The solution polymerization of 4‐bromomethylpyridine ( M1 ) and 3‐bromomethyl pyridine hydrobromides ( M2 ) was studied by NMR spectroscopy. A mechanism involving a series of bimolecular reactions of the monomer, dimer, and higher oligomers closely fits with the experimental variations of bromomethyl end group concentrations with time. M1 presents a higher reactivity than M2 and an unusual behavior, since the oligomers are more reactive than the monomer. An explanation based on a mesomeric phenomenon is proposed. The influence of the anion on the solubility and thermal stability of the poly(methylenepyridinium)s were studied after various anion exchanges. Bis(trifluoromethylsulfonyl)imide anion ( Tf 2 N ) yielded the more stable and the more organosoluble polymers.
The accurate characterization of molar‐mass distributions of poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA) by size‐exclusion chromatography (SEC) is addressed. Two methods are employed: direct aqueous‐phase SEC on P(M)AA and THF‐based SEC after esterification of P(M)AA to the associated methyl esters, P(M)MA. P(M)AA calibration standards, P(M)AA samples prepared by pulsed‐laser polymerization (PLP), and PAA samples prepared by reversible addition‐fragmentation chain transfer (RAFT) are characterized in a joint initiative of seven laboratories, with satisfactory agreement achieved between the institutions. Both SEC methods provide reliable results for PMAA. In the case of PAA, close agreement between the two SEC methods is only observed for samples prepared by RAFT polymerization with weight‐average molar mass between 80 000 and 145 000 g mol?1 and for standards with peak molar masses below 20 000 g mol?1. For standards with higher molar masses and for PLP‐prepared PAA, the values from THF‐based SEC are as much as 40% below the molar masses determined by aqueous‐phase SEC. This discrepancy may be due to branching or degradation of branched PAA during methylation. While both SEC methods can be recommended for PMAA, aqueous‐phase SEC should be used for molar‐mass analysis of PAA unless the sample is not branched.
A new hyperbranched poly(phenylene oxide) was synthesized from a simple AB2 type monomer, 3,5‐dibromophenol, by Ullmann polycondensation. The bromo‐terminated hyperbranched poly(phenylene oxide) was amorphous (Tg = 120 °C), but showed high thermal stability (T5d = 480 °C in nitrogen). The polymer with the degree of branching of 0.61 showed good solubility in organic solvents. The highly branched nature of the polymer effectively disrupted the crystalline characteristics of the linear poly(phenylene oxide) (Tm = 285 °C). When the bromine end groups of the polymer were transformed to lithium carboxylate groups, the resulting polymer became soluble in water. This carboxylate‐terminated hyperbranched poly(phenylene oxide) showed the characteristics of an unimolecular micelle in aqueous solution and behaved as a host for nonpolar organic guest molecules such as 1,4‐diaminoanthraquinone even under the critical micelle concentration of conventional surfactants.
DSC and TGA curves of the hyperbranched poly(phenylene oxide) 2 . 相似文献
Multiarm star copolymers consisting of the polyether‐polyol hyperbranched poly(ethylene glycol) (hbPEG) as core and poly(L ‐lactide) (PLLA) arms are synthesized via the organobase‐ catalyzed ring‐opening polymerization of lactide using hbPEG as a multifunctional macroinitiator. Star copolymers with high molecular weights up to 792 000 g mol?1 are prepared. Detailed 2D NMR analysis provides evidence for the attachment of the PLLA arms to the core and reveals that the adjustment of the monomer/initiator ratio enables control of the arm length. Size exclusion chromatography measurements show narrow molecular weight distributions. Thermal analysis reveals a lower glass transition temperature, melting point, and degree of crystallization for the star‐shaped polylactides compared to linear polylactide. 相似文献
Summary: Three hyperbranched poly(ε‐caprolactone)s were prepared with the architectural variation in the length of linear backbone segments consisting of 5, 10, and 20 ε‐caprolactone units (accordingly given the names HPCL–5, –10, and –20, respectively) and in the number of branching points as characterized by 1H NMR end group analyses. The non‐isothermal crystallizations of HPCLs and LPCL were performed using DSC at various cooling rates and the kinetic study was further performed by using both Ozawa and Kissinger methods. All the kinetic parameters such as the cooling functions and the apparent activation energy of crystallization indicated that HPCLs with longer linear segments and fewer number of branching points showed faster crystallization rates, whereas LPCL exhibited an intermediate rate between HPCL–10 and HPCL–20, i.e., HPCL–5 < HPCL–10 < LPCL < HPCL–20. The decrease in the crystallization rate is attributed to the presence of heterogeneous branching points in HPCLs with shorter segments, which hinders the regular chain packing to crystallize. In addition, the faster crystallization of HPCL–20 compared to LPCL was associated with the higher cooperative chain mobility in the melt.
