Precipitation polymer, pure aqueous solutions

A different effect occurs with the use of polycarboxy-lates in combination with zeolites. Small amounts of polycarboxylates or phosphonates can retard the precipitation of sparingly soluble calcium salts such as CaCOs (the threshold effect ). As they behave as anionic polyelectrolytes, they bind cations (counterion condensation), and multivalent cations are strongly preferred. Whereas the pure calcium salt of the polymer is almost insoluble in water, mixed Ca/Na salts are soluble, i.e. only overstoichiometric amounts of calcium ions can cause precipitation. Polycarboxylates are also able to disperse many solids in aqueous solutions. Both dispersion and the threshold effect result from the adsorption of the polymer on to the surfaces of soil and CaCOs particles, respectively. 

A mixture of 1,1 -bipyridyls (0.85 g, 5.4 mmol), bis(cyclooctadiene)nickel, (Ni(COD)2), (1.50 g, 5.4 mmol), cyclooctadiene (COD) (0.48 g, 4.5 mmol) in 15 mL of DMF is added to a solution of 1.68 g (4.5 mmol) of 3-octoxy-2,5-dibromothiophene in 18 mL DMF under an argon atmosphere. The reaction mixture is stirred at 60 °C for 18 h and 200 mL of acidic methanol is added to quench the reaction. The solid formed is filtered and washed with acidic methanol followed by aqueous solution of hot ethylenediaminetetraacetic acid (EDTA) and finally with water. Crude product is dissolved in chloroform and precipitated in methanol to get the final pure polymer as a blue violet solid. The polymer is obtained in good yields (70%) and is readily soluble in organic solvents (THF, chloroform, toluene). The weight-average molecular weight of the polymer was found to be 4.6 kDa with a PD of 1.35. °... 

The block-polymers containing a middle block of polystyrene and two blocks of polyethylene oxide have some unusual properties. They are soluble in methyl ethyl ketone and cannot be precipitated from this solvent by methanol. Addition of water produces a slight cloudiness but still no precipitation although the block polymer is not soluble in pure water. The polymer is also soluble in benzene, but addition of water to this solution causes its precipitation. On the other hand, neither homopolystyrene nor homo-polyethylene oxide or their mixtures are precipitated from benzene solution by addition of water. This strange behaviour is explained by Richards and Szwarc (45) in terms of hydrogen bonding which depends on the chemical potential of water in the aqueous layer and therefore also in the benzene solution. 

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