首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 16 毫秒
1.
Thermally cleavable multiarm star polymers containing thermo‐reversible furan–maleimide cycloadduct‐based core were synthesized using dendritic macroinitiators. Peripheries of dendritic macroinitiators were modified with bromine containing free radical initiators to obtain multiarm polymers by utilizing atom transfer radical polymerization (ATRP). Cleavage of thus obtained multiarm polymers was achieved via the retro Diels–Alder cycloreversion reaction of the furan–maleimide core at elevated temperatures. As an alternative approach, combination of multiarm polymers containing a furan and maleimide functional group at their core was attempted to realize that the steric bulk does not allow their formation. Hence the “grafting‐from” route using a thermally fragmentable trigger containing multiarm initiators provides a plausible methodology for fabrication of such thermally cleavable multiarm polymeric materials. Syntheses of dendritic initiators, formation of star polymers as well as their fragmentation were followed by proton nuclear magnetic resonance spectroscopy and size exclusion chromatography. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 885–893  相似文献   

2.
The carbosilane dendrimer of the fifth generation with the functional inner and nonfunctional outer shells in the molecular structure was synthesized for the first time. The efficiency of the hybrid scheme of carbosilane dendrimer synthesis based on the use of organomagnesium and organolithium reagents at different steps of molecular structure formation and hydrosilylation was shown.  相似文献   

3.
Azide end‐functionalized polyhedral oligomeric silsesquioxane (POSS‐N3) was incorporated into the periphery of well‐defined alkyne‐polystyrene50‐poly(divinyl benzene) (alkyne‐PS50‐polyDVB) and alkyne‐poly(tert‐butyl acrylate)43‐poly(divinyl benzene) (alkyne‐PtBA43‐polyDVB) multiarm star polymers via highly efficient azide‐alkyne click reaction, resulting in POSS‐PS50‐polyDVB and POSS‐PtBA43‐polyDVB multiarm star block copolymers respectively, in the solution of tetrahydrofuran/N,N‐dimethyl formamide, CuBr/N,N,N,N,N″‐pentamethyldiethylenetriamine (PMDETA) at room temperature for 24 h. Linear precursors and star polymers obtained in this study were characterized 1H NMR, gel permeation chromatography (GPC), and triple detection GPC (TD‐GPC). Absolute molecular weight, hydrodynamic radius, and intrinsic viscosity ([η]) values for all star polymers were determined by TD‐GPC. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010  相似文献   

4.
以氧化乙烯开环聚合为探针反应,考察了含噻二唑环的新型阴离子聚合引发剂(TDZ-K)的引发活性。反应在非均相中进行,分别用甲醇和甲基丙烯酰氯封端,得含双官能团的氧化乙烯聚合产物,其结构经IR,1H NMR,UV,VPO和GPC表征。加入乙酰丙酮,18-冠-6及PEO作助剂,有助于提高TDZ-K的引发活性。  相似文献   

5.
We report the synthesis of two 2nd generation dendritic terpolymers consisting of poly(butadiene) (PB) of 1,4 geometric isomerism, poly(isoprene) (PI) enriched in 3,4 geometric isomerism (at least 55% PI3,4) and polystyrene (PS). The main focus of this work was the synthesis of well‐defined dendritic terpolymers exhibiting high levels of molecular and compositional homogeneity. The preparation of these materials was achieved via anionic polymerization techniques in combination with chlorosilane linking chemistry. The molecular characterization of the intermediate products and the final dendritic materials was accomplished via gel permeation chromatography, membrane osmometry, differential scanning calorimetry, and 1H‐nuclear magnetic resonance spectroscopy, leading to the conclusion that they can be considered model polymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1567–1574, 2009  相似文献   

6.
Controlled one-step synthesis of a diblock copolymer   总被引:1,自引:0,他引:1  
Well-defined block copolymers were obtained from 4-hydroxy-butyl-2-bromoisobutyrate dual initiator, combining tert-butylmethacrylate ATRP and ε-caprolactone ROP in a one-step process. Using AlEt3 as coinitiator in a ROP catalytic process, the variation of the AlEt3/initiator ratio permits to modulate the ROP rate and so to control the final block copolymer composition. Nevertheless, slight interferences between the two polymerizations were observed.  相似文献   

