Three types of banded structures in highly birefringent poly(trimethylene terephthalate) spherulites

Poly(trimethylene terephthalate) (PTT), a highly birefringent aromatic polyester, has been utilized to understand the mechanisms of crystal assembly into diversified types of banded spherulites. PTT exhibits three main types of banded spherulites (i.e., concentric, single‐spiral, and double‐spiral) co‐existing in sample films melt‐crystallized at 165 °C, regardless of sample thickness. The three types differ in their banding structures, interference color distributions, and nuclei geometries (S‐shape, Z‐shape, or dot‐shape). Core diameter, band spacing ratio, and height difference (Δz) around the core are the three key parameters of different banding patterns in PTT spherulites. Formation mechanism for three types of banded spherulites has been interpreted, and found to be highly correlated with the initial geometry shapes of their nuclei. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1207–1216     

Morphological development of melt crystallized poly(propylene oxide) by in situ AFM: formation of banded spherulites

The morphology of poly(propylene oxide) (PPO) crystals grown from the melt was investigated. The spherulites of the optically pure S polymers displayed a regular pattern of concentric rings as observed by polarizing optical microscopy, while the stereocopolymer developed irregularly banded, or non-banded spherulites depending on the degree of undercooling. The organization of the lamellar crystals within the spherulites was examined by means of atomic force microscopy (AFM). For all cases, the lamellar structures appeared to adopt an alternating flat or edge-on orientation. Examination of the morphology of single crystals in the melt of the stereocopolymer revealed truncated-lozenge crystals, which were elongated in shape. Results from crystallization kinetics, obtained by in situ AFM observations, showed that the elongated habit is related to differences in the growth rates of the {2 0 0} and {1 1 0} facets. Interestingly, the melt-grown RS-PPO crystals developed a curved asymmetrical three-dimensional shape. Based on these observations it can be proposed that the chiral nature of the chain is transmitted to higher structural levels of ordering in the crystal aggregates.     

Ring‐banded spherulites in PCL and PCL/MWCNT solution‐casting films and effect of compressed CO2 on them

The ring‐banded spherulites in poly(ε‐caprolactone) (PCL) solution‐casting films in the absence and presence of multi‐walled carbon nanotube (MWCNT) are studied by atomic force microscopy (AFM), polarized optical microscopy (POM), transmission electron microscopy (TEM), and scanning electronic microscopy (SEM). The results indicate that birefringent ring‐banded spherulites of PCL can grow from solution below 50 °C, and the temperature is much lower than that from pure PCL melt. We also find out that the presence of MWCNT apparently widen the temperature range of forming ring‐banded structure. Furthermore, the mechanism for the ring‐banded structure forming is studied, and it is attributed to the twisting of lamellae crystals, and the driving force is suggested including the deflexion of lamellae bundles. In addition, effect of compressed CO₂ on the morphology of PCL and PCL/MWCNT solution‐casting film is also investigated, and the results reveal that both PCL and PCL/MWCNT films undergo recrystallization with the treatment of compressed CO₂ and accordingly, the related properties can be adjusted. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 784–792, 2009     

The Nucleating Effect of Carbon Nanotubes on Crystallinity in R‐BAPB‐Type Thermoplastic Polyimide

Summary: The relatively high degree of crystallinity of a new thermoplastic polyimide (PI) makes it a favorable matrix candidate for fiber reinforced composites. This advantage is the result of the ability of the matrix to recrystallize during the composite manufacturing process. In this study we examine the potential nucleating effect of carbon nanotubes on a thermoplastic PI. In addition to their inherent mechanical contribution, the carbon nanotubes help recover a significant proportion of the original crystallinity.

Scanning electron micrograph of the spherulitic structure of a recrystallized carbon nanotube/polyimide film.     

Crystallization kinetics of PGBG4: A sequential poly(ester amide) derived from glycine, 1,4‐butanediol,and adipic acid

Isothermal crystallization kinetics of a new sequential poly(ester amide) derived from glycine, 1,4‐butanediol, and adipic acid was investigated with differential scanning calorimetry and optical microscopy. The Avrami analysis was performed to obtain the kinetic parameters of primary and secondary crystallization. The experimental data indicate a heterogeneous nucleation with spherical growth geometry for the primary crystallization, whereas a linear growth within formed spherulites is characteristic of the last crystallization stages. The Lauritzen–Hoffman analysis was also undertaken to determine the different crystallization regimes, having estimated the corresponding nucleation constants. Temperature dependence of the normalized crystallization‐rate constants was tested with different theoretical equations. These allow an estimation of a temperature close to 90 °C for the maximum crystallization rate. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 903–912, 2003     

