Polymer mass distribution

In principle, MALDI-TOF (MALDI-Time Of Flight) analysis allows for the determination of the complete polymer mass distributions and, from that, the calculation of various molecular weight averages like Mn and Mw and the... 

Axelsson, J., Scrivener, E., Haddleton, D. M., and Derrik, P. J., Mass Dicrimination Effects in an Ion Dectector and Other Causes for Shifts in Polymer Mass Distribution Measured by Matrix-Assisted Laser Desorption/Ionization lime-of-Flight Mass Spectrometry, Macromolecules, 29, 8875,1996. 

Two well-known kinds of difficulties relating to the determination of polymer mass distributions by electrospray ionization are (i) the two-dimensional complexity associated to the unknown distribution of both mass m and charge z and (ii) the fact that many industrially important polymers are soluble only in nonpolar liquids, which are difficult or impossible to electrospray into drops small enough to yield reasonably clean ions. 

The discussion in the earUer section was in terms of the chain length probability distribution, W., or the chain length number distribution, n.=n,, M. Oftentimes, it is of direct interest to work with the polymer mass distribution n(M), which is the number of polymers of mass M. present in a population... 

Using derivatives of the onhne M (t) to compute the polymer mass distributions andpolydispersity indices. ACOMP measures the accumulated M (t) at each moment for most chain growth reactions, this involves an accumulation of dead chains, which form very quickly compared to the time scale for the total conversion of monomer. 

An interesting feature of these polymers is that they have a tetramodal molecular mass distribution which has been deliberately built in and which is claimed to improve processability. This is achieved by the following procedure ... 

When the styrene has been consumed, to give living polymers of narrow molecular mass distribution, more styrene and more catalyst is added. The styrene adds to the existing chains and also forms new polymer molecules initiated by the additional sec-butyl-lithium. 

Polymer. The polymer determines the properties of the hot melt variations are possible in molar mass distribution and in the chemical composition (copolymers). The polymer is the main component and backbone of hot-melt adhesive blend it gives strength, cohesion and mechanical properties (filmability, flexibility). The most common polymers in the woodworking area are EVA and APAO. 

Table 9.9 (6) gives some guidelines for proper SEC separation conditions when analyzing polymer standards with narrow molar mass distribution on a single 30-cm column. The conditions have to be adjusted when running industrial polymers (which are normally much wider in molar mass distribution). Depending on the width of the MMD, concentrations can be increased by a factor of 3 to 10 for such samples. As a general rule, it is advisable to keep the concentration of the injected solution lower than c [ j] < 0.2. 

In this stage of the investigation, poly(methyl methacrylates) (PMMAs) were selected as the polymeric probes of intermediate polarity. Polymers of medium broad molar mass distribution and of low tacticity (14) were a gift of Dr. W. Wunderlich of Rohm Co., Darmstadt, Germany. Their molar masses ranged from 1.6 X 10" to 6.13 X 10 g-mol. For some comparative tests, narrow polystyrene standards from Pressure Co. (Pittsburgh, PA) were used. 

Huber, A. (1992). In Analysis of Polymers/Molar-Mass and Molar-Mass Distribution of Polymers, Polyelectrolytes and Latices (W.-M. Kulicke, ed.), Hiithig Wepf Verlag, 61, 248. 

E. F. Vainstein, A. A. Sokolovskii, and A. S. Kuzminskii, Kinetics of the Changing Products Molecular-Mass Distribution in Thermodegradation of Associated Polymers, Polymer Yearbook, (R. A. Pethrick and G. E. Zaikov, eds.) Gordon and Breach, London, vol. 9, pp. 79-101 (1993). 

The molar mass distribution of hyperbranched polymers is, therefore, always larger than diat of titeir linear homologues and tends toward infinity when conversion becomes close to 1. The use of a B3, comonomer, acting as a chain limiter and core molecule, helps in reducing polydispersity and controlling the molar mass of the final polymer.197... 

The effect is that the polymer molecules are separated into fractions. These are measured by an appropriate detector located at the end of the column, and the detector records the response as a peak on a chart. The chromatogram thus consists of a series of peaks corresponding to different elution volumes, the shortest elution volume being due to the largest molar mass polymer molecules within the sample. Details of the molar mass distribution can be determined from the size and number of the individual peaks in the chromatogram. An example of a gel permeation chromatogram is shown as Figure 6.4. 

The program then requests specification as to type of polymer (line 320). If the "polymer" component is a collection of oligomers, the number of unique species is sought (line 360). The values for the mole (or weight) fraction, functionality and molecular weight of each species is then entered (lines 380-650). The number, site, and mass expectation values of the functionality and molecular weight (lines 650-810) are computed. The necessary site and mass distribution functions are also computed (lines 820-850). 

These parameters are used calculate the site and mass distribution functions assuming a Schulz-Zimm molecular weight distribution. The Schulz-Zimm parameters are calculated in lines 930-950. The weight fraction of diluent (as a fraction of the amount of polymer) is then sought. If there is no diluent enter 0. If there is a diluent, the functionality and molecular weight of the diluent is requested (line 1040). The necessary expectation values are computed (lines 1060-1150). 

The viscosity level in the range of the Newtonian viscosity r 0 of the flow curve can be determined on the basis of molecular models. For this, just a single point measurement in the zero-shear viscosity range is necessary, when applying the Mark-Houwink relationship. This zero-shear viscosity, q0, depends on the concentration and molar mass of the dissolved polymer for a given solvent, pressure, temperature, molar mass distribution Mw/Mn, i.e. 

Polymers in solution or as melts exhibit a shear rate dependent viscosity above a critical shear rate, ycrit. The region in which the viscosity is a decreasing function of shear rate is called the non-Newtonian or power-law region. As the concentration increases, for constant molar mass, the value of ycrit is shifted to lower shear rates. Below ycrit the solution viscosity is independent of shear rate and is called the zero-shear viscosity, q0. Flow curves (plots of log q vs. log y) for a very high molar mass polystyrene in toluene at various concentrations are presented in Fig. 9. The transition from the shear-rate independent to the shear-rate dependent viscosity occurs over a relatively small region due to the narrow molar mass distribution of the PS sample. 

SEC-GC-FID, according to Figure 7.40, has been used to carry out the simultaneous determination of the polymer average molecular masses and molar mass distribution and the concentration of additives [984]. The effluent was split and adsorbed on PTV packing material before GC analysis. The choice of PTV... 

For a free-radical polymerization and a condensation polymerization process, explain why the molar mass distribution of the polymer product will be different depending on whether a mixed-flow or a plug-flow reactor is used. What will be the difference in the distribution of molar mass ... 

Complex polymers are distributed in more than one molecular property, for example, comonomer composition, functionality, molecular topology, or molar mass. Liquid chromatographic techniques can be used to determine these properties. However, one single technique cannot provide information on the correlation of different properties. A useful approach for determining correlated properties is to combine a selective separation technique with an information-rich detector or a second selective separation technique. 

Currently, the most widely used chromatographic technique for the molecular mass distribution analysis of a polymer is SEC. The widespread use of SEC is because of its... 

Ionic chain polymerisations refer to chain mechanisms in the course of which the propagation step consists of the insertion of a monomer into an ionic bond. The strength of this ionic bond can vary, depending on the nature of the species, the temperature and the polarity of the solvent, between a closed ionic pair in contact up to free ions (see Figure 23). Final polymer microstructure (configuration,...) and molecular mass distribution depend on the actual nature of the active ionic species. 

Equilibrium molecular mass distribution in step polymers. 

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