Polydisperse macromolecules

The observed decrease in [ri] (see Fig. 16) can be understood when recalling that due to Marriman and Hermans [98] the intrinsic viscosity of polydisperse macromolecules is given by the ratio of two number averages... 

Size exclusion chromatography (SEC) polymer elution profiles yield information regarding the molecular size distributions of polydisperse macromolecules. Polymer molecular weight distribution (MWD) represents an intrinsic property which provides direct correlation with many end-use physical properties and a universal criterion for polymer characterization (1). In order to convert elution profiles or chromatograms into MWD information proper calibration methods are required. SEC molecular weight calibration techniques represent experimental approaches for transformation of polymer elution profiles into MWD information and are dependent upon instrumentation, columns, and the polymer/solvent system under study. 

Lignins are polydisperse macromolecules whose average molecular weights are rather low. Their determination by means of absolute methods becomes now easy owing to improvements in techniques, and this in spite of many problems inherent in the polymer itself. 

A.W. Chow, and G.G. Fuller, The rheo-optical response of rod-like chains subject to transient shear flow. Part I Model calculations on the effects of polydispersity, Macromolecules 18, 786 (1985) A.W. Chow, G.G. Fuller, D.G. Wallace and J.A. Madri, The rheo-optical response of rod-like chains subject to transient shear flow. Part II. Two-color flow birefringence measurements, Macromolecules 18,793 (1985) A.W. Chow, G.G. Fuller, D.G. Wallace and J.A. Madri, The rheo-optical response of rod-like shortened collagen protein to transient shear flow, Macromolecules, 18, 805 (1985). 

Linse P. 1994. Micellization of poly(ethelene oxide) poly(propylene oxide) block copol5mers in aqueous solution effect of polymer polydispersity. Macromolecules 27 6404 6417. 

Yokoyama, A., Miyakoshi, R., and Yokozawa, T. (2004) Chain-growth polymerization for poly(3-hexylthiophene) with a defined molecular weight and a low polydispersity. Macromolecules, SI, 1169—1171. 

Huang, X., and Wirth, M. J. (1999). Surface initiation of living radical polymerization for growth of tethered chains of low polydispersity. Macromolecules, 32(5) 1694-1696. 

Fig. 8. Representations of property distributions of polydisperse macromolecules (a) three-dimensional map (b) contour map (view from top of (a)).

FIGURE 10.6 IMS-MS snapshots of blends of polydisperse macromolecules using the homebuilt 3-m drift tube instrument. (A) Binary blend of PEG and PEGDME (2000 Da) doped with cesium chloride and differing only by methyl groups located on the end of each... 

Broseta D, Fredriekson G H, Helfand E and Leibler L 1990 Moleeular-weight effeots and polydispersity effeots at polymer-polymer interfaoes Macromolecules 23 132... 

S. Livne. A polydisperse polymer solution as a critical system. Macromolecules 27 5318-5328, 1994. 

The relation (103) will hold for any value of the scission yield, providing the macromolecules do not cross the boundary between the different streamlines, either by molecular diffusion or by flow turbulence. For samples having similar polydispersities and MWD, all the degradation data could be superimposed onto a single curve when plotted on a relative abscissa scale (e(0)/ef). 

Interest in anionic polymerizations arises in part from the reactivity of the living carbanionic sites4 7) Access can be provided to polymers with a functional chain end. Such species are difficult to obtain by other methods. Polycondensations yield ro-functional polymers but they provide neither accurate molecular weight control nor low polydispersity. Recently Kennedy51) developed the inifer technique which is based upon selective transfer to fit vinylic polymers obtained cationically with functions at chain end. Also some cationic ring-opening polymerizations52) without spontaneous termination can yield re-functional polymers upon induced deactivation. Anionic polymerization remains however the most versatile and widely used method to synthesize tailor made re-functional macromolecules. 

Burchard, W., Schmidt, M., and Stockmayer, W.H. Information on polydispersity and branching from combined quasielastic and integrated scattering. Macromolecules, 13, 1265, 1980. 

A way to narrow the MWD and to approach the structure of dendrimers is the addition of a small fraction of a/-functional initiator, to inimers [40,71]. In this process the obtainable degree of polymerization is limited by the ratio of inimer to initiator. It can be conducted in two ways (i) inimer molecules can be added so slowly to the initiator solution that they can only react with the initiator molecules or with the already formed macromolecules, but not with each other (semi-batch process). Thus, each macromolecule generated in such a process will contain one initiator core but no vinyl group. Then, the polydispersity index is quite low and decreases with / M /Mn l-i-l//. (ii) Alternatively, initiator and monomer molecules can be mixed instantaneously (batch process). Here, the normal SCVP process and the process shown above compete and both kinds of macromolecules will be formed. For this process the polydispersity index also decreases with/,but is higher than for the semi-batch process, M /Mn=Pn//. ... 

In order to understand polymer solution behaviour, the samples have to be characterised with respect to their molecular configuration, their molar mass and polydispersity, the polymer concentration and the shear rate. Classical techniques of polymer characterisation (light scattering, viscometry, ultracentrifugation, etc.) yield information on the solution structure and conformation of single macromolecules, as well as on the thermodynamic interactions with the solvent. In technical concentrations the behaviour of the dissolved polymer is more complicated because additional intramolecular and intermolecular interactions between polymer segments appear. 

In the model under consideration all macromolecules of fixed length Z have the same composition X(Z). However, owing to the substantial polydispersity of the products of free-radical copolymerization for length (even for polymer specimens obtained under low conversions), their composition distribution ... 

Stafford, C.M., Russell, T.P, and McCarthy T.J., Expansion of polystyrene using supercritical carbon dioxide, effects of molecular weight, polydispersity, and low molecular weight components, Macromolecules, 32, 7610, 1999. 

Hamau, L., Winkler, R. G., and Reineker, P., Influence of polydispersity on the dynamic structure factor of macromolecules in dilute solution, Macromolecules, 32, 5956, 1999. 

In contrast to biological macromolecules such as proteins, synthetic polymers are, in general, polydisperse. Their molar masses, which show a broad distribution of... 

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