Morphology investigation on high‐pressure crystallized bisphenol‐A polycarbonate/dioctyl phthalate blends

The high‐pressure crystallized bisphenol‐A polycarbonate/dioctyl phthalate (BAPC/DOP) blend samples were investigated using wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The specimens were prepared in a piston‐cylinder high‐pressure apparatus by varying the temperature, the pressure and the crystallization time for a BAPC/DOP (90/10, wt/wt) blend. The other four specimens were also prepared with different weight ratios of BAPC/DOP. The DSC results showed that the amorphous BAPC could be crystallized in 45 min by the blending with DOP and the subsequent high‐pressure treatment. A wide variety of morphologies of BAPC crystals were disclosed by SEM, including spherulites, spatial dendrites, crystalbars, platelets and regular polygonal crystals of different characteristics. The folded‐chain lamellar crystals were found to be the substructures of these observed BAPC microstructures. The SEM revealed a granular substructure of the lamellae in a low‐crystallinity sample as well, which indicated that the crystallization of BAPC in the multiphase system might possibly agree with the model developed by Strobl. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2715–2728, 2007     

The effect of film thickness on the depth‐wise chain orientation of rod‐shaped polyimide

Controlling the chain orientation of polyimide is important because it affects the physical and electrical properties of the film. When a polyimide film is thick, the chain orientation has an inhomogeneous distribution along the thickness direction. In this study, poly(amic acids), the precursor of polyimide, with different coating thicknesses are dried, and the distribution of chain orientation in the thickness direction is investigated by measuring the residual solvent content with Raman spectroscopy. The effect of film thickness on the imidization rate is also studied by measuring the depth‐wise degree of imidization at the curing step. With the final cured polyimide film, the depth‐wise chain orientation is quantified by introducing the Fraser distribution function using polarized Raman spectroscopy. The thicker film has a lower degree of in‐plane orientation of polyimide chains, particularly near the substrate. This distribution of polyimide chain orientation in the thickness direction is similar to that of poly(amic acid) after drying. Fast imidization with higher solvent content for thick polyimide retards the formation of a well‐ordered structure with a high degree of in‐plane orientation. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 848–857     

Synthesis of diallyl‐containing polyimide and the effect of allyl groups on properties

A diallyl‐containing bisphenol, 1,1‐bis(3‐allyl‐4‐hydroxyphenyl)‐1‐(6‐oxido‐6H ‐dibenzo [c,e][1,2] oxaphosphorin‐6‐yl) ethane ( 1 ), was prepared by a two‐step procedure. Then, a diallyl‐containing diamine, 1,1‐bis(3‐allyl‐4‐(4‐aminophenoxy)‐phenyl)‐1‐(6‐oxido‐6H‐dibenzo [c,e][1,2] oxaphosphorin‐6‐yl)ethane ( 3 ), was prepared from the nucleophilic substitution of ( 1 ) with 4‐fluoronitrobenzene, followed by the reduction by Fe/HCl. A flexible polyimide ( 4 ) with curable diallyl linkages was prepared from the condensation of ( 3 ) and 4,4′‐oxydiphthalic anhydride in m‐cresol in the presence of isoquinoline. Curing polyimide ( 4 ) at 300 °C leads to thermosetting polyimide ( 5 ). We discussed the amounts of allyl group on T_g, coefficient of thermal expansion, and thermal stability of thermosetting polyimides, and found that thermal properties and dimensional stability of thermosetting polyimides increase with the amounts of cured allyl moieties. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 513–520     

E‐glass/DGEBA/m‐PDA single fiber composites: New insights into the statistics of fiber fragmentation

The interfacial shear strength is a critical parameter for assessing composite performance and failure behavior. This parameter is usually obtained from a single‐fiber fragmentation test that induces sequential fracture with increasing strain of a single embedded fiber with output being the distribution of fragment lengths. An exact analytical form for the expected fragment length distribution is still not known. Such data are often fit empirically to Weibull, shifted‐exponential, or lognormal distribution functions. In this report, new insights into the sequential fiber fracture process are provided by detailed analyses of the fiber break locations along the length of the embedded fiber. From this approach, the high degree of uniformity of the break coordinate loci strongly suggests that there can be no mechanistic rationale for the use of the Weibull, or lognormal, or exponential functions to fit the fragment lengths. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2301–2312, 2009     

