Dimer effect on fractional polycondensation of poly(p‐oxybenzoyl)

Selective preparation of poly(p‐oxybenzoyl) (POB) crystals was examined from the viewpoint of a dimer effect on fractional polycondensation. Four different copolymerization systems were chosen as the combinations of p‐acetoxybenzoic acid (p‐ABA), m‐acetoxybenzoic acid (m‐ABA), and their dimers. The crystals obtained from the copolymerization of the dimer of p‐ABA (p‐ABAD) and m‐ABA contained only 3.1 mol % of m‐oxybenzoyl moiety even at high content of m‐oxybenzoyl moiety in feed (χ_f) of 40 mol %. p‐Oxybenzoyl homo‐oligomers were more rapidly formed from p‐ABAD in the solution than from p‐ABA, and they were crystallized to form the crystals with segregating co‐oligomers. While co‐oligomers containing more m‐oxybenzoyl moiety were formed in the solution, afterward they were unable to be phase‐separated because of higher miscibility. The further polycondensation proceeded in the precipitated crystal, and finally the POB crystal was selectively formed. Lower polymerization temperature and concentration enhanced the fractionability, and the POB crystals containing less than 1 mol % m‐oxybenzoyl moiety were prepared at χ_f of 30 mol %, 270 °C, and a concentration of 0.5%. The dimer effect on the fractional polycondensation was clearly observed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1598–1606, 2008     

Selective preparation of poly(p‐oxybenzoyl) by using fractional polycondensation

Selective preparation of poly(p‐oxybenzoyl) (POB) in the copolymerization system of p‐acetoxybenzoic acid (p‐ABA) and m‐acetoxybenzoic acid (m‐ABA) was examined by using reaction‐induced crystallization of oligomers. Polymer crystals mainly composed of p‐oxybenzoyl moiety were precipitated when the content of m‐ABA in the feed was 30 mol %. The formation of the polymer crystals was attributed to both the reactivity of monomer and the phase‐separation behavior of oligomer. Reactivity of p‐ABA was twice higher than that of m‐ABA, and thereby, the homo‐oligomers of p‐oxybenzoyl moiety were more rapidly formed in solution than do co‐oligomers at the early stage in polymerization. They were selectively precipitated by crystallization to form crystals because of low miscibility. Co‐oligomers containing m‐oxybenzoyl moiety were also formed in solution, but they were unable to be phase‐separated because of higher miscibility. Further polycondensation occurred between oligomers in the precipitated crystals, leading to the formation of POB. This polymerization proceeded with selecting certain monomers by crystallization and afforded a new methodology for fractional polycondensation. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2732–2743, 2006     

Preparation of single‐walled carbon nanotubes‐induced poly(p‐oxybenzoyl) crystals

Crystallization of oligomers was applied for the preparation of single‐walled carbon nanotubes (SWNTs)/poly(p‐oxybenzoyl) (POB) crystals using SWNTs as a nucleating agent. Polymerization conditions were investigated to induce the crystallization of POB oligomers through SWNTs. SWNTs/POB plate‐like or lozenge‐shaped crystals were successfully prepared by direct polymerization of p‐hydroxybenzoic acid (HBA) in a mixed solvent of DMF/Py with TsCl in the presence of functionalized SWNTs. The size of the plate‐like crystals were ～200 nm to 3 μm. The crystals consisted of some layers, ～3 nm thick plates. Model reactions showed that esterification reactions proceed between functionalized SWNTs and HBA monomers in the polymerization system. The obtained crystals exhibited unique morphology and high crystallinity, producing a novel SWNT/POB hybrid. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1265–1277, 2008     

Nonstoichiometric polycondensation of 4‐acetoxybenzoic acid in the presence of monoacetate

