The evaluation of the size and the structure of the interphase in composite particles containing a macromonomer studied by solid‐state NMR

The degree of coverage and the structure and thickness of interphases in composite latex particles consisting of a poly(butyl acrylate) (PBA) core incorporated with poly(methyl methacrylate) (PMMA) macromonomer of different molecular weight and a PMMA shell was analyzed by using solid‐state NMR spin‐diffusion measurements. By changing the temperature at a given filter strength or by adjusting the filter strength at a given temperature, the spin‐diffusion experiment could be performed in such a way that the overall structure could be detected. At filter strengths softer than necessary for the detection of the overall structure, information regarding larger structures can be obtained, whereas for stronger filters detailed information about small structures in the interphase region can be extracted. The data obtained by NMR were related to previous TEM and dynamic mechanical studies on these particles.

     

Novel Polymerization of Fluorinated 2‐Vinylcyclopropane in Aqueous Solution via Cyclodextrin Complexes

We report on the first examples of the free radical polymerization of a fluorinated 2‐vinylcyclopropane 1 and its copolymerization with an alkyl 2‐vinylcyclopropane 2 in aqueous solution via their host‐guest complexation with a random methylated β‐cyclodextrin (RAMEB) using a water‐soluble initiator (VA50). Upon polymerization, the dethreaded cyclodextrin remained in water solution, whereas the water‐insoluble polymer precipitated out and was isolated. The polymers prepared exhibited mesophase behavior over a wide range of temperature. Both T_g and T_i of the copolymers increased linearly with the amount of fluorinated co‐units.

Complexation of fluorinated vinylcyclopropane 1 with RAMEB and polymerization in water solution.     

Studies on Photoinduced ATRP in the Presence of Photoinitiator

Photoinduced reverse and simultaneous reverse and normal initiation (SR&NI) atom transfer radical polymerizations (ATRPs) of methyl methacrylate are investigated. The type and concentration of photoinitiators directly influences the photoinduced reverse ATRP. Although the polymerization can be initiated in the absence of alkyl halide, loss of control over the polymerization process is observed. The photoinduced SR&NI ATRP proceed in a well‐controlled manner under UV light at room temperature, as is evident in kinetic and chain extension studies. Better agreement between the experimental and theoretical molecular weights with a narrow molecular weight distribution is observed with photoinduced SR&NI ATRP system.

     

Synthesis and Characterization of Polymer Brushes on Micromechanical Cantilevers

Summary: A technique to cover microelectromechanical systems (MEMS), such as micromechanical cantilever (MC) sensors, with a covalently bound brush layer has been developed. The polymer layer was grown using a “grafting‐from” synthesis of polymer brushes under mild conditions, by surface‐initiated atom transfer radical polymerization. Atomic force microscopy (AFM) and ellipsometry have revealed a uniform thickness of about 12 nm from which a grafting density of polymer brushes of 0.19 chains · nm^?2 was estimated. The coating with polymer brushes can be realized on a selected surface. It was shown that a single‐sided brush layer swells reversibly in toluene, resulting in a bending of the micromechanical cantilever.

Schematic representation of the PMMA brush synthesis on the MC surface, by surface‐initiated ATRP.     

Well‐Defined Cyclohexene Oxide Mid‐Chain Functional Polystyrene Macromonomer: Synthesis,Characterization and Photoinitiated Cationic Homo‐ and Copolymerization

In this article, we present the results of a study of the preparation of a cyclohexene oxide (CHO) mid‐chain functional macromonomer via ATRP of styrene (St) and epoxidation on work‐up with 3‐chloroperoxybenzoic acid. The ATRP initiator, Br? CH? Br, was synthesized by the condensation of 3‐cyclohexene‐1,1‐dimethanol with 2‐bromopropanoyl bromide. The ATRP of St with Br? CH? Br and Cu(I)/bpy yielded well‐defined polystyrene with a cyclohexene mid‐chain group (PSt? CH? PSt). Epoxidation of the PSt? CH? PSt was performed using 3‐chloroperoxybenzoic acid. GPC, IR and ¹H NMR analyses revealed that a low polydispersity macromonomer of polystyrene with CHO functionality at the mid‐chain (PSt? CHO? PSt) was obtained. The photoinduced cationic polymerization of PSt? CHO? PSt yielded comb‐shaped and graft copolymers.

