Polymer narrow-distribution

Read the retention volume, VT, for each of the narrow distribution polymer standards. 

Using the retention volume, VT, for the narrow distribution polymers and their molecular weight, M, a calibration curve is constructed for log M versus Ve. Mw may be used for M. 

Fig. 5.18. Reduced compliance vs cM /qMc for solutions and undiluted sample of linear, narrow distribution polymers. The lines for polyethylene and (polydimethyl siloxane) are based on G (w) data as reported by Mills (204). Points are selected values for polyvinyl acetate solutions, O (176) and 9 (195), and undiluted 1,4 polybutadiene, (202) and - (203) The values of Mc were taken from Table 5.2...

The properties of i (0) for narrow distribution polymers have already been discussed in Section 5. The behavior of f jfy) at higher shear rates has only been determined for a few systems of well-characterized molecular structure. The experimental problems are more difficult than in the case of rj(y), so the conclusions here must be regarded as somewhat more tentative. Experimentally, t(y) and tj(y) depart from their zero shear values within the same range of shear rates (172). Shear rate sensitivity is much smaller when N is expressed as a function of shear stress (350). 

The conclusions of this review can be separated into those which concern the experimental rheology of networks and concentrated systems of narrow distribution polymers and those related to the ability of molecular theories to rationalize and predict these observations. 

Nemoto,N. Viscoelastic properties of narrow-distribution polymers. II. Tensile creep studies of polystyrene. Polymer J. (Japan) 1,485-492 (1970). 

Application of the Summative-Fractionation Method to the Determination of Mw/M for Narrow-Distribution Polymers... 

The summative-fractioruition method was extended to apply to narrow-distribution polymers with polydispersity (Mw/ Mn) less than 1.12. A fractionation parameter H, previously defined and calculated for theoretical molecular weight distributions for normal polymers, was computed for narrow-distribution polymers. The calculations were made both with and without correction for fractionation errors, using the Flory-Huggins treatment. The method was applied to a well-characterized anionic polystyrene with Mw = 97,000, for which the polydispersity was estimated by this technique to be 1.02 (in the range 1.014-1.027, 95% confidence limits). 

A major interest in narrow distribution polymers is for research and molecular weight calibrations in gel permeation chromatography. Narrow-molecular-weight polystyrenes are made by initiation with alkali metal alkyls that are particularly effective in this application but that only polymerize conjugated monomers like styrene or butadiene. 

Mixtures of narrow distribution polymers were used in several studies about mass discrimination problems in MALDI-TOF. " ... 

In conventional GPC, the system is calibrated by running a series of narrow-distribution polymer materials (calibrants) with known M. A calibration of versus retention time is produced. However, in many cases, the retention time of the polymer materials used as calibrants does not correspond directly with oligomers of the same of the polymeric substance material. 

The main problem associated with using narrow-MMD calibrants is the restricted range of polymer types available. Poly(styrene) calibrants are the main type used, and a very wide range of molecular masses is available. A small number of other polymer types is obtainable, but the molecular mass range is often rather limited. Poly(ethylene oxide) and poly(ethylene glycol) calibrants deserve special mention, because they can frequently be employed where poly(styrene) behaves anomalously, for instance in polar solvents such as dimethylformamide. Some of the narrow-distribution polymer calibrants available are listed in Table 3.1 and Appendix 2. 

Micro-emulsion Swollen monomer micelles dispersed in a continuous phase fairly large concentrations of surfactants required initiator dissolved in continuous phase Polymerisation initiated in the course of nucbation of monomer micelbs process characterised by continuous nucleation during entire reactbn fast rate of polymerisation (< 30 min) Particbs of very small si (diameter <100 nm) and narrow distribution polymer with ultra-high molecular weight (> 10 g/mol) copolymers with well-defined, homogenous composition... 

For polymers with hroad molecular weight distrihutions the viscosity appears to be a fiinction of the weight-average molecular weight M. This relationship fails for extreme binary blends with molecular weight ratios of 8 (87), 27 (88), and 380 (89). The blend data fall substantially below the cimre determined for narrow distribution polymers. 

In a few reported cases, the agreement for narrow distribution polymers has not been good (52). This can generally be attributed to the failure of the classical method at low molecular mass. For example, calibration of sec at low molecular mass is at best difficult. Furthermore, the effect of end groups on the detector response is often not taken into account nor is the effect of broadening on the computed moments properly taken into account at the lower molecular masses. For example, the DRI detector requires the dn/dc be constant, independent of molecular mass for the calculation performed by most current software programs. But dn/dc is known to be affected by end groups (65). 

Steady-State Compliances and Ratios to Plateau Compliances, Narrow Distribution Polymers, M M c ... 

Until about 40 years ago, the determination of the molar mass distribution was the prime objective of polymer fractionation by phase separation. Since the advent of size exclusion chromatography the need for such time consuming and essentially ineffective classic fractionation methods has disappeared. However, today chromatographic techniques are still incapable of producing large-size fractions of the order of 100 g and phase separation methods continue to be needed for the preparation of large amounts of narrow-distribution polymers that cannot be obtained by direct synthesis. The most important polyolefins, polyethylene and polypropylene, fall into this category and a discussion of fractionation by distribution between two... 

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