RAFT‐Based Synthesis and Characterization of ABC versus ACB Triblock Copolymers Containing tert‐Butyl Acrylate,Isoprene, and Styrene Blocks

The syntheses of the ABC and ACB triblock copolymer topological isomers poly(tert‐butyl acrylate)‐block‐polyisoprene‐block‐polystyrene (ABC) and poly(tert‐butyl acrylate)‐block‐polystyrene‐block‐polyisoprene (ACB) using the RAFT‐controlled radical polymerization method are described. The triblock copolymers were isolated with molecular weights on the order of 20 000 Da and molecular weight distributions of 1.3–1.5. The polymers described herein demonstrated thermal decompositions at 200 °C, characteristic of tert‐butyl esters, and their structure and composition were confirmed by a combination of infrared, ¹H, and ¹³C NMR spectroscopies.

     

Self‐Assembled Structures in Blends of Block Copolymer A‐block‐B with Homopolymer A: SAXS and SANS Study

Summary: The study describes the investigation of the microphase‐separated morphology of a block copolymer A‐block‐B with the parent homopolymer A, where A is polystyrene and A‐block‐B is poly(perdeuterated styrene)‐block‐poly(methyl methacrylate) (dPS‐block‐PMMA). The microdomain morphology and phase behavior in blends of dPS‐block‐PMMA with polystyrene of = 8 000 and 35 000 were investigated. Binary blends of the diblock copolymer and homopolymers were prepared with various amounts of homopolymers. The criterion for “wet and dry brush” taking into account different solubilization of homopolymer has been applied to explain the changes in microdomain morphology during the self‐assembling process.

     

Synthesis and Characterization of Poly(trimethylene oxide)‐block‐Polystyrene and Poly(trimethylene oxide)‐block‐Polystyrene‐block‐Poly(methyl methacrylate) by Combination of Atom Transfer Radical Polymerization (ATRP) and Cationic Ring‐Opening Polymerization (CROP)

Summary: Diblock copolymers, poly(trimethylene oxide)‐block‐poly(styrene)s abbreviated as poly(TMO)‐block‐poly(St), and triblock copolymers, poly(TMO)‐block‐poly(St)‐block‐poly(MMA)s (MMA = methyl methacrylate), with controlled molecular weight and narrow polydispersity have been successively synthesized by a combination of atom transfer radical polymerization (ATRP) and cationic ring‐opening polymerization using the bifunctional initiator, 2‐hydroxylethyl α‐bromoisobutyrate, without intermediate function transformation. The gel permeation chromatography (GPC) and NMR analyses confirmed the structures of di‐ and triblock copolymers obtained.

GPC curves of (a) poly(St); (b) diblock copolymer, poly(St)‐block‐poly(MMA) before precipitation; (c) poly(St)‐block‐poly(MMA) after precipitation in cyclohexane/ethanol (2:1); (d) triblock copolymer, poly(TMO)‐block‐poly(St)‐block‐poly(MMA).     

pH‐Sensitive Micelles Formed by Interchain Hydrogen Bonding of Poly(methacrylic acid)‐block‐Poly(ethylene oxide) Copolymers

pH‐sensitive micelles formed by interchain hydrogen bonding of poly(methacrylic acid)‐block‐poly(ethylene oxide) copolymers were prepared and investigated at pH < 5. Both and R_h of the micelles increase with decreasing pH of the solution, displaying an asymptotic tendency at low pH values. The observed micelles are well‐defined nanoparticles with narrow size distributions (polydispersity ΔR_h/R_h ≤ 0.05) comparable with regular diblock copolymer micelles. The CMCs occur slightly below c = 1 × 10^?4 g · mL^?1. The micelles are negatively charged and their time stability is lower than that of regular copolymer micelles based purely on hydrophobic interactions.