     

Synthesis of Defined Poly(silsesquioxane)s: Fast Polycondensation of Trialkoxysilanes in a Continuous‐Flow Microreactor

The polycondensation of trialkoxysilanes to PSSQs in a microreactor setup is demonstrated. While continuous‐flow processes involving microreactors found various applications in chain growth polymerization, their influence on step‐growth polymerization is less explored, and the polycondensation of multifunctional monomers has not been studied in detail. We found significantly increased yields and a decreased polydispersity of the obtained polymers in comparison to the batch process. By variation of the residence time molecular weights could be adjusted reproducibly ranging from = 1 900 to 11 000 g · mol^?1. Thus, the microreactor setup offers for the first time the possibility to synthesize PSSQ with adjustable properties.

     

Atom Transfer Radical Dispersion Polymerization of Styrene in the Presence of PEO‐based Macromonomer

Commercially available poly(ethylene oxide) macromonomers are successfully used as reactive stabilizers for atom transfer radical dispersion/precipitation polymerization of styrene. Polystyrene particles with PEO chains covalently anchored on the surfaces are obtained. Control over both the particle size and polymer chain growth is achieved using a two‐stage technique consisting of an initial free radical polymerization (FRP) for the nucleation followed by a reverse atom transfer radical polymerization (ATRP) for the controlled polymerization process. The limited monomer conversion at the FRP step ensures that the overall polymerization process is mainly controlled by the reverse ATRP step, resulting in the formation of particles containing well‐defined polymer chains.

     

Synthesis and ATRP Activity of New TREN‐Based Ligands

Summary: Ligands suitable for atom transfer radical polymerization (ATRP) were prepared by the Michael addition of several acrylates (allyl, benzyl, butyl, 2‐ethylhexyl, and 3‐(dimethoxymethylsilyl)propyl acrylates) with tris(2‐aminoethyl)amine (TREN). These ligands, readily prepared from inexpensive precursors, were used for the preparation of catalyst complexes suitable for polymerization of (meth)acrylates and styrene, providing activity comparable to catalysts currently used for these monomers. Catalysts containing ligands with a dimethoxymethylsilyl substituent were examined for copper removal after the reaction mixture was contacted with silica gel.

     

Low‐Temperature Polymerization of Olefins in the Presence of Titanium Monoamidinate/MAO Catalyst

This paper reports the predominantly syndiotactic‐specific polymerization of propylene in the presence of titanium monoamidinate/methylaluminoxane (MAO) catalysts. The same catalysts, depending on the reaction conditions, also promote either predominantly 1,4‐cis or 1,4‐trans polymerization of 1,3‐butadiene and polymerization of styrene either to highly syndiotactic or to stereoirregular polymer. Some preliminary information about the features of propylene polyinsertion is also reported.

Expansion of the 20–24 ppm region of the ¹³C NMR spectrum of sample 2. The starred resonance at 21.75 ppm and the shoulders are not assigned.     

Gas‐Phase Assisted Surface Polymerization of Vinyl Monomers with Fe‐Based Initiating Systems

Summary: Gas‐phase assisted surface polymerization (GASP) of methyl methacrylate (MMA) and styrene (St) was investigated with Fe‐based radical initiating systems, FeCl₂/2,2′‐bipyridine (Bpy)/methyl α‐bromophenylacetate (MBPA), etc. GASP with these initiating systems proceeded to produce corresponding polymers on substrate surfaces. The resulting PMMA had very high PDI values, suggesting an uncontrolled reaction. In an attempt to control the GASP, polymerization with a simple initiating system, Fe(0)/MBPA, was examined on Fe(0)‐metal surfaces, resulting in significant polymerization activity to produce high‐molecular‐weight PMMA. The results of time‐course tests on GASP of MMA and St suggested that a change had taken place to produce physically controlled propagation sites on the Fe(0) powder surfaces.

GASP schemes with a simple initiating system Fe(0)/MBPA.     

