Reaction-induced Crystallization Of Oligomers Research Articles

Preparation of helical crystals of aromatic poly(ester-imide) and on-off switching of helix formation

Abstract Preparation of poly[4-(5-oxy-1,3-dioxoisoindoline-2-yl)benzoyl] (PODB) crystals, which was an intractable aromatic poly(ester-imide), was examined by means of reaction-induced crystallization of oligomers during the polymerization. Highly crystalline PODB helical ribbons were obtained by the polymerization of N -(4-carboxyphenyl)-4-acetoxyphthalimide in aromatic solvent at 280–330 °C at a concentration of 0.5–1.0%. The PODB molecules aligned along the long axis of the helical ribbon. The pitch of the helix increased with the polymerization temperature and it could be controlled from 320 nm to 1.3 μm. Further, the fibrillar PODB crystals comprised of the helical and the non-helical blocks were prepared by the on-off switching of the helical morphology with the changing the temperature and the concentration of the polymerization. These results provided the methodology for the morphology control of polymer crystals.

Graphite nanoribbons prepared by graphitization of poly(4-phthalimide) nanoribbons

Highly crystalline polyphthalimide nanoribbons were prepared by the reaction-induced crystallization of oligomers during solution polymerization. Polymerization of 1-hexyl 4-aminophthalate and 2-hexyl 4-aminophthalate was carried out at 330°C in alkyl naphthalene oil. The polyphthalimide nanoribbons had an average width of 150nm, and were intertwined to form aggregates of diameter 1–2μm. The polyphthalimide nanoribbons were carbonized/graphitized at 1000–2800°C to yield graphite nanoribbons consisting of typical graphitized turbostratic carbon. These were polycrystalline with an average interlayer spacing of 0.34nm.

Micro-flowers of poly( p-phenylene pyromelliteimide) crystals

Morphology control of poly( p-phenylene pyromelliteimide) (PPPI) crystals was examined using reaction-induced crystallization of oligomers during solution polymerization of self-polymerizable N-(4′-aminophenyl)-3-carboxyl-4-alkoxycarbonylphthalimide. Micro-flowers of the PPPI needle-like crystals were formed in which the needle-like crystals grew radially from the center part as petals. The molecules aligned regularly along the long axis of the needle-like crystal. The structure of alkoxy group in the monomer and the monomer concentration influenced the size of the needle-like crystals, and their average length and width were changeable from 640 nm to 1.69 μm and from 110 nm to 210 nm, respectively. The average thickness was 20 nm. The obtained micro-flowers possessed high crystallinity and exhibited excellent thermal stability.

Direct Synthesis of Wholly Aromatic Polyamides by Using Reaction-Induced Crystallization

Direct synthesis of rigid-rod aromatic polyamides was studied without condensation reagents by using reaction-induced crystallization of oligomers during solution polymerization. Polymerizations of p-aminobenzoic acid were carried out in an aromatic solvent at a polymerization concentration of 20% at 350 °C. High molecular weight poly(p-benzamide) (PBA) was obtained in the form of plate-like crystals, and the highest molecular weight was 11.6 × 103. In this polymerization, the oligomers were formed in the solution by the condensation reaction with the elimination of water. When the molecular weight of oligomers exceeded the critical value, the oligomers were precipitated by crystallization via supersaturated state to form the plate-like crystals. The molecular weight increased by the polymerization between the oligomers on and in the crystals. Poly(p-phenylene isophthalamide) (PPIA) was also obtained in the form of plate-like crystals by the polymerization of p-phenylene diamine (PPDA) and isophthalic acid (IPA) under the same condition as that of PBA. These results exhibited the thermally direct synthesis of infusible aromatic polyamides. Sequential addition of monomers into this heterogeneous polymerization was examined to increase the molecular weight. In the step-growth polymerization, the addition of monomers into the homogeneous polymerization could not increase the molecular weight because it was determined by the extent of reaction and reshuffled by the transamidation reaction. However, the addition of PPDA and IPA during the polymerization resulted in the increase in the molecular weight of PPIA. This result gave possibly a novel procedure for the preparation of high molecular weight condensation-type polymers.

