A Facile Two‐Step Route to Branched Polyisoprenes via ABn‐Macromonomers

A facile two‐step synthesis for branched poly(isoprene)s (PI) based on polyaddition of AB_n‐type macromonomers is described. The synthesis of the macromonomers was achieved by anionic polymerization of isoprene and subsequent end‐capping of the polymers by addition of chlorodimethylsilane to the living carbanions. This led to PI‐based macromonomers with narrow polydispersity ( / < 1.15) and molecular weights in the range of 1 700 – 22 100 g · mol⁻¹. Synthesis of the branched polymers was carried out by a hydrosilylation‐based polymerization of the macromonomers. Characterization via SEC, SEC‐MALLS, coupled SEC‐viscosimetry and ¹H‐NMR‐spectroscopy supported the formation of branched structures. Interestingly, these branched polymers exhibited α‐values that were similar to those reported for hyperbranched polymers based on AB₂‐monomers.

     

Ferrocenyl‐functionalized long chain branched polydienes

A convenient two‐step approach for the synthesis of ferrocenyl‐functionalized long chain branched polydienes, based on both butadiene and isoprene, respectively, is presented. Classical living anionic polymerization was used to synthesize different AB_n type poly(diene) macromonomers with moderate molecular weights between 1700 and 3200 g/mol and narrow polydispersity. Quantitative end‐capping with chlorodimethylsilane resulted in the desired AB_n macromonomer structures. In the ensuing Pt‐catalyzed hydrosilylation polyaddition, branched, functionalized polydienes were obtained by a concurrent AB_n + AR type of copolymerization with mono‐ and difunctional ferrocenyl silanes (fcSiMe₂H or fc₂SiMeH). Molecular weights of the branched polymers were in the range of 10,000 to 44,000 g/mol (SEC/MALLS). Because of the large number of functional end groups, high loading with ferrocene units up to 63 wt % of ferrocene was achieved. Detailed studies showed full conversion of the functional silanes and incorporation into the branched polymer. Further studies using DSC, TGA, and cyclovoltammetry (CV) measurements have been performed. Electrochemical studies demonstrated different electrochemical properties for fcSiMe₂‐ and fc₂SiMe‐units. The CVs of polymers modified with diferrocenylsilane units exhibit the pattern of communicating ferrocenyl sites with two distinct, separate oxidation waves. The polymers were also deposited on an electrode surface and the electrodes investigated via CV, showing formation of electroactive films with promising results for the use of the materials in biosensors. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2518–2529, 2009     

Well‐Defined Flexible Polyelectrolytes with Two Cationic Sites per Monomeric Unit

Summary: Well‐defined flexible, annealed, and quenched polyelectrolytes with two cationic sites per monomeric unit are synthesized. The synthetic scheme involves the synthesis of narrowly distributed poly(p‐tert‐butoxystyrene) precursors by anionic polymerization high vacuum techniques, hydrolysis to poly(p‐hydroxystyrene), and subsequent quantitative functionalization by a Mannich‐type reaction, to yield annealed polyelectrolytes with two dimethylamino groups per monomer. In a last step, the dimethylamino groups are converted into quaternary ammonium salts by reaction with methyl iodide to give high‐charge‐density quenched cationic polyelectrolytes. The polymers are molecularly characterized by NMR and FT‐IR spectroscopy, while their solution behavior is studied by potentiometric titrations, turbidimetry, and fluorescence spectroscopy as a function of pH, in the case of the annealed polyelectrolytes, as well as by viscometry in the case of the quenched polyelectrolytes.

Schematic diagram of the synthesis of the polyelectrolytes.     

Photocontrolled Ring‐Opening Polymerization of Strained Dicarba[2]Ferrocenophanes: A Route to Well‐Defined Polyferrocenylethylene Homopolymers and Block Copolymers

The ring‐opening polymerization (ROP) behavior of a variety of substituted 1,1′‐ethylenylferrocenes, or dicarba[2]ferrocenophanes, is reported. The electronic absorption spectra and tilted solid‐state structures of the monomers rac‐[Fe(η⁵‐C₅H₄)₂(CHiPr)₂] ( 7 ), [Fe(η⁵‐C₅H₄)₂(C(H)MeCH₂)] ( 8 ), and rac‐[Fe(η⁵‐C₅H₄)₂(CHPh)₂] ( 9 ) are consistent with the presence of substantial ring strain, which was exploited to synthesize soluble, well‐defined polyferrocenylethylenes (PFEs) [Fe(η⁵‐C₅H₄)₂(C(H)MeCH₂)]_n ( 12 ) and [Fe(η⁵‐C₅H₄)₂(CHPh)₂]_n ( 13 ) through photocontrolled ROP. Polymer chain lengths could be controlled by the monomer‐to‐initiator ratio up to about 50 repeat units and, consistent with the “living” nature of the polymerizations, sequential block copolymerization with a sila[1]ferrocenophane led to polyferrocenylethylene–polyferrocenylsilane (PFE‐b‐PFS) block copolymers ( 14 and 15 ). PFE polymers 12 and 13 showed two reversible oxidation waves, indicative of appreciable Fe???Fe interactions along the polymer backbone. The diblock copolymers were characterized by NMR spectroscopy, GPC analysis, and cyclic voltammetry.     

