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1.
In the present work, we have demonstrated a facile approach to increase the luminescence of the poly (p-phenylenevinylene)s via controlling the molecular aggregates induced by pi-stacking. We have synthesized new bulky tricyclodecane (TCD) substituted PPVs: poly(2-methoxy-5-tricyclodecanemethyleneoxy-1,4-phenylenevinylene) (MTCD-PPV), poly(bis-2,5-tricyclodecanemethyleneoxy-1,4-phenylenevinylene) (BTCD-PPV), and a series of symmetrically substituted bulky PPV copolymers (P-1-P-7) covering the entire composition range from 0 to 100 mol %. The structures of the monomers and polymers were confirmed by 1H NMR and FTIR, and the molecular weights were determined by gel permeation chromatography. The composition analysis by NMR revealed that the bulky monomer was highly reactive and the incorporation of bulky units in MEH-PPV increased irrespective of the feed ratio. The polymers possess good solubility, high molecular weights, good thermal stability, and so forth. The molecular weights of the PPV copolymers were also significantly affected by the bulky substitution: the higher the incorporation of bulky units, the lower the molecular weight. The absorption and emission studies revealed that there was no influence on the MEH-PPV by TCD substitution in solution whereas in the solid state the photoluminescence intensity of PPV increased more than 10 times. The luminescence increase in PPV was observed throughout the entire bulk and was not confined to any particular domain in the polymer. The bulky PPV copolymers showed that both the luminescence intensity (in film) and quantum yields (in solution) increased with an increase in the extent of BTCD incorporation in the MEH-PPV and attained a maximum for 50% BTCD. The TCD unit has thus proved to be an efficient bulky susbstituent for PPV as it controls the pi-stack-induced molecular aggregates in the polymer chains by increasing the interchain distances. The new bulky PPV copolymers are highly soluble, thermally stable, and highly luminescent besides being economically cheap compared to the other materials reported so far for the bulkier approach in pi-conjugated materials.  相似文献   

2.
李永胜  李弘  何炳林 《化学学报》2002,60(8):1485-1489
首次报道以自制氯乙酸降冰片烯甲酯(NMCA)为引发剂的苯乙烯、甲基丙烯酸 甲酯的原子转移自由基(ATRP)本体聚合。详细考察了单体转化与反应时间、产物 分子量及分子量分布间的关系。研究发现,此引发引发甲基丙烯酸甲酯ATRP反应所 得聚合物的分子量分布较宽(PDI = 1.80~2.45),且实测值(GPC)与理论值偏差 较大。而NMCA引发的苯乙烯的ATRP反应可得分子量分布较窄(PDI = 1.54)、实验 值(GPC)与理论值基本吻合的产物。单体转化率随反应时间的变化及产物分子量 随单体转化率变化研究证明这一聚合反应具有活性聚合反应特征。产物的NMR分析 证明所合成产物分子中降冰片烯环上双键未参与聚合反应。  相似文献   

3.
The role of pi-stack induced molecular aggregation on solution and solid-state luminescent properties was investigated for the tricyclodecane substituted bulky (p-phenylenevinylene)s (BTCD-60, with 60% bulky group), oligophenylenevinylenes (MEH-OPV and BTCD-OPV)s, and their polymer-oligomer binary blends. The natures of the solvent, concentration, solvent combinations (good or bad), and temperature were employed as stimuli to probe the origin of the molecular aggregates in bulky conducting polymers. Absorption, photoluminescence (PL), and time-resolved fluorescence spectroscopic techniques were employed as tools to trace aggregation in solvents such as toluene, tetrahydrofuran (THF), THF and methanol, or THF and water as well as in the solid state. The absorbance spectra of poly(2-methoxy-5-(2-ethylhexyloxy))-1,4-phenylenevinylene (MEH-PPV) and BTCD-60 indicated that the films obtained from polymers that were dissolved in aromatic solvents such as toluene were found to possess more pi-stacking as compared to that of films obtained from a good solvent such as THF. The solid-state emission spectrum of BTCD-60 was found to show almost a 5-6 times enhancement in PL intensity as compared to that of MEH-PPV. Concentration dependent excitation spectra of the polymers confirmed the presence of aggregated polymer chains in MEH-PPV, which is the main reason for the quenching of luminescence intensity in the polymer. Solvent induced aggregation studies of polymers in THF and methanol mixture further supports the existence of strong aggregation in MEH-PPV as compared to that of bulky BTCD-60. Variable temperature absorption studies confirmed the reversibility of molecular aggregation on heating/cooling cycles, and the extent of aggregation was found more in MEH-PPV chains as compared to that of BTCD-60. MEH-PPV/OPV binary blends were prepared in the entire composition range from 0 to 100% via solution blending techniques. Through selective PL excitation techniques, the effect of oligomer-to-polymer energy transfer and also luminescent enhancement in MEH-PPV via interchain separation were investigated. Both the energy transfer and the interchain separation were found to be more effective on the enhancement of luminescence properties in the BTCD blends as compared to that of MEH blends. Time-resolved fluorescence studies confirmed the existence of two types of species corresponding to the free and aggregated chains in the polymer matrix with lifetimes in the range of 0.5-2.0 ns. In the present investigation, we have successfully shown that the molecular aggregation of the pi-conjugated polymers, oligomers, and their binary blends can be controlled via suitable bulky substitution to tune their emission properties in solution as well as in the solid state.  相似文献   