Preparation of Poly(4′-oxy-4-biphenylcarbonyl) Needlelike Crystals with the Aid of Copolymerization

Preparation of poly(4′-oxy-4-biphenylcarbonyl) (POBP) needlelike crystals was examined by using reaction-induced crystallization of oligomers during copolymerization of 4-(4-acetoxyphenyl)benzoic acid (APBA) and 4-acetoxybenzoic acid (ABA). Polymerizations were carried out in aromatic solvent at various ABA molar ratios in feed (χf). When the χf was 20−10 mol %, starlike aggregates of needlelike crystals and fibrillated slablike crystals were separately formed, exhibiting similar morphology to poly(4-oxybenzoyl) and POPB crystals. 4-(Oxyphenyl)benzoyl (OPB) homo-oligomers and co-oligomers rich in OPB moiety were more rapidly precipitated due to the lower solubility, and the slablike crystals were formed. Afterward, 4-oxybenzoyl (OB) homo-oligomers and the co-oligomers rich in OB moiety were precipitated to form spindlelike crystals. The OPB homo-oligomers and the co-oligomers rich in OPB moiety were continuously crystallized on both crystals due to the high degree of supersaturation, and the spindlelike crystals grew to the needlelike crystals mainly comprised of POBP. Copolymerization of 4-(4-acetoxybenzoyloxy)benzoic acid and APBA at χf of 10 mol % yielded the needlelike crystals without coexisting fibrillated slablike crystals. This result provides a new methodology for morphology control with the aid of copolymerization.

Preparation of brush-like crystals of poly[2,6-(1,4-phenylene)-benzobisimidazole

Poly[2,6-(1,4-phenylene)-benzobisimidazole] (PPBI) crystals were prepared by using reaction-induced crystallization of oligomers during solution polymerization of 1,2,4,5-tetraaminobenzene and diphenyl terephthalate. Polymerizations were carried out at a monomer concentration of 4.3×10−2molL−1 at 350°C for 6h. Brush-like PPBI crystals were obtained in a mixture of structural isomers of dibenzyltoluene, in which many needle-like crystals came out vertically from the surface of the ribbon-like crystals. Average width and thickness of the ribbon-like crystals were 0.75μm and 0.11μm, respectively. And average length and diameter of the needle-like crystals were 0.36μm and 50nm, respectively. The brush-like crystals possessed high crystallinity and exhibited good thermal resistance. The ribbon-like crystals were formed by the crystallization of imidazole oligomers at an initial stage of polymerization, and then the needle-like crystals grew from the surface of the ribbon-like crystals. Polymerization occurred on the crystals when the oligomers were crystallized, leading to the high molecular weight PPBI crystals.

Preparation of Poly(4-phthalimide) Nanoribbon by Reaction-Induced Crystallization

The morphology of poly(4-phthalimide) (PPI) crystals was examined by using reaction-induced crystallization of oligomers during solution polymerization. Polymerizations of alkyl 4-aminophthalates such as 1-ethyl 4-aminophthalate (1EAP), 2-ethyl 4-aminophthalate, 1-hexyl 4-aminophthalate, and 2-hexyl 4-aminophthalate were carried out at 330 °C in a mixture of isomers of dibenzyltoluene without stirring. Nanoscale PPI ribbons having smooth surface were formed by the polymerizations of these monomers. The ribbons prepared from 1EAP at a concentration of 2.0% for 24 h were averagely 12 µm in length, 150 nm in width, and 8 nm in thickness, in which the molecular chains aligned along the long axis of the ribbon. The phase-separated oligomers were fully cyclized imide oligomers, and this is of great importance for the formation of the ribbon. The obtained ribbons possessed high crystallinity and exhibited excellent thermal stability.

