Cellulose acetate polystyrene grafted

The properties of cellulosic graft copolymers have been studied to a considerable extent but mainly in the form of grafted fibers or films of ill-defined composition. However, a few properties have been measured on well defined grafts (147). It was found that solutions of cellulose acetate-polystyrene grafts in dimethyl formamide are less tolerant to the addition of polystyrene than cellulose acetate itself. This result was attributed to the greater coil expansion in the case of the graft copolymer. On the other hand, the tolerance of the grafts to each homo-... 

Deters (14) vibromilled a blend of cellulose and cellulose triacetate. The acetic acid content of cellulose acetate decreased with grinding time (40 h) while that of the cellulose increased, suggesting the formation of a block or graft copolymer or of an esterification reaction by acetic acid developed by mechanical reaction. Baramboim (/5) dissolved separately in CO polystyrene, poly(methyl methacrylate), and poly(vinyl acetate). After mixing equal volumes of solutions of equivalent polymer concentration, the solvent was evaporated at 50° C under vacuum and the resultant product ball-milled. The examination of the ball-milled products showed the formation of free radicals which copolymerized. 

The existence of a true graft copolymer was concluded from the weight increase not extractable by polystyrene solvents and by the eventual leveling off of the weight increase while homopolymerization continued. Moreover, the graft of cellulose acetate and styrene after dissolution and precipitation with various solvents and precipitants still showed the infrared absorption of both substituents. In addition to this, the results fitted well with the kinetic theoiy of grafting proved on other systems. 

Fig. 5. Intrinsic viscosity of a cellulose acetate graft copolymer (44.1% combined polystyrene) and the corresponding homopoly-mers in toluene-acetone mixtures...

Preparation of Cellulose-Polystyrene Graft Copolymers. The polystyr-yl mono- and di-carbanions were prepared in THF at -78 °C by using n-butyl lithium and sodium naphthalene as the initiators, respectively. The carban-ions were reacted with dry carbon dioxide. The products were precipitated in methanol, filtered, washed with water and methanol, and dried. Size exclusion chromatography (SEC) established that the molecular weight of the polystyryl monocarboxylate was 6,200 and that of the polystyryl di-carboxylate 10,2000. The mono- and di-carboxylates were reacted with mesylated cellulose acetate in dimethylformamide at 75 °C for 20 h to give the cellulose-polystyrene graft copolymer (GP 1) and crosslinked cellulose-polystyrene graft copolymer (GP 2), respectively. 

Similar polymer compatibilization effects were observed by Wellons and co-workers (19) on radiation graft copolymers of cellulose acetate and polystyrene and by Riess and his colleagues (20) on various block copolymers. Hughes and Brown (21) also reported some evidence of compatibilization in a... 

Pendant nitro groups are also effective in chain-transfer grafting reactions. Thus, graft copolymers of polystyrene with cellulose acetate p-nitrobenzoate and with poly(vinyl p-nitrobenzoate) form readily. Nitro groups appear to be more effective in formations of graft copolymers by a radical mechanism than are double bonds located as pendant groups. " ... 

Figure 5 shows the TGA of the polystyrene-cellulose acetate graft polymer in comparison with the polystyrene-oxycellulose graft polymers. The TGA curve of the polystyrene-cellulose acetate is clearly different from the polystyrene-oxycellulose graft polymers and the cellulose acetate. It shows much Biore thermal stability than the other three. 

Wu et al. (1992) measured the advancing water contact angles on the top surface of modified membranes by plasma surface polymerization of polystyrene grafting of cellulose acetate membranes to test their hydrophobicity. The water contact angles were found to increase with the radiation time and presented a minimum with discharge power. 

The acetylated true graft copolymer was dissolved in methylene chloride, acetone was added to the solution to obtain a 1 1 methylene chloride-acetone composition of the solvent, concentrated hydrochloric acid was added to obtain a 3N solution, and hydrolysis was carried out for 72 hr at 60 °C. The hydrolysis proceeded not in a homogeneous but in a highly swollen state. The branch was precipitated by pouring the hydrolysis mixture into methanol. A part of the precipitated branch was dissolved in m-cresol and filtered. The other part was treated with 1 2 acetic anhydride-pyridine mixture for 15 hr at 100 °C to acetylate cellulose fragments at the end of polystyrene brandies. 

The membrane surfaces have also been grafted or coated with polyacrylamide, poly(acrylic acid) [70, 71], poly(vinyl alcohol) and cellulose derivatives [72]. Another possibility for improving the membrane properties is the use of polymer blends. Blends of PVDF/PVP [73, 74], PVDF/poly(ethylene glycol) (PEG) [75], PVDF/sulfonated polystyrene [76], PVDF/poly(vinyl acetate) [77] and PVDF/ poly(methyl methacrylate) [78] have been used in the preparation of micropor-ous membranes. 

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