Synthesis of Blockcopolymers P3HT‐b‐PS Using a Combination of Grignard‐Metathesis and Nitroxide‐Mediated Radical Polymerization

The synthesis of π‐conjugated NMRP‐macroinitiators using GRIGNARD‐metathesis polymerization in combination with azide/alkyne‐“click” chemistry has been investigated. Alkoxyamine‐functionalized poly(3‐hexylthiophene)s (P3HTs) have been used for block copolymer preparations in presence of styrene. Molecular weight and molecular weight distribution of the polymers have been determined in SEC‐measurements, while end‐group determination was performed with MALDI‐ToF‐MS. The molecular weight of the P3HT macroinitiators was influenced by the amount of Ni‐catalyst during the GRIM reaction. Those macroinitiators have been used to prepare block copolymers in subsequent nitroxide‐mediated radical polymerization (NMRP). Thin‐layer‐morphologies of the block copolymers were investigated using tapping‐mode AFM. Short and disordered rods were observed, as well as continuous and parallel fibrils.

     

Free‐Standing Films of Semifluorinated Block Copolymer Brushes from Layer‐by‐Layer Polyelectrolyte Macroinitiators

Free‐standing semifluorinated polymer brushes from layer‐by‐layer (LbL) macroinitiators are demonstrated. LbL deposition of macroinitiators is followed by surface‐initiated atom transfer radical polymerization (SI‐ATRP). Increasing the number of LbL macroinitiator layers increases grafting density and thickness. The SI‐ATRP is conducted by first polymerizing a block of polystyrene followed by the semifluorinated poly‐2,2,2‐trifluoroethyl methacrylate block. Solvent selective response is investigated by AFM imaging and water contact angle measurements. Specifically, the solvent response of the semifluorinated block copolymer brushes exhibits alternate selectivity to cyclohexane and trifluorotoluene. Solvent responsive free‐standing films are also demonstrated.

     

Thermoresponsive Behavior of Mixtures of Epoxy Functionalized Oligo(ethylene glycol) Methacrylate Copolymers

Thermoresponsive random copolymers based on 2‐(2‐methoxyethoxy)ethyl methacrylate (MEO₂MA) and oligo(ethylene glycol) methyl ether methacrylate (OEG_8‐9MA) are synthesized by atom transfer radical polymerization (ATRP). In a second step, they are used as macroinitiators for the ATRP of glycidyl methacrylate (GMA), introducing a short end‐block with epoxy functionalities that allows the connection of the thermoresponsive polymers to a variety of molecules, surfaces, or particles. The resulting epoxy functionalized terpolymers exhibit lower critical solution temperatures (LCST), which can be adjusted by changing the feed monomer ratio of MEO₂MA and OEG_8‐9MA. Binary blends show one or two cloud points depending on the blend composition. A model for the polymer collapse in one mixed particle or in two different particles as function of composition is proposed.

     

Block Copolymers from Organomodified Siloxane‐Containing Macroinitiators by Atom Transfer Radical Polymerization

Alternating copolymers of 1,3‐diisopropenylbenzene and 1,1,3,3‐tetramethyldisiloxane were synthesized by hydrosilylation–polyaddition. These linear copolymers were functionalized at both ends with 2‐bromoisobutyryl or benzyl chloride moieties. Subsequently, the obtained organomodified siloxane‐containing macroinitiators were successfully used for the preparation of ABA‐type block copolymers by atom transfer radical polymerization (ATRP) of styrene and tert‐butyl acrylate. The high chain‐end functionality of the macroinitiators was confirmed by ¹H NMR analysis of the macroinitiators and GPC measurements of the obtained ABA‐type block copolymers. The macroinitiator peaks disappeared in GPC traces after ATRP, and the obtained block copolymers showed a significantly narrower molecular‐weight distribution than the macroinitiators.

Synthesis of ABA‐type block copolymers by means of ATRP using organomodified siloxane‐containing, benzyl chloride functionalized macroinitiators.     

Combination of Mechanochemical Degradation of Polymers with Controlled Free‐Radical Polymerization

The result of ultrasound on polymer solutions is the breakage of macromolecular C C‐bonds due to cavitation. The fact that termination reactions of mechanoradicals as disproportionation and combination are suppressed in the presence of radical scavengers makes the following method possible. Thus the use of nitroxides acting as chain‐terminating agents allows the creation of macroinitiators which can be used in controlled free‐radical polymerization. In this work, we investigate the mechanochemical degradation of poly(methyl methacrylate) (PMMA) in the presence of OH‐TEMPO and the application of the irradiated polymers as macroinitiators in a controlled radical polymerization. The content of OH‐TEMPO terminated chains in the degraded product is determined by a computer‐aided procedure on the basis of molecular weight distributions.

