Synthesis,Polymerization Of The New Acyl Azide Monomers And Applications Of The Acyl Azide Polymers

In addition to the same activity of azide groups, acyl azide groups could be changed into isocyanate groups by Curtius rearrangement with the heating or under UV light. The isocyanate groups are highly reactive functional groups and can react with hydroxyl and amino groups to form urethane and urea structures, therefore, acyl azide chemistry has been paid much attention in organic synthesis and organic reactions. With the development of polymer science, polymers scientists have shown much interest in the synthesis and application of acyl azide polymer. However, due to the instability of acyl azide monomers to heat and light, we noticed that quite a few papers were published on preparation of polymer by chain polymerization of unsaturated acyl azides as monomers. Therefore, the development of acyl azide polymers synthesized by free radical polymerization of acyl azide monomers is an important and challenging topic. If the living free radical polymerization of acyl azide monomers could be achieved, not only can the molecular weight be controlled with narrow molecular weight distribution, but also a promising strategy can be developed for design and synthesis of the well-defined novel acyl azide polymers with different architectures, such as block, graft, and star shapes. In recent years, our laboratory has been committed to the study of new acyl azide polymers and for the first time we have reported the synthesis of azido polymers via controlled/living free-radical copolymerization of acryl azido monomers under 60Coγ-ray irradiation. According to the relationship between the property and the structures, we have been seeking to find the more stable vinyl acyl azide monomers at room temperature and new polymerization methods for acyl azide monomers. The living radical polymerizations of acyl azide monomers were realized not only byγ-ray irradiation but also established by redox systems at room temperature. With the redox initiator, we designed and synthesized functional acyl azide copolymers and further studied the application. In addition, as an important way to prepare acyl azide polymerizations, the mechanism ofγ-ray irradiated living free radical polymerization was studied. Mainly divided into the following five parts:1. A new vinyl acyl azide monomer, 4-(azidocarbonyl) phenyl methacrylate (ACPM), has been synthesized and characterized by NMR and FTIR spectrum. The thermal stability of the new monomer has been investigated by FTIR and TG/DTA (Thermal Gravimetry/Differential Thermal Analysis) and the monomer is demonstrated to be stable below 50°C in solid state. The copolymerizations of the new monomer with methyl acrylate have been carried out at room temperature under 60Coγ-ray irradiation in the presence of benzyl 1H-imidazole-1-carbodithioate (BICDT). The results show that the polymerizations bear all of characteristics of controlled/living free radical polymerizations, such as the molecular weight increases linearly with monomer conversion, molecular weight distribution is narrow (< 1.20), and a linear relationship between ln([M]0/[M]) and polymerization time exists. The data of 1H NMR and FTIR confirmed that no change of the acyl azide groups occurred in the polymerization process and the acyl azide copolymers were obtained. Thermal stability of the polymers has also been investigated by TG/DTA and FTIR.2. Reversible Addition-Fragmentation Radical Transfer (RAFT) radical polymerizations of methacrylate (MA), methyl methacrylate (MMA) and styrene (St) were carried out at room temperature in organic media. A traditional redox system, benzoyl peroxide (BPO) and N, N-dimethylaniline (DMA) along with two dithiocarbonate RAFT CTAs, benzyl 1H-imidazole-1-carbodithioate (BICDT) and 2-cyanoprop-2-yl dithiobenzoate (CPDB), were employed. Contrast to the other Controlled/Living Free Radical Polymerizations, this new technique could be conducted at ambient temperature. Moreover, even a very low concentration of the redox used in the polymerization, it has shown a rapid polymerization and a high conversion of the monomer at ambient temperature with narrow polydispersity index.3. A novel amphiphilic block copolymers, poly(N-isopropylacrylamide-co-4-(acyl azido) phenyl methacrylate)-block-poly(ethylene oxide), abbreviated as PEO-b-P(NIPAM-co-AAPMA), have been designed and synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization at room temperature. Then self-assembly of the block copolymers has been studied and small cross-linked polymer nanoparticles have been successfully prepared. The units of acyl azido methacrylate play as hydrophobic moieties and crosslinking sites, PEO chains act as stabilizer for the formed particles, and PNIPAM chains make the particles sensitive to temperature. It was found that the size of the polymer particles was related to the unit ratio of NIPAM and AAPAM and by tuning the unit ratio we could easily prepare small cross-linked polymer nanoparticles in aqueous media without using any additional crosslinking agents. The size of polymer nanoparticles was characterized to be about 17 nm by atomic force microscopy (AFM) and transmission electron microscopy (TEM). And the distribution of the particles is very narrow from the Laser light scattering (LLS) characterization.4. Different fluorine content of Y-shaped amphiphilic fluorinated copolymers containing acyl azide monomers have been designed and synthesized by using redox initiated RAFT polymerization at room temperature. And with heating it is easy to introduce the copolymers onto the glass surface by the reaction between isocyanate groups and hydroxyl groups. The surface properties of the copolymer thin films were examined by static contact measurements using water and oil (hexadecane). All the water contact angles of the copolymers show better hydro-philic and oleophobic properties. Based on this result, we examined the anti-fog and oil-repellent pro- perties of the copolymer thin films on the glass surfaces. The experiment results show that the block copolymers exhibit simultaneously good anti-fog and oil-repellent properties.5. There has been a debate going on about the polymerization mechanism between the reversible addition fragmentation chain transfer (RAFT) mechanism and the reversible termination (RT) mechanism, since theγ-ray irradiated living/controlled radical polymerization in the presence of thiocarbonylthio compounds was reported by our group in 2001. In this paper, Monte Carlo method is first used to simulate the RT and the RAFT mechanisms forγ-Ray initiated living radical polymerization in the presence of thiocarbonylthio compounds based on the difference in source of primary radicals. The simulated results show that the RT mechanism is consistent with the characteristics of living/controlled free radical polymerization while the RAFT mechanism could not fit well especially at high rate of the absorbed dose. Moreover, a facile method, on-off irradiation experiment, was used to make sure the regeneration of the propagating radicals which is also different between the two mechanisms. The polymerizations of MA and BA were conducted respectively by the on-off irradiation experiment, and the evolution of the monomer conversion was tracked by both gravimetry and 1H NMR spectroscopy. All the experimental results show that the rate of the polymerization decreases sharply when taken off the irradiation. This can be attributed to decrease of the propagating radicals and can be explained by the RT mechanism instead of the RAFT because the bond cleavage of the thiocarbonylthio moiety capped polymer chain needs energy from the irradiation.