| Three previously known free radical initiators, azobisisobutyr- amidine hydrochloride (1), azobis-N,N'-dimethyleneisobutyramidine hydrochloride (2), and 4,4'-azobis(4-cyanopentanoic acid) (3), and four new initiators prepared by derivatization of (3), N,N'-dimethyl-4,4'-azobis (4-methyl-1-piperazine)-4-cyanopentanamide diodide (4), N-methyl-4,4'-azobis( 4-(3-hydroxypropyl)-1-piperazine -4-cyanopentanamide) idodide (5), N,N'-dimethyl-4,4'-azobis (dimethyl- aminopropyl)-4-cyanopentanamide dinitrate (6b), and 4,4'-azobis (4-aminosulfonylphenyl)-4-cyanopentanamide (7) were used to prepare monodisperse latexes having diameters between 0.2 and 0.7 (mu)m by soap free aqueous polymerization of styrene. The influences of initiator structure, degree of functional group ionization, and level of aqueous phase ionic strength on final particle size and polymer molecular weight were investigated. When the fraction f of charged initiator functions was 1.0 (latexes made using 1, 2, 3), the particle size (')D(,n) increased with increasing aqueous phase ionic strength I, the log((')D(,n)) versus log(I) relationship held, and the polymer molecular weight (')M(,w) decreased with increasing I (1 latexes). By contrast, when f was varied from less than 0.1 to greater than 0.9 (latexes made using 7) (')D(,n) did not correlate with I, but did correlate (inversely) with pH. As f was decreased, both (')D(,n) and (')M(,w) increased, and the distribution of polymer molecular weights narrowed.; The addition of water soluble polymers to high ionic strength poly- merizations using 1 increased the percent conversion to polymer, but produced polydisperse latexes having diminished particle electro- phoretic mobility. A dried latex polymer containing 6.2% by weight 88% PVOH formed a smooth, rub-resistant casting, which was further investigated by THF extractions and optical microscopy. A ('13)C nmr chemical shift study probed the interactions in D2O solution between the amidinium cation and models for the pendant groups of the poly- mer additives. Hydrolysis studies on model amidine hydrochlorides indicated that latexes prepared using 1 at a non-buffered "neutral" pH should retain all surface functions intact.; A proton FT-nmr method for measuring the rate constant for thermolysis of azo-type free radical initiators was developed, and compared favorably with results obtained by the classical UV spectrophotometric method. Thermodynamic parameters for the thermolysis of 1 and 2 were obtained. |