A novel AB2‐type blocked isocyanate monomer was synthesized which was de‐blocked to provide a hyperbranched poly(aryl ether urethane). Copolymerization of this monomer with a functionally similar AB monomer yielded polymers with molecular weights in the range 8.0–310 kDa with a DB of 41–59% that underwent two‐stage decomposition above 200 °C. The inherent viscosities of the polymers in DMF ranged from 0.09 to 1.10 dL · g?1. End‐group modification of hyperbranched poly(aryl ether urethane)s was carried out with PEG monomethyl ether and 1‐decanol and affected the thermal properties and solubilities of the polymers. Tg of the polymers was reduced significantly from 201 to 71 °C upon incorporation of AB monomer in the copolymerization.
Poly(propylene)s were prepared with metallocene catalyst rac‐SiMe2(2‐Me‐4‐PhInd)2ZrMe2/MAO (rac‐dimethylsilylbis(2‐methyl‐4‐phenylindenyl)dimethylzirconium/methylaluminoxane) in heptane solution at temperatures from 50 to 80 °C with varying concentrations of monomer, hydrogen, triisobutylaluminium (TIBA) and MAO. Polymer molar mass depended on the monomer, MAO, TIBA, and hydrogen concentrations and on polymerization temperature. The isotacticity was very high (mmmm > 95%), and only a slight decrease was detected at high temperatures. Regio selectivity was also high; the total amount of 2,1‐ and 3,1‐insertions was less than 0.4 mol‐%. Lowering the monomer concentration and raising the temperature increased the amount of 3,1 defects over the amount of 2,1 defects. End‐group analysis by 13C NMR spectroscopy revealed isobutyl and allyl end‐groups. Chain transfer to aluminium and β‐CH3 elimination were concluded to be the dominating chain‐termination mechanisms. The importance of β‐CH3 elimination increased with temperature. Hydrogen addition changed both the initiation and termination mechanisms as indicated by the presence of propyl, butyl and 2,3‐dimethylbutyl end‐groups. According to modeling studies, the molar mass follows a first‐order relationship with propylene and hydrogen concentrations, and a half‐order relationship with MAO concentration. Arrhenius‐type activation energy coefficients were 125 kJ · mol?1 for β‐CH3 elimination, 66 kJ · mol?1 for chain transfer to aluminium, and 53 kJ · mol?1 for chain transfer to hydrogen. A value of 45 kJ · mol?1 was used for the propagation.
New poly(urethane urea)s based on telechelic poly(methyl acrylate)s (PMAs) and different diisocyanates and diamines are prepared by a two‐step polyaddition process—formation of an isocyanate telechelic prepolymer followed by chain extension with a diamine to form the final poly(urethane urea)s. Hydroxyl‐telechelic or mixed amino‐hydroxyl‐telechelic PMAs are obtained by two different concepts: (i) according to the first concept methyl acrylate (MA) was polymerized by single electron transfer‐living radical polymerization (SET‐LRP) using 2‐hydroxyethyl 2‐bromoisobutyrate as initiator followed by nucleophilic substitution of the halogen end group with n‐butylamine, 2‐methylamino ethanol, or 3‐amino‐1‐propanol and (ii) according to the second concept after SET‐LRP under the same conditions the halogen end group is converted to an azide followed by a click reaction using sodium azide and propargyl alcohol in a one‐pot reaction. Applying the second concept, a hydroxyl‐functional PMA with a share of 83 mol% bifunctionality is obtained. This PMA‐diol is used in polyaddition reaction with different diisocyanates (isophorone diisocyanate (IPDI), 4,4′‐methylenebis(cyclohexyl isocyanate) (HMDI), and 4,4′‐methylenediphenyl diisocyanate (MDI)) resulting in an isocyanate‐telechelic prepolymer followed by chain extension with the corresponding diamines (isophorone diamine (IPDA), 4,4′‐methylenebis(cyclohexyl amine) (HMDA), and 4,4′‐methylenediphenyl diamine (MDA)). The polyurethane based on hydroxyl‐telechelic PMAs and IPDI/IPDA has a molecular weight of Mn = 44 500 g mol?1 and a dispersity ? = 3.5, respectively; those based on HMDI/HMDA and MDI/MDA have Mn = 24 600 g mol?1 and ? = 2.2 and Mn = 16 100 g mol?1 and ? = 2.0, respectively.