4.
A monomer design having a bulky terminal tricyclodecane (TCD) unit linked via hydrogen bondable urethane to an ethyleneoxy methacrylate unit, and capable of generating three‐dimensional honeycomb patterns upon solvent casting has been investigated. Random copolymers as well as a diblock copolymer Poly(Sty42b‐TCD18) of this monomer with styrene were prepared by free‐radical polymerization route and atom transfer radical polymerization (ATRP) route. Morphology characterization was carried out using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. Particle size was measured by dynamic light scattering measurements (DLS). Irrespective of the wide differences in molecular weight and polydispersity index values, the random copolymers having TCD content >30 mol % were found to form microporous films upon solvent casting from a THF/water 9:1 solvent combination. The amount of TCD in the copolymer was found to have an influence on the pore size formed. The diblock copolymer formed microspheres ~200 nm in diameter. The thermal properties of all the polymers were studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), and the copolymers were found to have good thermal stability. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1278–1288, 2008  相似文献   

5.
A series of poly(N‐(ω′‐alkylcarbazoly) methacrylates) tris(bipyridine) Ru‐centered bifunctional polymers with good filming, thermal, and solubility properties were synthesized and characterized. Atom transfer radical polymerization (ATRP) of N‐(ω′‐alkylcarbazoly) methacrylates in solution was used, where Ru complexes with one and three initiating sites acted as metalloinitiators with NiBr2(PPh3)2 as a catalyst. ATRP reaction conditions with respect to polymer molecular weights and polydispersity indices (PDI) of the target bifunctional polymers were examined. Electronic absorption and emission spectra of the resultant functional polymers provided evidence of chromophore presence within a single polymeric chain. The thermal properties of all polymers were also investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), and these analyses have indicated that these polymers possess higher thermal stabilities than poly(methyl methacrylate) (PMMA) obtained via free radical polymerization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6057–6072, 2005  相似文献   

6.
Linear (co)polymers and dimethacrylate‐end‐linked polymer networks of methyl methacrylate with 2‐(dimethylamino)ethyl methacrylate, cleavable in the middle of the polymer chain, either under thermolysis or alkaline hydrolysis conditions, were prepared via atom transfer radical polymerization (ATRP) using a specially designed bifunctional degradable initiator. This initiator was 2,6‐pyridinediethanol di(2‐bromo‐2‐methyl propanoate) (PyDEDBrMeP), bearing two 2‐(pyridin‐2‐yl)ethyl ester moieties, known for their thermal and hydrolytic (alkaline conditions) lability. As a control, a more stable bifunctional ATRP initiator, 2,6‐pyridinedimethanol di(2‐bromo‐2‐methyl propanoate) (PyDMDBrMeP), was also synthesized together with the corresponding linear polymers and polymer networks prepared from it. Thermal or hydrolytic treatment of the polymers prepared using PyDEDBrMeP led to a reduction in the molecular weights of the linear polymers by a factor of two, and to the conversion of the polymer networks to soluble branched (star) structures, consistent with the expected cleavage of the initiator residue located in the middle of the polymer chain. Thermal treatment of the polymers prepared using PyDMDBrMeP did not affect their molecular weight due to the thermal stability of the (pyridin‐2‐yl)methyl ester group, while treatment under alkaline hydrolysis conditions resulted in complete cleavage, similar to the PyDEDBrMeP‐prepared polymers. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2342–2355  相似文献   

7.
Independent one-, two-, and even three-dimensional nets interpenetrate each other in many solid-state structures of polymeric, hydrogen-bonded nets and coordination polymers. For example, the interpenetration of the adamantane units of two diamondlike nets is shown on the right. A detailed and systematic examination of many interpenetrating nets of this kind is made, and implications for crystal engineering are discussed.  相似文献   