Ultrasonic degradation of PMMA, decrease of molar mass (M _n), and polydispersity (Pd) as a function of irradiation time, power output = 200 W, ϑ = 45–50 °C.     

Combinatorial and High‐Throughput Methods in Macromolecular Materials Research and Development

Combinatorial and high‐throughput experimentation is used to accelerate the rate of experimentation in macromolecular science. Combinatorial and high‐throughput methods are used in macromolecular science to discover and optimize catalysts for polymerization reactions, discover compositions that have specific desired properties, and systematically explore polymer structure–property relationships. The use of high‐throughput methods can enable the discovery of complex catalyst systems or polymer compositions that would not be feasible using conventional experimental methods. In addition, combinatorial data can be used as inputs into computer models to enable the accurate prediction of material properties as a function of composition.

     

Modeling of Atom Transfer Radical Polymerization with Bifunctional Initiators: Diffusion Effects and Case Studies

Summary: A mathematical model for atom transfer radical polymerization (ATRP) with bifunctional initiators was developed. The model was validated with three case studies in bulk and solution polymerization. We used only polymer yield data to estimate some of the model parameters, while others were obtained from the literature. The model fits the polymer yield data and also predicts weight‐average molecular weights and polydispersities very well. The free volume theory was also incorporated to the model to study the effect of diffusion‐controlled reactions. The adjustable parameters in the free volume theory for the termination, propagation, activation, and deactivation reactions were varied to show the effect on monomer conversion, polymer chain length, and polydispersity. The model shows that diffusion‐limited termination reactions produce polymer with smaller polydispersities, while diffusion‐limited propagation reactions have the opposite effect. Both models, considering and neglecting diffusion effects on the kinetic rate constants, were compared with experimental data. Even though the model predictions for monomer conversion, number‐average molecular weight, and polydispersity are good in both cases, the simulations indicate that diffusion‐controlled reactions can be ignored for the cases studied in the three case studies described in this paper.

Comparison between model predictions and experimental data for BA polymerization of number‐average molecular weight in bulk at 90 °C.     

Synthesis and Characterization of Supramolecular Polymeric Materials Containing Azopyridine Units

Summary: The synthesis and characterization of a series of supramolecular polymeric complexes formed by H‐bonding interactions between benzoic acid and azopyridine derivatives are described. A series of polymeric networks have been synthesized using a polymethacrylate bearing benzoic acid units as side groups, and several polymers with azopyridine as H‐acceptor side groups. Furthermore, low‐molecular‐weight pyridine derivatives have been used to prepare an homologous side‐chain polymer, and a network with azopyridine as a non‐covalent crosslinker. Special attention was paid to the thermal and mesomorphic properties of these materials, which were studied by DSC, POM, and XRD.

Micrograph of the mesomorphic melt of a sample taken at 130 °C on cooling from the isotropic state.     

Phase Behavior of Vesicle‐Forming Block Copolymers in Aqueous Solutions

The binary phase diagram of amphiphilic poly(ethylene oxide)‐block‐poly(γ‐methyl‐ε‐caprolactone) block copolymers in water is examined for four polymers having the same hydrophilic block length but different hydrophobic block lengths across the whole concentration range. The bulk polymers show no ordered morphology. With increasing water concentration the polymers undergo transitions from lamellar phases to packed vesicles and subsequently all polymers self‐assemble into vesicles in dilute aqueous solutions. Additionally, the largest polymer forms an inverse hexagonal phase, and the smallest polymer self‐aggregates into rod‐like micelles and showed a hexagonal phase.

     

Synthesis of π‐Conjugated Polymer Possessing Mercapto‐Substituted 1,3‐Butadiene‐1,4‐diyl Units by Reaction of Regioregular Organometallic Polymer Having Titanacyclopentadiene Moieties in the Main Chain

A π‐conjugated polymer having 1,4‐bismercapto‐substituted 1,3‐diene units in the main chain was prepared by the novel polymer reaction of a regioregular organometallic polymer having titanacyclopentadiene‐2,5‐diyls units with benzenesulfenyl chloride. The number‐average molecular weight and the molecular weight distribution of the polymer derived from 1,4‐diethynyl‐2,5‐di(2‐ethylhexyloxy)benzene were estimated to be 5 700 and 1.6, respectively, from the GPC analysis. The π‐conjugated character, photoluminescence behavior both in solid‐state and solutions, and the electron‐donating properties of the π‐conjugated polymer are discussed on the basis of its UV‐vis spectrum, photoluminescence spectrum, and CV analysis.

