WAXD Results Research Articles

Effect of clay type on morphology and thermal stability of PMMA–clay nanocomposites prepared by heterocoagulation method

Poly(methyl methacrylate) (PMMA)–clay nanocomposites were prepared by a heterocoagulation method. A cationic PMMA emulsion was prepared by emulsion polymerization using a cationic initiator in the presence of free surfactant, cetyl trimethylammonium bromide (CTABr), followed by mixing with an aqueous clay slurry. Clays used in present research included montmorillonite (MMT), synthetic hectorites and fluorohectorites (with two different sizes). WAXD results and TEM images indicate that the morphologies of these nanocomposites depend on clay colloid stability as well as clay loadings. WAXD and TEM results also indicate the good morphology preservation of the nanocomposites during solution and melt processing. Thermal stability of these nanocomposites was studied by TG–DTG analyses; the mechanism of thermal stability improvement is discussed based on experimental results.

Chemical immobilization of retinoic acid within poly(ε‐caprolactone) nanoparticles based on drug–polymer bioconjugates

AbstractAll‐trans‐retinoic acid (RA) was chemically conjugated to biodegradable poly(ε‐caprolactone) (PCL10; number‐average Mw ≈ 1250) via an ester linkage. The conjugation was carried out using N,N‐dicyclohexylcarbodiimide and 4‐dimethyl aminopyridine as a coupling agent. The molar ratio of the drug to the polymer was 1.11 as determined by 1H‐NMR analysis. DSC and WAXD results showed that the formation of crystalline structures of RA was effectively suppressed by conjugation with PCL. The RA–PCL conjugates were formulated into nanoparticles by a spontaneous phase‐inversion technique. Morphological characteristics of the resultant nanoparticles and drug‐loading efficiencies were compared with those of free RA‐loaded nanoparticles. The drug‐loading efficiency of RA–PCL conjugates was almost 100%, while that of free RA was only ∼12%. The majority of unconjugated RA was found to form undesirable free‐drug crystals out of nanoparticles, as observed by TEM analysis. This study demonstrates that the conjugation approach of RA to PCL can be an effective means to immobilize and encapsulate RA within nanoparticles for pharmaceutical applications. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1631–1637, 2003

Shear-Induced Precursor Structures in Isotactic Polypropylene Melt by in-Situ Rheo-SAXS and Rheo-WAXD Studies

In-situ rheo-SAXS (small-angle X-ray scattering) and rheo-WAXD (wide-angle X-ray diffraction) studies were carried out to investigate the nature of shear-induced precursor structures in isotactic polypropylene (iPP) melt at 165 °C, near its nominal melting point. Immediately upon the cessation of shear, SAXS patterns clearly showed an evolution of oriented structures in hundreds of angstroms, while the corresponding WAXD patterns did not exhibit any crystal reflections. SAXS patterns at later times showed that the shish-kebab morphology was developed, and the kebabs possessed only a small amount of crystallinity (3%). The combined SAXS and WAXD results indicate that, at the early stages of crystallization, a scaffold (network) of oriented structures is formed. These structures contain (1) primary nuclei (through homogeneous nucleation) that may be crystalline or mesomorphic but having linear connectivity along the flow direction, which form the shish entity, and (2) shish-induced layered crystalline lamellae (kebabs) oriented perpendicularly to the flow direction that have poor lateral connectivity. Subsequent polymer crystallization takes place in the framework of the scaffold, which is probably dominated by the lower molecular weight species. Amounts of the crystalline primary nuclei and the layered crystalline lamellae in the precursor structures were estimated. The results verified, quantitatively for the first time, the well-known concept that minor amounts of linear nuclei induce multiple secondary nucleation sites for the growth of a large quantity of lamellae that grow radially outward from the central core. A mechanistic pathway for the early stages of crystallization in polymer melts under flow is proposed.

