Preparation of Polyurethane Microspheres via Dispersion Polycondensation Using Poly(1,4‐isoprene)‐block‐poly(ethylene oxide) as Steric Stabilizer

A novel dispersion polymerization of a diisocyanate and a diol for the preparation of spherical polyurethane particles is reported. An amphiphilic block copolymer, namely, poly(1,4‐isoprene)‐block‐poly(ethylene oxide) was used as a steric stabilizer. Monodisperse spherical particles were obtained in the size range from 0.2 to 2.0 μm. The polyurethane particle formation was dependent on the concentration of the steric stabilizer, the block segment molecular weight and the nature of dispersion medium. The polyurethane particles were stabilized by a mechanism involving physical adsorption of the steric stabilizer on the surface of the growing particle.     

Inversion of Phase Morphology in Polymer‐Blend Thin Films on Glass Substrates

Summary: The phase‐morphology inversion in two blend systems of polystyrene/poly(methyl methacrylate) (PS/PMMA) and polystyrene/poly(ε‐caprolactone) (PS/PCL) has been studied after their thin films were prepared on glass substrates by spin‐coating from a co‐solvent tetrahydrofuran (THF). Phase‐contrast microscopy (PCM), scanning‐electron microscopy (SEM) equipped with energy dispersive X‐ray spectroscopy (EDS), and atomic force microscopy (AFM) were used to obtain information on the morphology of the thin films during heat treatment. It was found that the PMMA‐rich and PCL‐rich phases are always continuous after annealing in either of the PS/PMMA and PS/PCL blend thin films, even though the PMMA and PCL are minor components in the blends. This should result from the better wetting abilities of PMMA and PCL on a glass substrate than PS in the blends. The effect of the viscosity in the evolution of the phase structure was also investigated by changing the molecular weight of PS in the PS/PCL blend thin films. Further more, it is found that the phase‐separation process and the wetting phenomenon of the blends on the glass substrate can be strongly suppressed after adding PS‐block‐PMMA diblock copolymer to the PS/PMMA blend system as a compatibilizer.

Scheme of the longitudinal section of the evolution of the phase structure of a PS:PMMA (70:30 w:w) blend film.     

Structural Behavior of Cylindrical Polystyrene‐block‐Poly(ethylene‐butylene)‐block‐Polystyrene (SEBS) Triblock Copolymer Containing MWCNTs: On the Influence of Nanoparticle Surface Modification

In this work, the influence of carbon nanotubes (CNTs) on the self‐assembly of nanocomposite materials made of cylinder‐forming polystyrene‐block‐poly(ethylene‐butylene)‐block‐polystyrene (SEBS) is studied. CNTs are modified with polystyrene (PS) brushes by surface‐initiated atom transfer radical polymerization to facilitate both their dispersion and the orientation of neighboring PS domains of the block copolymer (BCP) along modified CNT‐PS. Dynamic rheology is utilized to probe the viscoelastic and thermal response of the nanoscopic structure of BCP nanocomposites. The results indicate that nonmodified CNTs increase the BCP microphase separation temperature because of BCP segmental confinement in the existing 3D network formed between CNTs, while the opposite holds for the samples filled with modified CNT‐PS. This is explained by severely retarded segmental motion of the matrix chains due to their preferential interactions with the PS chains of the CNT‐PS. Moreover, transient viscoelastic analysis reveals that modified CNT‐PS have a more pronounced effect on flow‐induced BCP structural orientation with much lower structural recovery rate. It is demonstrated that dynamic‐mechanical thermal analysis can provide valuable insights in understanding the role of CNT incorporation on the microstructure of BCP nanocomposite samples. Accordingly, the presence of CNT has a significant promoting effect on microstructural development, comparable to that of annealing.     

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.     

Online HPLC‐NMR of PS‐b‐PMMA and Blends of PS and PMMA, 2 ‐ LCCC‐NMR at Critical Conditions of PMMA

PS‐b‐PMMA copolymers and blends of PS and PMMA were analyzed by the online coupling of LC at the critical point of adsorption and ¹H NMR. The separation of the polymers was carried out at chromatographic conditions which correspond to the critical point of PMMA and the size exclusion mode of PS. It was shown that blends of PS and PMMA homopolymers could be well separated at critical conditions of PMMA. The analysis of both the copolymers and the blends were carried out by online coupled ¹H NMR. The block copolymers were analyzed with respect to the chemical composition. LCCC‐NMR coupling was allowed to determine the individual blocks of the copolymers regarding molar mass. The data were compared with the separation at critical conditions of PS.