Summary: The blends of poly(hydroxyether sulfone) (PHES) with poly(N‐vinylpyrrolidone) (PVPy) were investigated by means of differential scanning calorimetry (DSC) and FTIR spectroscopy. The miscibility of the blend system was established on the basis of the thermal analysis results. DSC showed that the PHES/PVPy blends prepared by casting from N,N‐dimethylformamide (DMF) possessed single, composition‐dependent glass transition temperatures, indicating that the blends are miscible in the entire composition. The experimental glass transition temperatures have higher values than those calculated on the basis of additive behavior; the variation of the glass transition temperatures of the blends was accounted for by the Kwei equation. FTIR studies indicate that competitive hydrogen bonding interactions exist upon addition of PVPy to the system, which were involved in the self‐ and cross‐association, i.e., ? OH···O?S, ? OH···OH of PHES and ? OH···O?C< of PVPy. The FTIR spectra in the range of the sulfonyl stretching vibrations showed that the hydroxyl‐associated sulfonyl groups are partially “set free” upon addition of PVPy to the system. The IR spectroscopic investigation of both the model compounds and the PHES/PVPy blends suggests that the strength of the hydrogen bonding interactions in the blend system increases in the following order: ? OH···O?S, ? OH···OH and ? OH···O?C<.
Plot of glass transition temperature for PHES/PVPy blends as a function of weight fraction of PVPy. The prediction of the Kwei equation yields the values of k = 1 and q = 122. 相似文献
Four poly(N,N‐dimethylacrylamide)‐block‐poly(L ‐lysine) (PDMAM‐block‐PLL) hybrid diblock copolymers and two PLL homo‐polypeptides are prepared via ROP of ε‐trifluoroacetyl‐L ‐lysine N‐carboxyanhydride initiated by primary amino‐terminated PDMAM and n‐hexylamine respectively. The PLL blocks render the copolymers a multi‐responsive behavior in aqueous solution due to their conformational transitions from random coil to α‐helix with increasing pH, and from α‐helix to β‐sheet upon heating. The random coil‐to‐α‐helix transition is found to depend on the PLL length: the longer the peptide segment, the more readily the transition occurred. The same trend was observed for the α‐helix‐to‐β‐sheet transition, which was found to be inhibited for short polypeptides unless conjugated with the PDMAM block.
Summary: New hyperbranched poly(arylene ether amides) with fluorine or hydroxy end groups were synthesized from AB2 or A2B type monomers via a nucleophilic aromatic substitution (SNAr) reaction. Monomer syntheses were facilitated by chemo‐selective amidation reactions, and even a direct synthesis of hyperbranched polymer was possible without isolation of the monomer. The resulting hyperbranched poly(arylene ether amides) showed highly branched characteristics (DB = 0.43–0.53), high glass transition temperatures (Tg > 220 °C), and high thermal stability (Td10 > 420 °C). All hyperbranched polymers were readily soluble in aprotic polar solvents such as DMF, DMSO, and NMP regardless of the end groups. Such a similar solubility pattern may result from the high amide contents and longer branching distances between adjacent branching points in these hyperbranched polymer backbones.
