Water-soluble incompletely substituted cellulose acetate (CA) was synthesized by the hydrolysis of cellulose diacetate with hydrochloric acid. CA having a degree of substitution DS between 0.39 and 0.81 was water-soluble. TheCA (DS=0.49) whole polymer was fractionated into 15 parts, using water-methanol as the solvent-nonsolvent by the successive solution method. The CA (DS=0.49) polymer was soluble in highly polar organic solvents. Solution viscosity, light scattering, and membrane osmometry measurements were performed at 25 C on these fractions in N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), water, and formamide. The fractions had ratios of weight-to-number-average molecular weight M,../ M,. of approximately 1.3, independent of M,. .. The following relations between limiting viscosity number [11], :-average radius of gyration (S 2 ); 12 and Mw were obtained: [11] =0.19 (cm 3 g-1 ) and (S 2 ); 12 =0.50 x 10-" (em) in DMAc at 25 C. Flory's viscosity parameter

ABSTRACT:Cellulose triacetate(CTA, combined acetic acid content, 61.0wt%) was successfully fractionated on the basis of molecular weight by successive solutional fractionation using 1-chloro-2,3-epoxypropane as the solvent and hexane as the nonsolvent. The fractions cover a very wide range of molecular weights, having comparatively narrow molecular weight distribution (em). For CTA/DMAc system, the CTA chain is gaussian in the unperturbed state and a ( =dln

=Flory's viscosity parameter)=0.106 and the draining parameter X =2 were obtained. On the basis of the light scattering and viscosity data, the short-range interaction parameter A=l.46x 10-8 cm, the conformation parameter cr=3.14, and the characteristic ratio Coc.=20.4. These values were estimated by using method 2B, 2C, and 2G, proposed in the previous paper (This journal, 10, 409 (1978)). The A value in polar solvents (group I: DMAc, trifluoroacetic acid, and acetone) is significantly larger than that in non-polar solvents (group II: dichloromethane, tetrachloroethane, and trichloromethane). The effect of the degree of substitution on [17] and cr for cellulose acetate in acetone is just the reverse of those for cellulose nitrate in the same solvent. The CTA chain is semiflexible and the contribution of the volume effect on [17] is much smaller than that of the draining effect.

An attempt was made to verify the modern theory of molecular weight fractionation based on solubility behavior by experiment. Aractic polystyrene (PS) in methylcyclohexane (MCH) and in cyclohexane (CH) were employed for this purpose. The following quantities were determined experimentally and compared with theoretical values calculated with theaid ofan electronic computer: The partition coefficient CT, volume ratio of polymer-lean phase to polymer-rich phase R , polymer volume fraction in the two phases, up(,) and up(2), weight-average molecular weight a, and the breadth of the molecular weight distribution (the ratio of weight-to number-average molecular weight, &iw/an and standard deviation CT') of the polymers in both phases. The experimental data can be well explained in terms of theory if the concentration dependence of the polymer/solvent interaction parameter x, expressed by p , is reasonably taken into account, i.e., p=0,7for PS in MCH and p=0,6 for PS in CH. It was shown that CT depends slightly on molecular weight. ZUSAMMENFASSUNG:Es wurde versucht, die moderne Theorie zur Loslichkeitsfraktionierung nach dem Molekulargewicht experimentell nachzuprufen. Ataktisches Polystyrol (PS) in Methylcyclohexan (MCH) und in Cyclohexan (CH) wurden hierzu benutzt. Folgende GroBen wurden experimentell bestimmt und mit den theoretischen, durch einen Computer berechneten Werten verglichen: der Verteilungskoeffizient CT, das Volumenverhaltnis R von polymerarmer zu polymerreicher Phase, der Volumenbruch des Polymeren in den beiden Phasen up(l) und up(*) sowie das Gewichtsmittel &iw des Molekulargewichts und die Breite der Molekulargewichtsverteilung (als Verhaltnis aw/an und als Standardabweichung 0') des Polymeren in den beiden Phasen. Die experimentellen Daten lassen sich gut durch die Theorie erklaren, wenn die Konzentrationsabhangigkeit des Parameters der Polymer/Losungsmittel Wechselwirkung berucksichtigt wird. Letztere wird ziemlich gut durch p ausgedriickt, wenn p=0,7 fur PS in MCH und p=0,6 fur PS in CH ist. Es wurde gezeigt, daB CT geringfugig vom Molekulargewicht abhangt.

ABSTRACT:For the purpose of verifying the validity of modern fractionation theory by experimentation, atactic polystyrene in methylcyclohexane was fractionated by employing a successive solutional fractionation (SSF) method. SSF was duplicated under different operating conditions. The fractions thus prepared and those in a previous paper (Makromol. Chem., 117, 485 (1976)) were eluted through a GPC column, whose resolution factor h was very accurately determined in advance. The experimental relations of the ratio of the weight-to number-average molecular weight Mw/Mn vs. Mw obtained for three SSF runs fit in well with those predicted by the theory with p=O.

An attempt was made to prepare the polymer fractions having extremely sharp molecular weight distribution (MWD), by using a successive solutional fractionation (SSF) method, in which a polymer‐lean phase was separated as a fraction from a polymer‐rich phase. For this purpose a large‐scale preparative SSF apparatus was constructed. Atactic polystyrene (PS) high‐density polyethylene (PE), and cellulose di‐ and tri‐acetates (CDA and CTA) were fractionated by SSF. The fractions isolated from a quasi‐binary mixture (polymer/solvent system) have the same MWD as that predicted by the computer simulation technique. Even under the conventional fractionation conditions (initial polymer volume fraction vop = ∼ 0.01, total number of fractions nt = 10 ∼ 20) the fractions with the ratio of the weight to number‐average molecular weight Mw/Mn less than 1.1 for PS, 1.2 for PE, 1.3 for CDA and 1.4 for CTA were obtained, with exception of a few initial fractions. The advantage of the SSF method was clarified over the conventional preparative methods such as gel permeation chromatography and the column fractionation method.