Segmented Block Copolymers with Terephthalic‐Extended Poly(ethylene oxide) Segments

Segmented block copolymers comprised of flexible PEO segments and monodisperse crystallizable bisestertetraamide segments have been synthesized. The influence of the terephthalic units in the soft phase on the transitions and the thermal mechanical and elastic properties are studied. The presence of terephthalic units in the copolymer increases the glass transition temperature of the soft phase by ≈5 °C. The low‐temperature flexibility of the copolymers is improved because of the lower crystallinity and melting temperature of PEO. With the use of terephthalic‐extended PEO segments, segmented block copolymers with low moduli (G' < 15 MPa) and good elastic properties could be obtained.

     

Terpyridine‐Terminated Homo and Diblock Copolymer LEGO Units by Nitroxide‐Mediated Radical Polymerization

Summary: Novel block copolymers were synthesized in a controlled fashion by nitroxide‐mediated radical polymerization starting from a terpyridine‐modified alkoxyamine. An important feature for controlling the efficiency of the polymerization is the presence of excess nitroxide, responsible for the initial rate of deactivation, which eventually leads to a decrease of the polydispersity indices of the desired block copolymer. The materials obtained were characterized by means of ¹H NMR, UV‐vis spectroscopy, and GPC. The complexation of the terpyridine ligands resulted in the formation of A‐B‐[Ru]‐C, A‐B‐[Ru]‐B‐A, and A‐B‐[Fe]‐B‐A metallo‐supramolecular block copolymers.

Telechelic polymers bearing a terpyridine end‐group at the α‐position and a nitroxide at the ω‐position were prepared in a living fashion by nitroxide‐mediated polymerization.     

Synthesis of Amphiphilic and Double‐Hydrophilic Block Copolymers Containing Poly(vinyl amine) Segments by RAFT Polymerization of N‐Vinylphthalimide

We report on the controlled synthesis of amphiphilic and double‐hydrophilic block copolymers having poly(vinyl amine) segments by the reversible addition–fragmentation chain transfer (RAFT) polymerization of N‐vinylphthalimide (NVPI), followed by deprotection. The block copolymer poly(NVPI)‐b‐poly(N‐isopropylacrylamide) with a controlled molecular weight and low molecular mass distribution was obtained by the polymerization of N‐isopropylacrylamide (NIPAAm) using dithiocarbamate‐terminated poly(NVPI). The chain extension from the dithiocarbamate‐terminated polystyrene to NVPI could be controlled well under suitable conditions, and provided the block copolymer, polystyrene‐b‐poly(NVPI). We also investigated the thermoresponsive and optoelectronic properties and the aggregation behavior of double hydrophilic and amphiphilic block copolymers obtained after deprotection.

     

Application of Nitroxide‐Terminated Polymers Prepared by Sonochemical Degradation in the Synthesis of Block Copolymers

Summary: The ultrasonic irradiation of a polymer solution results in the breakage of macromolecular C? C bonds. In the presence of radical scavengers the formed macroradicals are prevented from termination reactions as combination or disproportionation. Using nitroxides as trapping agents the polymer is transformed into a macroinitiator, which can be used in controlled free‐radical polymerization to synthesize block copolymers. In this work several polymers were exposed to sonochemical degradation and terminated with various nitroxides, e.g. OH‐TEMPO and TIPNO. In a second reaction step the prepared polymer‐nitroxide‐adducts were applied as macroinitiators in controlled free‐radical polymerizations with styrene. The obtained products were mixtures of block copolymer and the corresponding homopolymers. The visco‐elastic properties were investigated by rheological analysis. A special separation technique with selective solvents was applied to determine the content of block copolymer.

Synthesis of block copolymers with sonochemically prepared macroinitiators.     

Self‐Assembly of Globular‐Protein‐Containing Block Copolymers

Self‐assembly has emerged as a powerful approach to control nanostructure in materials containing globular proteins, both through templated self‐assembly and direct self‐assembly of globular protein‐polymer conjugates or fusion proteins. The folded structures of globular proteins that are critical to their function introduce complex shapes and interactions into block copolymers that significantly alter the physics of self‐assembly. This article discusses the different methods for controlling the nanostructure of globular proteins using block copolymers, highlighting efforts at understanding the physics of self‐assembly in concentrated solution and solid‐state bioconjugate copolymers.