Nonstoichiometric polycondensation of 4‐acetoxybenzoic acid (ABA) was examined in the presence of three kinds of aromatic monoacetates: 4‐hexyloxyphenyl acetate, 4‐decyloxyphenyl acetate, and 4‐octadecyloxyphenyl acetate. Polymerizations were carried out in liquid paraffin at 320 °C under nonstoichiometric conditions, in which the acetoxy group was in large excess of the carboxyl group. Poly(4‐oxybenzoyl) (POB) was obtained as crystal at the molar ratio of monoacetates in feed (χ) of less than 80 mol %, meaning that the concentration of the acetoxy group was five times that of the carboxylic group. The obtained POB possessed much higher number average degree of polymerization (DP_n), ranging from 353 to 467, than the calculated DP_n on the basis of χ. High molecular weight polymer was synthesized even under nonstoichiometric conditions via crystallization of oligomers and the following solid‐state polymerization in the crystals. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1757–1766, 2005     

Morphology of poly(p‐oxybenzoyl) crystal prepared by direct polycondensation of p‐hydroxybenzoic acid with p‐toluenesulfonyl chloride in pyridine

Poly(p‐oxybenzoyl) (POB) crystals were prepared with the reaction‐induced crystallization of oligomers during the direct polycondensation of p‐hydroxybenzoic acid (HBA) with p‐toluenesulfonyl chloride (TsCl) and N,N‐dimethylformamide in pyridine. Sheaflike lozenge‐shaped POB crystals were obtained, of which the longer diagonal was 7.0–8.0 μm. The influence of the polymerization condition on the morphology was examined to optimize the preparative condition for the crystals exhibiting the clearest habit, and the favorable condition was determined as the molar ratio of TsCl to HBA of 1.3 and polymerization concentration of 3.0%. The crystals possessed extremely high crystallinity and outstanding thermal stability. The formation mechanism of the crystal was proposed as follows. When the number‐average degree of polymerization of the oligomers exceeded a critical value of about 4, they were precipitated to form the hexagonal lamellae. The crystals were grown very quickly to lozenge‐shaped crystal through screw dislocation with the continuous precipitation of oligomers from the solution. Finally, the further polymerization occurred in the precipitated crystal with developing polymer‐chain packing. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3275–3282, 2003     

Morphology of poly(p‐oxybenzoyl) prepared in perfluoropolyether

Solvent effect on the morphology of poly(p‐oxybenzoyl) (POB) prepared by the reaction‐induced phase separation of oligomers was examined by the polymerization of p‐acetoxybenzoic acid in perfluoropolyether Aflunox^TM (AFL2507 and AFL606). Polymerization was carried out at 320°C for 6 hr. POB microspheres were formed in AFL2507 by the liquid–liquid phase separation of oligomers due to the low miscibility of oligomers in AFL2507. The molecular weight of the solvent influenced the morphology, and the polymerization in AFL606 of which the molecular weight was lower than AFL2507 yielded whiskers formed by crystallization of oligomers induced by the increase in miscibility compared with that in AFL2507. The solvent structure and its molecular weight influenced the miscibility of oligomers and ultimately controlled the morphology from whisker to microsphere. Copyright © 2004 John Wiley & Sons, Ltd.     

Selective synthesis of poly(p‐oxybenzoyl) by fractional polycondensation: Enhancement of selectivity by shearing

