Atom Transfer Radical Polymerization of iso‐Butyl Methacrylate in Microemulsion with Cationic and Non‐Ionic Emulsifiers

Direct atom transfer radical polymerization (ATRP) of iso‐butyl methacrylate in microemulsion has been performed successfully for the first time. ATRP was performed at 40 °C with different emulsifier systems: i) the cationic emulsifier n‐tetradecyltrimethylammonium bromide (TTAB); and ii) mixed emulsifier systems based on TTAB and the non‐ionic emulsifiers Emulgen 911 or Emulgen 931. All polymerizations proceeded in a controlled/living fashion, and the microemulsions were transparent with particle diameters less than 15 nm. The emulsifier system TTAB/Emulgen 911 exhibited better control than TTAB only. This is proposed to be caused by complex formation between Emulgen 911 in the organic phase and CuBr₂ (the deactivator), thus reducing the extent of exit of CuBr₂ to the aqueous phase. The more hydrophilic Emulgen 931 did not lead to improved control.

     

Self‐Complementary Nucleoside‐Thiophene Hybrid Systems: Synthesis and Supramolecular Organization

Versatile synthetic methods towards a variety of thiophene‐nucleobase hybrid systems are reported. Adenine‐ and thymine‐based modified nucleosides characterized by a bithiophene unit linked to the C5′ or C8 position through an ethylenamino or an ethylensulfanyl bridge were synthesized and successfully polymerized in the presence of FeCl₃. The self‐organization properties of the pure polymers as well as their mixtures ‐ with complementary nucleobases ‐ were investigated by means of optical microscopy and AFM in cast film showing complex supramolecular structures resulting from the interplay of multiple intermolecular interactions.

     

Synthesis of Multinuclear Pyridylimine Based Palladium(II) Complexes with a Functionalized Star Polystyrene Core and Evaluation of Their Catalytic Activity Towards Ethylene Oligomerization

Summary: The synthesis of a novel series of multi‐nuclear macroligated pyridylimine based palladium(II) complexes conjugated to a synthetic star polymer core has been well‐described. Star shaped polystyrene with a finite number of arms were prepared by atom transfer radical polymerization (ATRP) and the chain ends were chemically modified in order to introduce the desired end functionality. Utilizing this polymer as organic supports for pyridylimine‐based ligands, palladium(II) complexes were synthesized. On activating with methylaluminoxane (MAO), this complex showed substantially high activity towards ethylene oligomerization, producing C₄ and C₆ compositions as major products. The plausible mechanistic insight concerning the process of ethylene oligomerization is also broached.

An example of trinuclear pyridylimine based palladium(II) complex having a functionalized star polystyrene core.     

A Facile Strategy for Constructing Boron‐Rich Polymer Nanoparticles via a Boronic Acid‐Related Reaction

We present here a facile strategy for constructing Dextran‐poly(3‐acrylamidophenylboronic acid) (Dextran‐PAPBA) nanoparticles (NPs) through a radical polymerization of the monomer 3‐acrylamidophenylboronic acid (APBA) bound by dextran via a boronic acid‐diol reaction in aqueous solution. The synthesized Dextran‐PAPBA NPs are stable in a wide pH range. Their size and composition are tunable by varying the feeding molar ratio of the glucopyranoside unit in dextran to APBA. Additionally, the NPs have good biocompatibility and cell membrane penetrability, as demonstrated by in vitro experiments. Doxorubicin was encapsulated in the NPs and exhibited a sustained and strongly pH‐dependent release profile that would greatly favor the in vivo drug delivery performance of the NPs. The facility of this strategy together with the tunable boron content and outstanding drug release and cellular membrane crossing performance of the produced NPs should greatly boost their applications in boron neutron capture therapy (BNCT) and chemotherapy for cancer treatment.

