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1.
Describing network formation during chainwise polymerization is more complex than for stepwise (condensation) systems. The kinetics of chain growth must be combined with probability laws for random linking between chains. This approach is used to derive molecular weight averages, gel point and sol fraction during living, anionic copolymerization of vinyl with divinyl monomers. Comparison of predicted molecular weight and gel point to experimental values from Worsfold (1970), Lutz, Beinert and Rempp (1982) and others indicate that a significant amount of intramolecular linking or cyclization occurs in this system.  相似文献   

2.
The relationships for copolymer composition and microstructure in reversible copolymerization at equilibrium are derived. They allow to predict the comonomer equilibrium concentrations and the structure of the copolymer at equilibrium if the initial state and equilibrium constants are known and provided that [I] ? [M1]0 + [M2]0 - [M1]e - [M2]e.  相似文献   

3.
Incompatible polymers yield two-phase binary blends at almost all compositions. In equilibrium, the blends consist of two coexisting phases which have frequently very one sided compositions: Much of one component contains little of the other. The small content of the minor component, the so-called “partial miscibility”, is important for some properties. But it is difficult to measure. Conventional techniques to determine miscibility gaps which rely on transparency and turbidity fail when the gaps are too wide. More reliably, the composition of the coexisting phases can be extracted from X-ray or neutron scattering data. A series of blends of poly(methyl methacrylate) (PMMA) and random copolymers SxMMAl?x of styrene and MMA, of which the degree of incompatibility was varied via the copolymer composition x, was studied by small angle neutron scattering. The interactions of the polymer components were measured in homogeneous and demixed blends. The demixed blends yield at high wave vectors a scattering equal to the scattering of the two coexisting phases, superposed. The composition of the coexisting phases was extracted from the slope of the Zimm curve which responds very sensitively even when the compositions are extreme. Miscibility gaps as wide as 99.7% could be determined.  相似文献   

4.
Ethyl vinyl sulfide (EVS) and phenyl vinyl sulfide (PVS) were found to undergo alternative copolymerization with maleic anhydride (MAn) even in the absence of radical initiators. It is noted that both the rates and the reduced viscosities in these alternative copolymerization show a maximum at 50 mole-% comonomer mixture, anticipating that a 1 : 1 charge transfer complex is formed preceding polymerization. From spectroscopic studies, it was also observed that the formation of such a complex between vinyl sulfide and MAn was confirmed, but their equilibrium constants were quite small, i.e. 0.090 l./mole for PVS-MAn in CHCl3 and 0.035 l./mole for EVS-MAn in CH2Cl2 at room temperature. The mechanism of these alternative copolymerizations is discussed.  相似文献   

5.
Copolymerizations of 2-vinyl-l,3-dioxane ( 1a ), 5,5-bis(hydroxymethyl)-2-vinyl-1,3-dioxane ( 1b ), and 5,5-dimethyl-2-vinyl-1,3-dioxane ( 1c ) with maleic anhydride (MA) and N-vinyl-2-pyrrolidone (NVP) were investigated. Copolymerization of the cyclic acetals 1 with MA yielded copolymers with perfectly alternating sequences independent of the initial monomer feed composition. Terpolymerization of 1a , MA, and styrene, also despite of monomer composition, yielded terpolymers with a molar composition of 50% in MA which confirms the participation of transfer complexes in these copolymerizations. The composition of the 1 /NVP copolymers (mole fraction) F1(NVP) ≈ 0,6–0,8 also varied little with the feed. The copolymerization rates passed through a maximum when the monomer mixture contained a mole fraction f1 (NVP) of ca. 0,7.  相似文献   