7.
To optimize the reaction of ω-carbanionic styrene or butadiene/styrene polymers with ethoxysilane based compounds, the influence of several experimental parameters on the orientation of the functionalization reaction and its yield was examined. The resulting end-functionalized polymers were systematically investigated by SEC, 1H NMR and elementary analysis. The orientation of the reaction was found to be directly depending on the chemical nature of the chain end and / or on the type of additive (ethers, LiCl). Best results were obtained with tetraethoxysilane, provided the functionalization is conducted around 5°C, and the active chain end of isoprenyl type. These reactions were extended to bifunctional polymers, the reaction product of butyllithium with m-diisopropenylbenzene being used as an initiator. The efficiency of this initiator for the synthesis of well-defined bifunctionalized polydienes almost quantitatively fitted with three alkoxy functions at both chain ends was demonstrated. Some preliminary results on the mechanical properties of mixtures of functionalized polymers with silica were mentioned.  相似文献   

8.
曹靖 《高分子科学》2015,33(11):1618-1624
The anionic polymerization of N-vinylcarbazole(NVC) by using optically active anionic initiators such as the lithium salts of(S)-1-(9H-fluoren-2-yl)-4-isopropyl-4,5-dihydrooxazole((S)-1-FIDH) and(S)-2-(9H-fluoren-2-yl)-4-isopropyl-4,5-dihydrooxazole((S)-2-FIDH) and complexes of(-)-Sparteine with n-butylithium(n-Bu Li-(-)-Sp) or fluorenyl lithium(FILi-(-)-Sp) was achieved. The yield and specific rotation of poly(N-vinylcarbazole)s(poly(NVC)s) were considerably affected by the molar ratio of(S)-FIDH to NVC. The highest yield and specific rotation were obtained with Li-(S)-1-FIDH as an initiator, with a molar ratio of monomer and initiator [M]/[I] = 10/1. The effects of the chiral initiators, type of solvent and the polymerization temperature were investigated. The obtained optical activity of polymers was attributed to asymmetric induction of the chiral initiators.  相似文献   

9.
The copolymerizations of two series of surface functionalized bis(acetylene) G1–G3 dendrimers, one ( S ‐ Gn ) having a structural rigid skeleton and the other ( L ‐ Gn ) a relatively more flexible architecture, with two platinum linkers, cis‐[(Et2PCH2CH2PEt2)PtCl2] ( 2 ) and [Cl(Et3P)2Pt‐C?C‐p‐C6H4‐]2 ( 3 ) were investigated. For both series of dendrimers, only linear and/or cyclic oligomers were formed when the cis‐platinum linker 2 was used. However, high molecular weight (100–200 kD) organoplatinum poly(dendrimer)s were obtained from both series when the elongated linear rod‐liked platinum linker 3 was employed and the formation of cyclic oligomers was greatly suppressed for both the structural rigid S ‐ Gn and the structural flexible L ‐ Gn series. These results are in sharp contrast to our earlier findings (S.‐Y. Cheung, H.‐F. Chow, T. Ngai, X. Wei, Chem. Eur. J. 2009 , 15, 2278–2288) obtained by using a shorter linear platinum linker trans‐[Pt(PEt3)2Cl2] ( 1 ), where a larger amount of cyclic oligomers was formed from the structural flexible L ‐ Gn dendrimers. A model was proposed to rationalize how the geometry and size of the platinum linker could control the copolymerization behaviours of these dendritic macromonomers.  相似文献   

10.
The synthesis and characterization of four families of anionic carbosilane dendrimers bearing carboxylate, phosphonate, naphthylsulfonate, and sulfate terminal groups prepared by cycloaddition of azide–alkyne catalyzed by copper (CuAAC) are presented here. For the preparation of these anionic carbosilane dendrimers, two strategies starting from azide‐terminated carbosilane dendrimers were followed: (i) click coupling of neutral alkynes followed by derivatization into anionic moieties or (ii) click coupling of anionic alkynes. Both strategies require different reaction conditions in order to accommodate the different substrate polarities. These anionic dendrimers, in general, do not present cell toxicity in vitro until concentration up to 20 µM. Therefore, they can be used in inhibition experiments in concentrations below this limit. We have observed that dendrimers bearing phosphonate groups possess poor anti‐HIV capabilities in vitro in PBMCs, while carboxylate dendrimers can reduce HIV infection levels moderately. On the other hand, sulfate and naphthylsulfonate dendrimers are powerful anti‐HIV agents and their antiviral activity is generation and concentration dependent. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1099–1112  相似文献   

