Synthesis and Properties of a Variety of Well-Defined Hyperbranched N-Alkyl and N-H Polyamides by Chain-Growth Condensation Polymerization of AB₂ Monomers

Abstract

Well-defined hyperbranched polyamides (HBPAs) were synthesized by means of chain-growth condensation polymerization of AB2 monomers from core molecules, making use of the change of substituent effects between the monomer and the polymer. Polymerization of 5-(methylamino)isophthalic acid ethyl ester 1c as an AB2 monomer with core 3b was carried out in the presence of lithium 1,1,1,3,3,3-hexamethyldisilazide (LiHMDS) and LiCl in THF at −30 °C to yield HBPA with low polydispersity (M w/M n ≤ 1.13) and well-defined molecular weight (M n = 2370–39300) depending on the feed ratio of the monomer to the core (from 7 to 200). The matrix-assisted laser desorption ionization time-of-flight (MALDI–TOF) mass spectra showed that the obtained HBPA included the core unit, indicating that the polymerization proceeds by selective reaction of the monomer with the core and the polymer ends, without side reactions. Polymerization of other AB2 monomers with N-ethyl, octyl, and 4-octyloxybenzyl (OOB) groups afforded the corresponding well-defined HBPAs. HBPA with the N-OOB group was converted to unsubstituted N-H HBPA with low polydispersity by treatment with trifluoroacetic acid (TFA). The solubility of HBPAs depended upon the nature of the N-alkyl groups and the terminal ester moieties. The glass transition temperature (T g) and 10% weight-loss temperature (T d 10) of HBPAs depended upon the molecular weight, as well as the nature of the N-alkyl groups and terminal ester moieties.

Synthesis of Well-Defined, Water-Soluble Hyperbranched Polyamides by Chain-Growth Condensation Polymerization of AB2 Monomer

“…This behavior was exactly the same as that reported in the case of the polymerization of ethyl 5-(methylamino)isophthalate with an initiator in the absence of LiCl [19]. Thus, the proton abstraction from the amino group of 1 slowed down as the base concentration decreased from the middle stage, and self-polymerization would be initiated by the reaction of 1, not the deprotonated compound, with the amide anion generated from 1.…”

“…The molecular weight distribution of the obtained HBPA, poly1, was relatively narrow (M w /M n = 1.33), but it was broader than that of polymers obtained by the polymerization of methyl 3-aminobenzoates bearing the N-TEG unit [21] or of ethyl or methyl 5-(N-alkylamino)isophthalates [18,19] (M w /M n < 1.19). On the other hand, controlled polymerization of 5-(N-alkylamino)isophthalic acid ester monomers requires LiCl as an additive to suppress self-polymerization, because LiCl decreases the reactivity of the amide anion generated from the monomer, thereby preventing the reaction of the LiCl-stabilized amide anion with the ester moiety of the non-deprotonated monomer [18,19]. Thus, the polymerization of 1 was next conducted in the presence of 5 equiv of LiCl at −30 °C (Entry 2).…”

“…The mass spectrum of the HBPA contains two series of peaks due to the K We attempted to estimate the degree of branching (DB) of poly1 by comparison with model compounds of the dendritic and linear units in the same manner as used to estimate the DB of HBPAs with N-alkyl groups [18,19]. However, due to the dendritic unit of poly1, the signal of H D2 was not observed at the chemical shift as expected from H b of the dendritic model 4 ( Figure 4).…”

“…Recently, we have reported a novel chain-growth condensation polymerization of 5-(N-alkylamino)benzoic acid ester as a AB 2 monomer with a core initiator, yielding hyperbranched polyamide (HBPA) with a narrow molecular weight distribution and controlled molecular weight depending on the feed ratio of the monomer to the core [18,19]. This method utilizes the change of substituent effects between the monomer and the polymer, in which the polymer terminal B group becomes more reactive than the B group of the AB 2 monomer, resulting in suppression of self-polymerization of the monomer.…”

“…This method utilizes the change of substituent effects between the monomer and the polymer, in which the polymer terminal B group becomes more reactive than the B group of the AB 2 monomer, resulting in suppression of self-polymerization of the monomer. The obtained HBPAs showed different solubility, glass transition temperature (T g ), 10% weight-loss temperature (T d 10 ), and surface segregation in a linear polystyrene matrix when the N-alkyl group of HBPA was changed [19,20]. Before this investigation, we had found that poly(m-benzamide) with tri(ethylene glycol) methyl ether (TEG) side chains on the amide nitrogens is soluble in water, even though the backbone is aromatic polyamide, and exhibited a lower critical solution temperature (LCST) [21].…”