Living Ring-Opening Polymerization of Cyclic Esters with Epoxide-Derived Titanium Alkoxides

Summary: The Ti^IIICp₂Cl-catalyzed radical ring opening of epoxides produces Ti alkoxides which initiate the ring-opening polymerization of ε-caprolactone. A linear dependence of on conversion, linear kinetics, low values, and the synthesis of block copolymers demonstrate a living process, while NMR spectroscopy confirms the presence of the initiator chain end. Epoxides are thus introduced as a new class of initiators for the Ti-catalyzed living ring-opening polymerization of cyclic esters.

The TiCp₂Cl-catalyzed radical ring opening of epoxides followed by the initiation of the living ring-opening polymerization of ε-caprolactone.     

Synthesis of Block Copolymers Modified with Phosphonate Ester Groups Using Nitroxide‐Mediated Radical Polymerization

Summary: Phosphonate groups were introduced into block copolymers of styrene derivatives either as single end‐groups or as small blocks using nitroxide‐mediated radical polymerization. In order to combine the hydrophobic and hydrophilic segments, block copolymers with N,N‐dimethyl acrylamide were synthesized. After hydrolysis to phosphonic acid groups, adsorption of the polymer onto metal oxides was possible.

Conversion of the phosphonate groups by transesterification with trimethylbromosilane (TMBS), followed by hydrolysis of the silylester group.     

Automated Parallel Temperature Optimization and Determination of Activation Energy for the Living Cationic Polymerization of 2‐Ethyl‐2‐oxazoline

Sixteen parallel polymerization reactions of 2‐ethyl‐2‐oxazoline have been performed at different temperatures in an automated synthesizer that allowed individual heating of each reactor. During the reactions samples were taken automatically, which were characterized by means of both online GPC and offline GC, in order to optimize the reaction temperature and to determine the activation energy of the polymerization.

     

Decatungstate (W10O)/Silane: A New and Promising Radical Source Under Soft Light Irradiation

The use of decatungstate in combination with silanes to generate silyl radicals under green fluorescence bulb irradiation as well as sunlight exposure is described. The mechanisms are investigated by ESR and laser flash photolysis experiments. The high potential of this reaction is evidenced here when using a decatungstate/silane/diphenyl iodonium salt combination as an initiating system for the ring opening photopolymerization of epoxides.

     

Correlation between Conformational Parameters and Rheological Properties of Molten Syndiotactic Polypropylenes

Summary: New rheological results with molten polypropylenes of different degrees of syndiotacticity are presented. The temperature dependence of their dynamic viscoelastic functions is correlated with the characteristic ratio. Relaxation time and Newtonian viscosity values are plotted as a function of molecular weight. The very high values of both rheological parameters found for the most syndiotactic polypropylenes are explained considering the reptation model, which links conformational parameters with the viscoelastic response in the molten state.

Disengagement or reptation time as a function of molecular weight.     

Novel Wormlike Nanostructures Self‐Assembled in a Well Defined Liquid Crystalline Diblock Copolymer with Azobenzene Moieties

Novel wormlike nanostructures were self‐assembled in bulk films of a well defined diblock copolymer with azobenzene moieties, which was prepared by atom transfer radical polymerization (ATRP). For comparison, a homopolymer with almost the same repeat units of azobenzene as those in the copolymer was also prepared. They both had well defined structures and exhibited a smectic liquid crystalline phase. Upon annealing the copolymer films, poly(methyl methacrylate) formed a matrix with excellent optical properties, and the azobenzene segment in the minority phase self‐assembled into a wormlike mesogenic domain in the bulk films. Such block copolymer films exhibited stability and transparency by eliminating the scattering of visible light, indicating their potential application as photoresponsive functional materials. Although wormlike morphologies have been obtained in micelles from block copolymer solutions, to the best of our knowledge, such wormlike nanostructures have never been explored in bulk films.

     

Modification of Polysaccharides Through Controlled/Living Radical Polymerization Grafting—Towards the Generation of High Performance Hybrids

This review covers the literature concerning the modification of polysaccharides through controlled radical polymerizations (NMP, ATRP and RAFT). The different routes to well‐defined polysaccharide‐based macromolecules (block and graft copolymers) and graft‐functionalized polysaccharide surfaces as well as the applications of these polysaccharide‐based hybrids are extensively discussed.

     

Photoinduced Controlled Radical Polymerization

Well‐controlled radical polymerization of methyl methacrylate can be achieved by in situ photochemical generation of copper (I) complex from air‐stable copper (II) species without using any reducing agent at room temperature. The living character of this polymerization was confirmed by both the linear tendency of molecular weight evolution with conversion and a chain extension experiment.

     

Phenylenevinylene Block Copolymers via Ring‐Opening Metathesis Polymerization

Fully conjugated block copolymers containing 1,4‐ and 1,3‐phenylenevinylene repeating units can be prepared by the sequential ring opening metathesis polymerization of strained cyclophanedienes, initiated by ruthenium carbene complexes (Grubbs metathesis catalysts). The molecular weight of the constituent blocks can be tightly controlled by changing the catalyst to monomer ratio and the volume fraction of the block copolymers independently tailored by the ratio of the monomers employed. Extensive phase separation between the constituent blocks is observed in thin films of these polymers by atomic force microscopy and efficient energy transfer between blocks containing 1,4‐ and 1,3‐phenylenevinylene units can be seen in the photoluminescence of these materials.