     

Thermo‐responsive Poly(methyl methacrylate)‐block‐poly(N‐isopropylacrylamide) Block Copolymers Synthesized by RAFT Polymerization: Micellization and Gelation

Summary: RAFT polymerization was used to prepare PMMA‐b‐PNIPAM copolymers. Two different chain transfer agents, tBDB and MCPDB, were used to mediate the sequential polymerizations. Micellar solutions and gels were prepared from the resulting copolymers in aqueous solution. When heated above T_c of PNIPAM (about 31 °C), DLS revealed that PNIPAM coronas collapsed, resulting in aggregation of the original micelles. The micellar gels underwent syneresis above T_c as water was expelled from the ordered gel structure, the lattice periodicity of which was determined by SANS. A large decrease in lattice spacing was observed above T_c. The gel became more viscoelastic at high temperature, as revealed by shear rheometry which showed a large increase in G″.

     

Synthesis of Saccharide‐Terminated Poly(ε‐caprolactone) via Michael Addition and ‘Click’ Chemistry

Maleimido‐terminated PCL (M‐PCL) and alkyne‐terminated PCL (A‐PCL) are prepared by the ring‐opening polymerization of ε‐caprolactone with N‐hydroxyethyl maleimide and 4‐pentyn‐1‐ol as initiators catalyzed by tin(II ) trifluoromethane sulfonate at 25 °C, respectively. A series of saccharide‐terminated PCLs have also been synthesized under mild conditions by two chemical strategies: 1). Michael addition of M‐PCL and amino‐containing maltose, and 2). a ‘click’ reaction of A‐PCL and azide‐containing saccharide. The amphiphilic nature of these maltose‐terminated PCLs make self‐assembly into aggregates in water possible. These aggregates have been characterized by transmission electron microscopy and dynamic light scattering measurements.

     

Effect of Block Order of ABA‐ and BAB‐Type NIPAAm/HEMA Triblock Copolymers on Thermoresponsive Behavior of Solutions

ABA and BAB triblock thermoresponsive copolymers (A = N‐isopropylacrylamide, B = 2‐hydroxyethyl methacrylate) have been synthesized by atom transfer radical polymerization (ATRP). BAB is shown to exhibit a higher transition temperature and a good solubility in water compared to ABA with the same composition and concentration. The differences are attributed to the distinct micellar structure, which is regulated by the block order of the copolymers. It is speculated that ABA and BAB copolymers separately form branch and flower micelles in water, which mainly influence the course of phase transition. The moduli of the ABA copolymer solution are higher than those of the BAB above gel point. In terms of hypothesized micelle models, it is proposed that the ‘branch’ micelles of the ABA solution preferably form more physical interconnections.

     

Furanic‐Aromatic Copolyesters by Interchange Reactions between Poly(ethylene terephthalate) and Poly[ethylene 5,5′‐isopropylidene‐bis(2‐furoate)]

Summary: Aromatic copolyesters containing bio‐based furanic units in the main chain were obtained by ester‐interchange reaction between poly(ethylene terephthalate) (PET) and poly[ethylene 5,5′‐isopropylidene‐bis(2‐furoate)] (PEF) at high temperatures in the bulk. Various copolyesters were synthesized by using PET/PEF mass ratios ranging from 90:10 to 50:50 and were characterized by ¹H NMR, MALDI‐TOF MS, DSC, and TGA. PET/PEF block copolymers were formed in the first stage of reaction and then slowly randomized. The degree of randomness, determined by ¹H NMR, was close to 1 after 2 h reaction. The randomization rate depended on the nature and the concentration of the end‐groups of starting homopolyesters and was much faster when a low molar mass hydroxy‐terminated PET was reacted.

Reaction scheme showing the insertion of furanic units in copolyester chains by ester interchange reaction.     

Synthesis of a pH‐Sensitive PEO‐Based Block Copolymer and its Application for the Stabilization of Iron Oxide Nanoparticles

PEO‐based amphiphilic block copolymers that exhibit a pH responsive phase transition behavior are synthesized. The amphiphilic block copolymers show sharp phase transitions in the physiological pH (7.2) range of aqueous media. The block copolymers were efficient stabilizers for the preparation of superparamagnetic iron oxide nanoparticles in aqueous media. The resulting iron oxide nanoparticles in the size range of 5–30 nm showed a relatively good image on the basis of the results on their phantom test. All the materials were characterized by the combination of ¹H NMR spectroscopy, size exclusion chromatography, UV/visible spectroscopic analysis, magnetization, transmission electron microscopy, electron diffraction, and X‐ray diffraction pattern analysis.

