Novel Water‐Soluble Poly(m‐benzamide)s: Precision Synthesis and Thermosensitivity in Aqueous Solution

Abstract

Summary: Chain‐growth polycondensations of 3‐aminobenzoic acid methyl esters 1a and 1b, bearing a tri‐ or tetra(ethylene glycol) methyl ether unit on the amino group, respectively, were carried out with lithium hexamethyldisilazide (LiHMDS) as a base and phenyl 4‐methylbenzoate (2) as an initiator in THF at 0 °C. The poly(m‐benzamide)s obtained in the presence of N,N,N′,N′‐tetramethylethylenediamine (TMEDA) possessed narrow molecular weight distributions ($\overline M _{\rm w} /\overline M _{\rm n}$ < 1.2) with molecular weights that were determined by the feed ratios of [1]0/[2]0. Poly1a and poly1b were each soluble in water and exhibited a lower critical solution temperature (LCST) in water. Furthermore, the phase separation in water depended on the length of the oligo(ethylene glycol) side chain and on the molecular weight and molecular weight distribution of poly1.

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

“…Furthermore, poly1 was soluble in not only organic solvents, but also water, although it was less soluble in water than poly(N-TEG-m-benzamide). These solubility characteristics are similar to those of poly(N-TEG-m-benzamide) [21]. The aqueous solution of poly1 exhibited a cloud point when heated in a similar manner to poly(N-TEG-m-benzamide).…”

“…This result indicated that the thermotransition of poly1 in an aqueous solution becomes sharper with increasing molecular weight until the molecular weight exceeds a certain value. The cloud point of poly1 was 21-23 °C, which was about 30 °C lower than that of a 0.5 wt.−% aqueous solution of poly(N-TEG-m-benzamide) [21]. One might think that the cloud point of hyperbranched polymer would be higher than that of the corresponding linear polymer because the former is generally more soluble than the latter.…”

“…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].…”

“…The polymerization of 1 with 3.2 mol% of initiator core 2a was carried out by the addition of 1 over 50 min to a mixture of 1.1 equiv of lithium 1,1,1,3,3,3-hexamethyldisilazide (LiHMDS) and 5 equiv of N,N,N',N'-tetramethylethylenediamine (TMEDA), which is the best additive for the chain-growth condensation polymerization of methyl 3-aminobenzoates bearing the N-TEG unit [21], in THF at −30 °C (Table 1, Entry 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).…”

“…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]. This fact led us to wonder whether an AB 2 monomer with the TEG side chain would undergo chain-growth condensation polymerization to yield water-soluble HBPA.…”