     

Reversible Addition Fragmentation Chain Transfer (RAFT) Polymerization with a Polymeric RAFT Agent Containing Multiple Trithiocarbonate Groups

Polytrithiocarbonates were prepared by the condensation polymerization of a dicarboxylic acid functional trithiocarbonate and a diol. These polymers were effective reversible addition fragmentation chain transfer (RAFT) agents for the bulk polymerization of polystyrene homopolymers and a poly[styrene‐block‐(tert‐butylstyrene)] block copolymer. Size exclusion chromatography (SEC) analysis of the original and amine cleaved polymers showed that the polydispersity of the polymer tended toward two with increasing polymerization time, but the polydispersity of the polymer units between trithiocarbonate groups was narrow (ca. 1.1–1.3) Also, the average number of trithiocarbonate groups per chain was found to be proportional to the number of trithiocarbonate groups in the starting RAFT agent. These polytrithiocarbonate RAFT agents will be useful for preparing multiblock copolymers over a range of chemistries, block numbers and molecular weights.

     

Novel Hybrid Polymer Brushes with Alternating Dendritic Wedges and Linear Side Chains

Summary: Novel hybrid polymer brushes with alternating dendritic wedge and linear chain as side chains were reported in this paper. Firstly, dendronized polymer initiators of generation one to three, GnMIBr (n = 1, 2, 3), were synthesized through the alternating copolymerization of styryl dendrons and maleimide derivative initiated by AIBN. The linear side chains were then generated through grafting‐from approach using ATRP of tBA initiated with the above‐mentioned macroinitiators. By combining such macromonomers and grafting‐from approach, a new kind of polymer brushes with alternating dendron and linear chain as side chains, GnMI‐g‐PtBA, were thus synthesized and characterized with ¹H NMR, SEC, AFM, etc. Morphology studies made by AFM indicate the polymer brushes display a uniform worm‐like structure with a very long contour length. After the hydrolysis of PtBA branches under acidic conditions, amphiphilic dendronized polymer brushes with hydrophilic linear PAA side chains and hydrophobic dendritic side chains of three generations have been prepared.

Schematic structure and AFM image of G1MI‐g‐PtBA‐2 dendronized polymer brushes.     

AB2 Functional Polyesters via Ring Opening Polymerization: Synthesis and Characterization

Aliphatic AB₂ functional polyesters were conveniently prepared by the ring opening polymerization of ε‐caprolactone and L ‐lactide in the presence of the AB₂ functional initiator 2,2‐bis(hydroxymethyl)propionic acid (bis‐MPA) and Sn(Oct)₂ as the catalyst. In L ‐lactide polymerization, both bis‐MPA hydroxyl groups initiated the polymerization reaction, but for ε‐caprolactone polymerization this depended on the monomer to initiator to catalyst ratio. Initiation at two hydroxyl groups occurred at high monomer to initiator ([M]/[I]) ratio and at high Sn(Oct)₂ to monomer ratio. The melting temperatures of the AB₂‐functional PLLA and PCL polymers were comparable to linear polymers with a equal to the per arm in the polymer.

     

Characterization of Linear and 3‐Arm Star Block Copolymers by Liquid Chromatography at Critical Conditions

Summary: LCCC for polyMA homopolymers was established in order to analyze the polyMA‐polySt linear and star block copolymers. The validity of the assumption that under the LCCC for polyMA, the polyMA segment in the polyMA‐containing block copolymer is chromatographically “invisible” was verified. It was found that within the scale of investigation ( ), the molecular weight and architecture of the polyMA segments had no evident influence on the retention behavior of the polySt‐polyMA block copolymers and the polyMA block in the copolymer was “invisible”. The critical conditions of polyMA were used for quantitative analysis of the polySt block in the linear and 3‐arm star polyMA‐polySt block copolymers, which were synthesized by AGET ATRP in miniemulsion. It was shown that the copolymer had completely different elution peak from its MI. The calculated molecular weights of polySt blocks in the block copolymers were similar to those obtained from normal SEC analysis. Transferring the eluates from the LCCC (the first dimension) column to a SEC column (the second dimension) produced LCCC × SEC two‐dimensional chromatogram, which contained information on both chemical composition and molecular weight of the synthesized copolymers. The combination of these liquid chromatography methods clearly confirmed the high initiation efficiency of the polyMA MIs during the synthesis of block copolymers and the presence of a byproduct formed by radical‐radical coupling.