     

Amphiphilic Block‐Graft Copolymers with a Degradable Backbone and Polyethylene Glycol Pendant Chains Prepared via Ring‐Opening Polymerization of a Macromonomer

Well‐defined amphiphilic block‐graft copolymers PCL‐b‐[DTC‐co‐(MTC‐mPEG)] with polyethylene glycol methyl ether pendant chains were designed and synthesized. First, monohydroxyl‐terminated macroinitiators PCL‐OH were prepared. Then, ring‐opening copolymerization of 2,2‐dimethyltrimethylene carbonate (DTC) and cyclic carbonate‐terminated PEG (MTC‐mPEG) macromonomer was carried out in the presence of the macroinitiator in bulk to give the target copolymers. All the polymers were characterized by ¹H NMR and gel permeation chromatography (GPC). The polymers have unimodal molecular weight distributions and moderate polydispersity indexes. The amphiphilic block‐graft copolymers self‐assemble in water forming stable micelle solutions with a narrow size distribution.

     

Multifunctional Poly(N‐vinylcarbazole)‐Based Block Copolymers and their Nanofabrication and Photosensitizing Properties

The synthesis of poly(N‐vinylcarbazole)‐based block copolymers functionalized with rhenium diimine complexes or pendant terpyridine ligands is reported. The copolymers are synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization, and they exhibit interesting morphological properties as a result of the phase separation between different blocks. The rhenium complex polymer block may function as a photosensitizer, while the terpyridine‐containing polymer block can be used as the template for nanofabrication by selective deposition of zinc complexes.

     

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.

     

Void Microstructuring in Lamellar Phase of Amphiphilic Macromolecules

The free volume (voids) distribution in the lamellae of the conventional symmetric and amphiphilic diblock copolymers is studied via Monte–Carlo simulation based on the standard bond fluctuation model. Both in the conventional and amphiphilic block copolymers the voids are found to concentrate on the interfaces between the incompatible units, the magnitude of the effect being unexpectedly significant. A crystalline‐like ordering of voids with increase of the incompatibility between the different repeated units in amphiphilic copolymers is first reported and implications of this peculiarity for the morphology and mechanical properties of the amphiphilic copolymers are discussed.

     

Studies on the Synthesis and Properties of Temperature Responsive and Biodegradable Hydrogels

Novel linear poly(NIPA‐co‐CL) copolymers have been synthesized by radical copolymerization of N‐isopropylacrylamide (NIPA) and 2‐methylene‐1,3‐dioxepane (MDO). The structure of copolymers was confirmed by ¹H NMR and IR spectroscopy. Cross‐linked poly(NIPA‐co‐CL) hydrogels have also been prepared in toluene using N,N′‐methylenebisacrylamide as cross‐linking agent. The hydrogels thus obtained exhibit good temperature response and are biodegradable in the presence of proteinase K.

Temperature influence on the enzymatic degradation by proteinase K of poly(NIPA‐co‐CL) hydrogel (G‐60).     

New Approach to the Synthesis of Polyacrylamide in Miniemulsified Systems

Summary: A new approach to the preparation of water soluble polymer in inverse miniemulsions is proposed. A redox initiation system consisting of ceric ions and carbohydrate‐based surfactant Span 60 as a reducing agent is successfully used for the polymerization of AAm. This initiation system provides chain nucleation and growth near interfacial boundaries. As a result, stable uniform latex with particle radius of about 50–70 nm is obtained. The prepared PAAm has a rather high of up to about 2 × 10⁶ Da.

     

Synthesis of Novel Rod‐Coil Amphiphilic Block Copolymers PAA‐b‐DPS with Fréchet‐Type Dendronized Polystyrene and Poly(acrylic acid)

A series of well‐defined rod‐coil PAA‐b‐DPS block copolymers, containing Fréchet‐type dendronized polystyrene (DPS) with different generation as a rod‐like hydrophobic block and poly(acrylic acid) (PAA) as a hydrophilic coil were synthesized. The procedure included the following steps: the precursor PMA‐b‐DPS copolymer was prepared through ATRP of Fréchet‐type dendritic styrene macromonomer bearing the first to the third generation (G1–G3), respectively, initiated by poly(methyl acrylate) (PMA‐Br). Then, by converting PMA into PAA by subsequent hydrolysis, the targeted amphiphilic copolymers were obtained. Moreover, by using the rod‐coil amphiphiles as building blocks, large compound micelles and vesicles were formed in a binary solvent mixture of DMF/H₂O. Morphological changes in self‐assembly showed dependence on the length of the dendronized block.

     

Synthesis and Thin Film Phase Behaviour of Functional Rod‐Coil Block Copolymers Based on Poly(para‐phenylenevinylene) and Poly(lactic acid)

We report the synthesis of a series of block copolymers consisting of a rod‐like semiconducting poly(2,5‐di(2′‐ethylhexyloxy)‐1,4‐phenylenevinylene) (DEH‐PPV) block and a flexible poly(lactic acid) (PLA) block that can be selectively degraded under mild conditions. Such selectively degradable block copolymers are designed as self‐assembling templates for bulk heterojunction donor–acceptor layers in organic solar cells. A lamellar microphase‐separated domain structure was identified for block copolymers with PLA volume fractions between 29 and 79% in bulk and thin films using SAXS, TEM, and AFM. Depending on the ratio of the two blocks we find either lamellae oriented parallel or perpendicular to the substrate in thin films.

     

Direct Synthesis of Poly(dimethylsiloxane) Copolymers with TPE‐Properties via CuAAC (Click Chemistry)

Poly(dimethylsiloxane) copolymers were synthesized directly from AA/BB monomers employing a CuAAC reaction (click chemistry) in a polyaddition approach. Using organic dialkynes and oligo(siloxane)s end‐functionalized with azide moieties it was possible to obtain siloxane‐based copolymers with TPE properties by click chemistry for the first time. As seen from DSC experiments, properties were strongly dependent on the incorporated organic comonomer.