     

Tunable Arrangement of Gold Nanoparticles in Epoxidated Poly(styrene‐block‐butadiene) Diblock Copolymer Matrices

A new approach to synthesize block‐copolymer‐mediated/gold nanoparticle (Au NP) composites is developed. Stable and narrowly distributed Au NPs modified with a 2‐phenylethanethiol ligand are prepared by a two‐phase liquid–liquid method. A new epoxidation of a poly(styrene‐block‐butadiene) diblock copolymer, to form poly(styrene‐block‐vinyl oxirane) (PS‐b‐PBO), is achieved through chemical modification. It is found that the Au NPs disperse well in the PS block segment by partially crosslinking the PBO block segment with poly(ethylene oxide bisamine) (D230), a curing agent. The aggregation of Au NPs leads to a red‐shift of the plasmon absorption with the increase in the D230 content. However, without crosslinking the PBO block segment with D230, Au NPs distributes in both the PS and PBO segments.     

Micellization of PS‐PMMA Diblock Copolymers in an Ionic Liquid

Three polystyrene‐block‐poly(methyl methacrylate) (PS‐PMMA) block copolymers with varying molecular content have been shown to form micelles when dissolved in the ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIM PF₆). The micellar structure was studied via cryogenic transmission electron microscopy and dynamic light scattering, and a morphological transition from spherical to cylindrical micelles was observed upon reduction of the PMMA volume fraction. The possibility of frozen micellar morphology was considered, due to the solution preparation method and high glass transition temperature (T_g) of the PS blocks that form the micellar cores. By comparison of the behavior of a 100 kDa PMMA homopolymer dissolved in both BMIM PF₆ and a known good solvent, acetone, it was determined that BMIM PF₆ behaves as a good solvent for PMMA. It was also observed that extended exposure to the electron beam during cryogenic transmission electron microscopy could damage the copolymer micelles and result in a reversal of contrast.

     

Rapid Synthesis of Poly(methyl methacrylate) Particles with High Molecular Weight by Soap‐Free Emulsion Polymerization Using Water‐in‐Oil Slug Flow

A flow process for the production of poly(methyl methacrylate) (PMMA) particles is proposed by soap‐free emulsion polymerization using a water‐in‐oil (W/O) slug flow in a microreactor. Thin oil films generated around the dispersed aqueous phase of the W/O slug prevent the prepared particles from adhesion to the microchannel wall, enabling the continuous production of PMMA particles without clogging. The effects of the linear flow rate of the slug flow and the addition of ethanol in the dispersed aqueous phase on the polymerization are evaluated. It is found that increasing the linear flow rate of the slug flow or the addition of ethanol in the dispersed aqueous phase results in PMMA particles with high molecular weight (≈1500 kg mol^?1) in 20 min reaction time. It is believed that this process would be a promising way to prepare polymer particles with high molecular weight in a short reaction time.     

Microphase‐Separated Poly(vinylpyridine) Block Copolymer Prepared with a Novel Bifunctional Initiator

A vinylpyridine block copolymer was prepared by stepwise controlled/living radical polymerization with a novel bifunctional initiator, 4‐(2‐bromopropanoyloxy)‐N‐(p‐methylbenzyloxy)‐2,2,6,6‐tetramethylpiperidine. The initiator was synthesized in a facile manner using commercially available p‐xylene and 4‐hydroxy‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl (4‐hydroxy TEMPO). Through stepwise atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) and nitroxide‐mediated radical polymerization (NMRP) of 4‐vinylpyridine (4VP), the PMMA‐b‐P4VP copolymer was prepared with a wide range of the copolymer compositions. Microphase‐separation was demonstrated in cross sectional TEM images of self‐standing block copolymer membranes.

     

Tunable Morphologies From Bulk Self‐Assemblies of Poly(acryloxypropyl triethoxysilane)‐b‐poly(styrene)‐b‐poly(acryloxypropyl triethoxysilane) Triblock Copolymers

Reactive poly(acryloxypropyl triethoxysilane)‐b‐poly(styrene)‐b‐poly(acryloxypropyl triethoxysilane) (PAPTES‐b‐PS‐b‐PAPTES) triblock copolymers are prepared through nitroxide‐mediated polymerization (NMP). The bulk morphologies formed by this class of copolymers cast into films are examined by small‐angle X‐ray scattering (SAXS) and transmission electron microscopy (TEM). The films morphology can be tuned from spherical structures to lamellar structures by increasing the volume fraction of PS in the copolymer. Thermal annealing at temperatures above 100 °C provides sufficient PS mobility to improve ordering.     