The influence of shear flow, especially the timing for the application of shearing, was examined to enhance the selectivity for the preparation of poly(p‐oxybenzoyl) (Pp‐OB) by using hydrodynamically induced phase separation during polymerization of 4‐(4‐acetoxybenzoyloxy)benzoic acid (p‐ABAD) and m‐acetoxybenzoic acid (m‐ABA). The polymers containing few m‐oxybenzoyl (m‐OB) moieties were obtained as precipitates even at high content of m‐OB moiety in feed (χ_f) under shear flow. The content of m‐OB moiety in the precipitates (χ_p) prepared under shearing throughout the polymerization at the shear rate (γ) of 489 s^?1 was 6.3 mol % even at χ_f of 60 mol %. Especially, the Pp‐OB was obtained as the precipitates at χ_f of less than 50 mol %. The timing of the application of the shearing influenced the selectivity significantly, and the shearing just after the precipitation of the oligomers started was quite efficient to enhance the selectivity more. The χ_p of the precipitates prepared with shearing at γ of 489 s^?1 just after the precipitation was only 3.9 mol % even at χ_f of 60 mol %. The shear flow reduced the difference in the reactivity between p‐ABAD and m‐ABA, resulting in the decrease in the selectivity with regard to the formation of p‐oxybenzoyl homo‐oligomer. However, the shear flow enhanced the difference in the miscibility between homo‐oligomers and co‐oligomers. This change in the miscibility by shear flow brought about the more rapid precipitation of homo‐oligomers, leading to the enhancement of the selectivity. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Preparation of poly(p‐oxybenzoyl) crystals using direct polymerization of p‐hydroxybenzoic acid in the presence of boronic anhydrides

Poly(p‐oxybenzoyl) (POB) crystals were prepared by reaction‐induced crystallization during direct polymerization of p‐hydroxybenzoic acid in the presence of boronic anhydrides. Polymerizations were carried out at 300 °C in dibenzyltoluene at a concentration of 1% with three kinds of anhydrides of boronic acid such as 3,4,5‐trifluorophenylboronic acid (TFB), 4‐methoxyphenylboronic acid (MPB) and 4‐biphenylboronic acid (BPB). The POB crystals were formed as precipitates in the solution and the morphology was considerably influenced by both the structure of the boronic anhydride and its concentration (c_B). Needle‐like crystals were firmed in the presence of TFB anhydride (TFBA) at c_Bs of 5 and 10 mol % by the spiral growth of lamellae. Spherical aggregates of slab‐like crystals were formed at c_Bs from 50 to 100 mol %. The polymerization with MPB anhydride and BPB anhydride (BPBA) also yielded the needle‐like crystals at c_Bs of 50 and 5 mol %, respectively. The polymerization with TFBA at lower c_B was favorable to prepare the needle‐like crystal. Molecular weight was also influenced by the structure of the boronic anhydride and c_B. M_n increased generally with c_B and BPBA gave the highest M_n of 14.7 × 10³ at c_B of 100 mol %. The loose packing of the molecules in the crystal caused by the bulkiness of the end‐groups made the polymerization in the crystals more efficiently. Morphology and molecular weight of the POB crystals could be controlled by the chemical structure and the content of boronic anhydride. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

One‐pot preparation of aromatic poly(azomethine ester) fibrillar crystals using reaction‐Induced crystallization

Polymerizations of 4‐(4‐acetoxybenzylideneamino)benzoic acid were performed in dibenzyltoluene (DBT) and a mixture of DBT and liquid paraffin at 350 °C for 6 h. Fibrillar crystals of poly[4‐(4‐oxybenzylideneamino)benzoyl] (POAB) having the width of 50–450 nm and the length of over 15 μm were obtained by the crystallization during the polymerization. The fibrillar crystals possessed high crystallinity and the molecular chains aligned perpendicular to the long axis of the fibrillar crystals. Plate‐like crystals were initially formed by the crystallization of oligomers, and then they changed to the fibrillar crystals via the formation of bundle‐like crystals after 1 h. Molecular weight increased by the further polymerization in the crystals. Based on these results, one‐pot preparation of the fibrillar POAB crystals was examined by the polymerization of 4‐acetoxybenzaldehyde and 4‐aminobenzoic acid. The polymerization at 180 °C for 2 h and then at 350 °C for 6 h afforded the fibrillar crystals with a small amount of the ribbon‐like crystals. Although the side‐reaction to generate the p‐benzamide sequences was not completely depressed, the sequence of heating in which 180 °C for the formation of the azomethine linkage and then 350 °C for the formation of the ester linkage was preferable to prepare the fibrillar POAB crystals. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Dual Self‐Assembling Polycondensation of p‐Acetoxybenzoic Acid and p‐Acetamidobenzoic Acid

The dual self‐assembling polycondensation of p‐acetoxybenzoic acid (ABA) and p‐acetamidobenzoic acid in Therm S 800 was examined at 300 °C. Needle‐like crystals and lath‐like crystals were formed simultaneously through reaction‐induced crystallization of oligomers at a molar ratio of 30–50 mol‐% ABA in the feed. The needle‐like crystals comprised more p‐oxybenzoyl units, whereas the lath‐like ones contained higher amounts of p‐benzamide moieties.