Preparation of a chemically amplified photosensitive polyimide based on norbornene‐end‐capped poly(amic acid ethoxymethylester)

A positive‐working chemically amplified photosensitive polyimide (PSPI) developable with basic aqueous solutions was obtained from poly(amic acid ethoxymethylester) (PAAE) as a polyimide precursor and diphenyliodonium 5‐hydroxynaphthalene‐1‐sulfonate (DINS) as a photoacid generator. The norbornene‐end‐capped PAAE based on 4,4′‐oxydiphthalic anhydride and 4,4′‐oxydianiline exhibited high transparency at 365 nm. The protection ratio of the ethoxymethyl groups was optimized to maximize the difference between the dissolution rates of the exposed and unexposed areas. The acid generated from DINS in the UV‐exposed region effectively deprotected the ethoxymethyl groups of PAAE by a chemical amplification mechanism. A 10‐μm‐thick film of the PSPI precursor system containing 16 wt % DINS exhibited a sensitivity (D^o) of 1100 mJ cm^?2 when developed with a 2.38 wt % aqueous tetramethyl ammonium hydroxide solution at room temperature. A fine, positive, 5‐μm line‐and‐space pattern was fabricated in a 15‐μm‐thick film with 1500 mJ cm^?2 of UV exposure. This resolution is excellent in comparison with those previously reported for chemically amplified PSPIs, and such a film can thus be used as a buffer coating in semiconductor packaging. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5520–5528, 2005     

The morphology and structure of PS‐b‐P4VP block copolymer films by solvent annealing: effect of the solvent parameter

Lamellae (symmetric) forming polystyrene‐b‐poly(4‐vinylpyridine) (PS‐b‐P4VP) block copolymers (BCPs) were used to produce nanostructured thin films by solvent (toluene) casting (spin‐coating) onto silicon substrates. As expected, strong micellization of PS‐P4VP in toluene results in poorly ordered hexagonally structures films. Following deposition the films were solvent annealed in various solvents and mixtures thereof. A range of both morphologies including micelle and microphase separated structures were observed. It was found that nanostructures typical of films of regular thickness (across the substrate) and demonstrating microphase separation occurred only for relatively few solvents and mixtures. The data demonstrate that simple models of solvent annealing based on swelling of the polymer promoting higher polymer chain mobility are not appropriate and more careful rationalization is required to understand these data. Analysis suggests that regular phase separated films can only be achieved when the copolymer Hildebrand solubility parameter is very similar to the value of the solvent. It is suggested that the solvent anneal method used is best considered as a liquid phase technique rather than a vapor phase method. The results show that solvent annealing methods can be a very powerful means to control structure and in some circumstances dominate other factors such as surface chemistry and surface energies. Copyright © 2009 John Wiley & Sons, Ltd.     

The synthesis and characterization of polyimide homopolymers based on 5(6)‐amino‐1‐(4‐aminophenyl)‐1,3,3‐trimethylindane

The isomeric diamine monomer 5(6)‐amino‐1‐(4‐aminophenyl)‐1,3,3‐trimethylindane (DAPI) was successfully synthesized via the dimerization of α‐methylstyrene followed by nitration and reduction. High molecular weight, soluble polyimides were synthesized via ester–acid solution imidization techniques and had glass‐transition temperature values ranging from 247 to 369 °C. The polymers were soluble in common organic solvents because of the asymmetric and nonplanar nature of DAPI and displayed good short‐term thermal stability by thermogravimetric analysis, as shown by their 5% weight‐loss values above 500 °C in air. The DAPI/(3,4‐dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) polyimide also showed 2‐h thermal stability at 400 °C under nitrogen, despite the partial aliphatic character. Refractive index values as low as 1.571 were observed for DAPI/6FDA, which allows an estimated dielectric constant of 2.47 to be derived. The permeation of O₂ and N₂ was conducted on thin dense films. The bulky, bent, and isomeric nature of DAPI imparted film‐forming membranes that permitted high O₂ permeability. In combination with 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA), DAPI had a good combination of O₂ permeability and O₂/N₂ selectivity values of 2.8 Ba and 7.3, respectively. The polymerization method utilized to facilitate the cyclization of DAPI/BTDA to the polyimide affected the final thermal properties of the resulting polymer. The chemical imidization of DAPI/BTDA generated a polyimide with a glass‐transition temperature value of 311 °C and a 5% weight‐loss value in air of 457 °C. However, thermal and ester–acid imidization routes yielded an increase in the thermal properties. The ester–acid solution imidization of DAPI/BTDA produced a polymer glass‐transition temperature value of 333 °C and a 5% weight‐loss value of 525 °C in air. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2840–2854, 2000     