Morphology and rheology of poly(methyl methacrylate)‐block‐poly(isooctyl acrylate)‐block‐poly(methyl methacrylate) triblock copolymers,and potential as thermoplastic elastomers

The phase morphology and rheological properties of a series of poly(methyl methacrylate)‐block‐poly(isooctyl acrylate)‐block‐poly(methyl methacrylate) triblock copolymers (MIM) have been studied. These copolymers have well‐defined molecular structures, with a molecular weight (MW) of poly(methyl methacrylate) (PMMA) in the range of 3 500–50 000 and MW of poly(isooctyl acrylate) (PIOA) ranging from 100 000 to 140 000. Atomic force microscopy with phase detection imaging has shown a two‐phase morphology for all the MIM copolymers. The typical spherical, cylindrical, and lamellar phase morphologies have been observed depending on the copolymer composition. MIM consisting of very short PMMA end blocks (MW 3 500–5 000) behave as thermoplastic elastomers (TPEs), with however an upper‐service temperature higher than the traditional polystyrene‐block‐polyisoprene‐block‐polystyrene TPEs (Kraton D1107). A higher processing temperature is also noted, consistent with the higher viscosity of PMMA compared to PS.     

Controlled synthesis of anthracene‐labeled ω‐amine polystyrene to be used as a probe for interfacial reaction with mutually reactive PMMA

Anthracene‐labeled polystyrene (PS) end‐capped by a primary amine has been synthesized by atom transfer radical copolymerization of styrene with 3‐isopropenyl‐α,α‐dimethylbenzyl isocyanate (m‐TMI). The m‐TMI co‐monomer (5.7 mol‐%) does not perturb the control of the radical polymerization of styrene. The pendant isocyanate groups of the copolymer chains of low polydispersity (M _w/M _n = 1.25) and controlled molecular weight (up to 35 000) have been derivatized into anthracene by a reaction with 9‐methyl(aminomethyl)anthracene. The anthracene‐labeled PS (ca. 2 mol‐% label) has been conveniently analyzed by size‐exclusion chromatography with a UV detector (SEC‐UV). Moreover, the ω‐bromide end‐group of the copolymer chains has been derivatized into a primary amine, making the labeled PS chains reactive towards non‐miscible poly(methyl methacrylate) (PMMA) chains end‐capped by an anhydride. The interfacial coupling of the mutually reactive PS and PMMA chains has been studied under static conditions (i.e., at the interface between thin PS and PMMA films) and successfully analyzed by SEC‐UV.

SEC‐UV traces for anth‐PS‐NH₂ (80 μg · ml⁻¹; sample A5; Table 1 ), and PMMA‐anh (80 μg · ml⁻¹; sample B1; Table 1 ).     

Compatibilizing Effect of Transesterification Copolymers on Bisphenol‐A Polycarbonate/Poly(ethylene terephthalate) Blends

After considerably long time of transesterification reactions between poly(ethylene terephthalate) (PET) and bisphenol‐A polycarbonate (PC) in the molten state, random copolymers, referred to be TCET's, can be obtained, which have fairly good compatibilizing effect on the immiscible PC/PET blend. The compatibilizing effect of these transesterification random copolymers is proved to be closely related to their compatibility with PET and PC. Being completely compatible both with PET and PC, the TCET50 copolymer with 50 wt.‐% ethylene terephthalate content is an efficient compatibilizer, it can greatly improve the compatibility between PET and PC. With increasing content of the TCET50 copolymer in the PC/PET/TCET50 ternary blend, the two glass transition temperatures, which belong to the PET‐rich and PC‐rich phase respectively, approach each other gradually. When the content of the TCET50 copolymer in the blend reaches 60 wt.‐%, only one glass transition temperature can be detected by differential scanning calorimetry (DSC). The TCET30 and TCET70 copolymer, which have 30 and 70 wt.‐% ethylene terephthalate content respectively, are less efficient in compatibilizing the PC/PET blend, since the TCET30 copolymer and PET, as well as the TCET70 copolymer and PC, are compatible to a certain degree instead of being completely compatible.     

On‐Line HPLC‐NMR of PS‐b‐PMMA and Blends of PS and PMMA: LCCC‐NMR at Critical Conditions of PS

Blends and copolymers of PS and PMMA were analysed by LC coupled to ¹H NMR at the critical point of adsorption. The separation of the polymers was achieved at chromatographic conditions that correspond to the critical point of PS and the size‐exclusion mode of PMMA. Copolymers and blends were analysed by on‐line coupled ¹H NMR. For the homopolymer blends, separation into the components was achieved, while the copolymers were separated with regard to the block lengths of the PMMA blocks. The tacticity of the PMMA blocks could be determined as a function of molar mass by HPLC‐NMR. This technique can deliver the true molar mass and the true chemical composition of the copolymers.

     

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.     

Polystyrene‐block‐poly(methyl methacrylate): Initiation Issues with Block Copolymer Formation Using ARGET ATRP

The synthesis, kinetics, and characterization of polystyrene and poly(methyl methacrylate) block copolymers produced by ARGET ATRP are discussed. Halogen exchange is used and the polymerization appears to be living in the generation of the second block. On further investigation, the GPC traces exhibit a shoulder, which suggests poor initiation of the macroinitiator. Previous reports suggest that to increase the initiation efficiency of the second block, 10% styrene monomer should be added to the mixture. Upon adding the 10% styrene for the second block ARGET ATRP polymerization, the appearance of a well‐initiated polymer is observed. However, at greater conversions the results clearly demonstrate the production of a homopolymer/block copolymer mixture.     

