Question

Propose a reaction scheme for the synthesis of hyperbranched polyamide, in which there is no possibility of gelation. What are the reaction characteristics, which would affect the molar mass of the polymer.

Answer 1

Hyperbranched polymers are highly branched macromolecules with three-dimensional dentritic architecture.

First, the hyperbranched polyamic acid precursors were prepared by reaction of the dianhydrides and 38 in N;Ndimethylacetamide (DMAc). Then, chemical or thermal imidization of the precursors gave rise to the final hyperbranched polyimides Reaction conditions, such as the monomer feed ratio, monomer addition manner, and concentration strongly influenced the polymerization results. A hyperbranched polyimide with amino terminal groups was obtained when a dianhydride solution was added to the solution of 38 with a 1/1 molar feed ratio of A2 to B3 (manner 1). In comparison, the addition of 38 to a dianhydride solution with a 2/1 molar feed ratio of A2 to B3 (manner 2) yielded the anhydride-terminated hyperbranched polyimide. The concentration of the added dianhydride or triamine approached zero during addition to avoid a high local concentration of added monomer, which could cause immediate gelation. Higher concentration of the feed monomers also led to crosslinking. The total feed monomer content should be kept below 0.2 mol/l for method 1 and 0.075 mol/l for method 2. 1H NMR spectra showed that the DB for the amine-terminated HP10, HP11, and HP12 were 0.64, 0.72 and 0.68, respectively.

HP10 based on the monomer 35 showed good solubility in strong polar solvents such as DMAc, NMP, and dimethyl sulfoxide (DMSO), and poor solubility in tetrahydrofuran (THF), acetone and 1,4-dioxane. However, the hyperbranched polyimides based on monomers 36 (HP11) and 37 (HP12) were insoluble in all of the aforementioned solvents.

The precursor and hyperbranched polyimides made by method A are hardly soluble in organic solvent at room temperature, but are soluble upon heating in strong polar solvents, and the solution remains homogeneous when cooled to room temperature. By comparison, the precursor and the hyperbranched polyimides made by method B are soluble in DMAc, DMF, DMSO and NMP at room temperature.

Reaction conditions such as temperature and monomer concentration have a strong effect on the Michael addition polymerization. No gelation occurred for polymerization with a 1/1 feed ratio. When the feed ratio was increased to 3/2, crosslinking was not yet observed in a dilute solution at low temperature. if the feed volume ratio of the two monomers to solvent was greater than 2/1, gelation occurred quickly; while gel did not appeared if the volume ratio was lower than 1/2.