ABSTRACT
OLIGOMERAs discussed earlier, ACP nanoparticles having micelle-like structures in aqueous phase could be prepared using reactive amphiphilic oligomers such as urethane acrylate anionomer, cationomer, and non-ionomer. These oligomers consist of hydrophilic and hydrophobic segments and have reactive vinyl groups at the same backbone. As hydrophilic and hydrophobic segments in the oligomers chains are chemically connected with each other via urethane linkages and acrylate groups are introduced at hydrophobic segments or end groups, these oligomers were named as amphiphilic urethane acrylate or water-dispersible urethane acrylate. According to the
type of hydrophilic segment, urethane acrylate can be classified as urethane acrylate anionomer (UAA), urethane acrylate cationomer (UAC), and urethane acrylate nonionomer (UAN). For example, urethane acrylate anionomer is an amphiphilic urethane acrylate containing anionic hydrophilic segments such as carboxylic acid and sulfonic acid groups. UAA chains can be synthesized with various processes using various chemicals. One of the representative processes is using dimethylol propionic acid (DMPA) as a hydrophilic anionic monomer. As DMPA has two hydroxyl groups and a carboxylic acid group at the same backbone, hydrophilic carboxylic groups can be introduced at the precursor backbone by the reaction of two hydroxyl groups with isocyanate groups [43-47]. In this chapter, UAA chains synthesized using DMPA were used for the preparation of anionic ACP nanoparticles. For the synthesis of UAA chains, poly(tetramethylene glycol) (PTMG, Mw = 1000) was first mixed with DMPA at various molar ratios and dissolved in N-methyl-2-pyrrolidone (NMP). Then, 2,4-toluene diisocyanate (TDI) was added to the mixture of PTMG and DMPA to form NCO-terminated urethane precursor containing carboxylic acid groups at the backbone. As a final step, 2-hydroxyethyl methacrylate (2-HEMA) was reacted with NCO groups of this urethane precursor to introduce reactive vinyl groups at the precursor chains. After completion of the three-step reaction, polytetramethylene oxide (PTMO)-based hydrophobic segments and hydrophilic carboxylic acid groups are randomly connected with each other via urethane linkage. In addition, this amphiphilic precursor has reactive vinyl groups at the both ends of hydrophobic segments. The hydrophobic/hydrophilic balance of UAA chains could be varied by changing the molar ratio of PTMG/DMPA in the synthesis. As molar ratio of DMPA to PTMG in the synthesis composition is increased, the number of carboxylic groups introduced at UAA chain is increased, resulting in increase of hydrophilicity of UAA chain. Symbol UAA64 represents UAA precursor chain synthesized at 6/4 molar ratio of PTMG/DMPA. The hydrophilicity of UAA chains increases in the order of UAA64, UAA55, and UAA28. The proposed chemical structure of UAA and the recipe for synthesis of UAA chains are shown in Fig. 2.1 and Table 2.1, respectively. The polystyrene equivalent molecular weight of synthesized UAN chains is a 3750-6,700 g/mol weight average molecular weight with a polydispersity of 1.93-2.01.
