Poly molar mass determination

Figure 15.1. MALDI spectrum of a polycarbonate sample along with peak assignment. In the inset, an expansion of the spectral region from 3.0 up to 3.7 kDa is shown. (Reproduced from Puglisi, C. et al., 1999. Analysis of Poly(bisphenol A Carbonate) by Size Exclusion Chromatography/Matrix-Assisted Laser Desorption/lonization. I. End Group and Molar Mass Determination. Rapid Communications in Mass Spectrometry, 13 2260-2267. With permission of John Wiley Sons, Inc.)...

Other examples of successful combinations of liquid chromatography and MALDI-TOF have been reported by Kruger et al. who separated linear and cyclic fractions of polylactides by LC-CC [184]. Just et al. were able to separate cyclic siloxanes from linear silanols and to characterize their chemical composition [185]. The calibration of an SEC system by MALDI-TOF was discussed by Mon-taudo et al. [186]. Poly( dimethyl siloxane) (PDMS) was fractionated by SEC into different molar mass fractions. These fractions were subjected to MALDI-TOF for molar mass determination. The resulting peak maximum molar masses were... 

Puglisi, C., Samperi, R, Carroccio, S., and Montaudo, G., SEC/MALDI Analysis of Poly(Bisphenol A carbonate). 1. End-Groups and Molar Masses Determination, Rapid Comm. Mass Spectrom., 13, 2260, 1999. 

Of technical interest is poly(dimethylsiloxane) (PDMS). PDMS is optically clear, and is considered to be inert, non-toxic, and non-flammable. The molar mass determines the viscosity of the polymer. In dependence of M PDMS are viscous oils, pastes, or greases. 

FIGURE 16.13 Schematic representation of separation of a block copolymer poly(A)-block-poly(B) from its parent homopolymers poly(A) and poly(B). The elnent promotes free SEC elntion of all distinct constitnents of mixtnre. The LC LCD procednre with two local barriers is applied. Poly(A) is not adsorptive and it is not retained within colnmn by any component of mobile phase and barrier(s). At least one component of barrier(s) promotes adsorption of both the homopolymer poly(B) and the block copolymer that contains poly(B) blocks, (a) Sitnation in the moment of sample introdnction Barrier 1 has been injected as first. It is more efficient and decelerates elntion of block copolymer. After certain time delay, barrier 2 has been introdnced. It exhibits decreased blocking (adsorption promoting) efficacy. Barrier 2 allows the breakthrongh and the SEC elution of block copolymer but it hinders fast elution of more adsorptive homopolymer poly(B). The time delay 1 between sample and barrier 1 determines retention volume of block copolymer while the time delay 2 between sample and barrier 2 controls retention volume of homopolymer poly(B). (b) Situation after about 20 percent of total elution time. The non retained polymer poly(X) elutes as first. It is followed with the block copolymer, later with the adsorptive homopolymer poly(B), and finally with the non retained low-molar-mass or oligomeric admixture. Notice that the peak position has an opposite sign compared to retention time or retention volume Tr. 

As explained in Sections 16.3.4, 6.4.1, and 16.4.2, SEC is a nonabsolute method, which needs calibration. The most popular calibration materials are narrow molar mass distribution polystyrenes (PS). Their molar mass averages are determined by the classical absolute methods—or by SEC applying either the absolute detection or the previously calibrated equipment. The latter approach may bring about the transfer and even the augmentation of errors. Therefore, it is recommended to apply exclusively the certified well-characterized materials for calibrations. These are often called PS calibration standards and are readily available from numerous companies in the molar mass range from about 600 to over 30,000,000g moL. Their prices are reasonable and on average (much) lower than the cost of other narrow MMD polymers. Other available homopolymer calibration materials include various poly(acrylate)s and poly(methacrylate)s. They are, similar to PS, synthesized by anionic polymerization. Some calibration materials are prepared by the methods of preparative fractionation, for example, poly(isobutylene)s and poly(vinylchloride)s. 

Since there had not been any measurements of thermal diffusion and Soret coefficients in polymer blends, the first task was the investigation of the Soret effect in the model polymer blend poly(dimethyl siloxane) (PDMS) and poly(ethyl-methyl siloxane) (PEMS). This polymer system has been chosen because of its conveniently located lower miscibility gap with a critical temperature that can easily be adjusted within the experimentally interesting range between room temperature and 100 °C by a suitable choice of the molar masses [81, 82], Furthermore, extensive characterization work has already been done for PDMS/PEMS blends, including the determination of activation energies and Flory-Huggins interaction parameters [7, 8, 83, 84],... 

The copolymer can be further fractionated by precipitation from acetone solution to n-hexanc at room temperature. In each case, only the first fraction should be used to obtain narrowly distributed high molar mass copolymer chains for LLS measurement, ll NMR can be used to characterize the copolymer composition. The ratio of the peak areas of the methine proton of the isopropyl group in NIPAM and the two protons neighboring the carbonyl group in VP can be used to determine the VP content. The composition of each NIPAM-co-VP copolymer was found to be close to the feeding monomer ratio prior to the copolymerization. The nomenclature used hereafter for these copolymers is NIPAM-co-VP/x/y, where x andy are the copolymerization temperature (°C) and the VP content (mol%), respectively. The solution with a concentration of as low as 3.0 x 10-6 g/mL can be clarified with a 0.45 cm Millipore Millex-LCR filter to remove dust before the LLS measurement. The resistivity of deionized water used should be close to 18 M 2 cm. The chemical structure of poly(NIPAM-co-VP) is as follows (Scheme 2). 

Fl-FFF is most attractive for water-soluble polymers [59] and can directly deliver the diffusion coefficient distribution and also a molar mass distribution via the relationship D=AM b. This was exploited for poly(ethylene oxide), poly(styrene sulfonate) and poly(vinyl pyrrolidone) and other polymers using published Mark-Houwink constants [361 ]. Many papers just report on the fractionation of polymers or the determination of the hydrodynamic size distribution of polymers. Examples include poly(styrene sulfonates) [59,165,243],poly(acrylic acid) [243] and poly(2-vinylpyridine) [59]. 

With new data for polyelectrolytes obtained with the techniques described above it should become possible to determine carefully the effects of ionic strength and externally controlled surface potential on the rate of adsorption of poly electrolytes. We hope that the effects of molar mass and charge density of the poly electrolyte, as well as the nature of that charge (annealed or quenched) can be established. This should stimulate further theoretical research aimed at constructing an adequate equivalent of the Von Smolu-chowsky-Fuchs theory for the rate of flocculation. At present, it would seem that an analysis of the adsorption process taking all complications into account necessitates a simulation-oriented approach. 

Because the HEUR thickeners are relatively low in molar mass (30000-100000 g mol ) compared to the alkali soluble or cellulosic associative thickeners, and the poly(ethylene oxide) backbone is so flexible, almost all of the thickening power comes from associations [106,107]. Molar mass must be high enough to provide efficient network formation, but veiy high molar mass simply dilutes the effectiveness of the hydrophobic clusters [108-110]. While the placement of the hydrophobes may have subtle effects on surface-active behaviour, the size and number of hydrophobes appear to be fee major determinants of performance [110,111]. 

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