End-functionalized Polystyrene Research Articles

Compatibilization of Polymer Blends by Ionic Bonding

Chemically dissimilar polymers are rarely miscible due to a specific entropy of mixing that scales as 1/N, where N is the degree of polymerization. As a consequence, the compatibilization of immiscible polymer blends presents a major challenge to plastics recycling efforts. We demonstrate that when the chain ends of two highly immiscible polymers are functionalized with reacting acid and base groups, ionic junctions form in situ by proton transfer, leading to the stabilization of interfaces and the suppression of macroscopic phase separation. Due to the dynamic nature of proton transfer, the microstructure can be tuned via ionic bond energy (h) and segregation strength (χN). In this work, a library of ionically end-functionalized polystyrene (PS) and polydimethylsiloxane (PDMS) is used to demonstrate the importance of end-group acidity/basicity and molecular weight on compatibilization. Well-ordered lamellae result from blending polymers with strong acid and base units, while less ordered, more swollen microphases occur in systems with weak acid and base end groups or larger molar mass. Heating the ionic blends results in reverse proton transfer and destruction of the close-contact ion pairs. As a result, domains are swollen with the resulting unbonded homopolymers, which in sufficient amounts, leads to macrophase separation. Moreover, external salt ions screen the electrostatic attractions and disturb ionic compatibilization. The self-consistent field theory (SCFT) of this system reveals that the ionic interactions can be tuned to create a broad range of morphologies, from microphases to macrophases.

Facile, scalable, and universal modification strategy of polyolefin utilizing noncatalytic C[sbnd]H insertion capability of azide: Sulfonyl azide end-functionalized polystyrene to modify polyethylene

Despite a broad range of commercial uses, applications of polyolefins have often been limited because of a lack of functionality and structural diversity, which has sparked the motivation to modify polyolefins, especially postpolymerization modifications (PPMs). The CH insertion capability of nitrene intermediates has been of interest due to its universal applicability to organic macromolecules containing CH bonds. In this study, a sulfonyl azide (SA) end-functionalized polystyrene (SAPS) is prepared as a model compound by synthesizing a SA containing azo-type radical initiator. SAPS is then used to modify commercial grade high-density polyethylene (HDPE) through simple melt process, affording HDPE-graft-polystyrene. The material exhibits homogeneous fractured surface, decreased crystallinity value, increased complex viscosity value, and relatively high Young’s modulus value, suggesting the formation of the polymer hybrids. This study demonstrates the capability of SA end-functionalized polymers as a noncatalytic platform for the PPM of polyolefins.

Synthesis and antimicrobial activity of chalcone containing polystyrene

Three different 4-propargyloxychalcones have been prepared starting from 4-propargyloxy benzaldehyde and chalcones with proper chemical transformation. Polystyrenes containing biologically active chalcone moiety in their structures have been successfully synthesised by the Click reaction from the 4-propargyloxychalones (terminal alkyne) and azido end-functional polystyrene (PS-N 3 ). All the desired products have been obtained with good yield and purity. The structure of the 4-propargyloxychalcones and the chalcone containing polystyrenes have been characterized by FT-IR, 1 H NMR and UV-Vis spectroscopy. The antibacterial activity of the synthesized 4-propargyloxychalcones their polystyrene derivatives have been evaluated against two bacterial strains, Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative). The results reveal that the tested chalcones and their polystyrene derivatives have moderate antimicrobial activity.

Synthesis of azido end-functional polystyrene: Azidoethyl-2-bromo-2-methylpropanoate initiator and effect of time on polymerization

Azidoethyl-2-bromo-2-methylpropanoate (AEBMP) has been synthesized from 2-azidoethanol and 2-bromo-2-methylpropionyl bromide under nitrogen atmosphere. The azido end-functional polystyrene (PS-N 3 ) has been synthesized by Atom Transfer Radical Polymerization (ATRP) technique using AEBMP initiator and styrene in conjugation with Cu(1)Br-bipyridine catalyst at 100°C. The polymerization was performed at three different periods of time, and it was found that both yield and number average molecular weight were increased linearly with increasing reaction time. Thermogravimetric analysis showed that the polystyrene is stable up to 300°C. The molecular weight of the polystyrene was determined using Gel Permeation Chromatography (GPC), and structures of the initiator AEBMP and polystyrene (PS-N 3 ) were characterized by 1 H NMR and FT-IR spectroscopy.

Noncovalent Supramolecular Diblock Copolymers: Synthesis and Microphase Separation.

