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1.
Polymerization, and copolymerization with styrene, of m,p-chloromethylstyrene have been carried out at 75°C, in chlorobenzene and in the presence of AIBN ([AIBN] ? 6 × 10?2, and 12 × 10?2m, respectively). The polymer molecular weights, determined by g.p.c., are: M?w = 8670, M?n = 5860, and M?w/-Mn = 1.48 for the homopolymer, poly(m,p-chloromethylstyrene), (1a); and M?w = 8805, M?n = 5144, and M?w/-Mn = 1.71 for the copolymer, copoly(m,p-chloromethylstyrene-styrene), (2a). A series of phosphine derivatives of both 1a and 2a are prepared by the reaction of the polymers with either chlorodiphenylphosphine/lithium, or diphenylphosphine/potassium tert. butoxide. A number of other potentially electroreactive derivatives of 2a are obtained by reacting the polymer with 2-aminoanthraquinone, 3-N-methylamino-propionitrile, or 2-(2-aminoethyl) pyridine. The phosphinated polymers are reacted with bis-benzonitrilepalladium-(II) chloride to obtain a series of polymer-palladium(II) complexes containing 8.5–12.9% palladium. Similarly, reaction of the last-named bidentate polymeric ligand with cupric acetylacetonate, or cupric sulphate pentahydrate, produces polymer-copper(II) complexes having 5.8, or 3.3% copper, respectively. The inter/intra-chain nature of some of the side reactions during the derivatization of the chloromethylated polymers, and that of the complex formation between transition metal centres and macromolecular ligands, are briefly discussed in view of the experimental results.  相似文献   

2.
The rate constant for end-to-end cyclization (k1) for polymer chains is predicted to decrease sensitively with increasing chain length. In this paper the techniques are examined critically for extracting values of k1 from experiments involving intramolecular pyrene excimer formation in polymers of the form pyrene-polystyrene-pyrene. For significance, results require samples of appropriately narrow molecular weight distribution (M?wM?n </ 1.13), as well as corrections for polydispersity differences among the samples. Particular attention is focussed both on experimental techniques and on the models used to interpret the kinetics of intramolecular pyrene excimer formation.  相似文献   

3.
A combination of steady-state and fluorescence decay techniques permits one to measure the dynamics of end-to-end cyclization of a polymer chain substituted at both ends with pyrene groups. In the limit of low concentration, the rate constant for cyclization, kcy, can be identified with the slowest relaxation rate τ1?1 of a Rouse—Zimm chain. Experiments are reported which allow kcy to be examined for two chain lengths of polystyrene substituted on both ends with pyrene groups. These chains have M?n = 9200 and 25 000 (M?wM?n ? 1.15). Added unlabelled polystyrene polymer [PS] causes k?cy to decrease in cyclohexane just above the θ-temperature, whereas in toluene, a good solvent, kcy is largely unaffected, even at [PS] concentrations of 50 wt%. These results are explained in terms of frictional effects—hydrodynamic screening—dominating in the poor solvent, whereas other factors tend to have offsetting effects in the good solvent.  相似文献   

4.
Samples of poly(ethylene terephthalate) (PET) modified with small amounts of trimesic acid groups and hence containing long chain branching have been prepared. From the content of trifunctional modifier and from the experimental value of the extent of reaction, the weight-average molecular weight M?w and branching density B?w have been calculated, assuming that all the end-groups are equally reactive and intramolecular reactions are absent. The values of M?w and B?w have been correlated with the experimental values of intrinsic viscosity [η] and the Newtonian melt viscosity η0. General relations of the following type have been obtained:
f1([η], Mw, Bw) = 0; f20, Mw, Bw) =0; f30, [η], Bw) = 0; f40, [η], Mw) = 0;
In particular, [η] and η0 increase on increasing M?w and decrease on increasing B?w, but, at equal [η] values, η0 increases with B?w. Through the last relation, the reliability limits of which should be experimentally checked, and from measurements of [η] and η0, it is possible to calculate M?w of a branched PET.  相似文献   

