A Novel Macroinitiator for the Synthesis of Triblock Copolymers via Atom Transfer Radical Polymerization: Polystyrene‐block‐poly(bisphenol A carbonate)‐block‐polystyrene and Poly(methyl methacrylate)‐block‐poly(bisphenol A carbonate)‐block‐poly(methyl methacrylate)

Summary: Bis(hydroxy)telechelic bisphenol A polycarbonate (PC) was prepared via melt polycondensation of bisphenol A (BPA) and diphenyl carbonate (DPC) using lanthanum(III ) acetylacetonate as a catalyst for transesterification. Subsequently, the polycarbonate was converted to a bifunctional macroinitiator for atom transfer radical polymerization (ATRP) with the reagent, α‐chlorophenylacetyl chloride. The macroinitiator was used for the polymerization of styrene (S) and methyl methacrylate (MMA) to give PS‐block‐PC‐block‐PS and PMMA‐block‐PC‐block‐PMMA triblock copolymers. These block copolymers were characterized by NMR and GPC. When styrene and methyl methacrylate were used in large excess, significant shifts toward high molecular weights were observed with quantitative consumption of the macroinitiator. Several ligands were studied in combination with CuCl as the ATRP catalyst. Kinetic studies reveal the controlled nature of the polymerization reaction for all the ligands used.

Formation of a bifunctional ATRP macroinitiator by esterification of bis(hydroxy)telechelic PC with α‐chlorophenylacetyl chloride.     

Features of Double‐Spiral “Valley‐Hills” Surface Topography Formation in Photochromic Cholesteric Oligomer‐Based Films and Their Changes Under Polarized Light Action

Using a novel experimental method combining of polarizing optical microscopy (POM) and atomic force microscopy (AFM), the surface topography and optical properties of chiral‐ photochromic LC systems were studied. For this purpose, a mixture of cholesteric cyclosiloxanes with azobenzene‐containing dopant was prepared. Correlations between the features of surface topography of mixture films and POM images of planarly oriented texture were found. Polarized light action (532 nm) leads to the formation of partially aligned surface structure features. The observed photooptical effects are associated with E‐Z, Z‐E isomerization cycles of azobenzene groups, anisotropic cooperative photoinduced rotational diffusion and directional mass‐transport of chromophores and mesogens in the films.     

Influence of the Addition of Polystyrene‐block‐poly(methyl methacrylate) Copolymer (PS‐b‐PMMA) on the Morphologies Generated by Reaction‐Induced Phase Separation in PS/PMMA/Epoxy Blends

Homogeneous solutions of polystyrene (PS) and poly(methyl methacrylate) (PMMA) in diglycidylether of bisphenol A, containing about 8 wt.‐% total thermoplastic, and with or without 0.5 wt.‐% of a PS‐b‐PMMA block copolymer, were polymerized in two ways (i) in the presence of a tertiary amine (benzyldimethylamine, BDMA), or (ii) using a stoichiometric amount of a diamine (4,4′‐diaminodiphenyl sulfone, DDS). A double phase‐separation was recorded by light transmission during polymerization. A PS‐rich phase was separated at low conversions and a PMMA‐rich phase was segregated at more advanced conversions. The addition of the block copolymer produced significant changes in the morphologies generated. For the BDMA‐initiated polymerization, the presence of the block copolymer made the small PMMA‐rich domains clearly discernible in transmission electron microscopy (TEM) micrographs. For the DDS‐cured system, the addition of the block copolymer led to a dispersion of small PS‐rich particles encapsulated by PMMA shells. The possibility of generating a stable dispersion of biphasic particles by polymerization‐induced phase separation opens a new way to modify thermosetting polymers for toughening purposes.     