Supramolecular block copolymers (PS-DAT-sb-PI-Thy) were synthesized via noncovalent hydrogen bonding between well-defined thymine end-functionalized polyisoprene (PI-Thy) and diaminotriazine (DAT) end-functionalized polystyrene (PS-DAT). Three covalently linked block copolymers were also synthesized for comparison with the noncovalent supramolecular block copolymers. The complementary DAT/Thy interaction resulted in the microphase separation of the supramolecular block copolymer system. Detailed characterization of all functionalized homopolymers and block copolymers was carried out via proton nuclear magnetic resonance (1H NMR) spectroscopy, gel permeation chromatography, matrix-assisted laser desorption/ionization-time of flight mass spectrometry, and differential scanning calorimetry. The self-assembly process of supramolecular block copolymers was evidenced by transmission electron microscopy. Small-angle X-ray scattering was also performed to study the microphase separation of supramolecular and covalently linked block copolymers. Comparison of microphase separation images of supramolecular block copolymers and the corresponding covalently linked analogues reveals differences in d-spacing and microdomain shape.

Synthesis of Conjugated Rod–Coil Block Copolymers by RuPhos Pd-Catalyzed Suzuki–Miyaura Catalyst-Transfer Polycondensation: Initiation from Coil-Type Polymers

A novel coil-first/grafting-from approach was developed for the synthesis of conjugated rod–coil block copolymers using RuPhos Pd-catalyzed Suzuki–Miyaura catalyst-transfer polycondensation (SCTP). First, aryl iodide end-functionalized polystyrene (PS) was prepared as a macroinitiator for SCTP via atom transfer radical polymerization (ATRP) followed by sequential end-group modifications, azidation, and click reactions. Then, RuPhos Pd-catalyzed SCTP using the PS macroinitiator was carried out in the presence of N-methyliminodiacetic acid boronate-containing 3-hexylthiophene monomer (M1), and this afforded well-defined PS-block-poly(3-hexylthiophene) with excellent control and high yield. The scope of this method was successfully expanded to include poly(methyl acrylate)-, poly(methyl methacrylate)-, and poly(ethylene oxide)-block-poly(3-hexylthiophene) with controlled molecular weight and low dispersity. Further, the combination of the conventional rod-first and newly developed coil-first approaches facilitated the straightforward synthesis of a unique ABC-type rod–coil–rod triblock copolymer that was limitedly accessible by other methods. We believe that this efficient and readily accessible synthetic platform would be highly useful for the preparation of novel conjugated rod–coil block copolymers that can be applied in optoelectronics, battery engineering, and chemical sensing.

Complexes of end-functionalized polystyrenes carrying amine end-group with transition metals: association effects in organic solvents

Linear end-functionalized polystyrenes of different molecular weights bearing amino end-group (NPS) were synthesized by anionic polymerization high vacuum techniques. The polymers were exposed to copper and iron salts (CuCl2.2H2O and FeCl3.6H2O) to form complexes with specific metal/amino molar ratios. The thermal stability of these complexes was studied by Thermogravimetric Analysis (TGA) and Differential Thermogravimetry (DTG), whereas their solution behavior was studied by Low Angle Laser Light Scattering (LALLS), Dynamic Light Scattering (DLS) and dilute solution Viscometry. Extended aggregation phenomena of these complexes were observed in organic solvents. The association behavior was influenced by the molecular weight of the polymer chain, the metal/amine group molar ratio, the chemical nature of the metal and the polarity of the solvent. A complex situation was revealed by DLS showing the existence of equilibrium between aggregates and clusters. Under the influence of shear forces applied in the capillary tube of the viscometer the clusters are disrupted.

Synthesis of Polystyrene-Coated Superparamagnetic and Ferromagnetic Cobalt Nanoparticles.

Polystyrene-coated cobalt nanoparticles (NPs) were synthesized through a dual-stage thermolysis of cobalt carbonyl (Co2(CO)8). The amine end-functionalized polystyrene surfactants with varying molecular weight were prepared via atom-transfer radical polymerization technique. By changing the concentration of these polymeric surfactants, Co NPs with different size, size distribution, and magnetic properties were obtained. Transmission electron microscopy characterization showed that the size of Co NPs stabilized with lower molecular weight polystyrene surfactants (Mn = 2300 g/mol) varied from 12–22 nm, while the size of Co NPs coated with polystyrene of middle (Mn = 4500 g/mol) and higher molecular weight (Mn = 10,500 g/mol) showed little change around 20 nm. Magnetic measurements revealed that the small cobalt particles were superparamagnetic, while larger particles were ferromagnetic and self-assembled into 1-D chain structures. Thermogravimetric analysis revealed that the grafting density of polystyrene with lower molecular weight is high. To the best of our knowledge, this is the first study to obtain both superparamagnetic and ferromagnetic Co NPs by changing the molecular weight and concentration of polystyrene through the dual-stage decomposition method.

