Application Of Bergman Cyclization In The Systhesis Of Ultra-Small Polymeric Nanoparticles

Polymeric nanoparticles are a kind of novel nanomaterials, including nanospheres, nanoshells, nanorods and other nanostructures. These nanomaterials not only possess ordinary surface effect, size effect, quantum size effect and macroscopical quantum tunnel effect, but also temperature-PH sensitivity and electromagnetic properties. Many synthetic methods have been developed for polymeric nanoparticles in the recent decades. For example, using traditional emulsion or microemulsion polymerization technologies can afford nanoparticles with size ranging from 20-50 nm; synthesizing dendritic polymer through organic methods will get nanoparticles within 10 nm; crosslinking micelles formed from self-assembly of block copolymer will give nanoparticles of about 20-200 nm. Overall, preparation of nanoparticle with size around 5-20 nm remains a challenge.A new kind of method called intramolecular chain collapse has emerged in last decade, which meets the needs of preparation of these ultra-small polymeric nanoparticles. The fundamental idea of intramolecular chain collapse is incorpation of crosslinkable functionalities onto the backbone of linear polymer chain. When crosslinking reaction is triggered, there will be two competitive reactions——intermolecular and intramolecular crosslinking reactions. In order to avoid unwanted intermoleular crosslinking, the reactions were usually carried out in a ultra-dilute solution or using continuous addition method to afford single chain collapsed nanoparticles.In this dissertation, enediyne compounds, which undergo Bergman cyclization under various stimuli, were chosen as crosslinkable funtionalities. Well-defined polymeric nanoparticles were obtained and some of their applications were explored subsequently. The specific contents are as follows:(1) Linear copolymers with enediyne moieties were obtained through living/control radical copolymerization or post-polymerization modification strategies. A series of intramolecular chain collapsed polymeric nanoparticles of different molecular weights and crosslinking density were then synthesized via thermal triggered Bergman Cyclization. The effectiveness of single chain collapse was confirmed with GPC, NMR, FT-IR, AFM analysis.(2) On the basis of the previous research, we designed and synthesized a ultra-violet activated enediyne unit. Single electron transfer living radical polymerization technology was used to copolymerize this enediyne monomer with different acrylates. Subsequently, different kind of polymeric nanoparticles were obtained by UV irradiation in dilute solution. Various characterizations were used to demonstrat it an effective appoarch to fabricate thermal sensitive polymeric nanopartcles.(3) Polymeric nanoparticles with different crosslinking density in work (1) were used as sacrifial pore generators for low dielectic porous silica thin films. Mixtures of poly(methylsilsequioxane) and nanoparticles were spin coated on Al-coated silicone wafer. Thermal curing of MSSQ matrix and removal of porogens under nitrogen atmosphere gave porous films. It was showed that tightly packed nanoparticles would exclude entanglement of segregation and generate well-defined pores and form films with good mechanical property. The measured dielectric constant is about 2.1.(4) The enediyne alcohol was incorperated into polybenzylacrylate through transesterification reaction and nanoparticles were possessed via thermal triggered Bergman cyclization route. The polyacrylic acid based nanoreactors were then prepared by hydrogenlysis of polybenzylacrylate nanoparticles. Inorganic quantum dots can be fabricated and encapsulated in such polymeric nanoreactors.(5) Similar to work (4), the enediyne alcohol was incorperated into polymethylacrylate backbone and polymeric nanoparticles were fabricated subsequently and used as soft templates for carbon nanoparticles. Different size of carbon dots were got after pyrolysis of nanoparticles with various enediyne fractions. These carbon materials show blue to green photoluminescent after surface oxidization and PEG passivation. The mechanism of luminescent was also discussed.