Temperature Sensitive Behavior of Poly(N‐isopropylacrylamide) Grafted Onto Electron Beam‐Irradiated Poly(propylene)

Summary: N‐Isopropylacrylamide (NIPAAm) was graft‐polymerized from its acetone solution onto poly(propylene) (PP) films, after electron‐beam irradiation in the presence of air oxygen. The effects of pre‐irradiation dose as well as monomer concentration, reaction temperature and reaction time on the grafting efficiency were investigated. Typical conditions for achieving maximum grafting yield were observed for 1 M monomer concentration, after PP pre‐irradiation with a 300 kGy dose and a reaction temperature of 50 °C. The location of the graft polymerization was examined by different methods including measurements of dimensional variations, calorimetry, SEM and AFM. The temperature‐responsive behavior of grafted copolymer was studied by swelling and contact angle measurements at different temperatures.

Temperature dependence of the swelling ratio in water as a function of temperature.     

Thermal Characterization of Upper Critical Solution Temperature m‐LLDPE/Poly(ethylene‐ran‐butene) Elastomer Blends

Summary: The phase and thermal characteristics of blends consisting of linear low‐density polyethylene (LLDPE) (0.7 mol‐% hexene copolymer) and poly(ethylene‐ran‐butene) (PEB) (26 mol‐% butene copolymer) have been investigated using optical microscopy (OM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). An upper critical solution temperature of 162 °C was exhibited. The addition of PEB not only slowed the overall crystallization rate of LLDPE but also changed the distribution of lamellar thickness or perfection of LLDPE crystals. The equilibrium melting temperature of LLDPE in the blends was reduced and kept relatively constant in the bi‐phase state. The blends showed a single‐stage degradation and an intermediate thermal stability between those of the individual components. It could be attributed to their homogeneous states at degradation temperatures and the similar decomposing mechanisms of two components. The kinetic analysis of thermal degradation also confirmed the above results.

Phase diagram of LLDPE/PEB blends.     

Radiation Crosslinking of Poly(ethylene‐co‐octene) with Electron Beam Radiation

Films of ethylene‐co‐octene copolymer are irradiated in air after moulding between Mylar® films with electron beam at different doses. To correlate the change in structure with properties, the irradiated and unirradiated samples are characterised by FTIR spectroscopy, swelling and mechanical measurements. Obtained changes are dependant on the radiation dose of the incident electron beam. Irradiation induces trans‐vinylene double bonds detected by FTIR spectroscopy in transmission mode. No hydroxyl (OH) and carbonyl (C?O) groups were recorded by FTIR spectroscopy. More drastic changes are observed with swelling method and by mechanical properties showing the crosslinking effect. Based on the results obtained by analytical techniques used in this study, free radicals mechanism involving mainly the pendant chains of the PE‐co‐O is proposed.

Strain at break versus gel fraction.     

Monodisperse Silica‐Polymer Core‐Shell Microspheres via Surface Grafting and Emulsion Polymerization

We describe a flexible method for preparing monodisperse silica‐polystyrene core‐shell microspheres. In this method, silica nanoparticles grafted with 3‐(trimethoxysilyl)propyl methacrylate (MPS) were employed as seeds in an emulsion polymerization. The thickness of the shells could be changed through varying the amount of the monomer. The monodispersity and diameters of the core‐shell microspheres were found to depend on the size of the grafted silica nanoparticles and the concentration of emulsifier. In addition, we investigated the formation mechanism of the core‐shell microspheres.

Schematic outline of the experimental procedure and TEM image of the monodisperse silica/PS core‐shell microspheres; inset: grafted silica nanoparticles (scale bar = 200 nm).     

Fabrication of Polylactide‐Based Biodegradable Thermoset Scaffolds for Tissue Engineering Applications

The fabrication of tissue engineering scaffolds based on the polymerization of crosslinked polylactide using leaching and batch foaming to generate well‐controlled and interconnected biodegradable polymer scaffolds is reported. The scaffold fabrication parameters are studied in relation to the interpore connectivity, pore morphology, and structural stability of the crosslinked PLA scaffold. In vitro cell culture and in vitro degradation are used to analyze the biocompatibility and biodegradability of the scaffolds. The new crosslinked PLA thermoset scaffolds are highly suitable for bone tissue engineering applications due to their complex internal architecture, thermal stability, and biocompatibility.

     

Enhanced Stereocomplex Crystallization of Biodegradable Enantiomeric Poly(lactic acid)s by Repeated Casting

Stereocomplex crystallization between PLLA and PDLA is known to be disturbed when their molecular weights increase to >10⁵ g · mol^?1. Here, solution casting of PLLA and PDLA with different solvents was performed repeatedly to increase the time for the PLLA/PDLA solution in the concentration range in which only stereocomplex crystallites are formed and thus to elevate the stereocomplex crystallinity in the materials. The results of WAXS and DSC show that for all solvents examined the crystallinities of stereocomplex crystallites and homocrystallites increased and decreased, respectively, with increasing number of castings, indicating that repeated casting is a promising method to enhance stereocomplex crystallization.

