New Improved Thermosets Obtained From Diglycidylether of Bisphenol A and a Multiarm Star Copolymer Based on Hyperbranched Poly(glycidol) Core and Poly(methyl methacrylate) Arms

A well‐defined multiarm star copolymer, hyperbranched poly(glycidol)‐b‐poly(methyl methacrylate) (PGOH‐b‐PMMA), is used as a modifier in the curing of diglycidylether of bisphenol A (DGEBA) using 1‐methyl imidazole (1MI) as anionic initiator. The effect of the polymer topology on the curing and gelation processes is studied. The addition of the PGOH‐b‐PMMA to the resin leaves the complex viscosity unaltered. The addition of the modifier decreases the shrinkage after gelation compared to that measured in the curing of the neat resin. By DMTA a single relaxation process in the pure DGEBA and modified thermoset is found. The addition of the star‐like modifier led to an improvement on the mechanical characteristics such as the impact strength and microhardness in comparison to the neat material.     

In Situ Encapsulation of Nile Red or Doxorubicin during RAFT‐Mediated Emulsion Polymerization via Polymerization‐Induced Self‐Assembly for Biomedical Applications

Hydrophobic agents, a fluorescent dye (Nile red, NR) or an anticancer drug (doxorubicin, DOX), are encapsulated into poly((N‐[3‐(dimethylamino) propyl] methacrylamide)‐b‐poly (methyl methacrylate) (PDMAPMA‐b‐PMMA) nanoparticles (NPs) via one‐pot reversible addition‐fragmentation chain‐transfer (RAFT)‐mediated emulsion polymerization in water. The macroRAFT, PDMAPMA, is chain‐extended with the methyl methacrylate (MMA), with the hydrophobic agents soluble in MMA, resulting in loaded NPs, with either NR or DOX via polymerization‐induced self‐assembly (PISA). The NR‐loaded NPs are visualized by structured illumination microscopy (SIM), thus indicating the successful loading of the fluorescent dye into the PMMA core. The DOX‐loaded NPs exhibit a sustained release profile over 5 d, showing a small burst effect during the first 2 h, as compared with the free DOX. The DOX‐loaded NPs show higher cell toxicity than the free DOX in RAW 264.7 cell line. The results demonstrate the potential of using emulsion polymerization for synthesis of tailored and reproducible NPs encapsulating hydrophobic agents.     

Anionic Grafting to Strategies for Functional Polymethacrylates: Convenient Preparation of Stimuli‐Responsive Block Copolymer Architectures

Functional block copolymers (BCP) are promising candidates for many important applications in fields of separations technologies, drug delivery, or (nano)lithography. Here, a universal strategy is described for the preparation of functional poly(methacrylate)s grafted (PMA) to polystyrene‐block‐polyisoprene (PS‐b‐PI) BCPs via a convenient postmodification strategy. PS‐b‐PIs are functionalized by means of hydrosilylation protocols for the introduction of chlorosilane moieties. Subsequent anionic grafting‐to polymerization of different functional PMA macro anions leads to grafted BCP. Various functional and non‐functional homopolymers, that is, poly(di(ethylene glycol) methyl ether methacrylate), poly(methacrylic acid), and poly(3‐methacryloxypropyl)heptaisobutyl‐T8‐silsesquioxane as well as poly(methyl methacrylate), poly(n‐butyl methacrylate), poly(iso‐propyl methacrylate), poly(tert‐butyl methacrylate), and poly(2‐hydroxy ethyl methacrylate) are block‐selectively incorporated into the PI segment. Applied grafting strategies for the non‐functional PMA derivatives, which feature different sizes of the alkyl substituent, reveal a strong influence on the grafting‐to efficiency. The grafted BCP architectures are capable of undergoing microphase separation in the bulk state, while the resulting morphology is significantly influenced by the introduction of PMA segments as shown by transmission electron microscopy measurements. Additionally, the structure formation and pH‐switching capability of the poly(methacrylic acid)‐grafted BCP is studied by dynamic light scattering, proving the feasibility for the herein investigated synthesis strategy.     

Anionic polymerization of alkyl methacrylates in the presence of diethylzinc

The anionic polymerizations of methyl methacrylate (MMA), isopropyl methacrylate (IPMA), and tert-butyl methacrylate (TBMA) in THF in the presence of diethylzinc were investigated. The addition of diethylzinc to the reaction mixture remarkably lowers the polymerization rates of the methacrylates initiated with potassium diphenylmethanide to afford polymers with the predicted molecular weights and very narrow molecular weight distributions, while PMMA and poly(IPMA) produced with potassium diphenylmethanide in the absence of diethylzinc have rather broad molecular weight distributions. The stereospecificities of PMMA, poly(IPMA) and poly(TBMA) are not affected by diethylzinc. From the result of the block copolymerization of MMA with TBMA, it was found that the presistency of the anionic propagating end of PMMA is significantly enhanced by the addition of diethylzinc. The retardation of the polymerization rates and the enhancement of the persistency of the propagating end in the presence of diethylzinc may be caused by the weak coordination of diethylzinc toward the enolate anions at the propagating end groups.     

