Non‐Isothermal Crystallization Kinetics of an Ethylene‐Vinyl‐Acetate. II. Time‐Temperature‐Crystallinity‐Superposition

Ethylene vinyl acetate (EVA) is a random copolymer of ethylene and varying amounts of vinyl acetate that interfere with poly‐ethylene chain packing reducing crystallinity, thus improving transparency and lowering the melting temperature to 40°C–60°C. The material viscoelastic properties in its working conditions may thus depend on the crystallinity degree. The crystallization process is here rheologically studied in non‐isothermal conditions and the frequency spectra are measured at different temperatures to investigate the viscoelasticity of EVA. Coupling the crystallization kinetics and the viscoelastic spectra at different temperatures, that is, at different degree of crystallinity, we here determine two independent shift factors, one for the time‐crystallinity shift, the other for the time‐temperature shift, so to propose a new time‐temperature‐crystallinity‐superposition to reconcile all the data on a single master curve. In this way, the experimentally observable frequency range has been widened significantly so to detect all the relaxation times of the material from the shortest to the largest ones. POLYM. ENG. SCI., 59:2550–2556, 2019. © 2019 Society of Plastics Engineers     

Gold‐ vs. Platinum‐Catalyzed Polycyclizations by O‐Acyl Migration. Solvent‐Free Reactions

Polycyclic derivatives incorporating a cyclopropyl group have been efficiently synthesized from propargyl acetates using platinum(II), gold(I) and gold(III) catalysis. These reactions which are also viable for the preparation of medium‐sized rings, proceed with a complete diastereocontrol and can also be run in neat conditions.     

Photografting of unable‐to‐be‐irradiated surfaces. I. Batch vapor‐phase process by one‐step method

Surfaces unable‐to‐be‐irradiated are those that could not be directly exposed to UV irradiation because of their irregular structure or instability under UV irradiation. It is difficult to conduct surface photografting on these kinds of surfaces with conventional photografting methods. Here, a novel one‐step surface photografting method is introduced, by which some monomers were smoothly grafted on the surface of polymer substrates located in a region out of the reach of UV radiation. The mechanism is that the photochemical reaction is separated into three events, absorbing UV light in one place, then transporting light energy to another place, and reacting there; in other words, the conventional photochemical reaction is separated by space and time, and the key point is that the substrate does not need to be exposed to UV irradiation. The occurrence of grafting polymerization was proved by UV–vis, ATR‐IR, SEM, XPS, and water contact angle measurements. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2269–2276, 2006     

Benzothiazole‐accelerated sulfur vulcanization. I. 2‐Mercaptobenzothiazole as accelerator for 2,3‐dimethyl‐2‐butene

2,3‐Dimethyl‐2‐butene (TME) was used as a model compound for polyisoprene in a study of 2‐mercaptobenzothiazole (MBT)‐accelerated sulfur vulcanization. Mixes that contained curatives only were heated in a DSC to various temperatures, while those that also contained TME were heated isothermally at 150°C in evacuated, sealed glass ampules. Heated mixtures were analyzed for residual curatives, intermediates, and reaction products by HPLC. It is proposed that MBT forms polysulfidic species (BtS_xH) in the presence of sulfur and that these react with TME via a concerted, substitutive reaction pathway to form polysulfidic hydrogen‐terminated pendent groups of varying sulfur rank (TME–S_xH). MBT is released as a by‐product of this reaction. Crosslinking occurs slowly as a result of the interaction of polythiol pendent groups, the rate being dependent on the pendent group concentration. H₂S is released on crosslinking. 2,3‐Dimethyl‐2‐butene–1‐thiol was synthesized and reacted in the presence of sulfur to confirm the formation of crosslinked products (TME–S_x–TME). Benzothiazole‐terminated pendent groups (TME–S_xBt) were not observed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1377–1385, 2000     

pH‐reversible hydrogels. IV. Swelling behavior of the 2‐hydroxyethyl methacrylate‐co‐acrylic acid‐co‐sodium acrylate copolymeric hydrogels