8.
A general new route to well-defined polymeric Lewis acids via borylation of silylated polymers is reported. Trimethylsilylated polystyrene (PS-Si) of controlled molecular weight and low polydispersity (PDI < 1.15) was obtained via atom transfer radical polymerization (ATRP) of 4-(trimethylsilyl)styrene. The functional polymer PS-Si was quantitatively borylated using BBr3 to give poly(4-dibromoborylstyrene) (PS-B), a novel soluble boron-containing polymeric Lewis acid. PS-B readily reacted with nucleophiles serving as a precursor to a family of new polymers with boron centers of variable Lewis acidity. Reaction of PS-B with Cu(C6F5) gave the highly Lewis acidic polymer poly[4-bis(pentafluorophenyl)borylstyrene], the first polymeric analogue of tris(pentafluorophenyl)borane.  相似文献   

9.
Ambient temperature atom transfer radical polymerization (ATRP) of methyl acrylate (MA), methyl methacrylate (MMA) and styrene (Sty) in the presence of polar solvents (dimethyl sulfoxide: DMSO, dimethylformamide: DMF and acetonitrile: MeCN) with a mixed transition metal catalyst system (Fe(0) as initial activator and CuBr2/Me6TREN complex as deactivator) provides a rapid synthesis of polymers with very low polydispersity (PDI) values and predetermined molecular weights. The polymethylacrylate (PMA) prepared using this novel approach contains the Br-terminated chain ends (functionality ∼100%) and can be successfully used for block copolymer synthesis (as demonstrated on the chain extension experiment performed using the PMA–Br macroinitiator). The key elementary reactions involved in this novel ATRP system and some preliminary mechanistic aspects of the process are also discussed.  相似文献   

10.
The strong dimerizing, quadruple hydrogen-bonding ureido-pyrimidone unit is used to obtain reversible polymer networks. A new synthetic route from commercially available starting materials is described. The hydrogen-bonding ureido-pyrimidone network is prepared using 3(4)-isocyanatomethyl-1-methylcyclohexyl-isocyanate (IMCI) in the regioselective coupling reaction of multi-hydroxy functionalized polymers with isocytosines. 1H- and 13C-NMR, IR, MS, and ES-MS analysis, performed on a model reaction using butanol, demonstrated the formation of the hydrogen-bonding ureido-pyrimidone unit in a yield of more than 95%. The well-defined, strong hydrogen-bonding ureido-pyrimidone network is compared with a traditional covalently bonded polymer network, a multi-directional hydrogen-bonded polymer network based on urea units, and a reference compound. The advantage of the reversible, hydrogen-bonded polymer networks is the formation of the thermodynamically most favorable products, which show a higher “virtual” molecular weight and shear modulus, compared to the irreversible, covalently bonded polymer network. The properties of the ureido-pyrimidone network are unique; the well-defined and strong dimerization of the ureido-pyrimidone unit does not require any additional stabilization such as crystallization or other kinds of phase separation, and displays a well-defined viscoelastic transition. The ureido-pyrimidone network represents the first example of a truly reversible polymer network showing these features. Furthermore, the ureido-pyrimidone dimerization is strong enough to construct supramolecular materials possessing acceptable mechanical properties. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3657–3670, 1999  相似文献   

11.
An "S"-shaped chiral motif of a p-xylylene-bridged bis(cyclic dipeptide) (1), having four hydrogen-bonding amide functionalities, formed a homochiral supramolecular polymer in solution. X-ray crystallography of a slightly modified version of 1 for an enhanced crystallinity showed one-dimensional columnar assemblies via four double hydrogen-bonding interactions. Model studies with half-protected analogues of 1 indicated a nearly perfect enantioselectivity in hydrogen-bonding dimerization. When 1 was not racemic but enriched in either of the enantiomers, a supramolecular polymer with a bimodal molecular weight distribution resulted, due to the formation of two homochiral polymers with different molecular weights. By taking advantage of this, separation of optically pure 1 from an enantiomerically unbalanced mixture was possible by means of size-exclusion chromatography.  相似文献   