     

Structure and Properties of Poly(butyl acrylate‐block‐sulfone‐block‐butyl acrylate) Triblock Copolymers Prepared by ATRP

Summary: A series of telechelic OH polysulfones (PSU) were converted to atom transfer radical polymerization (ATRP) macroinitiators by reaction with 2‐bromoisobutyryl bromide. Three macroinitiators with different chain lengths were extended with poly(butyl acrylate) (PBA) to form ABA triblock copolymers. The structure and dynamics of the ABA triblock copolymers with PSU central segments and various molecular weight PBA side chains were investigated by small‐angle X‐ray scattering and rheology. The block copolymers form micelles with a PSU core and PBA corona. The length of each block has an important effect on the structure and resulting dynamics of the copolymers. Dynamic mechanical measurements indicate three relaxation modes: (i) PBA segmental relaxation at high frequency; (ii) PBA relaxation of the corona block at intermediate frequency; (iii) an additional relaxation process related to structural rearrangement of the micelles at low frequency. The shear modulus plateau corresponding to a soft rubbery state extends over a very broad time or temperature range because of this slow additional relaxation.

Schematic illustration of the structural elements and the bulk supramolecular structure for a symmetric triblock copolymer with a stiff central segment strongly incompatible with the other constituent.     

Synthesis and characterization of poly(ethylene oxide) and poly(perfluorohexylethyl methacrylate) containing triblock copolymers

A new series of poly(perfluorohexylethyl methacrylate)‐block‐poly(ethylene oxide)‐block‐poly(perfluorohexylethyl methacrylate), PFMA‐b‐PEO‐b‐PFMA triblock copolymers has been synthesized by atom transfer radical polymerization using bifunctional PEO macroinitiators. The molecular structure of the block copolymers was confirmed by ¹H NMR spectroscopy and SEC. X‐ray scattering studies have been carried out to investigate their bulk properties. SAXS has shown cubic arrangement of spheres (bcc), hexagonally packed cylinders (hpc) and lamellar microdomain formation in the melt of triblock copolymers investigated, depending on composition. Crystallization was, however, found to destroy the ordered melt morphology and imposes a lamellar crystalline structure. WAXS, DSC and polarized light microscopy measurements confirmed the crystallization of PEO segments in block copolymers. Long PFMA blocks were found to have significant effect on PEO crystallization.

Synthesis of triblock copolymers of EO and FMA by ATRP.     

Photopolymerization of Reactive Mesogens

Summary: The photopolymerization of two reactive mesogens with photopolymerizable acrylate endgroups, the methyl substituted 1,4‐phenylene‐bis{4‐[6‐(acryloyloxy)hexyloxy]benzoate} 1 and acrylic acid 6‐{4‐[6‐(6‐acryloyloxyhexyloxy)naphthalen‐2‐yl]‐phenoxy}hexyl ester 2 has been investigated using Photo‐DSC measurements. Photocrosslinking of 1 in the nematic phase at 100 °C leads to a final conversion of 87% of the acrylate groups. It is possible to perform photopolymerization with very small amounts of photoinitiator. Even with 0.001% (10 ppm) of photoinitiator, 47% of the acrylate groups polymerize within 15 min. The polymerization of the reactive mesogen 2 proceeds faster in the smectic A phase at 100 °C compared to the isotropic phase at 120 °C and leads to a higher conversion of 75%. This can be explained by an increased local concentration of the acrylate groups between the layers of the smectic cores.

Photopolymerization of reactive mesogens.     

Synthesis of Flower‐Like Polybutadiene

Synthesis of complex macromolecular architectures exhibiting no chain ends such as flower‐like polymers is still of interest in the aim of investigating their physicochemical properties. For this purpose, poly(3,4‐dimethyl maleic imidoethyl acrylate)‐block‐polybutadiene‐block‐poly(3,4‐dimethyl maleic imidoethyl acrylate) triblock copolymer is synthesized in a convergent manner using a combination of living polymerization (anionic polymerization), reversible deactivation radical polymerization, and click chemistry. This copolymer is self‐assembled in a selective solvent (heptane/THF mixture) of the polybutadiene block leading to the formation of flower‐like micelles in thermodynamic equilibrium in dilute solution. These resulting transient architectures are fixed by covalently crosslinking the micelles core by inducing [2+2] cyclodimerization of the 3,4‐dimethyl maleic imidoethyl groups borne by the short solvophobic blocks under UV irradiation. Single flowers are isolated from residual non‐crosslinked chains by semipreparative size exclusion chromatography (SEC) and characterized by ¹H NMR, SEC, dynamic light scattering (DLS), and transmission electron microscopy (TEM).

