Various types of soluble crosslinked polymers obtained from the copolymerization of methylmethacrylate (MMA) and p-divinylbenzene (p-DVB) in the presence of a transfer agent (CBr4) have been discussed in relation to the variation of the structure during the reaction time. When [p-DVB]/[MMA] = 1.49 × 10?3 and [CBr4]/[MMA] = 1.28 × 10?4, only linear polymers (primary polymer; Mn = 1.0 × 105) with pendant vinyl groups are formed intially. Considerable branched structure is attained in rather large polymers (Mn = 2.5 × 105), but the number of pendant double bonds is not enough to reach the gelation. As the concentration of the transfer agent becomes high, the intermolecular crosslinking is depressed, and the formed polymers contain loops and short chains. At [p – DVB]/[MMA] = 7.43 × 10?3 and [CBr4]/[MMA] = 1.28 × 10?3, the shape of polymer with the same Mn became compact gradually with increasing reaction time. These results are considered to be useful for the preparation of soluble crosslinked polymer with controlled structure. 相似文献
Soluble microgels with several pendant vinyl groups were synthesized by radical copolymerization of methyl methacrylate (MMA) with p-divinyl benzene (p-DVB). The polymerization conditions used for intramolecular crosslinking of microgels were chosen from gel permeation chromatograph (GPC) measurements of the reaction products. The rate constant of intramolecular crosslinking (kpi) was estimated from the changes in the concentration of pendant vinyl groups of microgel by using photometrical measurements at 30°C assuming a unimolecular termination mechanism of polymer radicals. As a result, kpi showed larger values than kp of styrene and depended strongly on the internal structure of the microgels. 相似文献
Chemical shifts for tritons in ortho, meta and para positions in toluene have been determined using a 64 MHz tritium NMR spectrometer. The order of shift is meta>para>ortho, whereas the calculated shift order for protons is meta>ortho>para. 相似文献
The anionic polymerization of methyl methacrylate was carried out in the presence of potassium tert-butoxide (t-BuOK)/quaternary ammonium salts (QAS) in toluene and tetrahydrofuran at −60°C. It was found that in toluene some QAS additives substantially increase the syndiotacticity of poly(methyl methacrylate). Two types of QAS were distinguished, quite different in their action. The addition of QAS with one or two longchain alkyl groups (>C12), does not change significantly the mode of the monomer addition, whereas the polymerization in the presence of tetraalkylammonium salts with four equal substituents and dimethyldidodecylammonium bromide yields predominantly a syndiotactic polymer with high conversion and comparatively low polydispersity (M̄w/M̄w = 1.3−1.5). In some cases QAS additives are more effective modifiers than cryptand [2.2.2]. 相似文献
Polyquinazolones containing m-substituted phenyl groups (Br, Cl, F, CH3O, NO2, and CH3) on the quinazolone ring were synthesized in m-cresol, and their thermal properties were studied by using dynamic thermogravimetry and isothermal weight loss. Polyquinazolones with intrinsic viscosities in the range 0.2–1.6 dL/g were synthesized. The introduction of substituted groups into the pendant phenyl group resulted in a decrease in the glass transition temperature and the thermal stability. Oxidative thermal stability of the polyquinazolones was dependent on the position of substituted groups on the pendant phenyl group. The introduction of substituted groups into the meta position reduced thermal stability more than did the introduction into the para position. 相似文献
Multiple chlorinations and arylations at the tertiary positions of adamantane are promoted by FeCl3-doped K10 montmorillonite in CCl4 or in aromatic solvents. The process, remarkably easy to implement, can be tailored to selective formation of monosubstituted 1-adamantyl derivatives or 1,3-disubstituted adamantanes. The process achieves alkylation at the meta- and para-positions of toluene leading to a purely statistical distribution and displays no substrate specificity in competition experiments between toluene and benzene. 相似文献
A study was made on the effect of some para- and meta-substituted nitrobenzenes on the radical polymerization of vinyl acetate. It has been shown that −CH2X and −SO2X type substituents have merely an inductive effect on the reactivity of nitro groups. It has also been established that the inductive effect of substituents is more intensive when they are in the para position than when in the meta position, i.e.: λ = 1·15. 相似文献
Chemical shifts for the aromatic tritons of toluene decrease in the order meta>para>ortho for pure toluene, but in the order meta>ortho>para for dilute solutions of toluene in carbon tetrachloride, chloroform, cyclohexane and dimethyl sulphoxide; m-xylene shifts are 5>4,6>2 in the pure state and 5>2>4,6 in carbon tetrachloride and dimethyl sulphoxide; o-xylene shifts are 4,5>3,6 in the pure state and reversed in carbon tetrachloride. 相似文献
A combination of tert-butyllithium (t-BuLi) and bis(2,6-di-t-butylphenoxy)methylaluminium (MeAI(ODBP)2) was found to be an efficient initiator for heterotactic living polymerization of certain alkyl methacrylates in toluene at low temperatures. The polymerization of methyl methacrylate (MMA) with t-BuLi/MeAI(ODBP)2 (AI/Li=5 mol/mol) in toluene at −78°C gave heterotactic-rich poly(methyl methacrylate) (PMMA) with narrow molecular weight distributions (MWDs) (heterotactic triad fraction mr = 68%, ratio of weight- to number-average molecular weights M̄w/M̄n = 1.06-1.17). Other alkyl methacrylates also gave heterotactic polymers under the same conditions; in particular, ethyl and butyl methacrylates gave polymers with heterotactic triad fractions of 87%. The highest triad heterotacticity of 91.6% was obtained for the polymerization of ethyl methacrylate at −95°C. Some characteristic features of this stereospecific polymerization were discussed based on the polymerization results combined with other structural information of the polymer such as chain-end stereostructure and stereosequence distribution in the main chain. 相似文献
It has been shown that difluoro(dibenzoylmethanato)boron ((dbm)BF2) can be absorbed on silica gel in the form of fluorescent monomers and dimers with the emission properties that change in
the presence of vapors of volatile organic compounds, such as ethanol, acetone, toluene, and meta-xylene. Fluorescence quenching was observed for the (dbm)BF2 monomers and dimers in the case of ethanol and acetone, whereas the formation of fluorescent exciplexes with monomers and
enhancement of the dimer fluorescence were observed in the case of toluene and meta-xylene. Results of the quantum-chemical calculations of the structure of the (dbm)BF2 monomer complex with the matrix and toluene and (dbm)BF2 dimers with matrix are presented. 相似文献
Summary: The polymerization characteristics of (octylamino)benzoic acid dimer phenyl esters with para‐meta ( 2 ), meta‐para ( 3 ), and meta‐meta ( 4 ) orientation of the amino and carbonyl groups were investigated. While treatment of 2 or 3 with a base gave the cyclic dimer 6 as the main product, condensation of 4 with an initiator in the presence of a base afforded polymers with narrow molecular weight distributions.