Nonstoichiometric Synthesis of Poly(4,4‘-oxydiphenylene pyromelliteimide) by Reaction-Induced Crystallization of Oligomers

Nonstoichiometric synthesis of poly(4,4‘-oxydiphenylene pyromelliteimide) was examined by using reaction-induced crystallization of oligomers during solution polymerization. Polymerizations of pyromellitic dianhydride (PMDA) and 4,4‘-oxydianiline (ODA) were carried out in Barrel Therm 400 at 330 °C at various molar ratios of PMDA and ODA in feed (χ). Although high molecular weight polymer was usually prepared only under stoichiometric condition by a conventional solution polymerization, it was obtained as the crystals at χ of 0.5−2.0. The polymerization at χ of 0.77 afforded the highest polymer having Mw of 2.81 × 105, which was higher than that prepared by the solution polymerization. The oligomers were precipitated to form the crystals due to the low miscibility into the solvent. The precipitated oligomers were end-capped by excess monomers, but the end-capping groups were eliminated by transimidization reaction when they were registered into the crystals. The transimidization reaction also occurred in the crystals, leading to the increase in molecular weight. Since the nucleophilicity of amino end group was higher, the transimidization reaction proceeded more efficiently with eliminating ODA, and thereby the higher molecular weight polyimides were given in the range of χ < 1.0 than the range of χ > 1.0. The polymerization by the reaction-induced crystallization of oligomers was unsusceptible to the stoichiometry.

Fabrication of Poly(p-oxybenzoyl) Nanowhisker

Fabrication of poly(p-oxybenzoyl) (POB) nanowhiskers was examined by using reaction-induced crystallization of oligomers during the polymerization of p-acetoxybenzoic acid in liquid paraffin. Width of the POB whiskers was susceptible to polymerization temperature and it was efficiently controlled by a change in temperature during the polymerization. Increase in polymerization temperature just after nucleation (Han) reduced the degree of super saturation of oligomers (σ) resulting in the depression of the width increase by the crystallization of oligomers on side surface of the whiskers. Temperature drop just before nucleation (Cbn) enhanced the value of σ resulting in the generation of much more nuclei having the smaller width. On the basis of these results, the combination of these two methods Han and Cbn afforded the whiskers having the smallest width, and the POB nanowhiskers were prepared of which the width and the length were 190 nm and 18.6 μm, respectively.

Direct synthesis of poly(4?-oxy-4-biphenylcarbonyl) and poly(2-oxy-6-naphthoyl) under nonstoichiometric conditions

Direct synthesis of poly(4′-oxy-4-biphenylcarbonyl) (POBP) and poly(2-oxy-6-naphthoyl) (PON) was examined by polycondensation of 4′-hydroxy-4-biphenylcarboxylic acid (HBPA) and 2-hydroxy-6-naphthoic acid (HNA) in the presence of 4-ethoxybenzoic anhydride or 2-naphthoic anhydride as condensation reagents. Polymerizations were carried out at 320 °C in aromatic solvents and liquid paraffin. POBP, having a number-average degree of polymerization (DPn) of 38, was obtained as plate-like crystals at the molar ratio of HBPA and anhydride of 50 mol%. PON was also obtained as plate-like crystals but the DPn was only 13. HBPA and HNA were first converted to reactive acyloxyaromatic acid intermediates. Then the DPn was increased by means of reaction-induced crystallization of oligomers and subsequent solid-state polymerization via an acid–ester exchange under nonstoichiometric conditions caused by the monocarboxylic acid by-product. Even though the DPn of PON was not as high, direct polycondensation of HBPA and HNA proceeded successfully with aromatic anhydrides. Copyright © 2004 Society of Chemical Industry

Preparation of Aromatic Polyesters under Unstoichiometric Condition by Reaction-induced Crystallization of Oligomers. 1. Polymerization of p-Acetoxybenzoic Acid in the Presence of Alkyloxybenzoic Acid

The polymerization of poly(p-oxybenzoyl) (POB) from p-acetoxybenzoic acid was examined in the presence of three kinds of aromatic monofunctional compounds such as p-hexyloxybenzoic acid (HOBA), p-decyloxybenzoic acid (DOBA) and p-octadecyloxybenzoic acid (OOBA) under unstoichiometric polymerization conditions. Polymerizations were carried out in liquid paraffin at 320 °C. POB crystals were obtained by reaction-induced crystallization of oligomers. The obtained POB crystals were found to be consisted of high molecular weight polymers compared with the products obtained by the melt polymerization. Polycondensation proceeded under unstoichiometric condition through following mechanisms; When DPn of oligomers exceeds a critical value, they are crystallized to form the crystals. End-free oligomers are preferentially crystallized due to the lower solubility over end-capped oligomers. End-capped oligomers are also crystallized, and polycondensation proceeds with eliminating end-capping groups of oligomers by tra...