5.
Free and covalently bonded (esterified) nitroxyl radicals experienced in poly(ethylene glycols) (PEG; M?n 200–22 000) at temperatures T >Tg several different isotropic rotational relaxation regions. As a first approximation it was assumed, that in the polyglycols M?n ? 1000 there are at least three rotational relaxation regions: the liquid state (I), the melting state (II) and the solid state (III). The existence of the fourth region, the frozen solid state (IV), was also concluded. The existence of the relaxation region (II) indicated the close interaction between radicals and the crystalline phase. The order of rotational activation energies (Ea) was EIIa >EIIIa >EIa >EIVa (M?n ? 1000). In the polymer melts (I) Ea values of free and bonded radicals first diminished as a consequence of the decrease of the end group effect and they achieved constant high molecular weight values (~15 and 25 kJ respectively). Ea changed in the solid state as a function of M?n principally in the same manner except of the higher numerical values (~40 kJ).Ea of free and covalently bonded radicals in the transition region (II) gained a maximum at M?n 1550 (125 and 170 kJ) and another at M?n > 9500 (130 and 165 kJ) expressing the high degree of order in these polymers in the solid state.The results obtained correlated well with the proton magnetic resonance measurements but they did not correlate with the amorphous dielectric relaxation measurements.It was concluded that the following factors may affect the rotational relaxations of nitroxyl radicals in PEG: the free volume of the polymer, the crystallinity, the chain packing and the end-group effect. The segmental character of the relaxation process was clearly indicated.  相似文献   

6.
K. Dodgson  D. Sympson  J.A. Semlyen 《Polymer》1978,19(11):1285-1289
A preparative gel permeation chromatographic (g.p.c.) instrument has been constructed and used to separate broad fractions of cyclic poly(dimethyl siloxanes) into sharp fractions with heterogeneity indices M?wM?n = 1.05 ± 0.02. The number-average molecular weights M?n of the cyclic polymer fractions obtained were as high as 50 000, corresponding to number-average numbers of skeletal bonds n?n up to 1300. The concentrations of linear poly(dimethyl siloxanes) in all but the highest molecular weight cyclic polymer fractions prepared are believed to be negligible. The preparative g.p.c. instrument was also used to obtain some sharp fractions of linear poly(dimethyl siloxanes).  相似文献   

7.
8.
Dilute solution behaviour of poly(maleic anhydride-co-ethyl vinyl ether) and poly(maleic acid-co-ethyl vinyl ether) has been investigated by light scattering, osmotic pressure, and viscosity measurements. The molecular weights (M?w and M?n), the second virial coefficients A2, and the intrinsic viscosities [η] have been determined for three states of this copolymer: anhydride-form, H-form, and Na-salt independently. The constants in the Mark-Houwink relations were obtained for the above three states under different solvent conditions. The molecular weight of the anhydride-form is found to be higher than that of the acid-form or the Na-salt, suggesting the degradation in a process of hydrolysis. The second virial coefficient A2 as well as the Mark-Houwink relation indicates that the anhydride-form and H-form behave as flexible polymer chains in good solvents. However, the polymer coil of Na-salt is highly expanded even at saturated NaCl concentration.  相似文献   

9.
10.
Yasuhiko Onishi 《Polymer》1980,21(7):819-824
Effects of the molecular weight of dextran on its graft copolymerization with methyl methacrylate (MMA), initiated by ceric ammonium nitrate (CAN), have been investigated. The results indicate that grafting (%), graft polymerization (%) (ψ), the overall rate constant (k′) for consumption of Ce4+, and branch PMMA were influenced significantly by the molecular weight of the backbone polymer dextran. The number of branch PMMA chains per dextran molecule was 0.05 ~ 0.30 for M?w 9000 dextran (D1), 0.35 ~ 0.55 for M?w 61 000 (D2), and 0.8 ~ 1.6 for M?w 196 000 (D3), respectively. The relationship between the rate of graft polymerization and M?w (the weight-average molecular weight of dextran) was expressed by the equation: Rpg = ?AlogM?w + B. Another linear relationship was obtained between In (100 ? ψ) and reaction time (t) for both D1 and D2 samples or In t for D3. Detailed kinetic analysis has been made on the basis of the latter relationship. Mechanical properties were also studied on the moulded sample plates of these copolymers.  相似文献   

11.
Emulsion polymerization of vinylacetate leads to branched polymers which at high monomer conversions form microgels of the shape and size of the latex particles. Quasielastic light scattering measurements from samples in the pre-gel state give at small q2 a linear angular dependence of Dapp = Гq2 which resembles that of randomly branched chain molecules, where Г is the decay constant of the time correlation function. Extrapolation of Dapp towards zero scattering angle yields the translational diffusion constant Dz. The diffusion constant follows the molecular weight dependence Dz = 9.78 10?5Mw?0.478. The diffusion constant of the microgels, i.e. at molecular weights Mw > 14 106, remains constant because of the finite and constant size of the latex particles. The coefficients kf and kD in the concentration dependence of the frictional and diffusion coefficients are related according to the equation kD = kf ? 2A2Mw ? v? where A2 is the second virial coefficient and v? the partial specific volume of the particle. The coefficient kf is calculated from the experimentally determined quantities kD, A2 and Mw, and the result is compared with the theory by Pyun and Fixman. Accordingly the branched coils in the pre-gel state resemble soft spheres, but the microgels behave more like spheres of some rigidity.  相似文献   

