Synthesis Of Amphiphilic Stimulus-Responsive Graft Copolymers Through Living Free Radical Polymerization And Studies On Their Self-Assembly Behavior

In this thesis, the NMP of styrene (St) and p-chloromethylstyrene (p-CMS) were firstly carried out using benzoyl peroxide (BPO) as the initiator to obtain the random copolymers of P(St-co-(p-CMS)). Subsequently, the random copolymers were converted into macro-RAFT agents with fluorescent carbazole as Z-group through a simple method. Finally the macro-RAFT agents were used in the RAFT polymerization of N-isopropylacrylamide (NIPAAM) to prepare fluorescent amphiphilic and thermo-sensitive graft copolymer P(St-co-(p-CMS))-g-PNIPAAM with controlled molecular weights and well-defined structures. On the other hand, ATRP of styrene was conducted in DMF directly using above mentioned P(St-co-(p-CMS)) as macroinitiator and CuCl/PMDETA as catalyst to obtain graft copolymer P(St-co-(p-CMS))-g-PSt. Then a series of amphiphilic and pH-responsive graft copolymers of P(St-co-(p-CMS))-g-(PSt-b-P4VP) with different molecular weights were synthesized via ATRP of 4VP, using P(St-co-(p-CMS))-g-PSt as the macro-ATRP initiator and CuCl / Me6TREN as the catalyst. The graft copolymers obtained were characterized by gel permeation chromatography (GPC), 1H nuclear magnetic resonance (NMR) spectroscopy, and FT-IR spectroscopy. The self-assembly behavior of these two types of amphiphilic graft copolymers in different selective solvents was studied by high performance particle sizer (HPPS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The influence of varied factors such as the composition of copolymers, solvents, pH on the size, stability, and morphology of micelles was investigated respectively. The results showed that: the Z-average size of the micelles formed from P(St-co-(p-CMS))-g-PNIPAAM increased with the increase of molecular weights of PNIPAAM in side chain and TEM showed aggregates of nanosized spherical micelles. The aqueous solution of the micelles showed a lower critical solution temperature (LCST) at about 28 oC, which was below the value of NIPAAM homopolymer (32 oC). As for the pH-responsive graft copolymer of P(St-co-(p-CMS))-g-(PSt-b-P4VP), the Z-average sizes of the micelles in toluene were much larger than those in 2-propanol for the same sample. Furthermore, the PDIs of the micelles formed in toluene were also broader than those in 2-propanol, which showed a better stability for the micelles in 2-propanol. The TEM and SEM both showed spherical morphologies for the micelles formed in either toluene or 2-propanol. But flower-like micelles was observed by TEM for the ones prepared in aqueous solution of pH=2.