Copolymer molar mass determination

Norbornene molar fraction in copolymer ( C NMR, 1,2,4-trichlorobenzene, 100 °C). Copolymer molar mass determined by viscosimetry in 1,2,4-trichlorobenzene at 135 °C. 

Copolymer molar mass determinations were made by size occlusion dnomatogn hy (SEC) using viscometric detection and universal calibration and are absolute. Glass transition temperatures were determined by diffowitial scanning calorimetiy (DSC) undo nitrogo) at a heating rate of 10 °C/min. 

Molar mass determination of the acetylated true graft copolymer, the separated branch after acetylation and the acetylated mother cellulose, was carried out with a high speed membrane osmometer using chloroform, benzene, and chloroform, resp., as solvents. 

Molar mass determination requires the knowledge of the specific refractive index increment Ant Ac which in the case of complex polymers depends on chemical composition. Copolymer refractive index increments (dn/dc)copo can be accurately calculated for chemically monodisperse fractions, if comonomer weight fractions and homopolymer values are known ... 

Conventional GPC data processing is unable to determine other important polymer properties such as copolymer composition or copolymer molar mass. The reason is that the GPC separation is based on hydro-dynamic volume rather than the molar mass of the polymer and that molar mass calibration data are only valid for polymers of identical molecular structures. 

The major difficulty in the determination of the copolymer molar mass distribution is the fact that the GPC separation is based on the molecular size of the copolymer chain. Its hydrodynamic radius, however, is dependent on the type of the comonomers incorporated into the macromolecule as well as their placement (sequence distribution). 

In such cases, the copolymer molar mass M can be determined from the interpolation of homopolymer calibration curves M V) and the weight fractions w. of the comonomers k according to [1]... 

Among the various mass spectrometry techniques, MALDI is probably the most important as it provides an absolute method for molar mass determination and molar mass distribution, as well as information on end groups and copolymer composition. The MALDI process consists of the ablation of the polymer molecules dispersed in a matrix typically made up of aromatic organic acids. The matrix needs to be able to absorb at the wavelength of a laser (usually 337 nm). This process excites the matrix molecules, which vaporize at the same time, the polymer molecules desorb into the gas phase, where they are ionized. Thus, the role of the matrix is that of transferring the laser energy to the polymer molecnles. 

Since the knowledge about molar mass determination using viscosimetry and determination of the coil dimensions is of fundamental importance for technical problem solving, these are the main topics of this book. It will give detailed case studies and theoretical background about the different independent variables, like concentration, molar mass, quality of the solvent, chemical nature of the polymer, polyelectrolyte character, composition of copolymers, influence of the substitution pattern for renewable raw materials and the degree of branching. 

Pasch et al. have compared of copolymer molar masses from SEC and from LCCC for block copolymers PDMA-PMMA [61] and PS-PMMA [80]. From the molar mass of the individual blocks, which were measured under LCCC, the total molar masses of the block copolymers were calculated. Moreover, the expected nominal chemical composition was compared with the chemical composition determined by LCCC. While the molar mass of copolymers from SEC was used for comparison in some studies [61,80], molar mass of PS precursor used for preparation of corresponding copolymers has also been selected as reference value in [47]. Very good agreement of values was found, as documented by data in Table 6A,B extracted from [47,80]. 

Several attempts have been made to solve the calibration dilemma. Some are based on the tmiversal calibration concept, which has been extended for copolymers another approach to copolymer calibration is multiple detection. The advantages of multiple detection lie in its flexibility and the fact that it yields the composition distribution as well as molar masses for the copolymer under investigation [7]. This method requires molar mass calibration and an additional detector response calibration to determine the chemical composition at each point of the elution profile. No other kind of information, parameters or special equipment are necessary to carry out this kind of analysis and to calculate compositional drift, bulk composition, and copolymer molar mass [7a],... 