Rapid Synthesis and MALDI‐ToF Characterization of Poly(ethylene oxide) Multiarm Star Polymers

Multiarm PEO star polymers with a purely aliphatic polyether structure have been synthesized using hyperbranched polyglycerol (PG) with different molecular weights as a multifunctional initiator. Different degrees of deprotonation of the initiator were studied with respect to molecular weight control. The results show that the degree of deprotonation is a crucial parameter for the synthesis of well‐defined polymers with controlled molecular weights. Partial deprotonation of the PG hydroxyl groups (5–8%) was proven to represent an optimum for the synthesis of star polymers with molecular masses close to the theoretical values. Molecular weights of the stars ranged between 9 000 and 30 000 g · mol^?1. MALDI‐ToF spectra confirmed that the PEO arms in the star polymers possess homogeneous lengths.

     

Narrowly Distributed Surfactant‐Free Polystyrene Latex with a Water‐Soluble Comonomer

Summary: The surfactant‐free synthesis of latex polymers of styrene and sodium styrenesulfonate (NaSS) was investigated. The development of size and size distribution of the particles was studied by photo‐correlation spectroscopy (PCS) and transmission electronic microscopy (TEM). The effects of NaSS concentration and the order of addition of reactants were examined in detail. The results showed that the particle size decreases with an increase in the styrene sulfonate concentration. The polydispersity index can be reduced by mixing NaSS with styrene homogeneously before adding initiator, but this leads to a slightly larger mean particle size.

TEM image of surfactant‐free polystyrene latex made by the modified method.     

Preparation of Crosslinked Poly(2‐bromoethyl methacrylate) Microspheres and Decoration of Their Surfaces with Functional Polymer Brushes

Synthesis and crosslinking copolymerization of 2‐bromoethylmethacrylate in aqueous suspension is described for preparing bromoalkyl‐functional microbeads (125–420 µm). Highly transparent microspheres with a density of accessible bromoethyl groups of 1.55 mmol · g^?1 were prepared in the suspension, stabilized with poly(N‐vinyl pyrrolidone), by using methyl methacrylate as diluting co‐monomer and ethylene glycol dimethacrylate as crosslinker. Bromoalkyl groups on the microparticles were employed as initiation sites for either surface‐initiated ATRP of glycidyl methacrylate or ring‐opening polymerization of 2‐methyl‐2‐oxazoline to generate epoxy‐ and N‐acetylethyleneimine‐functional hairy grafts, tethered to the particle surfaces with hydrolytically stable linkages.

     

Controlled Ring‐Opening Polymerization of Lactones and Lactide Initiated by Lanthanum Isopropoxide, 2. Mechanistic Studies

The mechanism of ring‐opening polymerization of some lactones and lactide initiated by lanthanum isopropoxide has been comprehensively investigated. NMR and viscosity analyses demonstrated that three active polymer chains grow per lanthanum atom and that, depending on the coordinating ability of the monomer, propagation proceeds on aggregated or unaggregated active species. It is also demonstrated that inter‐ and intramolecular side reactions are limited and that lanthanum‐based initiator selectivity in ring‐opening polymerization is analogous to that of aluminum ones.

Part of the proposed mechanism for the lanthanum alkoxide initiated polymerization of ε‐caprolactone.     

Spectroelectrochemical and Photovoltaic Characterization of a Solution‐Processable n‐and‐p Type Dopable Pyrrole‐Bearing Conjugated Polymer

D‐A‐D‐type polymers are of high interest in the field of photovoltaics and electrochromism. In this study we report the synthesis and electrochemical properties of PPyBT along with its photophysical properties and photovoltaic performance. PPyBT is soluble in common organic solvents and both n‐ and p‐type dopable, which is a desired property for conjugated polymers. During electrochemistry studies, the onset potentials of the polymer were determined as +0.2 V for oxidation and ?1.4 V for reduction. Using these values, HOMO and LUMO energy levels were calculated. The photovoltaic properties of PPyBT were also studied. PL studies showed that there is a charge transfer between PPyBT (donor) and PCBM (acceptor).

     

Quantitative Analysis of Dielectric Constants from EFM Images of Multicomponent Polymer Blends

Summary: A simple quantitative model for the analysis of EFM images of three‐ or more‐component polymer blends is applied to determine the dielectric constants of the blend constituents. The value of the dielectric constant of PIPA calculated from the EFM images of POMA‐PIPA‐APP blend is determined in good agreement with the literature value.