The condensation of 4 with an initiator in the presence of a base afforded polymers with narrow molecular weight distribution. 相似文献
Styrene has been copolymerized at low conversion with minor quantities of p-divinyl-benzene (p-DVB) in (10–15%) solution in toluene and cyclohexane. Under these conditions the molecular weight of the polystyrene formed in the absence of p-DVB was controlled by chain transfer, and the copolymerization coefficients of the styrene and the p-DVB agreed with previous work. Polymer molecular weights were studied as a function of conversion. At very low conversions the number-average (2.2 × 105) and the weight-average (4.4 × 105) molecular weights were unaffected by substituting some of the styrene by p-DVB, but as the reaction continued M?n increased slowly and M?w much faster. On the other hand, even at the lowest conversions the intrinsic viscosity was drastically reduced by the introduction of p-DVB, and the radius of gyration, as measured by light scattering, fell. Infrared studies on the polymer show that the concentration of pendent double bonds in low-conversion copolymers is about half of the doubly substituted phenyl groups. It is concluded that the first polymer chains formed are extensively cyclized with the formation of a relatively large number of small rings. 相似文献
The mass spectra of a series of ortho, meta and para substituted isopropyl benzene derivatives have been determined where the second substituent is ? COOH, ? C(O)NH2, ? C(O)C6H5, ? C(Ph)(=NPh) or ? CH(Ph)(NHPh). Two bis-isopropylbenzophenones have also been studied. The spectra are characterized by prominent ortho effects which distinguish the ortho derivatives from the meta and para. 相似文献
Three sets of novel side-chain liquid crystalline polymers with monosubstituted azobenzene moieties in the side-chain have been studied. These are poly(p-(4′-methoxy-4-oxyhexyloxy azobenzene) benzyl methacrylate) (PPHABM), poly(m-(4′-methoxy-4-oxyhexyloxy azobenzene) benzyl methacrylate) (PMHABM) and poly(o-(4′-methoxy-4-oxyhexyloxy azobenzene) benzyl methacrylate) (POHABM). The chemical structure of the monomers was confirmed by 1H NMR, 13C NMR spectroscopy and elemental analysis. The structural characterisation of the polymers was performed by 1H NMR spectroscopy and gel permeation chromatography, and their phase behaviour and liquid crystalline properties were studied using differential scanning calorimetry, polarised optical microscopy and wide-angle X-ray diffraction. The results show that the transitional behaviour of side-chain liquid crystalline polymers containing monosubstituted azobenzene moieties depends strongly on the position of the substituent on the azobenzene moiety; for example, the ortho-monosubstituted polymers do not form liquid crystalline phases, but all the para- and meta-monosubstituted polymers exhibit a smectic A phase. Furthermore, the glass transition temperature (Tg) of the polymers decreases in the order, para > meta > ortho. For the PPHABM and PMHABM polymers the isotropic temperature (Ti) and liquid crystalline range (ΔT, from Tg to Ti) are found to be in the order, para > meta, although it is surprising that the associated enthalpy changes in these polymers is the opposite order, meta > para. 相似文献
The palladium-catalyzed crosscoupling reaction of boronic acids and benzyl bromides can be used successfully for the preparation of benzyls in high yield. This C-C coupling reaction was optimized for the synthesis of polybenzyls by model reactions. Different reaction channels were observed here with meta- and para-bis(bromomethyl)benzenes. The main product with 1,3-bis(chloromethyl)benzene was the corresponding 1,3-dibenzylbenzene, but the main product with 1,4-bis(chloromethyl)benzene was the corresponding biaryl resulting from homocoupling of aromatic boronic acid. 1.3-Linked polybenzyls were synthesized based on the results of the model reactions. M̄n's of 2 380 corresponding to a DP of 26 were found based on GPC. No structural defects were detected within the limits of detection. 相似文献