12.
The polymerization of MMA, at ambient temperature, mediated by dansyl chloride is investigated using controlled radical polymerization methods. The solution ATRP results in reasonably controlled polymerization with PDI < 1.3. The SET‐LRP polymerization is less controlled while SET‐RAFT polymerization is controlled producing poly(methyl methacrylate) (PMMA) with the PDI < 1.3. In all the cases, the polymerization rate followed first order kinetics with respect to monomer conversion and the molecular weight of the polymer increased linearly with conversion. The R group in the CTAs do not appear to play a key role in controlling the propagation rate. SET‐RAFT method appears to be a simpler tool to produce methacrylate polymers, under ambient conditions, in comparison with ATRP and SET‐LRP. Fluorescent diblock copolymers, P(MMA‐b‐PhMA), were synthesized. These were highly fluorescent with two distinguishable emission signatures from the dansyl group and the phenanthren‐1‐yl methacrylate block. The fluorescence emission spectra reveal interesting features such as large red shift when compared to the small molecule. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012  相似文献   

13.
Versatile miktoarm three-arm star polymers, (polystyrene)(polyε-caprolactone)2 ((PS)(PCL)2), (PS-b-poly(n-butyl acrylate))(PCL-b-PS-b-poly(n-butyl acrylate))2 ((PS-b-PnBA)(PCL-b-PS-b-PnBA)2) and (PtBA-b-PS)(PCL-b-PtBA-b-PS)2 were synthesized via combination of atom-transfer radical polymerization (ATRP), functional group transformation technique and ring opening polymerization (ROP) using 1,1-dihydroxymethyl-1-(2-bromoisobutyryloxy)methyl ethane (DHB) as a heterofunctional initiator. In the synthesis of (PS)(PCL)2 by combination of ROP of ε-caprolactone (ε-CL) and ATRP, the implementation sequence, ROP followed by ATRP, was proved to be effective to get a well-defined miktoarm star polymer than the reverse one. The two miktoarm star block polymers, (PS-b-PnBA)(PCL-b-PS-b-PnBA)2 and (PtBA-b-PS)(PCL-b-PtBA-b-PS)2, were prepared by one ROP step, one group transformation and ATRP steps using the same initiator. All the polymers have defined structures and their molecular weights are adjustable with good controllability.  相似文献   

14.
A new series of symmetrically substituted bulky PPV‐copolymers based on poly(bis‐2,5‐(2‐ethylhexyloxy)‐1,4‐phenylenevinylene) ( BEH‐PPV ) bearing tricyclodecane (TCD) pendants were synthesized to study the effect of chain aggregation in the π‐conjugated polymer backbone. The composition of the copolymers was varied up to 100 mol % and the structures of the copolymer were confirmed by NMR and FTIR. The molecular weights of the copolymers were obtained as Mw = 11,500–1,78,800 depending on the TCD‐incorporation in BEH‐PPV. The origin of the π‐aggregation was investigated using mixture of solvents (polar or nonpolar) or temperature as external stimuli. Absorption, photoluminescence, and time‐resolved fluorescence decay techniques were employed as tools to trace molecular aggregation in solution and solid state. The TCD‐substituted bulky copolymers showed almost twice the enhancement in photoluminescence compared with that of BEH‐PPV . Solvent‐induced aggregation studies of copolymers revealed the existence of strong molecular aggregation in BEH‐PPV compared with that of bulky copolymers. Variable temperature studies further evidence for the reversibility of molecular aggregation on heating/cooling cycles and showed isosbetic points with respect to free and aggregated polymer chains. Time‐resolved fluorescent studies confirmed the existence of free and aggregated π‐conjugated species with a life time of 0.1 to 1.0 ns. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2631–2646, 2009  相似文献   

15.
The combination of atom transfer radical polymerization (ATRP) and click chemistry has created unprecedented opportunities for controlled syntheses of functional polymers. ATRP of azido‐bearing methacrylate monomers (e.g., 2‐(2‐(2‐azidoethyoxy)ethoxy)ethyl methacrylate, AzTEGMA), however, proceeded with poor control at commonly adopted temperature of 50 °C, resulting in significant side reactions. By lowering reaction temperature and monomer concentrations, well‐defined pAzTEGMA with significantly reduced polydispersity were prepared within a reasonable timeframe. Upon subsequent functionalization of the side chains of pAzTEGMA via Cu(I)‐catalyzed azide‐alkyne cycloaddition (CuAAC) click chemistry, functional polymers with number‐average molecular weights (Mn) up to 22 kDa with narrow polydispersity (PDI < 1.30) were obtained. Applying the optimized polymerization condition, we also grafted pAzTEGMA brushes from Ti6Al4 substrates by surface‐initiated ATRP (SI‐ATRP), and effectively functionalized the azide‐terminated side chains with hydrophobic and hydrophilic alkynes by CuAAC. The well‐controlled ATRP of azido‐bearing methacrylates and subsequent facile high‐density functionalization of the side chains of the polymethacrylates via CuAAC offers a useful tool for engineering functional polymers or surfaces for diverse applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1268–1277  相似文献   