     

Nanomechanical Function Made Possible by Suppressing Structural Transformations of Polyarylacetylenes

Self‐assembling dendrons sterically disfavor the cisoid conformation through which 6π‐electrocyclization proceeds in cis‐polyarylacetylenes. Through the same mechanism, selected self‐organizable dendronized helical cis‐polyphenylacetylenes (cis‐PPAs) undergo an unprecedented thermally induced cisoid‐to‐transoid conformational isomerism in bulk. The motion of helix (un)winding can be converted to unidirectional motion in self‐organizable dendronized cis‐PPAs. By eliminating 6π‐electrocyclization, nanomechanical actuators capable of lifting a US dime have been prepared from self‐organizable dendronized cis‐PPAs.

     

Morphologies of Binary AB/AC Diblock Copolymer Blends

The self‐assembled structures of the mixtures of AB and AC diblock copolymers were investigated using transmission electron microscopy (TEM). For this purpose, two kinds of asymmetric polystyrene‐block‐polyisoprene (SI30 and SI87) and one symmetric polystyrene‐block‐poly(2‐vinylpyridine) (SVP) were anionically polymerized. Both macro‐ and microphase separations occur in all binary mixtures examined in this work, yielding various morphologies. The morphologies of the phase‐separated macrodomains are found to be the same as those of pure diblock copolymers. However, at the phase boundary where two diblock copolymers with different microphase‐separated structures are in contact with each other, the morphological transition is observed due to the preferential location of the common polystyrene (PS) blocks in two copolymers at the interface. From TEM observations and random phase approximation (RPA)‐based prediction, it is identified that the macrophase transition takes place prior to the microphase transition, leading to the interface‐induced ordering.

TEM micrographs of SI87/SVP 60/40 binary blend taken at different magnifications. The phase boundary between SI87 and SVP macrodomains and SVP‐rich macrodomains are shown, respectively.     

Physical Properties of PBMA‐b‐PBA‐b‐PBMA Triblock Copolymers Synthesized by Atom Transfer Radical Polymerization

The physical properties of well‐defined poly(butyl methacrylate)‐block‐poly(butyl acrylate)‐block‐poly(butyl methacrylate) (PBMA‐b‐PBA‐b‐PBMA) triblock copolymers synthesized by atom transfer radical polymerization (ATRP) are reported. The glass transition and the degradation temperature of copolymers were determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC measurements showed phase separation for all of the copolymers with the exception of the one with the shortest length of either inner or outer blocks. TGA demonstrated that the thermal stability of triblock copolymers increased with decreasing BMA content. Dynamic mechanical analysis was used for a preceding evaluation of adhesive properties. In these block copolymers, the deformation process under tension can take place either homogeneously or by a neck formation depending on the molecular weight of the outer BMA blocks and on the length of the inner soft BA segments. Microindentation measurements were also performed for determining the superficial mechanical response and its correlation with the bulk behavior.

Stress‐strain curves for the different PBMA‐b‐PBA‐b‐PBMA specimens at room temperature and at 10 mm/min.     

Study on Doping Behaviors of Vinyl Hydrogels with Pendant Terthiophenes

The water‐swollen poly(AA3T‐co‐NaSS) and poly(AA3T‐co‐PEG) gels were synthesized by radical copolymerization of the monomer, [(2,2′:5′,2″‐terthiophen‐5‐yl)methyl acrylate] (AA3T), containing pendant terthiophenes as an electron‐conducting material with a soluble monomer, sodium p‐styrenesulfonate (NaSS), or oligo(ethylene glycol) (PEG); their swelling, spectral, and doping behaviors were investigated. The degree of swelling of the poly(AA3T‐co‐PEG) gel was independent of the pH, whereas that of poly(AA3T‐co‐NaSS) gel increases abruptly below pH 3, which suggests self‐doping between the AA3T and NaSS groups. The self‐doping is not suppressed by cross‐linking. Both poly(AA3T‐co‐NaSS) and poly(AA3T‐co‐PEG) gels can be chemically doped with concentrated HCl or HClO₄ solution.

