The Research On The Preparation Of Heterotelechelic Polymers Generated By Atom Transfer Radical Polymerization And"Click" Chemistry

Thymine is a nucleic acid base in DNA and it has the propensity to both hydrogen bond and photodimerize. As a result, thymine functional polymer can be used for the preparation of supramolecular polymer materials based on hydrogen bonding interaction or photoresponse materials.Telechelic polymer was defined as macromolecules that contain two reactive end groups. It can be used as chain extenders, cross-linkers, and important building blocks for various macromolecular structures. This thesis is based on the research on telechelic polymer. Novel a,co-hetero-telechelic polymers were synthesized by a combination of ATRP and "click" chemistry. First, the thymine functional ATRP initiator was synthesized by two step reaction. Then an a-thymine functionalized poly n-butyl acrylate [Thy-PnBA-Br (3,3’)] was synthesized by atom transfer radical polymerization (ATRP) of n-butyl acrylate using the thymine functional ATRP initiator. The bromide of Thy-PnBA-Br(3,3’) was subsequently converted to the azide functionality.Finally, Thy-PnBA-DAT(7)(Mn,GPC=3900, PDI=1.05)/Thy-PnBA-Cou(9)(Mn;GPC=4000, PDI=1.03) was prepared by using the method of copper catalyzed azide/alkyne ’click’ chemistry. Thy-PnBA-DAT(7) can used for preparing supramolecular polymer materials and Thy-PnBA-Cou(9) is a photoresponse material. The1H NMR had proved the existence of the two novel polymers.The results from1H NMR of different concentration of Thy-PnBA-DAT(7) in CDC13indicated that when the concentration of the polymer in the solution was increased, the chemical shift of the imide proton signal of the thymine unit was found shifted further downfield, which was more obvious than that when the same amount of concentration of Thy-PnBA-Br(3) in the solution was increased. This phenomenon provide support for the existence of strong entropically driven hydrogen bonding interactions(Thy-DAT interaction) between complementary recognition units of the heterotelechelic polymers, leading to the formation supramolecular polymer material.The ultraviolet-visible absorption spectroscopy indicated that absorption peaks appear at283nm and328nm for the filmy sample of Thy-PnBA-Cou(9) irradiated by350nm UV light(15.5mW/cm2) for different times. With a rise in time, the peak height decreases. The phenomenon suggests that photodimerization process of the polymer. When the irradiation time rise to300min, the dimerization degree of Thy and Cou groups both approached to the equilibrium value, which were70.6%and89.4%respectively. It means that a good efficiency of photodimerization in the polymer under the circumstances and the photodimerization efficiency of Cou groups in the polymer was higher than that of Thy groups. The photodimerization property of Thy-PnBA-Cou(9) was further characterized by by Gel permeation chromatography (GPC), which indicated that the average molecular weight of the irradiated sample of Thy-PnBA-Cou(9) had increased, and was accompanied by an increase in the molecular weight distribution of the photo-products.In this study, the prepared two kinds of novel materials Thy-PnBA-DAT(7) and Thy-PnBA-Cou(9) combine the low Tg nature of PnBA and the property of end functional groups on the telechelic, which has the potential applications for preparing supramolecular self-healing materials or photo-stimulated self-healing materials respectively.