Vinylimidazole‐based asymmetric ion pair comonomers: Synthesis,polymerization studies and formation of ionically crosslinked PMMA

Vinylimidazole‐based asymmetric ion pair comonomers ( IPC s) which are free from nonpolymerizable counter ions have been synthesized, characterized and polymerized by free radical polymerization (FRP), atom transfer radical polymerization (ATRP), and reversible addition‐fragmentation chain transfer (RAFT) mediated polymerizations in solution and by dispersion polymerization in water. The asymmetric nature of IPC s is due to the fact that cationic component of these IPCs is derived from vinylimidazole (VIm) and anionic component is derived from either styrenesulfonate (SS) or 2‐acrylamido‐2‐methyl‐1‐propanesulfonate. Although under ATRP, conversions are either very low or negligible, FRP and RAFT produces polymers with high to moderate monomer conversions but with different solubility characteristics. This investigation provides insight to the polymerization behavior of each component of the asymmetric IPCs and also its effects on composition and solubility characteristics of the resulting polymers. The IPCs studied here are high temperature ionic liquid and thus the polymers synthesized from these IPCs are highly ionic in nature and possess very strong intermolecular interactions which makes some of these IPC based polymers completely insoluble in organic and aqueous solvents. This highly ionic interaction is exploited to synthesize ionically crosslinked PMMA. MMA on copolymerization with 5–6 mol % of IPC yielded copolymer which is insoluble in common organic solvents like THF, DMF, etc., unlike homo PMMA. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3260–3273     

Adhesion studies of latex film surfaces on the meso- and nanoscale

In this paper the effects of surface roughness and annealing temperature (T) of latex coating films on adhesion are discussed for the different stages of the film formation process. The surface free energy of latex films was assessed in terms of practical work of adhesion (W) (or adherence) using a custom-built adhesion-testing device (ATD), atomic force microscopy (AFM), and contact angle measurements. For preannealed latex films surface roughness averages (R_a) were determined from AFM height images and were related to the values of W obtained from ATD measurements at room temperature. The results obtained using these tests exhibiting surface behavior on different length scales indicate a dependence of the measured adhesion on surface roughness and temperature, as well as on the length scale of the measurements.First preannealed samples were studied, which were obtained by heat treatment above the respective glass transition temperatures (T_g). Increasing the temperature of preannealing resulted in a decrease of the adherence observed in ATD experiments at room temperature. However, on the nanoscale, using AFM, no significant variation of the adherence was observed. This observation can be explained by roughness arguments. Preannealing decreases roughness which results in lower adherence values measured by ATD while for essentially single asperity AFM experiments roughness has an insignificant effect. Specimens were also annealed over a constant period of time (90 min) at different temperatures. At the end of the heat treatment, adhesion was measured at the treatment temperature by ATD. The amplified effect of temperature observed in this case on adherence is attributed to the combination of roughness decrease and increasing test temperature. In a third set of experiments completely annealed samples were studied by ATD as well as by AFM as a function of temperature. With increasing T values ATD showed a decrease in adherence, which is attributed to a decreasing surface free energy of the annealed films at elevated T values. AFM, on the other hand, showed an opposite trend which is assigned to increasing penetration of the tip into the tip/wetting polymer samples versus increasing temperature. Finally, annealing isotherms as a function of time were investigated by ATD in situ at different temperatures. This last set of experiments allowed us to optimize annealing time and temperature to achieve complete curing.     

Probing buried carbon nanotubes within polymer-nanotube composite matrices by atomic force microscopy

Multi-walled carbon nanotubes (MW-CNT) inside a polyamide-6 (PA6)-MW-CNT composite were visualized by atomic force microscopy (i) in a field-assisted intermittent contact and (ii) in the tunneling (TUNA) mode. Individual buried MW-CNTs were clearly discerned within the PA6 matrix. An average diameter of 33 ± 5 nm of the MW-CNTs was determined based on field-assisted intermittent contact mode AFM images, which is consistent with the expected size of PA6-coated MW-CNTs. Single well dispersed MW-CNTs that are located in the sub-surface region of the composite were also observed in the TUNA mode. These new AFM approaches circumvent the tedious sample preparation based on ultramicrotoming required for high resolution electron microscopy studies to obtain “in-depth” morphological information and hence are expected to facilitate the analysis of CNT-based and other nanocomposites in the future.     

