Synthesis and characterization of cellulose esters prepared in DMSO:paraformaldehyde solutions



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The nature, prerequisites and solution mechanisms which afford the solubility of poly [ (l->4) -[beta]-D-glucopyranose] (cellulose) in mixtures of DMSO and paraformaldehyde (PF) were determined. Spectroscopic and viscometric analyses of DMOS:PF solutions of (cellulose were used to demonstrate the interrelationships between cellulose solution concentration, temperature, and stoichiometry. Proton magnetic resonance (PMR) studies of DMSO:PF solutions of cellulose and the in-situ reactions between various cellulose analogs and carbonyl compounds of varying electrophilicities demonstrated the progressive formation of carbonyl addition products (cellulose methylols). Methylol formation was shown to be prerequisite to the observed solubility of cellulose in DMSO:PF. The newly found solubility of cellulose in an organic solvent system was exploited by the evaluation and development of synthetic techniques to esterify cellulose in DMSO:PF solutions. It was demonstrated that mixtures of pyridine (Py) and organic anhydrides [(RCO)[lowered 2]0] easily acylate cellulose in 1.0 and 2.0 hours to yield cellulose esters with varying degrees of acyl substitution. These esters were characterized via infrared (IR) , ultraviolet (UV), and PMR spectral analyses, differential scanning calorimetry (DSC) thermal analyses, solubility studies and degree of acyl substitution analyses. In this work it was demonstrated that cellulose solutions of varying concentrations (0.1 to 2.5 percent cellulose) are easily prepared under mild conditions (70[degrees]C) and that these solutions may be used to prepare cellulose esters (Degree of Acyl Substitution = 0.0 to 2.0) in a one solution process within 1.0 to 2.0 hours. The resulting polymers vary in physical properties. They were hard thermoplastic granules or resinous liquids depending on the degree of acyl substitution and the nature of the esterifying anyhydfide. All were soluble in acetone and other solvents having solubility parameters between 9.0 and 12.7 6. These solutions were easily cast into films.