Measurement of in situ Monomer Sorption in Poly(propylene)

Summary: An experimental method has been developed to compare the amount of monomer absorbed in freshly produced poly(propylene) with the amount of monomer absorbed in the same material after degassing. It has been found that propylene sorption in freshly produced poly(propylene) is significantly higher than the sorption in the same but degassed polymer. The difference depends on the degree of drying and is time‐dependent. This fact can be an explanation for reduced activity often observed in the transition from liquid‐ to gas‐phase polymerization.

Pressure profile during the pressure‐swing part of the experiment.     

A New Concept for an Alkaline Developable Positive‐Tone Resist: Molecular Resist Utilizing Acid Catalyzed Isomerization from Oxabenzonorbornadiene to Naphthol

A novel positive‐tone molecular resist possessing oxabenzonorbornadiene moiety was developed for electron‐beam (EB) lithography. The synthesized resist material showed relatively high glass transition temperature and readily formed uniform amorphous films on a silicon wafer. The sensitivity of an EB resist was ca. 8 µC · cm⁻² and line and space patterns of 200 nm could be fabricated. The promising feature of the resist materials is that no outgassed products from base matrixes are theoretically produced under the exposure and post‐exposure bake procedure.

     

Size‐Dependent Interfacial Tension of Polymer Blends with Broad Composition Polydispersity

The surface tension as a function of system size of a pure blend with chemically polydisperse compatibilizer is investigated by simulation. The main finding is that such compatibilizers adsorb readily at the interface between the bulk phases giving rise to very broad interfacial zones. This phenomenon leads to a marked size dependence of the interfacial tension. However the adsorption only leads to a decrease of 40% of the interfacial tension of the blend without compatibilizer. The limited effect on interfacial tension is explained by the observation that a considerable fraction of the compatibilizing chains do not contribute to the interfacial tension, instead these chains become part of an inhomogeneous phase with extensive thermodynamic properties.

     

Design Criteria for Accurate Measurement of Bimolecular Radical Termination Rate Coefficients via the RAFT‐CLD‐T Method

The reversible addition‐fragmentation chain transfer chain length dependent termination (RAFT‐CLD‐T) technique allows a simple experimental approach to obtain chain‐length‐dependent termination rate coefficients as a function of conversion, k(x). This work provides a set of criteria by which accurate k(x) can be obtained using the RAFT‐CLD‐T method. Visualization of three‐dimensional plots varying all kinetic rate parameters and starting concentrations demonstrates that only certain combinations give an accurate extraction of k(x). The current study provides hands‐on guidelines for experimentalists applying the RAFT‐CLD‐T method.

     

Exfoliated Polylactide/Clay Nanocomposites by In‐Situ Coordination–Insertion Polymerization

Poly(L ‐lactide)/layered aluminosilicate nanocomposites were synthesized in bulk by ring‐opening polymerization in the presence of two organo‐modified montmorillonites. When the organo‐modifier consisted of an ammonium cation bearing primary hydroxyl groups, polymerization was initiated by the alcohol functions after adequate activation. The growing polymer chains were directly “grafted” onto the clay surface through the hydroxyl‐functionalized ammonium cations yielding exfoliated nanocomposites with enhanced thermal stability.

TEM image of a fully exfoliated Cloisite®30B‐based nanocomposite, showing delamination of the silicate layers.     

Magnetic Microcapsules with Low Permeable Polypyrrole Skin Layer

Summary: The paper describes a perspective approach to significantly decrease permeability of polyelectrolyte multilayered capsules and, therefore, to make them more efficient for encapsulation of small molecule species. The polyelectrolyte shell modification by a dense polymer (polypyrrole) provides the capsule shell with water‐resistant and sufficient barrier properties. However, high brittleness of polypyrrole coatings demands more gentle capsule processing conditions. Magnetite iron oxide nanoparticles were used as a shell constituent to provide the capsules with magnetic properties and, therefore, to propose a mild technological protocol for capsule treating.

CLSM image of TRITC filled PPy covered capsules prepared by magnetic sedimentation.     

Effect of Alkyl Spacer in the Betaine Moiety of Polycarboxybetaines on Their Complexing With Poly(methacrylic acid) and DNA

Summary: The affinity of polybetaines of pyridiniocarboxylate structure that differed by the number n of methylene groups in the betaine moieties (n = 1, 2, 4, and 5) to the tagged poly(methacrylic acid) or DNA was estimated by fluorescence quenching techniques. The revealed irregular change of the affinity with increase in n and the pronounced pH‐induced stabilization of the complexes in neutral media may be particularly beneficial in the development of (bio)separation techniques.

pH‐Dependence of stability of PCB‐n complexes with poly(methacrylic acid) in water‐salt solutions presented in relative units.     

Reinforcement Efficiency of Carbon Nanotubes – Myth and Reality

Different micromechanical models for the prediction of mechanical properties of CNT/polymer composites, taking into consideration filler percolation throughout the matrix, are considered. It is demonstrated that the critical filler volume fraction, where a percolating network of CNTs is forming, marks a “turning point” in the reinforcement efficiency. Expectations for the reinforcing effect of CNTs at concentrations above a percolating threshold with the current technology are in general unrealistic.

     

Effects of Fluctuation and Segregation in the Rate Acceleration of ATRP Miniemulsion Polymerization

In the ATRP and SFRP miniemulsion polymerization, a particle size range may exist in which the polymerization rate is larger than that of the corresponding bulk polymerization. Here, MC simulations are applied to clarify the reason for the acceleration. It is shown that the statistical variation of the trapping agent concentration (fluctuation effect) dominates the acceleration for good living conditions, while the segregation effect is important when the bimolecular termination is significant. Even for the segregation‐dominated conditions, the polymerization rate cannot be predicted accurately without accounting for the fluctuation effect.

     

Kinetic Monte Carlo Studies on the Importance of the Reaction Scheme in Segmental Exchange of Copolymer Chains

Kinetic Monte Carlo studies (confirmed by integration of the corresponding differential equations) are used to demonstrate the fundamental differences between the two most often accepted schemes of segmental exchange. Modeling of reshuffling systems, originally composed of homopolymers of various , various mass distributions, and different compositions, is carried out until the equilibrium copolymers are obtained. It is shown that one of the schemes leads always to a random microstructure (Bernoulli statistics) whereas modeling of the other one indicates possibility of formation of all achievable distributions of comonomer units (from multiblock to nearly alternate). The concepts of the degrees of randomness and reshuffling are discussed and new definitions are proposed.

     

Control of the Dynamic Motion of a Gel Actuator Driven by the Belousov‐Zhabotinsky Reaction

A novel self‐oscillating gel actuator with gradient structure, which generates a pendulum motion by fixing one edge of the gel without external stimuli was achieved. The gel was synthesized by copolymerizing the ruthenium catalyst for the Belousov‐Zhabotinsky reaction with N‐isopropylacrylamide and 2‐acrylamido‐2‐methylpropane sulfonic acid. Furthermore, we clarified that the period and amplitude for the self‐oscillating behavior of the gel actuator are controllable by changing the composition, temperature, and size of the gel. The maximum amplitude of the novel gel actuator is about a 100 times larger than that of the conventional self‐oscillating gel system.