Studies on the crystalline intercalate formed by poly(ethylene oxide) and two different kinds of guest molecules

The intercalate with poly(ethylene oxide) as the host compound and dichlorobenzene/dibromobenzene as the guest compounds (PEO-PDCL/PDBB) was studied by the aid of DSC, WAXD, and 13C CP/MAS NMR. No selectivity was observed during the intercalating process of poly(ethylene oxide) (PEO) with p-dichlorobenzene (PDCL) and p-dibromobenzene (PDBB). The orientated PDCL and PDBB molecules are randomly distributed in the benzenic layers between PEO sheets. With increasing PDBB molar fraction, the melting point of the intercalate rises up. WAXD results indicate that the size of orthorhombic crystal cells of PEO-PDCL/PDBB intercalates enlarges as PDBB molar fraction increases. Thereby, It is possible to control the size of crystal cell via adjusting PDBB content in the PEO-PDCL/PDBB intercalates. The 13C CP/MAS NMR experiments imply that the carbons of PEO chains in the PEO-PDCL/PDBB intercalate are in the same chemical environment. This again supports that neither PDCL nor PDBB has priority in interacting with PEO.

Influence of Crystallization Conditions on the Crystal Order and Dynamic Thermal Behavior of Nylon 1010

Nylon 1010 crystals with different size and perfection were prepared under various crystallization conditions. Temperature-varied X-ray diffraction and transmission electron microscopy were used to investigate the structure and morphology of these crystals. The pseudo-hexagonal phase (also known as γ modification) of nylon 1010 was obtained by heating the quenched sample to a high temperature, where this phase is stable. Cooling of the γ modification sample immediately resulted in a Brill transition into the triclinic form. The WAXD and TEM results showed that the crystal structure at room temperature as well as its thermal behavior on heating is strongly influenced by the crystallization conditions. No Brill transition temperature was observed for large or perfect crystals in both the heating and the cooling process, i. e. for melt-crystallized spherulitic crystals and lamellar single crystals grown from dilute solution. This shows that the Brill transition depends on the size and perfection of the crystal.

Synthesis and Characterization of Constitutional Isomeric Poly(amide-ester)s from Adipoyl Chloride and 4-(2-Aminoethyl)phenol

Ordered [head-to-head (H-H) or tail-to-tail (T-T)] poly(amide-ester) (6 a) was prepared by polycondensation from adipoyl chloride (1) and N,N ′-bis(4-hydroxy phenethyl)adipamide (5), which was prepared from the selective acylation of 4-(2-aminoethyl)phenol (2) with N,N ′-adipoylbis[benzoxazoline-2-thione] (4). And H-T ordered poly(amide-ester) (6 b) was prepared by self-polycondensation of 4-carboxy-N-(4-hydroxyphenethyl)-adipamide (7) in the presence of DBOP. Random poly(amide-ester) (6 c) was synthesized by polymerization of 1 with 2. The microstructure of the polymers obtained was investigated by 1H and 13C NMR spectroscopy, and it was found that the polymers obtained had the expected ordered structure. Furthermore, DSC and WAXD results demonstrated that the constitutional regularity of polymers influenced their thermal properties and crystallinity.

Crystallization behavior of PCL in hybrid confined environment

Poly(ϵ-caprolactone) (PCL) and silica (SiO 2) organic–inorganic hybrid materials have been synthesized by the sol–gel method. The crystallization behavior of PCL in silica networks has been investigated using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The degree of PCL crystallinity in PCL/SiO 2 hybrid networks reduces with increase of SiO 2. PCL is in an amorphous state when the concentration of PCL is lower than 40wt% in the hybrid system. The melting point of PCL in the networks is lower than, but close to that of pure PCL. WAXD and SEM results show that the crystalline behavior of PCL in PCL/ SiO 2 hybrid system is strictly confined.

Telechelic Ionomers: Molecular Structure and Kinetics of Physical Gelation of Unsaturated Polyester as Studied by Solid State NMR and X-ray

The kinetics of physical gelation and the structure of telechelic ionomers have been studied by 1H and 13C solid-state NMR, SAXS, and WAXD. The reaction of MgO with unsaturated polyesters containing carboxylic and hydroxyl end groups leads to about a 103−104-fold viscosity increase in the initial solution of polymer in styrene. The results of the present study suggest that the main mechanism, involved in the viscosity increase, is determined by strong electrostatic interactions between Mg2+ ions and the charged carboxylato chain ends, resulting in the formation of immobilized ionic multiplets and their aggregates or clusters. Molecular diffusion is the limiting step for cluster formation. SAXS, WAXD, and NMR results suggest a lamella-like structure of the clusters, which are composed of crystalline carboxylato−Mg−aqua complexes in the core part surrounded by a glassy polymer layer with a thickness of a few nanometers. Polyester chains interconnect multiplets, resulting in the formation of a physical network. The estimated distance between neighboring lamella is comparable with the end-to-end distance of network chains. The increase in the content of network chains and immobilized domains causes a large increase in viscosity and storage modulus. The effect of temperature and of ionic and hydroxyl containing additives on the thickening is discussed.