16.
Methyl methacrylate (MMA) and styrene (St) have been radically polymerized in the presence of chlorotrimethylsilane and CuCl/N,N,N′,N″,N″-pentamethyldiethyltriamine (Me3SiCl/CuCl/PMDETA). An analysis of the resultant polymers by 1H NMR discloses terminal silyl group and chlorine atom in all the obtained polymers. Kinetics studies have been carried out by measuring monomer conversions and polymer molecular weights against polymerization time. The results indicate that, for both MMA and St polymerizations, the monomer conversions exhibit a quasi-linear relationship with polymerization time, and the polymer number-average molecular weight (Mn) also increases with monomer conversion. The molecular weights of both PS and PMMA exceed one hundred thousand. Regardless of molecular weight, all the polymers show narrow molecular distributions (Mw/Mn = 1.2-1.5). These polymerization reactions are speculated to follow a mechanism similar to that of atom transfer radical polymerization (ATRP).  相似文献   

17.
We discovered that ultrafast cyclopolymerization of 1,6-heptadiyne derivatives reached completion in 1 min using a third-generation Grubbs catalyst. After optimization, this superior catalyst selectively produced conjugated polymers having a five-membered-ring structure with excellent molecular weight control and narrow polydispersity index (PDI). This living polymerization allowed us to prepare fully conjugated diblock copolymers with narrow PDIs. Lastly, this catalyst was active enough to polymerize macromonomers with G-3 dendrons in a living manner as well. This dendronized polymer with a highly regioregular polymer backbone and bulky dendrons was visualized by atomic force microscopy, which revealed the structure of a single molecular wire surrounded by insulating dendrons.  相似文献   

18.
Coordination polymerization of renewable 3‐methylenecyclopentene has been investigated for the first time using rare‐earth metal‐based precursors bearing various bulky ligands. All the prepared complexes catalyze controllable polymerization of 3‐methylenecyclopentene into high molecular weight polymers, of which the NPN‐ and NSN‐tridentate non‐Cp ligated lutetium‐based catalytic systems exhibited extremely high activities up to 11 520 kg/(molLu⋅h) in a dilute toluene solution (3.2 g/100 mL) at room temperature. The resultant polymers have pure 1,4‐regioregularity (>99 %) and tailorable number average molecular weights (1–20×104) with narrow molecular weight distributions (polydispersity index (PDI)=1.45–1.79). DFT simulations were employed to study the polymerization mechanism and stereoregularity control.  相似文献   

19.
Branched polystyrenes have been synthesized using atom transfer radical polymerization (ATRP) of styrene in the presence of divinyllbenzene (DVB) as branching comonomer. The synthesis was completed via facile one pot approach. Mole ratio of styrene to DVB in range of 5:1-30:1 was employed to obtain soluble polymers. The kinetics of the polymerization and evolution of polymer compositions were revealed by determining the conversions of reactants by gas chromatography (GC). The growth of molecular weight was monitored by GPC and the results indicate that the branched polymers were formed by self-condensing vinyl polymerization (SCVP) of AB monomer or macromonomers. The branched structure of the resulting polymers was confirmed by the remarkable discrepancies of the weight average molecular weights determined by GPC and multi angle laser light scattering (MALLS). The specific viscosity of the resulting polymer is also much lower compared with that of linear analogues. The influence of dosage of initiator and catalyst on the yield and molecular weights of the resulting polymers was also investigated.  相似文献   

20.
This study investigates atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) using activators generated by electron transfer (AGET) as the initiation technique in an emulsion well‐mixed 2L stirred tank reactor. The performance of the AGET ATRP of MMA is analyzed for five key independent variables, namely temperature, catalyst complex (CuBr2/dNbpy), initiator (EBiB), reducing agent (ascorbic acid), and surfactant (Brij 98). The reaction is carried out based on a two‐step polymerization procedure. A resolution 5 fractional factorial design technique is employed to assess the influence of the five independent variables on the monomer conversion, polymer average molecular weights, and polydispersity index (PDI). An input–output model is constructed from the data of 21 designed experimental tests. A statistical analysis of the results shows that the temperature is the most influential variable for the three output process responses. The initiator strongly affects the poly(methyl methacrylate) (PMMA) molecular weights. It is the least important key variable affecting MMA conversion and PDI, and the surfactant is the least one affecting PMMA Mn. On assessing the independent interactions effect, the interactions of temperature‐surfactant on conversion, and temperature‐initiator for PMMA Mn are considered. Process simulation in 3D mapping has demonstrated that model predictions agree well with experimental data.  相似文献   

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