Concentration dependence of the absorbency of the copolymers and gel.     

A Facile One‐Pot Synthesis to Dextran‐Based Nanoparticles with Carboxy Functional Groups

Summary: Stabilized nanoparticles functionalized with carboxy groups were synthesized directly from dextran and acrylic acid (AA), without using any organic solvent and surfactant. The composition and morphology of these dextran‐based nanoparticles, as well as the mechanism of this one‐pot synthesis, were also investigated in this paper. This approach is anticipated to be applicable to various water‐soluble polysaccharides to fabricate nanoparticles facilely.

Facile synthesis of stabilized nanoparticles functionalized with carboxy groups from dextran and AA.     

Pyrene End‐Labeled Diblock Glycopolymers: Synthesis and Aggregation

Summary: A pyrene end‐labeled amphiphilic block copolymer, poly(ε‐caprolactone)‐block‐poly[6‐O‐(4‐vinylbenzyl)‐D ‐galactose] (Py‐PCL‐b‐PVBG), was synthesized by a four‐step method. The aggregation behavior of the diblock copolymer in solution was studied by monitoring the fluorescence of pyrene. TEM measurements revealed that the aggregates obtained by first dissolving the copolymer in N,N‐dimethylformamide (DMF), followed by the addition of water, were primarily spheres with the PCL blocks in the core. The PVBG corona was then crosslinked with glutaraldehyde. Final removal of the PCL core was accomplished by degradation under basic conditions, which resulted in the formation of hollow glycopolymer nanospheres.

Structure of poly(ε‐caprolactone)‐block‐poly[6‐O‐(4‐vinylbenzyl)‐D ‐galactose].     

Allyl End‐Functionalized Poly(ethylene oxide)‐block‐poly(methylidene malonate 2.1.2) Block Copolymers: Synthesis,Characterization, and Chemical Modification

Summary: Poly(ethylene oxide)‐block‐poly(methylidene malonate 2.1.2) block copolymer (PEO‐b‐PMM 2.1.2) bearing an allyl moiety at the poly(ethylene oxide) chain end was synthesized by sequential anionic polymerization of ethylene oxide (EO) and methylidene malonate 2.1.2 (MM 2.1.2). This allyl functional group was subsequently modified by reaction with thiol‐bearing functional groups to generate carboxyl and amino functionalized biodegradable block copolymers. These end‐group reactions, performed in good yields both in organic media and in aqueous micellar solutions, lead to functionalized PEO‐b‐PMM 2.1.2 copolymers which are of interest for cell targeting purposes.

Synthetic route to α‐allyl functionalized PEO‐b‐PMM 2.1.2 copolymers.     

Synthesis,Characterization, and Intramolecular End‐to‐End Ring Closure of α‐Isopropylidene‐1,1‐dihydroxymethyl‐ω‐diethylacetal Polystyrene‐block‐polyisoprene Block Copolymers

Cyclic polystyrene‐block‐polyisoprenes of controlled dimensions have been synthesized for the first time by the direct coupling of α‐isopropylidene‐1,1‐dihydroxymethyl‐ω‐diethylacetal‐heterodifunctional linear polystyrene‐block‐polyisoprene precursors previously prepared by living anionic polymerization. Cyclization is achieved under high dilution by intramolecular coupling of the polymer ends under acid catalyst conditions. Using this strategy polystyrene‐block‐polyisoprene macrocycles of controlled chain dimensions are prepared in high yield (> 90%). Pure cycles were finally recovered by flash chromatography. The synthesis and characterization of both the linear α,ω‐heterodifunctional polystyrene‐block‐polyisoprenes block copolymers precursors and of the corresponding cyclized chain architectures are reported.