One‐Step Method for Synthesis of PDMS‐Based Macroazoinitiators and Block Copolymers from the Initiators

Summary: This paper presents a facile one‐step method for the synthesis of macroazoinitiator (MAI) by direct polycondensation of hydroxyalkyl‐terminated polydimethylsiloxane (PDMS) with 4,4′‐azobis‐4‐cyanopentanoic acid (ACPA) under mild conditions. The PDMS‐based MAI was characterized by FTIR, ¹H NMR, GPC, and UV spectroscopy, and further used as an initiator for polymerization of methyl methacrylate (MMA) to obtain PMMA‐co‐PDMS block copolymer. TEM observation and DSC analysis demonstrated that the PMMA‐co‐PDMS block copolymer had a microphase‐separated structure.

Schematic representation for syntheses of macroazoinitiators (MAI) by the direct polycondensation and corresponding block copolymers.     

Synthesis of Poly(N‐isopropylacrylamide)‐Block‐Poly(tert‐Butyl Methacrylate) Block Copolymer by Visible Light–Induced Metal‐Free Atom Transfer Polymerization

Atom transfer radical polymerization (ATRP) is one of the most powerful methodologies for polymerization. Well‐controlled ATRP of N‐isopropylacrylamide (NIPAAm) could be obtained in organic‐water mixture solvent with conventional metal catalyst/ligand catalyst system. However, the mixture solvent is not suitable for copolymerization of NIPAAm with hydrophobic monomers. Moreover, further purification of metal was required for biomedical polymerization. Here, poly(N‐isopropylacrylamide) (PNIPAAm) is synthesized by visible light–induced metal‐free ATRP using a photoredox catalyst. PNIPAAm is obtained with high conversion and controlled molecular weight with low dispersity. Moreover, poly(N‐isopropylacrylamide)‐block‐poly(tert‐butyl methacrylate) (PNIPAAm‐b‐PMAA) block copolymer can be synthesized by such metal‐free ATRP. PNIPAAm‐b‐PMAA can be obtained by following hydrolysis.     

Incorporation of Benzoxazine Pendants in Polymer Chains: A Simple Approach to Add‐Up Multi‐Responsive Functions

External stimuli responsive polymers can be derived from the functional side group in copolymers. Benzoxazine dimer is a good candidate for expressing multi‐responsive properties based on the type of phenol in combination with its metal complexation. The present work proposes a vinyl monomer containing a benzoxazine pendant, which contains an azo group as the functional monomer. The copolymerization with methylmethacrylate (MMA) via atom transfer radical polymerization leads to a block copolymer, specifically, PA‐Azo‐C3‐b‐PMMA, which forms uniform nanoparticles. The ring opening of benzoxazine monomer results in dimer pendants. The copolymer obtained, PA‐Azo‐C3‐b‐PMMA, shows multi‐responsive functions in terms of metal ion complexation, and UV responsiveness through the dimer pendants and azobenzene groups. The UV exposure results in loss of uniformity of the nanoparticles as well as a decrease in size. This work demonstrates the role of benzoxazine pendants in developing PMMA copolymer showing external stimuli responsive functions.     

Direct and Reverse ATRP of MMA in Aqueous Dispersed Medium in the Presence of a Bipyridine‐Functionalized Block Copolymer Support

Summary: In a recent communication (Macromol. Rapid Commun. 2002 , 23, 871), we reported the synthesis of a bipyridine containing amphiphilic polymer and its usage as macroligand in the atom transfer radical polymerization (ATRP) of MMA in aqueous dispersed medium. Investigations on the mechanism and locus of nucleation by transmission electron microscopy (TEM) studies herein of latex particles prepared by direct ATRP using oil‐soluble ethyl 2‐bromoisobutyrate as initiator revealed a broad particle size distribution between 250 nm and 1 μm, suggesting two nucleation sites, micelles and monomer droplets. By using the water‐soluble initiator 2,2′‐azoisobutyramidine‐dihydrochloride (V‐50) reverse ATRP experiments were conducted at 90 °C. Kinetic measurements showed a sigmoidal slope of monomer conversion versus time as a first indication for an emulsion‐like process. Controlled polymerization behavior was achieved at a ratio of radicals versus Cu(II ) deactivator of 1:8. TEM measurements of polymer latex particles obtained by reverse ATRP revealed particle sizes between 100 and 400 nm. Residual copper content of eight PMMA samples prepared by direct and reverse ATRP was determined to be 0.01–0.03 wt.‐% (theoretical 0.73 wt.‐%) and indicated that on average 96–99% of all copper used in a polymerization experiment can be removed from the polymer latex particles by a simple precipitation/washing step.