Synthesis of Well‐Defined Rod‐Coil‐Rod Polyhexylisocyanate‐block‐polystyrene‐block‐polyhexylisocyanate via One‐Pot Anionic Polymerization

A rod‐coil‐rod block copolymer, polyhexylisocyanate‐block‐polystyrene‐block‐polyhexylisocyanate, of controlled molecular weight was synthesized quantitatively via living anionic polymerization using potassium naphthalenide in the presence of sodium tetraphenylborate. The use of K⁺ as the counterion for the polymerization of styrene, and Na⁺ (NaBPh₄) for the polymerization of isocyanate leads to the formation of a well‐controlled novel triblock copolymer.

     

Large‐scale synthesis of arborescent polystyrenes

A method was developed for the large (100 g) scale synthesis of arborescent polystyrenes using acetyl coupling sites. Successive generations of dendritic graft polymers were obtained from cycles of polystyrene substrate acetylation with acetyl chloride and coupling in the presence of LiCl with “living” polystyryllithium chains capped with 2‐vinylpyridine units. The grafting yield for the synthesis of a generation zero (G0 or comb‐branched) arborescent polystyrene under the conditions previously reported for the 10 g scale reactions decreased from 95 to 75% when scaled up to 100 g. The lowered yield was linked to side chain dimerization and deactivation of the macroanions. The modified 100 g scale procedure, using end‐capping of the polystyryllithium with 1,1‐diphenylethylene and the addition of 3–6 equivalents per living end of 2‐vinylpyridine as a dilute solution, eliminated side chain dimerization and provided grafting yields of up to 95%. The large‐scale procedure developed was applied to the synthesis of arborescent polystyrenes of generations up to G2 with low polydispersity indices (M_w/M_n ≤ 1.04) and molecular weights increasing in an approximately geometric fashion for each cycle. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5742–5751, 2008     

Controlled Positioning of Activated Ester Moieties on Well‐Defined Linear Polymer Chains

The successful sequence‐controlled installation of an activated ester using a newly designed monomer pentafluorophenyl 4‐maleimidobenzoate is demonstrated. Pentafluorophenyl 4‐maleimidobenzoate is kinetically installed at different stages of a nitroxide‐mediated polymerization, namely, near the α‐chain end and in the middle of a PS chain. In addition, successful installation of apolar and polar functional groups is achieved via post‐polymerization functionalization, which demonstrated the versatility of the synthesis of a universal precursor for locally functionalized polymers.     

Functionalization of Carbon Nanotubes with Well‐Defined Functional Polymers via Thiol‐Coupling Reaction

Summary: Thiol‐reactive‐functionality decorated multi‐walled carbon nanotubes (MWNTs) have been obtained. Trithiocarbonate‐ended poly(N‐(2‐hydroxypropyl)methacrylamide) (PHPMA) is prepared by reversible addition‐fragmentation chain transfer (RAFT) polymerization of N‐(2‐hydroxypropyl)methacrylamide (HPMA) using S‐1‐dodecyl‐S′‐(α,α′‐dimethyl‐α″‐acetic acid)trithiocarbonate as chain transfer agent, subsequently, thiol‐terminated PHPMA (PHPMA‐SH) is obtained by treating trithiocarbonate‐ended PHPMA with hexylamine. The PHPMA‐S‐S‐MWNT conjugate is formed by simply stirring the mixture of thiol‐reactive‐functionality decorated MWNTs with PHPMA‐SH in phosphate buffered saline by a thiol‐coupling reaction. FT‐IR, HRTEM, ¹H NMR, and TGA results show that this thiol‐coupling reaction is effective to produce aqueous soluble polymer–MWNT conjugates under mild conditions.

Thiol‐reactive‐functionality decorated multi‐walled carbon nanotubes are modified with thiol end‐capped polymers by a thiol‐coupling reaction.     

