Liquid adsorption chromatography, in combination with full adsorption–desorption and precipitation–redissolution techniques, is a powerful procedure for the fractionation of mixtures in the synthesis of star polymers. An easy separation of 4‐ and 6‐arm star poly(methyl methacrylate)s from their single arm precursors could be carried out by both procedures, with differences of separation efficiency also depending on the molecular weight of the precursor and the number of arms.
Size exclusion chromatograms of retained and eluted fractions obtained by liquid adsorption chromatography/full adsorption–desorption separation with a tetrahydrofuran/cyclohexane eluent system (53:47 wt.‐%) for a crude reaction mixture (dotted line) containing a 4‐arm star PMMA polymer and a single‐arm precursor (solid lines a and b, respectively). 相似文献
Several monolithic macroporous polymer sorbents (pore size 1–2 µm) based on alkyl methacrylates and ethylene glycol dimethacrylate as a cross-linking agent were prepared by free radical copolymerization in columns 3×150 mm. The influence of compositions of the reaction mixture and porogens and the nature of the alkyl radical in a mixture of monomers on the hydrodynamic and chromatographic characteristics of the monoliths was studied. The monoliths based on n-butyl methacrylate have rigid macroporous morphology and excellent hydrodynamic characteristics (flow rate up to 5 mL min?1). The efficiency of separation of a mixture of benzene and its derivatives in the version of reversed-phase HPLC was shown to increase with an increase in the fraction of a lauryl methacrylate additive (LMA) in the reaction mixture. The maximum separation efficiency (number of theoretical plates (tp)) was 35 000 tp m?1 for the monolith based on n-butyl methacrylate with 7% LMA in the reaction mixture. 相似文献
The properties of membranes produced by nonsolvent-induced phase separation (NIPS) depend on the rate of mass transfer of mobile components. This paper reports the use of Fourier transform infrared-attenuated total reflectance (FTIR-ATR) using principle component regression (PCR) analysis to study the compositional change of polymer solution immersed into the water prior to the phase demixing. To correlate the compositional change with the macroscopic structure, the observation on the dynamics of NIPS is made by a low magnification optical microscope equipped with a video camera. The morphology of the films was also examined by scanning electron microscope. Acetone and N, N-dimethylformamide were chosen as solvents to present different behavior of poly (methyl methacrylate) (PMMA) solutions during the NIPS process. The ratio of solvent and nonsolvent exchange, flux ratio shows the mass transfer in the homogeneous polymer solution after immersion in a nonsolvent bath. The results show that the flux ratio ( ) is affected by solvents which probably affects the ultimate structures of the precipitated polymer. 相似文献
Abstract A simple, reliable HPTLC method has been developed for analysis of poly(ethyleneamine)s (PEAs). Ethylenediamine and all dimeric, trimeric, and tetrameric PEAs are separated without prior derivatization. Treatment with fluorescamine and visualization under ultraviolet light detects each PEA in quantities as low as 100 ng. 相似文献
Yb[C(SiMe3)3]2 initiates the living polymerization of methyl methacrylate (MMA) at −78°C to give the polymer with Mn of 51.0×104 (Mw/Mn=1.1) and high isotacticity (97%) in a quantitative yield. Mixing of the acetone solution of resulting polymer (Mn=16.3×104) with the acetone solution of syndiotactic poly(MMA) (Mn=15.7×104) prepared by the (C5Me5)2SmMe(THF) initiator produces desired stereocomplex in high yield bearing very high Tm whose tensile modulus is higher than the respective isotactic and syndiotactic poly(MMA)s. Yb[C(SiMe3)3]2 also generated isotactic (98%) poly[2-(dimethylamino)ethyl methacrylate] (DMEMA), and (C5Me5)2SmMe(THF) affords the syndiotactic (97%) polymer in high yields. The combination of isotactic poly(MMA)-block-poly(DMEMA) (97/3) and syndiotactic poly(MMA)-block-poly(DMEMA) (97/3) provides the amphiphathic stereocomplex. In sharp contrast to the catalysis of Yb[C(SiMe3)3]2 in toluene, the addition of THF or HMPA resulted in the formation of syndio-rich poly(MMA). 相似文献
The impact of the charge transfer complex on the dielectric relaxation processes in free poly(methyl methacrylate) (PMMA) polymer sheets was investigated. The frequency dependence of dielectric properties was obtained over the frequency range 0.1 Hz–1 MHz at temperatures ranging between 303 K and 373 K for perylene dye and acceptors (picric acid (PA) and chloranilic acid (CLA)) in an in situ PMMA polymer. The TG/dTG technique was used to investigate the thermal degradation of the synthesized polymeric sheets. Additionally, the kinetic parameters have been assessed using the Coats–Redfern relation. The dielectric relaxation spectroscopy of the synthesized polymeric sheets was analyzed in terms of complex dielectric constant, dielectric loss, electrical modulus, electrical conductivity, and Cole–Cole impedance spectroscopy. α- and β-relaxation processes were detected and discussed. The σ(ω) dispersion curves of the synthesized polymeric sheets show two distinct regions with increasing frequency. The impedance data of the synthesized polymeric sheets can be represented by the equivalent circuit (parallel RC). 相似文献