     

Toughening of Polystyrene with Ethylene‐Propylene‐Diene Terpolymer (EPDM) Compatibilized by Styrene‐Butadiene‐Styrene Block Copolymer (SBS)

Summary: Polystyrene (PS) was toughened with ethylene‐propylene‐diene terpolymer (EPDM) in the presence of styrene‐butadiene‐styrene block copolymer (SBS). Incorporation of SBS into the PS/EPDM blends clearly improved the impact properties. For PS/EPDM/SBS (mass ratio: 69/21/10) blends, the notched Charpy impact strength reached a maximum value of 26.3 kJ/m². Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that SBS was distributed on the interface between PS and EPDM. Butanone extraction and FTIR analysis found that there was a grafting reaction between PS and EPDM phase during melt compounding. Shearing and processing rheological behaviors of blends were evaluated with a Haake capillary rheometer and a torque rheometer, respectively.

     

Blends of a Main Chain Liquid‐Crystalline Polyester with a Diepoxide and with a Diepoxide/Amine Mixture Prepared in a Twin‐Screw Extruder

Summary: Blending of the commercial LC‐polyester Rodrun LC‐3000 with the bisphenol‐A‐diglycidyl ether based diepoxide DOW D.E.R.330 alone and with the mixture of the diamine (MCDEA) and D.E.R.330 by means of a twin‐screw extruder has been investigated. Conditions to suppress curing of epoxide and amine during blending have been established. Due to the very low solubility of Rodrun in the diepoxide only LCP‐rich blends with a minimum content of 60 wt.‐% Rodrun could be obtained. The blends were investigated by SEM and thermal analysis (DSC, DMTA). Binary blends are immiscible while ternary blends appear miscible from DMTA up to 30 wt.‐% of epoxy/amine.

SEM micrograph of Rodrun moulded at 230 °C.     

Polybenzimidazolium‐Based Solid Electrolytes

A series of methyl, benzyl, and mixed polybenzimidazolium halides was synthesised and characterised by NMR spectroscopy. Membranes were formed and ion exchanged with hydroxides. These membranes are of interest for use in potentially platinum‐free anionic exchange membrane fuel cells. Crosslinked membranes were obtained by the addition of α,α′‐dibromo‐p‐xylene to the casting solution. The ion conductivity of membranes was determined by impedance spectroscopy. A hydroxide conductivity of 29 mS · cm^?1 at 26 °C and 58 mS · cm^?1 at 60 °C was obtained. The thermal and hydrolytic stability was investigated and a pathway for hydrolytic degradation proposed. Hydroxide ions react at the 2 position, the intermediate carbinol opens to the amine–amide, and further degrades under chain scission to diamine and carboxylic acid.

     

Synthesis and Characterization of Biodegradable Poly(ε‐caprolactone)‐Polyglycolide‐Poly(ethylene glycol) Monomethyl Ether Random Copolymer

Summary: Poly(ε‐caprolactone)‐polyglycolide‐poly(ethylene glycol) monomethyl ether random copolymers were synthesized from ε‐caprolactone (ε‐CL), glycolide (GA) and poly(ethylene glycol) monomethyl ether (MPEG) using stannous octoate as catalyst at 160 °C by bulk polymerization. The copolymers with different composition were synthesized by adjusting the weight ration of reaction mixture. The resultant copolymer with a weight ratio (10:15:75) of MPEG2000, GA, and CL was characterized by IR, ¹H NMR, GPC and DSC. The new biodegradable copolymer has potential for medical applications since it is combined with properties of PCL, PGA and MPEG.

     

Synthesis and Characterization of Hyperbranched Poly(β‐ketoester) by the Michael Addition

Summary: A novel hyperbranched poly(β‐ketoester) was synthesized from 2‐(acetoacetoxy)ethyl acrylate by the Michael addition in the presence of 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) as catalyst. ¹H NMR integration experiments revealed that the degree of branching in the poly(β‐ketoester) was remarkably high at a level of 82.9%. The number‐average molecular weight of the polymer was between 2 100 and 12 000 and increased with reaction temperature and conversion.

Synthesis of hyperbranched polymer by Michael addition of AAEA.     