Eight types of cationic glycidyl triazole polymers (GTPs) are prepared from combinations of four quaternary ammonium cationic units (pyrrolidinium, piperidinium, morpholinium, and N,N‐diethyl‐substituted ammonium) and two N‐alkyl substituents (methyl and ethyl groups). These poly(ionic liquid)s are prepared using Cu(I)‐catalyzed azide‐alkyne cycloaddition reaction between the alkyne derivatives of ionic liquids and glycidyl azide polymer. The ionic conductivity is characterized by impedance measurement. The ionic conductivity depends on the type of the cationic unit, but the type of the N‐alkyl substituent shows little influence on the ionic conductivity. The order of the cationic units that afford high ionic conductivity is as follows: pyrrolidinium >N,N‐diethyl‐substituted ammonium > piperidinium > morpholinium. The highest anhydrous ionic conductivity obtained in this study is 9.8 × 10?6 S cm?1 at 30 °C for the GTPs with the 1‐methylpyrrolidinium unit. Based on electrode polarization analysis, the conducting ion (carrier) concentration and mobility are calculated.
The nucleophilic aromatic substitution (NAS) reaction of various fluoroaromatic/2,6‐O‐dimethyl‐β‐cyclodextrin complexes with poly(vinyl amine) (PVAm) has been studied in water at different pH. Increasing pH lowers the notable negative activation entropy of those types of NAS due to the PVAm chain segments becomes better accessible in basic media. At pH > 7, the zwitterionic intermediate in the course of NAS seems stabilized by intermolecular hydrogen bonds, which has an influence on the increase of activation energy for elimination the fluoride ion. As a consequence, the counter balance between activation entropy and activation energy determines the rate of the NAS with PVAm, which is shown for several functional fluoroaromatic compounds including fluoronitrobenzenes, fluoronitroanilines, and imine bases. 相似文献
The synthesis and thermal characterization of poly(p‐cyclohexylene alkylene)s (PPCs) is described. Polymers containing 1,4‐cyclohexylene units on every 15th, 19th, and 21st chain carbon are prepared by the acyclic diene metathesis polycondensation of symmetric α,ω‐dienes obtained from the α‐alkylation of cyclohexane‐1,4‐dicarbonitrile. Exhaustive hydrogenation of the unsaturated polymers yields fully cycloaliphatic polymers with excellent resistance to thermal degradation. The thermal analysis of the unsaturated and saturated materials reveals a strong influence of the cis‐alkene and cis‐1,4‐cyclohexylene on the final thermal properties of each material. PPC exhibits higher melting temperature and thermal stability than similar materials, in which the aliphatic ring is replaced by aromatic rings or short chain branches. The melting behavior is discussed in terms of the higher flexibility and enhanced intermolecular packing of the symmetrical 1,4‐cyclohexylene units incorporated within the chain.
Ionic liquids are used widely as solvents or electrolytes for electrochemical synthesis and applications due to their wide electrochemical windows, good electrical conductivity, and their excellent solubility to both organic and inorganic compounds. Until now, no papers have reported the use of ionic liquids as initiators in polymerization. In most cases, the kinetics of electro‐induced polymerization are studied by gas chromatography (GC), NMR, or the gravimetric method, which are complicated and time consuming. In this paper, the kinetics of electro‐induced polymerization of vinyl ethers using ionic liquid 1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMIMBF4) as initiator are investigated by real‐time Fourier transform near‐IR (FT‐NIR) spectroscopy. The results show that the ionic liquid BMIMBF4 is an efficient initiator for electro‐induced polymerization of vinyl ethers. The final double‐bond conversion and polymerization rate can be adjusted by the electric‐field intensity and the concentration of the ionic liquid BMIMBF4. Moreover, the post‐curing, as well as the obvious inhibition effects of KOH, indicate that the electro‐induced polymerization goes through a cationic process. The possible mechanism is also postulated.