A series of 2‐hydroxyethyl methacrylate (HEMA) and sodium acrylate (SA50) copolymeric gels were prepared from HEMA and the anionic monomer SA50 with various molar ratios. The influence of SA50 on the copolymeric gels on their swelling behavior in deionized water at different temperatures and various pH buffer solutions was investigated. Results indicated that the poly(2‐hydroxyethyl methacrylate) (PHEMA) hydrogels exhibited an overshooting phenomenon in their dynamic swelling behavior. The maximum overshooting value decreased with increasing of the temperature. The same results were also found in the HEMA/SA50 copolymeric gels with a lower SA50 content. On the contrary, the overshooting phenomenon for HEMA/SA50 copolymeric gels with a higher content of SA50 was exhibited only under higher temperature (over 35°C). These copolymer gels were used to assess drug release and drug delivery in this article. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1360–1371, 2001     

pH‐thermoreversible hydrogels. I. Synthesis and swelling behaviors of the (N‐isopropylacrylamide‐co‐acrylamide‐co‐2‐hydroxyethyl methacrylate) copolymeric hydrogels

A series of pH‐thermoreversible hydrogels that exhibited volume phase transition was synthesized by various molar ratios of N‐isopropylacrylamide (NIPAAm), acrylamide (AAm), and 2‐hydroxyethyl methacrylate (HEMA). The influence of environmental conditions such as temperature and pH value on the swelling behavior of these copolymeric gels was investigated. Results showed that the hydrogels exhibited different equilibrium swelling ratios in different pH solutions. Amide groups could be hydrolyzed to form negatively charged carboxylate ion groups in their hydrophilic polymeric network in response to an external pH variation. The pH sensitivities of these gels also depended on the AAm content in the copolymeric gels; thus the greater the AAm content, the higher the pH sensitivity. These hydrogels, based on a temperature‐sensitive hydrogel, demonstrated a significant change of equilibrium swelling in aqueous media between a highly solvated, swollen gel state and a dehydrated network response to small variations of temperature. pH‐thermoreversible hydrogels were used for a study of the release of a model drug, caffeine, with changes in temperature. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 221–231, 1999     

PP–PP‐g‐MAH–Org‐MMT nanocomposites. I. Intercalation behavior and microstructure

The melt‐direct intercalation method was employed to prepare poly(propylene) (PP)–maleic anhydride grafted poly(propylene) (PP‐g‐MAH)–organic‐montmorillonite (Org‐MMT) nanocomposites. X‐ray diffractometry (XRD) was used to investigate the intercalation effect, crystallite size, and crystal cell parameter in these composites. Two kinds of maleated PP, with graft efficiencies of 0.6 and 0.9 wt %, and two sorts of manufacturing processes were used to prepare nanocomposites and then to investigate their effects on intercalation behavior. The results showed that the intercalation effect was enhanced by increasing the content of PP‐g‐MAH, using maleated PP with higher graft efficiency, and adopting the mold process. The crystallite size of nanocomposites perpendicular to the crystalline plane, such as (040), (130), (111), and (041), reached the minimum value when the content of PP‐g‐MAH was 20 wt %. This result indicated that the crystallite size of PP in nanocomposites decreased by proper addition of PP‐g‐MAH. Maximum values in tensile strength (40.2 MPa) and impact strength (24.3 J/m) were achieved when the content of PP‐g‐MAH was 10 and 20%, respectively. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3225–3231, 2003     

Thermoreversible hydrogels. VII. Synthesis and swelling behavior of poly(N‐isopropylacrylamide‐co‐3‐methyl‐1‐vinylimidazolium iodide) hydrogels

A series of N‐isopropylacrylamide/3‐methyl‐1‐vinylimidazolium iodide (NIPAAm/MVI) copolymer gels were prepared from the various molar ratios of NIPAAm, cationic monomer MVI, and N,N′‐methylene bisacrylamide (NMBA) in this study. The influence of the amount of MVI in the copolymer gels on the swelling behaviors was investigated in various aqueous saline solutions. Results showed that the swelling ratios (SRs) of copolymer gels were significantly greater than those of NIPAAm homopolymer gels, and the higher the MVI content, the higher the volume phase transition temperature. The SRs for the NIPAAm/MVI copolymer gels decreased with an increase of the salt concentration. In various saline solutions, results showed that the effect of divalent ions on the SR was greater than that of monovalent ions for these hydrogels. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3242–3253, 1999     

Hydroxybenzaldoximes Are D‐GAP‐Competitive Inhibitors of E. coli 1‐Deoxy‐D‐Xylulose‐5‐Phosphate Synthase

