Living Polymerization of N,N‐Diphenylacrylamide with Triisobutylaluminum

Summary: N,N‐Diphenylacrylamide was polymerized in a living fashion with triisobutylaluminum in THF at 0 °C. The polymerization results showed an increase of molecular weight proportional to the amount of monomer consumed and a first‐order kinetics at −78 °C. The intermediates obtained with excess initiator at −78 °C revealed that the polymerization was initiated through 1,4‐addition of hydride from a triisobutyl group in the triisobutylaluminum and then proceeded through aluminum‐oxygen bond interchange.

N,N‐Diphenylacrylamide was polymerized in a living fashion with triisobutylaluminum in THF at 0 °C.     

Horseradish Peroxidase as a Catalyst for Atom Transfer Radical Polymerization

The hemoprotein horseradish peroxidase (HRP) catalyzes the polymerization of N‐isopropylacrylamide with an alkyl bromide initiator under conditions of activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) in the absence of any peroxide. This is a novel activity of HRP, which we propose to name ATRPase activity. Bromine‐terminated polymers with polydispersity indices (PDIs) as low as 1.44 are obtained. The polymerization follows first order kinetics, but the evolution of molecular weight and the PDI upon increasing conversion deviate from the results expected for an ATRP mechanism. Conversion, and PDI depend on the pH and on the concentration of the reducing agent, sodium ascorbate. HRP is stable during the polymerization and does not unfold or form conjugates.

     

Well‐aligned Nano‐fiberous Membranes Based on Three‐pole Electrospinning with Channel Electrode

Three‐pole electrospinning devices integrated with a blade‐cage collector were developed to fabricate well‐aligned nano‐fiberous membranes. The proposed three‐pole configuration with a channel electrode can be a powerful tool in aligning nano‐fibers with regular diameter because the generated electric field can be accurately controlled without severe fluctuation in comparison with other methods. The three‐pole electrospinning method is also valid for industrial mass production and accurate diameter control of the aligned nano‐fibers.

     

Narrowly Distributed Dendronized Polymethacrylates by Reversible Addition‐Fragmentation Chain Transfer (RAFT) Polymerization

Summary: RAFT is applied to the dendronized macromonomers of the first and second generation, 1 and 2 , respectively. Good results are obtained in the presence of AIBN as radical initiator, with compound 6 as mediator and at mediator to monomer ratios of 2:200 for monomer 1 ( = 320 000, PDI = 1.24) and monomer 2 ( = 178 000, PDI = 1.20). The common characteristics of a controlled polymerization are reasonably met. The more sterically demanding G2 monomer 2 requires higher polymerization temperatures.

     

Synthesis and Characterization of β‐Cyclodextrin Based Functional Monomers and its Copolymers with N‐isopropylacrylamide

Two novel monovinyl β‐cyclodextrin (β‐CD) monomers are synthesized. Their chemical compositions are characterized by means of element analysis, NMR and FT‐IR spectroscopy. The results show that the synthesis techniques used are convenient and efficient. Using N‐isopropylacrylamide as a comonomer, two novel linear copolymers can also be synthesized.

Synthesis route of monovinyl β‐CD monomers.     

Synthesis of Spherical Polyelectrolyte Brushes by Thermo‐controlled Emulsion Polymerization

A novel method of thermo‐controlled emulsion polymerization has been employed to synthesize spherical polyelectrolyte brushes that consist of a solid polystyrene core and a poly (acrylic acid) (PAA) shell covalently attached on the core surface densely by one end. The growth of brushes from the core surface was monitored by dynamic light scattering (DLS). The particle size of PS core latex showed a narrow size distribution when observed by scanning electron microscopy (SEM). The brush size changed significantly upon changing pH value and ionic strength, and displayed similar behavior to brushes prepared by photo‐emulsion polymerization. The grafting density of the PAA brush, which was determined by cutting off the PAA chains using alkali hydrolysis, confirmed the formation of PAA brushes.

     

Penultimate Propagation Kinetics of Butyl Methacrylate,Butyl Acrylate,and Styrene Terpolymerization

The pulsed‐laser polymerization technique is used to determine the composition‐averaged free‐radical propagation rate coefficient (k_p,ter) for terpolymerization of butyl methacrylate, butyl acrylate, and styrene between 60 and 120 °C. A significant deviation from terminal model predictions is observed for the ternary system, indicating that penultimate kinetics are important at these industrially relevant temperatures. The implicit penultimate propagation model, with all the coefficients taken from previous studies of the binary systems, provides a good prediction of the experimental k_p,ter results.

