Chain‐growth condensation polymerization approach to synthesis of well‐defined polybenzoxazole: Importance of higher reactivity of 3‐amino‐4‐hydroxybenzoic acid ester compared to 4‐amino‐3‐hydroxybenzoic acid ester

Abstract

Application of chain‐growth condensation polymerization (CGCP) to obtain well‐defined polybenzoxazole (PBO) was examined. CGCP of both phenyl 3‐{(2‐methoxyethoxy)methoxy (MEM‐oxy)}‐4‐(octylamino)benzoate (1b) (para‐substituted monomer) and phenyl 4‐MEM‐oxy‐3‐(octylamino)benzoate (3b) (meta‐substituted monomer) was examined in the presence of metal disilazide base and phenyl 4‐nitro‐ or methylbenzoate 2 as an initiator. Polymerization of the latter monomer, but not the former, afforded polymer with controlled molecular weight based on the feed ratio of monomer to initiator and with a narrow molecular weight distribution. Accordingly, monomer 3c, in which the octyl group on the amino nitrogen of 3b was replaced with a 4‐(octyloxy)benzyl (OOB) group, was polymerized in the presence of lithium 1,1,1,3,3,3‐hexamethyldisilazide (LiHMDS), phenyl 4‐methylbenzoate (2b), and LiCl in THF at 0 °C to yield poly3c with well‐defined molecular weight (Mn = 4520–9080) and low polydispersity (Mw/Mn ≤ 1.11). Treatment of poly3c with trifluoroacetic acid simultaneously removed the MEM and OOB groups, affording poly(o‐hydroxyamide) (poly4) without scission of the amide linkages. Cyclodehydration of poly4 proceeded at 350 °C to yield PBO (poly5), which was insoluble in organic solvents and acids. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1730–1736

Transformation of Step-Growth Polymerization into Living Chain-Growth Polymerization

“…Monomer 5 with a methoxyethoxymethyl (MEM)-protected hydroxyl group and OOB-protected amino group afforded the corresponding polyamide, although the para counterpart was hardly polymerized. The protecting groups on the oxygen and amide nitrogen of the polyamide were simultaneously removed with TFA to afford well-defined poly­(amidophenol), which was converted to poly­(benzoxazole) by heating . AB 2 -type monomer 6 also underwent CGCP to give a hyperbranched polyamide, the molecular weight of which can be controlled up to 40000 while retaining low polydispersity ( M w / M n < 1.2). − …”

“…meta -Substituted phenylene monomers undergo CGCP, leading to polyamides under optimized conditions, − although the inductive effect is less efficiently transmitted, compared to the resonance effect (Table ). Monomer 5 with a methoxyethoxymethyl (MEM)-protected hydroxyl group and OOB-protected amino group afforded the corresponding polyamide, although the para counterpart was hardly polymerized.…”

“…The protecting groups on the oxygen and amide nitrogen of the polyamide were simultaneously removed with TFA to afford well-defined poly(amidophenol), which was converted to poly(benzoxazole) by heating. 44 give a hyperbranched polyamide, the molecular weight of which can be controlled up to 40000 while retaining low polydispersity (M w /M n < 1.2). 45−47…”

Chain‐growth polycondensation via the substituent effect: Investigation of the monomer structure on synthesis of poly(N‐octyl‐benzamide)

“…The phenyl ester monomer (1g) has been previously utilized to prepare a variety of aromatic polyamide structures by CGC polymerization and is typically the ester of choice with these polymerizations, due to its relatively high reactivity, compared with the methyl ester. [ 29,36–39 ] In addition, the preliminary solubility studies discussed above demonstrated that the resulting solutions for all the tested phenoxides, derived from the phenyl ester monomers (1g‐1k), were soluble. Based on these factors, the effectiveness of the different phenyl ester monomers in CGC polymerizations was investigated.…”

Simultaneous Anionic Ring-Opening and Condensation Reactions for the Synthesis of Aliphatic–N-Alkyl Aromatic Copolyamides

“…Looking now at the synthesis of fully aromatic polyamides, it is well-known that step-growth condensation polymerization is the main route. − Chain-growth condensation polymerization (CGCP) was also proposed − to give controlled and living characteristics to their synthesis. This approach was also proposed for the synthesis of aromatic poly­(ether ketone) for instance …”