The Structure And Properties Of Comb Polymer

Comb shaped polymers are a kind of polymer with unique structure and novel properties. This thesis would investigate the structure of comb shaped polymer in solution and in bulk, and study the relationship between its structure and its properties. On the basis of reviewing of the progress of other scientists working on this topic, we synthesized two kinds of comb polymer, and studied their structure and properties detailly. In the first part of this study, we synthesized a comb shaped polymer with Poly(L-lactide) (PLLA) with a novel comb conformation was synthesized and its crystallization and thermal properties was studied. PLLA on poly(2-hydroxyethyl methacrylate) (PHEMA) backbone was prepared by a combination of atom transfer radical polymerization (ATRP) and ring-opening polymerization (ROP). The structure of the comb PLLA was analyzed by wide angle x-ray diffraction (WAXD), small angle x-ray scattering (SAXS) and differential scanning calorimetry (DSC). WAXD result indicates that the comb polymer has a crystalline modification with a 103 helical conformation. Lamellar parameters of the crystalline structure were obtained by one-dimension correlation function (1DCF) calculated from SAXS results. The calculations show that the thickness of crystalline layer is controlled by annealing temperature and comb structure. DSC was applied to study kinetics of the crystallization and melting behavior. Avrami exponents at different crystallization temperature were obtained and did not show dependence on annealing temperature, but tend to be decreased by branching conformation. The melting curves show two melting peaks, which was attributed to melt recrystalliztion and the influence of the comb structure on it was discussed. In addition, we blended the comb PLLA with poly(ethyleneoxide), the influences of comb structure on the compatibility and crystalline structure of the blends were discussed.An amphiphilic comb polymer with pendant pyrene groups and poly(N-isopropylacrylamide) (PNIPAM) side chains was synthesized based on click chemistry and reversible addition-fragmentation chain transfer polymerization. Gel permeation chromatography, FTIR and 1H NMR results all indicated successful synthesis of well-defined comb polymer. The photophysical properties and self-assembly of the polymer in solution were studied by UV-Vis spectroscopy, fluorescence technique and transmission electron microscopy. The intensity ratio of the excimer peak (IE) to the monomer peak (IM) of the comb polymer in THF, was used to monitor the formation of inter-or intramolecular excimer. At low polymer concentration, the value of IE/IM kept unchanged indicating the formation of intramolecular excimer; at high polymer concentration the value increased rapidly with concentration because of the formation of intermolecular excimer. The change of the intensity ratio of the first to the third vibronic band (I1/I3) on the monomer emission of the comb polymer also proved the association of the pendant pyrene groups in THF at high polymer concentration. In aqueous solution, the comb polymer chains self-assembled into vesicles with pyrene groups in the walls and PNIPAM side chains in the coronae. The value of the critical aggregation concentration of the polymer was determined by fluorescence technique. Temperature exerted significant effect on the size and morphology of the vesicles. At a temperature above lower critical solution temperature (LCST) of PNIPAM, PNIPAM brushes in the coronae of vesicles collapsed on the surface of the structures forming nano-sized domains, and vesicles with smaller size were obtained. Fluorescence quenching experiments indicated that the collapsed PNIPAM chains protected a part of pyrene groups from being quenched by nitromethane at a temperature above LCST of PNIPAM.