     

Nanoscale interfibrillar adhesion in UHMWPE fibers

The goal of this research is to quantify the fibrillar adhesive energy in ultra‐high molecular weight polyethylene fibers, characteristic of nanoscale fibril interactions. Quantification of these energies is vital to the understanding of fibrillar deformation mechanisms that have been shown to play an important role in fiber performance. This is achieved through the development and implementation of a nanosplitting technique developed through the use of AFM‐enabled nanoindentation. This technique allows the quantification of nanoscale adhesive energies through careful monitoring of load and unload curves as well as examination of the residual split through high‐resolution AFM images. Results indicate that the average nanoscale fibril adhesive energy is over 3 times larger than the energy expected from van der Waals interactions alone. This indicates that a significant degree of physical interactions exist between fibrils, beyond van der Waals interactions, in the form of tie‐molecules, fibrillar network junctions, and bridging lamellar crystals. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 391–401     

Heterogeneous polycondensation for composition control of poly(p‐mercaptobenzoyl‐co‐p‐benzamide) by shearing

Composition control of aromatic poly(thioester‐amide) was examined by the reaction‐induced phase separation during polymerization of S‐acetyl‐4‐mercaptobenzoic acid (AMBA) and p‐acetylaminobenzoic acid (AABA) in aromatic solvent. The poly(thioester‐amide)s were obtained as precipitates and their yields became lower at the middle range of the content of AMBA in feed (χ_f). The contents of p‐mercaptobenzoyl (MB) moiety (χ_p) in the precipitates prepared without shearing were in good agreement with the χ_f values. In contrast to this, the χ_p values of the precipitates prepared at χ_f of 50–70 mol % under shearing were much lower than the χ_f values. The reaction rate of AMBA increased with shearing, whereas that of AABA was unchanged by shearing. This shearing effect on the reaction rates accelerated to form the homo‐oligomers. The solubility of MB oligomers enhanced by shearing, whereas that of p‐benzamide oligomers did not enhance owing to the strong interaction through hydrogen bonding. The MB oligomers were inhibited to be precipitated, resulting in the lower χ_p values than the χ_f values. The composition could be controlled by the application of the shearing to the heterogeneous polymerization. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4301–4308     

A new route of manipulation of poly(L‐lactic acid) crystallization by self‐assembly of p‐tert‐butylcalix[8]arene and toluene

A novel nucleating agent (TBC8‐t), self‐assembled with p‐tert‐butylcalix[8]arene (TBC8) and toluene, was used to manipulate the crystallization behavior of poly(L ‐lactic acid) (PLLA). Toluene molecules were used to adjust the crystallization structure of TBC8. Differential scanning calorimetry results show that the crystallization peak temperature (T_c) and crystallization rate (ΔH_c/time) of PLLA nucleated with TBC8‐t are 132.3 °C and 0.24 J/gs, respectively, which are much higher than that with conventional nucleating agent‐talc (T_c = 119.3 °C, ΔH_c/time = 0.13 J/gs). The results of polarized optical microscopy demonstrate that TBC8‐t could greatly enhance the crystallization rate of PLLA by increasing the nucleation rate rather than crystal growth rate. Along with an improvement of the crystallization rate, the crystalline morphology of PLLA is also affected by TBC8‐t. The addition of TBC8‐t transforms most of the original spherulite crystals into sheaf‐like crystals. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1235–1243, 2010     