     

Magnetic Molecularly Imprinted Polymer Particles Synthesized by Suspension Polymerization in Silicone Oil

Summary: Magnetic nanoparticles have been prepared by a co‐precipitation method and modified with methacryloxypropyltrimethoxysilane. Magnetic molecularly imprinted polymer particles have been prepared by suspension polymerization in silicone oil. The particles possess a high affinity to the template molecules and are rapidly separated under a magnetic field.

SEM photograph of magnetic MIP particles.     

Microwave‐Assisted Synthesis of Crosslinked Poly(vinyl alcohol) Nanocomposites Comprising Single‐Walled Carbon Nanotubes,Multi‐Walled Carbon Nanotubes,and Buckminsterfullerene

We report a facile method to accomplish the crosslinking reaction of PVA with SWNTs, MWNTs, and C‐60 using MW irradiation. Nanocomposites of PVA crosslinked with SWNT, MWNT and C‐60 were prepared expeditiously by reacting the respective carbon nanotubes with 3 wt.‐% PVA under MW irradiation, maintaining a temperature of 100 °C, representing a radical improvement over literature methods to prepare such crosslinked PVA composites. This general preparative procedure is versatile and provides a simple route to manufacture useful SWNT, MWNT and C‐60 nanocomposites.

     

The First Example of Main‐Chain Cyclic Azobenzene Polymers

A novel main‐chain azobenzene cyclic polymer, cyclic‐PEHPA, has been successfully synthesized by ‘click’ cyclization of the α‐alkyne‐ω‐azido hetero‐difunctional linear precursors (linear‐PEHPA), which is synthesized by a step‐growth polymerization of the 3′‐ethynylphenyl[4‐hexyl‐(2‐azido‐2‐methyl‐ propionate) phenyl] azobenzene (EHPA). Gel permeation chromatography, and ¹H NMR and FT‐IR spectra confirmed the complete transformation of linear‐PEHPA into cyclic‐PEHPA. With the same molecular weights, the cyclic‐PEHPAs are found to have higher glass transition temperatures than the linear‐PEHPAs, but almost the same decomposition temperatures. In addition, the obtained cyclic azobenzene polymer with lower molar mass shows a slightly better trans–cis–trans photoisomerization ability than the corresponding linear‐PEHPA.

     

Polymerization of Styrene in Cyclodextrin Channels: Can Confined Free‐Radical Polymerization Yield Stereoregular Polystyrene?

Summary: Modeling of polystyrenes (PS) with various stereosequences in the narrow cylindrical channels corresponding to those found in γ‐cyclodextrin inclusion compounds (CD ICs) has been conducted. Based on the conformational modeling of stereoisomeric polystyrenes (PSs) in narrow channels, it was suggested that polystyrene with unusual microstructures might be produced by the constrained polymerization of styrene monomer in its γ‐CD‐IC crystals. The in‐situ polymerization of styrene inside the narrow channels of its γ‐CD‐IC crystals was performed in both organic and aqueous media. The ¹³C NMR spectrum of PS synthesized inside the γ‐CD channels in an aqueous medium shows some differences when compared to the ¹³C NMR spectrum of PS synthesized in toluene. These are presumably because of differences in their stereosequences. Here, we report our preliminary findings.

Schematic of cyclodextrin inclusion compound (CD‐IC) channels with included polymer guests.     

An Improved Catalytic Method for Alkoxyamine Synthesis – Functionalized and Biradical Initiators for Nitroxide‐Mediated Radical Polymerization

Mn(salen)Cl was applied as a low‐cost catalyst for the formation of alkoxyamines from nitroxides and substituted styrenes. These “unimolecular initiators” for nitroxide‐mediated radical polymerization (NMRP) were synthesized using 2,2,6,6‐tetramethyl‐1‐piperidine‐1‐oxyl and 2,2,5‐trimethyl‐4‐phenyl‐3‐azahexane‐3‐oxyl. Functionalized alkoxyamines were obtained from 4‐vinylbenzyl chloride and 4‐vinylbenzyl alcohol. The divinyl compound 1,2‐bis(4‐vinylphenyl)ethane was converted to an alkoxyamine monomer and to bisaminooxy compounds, which can be used as “biradical initiators” for NMRP.