Confined crystallization behavior of PEO in silica networks

Poly(ethylene oxide) (PEO) and silica (SiO 2) organic–inorganic hybrid materials have been synthesized by sol–gel approach. The crystallization behavior of PEO in silica networks has been investigated by differential scanning calorimeter (DSC) and scanning electron micrograph (SEM). The degree of PEO crystallinity in PEO/SiO 2 hybrid networks reduces with the increase of SiO 2. PEO is in amorphous state when the concentration of PEO is lower than 50 wt% in the hybrid materials. The melting points of PEO in the networks are lower than that of pure PEO, but the melting point of PEO in the networks almost has the same melting point. WAXD and SEM results show that the crystalline behavior of PEO in PEO/SiO 2 hybrid system is sternly confined.

Elastomeric Polypropylenes from Unbridged 2-Phenylindene Zirconocene Catalysts: Temperature Dependence of Crystallinity and Relaxation Properties

The solid-state structure and physical behavior of an elastomeric polypropylene (PP1) synthesized with unbridged 2-phenylindene zirconocene catalyst were examined using solid-state 13C NMR spectroscopy, differential scanning calorimetry, wide-angle X-ray powder diffraction, and birefringence measurements of relaxation behavior. Extraction of these elastomeric polypropylenes with boiling ether and heptane yielded three fractions of different molecular weight and tacticity. The ether-soluble fraction is the lowest in isotactic pentad content and exhibits no detectable crystallinity. For the other fractions and the parent homopolymer, the degrees of crystallinity estimated from DSC and WAXD results are similar. The amount of the immobile phase determined by solid-state NMR, however, appears much higher than the degree of crystallinity. An increase in temperature from 20 to 80 °C results in a loss in the relative fraction of mobile and immobile phase as measured by solid-state NMR and a corresponding loss in ...

Miscibility and Crystallization of Poly(β-hydroxybutyrate)/Poly(vinyl acetate-co-vinyl alcohol) Blends

Poly(vinyl acetate-co-vinyl alcohol) copolymers (P(VAc-co-VA)) were synthesized by hydrolysis−alcoholysis of PVAc. The miscibility, crystallization, and morphology of poly(β-hydroxybutyrate) (PHB) and P(VAc-co-VA) blends were studied by differential scanning calorimetry, optical microscopy (OM), and SAXS. It is found that the P(VAc-co-VA)s with vinyl alcohol content of 9, 15, and 22 mol % will form a miscible phase with the amorphous part of PHB in the solution-cast samples. The melting-quenched samples of PHB/P(VAc-co-VA) blends with different vinyl alcohol content show different phase behavior. PHB and P(VAc-co-VA9) with low vinyl alcohol content (9% mol) will form a miscible blend in the melt state. PHB and P(VAc-co-VA15) with 15 mol % vinyl alcohol will not form miscible blends while PHB/P(VAc-co-VA15) blend with 20/80 composition will form a partially miscible blend in the melt state. PHB and P(VAc-co-VA22) with 22 mol % vinyl alcohol are not miscible in the whole composition range. The single glass transition temperature of the blends within the whole composition range suggests that PHB and P(VAc-co-VA9) are totally miscible in the melt. The crystallization kinetics was studied from the whole crystallization and spherulite growth for the miscible blends. The equilibrium melting point of PHB in the PHB/P(VAc-co-VA9) blends, which was obtained from DSC results using the Hoffman−Weeks equation, decreases with the increase in P(VAc-co-VA9) content. The negative value of the interaction parameter determined from the equilibrium melting point depression supports the miscibility between the components. The kinetics of spherulitic crystallization of PHB in the blends was analyzed according to nucleation theory in the temperature range studied in this work. The best fit of the data to the kinetic theory is obtained by employing WLF parameters and the equilibrium melting points obtained by DSC. The addition of P(VAc-co-VA) did not affect the crystalline structure of PHB, as shown by the WAXD results. The long periods of blends obtained from SAXS increase with the increase in P(VAc-co-VA) content. It indicates that the amorphous P(VAc-co-VA) was rejected to interlamellar phase corporating with the amorphous part of PHB.