11.
We described the obtention of A2B star block copolymers through the use of a new heterotrifunctional initiator. That way, well‐defined (PCL)2‐arm‐PtBuMA and (PCL)2‐arm‐PS star block copolymers have been synthesized from a heterotrifunctional initiator bearing two hydroxyl groups able to initiate ROP of CL (with AlEt3 or Sn(Oct)2 as coinitiator) and a bromide function able to initiate ATRP of tBuMA or styrene. Firstly, we have proceeded using a sequential process (two‐steps), leading to an intermediate macroinitiator. Secondly, attempt to polymerize these two monomers in a simultaneous process (one‐step), that is directly from the mixture of monomers, initiator, coinitiators, and solvent, has been realized and has shown that some interferences between the two polymerizations occurred, leading to an inhibition of ATRP when Sn(Oct)2 was used and an unexpected increase in control when AlEt3 was used as catalyst for the ROP (obtention of well‐defined (PCL)2‐arm‐PtBuMA with pdi of 1.18). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1796–1806, 2006  相似文献   

12.
A novel dendritic polyisophthalate with 12 naphthyl groups at the chain ends was synthesized from 5‐hydroxyisophthalic acid as an AB2 monomer, 1,3,5‐benzenetricarbonyl trichloride as an ‘initiator core’ molecule, and β‐naphthol as an endcapping reagent, via a stepwise growth process. An average molecular weight of 2860 g mol?1, and a refractive index of 1.618 at 650 nm were obtained by gel permeation chromatography and ellipsometry, respectively. A photopolymerizable recording dry film incorporating this dendrimer as a polymeric binder was used for holographic recording. Diffraction gratings with diffraction efficiency exceeding 80%, together with a modulation index of 10?2 were obtained. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

13.
Persulfurated p-phenylene sulfide (PPS) molecular asterisks (6-9) from "generations" 1 to 4 were efficiently prepared. They represent a new class of electron-accepting PPS star-shaped nanomolecules. Spectroelectrochemistry, cyclic voltammetry and UV-visible studies were performed for the asterisks and for functionalized p-phenylene sulfide oligomers (1-4). These data confirmed for the first time that an electronic delocalization through the whole asterisk molecule exists in the radical anionic or dianionic forms, in spite of divalent sulfur bridges between phenyl groups. They could be seen as globular spheres with a three-dimensional electronic network and delocalization. Electrochemical studies indicated that sulfur substituents strongly stabilize the reduced form of the asterisk relative to coronene itself, and the ease of reduction depends on the PPS chain length.  相似文献   

14.
A novel heterofunctional initiator, synthesized from pentaerythritol in a three step reaction sequence with two ring opening polymerization (ROP) and two atom transfer radical polymerization (ATRP) initiating sites, was used to prepare A2B2 miktoarm star copolymers of poly(ε‐caprolactone), PεCL, with polystyrene, PS, poly(methyl methacrylate), PMMA, poly(dimethylaminoethyl methacrylate), PDMAEMA, and poly(2‐hydroxyethyl methacrylate), PHEMA. A2B miktoarm stars, A being PεCL or poly(δ‐valerolactone), PδVL and B PS were also prepared from ω,ω‐dihydroxy‐PS, synthesized from ω‐Br‐PS and serinol, by ROP of εCL or δVL. All polymers were characterized by size exclusion chromatography, 1H NMR spectroscopy, and membrane osmometry. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5164–5181, 2007  相似文献   

