Molecular weight analysis polyethers

The composition of the star-shaped block copolymer is easily determined by proton NMR analysis from this and the mean number average molecular weight (Mn) of the sequence PA, Mn of the polyether component can be calculated. The later is very similar to the value from membrane osometry. Hydroxyl end group of PA(P0)2 star-shaped block copolymers have been titrated and their mean number per copolymer (1.85) agrees with the presence of two polyoxirane branches. On the average, the polydispersity of the star-shaped block copolymers varies between 1.2 and 1.3 (Figure 6). 

The functionality / of low-molecular-weight functionalized prepolymers (e.g., polyether polyols used in the preparation of polyurethanes) is often determined from Eq. (4.31) by combining functional group analysis with another suitable method of molecular weight determination such as vapor phase osmometry. Note that in this respect the functional groups do not have to be end groups. 

Cheng and English edited ACS symposium series which covers the solution and solid state NMR investigations for dendrimers, cellulose, polyurethane, polyolefins biopolymers, copolymers and so on. Spiess described a historical overview of role of NMR spectroscopy in polymer science. Newmark summarizes the two dimensional and pulsed gradient diffusion NMR experiments and their applications to polymers Shit et al. reviewed the analysis of polymer molecular weight and copolymer composition by NMR. Sasanuma summarized the the analysis of polyethers and polysulfides by NMR and theoretical calcula-tions Ardelean et al described the principle and its applications of diffusion studies by NMR. Roy et al summarized the structural analysis of Novolak resins by multidimensional NMR. Reviews about NMR study of surfactant polymer blends and the structural elucidation of supramocules are published. 

Some preliminary work has been done on low molecular weight polyethers whose chains are so short that they are actually liquids at room temperature. These liquids certainly retain the chemistry of their longer-chained analogues (except for a higher concentration of end-groups), while being single-phase amorphous systems. In addition, they are easily handled and lend themselves readily to electrochemical, spectroscopic and viscometric analysis. Thus, they are suitable model systems, at least for the chemical interactions which occur in polyether-based systems. 

Additionally, polyesters and polyethers may contain several impurities derived from their methods of manufacture and being polymeric materials may vary in molecular weight and type of end-group. For routine analysis of raw materials, a determination of hydroxyl value, acid value and water content is usually sufficient. The reactivity of polyesters of the same chemical type can vary widely and for this reason it is sensible that an activity test be performed similar to that for diisocyanates using a diisocyanate of standardized activity. 

Selective degradation reactions combined with MALDI analysis were applied for molecular weight determination of polyether and polyester polyurethane soft blocks. Size exclusion chromatography was combined with MALDI to provide accurate molecular weight determination. 44 refs. USA... 

The selection of an appropriate liquid phase for an analysis depends on several factors but principally on the compounds to be separated. Phases which may be suitable for the separation of a small selected group of organic acids may not be suitable when other acids are present. Clearly, non-polar phases separate compounds with respect to boiling point or molecular weight and will only permit elution of compounds which are volatile within the thermal stability range of the phase. Equivalent constraints apply to polar phases. Prior to the introduction of the modified silicone oil liquid phases, the phases most commonly in use were, for non-polar conditions, silicone grease or Apiezone L and for polar columns the polyglycols, polyesters or polyethers. 

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