Synthesis and thermal transitional properties of side-chain liquid crystalline polyacrylates containingpara-nitroazobenzene as mesogenic groups

The synthesis and characterization of side-chain liquid crystalline (LC) polyacrylates containing para-nitroazobenzene (Pn) as mesogenic groups were described. Homopolymers with 3 and 4 carbon atoms in the spacers were non-LC polymers; for homopolymers with 6 carbon atoms in the spacer, nematic LC behavior was observed. Copolymers with acrylic acid as one component exhibited an S-Ad phase according to the WAXD results which showed the d/l of 1.4-1.54 for the copolymers with 3, 4, and 6 carbon atoms in the spacers. Considering the molecular structure as well as the WAXD results of the copolymers, the possible molecular arrangement in the smectic Sad phase was proposed, in which the smectic layers were composed of the antiparallel mesogens and the antiparallel arrangement was considered to be enhanced due to the H bond between - COOH and - NO2. The stress-induced orientational phenomena of Pn in the LC states was also discussed. (C) 1996 John Wiley & Sons, Inc.

Synthesis and dielectric analysis of aliphatic poly(carbonate‐sulfone)s based on 1,4‐bis(3‐hydroxypropylsulfonyl) butane

AbstractHigh molecular weight aliphatic poly(carbonate‐sulfone) homopolymer (PC‐343) and random copolymer (PC‐343‐10) were synthesized from 1,4‐bis(3‐hydroxypropylsulfonyl)butane (Diol‐343) and a 1/1 molar mixture of Diol‐343 and 1,10‐decanediol, respectively. As a comparison, an aliphatic polycarbonate homopolymer (PC‐10) was prepared from 1,10‐decanediol. While PC‐10 exhibited a single melting peak during its DSC heating scan, both PC‐343 and PC‐343‐10 exhibited multiple reproducible first‐order transitions during DSC heating scans. Both PC‐343 and PC‐343‐10 showed broad reflections in their WAXD diagrams; the crystalline order of PC‐343 is higher than that of PC‐343‐10. Based on the DSC and WAXD results and our discovery on the liquid crystalline behavior of aliphatic poly(carbonate‐sulfone)s from 1,3‐bis(hydroxypropylsulfonyl)propane, we suggest PC‐343 and PC‐343‐10 are liquid crystalline and the liquid crystalline phase formation is directed by the dipole–dipole interactions between sulfone groups. Films were obtained from these polymers by compression molding and dielectric analyses were conducted on them. One glass transition related dielectric relaxation was observed in PC‐343‐10. One glass transition related dielectric relaxation and one sub‐glass transition related dielectric relaxation were observed in PC‐343. The glass transition temperature increases with the increase of sulfone content in the polymers. A dramatic rise in dielectric constant with temperature was observed in PC‐343 and PC‐343‐10 at low frequencies, which is probably due to the sulfone dipole interaction with the electrical field. © 1994 John Wiley & Sons, Inc.

Effect of the reaction conditions on the properties of poly(4,4?-diphenylether-1,3,4-oxadiazole)s

Poly(4,4′-diphenylether-1,3,4-oxadiazole)s have been prepared by polycondensation of 4,4′-diphenylether dicarboxylic acid and hydrazine sulphate, HS, in poly(phosphoric acid), PPA, under different reaction condictions. The products were characterized by viscometry, gel permeation chromatography, 1H-NMR spectrometry and thermogravimetric analysis. Dense membranes have been prepared and submitted to gas transport and wide angle X-ray diffraction, WAXD, experiments. The differences found in permeability and selectivity parameters, as well as in density and WAXD results, are discussed in terms of their solution viscosities and hydrazide repeat unit contents.