The major difficulty in the determination of the copolymer molar mass distribution is the fact that the GPC separation is based on the molecular size of the copolymer chain. Its hydrodynamic radius, however, is dependent on the type of comonomers incorporated into the macromolecule and their placement (sequence distribution). Consequently, there can be a coelution of species having different chain lengths and different chemical compositions. The influence on the chain size of different comonomers copolymerized into the macromolecule can be measured by GPC elution of homopolymer standards of this comonomer. Unfortunately, the influence of the comonomer sequence distribution on the hydrodynamic radius cannot be described explicitly by any theory at present However, there are limiting cases that can be discussed to evaluate the influence of the comonomer placement in a macromolecular chain. 

An independent task of copolymer analysis is the determination of meaningful copolymer molar masses. Obviously, results based on a single molar mass calibration generated with standards will not give accurate results, as the calibration will depend on the local composition of the species. A way to overcome this calibration dilemma is the use of online viscometers. An empirical method for samples with few hetero-contacts (e.g., block copolymers and graft copolymers) is using the multiple concentration detector approach. 

From a SEC point of view, an AB block copolymer, where a sequence of comonomer A is followed by a block of B units, is a simple copolymer. The only hetero-contact in this chain is the A-B link, the A and B segments of the block copolymer will hydrodynamicaUy behave like a pure homopolymer of the same chain length. In the case of long A and B segments, the A-B link acts as a defect position and will not change the overall hydrodynamic behavior. Consequently, the molar mass of the copolymer chain can be approximated by the molar masses of the respective segments. Similar considerations are true for ABA, ABC, and other types of block stmctnres and for comb-shaped copolymers with low side-chain densities. In snch cases, the copolymer molar mass can be determined from the interpolation of the two homopolymer calibration curves M V) and the weight fractions of the comonomers k [26] ... 

Tillier and co-workers [49] performed a SEC analysis on polyethylene terephthalate-6 caprolactone copolymer. After fractionation sample with an 1 between 1.09 and 1.09 (fraction 14-38 in Figure 5.14) were subject to molar mass determinations by... 

Volume fractions imply a temperature dependence and, as they are defined in equation (38), neglect excess volumes of mixing and, very often, the densities of the copolymer in the slate of the solution are not known correctly. However, volume fractions can he calculated without the exact knowledge of the copolymer molar mass (or its averages). Base mole fractions are seldom applied for copolymer systems. The value for A o, the molar mass of a basic unit of the copolymer, has to he determined according to the corresponding average chemical composition. Sometimes it is chosen arbitrarily, however, and has to he specified. 

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. 

Bravo, 1984). Hybrids of these systems, where chromatography and electrophoresis are used in each spatial dimension, were reported nearly 40 years ago (Efron, 1959). Belenkii and coworkers reported on the analysis of block copolymers by TLC (Gankina et al., 1991 Litvinova et al., 1991). Two-block copolymers of styrene and f-butyl methacrylate were separated first with regard to chemical composition by TLC at critical conditions, followed by a SEC-type separation to determine the molar masses of the components. 

Statistical and block copolymers based on ethylene oxide (EO) and propylene oxide (PO) are important precursors of polyurethanes. Their detailed chemical structure, that is, the chemical composition, block length, and molar mass of the individual blocks may be decisive for the properties of the final product. For triblock copolymers HO (EO) (PO)m(EO) OH, the detailed analysis relates to the determination of the total molar mass and the degrees of polymerization of the inner PPO block (m) and the outer PEO blocks (n). 

In addition, the molar mass (which is proportional to the intrinsic viscosity, [t]]. Tab. 6.17) of the copolymer decreases with increasing potential in the silent system, whereas in the sonicated case it is effectively constant. Overall ultrasound also appears to produce a more uniform reaction system in that in the silent system the reactivity ratio (determined by infra red spectroscopy) increases with electrode potential, whilst under sonication it remains fairly constant. 

The relative retention a=k/ki is a measure of the separation selectivity for two compounds i and j with retention factors ki and kj, respectively, differing by one repeat structural unit, An=l.p in Equation 5.16 is the end-group contribution to the retention factor. The conventional theory describes adequately the retention of oligomers and lower homopolymers and copolymers up to the molar masses 10,000-30,000Da for higher polymers the accuracy of the determination of retention model parameters is too low [95]. 

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. 

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