     

Synthesis of Novel Linear PEO‐b‐PS‐b‐PCL Triblock Copolymers by the Combination of ATRP,ROP, and a Click Reaction

A new strategy to synthesize a series of well‐defined amphiphilic PEO‐b‐PS‐b‐PCL block copolymers is presented. First, bromine‐terminated diblock copolymers PEO‐b‐PS‐Br are prepared by ATRP of styrene, and converted into azido‐terminated PEO‐b‐PS‐N₃ diblock copolymers. Then propargyl‐terminated PCL is prepared by ROP of ε‐caprolactone. The PEO‐b‐PS‐b‐PCL triblock copolymers with from 1.62 × 10⁴ to 1.96 × 10⁴ and a narrow PDI from 1.09 to 1.19 are finally synthesized from these precursors. The structures of these triblock copolymers and their precursors have been characterized by NMR, IR, and GPC analysis.

     

Amphiphilic Block Copolymer from Hydroxyl‐Terminated Polymers Functionalized with TEMPO. A New Synthetic Method Using Oxoammonium Salt

A simple approach for the end‐functionalization of hydroxyl‐terminated polymers with nitroxide moieties using oxoammonium salts (OS) is presented. The functionalization is carried out using only one synthetic pathway in which high levels of functionalization (90%) are found. A mechanism for the functionalization with TEMPO moieties using OS is proposed in which the formation of peroxide groups is suggested. The structures of the functionalized polymers are characterized in detail by ¹H NMR, ¹³C NMR, DQF‐COSY, and HETCOR. Bifunctional macroalkoxyamines are used to demonstrate how to extend the polymer chain for the synthesis of amphiphilic triblock copolymers by polymerizing St in a second block mediated by a nitroxide radical which provides the block length control.

     

On the Monolayer Adsorption of Thiol‐Terminated Dendritic Oligothiophenes onto Gold Surfaces

The self‐assembled monolayer formation of a series of thiophene dendron thiols with different generations and alkyl chain lengths onto gold surfaces is studied. Average film thicknesses and dielectric constants were calculated from SPR using a two‐subphase differential method. The in situ adsorption of the thiophene dendron thiols was monitored by SPR kinetics measurements and fitted using an empirical three‐step model. Electrochemical redox molecular probing experiments provided additional insight into surface coverage, which showed different abilities to block electron transfer at the monolayer/electrode interfaces. The surface coverage of the films was also estimated by QCM measurements and supported by static WCA measurements.

     

Synthesis,Characterization, and Thermal Properties of Block Copolymers Containing Poly(styrene‐co‐4‐vinylpyridine) and Poly(styrene‐co‐butyl acrylate) by Controlled Radical Polymerization

Radical polymerization of styrene and mixtures of styrene and 4‐vinylpyridine was performed in the presence of 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) producing polymers with controlled molecular weights and molecular weight distributions. The living nature of these polymers was confirmed by using them as macroinitiators in the block copolymerization of styrene and butyl acrylate. The thermal properties of the synthesized statistical diblock copolymers measured by differential scanning calorimetry indicated that a phase‐separated morphology was exhibited in most of the block copolymers. The results were confirmed by transmission electron microscopy (TEM) and small angle X‐ray scattering (SAXS) showing microphase‐separated morphology as is known for homo A‐B diblock polymers.

SAXS of a block copolymer synthesized from S/V 70:30 macroinitiators (03) with one detected T_g.     

Characterization of Polydimethylsiloxane‐block‐polystyrene (PDMS‐b‐PS) Copolymers by Liquid Chromatography at Critical Conditions

In this study, liquid chromatography at critical conditions (LCCC) is used to determine the block lengths and molar masses of polydimethylsiloxane‐block‐polystyrene copolymers synthesized via atom transfer radical polymerization (ATRP) techniques. In addition, the analysis allows for the determination of the presence of homopolymers in the samples. LCCC at the critical point of polydimethylsiloxane (PDMS) on a reversed phase column allows for the determination of PDMS homopolymer and the length of the polystyrene (PS) block in the block copolymer which elutes in the size exclusion chromatography (SEC) regime under these conditions. The PDMS block length and PS homopolymer can be obtained under normal phase conditions. The results of LCCC are compared with data from conventional SEC.