Effect of polymer chain stiffness on initial stages of crystallization of polyetherimides: Coarse‐grained computer simulation

We use dissipative particle dynamics simulation to study the role of the intramolecular stiffness in the crystallization process of aromatic polyetherimides. We have developed and parameterized a coarse‐grained model for polyimides R‐BAPB and R‐BAPS, which have similar chemical structures but different macroscopic properties. The former one is known as semicrystalline, while the latter one is amorphous. In our model, the only difference between these two polyimides is the intramolecular stiffness. We show that this model can reasonably reproduce the structure formation in polyimide melts. We observe initial stages of crystallization of polyimide R–BAPB while R‐BAPS stays amorphous. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1254–1265     

Synthesis and characterization of novel photosensitive polyimide based on 5‐(2,5‐dioxotetrahydrofuryl)‐3‐methyl‐3‐cyclohexene‐1,2‐dicarboxylic anhydride

A negative type photosensitive polyimide with alicyclic moiety (NPI) was synthesized from 5‐(2,5‐dioxotetrahydrofuryl)‐3‐methyl‐3‐cyclohexene‐1,2‐dicarboxylic anhydride and 4,4‐diaminobenzophenone by one‐step polymerization in m‐cresol. Properties of the polyimides were characterized and a photo‐crosslinking mechanism was investigated using DEPT ¹³C‐NMR and FT‐IR spectroscopy. The negative polyimide showed good photosensitivity on exposure to UV light from a mercury xenon lamp. The polyimide showed remarkable solubility difference after photo‐ irradiation with an exposure dose of 500 mJ/cm². The resulting negative pattern of the photo‐cured NPI exhibited 10 μm resolution. Glass transition temperature of the photo‐crosslinked polyimide was about 307°C, which increased by 10°C compared to that of the polyimide before UV exposure. Transmittance of NPI after photo‐irradiation was about 87% at 500 nm. Copyright © 2004 John Wiley & Sons, Ltd.     

Morphological changes of annealed poly‐ε‐caprolactone by enzymatic degradation with lipase

The effects of crystallinity and temperature on enzymatic degradation of poly‐ε‐caprolactone (PCL) films and structural changes after degradation have been studied using weight loss, differential scanning calorimetry, and optical microscopy. The weight loss during the enzymatic degradation of PCL suggested that the extent of biodegradation and the rate of degradation strongly depend on the initial crystallinity. PCL films of lower crystallinity (24%) degraded much faster than films of higher crystallinity (45%). The crystallinity of low‐crystalline PCL films increased with increasing degradation time, whereas the crystallinity of high‐crystalline PCL films decreased with time. The spherulite size increased with increasing degradation time for low‐crystalline samples but decreased with time for high‐crystalline samples. These results revealed that degradation occurs first in the amorphous region where the degradation rate is much higher, and the crystalline region of the PCL film started to degrade simultaneously for those PCL with higher crystallinity. The enzymatic degradation of PCL proceeded from the free amorphous to restricted amorphous followed by lamellar edges, where PCL chains have higher mobility irrespective of hydrolysis temperature. Caproic acid was identified as the primary product formed after degradation and confirmed by proton nuclear magnetic resonance spectroscopy, suggesting that degradation occurs through the depolymerization mechanism. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 202–211, 2010     

Ring‐banded spherulites in poly(pentamethylene terephthalate): A model of waving and spiraling lamellae

A new aryl polyester, poly(pentamethylene terephthalate) (PPT) with five methylene groups in the repeat unit, was synthesized. Its multiple‐melting behavior and crystal structure were analyzed with differential scanning calorimetry and wide‐angle X‐ray diffraction. In addition, the spherulitic/lamellar morphology of melt‐crystallized PPT was investigated. Typical Maltese‐cross spherulites (with no rings) were seen in melt‐crystallized PPT at low temperatures (70–90 °C), but ring patterns were seen in PPT crystallized only at temperatures ranging from 100 to 115 °C, whereas rings disappeared with crystallization above 120 °C. The mechanisms of the rings in PPT were explained with several coordinated directional changes (wavy changes, twisting changes, and combinations) in the lamellae during growth. Scanning electron microscopy, in combination with atomic force microscopy, further proved that the ringed spherulites originated from the aggregation of sufficient numbers of edge‐on lamellar crystals; the radial‐growth edge‐on/flat‐on lamellae could be twisted and/or waved to form realistic band patterns. A postulated model properly described a possible origin of the ring bands through combined mechanisms of waving (zigzagging) and twisting (spiraling) of the lamellae during crystallization. Superimposed twisting and/or wavy models during crystallization were examined as examples. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4421–4432, 2004     