Direct and reverse ATRP experiments of MMA in aqueous media in the presence of an amphiphilic, water‐soluble block copolymer with pendent bipyridine units.     

Double Hydrophilic Poly(ethylene oxide)‐block‐Poly(dehydroalanine) Block Copolymers: Comparison of Two Different Synthetic Routes

Two different synthetic pathways give access to the amphiphilic block copolymer poly(ethylene oxide)‐block‐poly(tert‐butoxycarbonylaminomethylacrylate). In the first approach, two end‐functionalized segments are linked via click chemistry; and in the second approach, a poly(ethylene oxide) (PEO) based macroinitiator is chain extended via atom transfer radical polymerization (ATRP). In both cases the linking unit consists of an amide group, which is necessary to effectively deprotect the corresponding polymer precursor without cleavage of both segments. For this, amide‐containing ATRP initiators are employed and successful synthesis by nuclear magnetic resonance (NMR) and size exclusion chromatography (SEC) analyses before comparing both pathways is demonstrated. After deprotection, a novel double hydrophilic block copolymer, poly(ethylene oxide)‐block‐poly(dehydroalanine), is obtained, which is investigated using SEC (aqueous and DMSO) and ¹H‐NMR spectroscopy. Containing a potentially zwitterionic PDha segment and a high density of both amino and carboxylic groups, pH‐dependent aggregation of the block copolymer is expected and is studied using dynamic light scattering, revealing interesting solution properties. The corresponding polymers are applied in various areas including drug delivery systems or in biomineralization.     

Synthesis and Self‐Assembly Behavior of Organic–Inorganic Poly(ethylene oxide)‐block‐Poly(MA POSS)‐block‐Poly(N‐isopropylacrylamide) Triblock Copolymers

In this work, the synthesis of 3‐methacryloxypropylheptaphenyl POSS, a new POSS macromer (denoted MA‐POSS) is reported. The POSS macromer is used to synthesize PEO‐b‐P(MA‐POSS)‐b‐PNIPAAm triblock copolymers via sequential atom transfer radical polymerization (ATRP). The organic‐inorganic, amphiphilic and thermoresponsive ABC triblock copolymers are characterized by means of nuclear magnetic resonance spectroscopy (NMR) and gel permeation chromatography (GPC). Differential scanning calorimetry (DSC) and atomic force microscopy (AFM) show that the hybrid ABC triblock copolymers are microphase‐separated in bulk. Cloud point measurements show that the effect of the hydrophiphilic block (i.e. PEO) on the LCSTs is more pronounced than the hydrophobic block (i.e. P(MA‐POSS)). Both transmission electron microscopy (TEM) and dynamic light scattering (DLS) show that all the triblock copolymers can be self‐organized into micellar aggregates in aqueous solutions. The sizes of the micellar aggregates can be modulated by changing the temperature. The temperature‐tunable self‐assembly behavior is interpreted using a combination of the highly hydrophobicity of P(MA‐POSS), the water‐solubility of PEO and the thermoresponsive property of PNIPAAm in the triblock copolymers.     

