Synthesis And Properties Of The Novel Hyperbranched Polymers And Dendrimers

Hyperbranched polymer is an important nonlinear polymer. They have many novel physical and chemical properties, such as low viscosity, high fluidity, good solubility and a large number of terminal groups, and are broadly applied in medicine carriers, nonlinear optics, nanometer materials and catalysis. Therefore, they have attracted polymer scientists' considerable attention. Various novel hyperbranched polymers have been synthesized successfully. Generally, there are three main synthetic approaches of hyperbranched polymers: (1) step-growth polycondensation of multifunctional groups monomers; (2) self-condensing vinyl (co)polymerization (SCV(C)P) and (3) self-condensing ring opening polymerization (SCROP).Dendrimers are structurally perfectly branched macromolecules. They have better qualities than hyperbranched polymers, but are more difficult to be synthesized. In the past decade, a novel type of molecular architecture, named dendrimer-like polymer, has been synthesized and studied by polymer scientists, in which polymer chains are used as structural units of dendrimer. They have potential applications, such as in drug delivery and catalysis, due to their unique physical and chemical properties. Dendritic-linear block copolymers are also a type of structurally novel polymers, which have a flexible linear chain and one or two semirigid dendritic blocks. The copolymers have many unique melt and solution properties, their basic theory and practical applications have been studied.All these facts are the origin and impetus of this thesis. The main results obtained in this thesis are as follows:1. To solve the problem of gelation in A3+B3 type hyperbranched polymerization systems, hyperbranched poly(ester amine)s were synthesized by Michael addition polymerization of trimethylol propane triacrylate (A₃) and 1-(2-aminoethyl) piperazine (B3). The mechanisms of the polymerizations were investigated by using ¹³C NMR to in situ monitor the polymerization process. When the feed ratios of TMPTA and AEPZ are 1/2 or 2/1, gelation didn't occur. All of the polymers are considered forming by polymerization of AB₂ or AB₄ intermediates. Due to low reactivity of 2°amines (formed) at -15℃, TMPTA and AEPZ can be reacted on 1/1 feed ratio. Glass transition temperatures of the obtained hyperbranched polymers were characterized by DSC measurements, and the proportions of three kinds of amine in the polymers are main influencing factor on T_g of the polymers.2. To synthesize hyperbranched polymer using glycidyl methacrylate(GMA), we studied the homopolymerization of GMA and the copolymerization of GMA and St by combining Cp₂Ti(III)Cl catalyzed the epoxide radical ring opening and self-condensing vinyl polymerization(SCVP), and using Cu(II)X₂ (X = Br or Cl) to control the polymerization. Before the conversion of monomers reached 60%, no gel was generated. The GPC traces show multi-peaks and rapid increasing of molecular weights of the polymers. It indicates that coupling termination may exist. We confirmed the branching structure of the polymers by ¹H NMR spectra and hydrolysis test. The degrees of branching (DBs) of the polymers were decided by the feed ratios of Cp₂TiCl/GMA and GMA/St and polymerization time. The hyperbranched star (hyperstar) polymers with HPGMA as cores and PSt as arms were synthesized by atom transfer radical polymerization of St using HPGMA as macroinitiator. At last we studied the modifications of the hyperbranched polymers with various acids and amines.3. To synthesize "HyperMacs" of PSt using click chemistry method, we synthesized AB₂ type of PSt macromonomers with a propargyl group and two azide groups and A₂B type of PSt macromonomers with two propargyl groups and an azide group, respectively. The two macromonomers were polymerized by click reaction, and the obtained hyperbranched polymers were characterized by GPC and ¹H NMR. GPC curves show multi-peaks and broad distributions of molecular weights. M_W/M_ns gradually decrease with proceeding of the reactions. After 60 h polymerization at 60°C, the degrees of polymerization (DPs) are over 15.4. To prepare nanometer hollow sphere using dendrimer-like copolymer containing degradable polymer chains, we synthesized the three generations dendrimer-like copolymers C(PSt(PLLA(PSt-PNAS)₂)₂)₃ and C(PSt(PLLA(PSt-PNAS)₂)₂)₄ by combination of ATRP and ROP. Diethanol amine and 2,2-bis(methylene-2-bromoisobutyrate) propionyl chloride (BMBIBPC) were used as divergent reagents respectively before preparations of the second and the third generations. The resultant polymers were characterized by GPC and ¹H NMR. Then the outermost PSt-PNAS in the dendrimer-like copolymers was cross-linked via substitution reaction of NAS with ethylene diamine, and at the same time, the PLLA segments in the second generation were decomposed in dilute THF or CHCl₃ solution, forming hollow particles. The morphologies formed were characterized by SEM and DLS methods, and spherical particles with various sizes were observed.5. To obtain a amphiphilic dumbbell-shaped copolymer, we successfully synthesized dendritic-linear-dendritic triblock copolymers composed of linear polystyrene (PSt) and poly(amido amine) dendrons. Two bromines-terminated PSt with M_n=13,000 was prepared by atom transfer radical polymerization (ATRP) usingα,α'-dibromo-p-xylene as initiator. Then the terminal bromines at both ends of PSt chains were replaced by one imine group of piperazine (PZ), and further Michael addition reaction of terminal PZ with excess 1,3,5-triacryloylhexahydro-1,3,5-triazine (TT) produced the first generation (G₁) of the triblock copolymer. Continuous growth of dendrons from G1.5 to G4 at the both ends of PSt chains was carried out by the iterative Michael addition reactions with excess PZ and following TT. Structures of the triblock polymers were characterized by GPC and ¹H NMR spectra. Thermal phase transitions of the polymers were studied by DSC measurements. The triblock copolymers with terminal PZ groups have higher T_gs due to hydrogen bonding interaction.