Influence of various reaction media on the thermal and rheological properties of poly(acrylamide‐co‐N‐hexadecylacrylamide)

A hydrophobically modified polyacrylamide (PAM) was synthesized by the copolymerization of acrylamide (Am) and N‐hexadecylacrylamide (hAm) through solution copolymerization in a polar organic solvent. Polymer synthesis was performed in three nonaqueous media, including dimethyl sulfoxide (DMSO), a mixture of DMSO and an anionic surfactant such as sodium dodecyl sulfate, and a mixture of DMSO and an acidic surfactant such as dodecyl benzene sulfonic acid. The obtained copolymer, poly(acrylamide‐co‐N‐hexadecylacrylamide) [poly(Am‐co‐hAm)], was characterized by ¹H‐NMR. The physical properties of poly(Am‐co‐hAm)s synthesized in different media were compared with those of PAM and with each other by viscosity measurement, X‐ray diffraction, thermogravimetric analysis, and differential scanning calorimetry. We investigated the ways in which the polymerization medium affected the hydrophobic distribution within the resulting copolymer structure. This aspect, in turn, should have altered the solution properties and the microstructure of the copolymer. For this purpose, we studied the viscometric behavior in diluted solutions, the thermal behavior and thermal stability of the copolymers, and finally, the crystalline structure of the copolymers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39939.     

Gelatin‐carbohydrate phase‐separated hydrogels as bioactive carriers in vaginal delivery: Preparation and physical characterizations

The current study focuses on the alteration of properties of the gelatin hydrogels using polysaccharides (e.g., maltodextrin, dextran, and sodium carboxymethyl cellulose) for probable use in vaginal delivery of antimicrobials. The hydrogels were prepared by varying the proportions of gelatin and polysaccharides and were characterized by microscopy, mechanical testing, and impedance spectroscopy. Metronidazole (MZ), drug of choice for the treatment of bacterial vaginosis, was incorporated within the hydrogels. In vitro release studies of MZ from the hydrogels was studied in‐depth using modified Franz's diffusion cell. Antimicrobial efficiency of the MZ‐loaded hydrogels was tested against E. coli and B. subtilis. The results suggested that the incorporation of polysaccharides resulted in the phase‐separated hydrogels. The properties of the hydrogels was found be suitable for vaginal delivery. The drug release and antimicrobial efficiency from the hydrogels suggested that the developed hydrogels may be used for the delivery of antimicrobials in the vaginal lumen. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40445.     

Low temperature curable epoxy siloxane hybrid materials for LED encapsulant

A thermally cured epoxy‐siloxane hybrid material that is curable at low temperature (L‐expoxy hybrimer) was investigated for use as an LED encapsulant. This new hybrimer was fabricated using thermally initiated, cationic polymerization of cycloaliphatic epoxy oligosiloxane (CAEO) resin, derived from non‐hydrolytic sol – gel, mixed with oxetane hardener in the presence of a hexafluoroantimonate‐type thermo‐cationic initiator. The L‐epoxy hybrimer was cured at a lower temperature (below 120 ° C) than previously reported for an epoxy hybrimer with anhydride hardener (above 180 ° C). The L‐epoxy hybrimer showed high thermal resistance to yellowing under long‐term high temperature condition, and maintained good optical transmittance. Also, it had a high refractive index (up to 1.57), as well as the hardness (Shore D 80), and low water‐vapor permeability, w hen the new hybrimer was used to encapsulate an LED, it showed good adhesion without cracks or delamination and maintained their initial performance after the long‐term aging tests (120 and 85 ° C at 85% humidity). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39968.     