     

Synthesis of Photocleavable Amphiphilic Block Copolymers: Toward the Design of Photosensitive Nanocarriers

The synthesis of a novel amphiphilic block copolymer containing a photodegradable linker as a junction point between hydrophilic and hydrophobic chains is presented. PmCL–ONB–PAA block copolymers were synthesized via a combination of ROP and ATRP from a difunctional photoresponsive initiator (ONB). The copolymers are biodegradable and biocompatible, they can self‐assemble into different structures, including micelles and vesicles which are photoresponsive. When polymer solutions were exposed to UV we observed significant changes in size and number of particles. We are currently investigating the promising potential of this system as photosensitive nanocarrier.

     

Morphology Control of Highly Sulfonated Block Copolymers by a Simple Thermal Process

Well‐defined sulfonated block copolymers were prepared by direct thermolysis with block copolymers of n‐butyl acrylate (nBA) and neopentyl styrene sulfonated (NSS), which were synthesized by Cu‐based living radical polymerization ( <1.20). A simple thermal process for 10 min at 150 °C completely deprotected the neopentyl groups in the poly(NSS) block segment to give fully sulfonated polystyrene backbone. SAXS profile of the block copolymer with 47 wt.‐% of poly(NSS) showed lamella structure, which appeared more clearly with long ranged order after sulfonation of the block copolymer.

     

Polystyrene Brushes on Fully Deuterated Organic Nanoparticles by Surface‐Initiated Nitroxide‐Mediated Radical Polymerization

The synthesis of polystyrene (PS) brushes on fully deuterated PS nanoparticles by surface‐initiated nitroxide‐mediated radical polymerization (SI‐NMRP) is reported. Due to the high demand of deuterated monomers, an efficient deuteration procedure of suitable and readily available precursors is developed. SI‐NMRP of styrene is improved regarding reaction control, grafting density, and conversion. Insights into the scaling behavior and conformational features of surface‐attached PS chains on deuterated particles are investigated by using dynamic light scattering measurements, proving that polymer brushes are formed. The particles with surface‐attached initiator are shown to be uniform spherical core‐shell particles by small‐angle neutron scattering measurements.

     

Synthesis and pH/Temperature‐Responsive Behavior of PLLA‐b‐PDMAEMA Block Polyelectrolytes Prepared via ROP and ATRP

Well‐defined diblock poly(L ‐lactide)‐block‐poly(dimethylamino‐2‐ethyl methacrylate) (PLLA‐b‐PDMAEMA) copolymers were synthesized by combining ROP of LLA and ATRP of DMAEMA, from a dual‐initiator 2‐hydroxylethyl 2‐bromoisobutyrate. The molecular characterization of these diblock copolymers was performed using ¹H NMR, FT‐IR, and GPC‐MALLS analysis. The responsive behavior of these diblock copolymers in aqueous solutions at different pH and temperatures were investigated using DLS. Results show that both higher pH and temperature result in a higher degree of neutralization, weaker hydrogen bonding, and micellar aggregation. As observed by TEM, changes in micellar morphology are in accordance with DLS results.

     

Functionalization of Graphene Sheets by Polyacetylene: Convenient Synthesis and Enhanced Emission

For the first time, graphene materials have been conveniently covalently functionalized with polyacetylene through the nitrene chemistry reaction. The resultant functional polyacetylenes became soluble in different organic solvents and were well characterized, thus providing a new approach to prepare graphene‐polymer composite materials.

     

Gradient Density Grafted Polymers on Ground Tire Rubber Particles by Atom Transfer Radical Polymerization

Summary: The graft polymerization of styrene and (meth)acrylic monomers via ATRP from cross‐linked rubber particles, produced by recycled tires (“ground tire rubber”, GTR), is reported. GTR particles, obtained by cryogenic grinding process, still contain C?C unsaturations on the surface, which were first oxidized to hydroxyl groups and then modified by reaction with 2‐bromoisobutyryl bromide to serve as ATRP macroinitiators. Graft polymerizations were carried out using CuBr/CuBr₂/N,N,N′,N″,N″‐pentamethyldiethylenetriamine as catalytic system in bulk or in anisole at high temperature. The grafted particles were analyzed by ATR‐IR (spectra were recorded on particles surface and cross‐sectional slices), TGA, SEM and X‐ray microanalysis.

Arrangement of surface‐grafted polymer assemblies along the particles section.