1‐Deoxy‐D ‐xylulose 5‐phosphate (DXP) synthase is the first enzyme in the methylerythritol phosphate pathway to essential isoprenoids in pathogenic bacteria and apicomplexan parasites. In bacterial pathogens, DXP lies at a metabolic branch point, serving also as a precursor in the biosynthesis of vitamins B1 and B6, which are critical for central metabolism. In an effort to identify new bisubstrate analogue inhibitors that exploit the large active site and distinct mechanism of DXP synthase, a library of aryl mixed oximes was prepared and evaluated. Trihydroxybenzaldoximes emerged as reversible, low‐micromolar inhibitors, competitive against D ‐glyceraldehyde 3‐phosphate (D ‐GAP) and either uncompetitive or noncompetitive against pyruvate. Hydroxybenzaldoximes are the first class of D ‐GAP‐competitive DXP synthase inhibitors, offering new tools for mechanistic studies of DXP synthase and a new direction for the development of antimicrobial agents targeting isoprenoid biosynthesis.     

Poly(styrene‐block‐butadiene‐block‐styrene‐block‐butadiene) and poly(styrene‐block‐butadiene‐block‐methyl methacrylate) copolymers as compatibilizers in PPO–SAN blends. I. Morphology and fracture behavior

The toughness behavior of PPO–SAN blends with the modifier poly(styrene‐block‐butadiene) (SBSB) and with poly(styrene‐block‐butadiene‐block‐methyl methacrylate) copolymers (SBM) under impact loading conditions has been investigated. The observed morphology of blends compatibilized with SBM, in which the rubber phase discontinuously accumulated at the PPO–SAN interface, correlated with about 20 times higher energy dissipation up to maximum force and about seven times higher deformation capacity compared to pure PPO–SAN blends. In contrast, the fracture behavior of the SBSB‐modified blends was not as strongly dependent on the rubber content. It is especially noteworthy that although the SBM modification resulted in a strong increase in toughness of the PPO–SAN blends, no decrease in stiffness could be found with up to 15% rubber additions. The values of Young's moduli remained at the same high level of the nonmodified material. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2037–2045, 2000     

Photografting polymerization of polyacrylamide on poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) films. II. Wettability and crystallization behaviors of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)‐graft‐polyacrylamide films

The wettability and crystallization behaviors of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV)‐graft‐polyacrylamide (PAM) films were studied. X‐ray photoelectron spectroscopy analyses illustrated that about 62 atom % of the total polar functionalities on the grafted film with 17% grafting percentage (GP) was amide groups. Wide‐angle X‐ray diffraction results suggest that grafted PAM induced defects in PHBV crystals and influenced their crystal structure. Differential scanning calorimetry (DSC) spectra showed the two melting regions, 60–90 and 145–170°C, of the imperfect PHBV crystals of the grafted films. Grafted PAM could suppress the recrystallization of PHBV, which was consistent with the polarizing optical microscopy results, in which the maximum PHBV spherulite diameter decreased from 350 μm for the PHBV film to 50 μm for the film with 53% GP. In addition, DSC studies revealed that the crystallinity of the grafted films decreased with increasing GP, which facilitated the diffusion of water into the films. The water contact angle of grafted films decreased and the water‐swelling percentage increased as GP went up. These results demonstrate the potential of PHBV‐g‐PAM for wettable surface constructs in tissue engineering applications. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Water‐soluble acrylamide copolymers. X. Flocculation efficiencies of poly[acrylamide‐co‐N,N‐dimethylacrylamide], poly[acrylamide‐co‐methacrylamide], poly[acrylamide‐co‐N‐t‐butylacrylamide], and their cationic derivatives

A hydrated, 1% by weight Na‐kaolinite suspension in deionized water was prepared, completely characterized, and reproducible measures of flocculation efficiency were validated. Flocculation tests of copolymers of acrylamide (AM) with dimethylacrylamide (DMA), methacrylamide (MeAM), or N‐t‐butylacrylamide (NTBAM) with 1% Na‐kaolinite suspensions gave average settling rate rates which decreased as the proportion of DMA, MeAM, or NTBAM in the copolymer increased. However, for a similar weight‐average molecular weight and slightly lower 〈r_g〉, the copolymer from DMA‐co‐AM‐3 gave settling rates and supernatant turbidities comparable to similar types of commercial polymers. This new copolymer was also more resistant to changes in pH or the presence of an electrolyte than were the tested commercial polymers. Cationic derivatives of the new copolymers gave lower average settling rates and higher supernatant turbidities than those of Percol 721 (cationic PAM), probably because of their lower charge densities. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2090–2108, 2002; DOI 10.1002/app.10562     