Formation of alkoxyamines using Mn(salen)Cl as the catalyst.     

One Decade of Microwave‐Assisted Polymerizations: Quo vadis?

The application of microwave irradiation in polymer syntheses and modifications is of continuously growing interest and has received significant international interest since the beginning of the millennium. Preceded by a review that was published 6 years ago, the present paper summarizes the most recent trends in this research area. Radical as well as step‐growth and ring‐opening polymerizations will be addressed; furthermore, the evolution from microwave‐assisted polymerizations to microwave‐assisted material fabrication will be described on the examples of polymeranalogous reactions, polymer/metal composites and bio‐based materials.

     

Preparation of Magnetite Nanoparticles Coated with an Amphiphilic Block Copolymer: A Potential Drug Carrier with a Core‐Shell‐Corona Structure for Hydrophobic Drug Delivery

Summary: The synthesis of magnetic magnetite nanoparticles coated with amphiphilic block copolymers of poly(ethyl methacrylate)‐block‐poly(2‐hydroxyethyl methacrylate) for use as new potential carriers for hydrophobic drug delivery is reported. The results show that a new core‐shell‐corona structural material is obtained with a very narrow molecular weight distribution of the hydrophobic segment (PDI = 1.10). UV‐Vis results show that 37% of progesterone is released from the nanoparticles after 22 h, much slower than free release (99% after 14 h), which demonstrates that the presence of the hydrophobic segment can effectively control the release of hydrophobic drugs.

Synthesis of an amphiphilic block polymer poly(ethyl methacrylate)‐block‐poly(2‐hydroxyethyl methacrylate) on magnetite nanoparticles and their use as potential drug carriers     

Effect of Molecular Weight on Photoinduced Birefringence in a Chiral Liquid Crystalline Azodye Polymer

Summary: The evolution of the photoinduced birefringence in thin films of narrow polymer fractions is studied and compared with the behavior of the non‐fractionated polymer. The Δn_ind value decreases by increasing the degree of polymerization ( ) within the oligomeric range but becomes independent of molecular weight starting from a of ≈70. Thermal pretreatment of the films results in higher photoinduced birefringence. The films show good stability of the photorecording.

Birefringence induced after 10 min, Δn_ind(600) and its growth rate at the same moment versus molecular weight.     

Molecular Weight Distribution of Living Radical Polymers

Summary: The molecular weight distribution formed in an ideal living radical polymerization is considered theoretically. It was found that the hypergeometric function that combines the most probable and the Poisson distribution represents a fundamental distribution of the living radical polymers. The number‐ and weight‐average molecular weights are derived for this fundamental distribution, together with those for polymerizations in a batch and in a continuous stirred tank reactor. These average molecular weight functions are obtained based on the arithmetic calculations without deriving the distribution functions. The effect of the monomer transfer reactions on the formed MWD is also considered. The present study clarifies the relationship between the reaction mechanism and the formed molecular weight distribution as well as the fundamental characteristics of living radical polymers.

Calculated number fraction distribution N(r) development with (dashed) and without (solid) the monomer transfer reactions.     

Parametric Analysis of the Intermediate Concentration in a RAFT Polymerization and its Influence upon the Polymerization Kinetics

Summary: A kinetic analysis of living/controlled radical polymerizations in bulk mediated by RAFT is presented. The main objective is to show how the kinetics of the RAFT process and, in particular, of the RAFT intermediate radical is affecting the overall polymerization rate. Namely, three different cases are analyzed: (i) slow fragmentation of the RAFT intermediate; (ii) cross‐termination of the RAFT intermediate with other radicals; and (iii) slow re‐initiation of the RAFT agent leaving group. Simplified analytical formulas are derived for the time‐dependent concentrations of the involved species as well as for conversion. They are supported by numerical simulations and are qualitatively compared to literature experimental findings. Criteria are also given to judge the influence of the RAFT reaction kinetic rate constants on the different phenomena observed experimentally in RAFT polymerization, namely inhibition and retardation. Since these criteria are given by using non‐dimensional groups, they can be readily applied to a broad spectrum of experimental conditions.