Effect of Nanoclay on in situ Preparation of “All Acrylate” ABA Triblock Copolymers via ATRP and Their Morphology

The preparation and characterization of a series of poly(methyl methacrylate)‐block‐poly(butyl acrylate)‐block‐poly(methyl methacrylate) ABA triblock copolymers and their clay nanocomposites via in situ ATRP is reported. The molecular weights and the chemical structures of these nanocomposites are characterized by means of GPC, FTIR, and NMR analyses. DSC, AFM, and SAXS analyses prove a nanophase‐separated morphology in the block copolymer/clay nanocomposites. DMA analysis demonstrates an additional reinforcing effect of nanoclay in the block copolymer nanocomposites. AFM analysis indicates that the bulk polymer has a cylindrical morphology that is unaffected in the nanocomposite, as corroborated by SAXS analysis.     

The Aggregation Behavior of Poly(ethylene oxide)‐Poly(methyl methacrylate) Diblock Copolymers in Organic Solvents

Poly(ethylene oxide)‐poly(methyl methacrylate) and poly(ethylene oxide)‐poly(deuteromethyl methacrylate) block copolymers have been prepared by group transfer polymerization of methyl methacrylate (MMA) and deuteromethyl methacrylate (MMA‐d₈), respectively, using macroinitiators containing poly(ethylene oxide) (PEO). Static and dynamic light scattering and surface tension measurements were used to study the aggregation behavior of PEO‐PMMA diblock copolymers in the solvents tetrahydrofuran (THF), acetone, chloroform, N,N‐dimethylformamide (DMF), 1,4‐dioxane and 2,2,2‐trifluoroethanol. The polymer chains are monomolecularly dissolved in 1,4‐dioxane, but in the other solvents, they form large aggregates. Solutions of partially deuterated and undeuterated PEO‐PMMA block copolymers in THF have been studied by small‐angle neutron scattering (SANS). Generally, large structures were found, which cannot be considered as micelles, but rather fluctuating structures. However, ¹H NMR measurements have shown that the block copolymers form polymolecular micelles in THF solution, but only when large amounts of water are present. The micelles consist of a PMMA core and a PEO shell.     

Tannic Acid‐Inspired Star‐Like Macromolecules via Temporally Controlled Multi‐Step Potential Electrolysis

Inspired by tea stains, a plant polyphenolic‐based macroinitiator is prepared for the first time by partial modification of tannic acid (TA) with 2‐bromoisobutyryl bromide. In accordance with the “grafting from” methodology, a naturally occurring star‐like polymer with a polar gallotannin core and a hydrophobic poly(n‐butyl acrylate) side arms is synthesized via a simplified electrochemically mediated ATRP (seATRP), utilizing multiple‐step potential electrolysis. To investigate the kinetics of the electrochemical catalytic process triggered by reduction of Cu(II) or Fe(III) catalytic complex in the presence of the multifunctional initiator, cyclic voltammetry measurements are conducted. The naturally derived tannin macromolecule shows narrow MWDs (? = 1.57). Moreover, solvolysis of the star polymer to cleave the side arms and characterize them indicates that all chains grow to the same length (homopolymers with M_w/M_n <1.17), which confirms the well‐controlled seATRP. The structure of the obtained TA‐based systems is characterized microscopically (AFM) and spectroscopically (¹H NMR, FT‐IR). Atomic force microscopy measurements precisely determine the diameters of the obtained star polymers (19.7 ± 3.3 nm). These new star polymers may find biomedical applications as drug delivery systems and antifouling or antimicrobial coatings.     

Tunable Shell Thickness in Silica Nanospheres Functionalized by a Hydrophobic PMMA‐PSt Diblock Copolymer Brush via Activators Generated by Electron Transfer for Atom Transfer Radical Polymerization

An improved strategy to synthesize SiO₂‐PMMA nanoparticles with tunable shell thickness is demonstrated, via iron (III) catalyst‐mediated activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP). To investigate the effect of the content monomer and ligand on the PMMA shell thickness, hydrophobic PMMA‐PSt diblock copolymer brushes on the surface of the silica nanospheres are designed and synthesized by AGET ATRP. Transmission electron microscopy (TEM) and field‐emission scanning electron microscopy (FESEM) show that the product has a core‐shell‐like structure and that the average shell thickness of the PMMA can easily be tuned by simply adjusting the amount of monomer or ligand. In addition, the M _n of the PMMA can be tuned from 37 800 to 62 400 g mol^?1 by changing the shell thickness, and the PDI is 1.213–1.473. These results confirm the living nature of the polymerization.