The study of electroactive block copolymer containing aniline pentamer isolated from different solvents

For the films and powder of polymers containing conductive oligomer are usually obtained from solution, the choice of better solvents for the regular arrangement of oligomers is very important for the higher conductivity. Because of the poor solubility of the oligomers, it is difficult to study the arrangement directly in most common solvents, so, we synthesized a triblock copolymer, mPEG2k‐aniline pentamer‐mPEG2k, as the model to investigate the arrangement–solvent relationship. For the poor solubility of the AP block in common solvents, the copolymer self‐assembled into spheric micelles in toluene and into lamellar crystals in water and THF. The crystallinity (X_c) and crystallization temperature (T_c) values of mPEG blocks in powders prepared from different solvents differed obviously, which may be the effect of different self‐assembled structures. From the two‐phase model of one‐dimensional electron density correlation function of SAXS, the long period of copolymer prepared from THF was presumably equal to the long period of pure mPEG plus the chain length of AP, which demonstrates that the AP blocks arrange regularly in the noncrystalline regions. In the selected solvents, the ones with higher polarity and better solubility induced more regular arrangement of AP blocks, which may be useful for choosing solvents for preparation of higher conductivity polymers' films containing aniline oligomers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1298–1307, 2009     

Fddd network phase in ABA triblock copolymer melts

Using self‐consistent field theory, we investigate the stability of the orthorhombic Fddd network phase (O⁷⁰) in ABA triblock copolymer melt systems. Consistent with previous findings, we observe that the gross topology of phase behavior is unchanged with varying chain asymmetry. However, the mean field critical point is displaced from the diblock copolymer value of f_A = 0.5 (f_A is the A segment volume fraction) to larger values as the triblock copolymer symmetry is broken with unequal A block lengths. This deviation significantly shifts the order‐order phase boundaries, resulting in an appreciable region of O⁷⁰ stability in the phase diagram of asymmetric ABA triblock copolymers. More importantly, the stability of the O⁷⁰ phase extends to the intermediate segregation regime for select chain asymmetries. Both features are desirable for achieving a synthetic realization of the phase in binary AB block copolymer systems. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1112–1117     

A novel nanoporous structure on the surface of bubbles in polycarbonate foams

We found that novel nanoporous structures such as ellipsoidal‐ or string‐shaped nanopores were formed on the surface of the spherical bubbles in polycarbonate foams by annealing CO₂‐saturated polycarbonate. The pores were surrounded by polycarbonate nanofibrils, and birefringence with spherical symmetry was seen on the surface of the spherical bubbles. Thus, the formation of such a characteristic structure might be attributed to orientation‐induced crystallization of CO₂‐saturated polycarbonate on the surface of the bubbles and the exclusion of CO₂ from the fibrillar crystals thus obtained. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 843–846, 2008     

Morphosynthesis of poly[4‐(1,4‐phenylene)oxyphthalimide] and copolymers prepared by reaction‐induced crystallization during polymerization

Morphosynthesis of poly[4‐(1,4‐phenylene)oxyphthalimide] (POPI) and poly[4‐(1,4‐phenylene)oxyphthalimide‐co‐4‐phthalimide] (POPI‐PPI) was examined by using the crystallization during the polymerization. The POPI fibrillar crystals were obtained as precipitates with the formation of spherical aggregates of plate‐like crystals. Some of the POPI fibrillar crystals were longer than 15 μm. They possessed high crystallinity and the molecules aligned perpendicular to the long direction of the fibers. On the other hand, one‐dimensional structures of POPI‐PPI such as ribbon, cone, rod, and fiber were obtained as precipitates by the copolymerization. The copolymer molecules might align along the long direction of the cone‐like crystals. The morphology of these poly(ether‐imide)s could be controlled by not only the polymerization condition but also with the aid of copolymerization. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Crystallization and morphology of poly(ethylene oxide‐b‐lactide) crystalline–crystalline diblock copolymers

