Molecular weight detennination

Polyurethanes are characterised by the conventional analytical and spectroscopic techniques in the same way as other polymers. The standard techniques used for detennining physical properties such as viscosity, specific gravity, drying time, hydroxyl value and isocyanate value (by butyl amine method) have been discussed in earUer chapters. Structural confirmation, molecular weight detennination, rheological behaviour and thermal characterisation are generally carried out by spectroscopic techniques such... 

Most properties of linear polymers are controlled by two different factors. The chemical constitution of tire monomers detennines tire interaction strengtli between tire chains, tire interactions of tire polymer witli host molecules or witli interfaces. The monomer stmcture also detennines tire possible local confonnations of tire polymer chain. This relationship between the molecular stmcture and any interaction witli surrounding molecules is similar to tliat found for low-molecular-weight compounds. The second important parameter tliat controls polymer properties is tire molecular weight. Contrary to tire situation for low-molecular-weight compounds, it plays a fimdamental role in polymer behaviour. It detennines tire slow-mode dynamics and tire viscosity of polymers in solutions and in tire melt. These properties are of utmost importance in polymer rheology and condition tlieir processability. The mechanical properties, solubility and miscibility of different polymers also depend on tlieir molecular weights. 

Small molecules can penetrate and penneate tlirough polymers. Because of this property, polymers have found widespread use in separation teclmology, protection coating, and controlled delivery [53]. The key issue in these applications is the selective penneability of the polymer, which is detennined by the diffusivity and the solubility of a given set of low-molecular-weight compounds. The diffusion of a small penetrant occurs as a series of jumps... 

Fig. 11-20. The detennination of the molecular weight M, and area per molecule 5, from the nS(n) isotherm...

Problem 3.27 For a fractionated sample of cis-l,4-polybutadiene of molecular weight 1.23x10° intrinsic viscosities were measured (Moraglio, 1965) in three different solvents at respective theta temperatures. From the results given below detennine the variation of the unperturbed dimensions of the polymer molecule with temperature. 

Akin, D., et al. (1985). The Detennination of Molecular Weights of Biologically Active Proteins by Cetyltri-methylammoniumbtomidcMinus-Polyacrylamide Gel Electrophoreses, Anal. Biochem. 145 170-176. 

Number-average molecular weights naturally can also be calculated from methods that provide a detennination of molecular weight distribution. These include fractional precipitation, ultracentrifugation, and gel permeation chromatography. From such determinations, M is nearly gratis information to be accepted with reservation. 

Absolute molecular weight was determined by GPC with a laser light scattering measurement. The dn/dc at 690 nm was detennined to be 0.268 mL g. ... 

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