     

Plasma‐Initiated Controlled/Living Radical Polymerization of Methyl Methacrylate in the Presence of 2‐Cyanoprop‐2‐yl 1‐dithionaphthalate (CPDN)

Summary: Plasma‐initiated controlled/living radical polymerization of methyl methacrylate (MMA) was carried out in the presence of 2‐cyanoprop‐2‐yl 1‐dithionaphthalate. Well‐defined poly(methyl methacrylate) (PMMA), with a narrow polydispersity, could be synthesized. The polymerization is proposed to occur via a RAFT mechanism. Chain‐extension reactions were also successfully carried out to obtain higher molecular weight PMMA and PMMA‐block‐PSt copolymer.

Dependence of ln([M]₀/[M]) on post‐polymerization time (above), and \overline M _{\rm n} and PDI against conversion (below) for plasma initiated RAFT polymerization of MMA at 25 °C.     

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.

     

PMMA/Zinc Oxide Nanocomposites Prepared by In‐Situ Bulk Polymerization

Summary: Dispersing surface‐modified zinc oxide nanoparticles (ZnO) in methyl methacrylate (MMA) improves the free radical bulk polymerization process as well as the thermal stability of the formed polymer. Hydroxy groups available on the ZnO surface may induce a degenerative transfer. This suppresses the gel effect, which leads to a better control of the heat evolution during the late stages of polymerization. The formation of chains having vinylidene end groups and head‐to‐head links is suppressed, which shifts the onset of thermal decomposition to the regime where decomposition occurs by random chain scission.

Thermal degradation profiles of PMMA and its composite with ZnO at 11 wt.‐%.     

Successive Chain‐Growth Condensation Polymerization for the Synthesis of Well‐Defined Diblock Copolymers of Aromatic Polyamide and Aromatic Polyether

Well‐defined diblock condensation copolymers composed of an aromatic polyamide and an aromatic polyether have been synthesized by means of successive chain‐growth condensation polymerizations. Polymerization of a polyamide monomer with an orthogonally difunctional initiator is accompanied with side reactions. On the other hand, polymerization with a monofunctional initiator afforded well‐defined polyamide, which has been converted into a macroinitiator by introduction of a terminal 4‐fluorobenzophenone unit. Well‐defined diblock copolymers are obtained by polymerization of a polyether monomer in the presence of this macroinitiator.

     

Hybrid Nanocomposite Films from Mono‐ and Multi‐Functional POSS Copolyacrylates in Miniemulsion

Summary: The synthesis of aqueous dispersions of hybrid acrylic copolymer particles with either a monofunctional or a multifunctional polyhedral oligomeric silsesquioxane methacrylate comonomer has been performed by free radical heterophase polymerization. The miniemulsion process gives stable latexes, whereas the less controlled emulsion route results in colloidal instability of the products. The thermal and mechanical properties of the nanocomposite latex films have been preliminarily investigated.

The nanocomposite latex particles based on hybrid copolyacrylates with highly dispersed POSS cages.     

Enzyme‐Catalyzed Preparation of Aliphatic Polythioester by Direct Polycondensation of Diacid Diester and Dithiol

Summary: Aliphatic dithiol‐diacid type polythioesters were first enzymatically prepared by the direct polycondensation of hexane‐1,6‐dithiol and diacid diesters using the immobilized lipase from Candida antarctica (lipase CA). As a typical example, diethyl sebacate and hexane‐1,6‐dithiol were polymerized using lipase CA in bulk in the presence of molecular sieves 4A to produce the corresponding polythioester with an of 10 200 in 90% yield. Both the melting and crystallization temperatures of the produced polythioesters were higher when compared to those of the corresponding polyoxyesters. A higher molecular weight polythioester was produced using lipase in a two‐step procedure, i.e., cyclization with subsequent ring‐opening polymerization.

Preparation of polythioester and melting temperature of various polythioesters and polyoxyesters.     