The crystallization behaviors and morphology of asymmetric crystalline–crystalline diblock copolymers poly(ethylene oxide‐lactide) (PEO‐b‐PLLA) were investigated using differential scanning calorimetry (DSC), wide angle X‐ray diffraction (WAXD), and microscopic techniques (polarized optical microscopy (POM) and atomic force microscopy (AFM)). Both blocks of PEO₅‐b‐PLLA₁₆ can be crystallized, which was confirmed by WAXD, while PEO block in PEO₅‐b‐PLLA₃₀ is difficult to crystallize because of the confinement induced by the high glass transition temperature and crystallization of PLLA block with the microphase separation of the block copolymer. Comparing with the crystallization and morphology of PLLA homopolymer and differences between the two copolymers, we studied the influence of PEO block and microphase separation on the crystallization and morphology of PLLA block. The boundary temperature (T_b) was observed, which distinguishes the crystallization into high‐ and low‐temperature ranges, the growth rate and morphology were quite different between the ranges. Crystalline morphologies including banded spherulite, dendritic crystal, and dense branching in PEO₅‐b‐PLLA₁₆ copolymer were formed. The typical morphology of dendritic crystals including two different sectors were observed in PEO₅‐b‐PLLA₃₀ copolymer, which can be explained by secondary nucleation, chain growth direction, and phase separation between the two blocks during the crystallization process. Lozenge‐shaped crystals of PLLA with screw dislocation were also observed employing AFM, but the crystalline morphology of PEO block was not observed using microscopy techniques because of its small size. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1400–1411, 2008     

Compressed‐gas‐induced crystallization in tert‐butyl poly(ether ether ketone)

tert‐Butyl‐substituted poly(ether ether ketone) (tBuPEEK), which does not undergo crystallization with thermal annealing, crystallizes readily when treated with compressed CO₂. The dissolved CO₂ causes a reduction in the glass‐transition temperature of the polymer–gas system and enhances the chain mobility of the macromolecules, thereby bringing about crystallization. In the presence of CO₂, crystallization is increasingly favored with increasing CO₂ pressure and treatment temperature. The melting point of tBuPEEK crystals increases linearly with the CO₂ pressure applied in the treatment, indicating an increase in the order and/or size of the crystals. The extent of crystallinity increases when small amounts of methanol or dichloromethane are used as a cosolute with CO₂. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1505–1512, 2001     

Structure and properties of polyimide fibers containing benzimidazole and Amide Units

Co‐polyimide (co‐PI) fibers with outstanding mechanical properties were fabricated via thermal imidization of polyamic acids, derived from a new design of combining the amide and benzimidazole diamine monomers, 4‐amino‐N‐(4‐aminophenyl)benzamide (DABA) and 2‐(4‐aminophenyl)‐5‐aminobenzimidazole (BIA), with 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA). The crystalline structure and micromorphology of the prepared co‐PI fibers were investigated by synchrotron wide‐angle X‐ray diffraction (WAXD) and small‐angle X‐ray scattering (SAXS). The two‐dimensional WAXD spectra imply that the co‐PI fibers possess a structure between smectic‐like and three‐dimensionally ordered crystalline phase, and all the obtained fibers are highly oriented along the fiber axis. SAXS patterns exhibit a pair of meridional scattering streaks for the homo‐PI (BPDA/BIA) fiber, suggesting the presence of periodic lamellar structure. The incorporation of DABA into the polymer chains destroyed the lamellar structure but led to smaller size of microvoids upon increasing DABA moiety, based on SAXS analysis. The co‐PI fibers, with the molar ratio of BIA/DABA being 7/3, exhibited the optimum tensile strength and modulus of 1.96 and 108.3 GPa, respectively, attributed to the well‐defined ordered and dense structure. The chemical structure and molecular packing significantly affected the thermal stability of fibers, resulting in the different glass transition temperatures (T_g) from 350 to 380 °C. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 183–191