p-(Iodomethyl)styrene was polymerized under the action of a radical initiator (AIBN). The polymerization proceeds with degenerative chain transfer and leads to well defined branched polymers with functional primary and secondary iodomethyl groups as revealed by NMR studies. The obtained polymer can be further used as macroinitiator for radical polymerization of styrene. This polymerization proceeds in controlled way to polystyrene star polymers with reactive groups at the end of their arms. The characterization of branched and star structures was performed by NMR and GPC with absolute molar mass detection (MALLS). 相似文献
Strain-promoted azide-alkyne cycloaddition “click” reaction (SPAAC) was successfully used as a tool in synthesis of star polymers by grafting onto approach. The application of SPAAC method in star polymer synthesis was investigated for coupling reaction of the dibenzocyclooctyne (DIBO) end group of polystyrene (PS) and poly(ethylene glycol) (PEG) with coupling agents bearing 2, 3, or 4 azido groups. Firstly, well-defined linear DIBO-terminated PS was obtained by atom transfer radical polymerization (ATRP) of styrene using a DIBO containing ATRP initiator and linear DIBO-terminated PEG was obtained by terminal functionalization of PEG monomethyl ether (PEG-OH). Then a series of star PS and PEG bearing two, three and four arms were prepared respectively by subjecting SPAAC coupling reaction between the linear polymer-DIBO and the azido tethered core molecules at 30 °C without catalyst. The obtained star PS showed a well-defined structure after fractional precipitation to remove slightly excess linear polymers, and all the star polymers were characterized via Fourier transform infrared spectroscopy (FTIR), 1H nuclear magnetic resonance spectroscopy (1H NMR), size exclusion chromatography (SEC) and matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS). 相似文献
The polymerization of p-(iodomethyl)styrene (PIMS) yields well-defined branched polymers with reactive iodomethyl groups. The branched poly[p-(iodomethyl)styrene] was used as the transfer agent in the iodine mediated radical polymerization of vinyl monomers. The polymerization proceeds in a controlled way and yields polystyrene and poly(t-butyl acrylate) star polymers with reactive groups at the end of their arms. Polymers so obtained were also used to prepare stars with block copolymer arms: polystyrene-block-poly(t-butyl acrylate). The characterization of star structures was performed by NMR and gel permeation chromatography with absolute molar mass detection (MALLS). Preliminary characterization of the thermal properties of these novel materials is reported. 相似文献
The synthesis of well-defined H-shaped block copolymer based on the enzymatic ring-opening polymerization
(eROP) and atom transfer radical polymerization (ATRP) is described. The dihydroxyl polycaprolactone (PCL)
was synthesized by the eROP of ε-caprolactone (ε-CL) in the presence biocatalyst Novozyme 435
and initiator ethylene glycol. Subsequently, the resulting PCL was converted to tetrafunctional macroinitiator
by the esterification with 2,2-dichloro acetyl chloride (DCAC). The H-shaped block copolymer was then
synthesized by the ATRP of styrene. The polymers were characterized by NMR and GPC. Linear first-order
kinetics, linearly increasing molecular weight with conversion, and low polydispersities observed from
the ATRP of St showed that the polymerization was well controlled. (PSt)2-b-PCL-b-(PSt)2 block
copolymers with varying molecular weight and controllable composition were obtained. 相似文献
Summary: Coupling reactions between terminal functionalized polymer chains were chosen for the synthesis of star‐like polymers consisting of polystyrene and polystyrene‐block‐poly[styrene‐co‐(butyl acrylate)] arms. For the preparation of terminal functionalized polymer chains a side reaction of the 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) mediated free radical polymerization of methacrylates could be used successfully to convert TEMPO terminated polymers into end functionalized polymers. The number of functionalized monomer units attached to the polymer chain is directly related to the TEMPO concentration during this reaction. Different polystyrenes and polystyrene‐block‐poly[styrene‐co‐(butyl acrylate)] block copolymers were functionalized with a variable number of epoxide and alcohol groups at the chain end. For the determination of the optimal reaction parameters for the coupling reactions between these polymer chains, epoxy functionalized polystyrenes were converted with hydroxy functionalized polystyrenes under basic and acidic conditions. By activation with sodium hydride or boron trifluoride star‐like polymers were synthesized under mild conditions. The transfer of the reaction conditions to coupling reactions between end functionalized polystyrene‐block‐poly[styrene‐co‐(butyl acrylate)] copolymers showed that star‐like polymers with more than 12 arms were formed using boron trifluoride as activating agent.