6.
The copolymerization of styrene (S) with maleic anhydride (MAn) in 1,4-dioxane at 60, 70 and 80°C up to high conversion (≈ 98%) was followed by differential scanning calorimetry. The rate of copolymerization increases up to 20 – 40% conversion of both monomers and then gradually decreases to zero. The increase in the copolymerization rate is more pronounced for equimolar ratios [S]/[MAn] as compared to ratios with an excess of S. For a given mole ratio of S and MAn the copolymerization rate in 1,4-dioxane is higher at higher total monomer concentrations and/or at higher temperatures. The heat of copolymerization is 81,6 kj · mol?1 for the equimolar [S]/[MAn] mixture. For mixtures with [S]/[MAn] > 1 the heat of reaction is between 70 and 80 kj · mol?1. The limitingconversion of styrene for [S]/[MAn] = 1 is about 98%, and for [S]/[MAn] > 1 it is a function of the [S]/[MAn] ratio. Assuming exclusively the formation of an alternating S/MAn copolymer the following relation is derived. for the ratio of the apparent rate constants of propagation k?p, and termination k?</t.  相似文献   

7.
By ring-opening copolymerization of 1,4-anhydro-2,3-di-O-ethyl-D-erythritol (cis-3,4-diethoxyoxolane, 1 ) or 1,4:2,5:3,6-trianhydro-D-mannitol ( 3 ) with tetrahydrofuran carbohydratecontaining copolyether polyols were obtained. Using trifluoromethanesulfonic acid as catalyst the molecular weights were in a range from M?w = 13 000 up to 25 000 with about 10% of carbohydrate constituent. The novel copolyethers were studied by polymer analytical procedures, their structures 4 and 5 tentatively assigned and compared to the homopolymerization products of the monomers. The present procedure features an approach to novel partially functionalized high molecular weight copolymer polyols based on carbohydrate-derived materials.  相似文献   

8.
The cationic copolymerization of dioxolan (DOL) and tetroxan (TEX) at a mole-ratio of 9/1 with BF3OEt2 in toluene was studied by gas chromatography and NMR. The very reactive TEX was consumed at an early stage, whereas DOL was consumed slowly until an equilibrium conversion was reached. Correspondingly, the fraction of formal units in the copolymers decreased gradually with conversion. Therefore TEX is both kinetically and thermodynamically more reactive than DOL. As a by-product, a significant amount of trioxepan was found, which indicates a rather facile back-biting reaction.  相似文献   

9.
Vinylferrocene was shown to undergo readily cationic polymerization by FRIEDEL-CRAFTS and other cationic catalysts. The polymers obtained possessed rather low molecular weights, the highest being 3500. In spite of the high reactivity of the ferrocene nucleus towards electrophilic substitution, no mode of propagation other than vinyl addition was detected when the infrared spectra of polymers prepared by cationic and free radical reactions were compared. The electronic spectra of polyvinylferrocene and its oxidized form were similar to those of ferrocene and ferricinium ion, respectively. In the cationie copolymerization with styrene, the latter was incorporated into the polymer only when the styrene content in the monomer feed exceeded 90%. The copolymerization with vinyl isobutyl ether (M2) by BF3OEt2 in toluene at 0°C gave the reactivity ratios: r1 = 0.1 ± 0.1, r2 = 9.7 ± 1.0. The high cationic reactivity of vinylferrocene is consistent with the stability of the α-ferrocenylearbonium ion inferred from solvolysis and other reactions.  相似文献   

10.
Statistical copolymers of allyl methacrylates with methyl and ethyl methacrylates are synthesized. Moderate conversions are used. Reactivity ratios are calculated by linearised methods which take composition drift into account as well as by non-linear least-squares approximation. For the allyl methacrylate/methyl methacrylate system, rallyl values obtained by various methods are between 1,62 and 1,60 and rmethyl values between 0,36 and 0,34. For the allyl methacrylate/ethyl methacrylate system, rallyl values are between 1,37 and 1,16 and rethyl values between 0,40 and 0,47.  相似文献   