Planet‐Like Nanostructures Formed by an ABC Triblock Terpolymer

A novel planet‐like nanostructure formed by an asymmetric polystyrene‐block‐polyisoprene‐block‐poly(methyl methacrylate) (SIM) triblock terpolymer is presented, where polystyrene (PS) forms spherical microdomains, covered by polyisoprene (PI) rings/helices/polar caps and poly(methyl methacrylate) (PMMA) forms the matrix. The new nanostructure is the result of a thermally induced morphological transition of a kinetically trapped helical nanostructure by thermal annealing above its glass transition temperature. This new nanostructure is observed when the triblock terpolymer solution is cast from chloroform (CHCl₃). When cast from tetrahydrofuran (THF) or toluene, mainly cylindrical and to a lesser extent spherical microdomains are observed. This is caused by a selectivity of the CHCl₃ for the PS and PMMA microdomains. The SIM triblock terpolymer is synthesized by anionic polymerization, and the morphology is characterized by transmission electron microscopy, atomic force microscopy, and small angle X‐ray scattering.     

Self‐Assembled Acrylic ABA Triblock Copolymer Hydrogels with Various Block Compositions: Water Absorbency,Rheology, and SAXS

A series of well‐defined symmetric poly(methyl methacrylate)‐b‐poly(sodium methacrylate)‐b‐poly(methyl methacrylate) (PMMA‐b‐PSMA‐b‐PMMA) triblock copolymers with various block compositions is synthesized. The amphiphilic ABA triblock copolymers form polyelectrolyte hydrogels in water by self‐assembly. The hydrophobic PMMA endblocks act as physical cross‐links in the form of frozen micelles, while the hydrophilic PSMA midblocks span the 3D network. The influence of various synthetic parameters on the self‐assembly and the macroscopic properties of these hydrogels is systematically investigated by water absorbency, oscillatory shear rheology, and small‐angle X‐ray scattering. The polymer concentration during the hydrogel formation affects the ratio between looping and bridging chains. The number of MMA units per endblock (n_A) determines the size and the relaxation rates of the physical cross‐links and thus, the mechanical stability of the hydrogels. More SMA units in the midblock (n_B) increase the water absorbency, while the mechanical moduli decrease. Even lower G‐moduli are achieved by partly exchanging the symmetric ABA triblock with AB diblock copolymers, which can only form non‐elastic dangling ends.     

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.     

Synthesis of Block Copolymers Containing Polybutadiene Segments by Combination of Coordinative Chain Transfer Polymerization,Ring‐Opening Polymerization,and Atom Transfer Radical Polymerization

Two triblock copolymers, polybutadiene‐block‐poly(ε‐caprolactone)‐block‐poly(methyl methacrylate) (PBD‐b‐PCL‐b‐PMMA) and polybutadiene‐block‐poly(ε‐caprolactone)‐block‐polystyrene (PBD‐b‐PCL‐b‐PS), are synthesized by combination of coordinative chain transfer polymerization (CCTP), ring‐opening polymerization (ROP), and atom transfer radical polymerization (ATRP). The molecular structures of these polymers are determined by ¹H NMR and gel‐permeation chromatography (GPC) analysis. The resulting triblock copolymers are evaluated as compatibilizing agents for highly immiscible binary PBD/PMMA and PBD/PS blends. The presence of these compatibilizers substantially reduces the average PMMA or PS droplet size. Furthermore, static water contact angle experiments are employed to assess the modification of the surface properties of nonpolar PBD.

     

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.

     

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.     