12.
The limiting viscosity number in polystyrene-cyclopentane system has been determined over the temperature range of θu to θl in which θu and θl are the θ or Flory temperature for the upper and lower critical solution temperatures. The temperature coefficient of unperturbed mean square end-to-end distance observed for the polystyrene (Mw=20×104, MwMn<1·06 and Mw=67×104, MwMn<1·10) in cyclopentane is negligibly small. The observed temperature dependence of the polymer chain dimension over the temperature range of θu=19·6° to θl=154·2°C shows a parabolic curve with a maximum in the neighbourhood of 90°C and is qualitatively interpreted by the free volume theory of polymer solution, which gives a new χ1-temperature function.  相似文献   

13.
The effects of temperature and catalyst homogeneity on the molecular weight distribution (MWD) and stereochemical regulation of polypropylenes produced by Ti(OC4H9)4Al2(C2H5)3Cl3 system have been investigated. The MWD of polymers obtained at temperatures below 21°C were unimodal and narrow (M?wM?n?2.0), whereas those obtained at temperatures higher than 31°C were bimodal with one narrow distribution and the other broad one (M?wM?n=18) at higher molecular weights. The existence of two different types of catalyst, one soluble with homogeneous catalytic centres and the other insoluble with heterogeneous catalytic centres was found in the polymerization at 41°C. At temperatures below 21°C only soluble catalyst was present and produced isotactic polypropylenes with [m]=0.65. The isospecific nature of soluble titanium-based catalyst is greatly contrasted to the syndiospecific nature of soluble vanadium-based catalyst.  相似文献   

14.
N. Kuwahara  M. Nakata  M. Kaneko 《Polymer》1973,14(9):415-419
Cloud-point curves for solutions of five polystyrene samples, including three well-fractionated polystyrenes, in cyclohexane have been examined near their critical points. Even for a solution of polystyrene characterized by MwMn<1.03, the critical point determined by the phase-volume method is generally situated on the right hand branch of the cloud-point curve. The precipitation threshold concentration is appreciably lower than the critical concentration, while the threshold temperature slightly deviates from the critical temperature. The agreement of the precipitation threshold point with the critical point has been found for a solution of polystyrene characterized by Mw=20×104 and MwMn<1.02 in cyclohexane. The η(φ) function derived from critical miscibility data is expressed by χ(φ) = 0.2798+67.50T+0.3070φ+0.2589φ2, which yields θ of 33.2°C and ψ1 of 0.22.  相似文献   

15.
Extremely high molecular weight polystyrenes with a M?w in the range 10.8 × 106 to 2.2 × 107 were prepared by emulsion polymerization initiated with a heterogeneous initiator at 30°C, which has a ‘living character’. Samples of polystyrene were characterized by light scattering and viscometry in toluene and benzene at 25°C, and in θ-solvent cyclohexane at 34.8°C. Also determined were the relationships of mean-square radius of gyration 〈s2〉 (m2) and the second virial coefficient A2 (m3 mol kg?2) on the molecular weight, which for toluene and benzene are described in equations: Toluene (25°C) 〈s2〉=1.59 × 10?23M?w1.23; A2=4.79 × 10?3M?w?0.63; Benzene (25°C) 〈s2〉=1.23 × 10?22M?w1.20; A2=2.59 × 10?3M?w?0.59. The parameters in the Mark-Houwink-Sakurada equation were established, for extremely high molecular weight polystyrene in toluene and in benzene, at 25°C into the form giving for [η] (m3kg?1): [η] = 8.52 × 10?5M?w0.61; [η] = 1.47 × 10?4M?w0.56. The mentioned relations, as well as the obtained values of Flory parameter ?0 and of ratio [η]M?w0.5 were compared with solution properties of high molecular weight polystyrene with narrow molecular weight distribution prepared by anionic polymerization by Fukuda et al.  相似文献   