Synthesis of Poly(methyl‐co‐trifluoropropyl)silsesquioxanes and Their Thin Films for Low Dielectric Application

Poly(methyl‐co‐trifluoropropyl)silsesquioxanes (P(M‐co‐TFP)SSQs) were prepared using methyltrimethoxysilane (MTMS) and trifluoropropyltrimethoxysilane (TFPTMS). The molecular weight, microstructure of the copolymers and properties of their thin films have been changed by adjusting reaction parameters such as the molar ratio of water to silane, the molar ratio of catalyst to silane, reaction time, solvent content, and temperature. The refractive index of the copolymer thin film decreased from 1.404 to ca. 1.348 as curing temperature was increased to 420 °C. The dielectric constant of the film decreased with an increase of the molecular weight of the copolymer, and the lowest dielectric constant obtained was ca. 2.2. Hardness and elastic modulus of the thin films were 0.7 and 5 GPa, respectively. Crack velocity was measured to be 10^?11 m/s at the film thickness of around 0.9 μm under aqueous environment.

     

Poly(propylene)/Clay Nanocomposites Prepared by Reactive Compounding with an Epoxy Based Masterbatch

Summary: Poly(propylene) (PP)/clay nanocomposites have been prepared via a novel reactive compounding approach, in which an epoxy based masterbatch consisting of 20 wt.‐% clay was introduced to poly(propylene) with the aid of a maleic anhydride grafted PP (MAPP). The masterbatch was prepared using a recently developed “slurry compounding” technique. After melt compounding, most clay particles have been exfoliated and dispersed into small stacks with several clay layers. WAXD data shows that the dispersion of clay is better at low clay content or high MAPP content. Due to the novelty of the preparation process and complication of the system, the tensile properties of nanocomposites exhibit some unique tendencies with varying the content of MAPP or masterbatch. It is believed that the yield strength and Young's modulus can be dramatically improved after minimizing the excess of unreacted epoxy and optimizing the dispersion of clay.

TEM micrograph of PP/clay nanocomposites prepared with epoxy based masterbatch.     

Design of a Microfluidic System to Investigate the Mechanical Properties of Layer‐by‐Layer Fabricated Capsules

A microfluidic system was designed, fabricated and implemented to study the behavior of polyelectrolyte capsules flowing in microscale channels. The device contains microchannels that lead into constrictions intended to capture polyelectrolyte microcapsules which were fabricated with the well‐known layer‐by‐layer (LbL) assembly technique. The behavior of hollow capsules at the constrictions was visualized and the properties of the capsules were investigated before and after introduction into the device.

Time series of video frames showing capsules being compressed into a constriction.     

Simulation of Nylon 6 Polymerization in an Industrial Two‐Step VK Tubular Reactor

A commonly used nylon 6 two‐step VK tubular reactor is simulated in this work. To verify the reliability of the model, careful comparison with results obtained on different continuous plants is made. The effect of various conditions and parameters, e.g. feed composition, temperature, pressure, etc. on the product properties such as caprolactam conversion, degree of polymerization (DP), dimer, integral heat and their distribution index is studied. It is observed that the caprolactam conversion and DP of the product may be affected by various conditions in the first stage and the temperature profile at the top of the second stage, but they finally reach the equilibrium values if the residence time is long enough. The most effective way to increase DP of the product is to increase the vacuum at the top of the second stage.

CPL conversion and DP profile for pressure of tube 2: 0.032, 0.037, 0.042 mPa; other parameters as given for example A of Table 5 .     

An Application of Silica‐Based Monolithic Membrane Emulsification Technique for Easy and Efficient Preparation of Uniformly Sized Polymer Particles

Summary: Uniformly sized polymer particles were prepared by an emulsification and polymerization technique utilizing a silica monolithic membrane, namely the “silica monolithic membrane emulsification technique”. In this paper, we utilized silica monolithic membrane as a device for the preparation of uniformly sized polymer particles. A mixture of monomers, diluents and oil‐soluble initiator was emulsified into a continuous medium through the silica monolithic membrane and polymerized. The particles obtained had a higher size uniformity than that of particles prepared by previously reported membrane emulsification techniques, such as the Shirasu Porous Glass (SPG) emulsification technique. Through the silica monolithic membrane emulsification technique, we could prepare particles having availability as a possible packing material for solid‐phase extraction (SPE) and high performance liquid chromatography (HPLC).

SEM photograph of silica particles prepared through capillary plate membrane.     

Gamma Ray Irradiation‐Initiated Copolymerization of a Binary Casting System Involving DPBMIn and Vinylpyrrolidone

Summary: When initiated by gamma ray irradiation, a series of homogenous binary casting systems composed of bismaleimide oligomer DPBMI_n with different chain length and reactive solvent vinylpyrrolidone were capable of copolymerization via radical mechanism to form copolymer resins with crosslinked network. Postcuring was performed by thermal treatment subsequent to gamma ray irradiation. The influences of irradiation dose, postcure, DPBMI_n content, and chain length of DPBMI_n on mechanical properties, water uptake, and thermal property of copolymer resins were investigated in details. Fracture morphologies of copolymer resins based on different DPBMI_n were studied by SEM.

SEM images of the copolymer resins.