Structured Hybrid Nanoparticles via Surface‐Initiated ATRP of Methyl Methacrylate from Ordered Mesoporous Silica

Structured hybrid nanoparticles were synthesized via surface‐initiated atom transfer radical polymerization of MMA from ordered mesoporous silica (OMS) nanoparticles with various morphologies. The design of the OMS particles was adjusted to target either spherical core‐shell or cylindrical morphologies with a mean diameter below 400 nm. The polymer growth via ATRP from the silica surface was well‐controlled as demonstrated by the macromolecular characteristics of the grafted chains. Original hybrid multilayered nanoparticles composed of either a dense silica core or hollow core; an inner OMS shell showing radial orientation of the mesopores and an outer PMMA shell with controlled thickness were successfully prepared.

     

Effect of the Molar Volume on the Elastic Properties of Vinylic Polymers: A Static Molecular Modeling Approach

The effect of the molar volume on the mechanical properties of three polymers is computed using molecular mechanics. It is demonstrated that elastic properties significantly depend on the molar volume. To be reproducible they must be determined for a series of “stable” glassy configurations for which the potential energy is minimized not only according to the coordinates but also to the molar volume. If these conditions are not fulfilled, a great disparity in values between experiment and simulation is observed. The procedure is first applied to PVC. It is then argued that coherent results stemming from the application of this approach to both tacticities of PMMA justifies its application toward other polymers.

     

Estimating Kinetic Parameters for the Spontaneous Polymerization of Glycidol at Elevated Temperatures

The ring‐opening polymerization of glycidol at elevated temperatures is investigated. To improve the synthesis of dendritic polyether polyols, experiments are carried out without initiator to identify the influence of thermal side reactions. This results in a step‐growth polymerization caused by the spontaneous combination of monomers. Kinetic parameters of the side reactions are estimated by fitting simulated number‐ and weight‐average molecular weights to the experimental values measured at different reaction times during the polymerization. The reactions are conducted at three different temperatures of 90, 105, and 120 °C. It is shown that thermal side reactions lead to high dispersities of the final product and are highly sensitive to the reactor operating temperature.

     

Photoinitiators with Functional Groups, 8

Summary: Bimolecular type‐II photoinitiators for radical photopolymerization suffer from a diffusion‐controlled limitation of reactivity and from deactivation by back electron transfer. Here, a very efficient concept to increase the photoinitiator activity by the covalent binding of phenylglycine to benzophenone using a methylene spacer is presented. Photo‐DSC experiments proved that the rate of polymerization can be tripled in comparison to a physical mixture of the components or an industrially applied system with triethanolamine as coinitiator.

Structure of the new photoinitiator synthesized here.     

Smart Surface of Gold Nanoparticles Fabricated by Combination of RAFT and Click Chemistry

A simple efficient post‐modification route to the fabrication of hybrid gold nanoparticles with poly(N‐isopropylacrylamide) (PNIPAm) based on click chemistry is described. The PNIPAm was prepared by reversible addition fragmentation chain transfer radical polymerization (RAFT). The PNIPAm was immobilized onto gold nanoparticles with grafting densities of 5.8 chains · nm⁻² by a click reaction. The hybrid gold nanoparticles showed a temperature responsive phenomenon as the temperature changed between 20 and 45 °C.

     

Multiscale Modeling of Branch Length in Butyl Acrylate Solution Polymerization

Branch lengths resulting from both backbiting and intermolecular chain transfer to polymer are examined for the solution polymerization of butyl acrylate, using a rate‐equation model and ordinary differential equations. Backbiting is allowed to generate branches of varying length, according to a cumulative distribution function obtained from a lattice kinetic Monte Carlo simulation. About 8% of the branches produced by backbiting are 10 mers or longer. In contrast to common assumptions about the origins of short‐chain and long‐chain branches, the model indicates that nearly all of the long‐chain branches may be produced by backbiting, rather than intermolecular chain transfer to polymer.

     

Polymer/Laponite Composite Latexes: Particle Morphology,Film Microstructure,and Properties

Transparent film materials with excellent mechanical and thermal properties were elaborated by drying a latex suspension of armored polymer/Laponite composite particles. Low‐temperature TEM observation of ultrathin cross‐sections of the films indicated a unique network morphology characterized by a “honeycomb” distribution of the Laponite platelets remindful of the original particles morphology.