     

Chain End‐Functionalized Polymer Brushes with Switchable Fluorescence Response

Herein is described the switchable fluorescence response of poly(methyl methacrylate) (PMMA) brushes. Chain end fluorescein labeled PMMA brushes are prepared by combining surface‐initiated atom transfer radical polymerization (SI‐ATRP) with a copper‐catalyzed alkyne‐azide cycloaddition (CuAAC) click reaction. Successful attachment of fluorescein is confirmed by measuring fluorescence of the as‐prepared films. Utilizing co‐solvency of PMMA in isopropanol‐water mixtures, responsive behavior of the end‐functionalized brushes is demonstrated by measuring the changes in fluorescence intensity between the swollen and collapsed states.     

Controlled Synthesis and Characterization of Poly[ethylene‐block‐(L,L‐lactide)]s by Combining Catalytic Ethylene Oligomerization with “Coordination‐Insertion” Ring‐Opening Polymerization

Model poly[ethylene‐block‐(L ,L ‐lactide)] (PE‐block‐PLA) block copolymers were successfully synthesized by combining metallocene catalyzed ethylene oligomerization with ring‐opening polymerization (ROP) of L ,L ‐lactide (LA). Hydroxy‐terminated polyethylene (PE‐OH) macroinitiator was prepared by means of ethylene oligomerization on rac‐dimethyl‐silylen‐bis(2‐methyl‐benz[e]indenyl)‐zirconium(IV)‐dichloride/methylaluminoxane (rac‐MBI/MAO) in presence of diethyl zinc as a chain transfer agent, and subsequent in situ oxidation with synthetic air. Poly[ethylene‐block‐(L ,L ‐lactide)] block copolymers were obtained via ring‐opening polymerization of LA initiated by PE‐OH in toluene at 100 °C mediated by tin octoate. The formation of block copolymers was confirmed by ¹H NMR spectroscopy, fractionation experiments, thermal behavior, and morphological characterization using AFM and light microscopy techniques.

     

Visible Light–Induced RAFT Polymerization of Methacrylate with 4‐(N,N‐diphenylamino)benzaldehyde as Organophotoredox Catalyst and the Effect of Temperature on the Polymerization

With UV–vis absorption in the range of 270–435 nm, 4‐(N,N‐diphenylamino)benzaldehyde (DPAB) takes efficient photoreduction quench with 4‐cynao‐4‐(phenylcarbonothioylthio)pentanoic acid (CTP). The polymerization rates of methyl methacrylate (MMA) are 0.019, 0.056, and 0.102 h^?1 at 33, 40, and 50 °C, respectively, in the presence of DPAB and CTP under visible‐light irradiation. Dark reaction produces no PMMA at 50 °C for 120 h. The living feature is demonstrated by linearly increasing M_n with the monomer conversions and narrow polydispersity index (PDI), chain extension, and block polymerizations with benzyl methacrylate (BnMA) and poly(ethylene glycol) monomethyl ether methacrylate (PEGMA). With PMMA‐CTP (M_n = 6800, PDI = 1.17), chain extension gives PMMA with M_n = 15 900 and PDI = 1.15. With PMMA‐CTP (M_n = 6000, PDI = 1.21) as macro‐RAFT, PMMA‐b‐PBnMA of M_n = 12 600 (PDI = 1.44) and M_n = 18 500 (PDI = 1.31) are prepared. These results support that there is a positive synergistic effect between polymerization temperature and visible‐light irradiation on the photo‐RAFT without losing the living features.     

