Molecular weight distribution Nylon

Howardt describes a model system used to test the molecular weight distribution of a condensation polymer The polymer sample was an acetic acid-stabilized equilibrium nylon-6,6. Analysis showed it to have the following end group composition (in equivalents per 10 g) acetyl = 28.9,... 

Estimation of Molecular Weight Distribution of Polyamide Blocks. The molecular weight distribution of the polyamide blocks was estimated by gel permeation chromatography (GPC) using two instruments, model HLC-802R (Toyo Soda Industry Co., Ltd.) and model GPC-2i U (Waters Associates, Inc.). Polystyrene and nylon oligomer were used as standards. 

Hydrolysis of Copolyamide-esters (CPAEs) by Lipase (jj,). CPAEs were synthesized by the amide-ester interchange reaction between polyamide and polyester. The length of the polyamide blocks was measured after hydrolysis of ester bonds in CPAE by alkali at 30 C. The infrared spectra after hydrolyzing ester bonds on CPAEs showed that the ester bonds were almost completely removed. The molecular weight distribution of polyamide blocks was examined by GPC (Table II). The following samples were used CPAE-1 (reaction time for synthesis, 1 hr) and CPAE-2 (reaction time, U hr) composed of nylon 6 and PCL at a 50/50 molar ratio, CPAE-3 (reaction time, 1 hr) and CPAE-U (reaction time,... 

Molecular-Weight Distribution of Condensation Polymers Kinetics and Mechanism of Nylon 66 Polyamidation Amidation... 

The molecular weights of nylon-6 are generally in the same range as nylon-6,6. Its molecular weight distribution as prepared under the above conditions is also the same as linear nylon-6,6 and other linear condensation polymers with M /M = +p,or about two. However, nylon-6 and AB polyamides are unique in that a narrower molecular weight distribution can be attained by adding a bifunctional stabilizer such as the Bb-type dicarboxylic add [37]. An AB polymer chain can only pick up one BB unit and becomes terminated with B end groups at both ends. For example, if 40 equiv. 10 g. of BB units are added and the concentration of A ends [NH2] is reduced to 10 equiv. 10 g, M jM = 1.6. It would be possible to increase by 25% in that case. 

Molecular Weight Distribution Data for Nylon 6, Polycarbonates, and Other Polymers ... 

The development ofand new trends in the determination of molecular weights and molecular weight distribution of aliphatic unsubstituted linear polyamides (nylons) are reviewed here. Critically discussed are intrinsic viscosity - molecular weight relationships and the conformational regidity of nylon chains. Attention is also given to some peculiarities in the behavior of nylons in multicomponent solvents. 

This article is an attempt at a comprehensive survey of papers dealing with dilute solutions of nylons, especially of nylons 6,6,6,4 and 12. The uuhvidual chapters will be devoted to the determinations of nwlecular wei tt and molecular weight distribution, to the hydrodynamic properties and ccaiformation of nyirm molecules, and finally to some specific features of the behavior of nylons in multicomponent solvents. Since the solution properties of these nylons are alike, the individual nylons are not dealt with separately differences in the behavica of various nylons are pointed out in the respective chapters. 

The aim of preparative fractionation of nylons is to obtain fractions vdiich may be used eithn in the determination of the molecular weight distribution curve or in the determination of the relaticmship between intrintic viscosity and molecular weight. In both cases, the goal is to obtain as narrow fractions as possible in the determination of the molecular weight distribution a fuU recovery of the sample is mandatory. 

Fig. 4. Integral molecular weight distribution curves of nylon 6j6 on the basis of fractionation in m-cresol/cydohexane. The number of fractions inoeases in the sequence 1, 2,3 9)...

The effect of the number and quality of fractions was demonstrated in rady attempts to determine the molecular weight distribution of equilibrium-polymerized nylons 6 and 6,6. While some authors confirmed that equifitmum-pol merized nylons had the most probable distribution predicted by Flory , others found distributions which were coiisiderably narrower. While the most Hfobable distribution was established from a large number of fractions obtained by lefractionation of primary fractions narrower distributions resulted from fractionations with a smaller number of fractions ... 

The data published so far on nylon 6 and 6,6 allow the conclusion that turbi-dimetric titration is not a suitable method for an accurate determination of the molecular weight distribution, but that owing to its speed, it may be en loyed, e g., in preliminary comparative studies of the relative changes of distributirms ... 

Figure 4.) Shown here is the experimental molecular weight distribution u k for nylon, as a function of chain length k. This quantity is given by u k = (constant) experimental data for nylon. Source PJ Flory, Principles of Polymer Chemistry, Cornell University Press, Ithaca, 1953. Data are from GB Taylor, J. Am Chem Soc 69, 638 (1947). 

The data show that n is approximately the same for polymerizations carried out with py-K/C02 in the presence and absence of an onium salt. If TMAC were an initiator, a large increase in n would be expected. The fact that N-acetylpyrrolidone, a typical initiator, gives a much larger n is consistent with this analysis. It should be pointed out that for TMAC and N-acetylpyrrolidone pol3aneriza-tions the differ ce between the apparent number of chains would be even greater if Mn were used to calculate n because of the narrower molecular weight distribution of the onium salt prepared nylon 4. 

While Bell Labs was not a producer of polymers, AT T was one of the largest users in the world. The basic approach was to know more than anyone about the materials that were used for telecommunications. The British company ICI synthesized crystalline polyethylene, but Bell Labs discovered how to properly process this material and what microscopic parameters were important, such as the molecular weight distribution. DuPont synthesized nylon, but Bell Labs discovered how to make it useful as a stable material for long-term use. Cellulose polymers were an old technology, but Bell Labs discovered new ways to process it that achieved remarkable new properties and uses. Baker was the genius behind the philosophy and much of the early work. He wanted to know the actual truth about materials and reached out to the very best scientists. Peter Debye was a regular visitor to Bell Labs during the Baker era. 

Polymers from step-reaction polymerizations have structures that are far more uniform than those prepared by chain-reaction polymerizations. The molecular weight distributions obtained are narrow. Examples are nylons, polyesters and polyurethanes. The structures can be determined directly by infrared or nuclear magnetic resonance techniques or after hydrolysis and isolation of the monomers used in polymerization. 

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