Blends of Immiscible Polystyrene/Polyamide 6 via Successive In‐Situ Polymerizations

Summary: A novel method has been successfully developed to prepare binary blends of PS and MCPA6. The blends are formed by the radical polymerization of styrene in CL, followed by the in‐situ anionic ring‐opening polymerization of CL in the presence of PS. The phase morphology investigated using SEM reveals that PS/MCPA6 blends with a PS content of 10 wt.‐% or lower consists of a MCPA6 matrix and a dispersed PS minor phase. Remarkably, phase inversion occurs in blends that have a PS content of 15 wt.‐% or higher, in which MCPA6 is no longer continuous but finely dispersed in the PS continuous phase. The phase inversion occurs at an extremely low PS content, and this phenomenon is unusual for traditional polymer blends prepared by melt blending. The probable reason for the particular phase morphology development is explained. The stability of the phase morphologies of the PS/MCPA6 blends after annealing at 250 °C is also investigated by SEM.

SEM micrograph of the fractured surface of a PS/MCPA6 blend with a PS content of 20 wt.‐%, in which MCPA6, as spherical particles, is dispersed in the PS continuous phase.     

Miscibility and morphology of AB/C-type blends composed of block copolymer and homopolymer or random coploymer, 2. Blends with random copolymer effect

This work is an extension of the concept of miscibility window in homopolymer/random copolymer blends to blends containing block copolymers. The miscibility and morphology of THF-cast blends composed of the block copolymer polyisoprene-block-poly(methyl methacrylate) (Pl-b-PMMA) and the random copolymer poly(styrene-ran-acrylonitrile) (SAN) (22 wt.-% AN) has been studied by transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). Most blends show miscibility between PMMA blocks and SAN, presenting a homogeneous microdomain structure. Coupling of macrophase separation occurs only when the ratio of molecular weights of SAN to the PMMA bock is very large and SAN becomes the dominant component. The excellent miscibility in the block copolymer/random copolymer blends can be understood by considering that the monomer unit composition of SAN is within the miscibility window in PMMA/SAN blends. The main driving force for the miscibility is repulsion between S and AN units rather than hydrogen bonding between SAN and PMMA, since a proton-acceptor type solvent does not show any effect on the miscibility in the blends. Apparent broadening of the glass transition of the ‘hard phase’ is observed and explained with the aid of the segment density gradient model.     

Preparation of Monodisperse and Anion‐Charged Polystyrene Microspheres Stabilized with Polymerizable Sodium Styrene Sulfonate by Dispersion Polymerization

A novel dispersion polymerization system to produce “clean” polystyrene (PS) particles, using a polymerizable sodium styrene sulfonate (NaSS) as stabilizer, and a mixture of methanol/water (MeOH/H₂O) as the reaction medium was investigated. The effects of the polymerization parameters, such as the methanol/water ratio in the medium, the concentration of the stabilizer, the initiator and the monomer on the resulting particles were studied. By observing the morphological changes of the PS particles by SEM and analyzing the surface chemical composition of these particles by XPS, it is found that this system had the following unique features: as little as 0.05 wt.‐% of NaSS (based on styrene as opposed to 5 wt.‐% for a routine dispersion polymerization system) was enough to prepare stable latex with monodisperse particles; as high as 20 vol.‐% of monomer (as opposed to 5 wt.‐% for polymerization system in the absence of surfactants) could be added into the polymerization system to produce monodisperse particles; surface‐charged and monodisperse particles with average diameters of approximately 470–1600 nm could be directly obtained.

     

Visible‐Light‐Induced Controlled Polymerization of Hydrophilic Monomers with Ir(ppy)3 as a Photoredox Catalyst in Anisole

With fac‐Ir(ppy)₃ as photoredox catalyst and ethyl 2‐bromoisobutyrate (EBiB) as initiator, the homopolymerization of methyl methacrylate (MMA) in different solvents, such as N,N‐dimethylformamide (DMF), acetonitrile, and anisole are run under irradiation of an LED lamp. The results show that anisole is a better solvent for the polymerization with regard to the polydispersity index (PDI). A well‐controlled polymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA) is demonstrated and the clean block copolymer of PMMA‐b‐PPEGMA is prepared with PDI less than 1.3; however, the 2‐(dimethylamino) ethyl methacrylate (DMAEMA) polymerization is poorly controlled. With the PMMA as macromolecular initiator, the block copolymer PMMA‐b‐PDMAEMA can be prepared with PDI around 2.0.