PBA–PMMA 3‐Arm Star Block Copolymer Thermoplastic Elastomers

A series of well‐defined poly(methyl methacrylate)‐block‐poly(butyl acrylate) 3‐arm star block copolymers have been synthesized by ATRP. The incorporation of polar hard segment of PMMA was made possible with the aid of halogen exchange technique. Phase‐separated morphology of cylindrical PMMA domains hexagonally arranged in the pBA matrix was observed by small angle X‐ray scattering in all studied materials. The mechanical and thermal properties of the PBA–PMMA 3‐arm star block copolymers have been thoroughly characterized and their thermoplastic elastomer behavior was studied. It was found that the tensile properties of these materials are comparable with those of their linear ABA type block copolymer counterparts with similar compositions.

     

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.     

Atom‐Transfer Radical Polymerization: A Strategy for the Synthesis of Halogen‐Free Amino‐Functionalized Poly(methyl methacrylate) in a One‐Pot Reaction

Summary: An initiator containing an alkyl bromide unit and a protected amine functional group is used with CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA), in a 1:2 molar ratio with respect to initiator concentration, in order to obtain amino‐group terminated as well as halogen‐free poly(methyl methacrylate) (PMMA) in a one‐pot atom‐transfer radical polymerization (ATRP). The terminal bromines are replaced by hydrogen atoms of the PMDETA ligand, which acts as a transfer agent. However, terminating side reactions like disproportionation or dehydrobromination occur from the beginning of the polymerization. Kinetic studies by in‐line Raman spectroscopy and off‐line ¹H NMR spectroscopy revealed that the controlled character of the ATRP is lost under these conditions. The measured molecular weights were consistently higher than the theoretical ones and the molecular weight distributions are relatively broad. Thermal analysis of the obtained poly(methyl methacrylate) shows two main degradation steps, one starting from unsaturated end groups (depolymerization), and one caused by main‐chain scission, a further proof for the occurrence of terminating side reactions.

Structural analysis of PMMA by matrix‐assisted laser desorption‐ionization mass spectrometry.     

Bioinspired All‐Polyester Diblock Copolymers Made from Poly(pentadecalactone) and Poly(3‐hydroxycinnamate): Synthesis and Polymer Film Properties

A bioinspired diblock copolymer is synthesized from pentadecalactone and 3‐hydroxy cinnamic acid. Poly(pentadecalactone) (PPDL) with a molar mass of up to 43 000 g mol^?1 is obtained by ring‐opening polymerization initiated by propargyl alcohol. Poly(3‐hydroxycinnamate) (P3HCA) is obtained by polycondensation and end‐functionalized with 3‐azido propanol. The two functionalized homopolymers are connected via 1,3‐dipolar Huisgen addition to yield the block copolymer PPDL‐triazole‐P3HCA. The structure of the block copolymer is confirmed by proton NMR, FTIR spectroscopy and GPC. By analyzing the morphology of polymer films made from the homopolymers, from a 1:1 homopolymer blend, and from the PPDL‐triazole‐P3HCA block copolymer, clearly distinct micro‐ and nanostructures are revealed. Quantitative nanomechanical measurements reveal that the block copolymer PPDL‐triazole‐P3HCA has a DMT modulus of 22.3 ± 2.7 MPa, which is lower than that of the PPDL homopolymer (801 ± 42 MPa), yet significantly higher than that of the P3HCA homopolymer (1.77 ± 0.63 MPa). Thermal analytics show that the melting point of PPDL‐triazole‐P3HCA is similar to PPDL (89–90 °C), while it has a glass transition temperature similar to P3HCA (123–124 °C). Thus, the semicrystalline, potentially degradable all‐polyester block copolymer PPDL‐triazole‐P3HCA combines the thermal properties of either homopolymer, and has an intermediate elastic modulus.