The well-ordered structures of block copolymer formed by self-assemble have attracted much attention as potentially interesting optical materials, especially as photonic crystals1,2. In order to achieve desirable photonic crystal properties, the morphologies of block copolymers should be controlled, including obtaining the correct size of domains for the optical frequencies of interest and attainment of long-range domain order and appropriate orientation. We know that the morphology of one blo… 相似文献
Crystallinity of bottlebrush polymers due to side chain crystallization has been considered to be related to the length of the side chains only under the assumption of complete participation of crystallization by all side chains.Recent experimental results revealed that in poly(n-alkyl methacrylate)s a fraction of side chains could not crystallize due to constraints imposed by the trapped main chain entanglements and required expansion of main chain-main chain distance.This result renders the or... 相似文献
Pyrene fluorescence spectra have been recorded in five poly(alkyl methacrylate)s (where alkyl is ethyl butyl, isobutyl, cyclohexyl and hexadecyl) over a 20–400 K temperature range. The changes in the position and the full width at half maximum (FWHM) of the 0–0 emission band (peak I) have been correlated with the structural characteristics of the alkyl groups in the different relaxation regimes of the polymers to assess the degree of coupling of the excited singlet states with the polymer cybotactic regions. Data treatment of the peak I positions using an electron–phonon model indicates that longitudinal optical modes are involved, and that the magnitude of coupling depends on the polymer structure and follows the same trend as the glass transition temperatures. The same spectral parameters have been correlated also with “hole” free volumes from positron annihilation spectroscopy over temperature ranges which span the glass or melting transitions of the polymers. Reasons why free volume and FWHM measurements follow the same trends, and other aspects of the systems, are discussed. 相似文献
Coumarin‐containing poly(alkyl (meth)acrylates) were prepared via 70–80% esterification of hydroxy‐containing acrylic copolymers, then solution cast into thin films and photocrosslinked via the dimerization of coumarin derivatives with UVA light. The coumarin‐modified polymers crosslinked upon exposure and exhibited gel fractions between 74 and 99%. Coumarin dimerization efficiency increased with higher polymer mobility at the irradiation temperature. The effects of light intensity and irradiation time in photo‐dimerized systems followed the Bunsen‐Roscoe reciprocity law indicating that coumarin photodimerization depended only on dose. Thus, low intensities are overcome with longer times. This is an important advantage over photoinitiated free radical crosslinking which depends on irradiation intensity to the ½ power. 相似文献
Polymers containing hydrolytically labile trialkylsilyl ester side groups were synthesised via a conventional and a controlled radical polymerization. The trialkylsilyl methacrylate monomer unit was chosen for its capacity to hydrolyse into basic, acid or sea water varying the hydrophilic character of the resulting polymer backbone with time. The hydrolysis or saponification reaction of the ester bond of the trialkylsilyl methacrylate was monitored through a 1H NMR study showing the formation of siloxane side-products. Several copolymers and polymer blends were prepared as matrixes for controlled erodible systems. Their capacity to hydrolyse was demonstrated through SEM investigations with selective dissolution of free films containing hydrolysable copolymers and PMMA blends. Well-defined random and diblock copolymers with methyl methacrylate were investigated to show the effect of the microstructure on the erosion properties of the corresponding coatings. Poly(methyl methacrylate-b-tert-butyldimethylsilyl methacrylate) diblock copolymers synthesised through the RAFT process showed a better control of the erosion with a constant erosion rate over a long-time service in sea water at pH = 8.2. In addition, experiments showed that the erosion rate could be modulated by varying the molar proportion of hydrolysable side groups onto the copolymer backbone and the weight amount of copolymers mixed with PMMA in toluene solution. 相似文献
Poly(methyl methacrylate)s containing pendant octamethylcalix[4]pyrrole subunits were prepared and demonstrated to be capable of extracting tetrabutylammonium chloride and fluoride salts from aqueous media. 相似文献
An approach to the synthesis of highly branched vinyl copolymers containing thiol and C=C crosslinking groups is proposed. This method was exemplified by the emulsion copolymerization of methyl methacrylate (MMA) and 1,6-hexanediol diacrylate (HDDA) with 2-mercaptoethyl sulfide (MES) as chain transfer agent at 70°C with 4,4′-azobis(4-cyanovaleric acid) (ACVA) as the initiator. The resulting highly branched copolymers contain both thiol and acryloyl groups. The apparent Mw (by SEC) of the resulting copolymers increased with increasing ACVA concentration, whereas the pendent acryloyl and -SH groups decreased from 6.4% to 0.8% (relative to MMA units) and 45 ×10?5 to 5 × 10?5 mol/g, respectively. The copolymers of MMA could be self-crosslinked thermally or by exposure to UV irradiation. The gel fraction of the thermally treated samples decreased from 46% to 7.2%, with the increasing of ACVA in the polymer synthesis, while the gel fraction of UV irradiated samples changed only slightly around 70%. 相似文献