Logarithmic non‐dimensional concentration for the radicals (r) and intermediate radicals (q) versus the non‐dimensional polymerization time ( ).     

α,ω‐Nitroxide‐Capped Polystyrenes and Poly(butyl acrylate)s as Macroinitiators for the Free‐Radical Polymerization of Methyl Methacrylate

The use of a bisaminooxy compound as initiator for nitroxide‐mediated radical polymerization (NMRP) of styrene or n‐butyl acrylate allows the synthesis of α,ω‐nitroxide‐capped polymers. At high temperatures and with the addition of acetic anhydride, it was found that these polymers could be applied as macroinitiators in the free‐radical polymerization of methyl methacrylate. This enables the synthesis of block copolymers with only minor contents of homopolymer.

The structure of bis‐TIPNO, the bisaminooxy compound used as an initiator for the nitroxide‐mediated radical polymerization of styrene or n‐butyl acrylate.     

Use of the Interpolyelectrolyte Complexes of Poly(acrylic acid)‐Chitosan as Inductors of Tolerance Against Pathogenic Fungi in Tomato (Lycopersicon esculentum Mill. var. Floradade)

The interpolyelectrolyte complexes of poly(acrylic acid)‐chitosan were investigated as inductor of systemic resistance potentially useful in the organic production of vegetables. These complexes, which are water soluble, were tested in tomato (Lycopersicon esculentum Mill. var. Floradade). The seed treatments were carried out using solutions consisting of 0.1 vol.‐% of the complex and 5 g · L^?1 NaCl in water. The data showed that this treatment produced a higher resistance to the attack by Fusarium oxysporum and Phytophthora capsici pathogens in tomato seedlings.

Formation of the interpolyelectrolyte complex of poly(acrylic acid) and chitosan.     

Controlled/Living Radical Polymerization of Methacrylic Monomers in the Presence of Lewis Acids: Influence on Tacticity

Summary: Atom transfer radical polymerization (ATRP) and reversible addition‐fragmentation transfer (RAFT) polymerization of N‐methyl methacrylamide and methyl methacrylate were investigated in the presence of rare‐earth triflates known to enhance polymer isotacticity. Poly(N‐methyl methacrylamide) with controlled molecular weight, low polydispersity, and enhanced isotacticity was prepared by ATRP and RAFT in the presence of catalytic amounts of yttrium trifluoromethanesulfonate or ytterbium trifluoromethanesulfonate. The tacticity of poly(N‐methyl methacrylamide) depends on the Lewis acid concentration: well‐defined polymers with predominantly either syndiotactic, atactic, or isotactic triads were prepared by adjusting the concentration of the Lewis acid. Simultaneous control of molecular weights, polydispersities, and tacticities in the polymerization of methyl methacrylate was less successful.

Free radical propagation in the presence of a Lewis acid (LA) giving rise to chelate control.     

Synthesis and Self‐Assembly of Amphiphilic Diblock Copolymers using a Fluorescently Labeled N‐Alkoxyamine Initiator

Summary: An initiator for nitroxide mediated ‘living’ free radical polymerization was prepared with a fluorescent tag attached to the initiating alkyl radical terminus. This was used to synthesize amphiphilic poly(acrylic acid)‐block‐polystyrene diblock copolymers, which self assembled in a tetrahydrofuran/buffer solution to form structures that are visible by fluorescence.

     

Controlled Alternating Copolymerization of (Meth)acrylates and Vinyl Ethers by Using Organoheteroatom‐Mediated Living Radical Polymerization

Alternating copolymers comprised of (meth)acrylates and vinyl ethers with controlled molecular weights and polydispersities were synthesized for the first time by living radical polymerization using organotellurium, stibine, and bismuthine chain transfer agents. Combining living alternating copolymerization and living radical or living cationic polymerization afforded hitherto unavailable block copolymers with controlled macromolecular structures.