Metal-Free Atom Transfer Radical Polymerization of PVDF-Based Block Copolymers Catalyzed by Organic Photoredox Catalysts

Poly(vinylidene fluoride) (PVDF) and its copolymers represent a class of electroactive fluoropolymers with very attractive piezo/ferroelectric properties that can be chemically modified to achieve high-quality composites with improved properties. Here, the synthesis of poly(methyl methacrylate)-b-poly(vinylidene fluoride)-b-poly(methyl methacrylate) (PMMA-b-PVDF-b-PMMA) triblock copolymers via metal-free light-catalyzed atom transfer radical polymerization (ATRP) using organic photoredox catalysts (OPRC) and light of suitable wavelength is reported. Using benzoyl peroxide bearing an ATRP active group at both ends of the molecule, telechelic PVDF is synthesized, and is used as a macroinitiator in the metal-free, light-catalyzed ATRP in presence of methyl methacrylate (MMA), an OPRC, and light of suitable wavelength. Kinetic studies are performed by monitoring the monomer consumed in solution and by using ¹H-NMR to calculate the formation of the new PMMA blocks. Three of the five tested OPRC, operating through an oxidative quenching pathway, guarantee a good control over the polymerization, confirmed by the constant concentration of radicals during the process and by the linear growth of the conversion versus the percentage of monomer consumed. Chain extension reactions are also performed to prove chain-end fidelity, as well as “light ON/light OFF” reactions to test the temporal control guaranteed by the external stimuli used to catalyze the polymerization.     

Temporally Controlled Ultrasonication‐Mediated Atom Transfer Radical Polymerization in Miniemulsion

Due to the increasing requirement for more environmentally and industrially relevant approaches in macromolecules synthesis, ultrasonication‐mediated atom transfer radical polymerization (sono‐ATRP) in miniemulsion media is applied for the first time to obtain precisely defined poly(n‐butyl acrylate) (PBA) and poly(methyl methacrylate) (PMMA) homopolymers, and poly(n‐butyl acrylate)‐block‐poly(tert‐butyl acrylate) (PBA‐b‐PtBA) and poly(n‐butyl acrylate)‐block‐poly(butyl acrylate) (PBA‐b‐PBA) copolymers. It is demonstrated in the reaction setup with strongly hydrophilic catalyst copper(II) bromide/tris(2‐pyridylmethyl)amine (Cu^IIBr₂/TPMA) responsible for two principal mechanisms – interfacial and ion‐pair catalysis reflecting single‐catalyst approach. This solution turns out to be an excellent tool in controlled preparation of well‐defined polymers with narrow molecular weight distribution (up to Ð = 1.28) and preserves chain‐end functionality (DCF = 0.02% to 0.32%). Temporal control over the polymer chain growth is successfully conducted by turning the ultrasonication on/off. Taking into consideration long OFF stage (92.5 h) during ultrasonication‐induced polymerization in miniemulsion, synthesis is efficiently reinitiated without any influence on controlled characteristics maintaining the precise structure of received PBA homopolymers, confirmed by narrow molecular weight distribution (Ð = 1.26) and high retention of chain‐end functionality (DCF = 0.01%). This procedure constitutes an excellent simple and eco‐friendly approach in preparation of functional polymeric materials.     

Chain transfer polymerization of methyl methacrylate initiated by organolanthanide complexes

A novel chain transfer polymerization mediated by Cp*₂ Sm(III) species and organic acids is described. The chain transfer polymerization involves the reaction of organic acids such as thiols or ketones with an active bond between samarium(III) and the enolate at a living chain end of poly(methyl methacrylate) (PMMA). This chain transfer reaction resulted in termination of the living chain end and the regeneration of the active initiator which would consist of (C₅Me₅)₂Sm(III) and deprotonated organic acids. The chain transfer polymerization were confirmed by turnover numbers (TON). tert‐Butyl thiol exhibited the chain transfer reactivity effectively to control the molecular weight of PMMA without decreasing of the polymer yield and the stereoregularity. As a result of this chain transfer polymerization, thermal and optical properties of the PMMA obtained were improved by the control of chain end groups or by reducing a large amount of the samarium initiator.     

Functional Surfaces Constructed with Hyperbranched Copolymers as Optical Imaging and Electrochemical Cell Sensing Platforms

In the present study, hyperbranched copolymers (HBCs), namely poly(methyl methacrylate) (PMMA)‐co‐poly(2‐hydroxyethylmethacrylate) and PMMA‐co‐poly(2‐dimethylamino ethyl methacrylate), are photochemically synthesized by self‐condensing vinyl polymerization of methyl methacrylate with the corresponding inimer using Type II photoinitiators. HBCs with different functional group and branching densities are used as surface coating materials in cellular adhesion and the respective electrochemical‐based studies. After the main surface characterization of the synthesized three HBCs with contact angle measurements and atomic force microscopy, HaCaT keratinocytes and human neuroglioblastoma (U‐87MG) cell lines to the surfaces are conducted. The adherence of cells is proven by both fluorescence cell imaging and electrochemical methods such as cyclic voltammetry and differential pulse voltammetry. The described strategy involving hyperbranched polymers offers great potential for fabricating various new surfaces in particular “on‐chip‐sensing” applications.     