To address the issue of the aggregation in second-order nonlinear optical (NLO) polymers we developed an approach based on the synthesis of a multifunctional macromolecular chain transfer agent. The controlled monomer insertion polymerization into the main chain by a ‘reversible addition-fragmentation chain transfer’ (RAFT) mechanism allows the spatial arrangement of the NLO chromophores along the polymeric chain in order to obtain sequence-ordered polymers. In a first step, a novel trithiocarbonate based macroinitiator containing the disperse red 19 (DR19) units in the main chain was synthesized by polycondensation; in a second step, this polymeric precursor was applied to the synthesis of a sequentially ordered polymer by controlled insertion radical polymerization of styrene. Size exclusion chromatography (SEC), nuclear magnetic resonance (NMR) data revealed that, (i) for the first time, polystyrenes (PS) bearing DR19 dyes covalently bounded were obtained, and (ii) both the insertion reaction and the length of the polystyrene segments were accurately controlled. Whatever the incorporated dye amount, all the copolymers were soluble in common solvents. Second-order optical nonlinearity in corona-poled thin films was evaluated, and second harmonic coefficients up to 80 pm/V were determined for loading ratio lower than 10 wt-% (DR19/PS). This approach opens up opportunities for the incorporation of more efficient chromophores even in apolar matrices. 相似文献
Reversible addition-fragmentation chain transfer (RAFT) polymerizations of styrene in bulk at 80 °C using tri-, tetra-, and hexafunctional trithiocarbonates, in which the active RAFT groups are linked to the core via the stabilizing Z-group, were studied in detail. These Z-RAFT star polymerizations of styrene showed excellent molecular weight control up to very high monomer conversions and star sizes of more than 200 kDa. The application of high pressure up to 2600 bar was found to significantly increase the relative amount of living star polymer. Not even at very high monomer conversions and for large star molecules, a shielding effect of growing arms hampering the RAFT process could be identified. Absolute molecular weights of star polymers using a conventionally calibrated SEC setup were determined with high precision by using a mixture of linear and star-shaped RAFT agents. When using phenylethyl as the leaving R-group, well-defined star polymers that perfectly match the theoretical predictions were formed. However, when using benzyl as the leaving group, a pronounced impact of monomer conversion on the star polymer topology was observed and pure star polymers with the expected number of arms could not be obtained. 相似文献
The novel trifunctional reversible addition-fragmentation chain transfer (RAFT) agent, tris(1-phenylethyl) 1,3,5-triazine-2,4,6-triyl trithiocarbonate (TTA), was synthesized and used to prepare the three-armed polystyrene (PS3) via RAFT polymerization of styrene (St) in bulk with thermal initiation. The polymerization kinetic plot was first order and the molecular weights of polymers increased with the monomer conversions with narrow molecular weight distributions (Mw/Mn ≤ 1.23). The number of arms of the star PS was analyzed by gel permeation chromatography (GPC), ultraviolet visible (UV-vis) and fluorescence spectra. Furthermore, poly(styrene-b-N-isopropylacrylamide)3 (PS-b-PNIPAAM)3, the three-armed amphiphilic thermosensitive block copolymer, with controlled molecular weight and well-defined structure was also successfully prepared via RAFT chain extension method using the three-armed PS obtained as the macro-RAFT agent and N-isopropylacrylamide as the second monomer. The copolymers obtained were characterized by GPC and 1H nuclear magnetic resonance (NMR) spectra. The self-assembly behaviors of the three-armed amphiphilic block copolymers (PS-b-PNIPAAM)3 in mixed solution (DMF/CH3OH) were also investigated by high performance particle sizer (HPPS) and transmission electron microscopy (TEM). Interestingly, the lower critical solution temperature (LCST) of aqueous solutions of the three-armed amphiphilic block copolymers (PS-b-PNIPAAM)3 decreased with the increase of relative length of PS in the block copolymers. 相似文献
