysis. Figure 2 indicates that the PM-2-MA samples undergo weight loss at 130-210 \({}^{\circ}\)C. The recorded weight loss is due to the decomposition of the primary-tertiary peroxide groups in the PM-2 units of the copolymer. Figure 2: Thermogravimetric analysis of PM-2-MA. An insurf PM-2-MAc with carboxyl groups or carboxylate (salt) groups was formed via the hydrolysis of the PM-2-MA copolymer at different pH levels (Scheme 4). Amphiphilic PM-1-MAc and PM-2-MAc copolymers (Schemes 2 and 4) were used as insisurfs in emulsion polymerization to synthesize peroxididized latex particles. To provide particles with surface activity and the ability to stabilize a Pickering emulsion in colloidosome synthesis, these particles must exhibit amphiphilic behaviors, i.e., combine hydrophilic and hydrophobic molecular moieties at the surface. In the case of peroxididized latexes, hydrophilic properties are provided by the hydrolysis of PM-1-MA or PM-2-MA maleic anhydride groups (Scheme 2 and blue area in Scheme 4) and form the carboxyl groups of PM-MAc at pH \(<\) 7 or PM-MAc (salt) at pH \(>\) 7 insurf macromolecules, whereas non-polar fragments of the peroxide monomers in the copolymer (Scheme 2 and orange area in Scheme 4) and polystyrene (core material of latex) provide hydrophobic properties to the particle's surface. To investigate the ability to vary the nature of the peroxide groups and the amount of carboxyl groups on the surface of latex particles, and thus their reactivity and surface activity, a series of peroxididized latexes were synthesized at pH 10 using PM-1-MAc at various concentrations (6, 8, and 10 wt.% based on monomer weight) and at pH 5.5, 7.5, and 9.5 using PM-2-MAc at various concentrations (0.3, 1, 2.5, 5, and 7.5 wt.% based on monomer weight). The water soluble copolymers PM-1-MAc and PM-2-MAc exhibit surface activity that decreases the surface tension at the water-air interface to 30-40 mN/m. In an aqueous medium, they form micellar structures, which are able to solubilize hydrophobic substances [28]. This allows for the application of PM-1-MAc and PM-2-MAc as polymeric surfactants in emulsion polymerization. The peroxide groups in the polymeric surfactant macromolecules enable their ability to initiate free radical processes [31; 32; 33]. The amphiphilic nature of the PM-1-MAc and PM-2-MAc macromolecules with the hydrophilic units of maleic acid and the hydrophobic units of the peroxide monomer facilitates the stabilization of latex particles in emulsion polymerization. The solubilization of the styrene monomer in emulsion polymerization followed by the formation of adsorption layers at the surface of latex particles occurs due to hydrophobic interactions and the hydration of ionized carboxylate groups oriented towards an aqueous phase (Figure 3). The stability of the latex particles is achieved due to the combination of steric and electrostatic stabilization [28]. An advantage of the application of PM-1-MAc and PM-2-MAc as polymeric insurfs is the presence of peroxide groups in the hydrophobic PM units, which are regularly distributed along the macromolecules.