15.
16.
Well‐defined multiarm star copolymers, hyperbranched poly(glycidol)‐b‐poly(ε‐caprolactone), with an average of 100–110 arms per molecule and a molecular weight of arms of 3000 g/mol (PGOH‐b‐PCL30) and 1000 g/mol (PGOH‐b‐PCL10) were synthesized by cationic ring‐opening polymerization of ε‐caprolactone from a poly(glycidol) core and used to modify diglycidylether of bisphenol A formulations. The curing process, studied by dynamic scanning calorimetry, was only slightly retarded when PGOH‐b‐PCLx were added to the formulation. By rheometry, the effect of this new topology and the arm length on the complex viscosity (η*) and gelation of the reactive mixture was analyzed in detail. The addition of these new reactive modifiers decreases the global shrinkage and increases the conversion at gelation. In addition, the modified thermosets have an improved reworkability. The homogeneity of pure DGEBA and modified thermosets was proved by dynamic thermomechanical analysis and electronic microscopy (FESEM). Addition of star‐like structures led to a more toughened fracture of the thermoset in comparison to pure DGEBA. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011  相似文献   

17.
Let's stick together : The gelation ability of a dendritic gelator has been enhanced by its complexation with a polyelectrolyte (see figure). This concept provides a route to construct novel functional or ordered materials by complexation of other low‐molecular‐mass functional species with polyelectrolytes.

  相似文献   


18.
Synthesis of 2nd generation dendritic polymeric materials via anionic polymerization procedures in combination with chlorosilane chemistry, consisting either from one polydienic segment (homopolymers) or from two chemically different polydienic components (copolymers), is described. The polydienes used were poly(butadiene) (PB) with ∼90% 1,4-isomerism and poly(isoprene) (PI) with increased 3,4-isomerism (∼60%). Molecular characterization of intermediate products and the final dendritic materials was made with Gel Permeation Chromatography (GPC), Membrane and Vapour Pressure Osmometry (MO and VPO respectively), Gas Chromatography –Mass Spectroscopy (GC-MS) and 1H-Nuclear Magnetic Resonance (1H-NMR) Spectroscopy, leading to the conclusion that they can be considered model polymers. Morphological studies solely with Transmission Electron Microscopy (TEM) have been conducted on two of the four synthesized copolymer samples exhibiting microphase separation between the two polydiene segments.  相似文献   

19.
A ribbon‐shaped chiral liquid crystalline (LC) dendrimer with photochromic azobenzene mesogens and an isosorbide chiral center (abbreviated as AZ3DLC) was successfully synthesized and its major phase transitions were studied by using differential scanning calorimetry (DSC) and linear polarized optical microscopy (POM). Its ordered structures at different temperatures were further identified through structure‐sensitive diffraction techniques. Based on the experimental results, it was found that the AZ3DLC molecule exhibited the low‐ordered chiral smectic (Sm*) LC phase with 6.31 nm periodicity at a high‐temperature phase region. AZ3DLC showed the reversible photoisomerization in both organic solvents and nematic (N) LC media. As a chiral‐inducing agent, it exhibited a good solubility, a high helical‐twisting power, and a large change in the helical‐twisting power due to its photochemical isomerization in the commercially available N LC hosts. Therefore, we were able to reversibly “remote‐control” the colors in the whole visible region by finely tuning the helical pitch of the spontaneously formed helical superstructures.  相似文献   

20.
A method is presented for the synthesis of defined sparsely branched polystyrene‐based homopolymer model combs. By the use of poly(p‐methylstyrene) (PpMS) as backbone and side chains, a low, but well controlled amount of branching of typically less than 1 mol‐% (e.g., 1 branch per approx. 200 backbone C‐atoms) can be achieved. The used anionic synthesis offers full control of the molecular weight in combination with low polydispersity. Molecular weight and polydispersity were determined by SEC‐MALLS, confirming the well defined synthesis with low polydispersity ( < 1.07). The melt rheological properties of the synthesized linear and comb polymers were obtained in both oscillatory shear and uniaxial extensional flow. Using the so‐called van Gurp–Palmen plot, clear differences between both synthesized topologies are clearly seen. The appearance of a second minimum for lower values of the complex modulus in shear is a clear indication of a second relaxation process attributable to the entangled side chains. The presence of the entangled side chains is responsible for the observed strain hardening obtained in extensional viscosity experiments, as compared to the linear polymers. These model samples open up the possibility to compare different advanced rheological methods, e.g., FT‐rheology or extensional rheology, towards limiting sensitivity.

  相似文献   


设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号