Studies On The Chemistry And Physics Of New PS-b-PLA/Nanocrystal Hybrid Material

Nano-materials have been extensively applied in catalyst, superconductor, composite material and biotechnology et al, due to their specific physical and chemical properties, which is becoming the hot-point in the field of material science in 21th century. Loading organic nanoparticle into microphase-separated block copolymer matrix by molecular self-assembly is an effective approach to prepare high-ordered nanoparticle/block copolymer hybrid. Inspirited by the fact that macromolecules can self-assembly into ordered aggregate by recognition, we hope to prepare high ordered nanoparticel/block copolymer hybrid by combining the self-assembly of block copolymer and nanoparticle with chiral recognition. In order to reach this goal, research works in this thesis was divided into several parts as following:1. Design, synthesis and characterization of optical active block copolymer PS-b-PLLA and PS-b-PDLA and their homopolymer PLLA and PDLAFirst, a series of enantiomeric PS-b-PLLA and PS-b-PDLA diblock coplymer bearing a PS (Mn,NMR=30.0 KDa, PDI=1.11) and various PLA blocks were synthesized via combination of ATRP of styrene and living ring-opening polymerization (ROP) of enantiomeric l-/d-lactide. By means of nuclear magnetic resonance spectrometer (NMR), gel permeation chromatography (GPC), polarimeter and thermal gravimetrical analyzer (TGA), macromolecular structures and therm physical properties of the synthesized diblock copolymers were characterized. By the same approach, two series of homopolymer PLLA and PDLA were also synthesized and characterized.2. Design and syntheses of new biodegradable poly(l-lactide) disulfides and successive preparation of their stabilized photoluminescent CdSe Quantum Dots HO-PLLA@CdSe QDFirst, new aliphatic poly(l-lactide) disulfides HO-PLLA-SS-PLLA-OH were designed and synthesized and then were reduced intoα-hydroxyl-ω-mercapto heterofunctional poly(l-lactide) (HO-PLLA–SH).With these less toxic HO-PLLA–SH , photoluminescent CdSe QDs (HO-PLLA@CdSe QD-I series) were successively prepared through a surface ligand exchanging process. In an alterative strategy, the biodegradable poly(l-lactide) surface stabilized CdSe QDs (HO-PLLA@CdSe QD-II series) were comparatively synthesized by surface hydroxyl initiated ROP of (l-)-lactide from a prepared 11-mercapto-1-undecanol (MUD) stabilized CdSe QD precursor (MUD@CdSe QD).Chemical and crystal structures of the two series of QDs were characterized by NMR ,FT-IR ,WAXD,TEM ,UV and PL,the effect of preparation conditions on the quantum yields (QY) were investigated in detail.3. Growth kinetic and mechanism of stereocomplex aggregates by PS-b-PLLA/PS-b-PDLA (or PLLA) in nonselective solventIn-situ self-assembly in non-selective solvents THF was explored at ambient temperature for the mixtures of a pair of enantiomeric diblock PS-b-PLLA and PS-b-PDLA. It was noted that the growth kinetic of in-situ self-assembly depended on the concentration and molecular weight of enantiomeric PLA block population as well as preparation condition such as agitation, and the isolated self-assemblies were found to form PLLA/PDLA racemic crystal structures as analyzed by means of DSC, WAXD, and FT-IR. Therefore, in a view of the mechanism of aggregations formed in current system, it was suggested to be solely driven by the interplay of stereocomplexation between the PLLA and PDLA blocks. At last, utilizing the new achieved HO-PDLA@CdSe QD as a suitable fluorescent label, in-situ aggregation in THF driven only by the stereocomplexation of enantiomeric PLLA and PDLA blocks and morphologies of the aggregated stereocomplex microparticles were investigated by confocal laser fluorescent microscope (CLFM) and SEM.4. Thermal physical properties and crystallization behavior of chiral block copolymer PS-b-PDLAWith the help of DSC and MDSC, the thermal physical properties and crystallization of PS-b-PDLA were investigated and compared with homopolymer PDLA. It was found that: with the decrease of PDLA block length, therm physical parameters and crystallization capability of PS-b-PDLA reduce accordingly,and adding PLLA can improved the thermal property and crystallization capability of PS-b-PDLA due to the nucleation of stereocomplex. However, too much addition of PLLA resulted in retain of PDLA in the abundant stereocomplex matrix, which would reduce the total crystallization capability of PS-b-PDLA. The study on the growth kinetic of spherocrystal by POM displayed that growth rate of spherulite of PS-b-PDLA depended on the isotherm temperature, volume fraction of PDLA block and amount of PLLA.5. Study on the organic nanoparticle/block copolymer hybrid based on the chiral recognition and self-asssembly of block copolymer and nanoparticleAt first, the study on the micro-phase behavior of PS-b-PDLA in bulk by SAXS showed that the degree of order of micro-phase separated domain not only depended on the state of sample and temperature, but can be improved by means of method such as isotherm crystallization, annealing and shearing et al.Then, dependence of preparation conditions on the self-assemble behavior of PS-b-PDLA thin film on a neutral surface was investigated in detail. At last, the effects of incorporation of nanopartilcles on the microphase speration behavior of block copolymer in bulk and in thin film were investigeated in detail.In summary, high ordered nano-particel/block copolymer hybrid can be obtain by combining the self-assembly of block copolymer and nanoparticle with chiral recognizing, and the degree of order of micro-domain can be improved by isotherm crystallization and solvent annealing et al. Therefore, current result provided an alternative facile way to prepared industrial applicable and high-ordered nanoparticle/block copolymer template.