Aromatic poly(benzothiazole)s (PBT)s were prepared by direct polycondensation of multi‐ring dicarboxylic acids containing aryl ether or 2,2′‐hexafluoroisopropylidene flexible groups and 2,5‐diamino‐1,4‐benzenedithiol (PBT I) or 3,3′‐oxybis(6‐aminobenzenethiol) (PBT II) using poly(phosphoric acid) or poly(phosphoric acid)/methanesulfonic acid as condensing agent and solvent. Inherent viscosities were in the range 0.62–2.68 dL/g, indicating moderate polymerization degrees. The molecular structure was checked by FTIR and 1H NMR spectroscopy. Good solubility in polar aprotic organic solvents was observed for PBTs derived from monomers containing flexibilizing groups in both moieties. Glass transition temperatures ranged between 268 and 312°C for PBTs I, and between 219 and 233°C for PBTs II. Both PBTs I and II possessed good thermal and thermooxidative stability. 相似文献
PNCPy was prepared by anodic polymerization and its properties in both doped and undoped state were characterized. The doping level of the oxidized material has been found to be larger than that of other conducting polymers; the more relevant electrochemical properties of the doped material were retained after undoping. SEM and AFM data are consistent with a lumpy surface and a multidirectional growing of the polymer chains. Finally, PNCPy has been combined with PEDOT to prepare three‐layer systems with enhanced electroactivity and electrostability. Results suggest that PNCPy is a potential candidate for the fabrication of electric circuit components that are able to block the current flow below a given potential.
A systematic comparison between graft poly(l‐ lactide) copolymers with different topologies and their ability to form stereocomplexes with poly(D ‐lactide) (PDLA) is performed. Comb and hyperbranched copolymers based on functional poly(ethylene glycol) and poly(l‐ lactide) with molecular weights in the range of 2000–90 000 g mol?1 and moderate molecular weight distributions (Mw/Mn = 1.08–1.37) are prepared via the combination of anionic and ring‐opening polymerization. Two “topological isomers,” a linear poly(ethylene oxide)/poly(glycerol) (PEG/PG) copolymer and a branched PEG/PG copolymer are used as backbone polymers. Furthermore, the stereocomplex formation between PDLA and the hyperbranched and comb copolymers containing poly(l‐ lactide) arms is studied. Stereocomplex formation is confirmed by DSC as well as by Fourier transform IR (FTIR) and Raman spectroscopy.
Poly(L ‐lactide) (PLLA) is melt blended with poly(ether urethane) (PEU) based on poly(ethylene glycol) blocks via a chain‐extension reaction by diisocyanate as a chain extender to improve its flexibility without sacrificing comprehensive performance. The elongation at break of the blends with triphenyl phosphate (TPP) as a reactive blending additive is much higher than that without TPP by physical blending. When 10 wt% PEU is blended, the former elongation reaches to 298%, while the latter one is only approximately 20%. The reactive blending forms a PLLA–PEU block copolymer, thus improving their compatibility. When the weight‐average molecular weight (Mw) of PEUs is 18–90 kg mol?1, the effect of Mw is very little on tensile properties of blends. The rheological properties of the blends are modified through the content and molecular weight of PEU. The complex viscosity (η*) of PLLA/PEU blends increases with increasing Mw of PEU. The η* of the PLLA blend containing 5 wt% PEU in Mw 73 kg mol?1 is higher than that of neat PLLA. The water absorption of the PLLA/PEU blends enhances because of the hydrophilicity of PEUs versus neat PLLA.
Cyclic imino ethers (CIEs), such as 2‐oxazolines and 2‐oxazines are a unique class of monomers, which because of their manifold reactivities can be polymerized via multiple techniques. Most prominent, the living cationic ring‐opening polymerization (CROP) of CIEs enables the synthesis of well‐defined tailor‐made poly(CIEs), which have tremendous importance as functional and biocompatible polymers. On the other hand, CIEs are also powerful monomers in polyadditions resulting in the formation of a variety of biodegradable polyamide‐based systems. In this contribution, the enormous potential of CIEs as functional building blocks is discussed, which goes well beyond the CROP. Besides trends in the CROP of CIEs, recent developments in step‐growth polymerizations of CIEs are highlighted, including the spontaneous zwitterionic copolymerization (SZWIP) which provides access to functional alternating N‐acylated poly(amino ester)s (NPAEs) and polyadditions of multifunctional CIEs which give main‐chain poly(ester amide)s (PEAs).
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