16.
Wyn Brown  Peter Stilbs 《Polymer》1983,24(2):188-192
Transport in ternary polymer1, polymer2, solvent systems has been investigated using an n.m.r. spin-echo technique. The dependence of the self-diffusion coefficient of poly(ethylene oxide) polymers on the concentration and molecular size of dextran in aqueous solution has been measured. Monodisperse poly(ethylene oxide) fractions (M?w=7.3×104, 2.8·105 and 1.2·106) and dextrans (M?w=2·104, 1·105 and 5·105) have been employed over a range of concentration up to the miscibility limit in each system. It is found that when the molecular size of the diffusant is commensurate with or exceeds that of the matrix polymer, a relationship of the form: (DD0)PEO=exp?k(C[η]) is applicable, where C[η] refers to the dextran component and is considered to describe the extent of coil overlap in concentrated solution. (DD0) is independent of the molecular size of the poly(ethylene oxide), at least in the range studied (Mw<300 000).  相似文献   

17.
B. Nyström  J. Roots  R. Bergman 《Polymer》1979,20(2):157-161
Sedimentation velocity measurements on polystyrene (M = 110 000) in cyclopentane over an extended concentration region and from 5°C (close to the upper critical solution temperature) to 40°C are reported. The concentration dependence parameter (ks)w increases from 2 to 5°C to 27 at 40°C. For all temperatures except 5°C, s0s vs. w[η]w shows an upward curvature at w[η]w ≈ 1; at 5°C, on the other hand, s0s is independent of concentration over the region considered. Furthermore, measurements have also been performed at 20°C (θ-conditions) over a large concentration interval for the molecular weights M = 20 400, 390 000 and 950 000. The parameters s0 and (ks)w were both found to be proportional to M?1/2w. In the ‘hydrodynamically normalized’ plot s0s vs. w[η]w the sedimentation behaviour can approximately be represented by a single curve for all the molecular weights.  相似文献   

18.
The technique of small-angle neutron scattering (SANS) has been used to study the chain configuration in pressure crystallized polyethylene. Two narrow molecular weight fractions of deuterated molecules (PED) of Mw 23 000 and 54 000 were solution blended with a protonated matrix polymer of Mw 81 500. Although pressure crystallization was shown to have produced a clustering of the PED molecules, the radii of gyration S2z12 were, nevertheless, shown to be consistent with a model in which the PED molecules possessed rod-like configurations. The predicted rod lengths were in close agreement with the molecular stem lengths of the PEH matrix polymer, which were independently determined by nitric acid etching. Furthermore, a doubling of the PED molecular weight produced no change in the value of 〈S2z12. This was interpreted in terms of a chain folding mechanism in which a molecule is bounded by the surfaces of a lamellar block and is therefore unable to increase its' rod length.  相似文献   

19.
The synthesis and characterization of methacrylate-ended macromers (M?n 500 to 10 000) and their copolymerization with styrene (M2) is described. The experimental errors in the values of the reactivity ratios r1 render them meaningless. Values of r2 can be determined with more precision and increase from 1.06 to 1.55 as the molecular weight of the macromer increases. This behaviour is due to steric effects, not diffusion-controlled propagation. It is shown that the assumptions that 1 > r1[M1][M2] and r2 >[M1][M2] are only valid for macromers of M?n > ca. 10 000.  相似文献   

20.
J.E.L. Roovers 《Polymer》1975,16(11):827-832
A new method for the synthesis of comb shaped polystyrenes of predetermined structure is described. Silicon-chlorine bonds are introduced into the backbone polystyrene by reaction of SiMe2Cl2 with hydrolysed styrene/vinyl acetate copolymers and coupled with polystyryl-lithium in benzene. From a common backbone polymer a series of comb polymers are prepared that have a constant number of branches but vary in branch length. The MwMn of the whole comb polymers is about 1.3. The comb polymers with high branch density show θ (A2) temperatures lower than that for linear polystyrene. The radius of gyration at θ (A2) [〈S2θ (A2)] is always larger than calculated from random flight statistics. For comb polymers with 20–30 branches 〈S2θ (A2)〈S20,bb increases with λ?0.46 where λ is the fraction of polymer in the backbone. The intrinsic viscosities of the comb polystyrenes at θ (A2) are equal to that of the parent backbone polymer when λ > 0.25 and increase only little when λ becomes equal to 0.1. Similar behaviour is found in toluene. Intrinsic viscosities in cyclohexane at 35°C show a complex pattern because of the θ-temperature variation.  相似文献   

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