Synthesis of Block Copolymers Based on Polyethylene by Thermally Induced Controlled Radical Polymerization Using Mn2(CO)10

Iodo functionalized polyethylene (PE‐I), prepared by the addition of iodine after catalyzed poly­ethylene chain growth on magnesium, is demonstrated to be an efficient macroinitiator for thermally induced, controlled free radical polymerization using dimanganese decacarbonyl (Mn₂(CO)₁₀). The free radical polymerization of methyl methacrylate is initiated by thermal homolysis of (Mn₂(CO)₁₀) at 80 °C, forming reactive manganese pentacarbonyl radical species [?Mn(CO)₅] capable of activating the C?I bond of PE‐I. The metal catalyzed radical generation and degenerative iodine processes yielded polyethylene‐b‐poly(methyl methacrylate) (PE‐b‐PMMA) block copolymers with relatively low dispersities. The end group functionality of the block copolymer is confirmed by the successful thermal polymerization of styrene by using PE‐b‐PMMA as a macro­initiator in the described process. This work conclusively provides a new approach for combining polyethylene with vinyl polymers via manganese chemistry in a simple and efficient pathway of importance in synthetic polymer chemistry and other related applications.

     

Time‐Resolved Emission Anisotropy of Anthracene Fluorophore in the Backbone of Stereoregular Poly(methyl methacrylate)

Syndiotactic fluorescent poly(methyl methacrylate) labeled with anthracene in the middle of the polymer chain was prepared by living anionic polymerization (s‐PMMA‐A). Absorption and emission transition moments of the label are oriented in the direction of the polymer backbone, therefore the fluorophore really reflects the mobility of polymer segments. Stereocomplex formation between isotactic poly(methyl methacrylate) (i‐PMMA) and s‐PMMA‐A was studied by time‐resolved fluorescence depolarization method in solvents with different complexing ability and at different i‐PMMA/s‐PMMA‐A ratios. The stoichiometry of the stereocomplex i‐PMMA/s‐PMMA‐A was 1/2 and 1/1.5 in N,N‐dimethylformamide and 1,4‐dioxane, respectively. The stereocomplex was not formed in chloroform. Determination of the rotational correlation times at different temperatures enabled us to evaluate the height of the potential barrier to rotational motion of the anthracene fluorophore (ΔU_r) or activation enthalpy and entropy (ΔH^≠, ΔS^≠) of this process in the presence and absence of the stereocomplex. Time‐resolved emission anisotropy data, r (t), were analyzed by intermediate zone formula of the torsion dynamics theory for stiff macromolecules. The torsional rigidity of the stereocomplex i‐PMMA/s‐PMMA‐A, α = 1.9×10^–18 N·m in N,N‐dimethylformamide at 30°C, is larger than that obtained for DNA (α = 3.8×10^–19 N·m). Self‐aggregation of s‐PMMA takes place probably in N,N‐dimethylformamide.     

The Use of ε‐Caprolactone as a Polymerizable Solvent for the Atom Transfer Radical Polymerization of MMA at Low Temperature

This paper reports on the decisive effect that solvent has on the atom transfer radical polymerization of methyl methacrylate (MMA) at low temperature. In butanone and in the presence of a copper(I)/bipyridine complex, the polymerization is controlled and the molecular weight distribution is narrow, at 0°C and even lower. This control is maintained when ε‐caprolactone (CL) is substituted for butanone. The use of this polymerizable solvent together with a novel dual initiator, 2‐hydroxyethyl, 2′‐methyl‐2′‐bromopropionate, is an efficient strategy to prepare PMMA‐b‐PCL diblock polymers in a one‐pot process.     

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.     

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.     

The Synthesis of Liquid Crystalline Copolymers with Block Copolymer Grafts

The synthesis of novel copolymers consisting of a side‐group liquid crystalline backbone and poly(tetrahydrofuran)‐poly(methyl methacrylate) block copolymer grafts was realized by using cationic‐to‐free‐radical transformation reactions. Firstly, photoactive poly(tetrahydrofuran) macroinimers were prepared by cationic polymerization of tetrahydrofuran and subsequent termination with 2‐picoline N‐oxide. Secondly, the macroinimers and acrylate monomers containing different spaced cyanobiphenyl mesogenic groups were copolymerized to yield the respective graft copolymers. Eventually, these were used for indirect photochemical polymerization of methyl methacrylate by UV irradiation in the presence of anthracene as a photosensitizer leading to the final copolymers with block copolymer grafts. The liquid crystalline, semicrystalline, and amorphous blocks were micro‐phase separated in the graft copolymers.