Cyclic Hyperbranched Poly(ether ketone)s Derived from 3,5-Bis(4-fluorobenzoyl)phenol

Abstract

Bis(4-fluorobenzoyl)phenol was polycondensed under various reaction conditions. Low molecular weights were obtained (Mn < 8000 Da), and MALDI-TOF mass spectrometry indicated that the chain growth was limited by cyclization. In the best mass spectra the cyclic, hyperbranched poly-(ether ketone)s were detectable up to masses around 14 000 Da. When 4,4′-difluordiphenyl sulfone was added, star-shaped polymers having a diphenyl sulfone star center were formed, but cyclization was not completely suppressed. The results were compared to those obtained from "linear polycondensations" based on 4,4′-difluorobenzophenone (DFBP) and 4-tert-butylcatechol or bisphenol A. The poly(ether ketone)s of DFBP had also low molecular weights and contained high fractions of cycles. It is concluded that also in the case of hyperbranched polymers cyclization competes with propagation at any stage of the polycondensation at any concentration. Therefore, the fundamental trend of any "abn" polycondensation is the formation of star-shaped polymers having a cyclic core and hyperbranched star arms. Experimental SectionMaterials. Hexamethyldisilazane (HMDS), 5-hydroxyisophthalic acid, fluorobenzene, bisphenol A, 4-tert-butylcatechol, 4,4′-difluorobenzophenone (DFBP), and 4,4′-difluorodiphenyl sulfone (DFDPS) were purchased from Aldrich Co. (Milwaukee, WI) and used as received. Dimethyl sulfoxide (DMSO), sulfolane, and N-methylpyrrolidone (NMP) were purchased from E. Merck KG (Darmstadt, Germany). DMSO was used as received, whereas sulfolane and NMP were distilled over P 4O10 in vacuo.Monomers. 3,5-Bis(4-fluorobenzoyl)phenol 12 (1) was prepared from 5-hydroxyisophthalic acid and 5-methoxyisophthalic acid via Friedel-Crafts acylation of fluorobenzene with 5-methoxyisophthaloyl chloride. After recrystallization from toluene (twice), monomer 1 had a melting point of 152-153 °C.Polycondensations of 1 (Table 1). Monomer 1 (20 mmol) and dry K 2CO3 (21 mmol) were weighed into a 150 mL threenecked flask, and DMSO (80 mL) and toluene (20 mL) were added. This mixture was stirred at a bath temperature of 140 °C, whereby the toluene was slowly distilled off. The loss of toluene was compensated from a dropping funnel. After 6 h, the reaction mixture was cooled and precipitated into water. The isolated polymer was intensively washed with hot water and dried at 100 °C in vacuo. In a second experiment, xylene was used to remove the water, and the bath temperature was fixed around 170 °C.Analogous experiments were performed in sulfolane or NMP instead of DMSO. For the polymer isolated from the sulfolane/ toluene mixture (no. 3, Table 1) elemental analyses were performed:

Cyclic polymers: Synthetic strategies and physical properties

“…However, with one exception, 47 the extent of cyclization was not studied by other research groups. A reinvestigation of polycondensations based on 3,5-bis(4-fluorobenzoyl) phenol (Scheme 9) performed by the authors 48 yielded a product almost completely consisting of hyperbranched poly(ether ketone)s having a cyclic core.…”

The Role of Self‐Dilution in Step‐Growth Polymerizations

“…In contrast to Flory's cascade theory [3,4] and in contrast to a report of Chu et al [57] it has been recently demonstrated for various ''ab n '' polycondensations that cyclization competes with chain growth. [58][59][60][61][62][63] Cyclization has the consequence that molecules with a cyclic core and hyperbranched ''star-arms'' are formed (Scheme 4). Since cyclization consumes the only ''a''-function in a hyperbranched molecule, it limits the average molar mass (M n ) of a sample according to Equation (2) quite analogous to two-dimensional polycondensations.…”

“…Gooden et al [62] reported for polycondensations of the monomers 1 and 2 (Scheme 5) that up to 60 mol% of the polycondensates from 1 possess a cyclic core, and up to 90% of the polymer derived from 2. Polycondensations of monomers 3a and 3b were studied by Kricheldorf et al [63] and the reaction conditions were optimized for a clean polycondensation with maximum conversion. A hyperbranched poly(ether ketone) was obtained.…”

Polycondensation of ‘a − bn’ or ‘a2 + + bn’ Monomers ‐ A Comparison

“…None-the-less, these results disagree with Flory's cascade theory, and support the polycondensation theory of the author. More recently, Kricheldorf et al [108] reinvestigated polycondensations of the 3,5-bisfluorobenzoyl phenol (53) and its trimethylsilyl derivative with regard to the formation of cycles (polycondensations of 49a were first described by Miller et al [109] ). Sulfolane as reaction medium yielded particularly clean polycondensations with high conversions.…”