200 MHz ¹H NMR spectrum (CDCl₃) of cyclized polystyrene‐block‐polyisoprene copolymer (M _n = 12 000).     

Stable Free‐Radical Copolymerization of Styrene with Acrylates Using OH‐TEMPO

Summary: Stable free‐radical copolymerizations (SFRP) of styrene with N‐acryloyl morpholine (AMo), 2‐ethoxyethyl acrylate (EOEA) and isobornyl acrylate (iBoA), respectively, were carried out under control of the stable nitroxide radical 4‐hydroxy‐2,2,6,6‐tetramethylpiperidine‐N‐oxyl (OH‐TEMPO). The polymerizations were initiated by a polystyrene macroinitiator (PS‐MI). No accelerating agents were used. In contrast to the experiences made with methacrylates there was no decrease in the polymerization rates up to 50 mol‐% of AMo or EOEA in the monomer mixture. This behavior was ascribed to a compensation of the lack of thermal initiation by the high propagation rate constants of the acrylates. The produced AB diblock polymers were successfully employed in block extension reactions in styrene yielding ABA triblock polymers. Copolymerization reactivity ratios (r‐values) and glass transition temperatures have been estimated.

Monomer structures.     

Synthesis of New Poly(ether ketone)s Derived from Biobased Diols

A new class of poly(ether ketone)s (PEKs) is prepared by polycondensation of various diols produced from biomass and various difluoro aromatics. After optimization of the reaction conditions, polycondensation of isosorbide and 4,4′‐difluorodiphenylketone (2a) gives PEK1 with a high yield, moderate viscosity (0.31 dL g^?1), and a glass‐transition temperature (T_g) of 170 °C. The optimum conditions are applied to the synthesis of a series of PEKs (PEK 2–9) from difluoro agents and sugar diols. The polycondensation of isomannide (1b) with 1,4‐di(p‐fluorobenzoyl)benzene (2b) gives the best results with an inherent viscosity of 0.52 dL g^?1 and the mass spectrum shows an abundance of cyclic structures. Similar conditions are used for the preparation of high‐molar‐mass copoly(ether ketone)s from a stoechiometric mixture of isosorbide/bisphenol‐A.

     

Effect of Molecular Structure and Thermal Treatment on Photo‐optical Properties of Photochromic Azobenzene‐containing Polymer Films

Three novel photochromic azobenzene‐containing comb‐shaped polyacrylates are synthesized and their phase behavior and photo‐optical properties are studied. The influence of the side photochromic group structure, thermal treatment, and light irradiation on aggregation of azobenzene chromophores in thin spin‐coated films of the polymers is investigated in detail. Special attention is paid to studying the photo‐orientation processes in polymers films induced by polarized blue light (473 nm). The relationship between the photochromic group architecture, phase behavior, thermal treatment of films, and kinetics of chromophore photo‐orientation is established and discussed. It is found that the position of the N?N bond in chromophores plays an important role in the kinetics of the process, but does not affect the maximum value of dichroism.

     

Block‐Selective Solvent Influence on Morphology of the Micelles Self‐Assembled by PS38‐b‐P(AA190‐co‐MA20)

Summary: The influence of block‐selective solvent on the self‐assembly of polystyrene‐block‐poly[(acrylic acid)‐co‐(methyl acrylate)] was studied. The nature of the block‐selective solvent, which is a binary solvent mixture with different composition, exerts remarkable influence on the morphology of the resulting micelles. When the block‐selective solvent is a binary solvent mixture of acetone and water with acetone content ranging from 0 to 90 vol.‐%, the resulting aggregates are core‐shell spheres with diameter about 60 nm, porous aggregates with diameter of 100, 180 and 250 nm, and core‐shell cauliflower‐like aggregates with size about 200 nm, respectively. The reason that the morphology of resulting micelles changes with acetone content has been discussed. The structure of the resulting micelles is further characterized in detail by DLS and SLS. Morphological tuning is also achieved by using a binary solvent mixture of ethanol and water or a binary solvent mixture of DMF and water as block‐selective solvent. In these cases, core‐shell spheres, hollow aggregates, and incompact aggregates are formed with the ethanol or DMF concentration ranging from 10 to 80 vol.‐%.