PE/PE‐g‐MAH/Org‐MMT nanocomposites. II. Nonisothermal crystallization kinetics

The nonisothermal crystallization kinetics of high‐density polyethylene (HDPE) and polyethylene (PE)/PE‐grafted maleic anhydride (PE‐g‐MAH)/organic‐montmorillonite (Org‐MMT) nanocomposite were investigated by differential scanning calorimetry (DSC) at various cooling rates. Avrami analysis modified by Jeziorny, Ozawa analysis, and a method developed by Liu well described the nonisothermal crystallization process of these samples. The difference in the exponent n, m, and a between HDPE and the nanocomposite indicated that nucleation mechanism and dimension of spherulite growth of the nanocomposite were different from that of HDPE to some extent. The values of half‐time (t_1/2), K(T), and F(T) showed that the crystallization rate increased with the increase of cooling rates for HDPE and composite, but the crystallization rate of composite was faster than that of HDPE at a given cooling rate. Moreover, the method proposed by Kissinger was used to evaluate the activation energy of the mentioned samples. It was 223.7 kJ/mol for composite, which was much smaller than that for HDPE (304.6 kJ/mol). Overall, the results indicated that the addition of Org‐MMT and PE‐g‐MAH could accelerate the overall nonisothermal crystallization process of PE. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3054–3059, 2004     

Surface modification of ultra‐high‐molecular‐weight polyethylene. I. Characterization and sintering studies

We performed surface modification of ultra‐high‐molecular‐weight polyethylene (UHMWPE) through chromic acid etching with the aim of improving the performance of UHMWPE's composites with poly(ethylene terephthalate) fibers. In part I of this study, we evaluated the effects of chemical modification on the surface properties of UHMWPE with X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and contact angle measurements. The thermal properties, rheology, and sintering behavior of the modified UHMWPE were compared to those of the base material. XPS and FTIR analysis confirmed the presence of carboxyl and hydroxyl groups on the surface of the modified powders. The substitution of polar groups into the backbone of the polymer decreased its contact angles with water and hexadecane and increased its surface energy, as evidenced by contact angle measurements. The modified UHMWPE was more crystalline than the base resin and less prone to thermal degradation. Although the rheological properties were virtually identical, the modified powders sintered more readily, presumably due to their higher surface energy, which suggested enhanced processability by compression molding. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Modified chitosan. I. Optimized cerium ammonium nitrate‐induced synthesis of chitosan‐graft‐polyacrylonitrile

Chitin was extracted from shrimp shells and then deacetylated to obtain chitosan. The degree of deacetylation of the chitosan was determined to be 0.76 using pH‐metric titration. A large number of cyanide functional groups were introduced onto chitosan by grafting with polyacrylonitrile as an efficient way of modification. The graft copolymerization reactions were carried out under argon atmosphere in a homogeneous aqueous phase (containing a small portion of acetic acid) by using ceric ammonium nitrate as an initiator. Evidence of grafting was obtained by comparing FTIR spectra of chitosan and the graft copolymer as well as solubility characteristics of the products. The synthetic conditions were systematically optimized through studying the influential factors, including temperature and concentrations of the initiator, acrylonitrile monomer (AN), acetic acid, and chitosan. The effect of individual factors was investigated by calculating and monitoring the variations of the grafting parameters [i.e., grafting ratio (Gr), grafting efficiency (Ge), add‐on value (Ad), homopolymer content (Hp), and total conversion (Ct)]. Under optimum conditions, the grafting parameters were achieved as 535, 98, 81, 2, and 102%, respectively. A mechanism for the free‐radical grafting was proposed. As empirical rates of polymerization and graft copolymerization were plotted against [AN] and [Ce⁴⁺]^1/2, the experimental kinetic data displayed a good match to a reported rate statement. The overall activation energy for the graft copolymerization was determined to be 44.9 kJ/mol. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2048–2054, 2003     

The Low‐Temperature High‐Pressure Phase Diagram of Energetic Materials: I. Hexahydro‐1,3,5‐Trinitro‐s‐Triazine

The reaction phase diagram of hexahydro‐1,3,5‐trinitro‐s‐triazine (RDX) has been studied as a function of temperature and pressure by Raman spectroscopy to 29 GPa and temperatures ranging from 4 to 298 K. Three stable phases (α, γ, and δ) have been found and their phase stabilities have been investigated. Phase boundaries were studied as a function of pressure and temperature, permitting a delineation of the various polymorph stability fields. A pressure–temperature reaction/phase diagram is constructed from the results of this study and compared to previous high temperature work.     