The effect of amide solvent structure on the direct arylation polymerization (DArP) of 2‐Bromo‐3‐hexylthiophene

In this work, we investigate the influence of the amide solvent chemical structure on the properties of poly(3‐hexylthiophene) (P3HT) prepared via direct arylation polymerization (DArP). Our findings indicate that for successful polymerization the amide must possess an acyclic aliphatic structure since cyclization of an amide results in a complete shutdown of DArP reactivity as evidenced by failed polymerization in N‐methylpyrrolidone, whereas the presence of an aromatic motif renders the amide solvent susceptible to C? H activation and leads to incorporation of the solvent structure into the P3HT backbone, as demonstrated on the example of N,N‐diethylbenzamide. Additionally, we observed that the steric bulk of alkyl substituents on both the nitrogen atom and the carbonyl group within the amide structure has to be delicately balanced for optimal DArP reactivity. In the optimal cases, P3HT is obtained in high yield, with high molecular weight and contains a minimal amount of structural defects. The obtained polymer samples were comprehensively studied in terms of their chemical structure, optical, thermal and solid‐state properties in thin films using GPC analysis, ¹H NMR, MALDI, UV–vis, GIXRD spectroscopy, and DSC. We additionally note a drastic difference of the amide solvent effect between DArP and Stille polymerization. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2494–2500     

Ab initio QM/MM study of excited state electron transfer between pyrene and 4,4′‐bis(dimethylamino)‐diphenylmethane with different solvent systems: Role of hydrogen bonding within solvent molecules

The exciplex is a charge transfer species formed in the process of electron transfer between an electron donor and an electron acceptor and hence is very sensitive to solvent polarity. In order to understand the role of solvent in exciplex formation between pyrene (PY) and 4,4′‐bis(dimethylamino)diphenylmethane (DMDPM), we used two types of solvent approximations: an implicit solvent model and an explicit solvent model. The difference in energies between the excited and the meta‐stable Frank–Condon state (ΔE) of the structures were assumed to correspond to the emission maximum of the exciplex in different solvents. The ΔE values show the trend of stabilization of the exciplex with an increase in solvent polarity. This trend in stabilization is substantially more prominent in the explicit solvent model than that with the implicit solvent model. The ΔE value obtained in methanol reflects equal stabilization compared to that in a more polar solvent, N,N‐dimethylformamide. This extra stabilization of the exciplex may be explained on the basis of the H‐bonding capability of the protic solvent, methanol. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Synthesis,morphology, and properties of hydroxyl terminated‐POSS/polyimide low‐k nanocomposite films

Polyhedral oligomeric silsequioxane (POSS), having eight hydroxyl groups for the preparation of nanocomposites with polyimide (PI) was synthesized by the direct hydrosilylation of allyl alcohol with octasilsesquioxane (Q₈M₈^H) with platinum divinyltetramethyl disiloxane Pt(dvs) as a catalyst. The structure of allyl alcohol terminated‐POSS (POSS‐OH) was confirmed by FTIR, NMR, and XRD. A high performance, low‐k PI nanocomposite from pyromellitic dianhydride (PMDA)‐4,4'‐oxydianiline (ODA) polyamic acid cured with POSS‐OH was also successfully synthesized. The incorporation of POSS‐OH into PI matrix reduced dielectric constant of PI without loosing mechanical properties. Furthermore, the effects of POSS‐OH on the morphology and properties of the PI/POSS‐OH nanocomposites were investigated using UV–vis, FTIR, XRD, SEM, AFM, transmission electron microscope (TEM), TGA, and contact angle. The homogeneous dispersion of POSS particles was confirmed by SEM, AFM, and TEM. The nanoindentation showed that the modulus increased upon increasing the concentration of POSS‐OH in PI, whereas the hardness did not increase very much with respect to loading of POSS, due to soft‐interphase around POSS molecules in the resulting nanocomposites. Overall results demonstrated the nanometer‐level integration of the polymer and POSS‐OH. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5887–5896, 2008