Kinetics of the Anionic Polymerization of 1,3‐Butadiene Using an Initiator Composed of Alkyl Aluminium,n‐Butyllithium and Barium Alkoxide to Produce High trans‐1,4‐Polybutadiene

A kinetic model that considers three geometric active sites—cis, trans and vinyl—was proposed to the study polymerization reaction of high 1,4‐trans‐polybutadiene (TPBD) prepared by means of anionic living polymerization using an initiator composed of alkyl aluminium, n‐butyllithium and barium alkoxide. The conversion and dyad sequence distribution was correctly predicted; the kinetic results indicated that the microstructure and sequence distribution do not change with the conversion and temperature within the range of temperature investigated (40–80 °C). In addition, it was observed that the addition mechanism of butadiene to the active sites is entropic.

     

Living Polymerization via Anionic Initiation for the Synthesis of Well‐Defined PPV Materials

The anionic polymerization of PPV via the sulfinyl precursor route is further investigated. When LHMDS is employed as the base to form the actively propagating quinodimethane system and THF as the solvent, anionic polymerizations can be observed. With the use of tert‐ butyl‐substituted anionic initiators, specific functional groups can be built in the polymer chain and the chain length can be efficiently controlled, which is demonstrated here for the first time. With introduction of branched side chains on the aromatic core, soluble conjugated PPV material can be obtained with molecular weights in the range of 5000–16 000 g mol⁻¹.     

Rigid Crosslinked Polyacrylamide Monoliths with Well‐Defined Macropores Synthesized by Living Polymerization

Rigid crosslinked polyacrylamide monoliths with well‐defined macropores have been successfully fabricated by organotellurium‐mediated living radical polymerization (TERP) accompanied by spinodal decomposition. The TERP forms homogeneous networks derived from N,N‐methylenebis(acrylamide) (BIS), in which spinodal decomposition is induced to form macropores. Macropore diameter can be controlled from submicrons to a few microns, and also the obtained networks contain mesopores in the macroporous skeletons, which are collapsed by evaporative drying. They are promising materials with hydrophilic polyacrylamide surfaces and have enough strength to preserve the macropores from the surface tension arising in the repetitive swelling and drying that may occur in many applications.

     

Diversified Applications of Chemically Modified 1,2‐Polybutadiene

Commercially available 1,2‐PB was transformed into a well‐defined reactive intermediate by quantitative bromination. The brominated polymer was used as a polyfunctional macroinitiator for the cationic ring‐opening polymerization of 2‐ethyl‐2‐oxazoline to yield a water‐soluble brush polymer. Nucleophilic substitution of bromide by 1‐methyl imidazole resulted in the formation of polyelectrolyte copolymers consisting of mixed units of imidazolium, bromo, and double bond. These copolymers, which were soluble in water without forming aggregates, were used as stabilizers in the heterophase polymerization of styrene and were also studied for their ionic conducting properties.

     

A Facile Strategy for Preparation of α‐Heterobifunctional Polystyrenes with Well‐Defined Molecular Weight

A facile strategy for synthesis of α‐heterobifunctional polystyrenes is reported. The novel functional polystyrenes have been successfully synthesized via a combination of atom transfer radical polymerization (ATRP) and chemical modification of end‐functional groups. First, ε‐caprolactone end‐capped polystyrenes with controlled molecular weight and low polydispersity were prepared by ATRP of styrene using α‐bromo‐ε‐caprolactone (αBrCL) as an initiator. Then, removal of the terminal bromine atom was performed with iso‐propylbenzene in the presence of CuBr/PMDETA. Finally, ring‐opening modifications of the caprolactone group were carried out with amines, n‐butanol and H₂O to produce novel polystyrenes containing two different functional groups at one end.

     

Facile Access to Hydroxy‐Functional Core–Shell Microspheres via Grafting of Ethylene Oxide by Anionic Ring‐Opening Polymerization

We present a facile access route to hydroxy‐functional narrow disperse microspheres of well‐defined grafting density (GD). Ethylene oxide has been grafted from highly crosslinked poly(divinyl benzene) microspheres by anionic ring‐opening polymerization using sec‐butyllithium as activator together with the phosphazene base t‐BuP₄. Initially, core microspheres have been prepared by precipitation polymerization utilizing divinyl benzene (DVB, 80 wt.‐%). The grafting of poly(ethylene oxide) (PEO) from the surface resulted in the formation of functional core–shell microspheres with hydroxy‐terminal end groups. The number average particle diameter of the grafted microspheres was 3.6 µm and the particle weight increased by 5.7%. The microspheres were characterized by SEM, FT‐IR spectroscopy, elemental analysis, and fluorescence microscopy. The surface GD (determined via two methods) was 1.65 ± 0.06 and 2.09 ± 0.08 chains · nm⁻², respectively.