Summary Dendritic star poly(L-lactide)s (PLLAs) were prepared by ring opening polymerization using a hyperbranched aliphatic polyester
as the core. The stars were characterized by gel permeation chromatography (GPC) and nuclear magnetic resonance spectroscopy
(NMR). The result shows the star PLLAs have narrow molecular weight distribution and the length of arms can be well controlled
in terms of the molar ratios of L-lactide to the initiator. The structure and thermal properties of the star polymers were
investigated by means of X-ray diffraction (XRD) and differential scanning calorimetry (DSC). XRD shows that the formation
of star structure does not alter the structure of crystal of PLLA. The results of DSC indicate that the glass transition temperature
(Tg) and the crystallinity of the star polymers increased with increasing the lengths of arms. It is identified that the crystallization
of PLLA was effectively suppressed by the formation of star topology. 相似文献
A series of four arm stars with copolymer arms composed of poly(tert-butyl-glycidylether)-b-polyglycidol were prepared using a multi-step process based on anionic ring-opening polymerization. Control of the length of the arms and the number of functional (hydroxyl) reactive groups was achieved by anionic polymerization. Stars with molar masses up to 12200 g/mol were prepared. The amphiphilic character of the star structure was varied using different polyglycidol block lengths. The star structure and molar mass of the obtained stars were characterized by SEC-MALLS and NMR spectroscopy.The temperature behavior of an aqueous solution of the obtained polymers was also investigated. The phase transition temperature was strongly dependent on the hydrophilic-hydrophobic balance of the star structure and varied in the range of 25-59 °C. As shown by DLS and SEM, the stars formed temperature-sensitive spherical aggregates in aqueous solution. The aggregates may be used for controlled transport and release of active compounds. 相似文献
A facile synthetic strategy for well-defined multiblock copolymers utilizing ‘living’ free-radical polymerization macroinitiator has been presented. Polyurethane composed of alkoxyamine initiating units and poly(tetramethylene oxide) (PTMO) segments was prepared by polyaddition of tolylene 2,4-diisocyanate terminated PTMO with an alkoxyamine-based diol. Polymerization of styrene with the polyurethane macroinitiator was carried out under nitroxide-mediated free-radical polymerization (NMRP) condition. GPC, NMR, and IR data revealed that the polymerization was accurately controlled and well-defined polystyrene chains were inserted in the main chain of macroinitiator to give the poly(tetramethylene oxide)-b-polystyrene multiblock copolymers. The synthesized multiblock copolymers were characterized by tensile test, differential scanning calorimetry, and dynamic mechanical analysis. Mechanical properties of the multiblock copolymers can be tuned by the sufficient molecular weight control of PS chains. Soft segment of PTMO and hard segment of PS were apparently compatible due to the multiblock structure of low molecular weight segments and polar urethane groups. 相似文献
An alternative approach to the synthesis of well-defined star polymers with hetero-arms was described. An azide-functionalized dithioester chain transfer agent (CTA-N3) was designed and synthesized. Using CTA-N3 as the reversible addition-fragmentation chain transfer (RAFT) agent, styrene was polymerized in a controlled manner. The so-obtained polystyrene showed a high proportion of azide-functionalized chains (PS-N3, about 92%). The azide end-capped PS-N3 could be assembled, via click reaction with a bromide-containing trialkyne coupling agent, to form a 3-arm star polystyrene (PS3-Br) with a narrow molecular weight distribution. PS3-Br could further serve as a macro-initiator for the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA). Accordingly, well-defined star polymers containing three polystyrene and one poly(methyl methacrylate) (PMMA) arms, and with a narrow molecular weight distribution, were successfully prepared. 相似文献