Synthesis of poly(arylene ether ketone)s bearing skeletal crown ether units for cation exchange membranes

Poly(arylene ether ketone)s (PAEKs) are the most commonly known high‐performance materials used for ion exchange and fuel cell membranes. Described here is the design of novel sulfonated PAEKs (SPAEKs) and nonsulfonated PAEKs containing crown ether units in the main chain, which can be used in sensing applications and ion‐selective membranes. To this end, 4,4′(5′)‐di(hydroxybenzo)‐18‐crown‐6 was synthesized and used as monomer in a step growth polymerization to form crown ether‐containing PAEKs and SPAEKs. The successful synthesis of PAEKs containing 18‐crown‐6 and sulfonate groups was confirmed by gel permeation chromatography, Fourier transform infrared spectroscopy, and nuclear magnetic resonance spectroscopy. Membranes are fabricated from the sulfonated polymers. Potassium ion transport properties of the SPAEK and crown ether‐containing SPAEK membranes are assessed by diffusion dialysis. Potassium ion diffusion in the crown ether‐containing SPAEK membranes is almost four times lower than K⁺ diffusion in the native polymer membranes, without crown ether. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2786–2793     

Patterns of surface immobilized block copolymer vesicle nanoreactors

The immobilization and positioning of ultra small reaction vessels on solid supports open new pathways in applications such as lab-on-a-chip, sensors, microanalyses and microreactors. In our work block copolymer vesicles made from polystyrene-block-polyacrylic acid (PS-b-PAA) were immobilized from aqueous medium onto 3-amino propyl trimethoxysilane functionalized silicon surfaces exploiting electrostatic interactions. The immobilization of the vesicles was investigated by Fourier transform infrared (FTIR) spectroscopy, as well as fluorescence optical and atomic force microscopy (AFM). In addition, the influence of pH and ionic strength on the surface coverage of vesicles bound to the surface was elucidated. Finally micro-molding in capillaries (MIMIC) was utilized to create line patterns of the vesicles containing the enzyme trypsin and the fluorogenic substrate rhodamine 110 bisamide. The selective positioning of vesicle nanoreactors in conjunction with electrostatic immobilization serves as a proof of principle for potential applications in real-time observation of confined chemical reaction inside vesicles as nanocontainers and for the fabrication of integrated microarray systems.     

An overview on 12-polyurethane: Synthesis, structure and crystallization

The knowledge on linear aliphatic polyurethanes n-PUR has increased significantly due to a series of works made in these last years and published in recent literature. An overview of 12-polyurethane (12-PUR) embracing its synthesis, thermal properties, crystal structure and crystallization is given in this paper. The purpose is to provide a representative example able to reflect comprehensively the state of the art reached for the whole family. The synthesis of 12-PUR was accomplished in good yield and with acceptable molecular weight from 12-amino-1-dodecanol by applying a two-step method without isolation of the isocyanate alcohol precursor. 12-PUR is a semicrystalline polymer with an equilibrium melting temperature of 157 °C. It adopts a layered crystal structure similar to the α-form of nylons with chains in fully-extended conformation and arranged in hydrogen-bonded sheets in the antiparallel mode. This structure is thermally stable up to melting and is unable to undergo Brill transition. 12-PUR crystallized from dilute solution affording well-shaped lamellar crystals with a thickness of 8-9 nm and from the melt yielding either banded or fibrillar spherulitic textures displaying negative birefringence. Isothermal crystallization of 12-PUR from the melt took place with heterogeneous nucleation, while both crystallization rate and the finally attained crystallinity degree were highly depending on crystallization temperature.     

pH Responsive Polymeric Brush Nanostructures: Preparation and Characterization by Scanning Probe Oxidation and Surface Initiated Polymerization

pH‐responsive PHEMA‐based polymeric nanostructures were grown in a controlled manner by ATRP‐based surface‐initiated polymerization. Initiator nanopatterns were obtained on silicon wafers covered with OTS resists made by AFM scanning probe oxidation lithography. AFM images confirmed isolated grafting of stimuli‐responsive hedge and dot brush structures exhibiting dimensions corresponding to a few tens of chains.