Preparation and characterization of poly(ethylene terephthalate) copolyesters modified with sodium‐5‐sulfo‐bis‐(hydroxyethyl)‐isophthalate and poly(ethylene glycol)

Two types of poly(ethylene terephthalate) (PET) copolyesters were successfully prepared with sodium‐5‐sulfo‐bis‐(hydroxyethyl)‐isophthalate (SIPE) and poly(ethylene glycol) (PEG) units with different molecular weights named as cationic dyeable polyester and easy cationic dyeable polyester. Their chemical and crystalline structures were characterized by the nuclear magnetic resonance (NMR), wide angle X‐ray diffraction (WAXD), and small angle X‐ray scattering measurement, and their thermal properties were tested by differential scanning calorimetry and thermogravimetric analysis, respectively. NMR experimental results showed that the actual molar ratio of comonomers was basically consistent with the correlative feed ratio. WAXD results indicated that the crystalline structures of prepared copolyesters were similar to that of PET. Moreover, the glass transition temperature, melting temperature, and thermal degradation temperature were found to decrease with the reduction of the of PEG units as the incorporation of lower of PEG units brought more ether bonds into molecular chains, which increased the irregularity of molecular chain arrangement and led to lower crystallinity. In addition, because the incorporation of PEG units with lower molecular weight led to more ether bonds and hydroxyl end‐groups in molecular chains, the value of contact angle of PET copolyesters dropped, manifesting PET copolyesters had better hydrophilicity with the decreasing molecular weight of PEG units.© 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39823.     

Cassava starch‐graft‐polymethacrylamide copolymers as flocculants and textile sizing agents

Cassava starch‐graft‐polymethacrylamide (PMAM) copolymers were synthesized by a free‐radical‐initiated polymerization reaction, and the products were tested for their efficiency as flocculants and textile sizing agents. The highest percentages of grafting and monomer conversion were 79.9 and 78.0%, respectively. The grafted starches were characterized by Fourier transform infrared spectroscopy, X‐ray diffraction analysis, scanning electron microscopy, differential scanning calorimetry, and thermogravimetric analysis. The average molecular weight of PMAM chains in the grafted starches ranged from 15.9 to 30.8 × 10⁵ g/mol. The grafted starches exhibited a higher peak viscosity and paste stability in comparison to the native starch (NS). Dynamic mechanical analysis showed that grafting provided fairly shear‐stable hydrogels, and the highest storage modulus obtained was 17,900 Pa compared to 1879 Pa for NS. The flocculation studies demonstrated the superiority of starch‐g‐PMAM over cassava starch and PMAM as an efficient flocculant. The tensile strength of cotton yarns sized with the starch‐grafted copolymer was significantly higher (104 MPa) compared to that sized with NS (34 MPa). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39810.     

A thiol‐ene clickable hyperbranched polyester via a simple single‐step melt trans‐esterification process

Self‐condensation of AB₂ type monomers (containing one A‐type and two B‐type functional groups) generates hyperbranched (HB) polymers that carry numerous B ‐type end‐groups at their molecular periphery; thus, development of synthetic methods that directly provide quantitatively transformable peripheral B groups would be of immense value as this would provide easy access to multiply functionalized HB systems. A readily accessible AB₂ monomer, namely diallyl, 5‐(4‐hydroxybutoxy)isophthalate was synthesized, which on polymerization under standard melt‐transesterfication conditions yielded a peripherally clickable HB polyester in a single step; the allyl groups were quantitatively reacted with a variety of thiols using the facile photoinitiated “thiol‐ene” reaction to generate a wide range of derivatives, with varying solubility and thermal properties. Furthermore, it is shown that the peripheral allyl double bonds can also be readily epoxidized using meta‐chloroperoxybenzoic acid to yield interesting HB systems, which could potentially serve as a multifunctional cross‐linking agent in epoxy formulations. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40248.     

Thermal stability of modified end‐capped poly(lactic acid)

The influence of functional end groups on the thermal stability of poly(lactic acid) (PLA) in nitrogen‐ and oxygen‐enriched atmospheres has been investigated in this article using differential scanning calorimetry, thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA). Functional end groups of PLA were modified by succinic anhydride and l ‐cysteine by the addition–elimination reaction. PLA was synthesized by azeotropic condensation of l ‐lactic acid in xylene and characterized by nuclear magnetic resonance. The values of the activation energies determined by TGA in nitrogen and oxygen atmospheres revealed that the character of functional end groups has remarkable influence on the thermal stability of PLA. Moreover, DMA confirmed the strong influence of functional end groups of PLA on polymer chains motion. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41105.     

