Romeu Casarano

Acylation of cellulose in a novel solvent system: solution of dibenzyldimethylammonium fluoride in DMSO.

A novel electrolyte, dibenzyldimethylammonium fluoride has been obtained essentially anhydrous (BMAF-0.1H2O) by a simple route. Its thermal stability, relative to tetra(1-butyl)ammonium fluoride trihydrate (TBAF3H2O) has been demonstrated by thermogravimetric analysis. DMSO solution of (BMAF-0.1H2O) dissolves microcrystalline- and fibrous celluloses; the dissolved biopolymers have been acylated by ethanoic-, butanoic-, and hexanoic anhydride. The degrees of substitution of the esters are higher than with TBAF3H2O/DMSO. The reasons are discussed in terms of differences in electrolyte structure and contents of water of hydration, whose presence leads to side reactions and decreases of the basicity of (F(-)). This conclusion is corroborated by molecular dynamics simulations of the interactions of glucose dodecamer/R4NF-hydrate/DMSO. These show that the interactions oligomer-F(-)-water is operative only for TBAF3H2O/DMSO. The efficiency of BMAF-0.1H2O/DMSO is explained based on better accessibility of the biopolymer due to efficient hydrogen-bonding between its hydroxyl groups and the essentially desolvated (F(-)).

Synthesis and structural characterization of block and random low molecular weight copolymers composed of L-lactic acid and isosorbide succinate moieties

Residuos de succinato de isosorbideo foram incorporados na cadeia principal de poli(L-lactideo) (PLLA) visando a obtencao de uma nova classe de polimeros biodegradaveis com propriedades melhoradas. Este artigo descreve a sintese e caracterizacao de quatro tipos de copolimeros de baixa massa molar. O copolimero I foi obtido da mistura dos monomeros L-lactideo, isosorbideo e anidrido succinico; II do oligo(L-lactideo) (PLLA), isosorbideo e anidrido succinico; III do oligo(succinato de isosorbideo) (PIS) e L-lactideo; e IV de reacoes de transesterificacao entre PLLA e PIS. Analises de MALDI-TOFMS e 13C-NMR apresentaram evidencias de que cooligomerizacao foi alcancada em todos os casos. Os dados sugerem que o produto I e um cooligomero aleatorio e que os produtos II-IV sao cooligomeros em bloco.