     

Structures and Chiroptical Properties of Thermoresponsive Block Copolymers Containing L‐Proline Moieties

Amino acid‐based block copolymers containing poly(A‐Pro‐OMe) have been synthesized by RAFT polymerization using the dithioester‐terminated poly(DMA) as a macro‐CTA. An amphiphilic block copolymer composed of polystyrene as a hydrophobic segment and poly(A‐Pro‐OMe) as a hydrophilic segment was also prepared using polystyrene as the macro‐CTA. The chiroptical properties of the block copolymer, poly(DMA)‐block‐poly(A‐Pro‐OMe), was evaluated by specific rotation, CD, and UV‐vis spectroscopy. The assembled structure of the block copolymer on a mica surface was characterized by SFM. Thermally induced phase separations of the random and block copolymers were also studied in aqueous solution.

     

Thermo‐Reversible Hydrogels Based on Poly(N,N‐diethylacrylamide)‐block‐poly(acrylic acid)‐block‐poly(N,N‐diethylacrylamide) Double Hydrophilic Triblock Copolymer

Summary: A novel double hydrophilic poly(N,N‐diethylacrylamide)‐poly(acrylic acid)‐poly(N,N‐diethylacrylamide) (PDEAAm‐PAA‐PDEAAm) triblock copolymer was synthesized by sequential anionic polymerization and modification of the poly(tert‐butyl acrylate) middle block by selective hydrolysis and neutralization to its ionic functions. Due to the pH‐sensitivity of the PAA central block and the thermo‐sensitivity of the PDEAAm end‐blocks, it exhibits responsive behavior in aqueous media. At low temperatures and high pH, it is molecularly dissolved while at temperatures above the LCST of the PDEAAm end‐blocks, a sol–gel transition was observed which should be ascribed to the formation of a three‐dimensional transient network comprising PDEAAm hydrophobic physical crosslinks interconnected by PAA negatively charged elastic chains. The sol–gel transition and the rheological properties of the physical gel are strongly influenced by the presence of salt.

Temperature induced sol–gel transition in PDEAAm‐PAA‐PDEAAm aqueous solutions.     

Solution Self‐Assembly of Core‐Labeled Block Random‐Copolymers Prepared by Ring Opening Metathesis Polymerization

Herein, the synthesis of block random‐copolymers via ring opening metathesis polymerization (ROMP) is presented. A random‐copolymer of norbornene dimethyl ester with different xanthen‐functionalized norbornene derivatives was used as a hydrophobic block while, the hydrophilic part was built from an ethylene glycol‐substituted monomer. The self‐association of these block random‐copolymers in MeOH was strongly influenced by the ionization state of the dye molecules, as shown by a combination of UV–Vis absorption and dynamic light scattering measurements. Aggregate sizes were significantly smaller for samples with charged dye molecules in the core of the aggregate. These findings were attributed to ion pair formation of the charged dye molecules and the according counter ions, thus, inducing strongly attractive dipole–dipole interactions. The optical properties of the dyes under investigation, however, were preserved within the polymer aggregates.

     

Disulfide‐Crosslinked Biomimetic Micelles: Formation,Thiol Reactivity and Cytotoxicity Behavior

A series of amphiphilic random copolymers with MPC as the hydrophilic segment, SMA as the hydrophobic segment and GMA as the reactive segment were synthesized. Polymeric micelles with different sizes were obtained through tuning the hydrophilic/hydrophobic segment ratios in the copolymers. The formation and properties of these micelles were investigated using ¹H NMR spectroscopy, fluorescence probe techniques and DLS. The reactive polymeric micelles were crosslinked with a di‐functional reagent. The crosslinked micelles showed improved stability and thiol reactivity. Cell viability tests indicated that the bioinspired phosphorylcholine‐based micelles showed excellent biocompatibility, thus promising great potential for applications in the field of nanocarrier systems.

     

Synthesis and Characterization of PDMS‐, PVP‐, and PS‐Containing ABCBA Pentablock Copolymers

Amphiphilic ABCBA pentablock copolymers based on PVP, PS, and PDMS were synthesized using a combination of ATRP and RAFT polymerizations. The PVP‐block‐PS‐block‐PDMS‐block‐PS‐block‐PVP pentablock copolymer was characterized using a variety of chromatography and spectroscopic methods which showed that a high degree of end group and molecular weight control can be achieved. Preliminary analysis of the aqueous solution behavior of the pentablock copolymer showed that it self‐assembles in water in order to shield the PDMS and PS segments from the water.