     

A Straightforward Method for Preparing Well‐Defined Responsive Diselenide‐Containing Polymers Based on ATRP

Diselenide‐containing polymers are facilely synthesized from polymers prepared by atom transfer radical polymerization (ATRP). Benefiting from the ATRP technology, this protocol provides a flexible route for controlling the polymer structure, which allows for a great variety of architectures of selenium‐containing polymer materials for applications in various fields. The oxidative and reductive responsive behavior of the obtained diselenide‐containing polymers is also investigated.

     

Palladium‐Mediated Surface‐Initiated Kumada Catalyst Polycondensation: A Facile Route Towards Oriented Conjugated Polymers

Palladium‐mediated surface‐initiated Kumada catalyst transfer polycondensation is used to generate poly(3‐methyl thiophene) films with controlled thickness up to 100 nm. The palladium initiator density is measured using cyclic voltammetry and a ferrocene‐capping agent, where the surface density is found to be 55% (1.1 × 10¹⁴ molecules per cm²). UV–Vis spectroscopy and AFM show increased aggregation in palladium‐initiated films due to the higher grafting density of palladium initiators on the surface. The anisotropy of the P3MT films is determined using polarized UV–Vis spectroscopy, which indicates a degree of orientation perpendicular to the substrate. Evidence that palladium can maintain π‐complexation even at elevated temperatures, is also shown through the exclusive intramolecular coupling of both a phenyl and thiophene‐based magnesium bromide with different dihaloarenes.     

Synthesis of 4μ‐PS2PEO2, 4μ‐PS2PCL2, 4μ‐PI2PEO2, and 4μ‐PI2PCL2 star‐shaped copolymers by the combination of glaser coupling with living anionic polymerization and ring‐opening polymerization

4μ‐A₂B₂ star‐shaped copolymers contained polystyrene (PS), poly(isoprene) (PI), poly(ethylene oxide) (PEO) or poly(ε‐caprolactone) (PCL) arms were synthesized by a combination of Glaser coupling with living anionic polymerization (LAP) and ring‐opening polymerization (ROP). Firstly, the functionalized PS or PI with an alkyne group and a protected hydroxyl group at the same end were synthesized by LAP and then modified by propargyl bromide. Subsequently, the macro‐initiator PS or PI with two active hydroxyl groups at the junction point were synthesized by Glaser coupling in the presence of pyridine/CuBr/N,N,N ′,N ″,N ″‐penta‐methyl diethylenetri‐amine (PMDETA) system and followed by hydrolysis of protected hydroxyl groups. Finally, the ROP of EO and ε‐CL monomers was carried out using diphenylmethyl potassium (DPMK) and tin(II)‐bis(2‐ethylhexanoate) (Sn(Oct)₂) as catalyst for target star‐shaped copolymers, respectively. These copolymers and their intermediates were well characterized by SEC, ¹H NMR, MALDI‐TOF mass spectra and FT‐IR in details. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Facile Synthesis of Well‐Defined Branched Sulfur‐Containing Copolymers: One‐Pot Copolymerization of Carbonyl Sulfide and Epoxide

Topological polymers possess many advantages over linear polymers. However, when it comes to the poly(monothiocarbonate)s, no topological polymers have been reported. Described herein is a facile and efficient approach for synthesizing well‐defined branched poly(monothiocarbonate)s in a “grafting through” manner by copolymerizing carbonyl sulfide (COS) with epichlorohydrin (ECH), where the side‐chain forms in situ. The lengths of the side‐chains are tunable based on reaction temperatures. More importantly, enhancement in thermal properties of the branched copolymer was observed, as the T_g value increased by 22 °C, compared to the linear analogues. When chiral ECH was utilized, semicrystalline branched poly(monothiocarbonate)s were accessible with a T_m value of 112 °C, which is 40 °C higher than that of the corresponding linear poly(monothiocarbonate)s. The strategy presented herein for synthesizing branched polymers provides efficient and concise access to topological polymers.     

Polymerizations Mediated by Well‐Defined Rhodium Complexes

This Minireview details the current state‐of‐the‐art relating to (co)polymerizations mediated by well‐defined Rh^I‐ethynyl, vinyl, and aryl complexes. In particular, we focus on Rh^I species suitable for the (co)polymerization of phenylacetylenes, arylisocyanides, as well as propargyl esters and amides.