Calendered linear low‐density polyethylene consolidated meat and bone meal composites

Bioplastics produced from meat and bone meal (MBM) suffer from rapid and drastic mechanical property deterioration because of their hydrophilic nature. This study investigates mechanical and water stability of composites produced from introduction of a minor component of a synthetic polyethylene as a binder phase to consolidate MBM. The milled and sieved MBM was compounded with 5–60 wt % linear low‐density polyethylene (LLDPE) and formed into composite sheets by calendering, which is an industrially relevant process. Results indicated that a minimum of 15 wt % LLDPE content was required to form a nominally continuous binder phase that allowed for good processability and environment stability of the composites. As expected, the water vapor permeability (WVP) and water absorption characteristics of the composites were intermediate between those of MBM and LLDPE. Sheets containing 15 wt % LLDPE absorbed up to 35 wt % water. Composites tested after being soaked in water showed an initial decrease in TS of about 30% for the first hour but then remained fairly unchanged in the next 72 hours, confirming their moderate environment stability. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41145.     

Developing toughened aromatic polybenzoxazines using thermoplastic oligomers and telechelics,part 1: Preparation and characterization of the functionalized oligomers

The preparation and characterization of three families of thermoplastic oligomers (M_n = 2918–13263 g mol^?1) based on polyarylsulfone (PSU) differing in both molecular weight and terminal functionality and one series of polyarylethersulfone (PES) of different molecular weights is reported. Infrared and nuclear magnetic resonance spectroscopy data support the formation of both the hydroxyl terminated oligomers and conversion (67–89% depending on molecular weight) to the telechelic PSU oligomer bearing reactive benzoxazine groups. Differential scanning calorimetry reveals that the onset of homopolymerization in the telechelic PSU oligomer occurs at around 100°C (peak maximum 125°C at 10 K/min) and rescans show values of the glass transition (for the homopolymers) ranging from 124 to 167°C depending on molecular weight. The influence on the oligomer backbone and terminal functionality is examined using thermal analysis. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40875.     

Investigation on the morphology and tensile behavior of β‐nucleated isotactic polypropylene with different stereo‐defect distribution

Large amount of work has been published on the tacticity‐properties relationship of isotactic polypropylene (iPP). However, the stereo‐defect distribution dependence of morphology and mechanical properties of β‐nucleated iPP (β‐iPP) is still not clear. In this study, two different iPP resins (PP‐A and PP‐B) with similar average isotacticity but different uniformities of stereo‐defect distribution were selected, their β‐iPP injection molding specimens were prepared, and the morphology evolution and tensile behaviors were studied by means of differential scanning calorimetry (DSC), 2D wide‐angle X‐ray diffraction (2D‐WAXD) and scanning electron microscope (SEM). DSC results showed that with the same concentration of β‐nucleating agent (0.3 wt % WBG‐II), PP‐B with more uniform stereo‐defect distribution exhibited more amount of β‐phase than that of PP‐A with less uniform stereo‐defect distribution, indicating that PP‐B is more favorable for the formation of β‐phase. SEM results showed that PP‐B formed more amount of β‐crystals with relatively high structural perfection, while in PP‐A a mixed morphology of α‐ and β‐phase with obviously higher amount of structural imperfection emerges. The results of room‐temperature tensile test indicated that the yield peak width of PP‐B was obviously wider, and the elongation at break of PP‐B was higher than that of PP‐A, showing a better ductile of PP‐B. The morphology evolution results of SEM, 2D‐WAXD and DSC suggest that, a combination of lamellar deformation and amorphous deformation occurred in PP‐A, while only amorphous deformation mainly took place in PP‐B, which was thought to be the reason for the different tensile behaviors of the samples. In the production of β‐PP products via injection molding, the uniformity of stereo‐defect distribution was found to be an important factor. PP with more uniform distribution of stereo‐defect favors the formation of large amount of β‐phase with high perfection, which exhibit superior ductile property. The related mechanism was discussed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40027.