11.
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13.
The miscibility and morphology of polyimide/polyimide blends, PEI-E/PTI-E
  • 1 PEI-E: poly(ether imide-ether), PTI-E: poly(thioetherimide-ether), PBPI-E: poly(biphthalimide-ether); cf. exptl. part.
  • and PBPI-E/PTI-E , have been studied by means of 13C CPMAS NMR technique. The results indicate that PEI-E/PTI-E blends are miscible on a molecular level, but molecular aggregation exists in pure PBPI-E specimen as well as PBPI-E/PTI-E blends with high content of PBPI-E, which vanishes in the blends with high content of PTI-E. When the content of PBPI-E is higher than that of PTI-E, the addition of PTI-E to PBPI-E has almost no effect on the size of the PBPI-E rigid domains, but has a large effect on the populations of the PBPI-E rigid domains. It is the intermolecular charge-transfer interaction that plays a critical role in the miscibility of PEI-E/PTI-E and PBPI-E/PTI-E blends.  相似文献   

    14.
    Unsaturated copolyacetals have been prepared by anionic copolymerization of acrolein with aldehydes, such as, acetaldehyde, benzaldehyde, propionaldehyde, pivaldehyde and others. The dependence of the structure of the copolymers on the dielectric constant of the solvent, and on the temperature, the aldehyde, the catalyst and the extension of the reaction has been studied.  相似文献   

    15.
    The free radical copolymerization of butadiene and vinylferrocene was studied at 60°C in 1,4-dioxane. Copolymerization occurs readily to give low molecular weight random copolymers. The reactivity ratios are r1 (butadiene) = 3,5±0,5 and r2 (vinylferrocene) = 0,30±0,10 and the Q and e values for vinylferrocene are 0,68 and ?1,05, respectively. The copolymers are shown to contain a paramagnetic species which is identified as a high spin Fe(III) complex.  相似文献   

    16.
    Methyl methacrylate has been grafted onto cellulose pulp using manganic ion as the initiator. The variable parameters studied are initiator and monomer concentrations, temperature and reaction time. The grafting efficiency, degree of grafting and frequency of grafting are found to be dependent on the above mentioned variables.  相似文献   

    17.
    Cationic copolymerization of 1,3-dioxolane with styrene was performed in toluene solution at 25°C. using boron fluoride etherate as catalyst. Determination of formaldehyde units in the copolymer showed that the two monomer units formed somewhat longer sequences in the copolymer chain than calculated on the assumption that these monomer units are statistically distributed in the copolymer chain according to their copolymerization parameters.  相似文献   

    18.
    Kinetics and mechanism of photo-induced copolymerization of cyclohexene with maleic anhydride in chloroform were studied. The UV spectra suggested the formation of a chargetransfer complex between the comonomers. This complex was excited under irradiation and then underwent hydrogen abstraction to produce two kinds of radicals for initiation. The polymerization produces an alternating copolymer in the composition range of 25 to 75 mol-% of either comonomer. The chain-transfer role of cyclohexene was also investigated.  相似文献   

    19.
    Styrene homologues (styrene, α-methylstyrene, and β-methylstyrene) were copolymerized with oxygen to produce optically active copolymers in the presence of a chiral Co(II) (Schiffbase) complex. The absolute configuration of the carbon atom in the copolymer chain was determined by hydrogenolysis of the copolymer to phenylethanediol derivatives. In the cases of styrene and α-methylstyrene, (R)-(+)-1-phenylethanediol and (R)-(+)-2-phenyl-1,2-propanediol were preferentially formed, respectively. In the reaction of β-methylstyrene, the preferential formation of (1S, 2R)-(?)- and/or (1R, 2R)-(?)-1-phenyl-1,2-propanediol was observed. The chiral Co(II) (Schiff-base) complex seems to stabilize both the peroxy-and the peroxyalkyl radical.  相似文献   

    20.
    Vinylferrocene was polymerized by means of anionic initiators such as n-BuLi, s-BuLi and distyryl disodium in tetrahydrofuran as solvent. In all cases the polymerization shows the characteristics of a living polymerization. Depending on the sequence of the monomer addition, either block copolymers of the ABA or the AB type were synthesized.  相似文献   

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