Rheology of 1‐butyl‐3‐methylimidazolium chloride cellulose solutions. I. Shear rheology

In this article, shear rheology of solutions of different concentrations obtained by dissolution of cellulose in the ionic liquid (IL) solvent 1‐butyl‐3‐methylimidazolium chloride ([Bmim]Cl) was studied by measuring the complex viscosity and dynamic moduli at different temperatures. The obtained viscosity curves were compared with those of lyocell solutions and melt blowing grade polypropylene melts of different melt flow rates (MFR). Master curves were generated for complex viscosity and dynamic moduli by using Carreau and Cross viscosity models to fit experimental data. From the Arrhenius plots of the shift factors with respect to temperature, the activation energies for shear flow were determined. These varied between 18.99 and 24.09 kCal/mol, and were compared with values for lyocell solutions and different polymeric melts, such as polyolefins, polystyrene, and polycarbonate. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Functional copolymer/organo‐MMT nanoarchitectures. II. Dynamic mechanical behavior of poly(MA‐co‐BMA)s‐organo‐MMT clay nanocomposites

Functional copolymer/organo‐silicate [N,N′‐dimethyldodecyl ammonium cation surface modified montmorillonite (MMT)] layered nanocomposites have been synthesized by interlamellar complex‐radical copolymerization of preintercalated maleic anhydride (MA)/ organo‐MMT complex as a ‘nano‐reactor’ with n‐butyl methacrylate (BMA) as an internal plasticization comonomer in the presence of radical initiator. Synthesized copolymers and their nanocomposites were investigated by dynamic mechanic analysis, X‐ray diffraction, SEM, and TEM methods. It was found that nanocomposite dynamic mechanical properties strongly depend on the force of interfacial MA … organo‐MMT complex formation and the amount of flexible n‐butyl ester linkages. An increase in both of these parameters leads to enhanced intercalation and exfoliation in situ processes of copolymer chains and the formation of hybrid nanocomposites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Polymer complexes. XXXI. Potentiometric and thermodynamic studies of 2‐acrylamido‐2‐amino‐3‐hydroxy pyridine and its metal complexes

Proton ligand dissociation and metal ligand stability constants of 2‐acrylamido‐2‐amino‐3‐hydroxy pyridine (AAHP) with some transition metal ions in 0.1 M KCl and 50% (v/v) ethanol–water mixture were calculated potentiometrically. In the presence of 2,2′‐azobisisobutyronitrile as initiator the proton‐polymeric ligand dissociation and metal polymeric ligand stability constants were also evaluated. The influence of temperature on the dissociation of AAHP and the stability of its metal complexes in the monomeric and polymeric forms were critically studied. On the basis of the thermodynamic functions, the dissociation process of AAHP was found nonspontaneous, endothermic, and entropically unfavorable, although the formed metal complexes showed spontaneous, endothermic, and entropically favorable behavior. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2552–2557, 2000     

Rheology of 1‐butyl‐3‐methylimidazolium chloride cellulose solutions. III. Elongational rheology

The elongational rheology of solutions of cellulose in the ionic liquid solvent 1‐butyl‐3‐methylimidazolium chloride ([Bmim]Cl) was measured at 80, 90, and 100°C; 8, 10, and 12 wt% cellulose; Hencky strains 5, 6, 7; and strain rates from 1 to 100 s^?1. Master curves were generated by shifting the elongational viscosity curves with respect to temperature and Hencky strain. Also, general master curves were generated by simultaneously shifting with respect to both temperatures and Hencky strain. From the Arrhenius plots of the temperature shift factors, the activation energy for elongational flow was determined. The elongational rheology of these solutions was elongational strain rate thinning similar to that of their shear behavior and polymer melts and they were also strain hardening. Both effects and the viscosity increased with cellulose concentration. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008