     

Peculiar Catalytic Behavior of Poly(vinylidene fluoride) for Cationic Polymerization

Summary: A cationic polymerization of isobutylene, isobutyl vinyl ether, ethyl vinyl ether, vinylcarbazole and α‐methylstyrene was induced by mixing with poly(vinylidene fluoride) (PVDF) powder. The polymerization was an exothermic reaction and gave a high yield. An electron was abstracted from the monomer by PVDF. By the abstraction of the electron, the monomer was converted to a cation radical which induced polymerization. The generation of the cation radicals of the vinyl ethers was confirmed by an ESR spin trapping method, although the cation radicals could be coupled immediately. The resulting polymer was isolated from PVDF (not grafted) and characterized by size exclusion chromatography, IR, UV‐Vis and NMR spectroscopy. The copolymerization of vinyl ethers or vinyl ether/vinylcarbazole was carried out successfully to obtain their random copolymer. PVDF is regarded as a reusable catalyst for cationic polymerizations.

Reaction mechanism of the cationic polymerization of iBVE.     

Atom Transfer Radical Polymerization Using Multidentate Amine Ligands Supported on Soluble Hyperbranched Polyglycidol

Summary: Controlled polymerization of styrene in toluene was achieved by atom transfer radical polymerization (ATRP) using hyperbranched polyglycidol‐supported multidentate amine ligands/Cu^IBr catalyst systems. These catalyst systems with nanoscopic dimensions were more active than the corresponding low‐molecular‐weight ligands. The controlled/living nature of the polymerization is supported by linear first order plots (ln[M]_o/[M] versus time) and a linear increase of versus conversion as well as low polydispersity. Similar controlled polymerization of methyl methacrylate was possible in acetonitrile. Up to 97% of total copper used for polymerization could be removed from the polymer by simple precipitation in methanol and filtration.

Molecular weight characteristics for styrene polymerization using PG‐triamine as a ligand.     

Formation of Thermoresponsive Gold Nanoparticle/PNIPAAm Hybrids by Surface‐Initiated,Atom Transfer Radical Polymerization in Aqueous Media

Summary: We investigated the formation of thermoresponsive gold nanoparticle/poly(N‐isopropylacrylamide) (AuNP/PNIPAAm) core/shell hybrid structures by surface‐initiated, atom transfer radical polymerization (SI‐ATRP) in aqueous media and the effect of cross‐linking on the thermoresponsiveness of the AuNP/PNIPAAm hybrids. The disulfide containing an ATRP initiator was attached onto AuNPs and the monomer, NIPAAm, was polymerized from the surface of AuNPs in the absence or presence of a cross‐linker, ethylene diacrylate, in aqueous media at room temperature. The resulting brush‐type and cross‐linked AuNP/PNIPAAm hybrids were characterized by Fourier‐transform infrared spectroscopy, transmission electron microscopy, and variable temperature dynamic light scattering.

     

Polystyrene with Improved Chain‐End Functionality and Higher Molecular Weight by ARGET ATRP

The bromine chain‐end functionality of polystyrene (PSt) prepared by activators regenerated by electron transfer for atom transfer radical polymerization (ARGET ATRP) was analyzed using 500 MHz ¹H nuclear magnetic resonance (NMR). Bulk polymerization of styrene (St) was carried out with 50 ppm of copper in the presence of tris[2‐(dimethylamino)ethyl]amine (Me₆TREN) ligand and tin(II) 2‐ethylhexanoate [Sn(EH)₂] reducing agent at 90 °C. Due to the use of a low concentration of an active Cu/ligand catalyst complex, it was possible to significantly decrease the occurrence of catalyst‐based side reactions (β‐H elimination). As a result, compared to PSt prepared via normal ATRP, PSt with improved chain‐end functionality was obtained. For example, at 92% monomer conversion in normal ATRP only 48% of chains retained chain‐end functionality, whereas 87% of the chains in an ARGET ATRP still contained halogen functionality. PSt with controlled molecular weight ( = 11 600 g · mol^?1, = 9 600 g · mol^?1) and narrow molecular weight distribution ( = 1.14) was prepared under these conditions. In addition, as a result of decreased frequency of side reactions in ARGET ATRP, PSt with relatively high molecular weight was successfully prepared ( = 185 000 g · mol^?1, = 1.35).