Perfluoroalkyl end-functionalized polystyrene show lower glass transition temperatures. DSC and optical transmission studies

A series of polystyrenes (10-30k) end-functionalized with perfluoroalkyl (RF = C7F16, C10F21 and C13F27) groups were synthesized by atom transfer radical polymerization (ATRP) of styrene initiated by RF functionalized initiators and studied using optical transmission, differential scanning calorimetry and thermogravimetric analysis. Large decreases (≤40–50%) in optical transmission of the C13F27 end functionalized PS were observed compared with the non-functionalized isobaric PS consistent with the formation of large RF domains. This association increases with RF concentration and length with the latter being especially significant. A melting endotherm attributed to semi-crystalline perfluorocarbon domains was seen only for a low MW(10k) C13F27 end functionalized sample. Interestingly, compared with the matching PS, the glass transition temperatures of the RF-PS polymers were found to decrease by as much as 15 °C and with the RF lengths having the larger effects.

Liquid Tubule Formation and Stabilization Using Cellulose Nanocrystal Surfactants.

Structured liquids, generated by the interfacial formation, assembly, and jamming of nanoparticle (NP)-surfactants at liquid/liquid interfaces, maintain all the desirable characteristics of each liquid, while providing a spatially structured framework. Herein, we show that rod-like cellulose nanocrystal (CNC)-based NP-surfactants, termed CNC-surfactants, are formed rapidly at the liquid/liquid interface, assemble into a monolayer, and, when jammed, offer a robust assembly with exceptional mechanical properties. Plateau-Rayleigh (PR) instabilities of a free-falling jet of an aqueous medium containing the CNCs into a toluene solution of amine end-functionalized polystyrene are completely suppressed, allowing the jetting of aqueous tubules that are stabilized when the CNC-surfactants are jammed at the interface. These results open a new platform for the additive manufacturing techniques, for example, three-dimensional (3D) printing, of all-liquid constructs.

Precise molecular weight determination and structure characterization of end-functionalized polymers: An NMR approach via combination of one-dimensional and two-dimensional techniques

We present here the application of one-dimensional and two-dimensional NMR techniques to characterize the structure of methoxyl end-functionalized polystyrenes (PS). The peaks in 1H-NMR spectra corresponding to main-chain, side-chain and chain-end groups are assigned by 1H-1H gCOSY, 1H-13C gHSQC and gHMBC spectra. For the first time, the spin-lattice relaxation time (T1) of protons of the chain-ends is revealed to be affected more by polymer molecular weight (MW) than by the protons of the main-chains and the side-chains (almost independent from MW). As a result, a much higher delay time (d1) for chain-ends (d1 > 20T1) is needed for quantitative NMR measurement when using end-group estimation method to obtain the MW of PS, which is in accordance with the value estimated by GPC. An improved method for the polymer MW determination is established, by combination of different NMR techniques to distinguish the peaks, and a large d1 setting to achieve quantitative NMR analysis.

Preparation of Protein Nanoparticles Using NTA End Functionalized Polystyrenes on the Interface of a Multi-Laminated Flow Formed in a Microchannel

This paper challenges the production of the protein nanoparticles using the conjugation of Ni2+ complexed nitrilotriacetic acid end-functionalized polystyrene (Ni-NTA-PS) and histidine tagged GFP (His-GFP) hybrid. The microfluidic synthesis of the protein nanoparticle with the advantages of a uniform size, a fast reaction, and a precise control of preparation conditions is examined. The self-assembly occurs on the interfacial surface of the multi-laminated laminar flow stably formed in the microchannel. The clogging of the produced protein nanoparticles on the channel surface is solved by adding a retarding inlet channel. The size and shape of the produced protein nanoparticles are measured by the analysis of transmission electron microscopy (TEM) and scanning electron microscope (SEM) images, and the attachment of the protein is visualized with a green fluorescent image. Future research includes the encapsulation of vaccines and the coating of antigens on the protein surface.

Kinetic Studies on Bulk Atom Transfer Radical Polymerization of Styrene

The long chain vinyl end-functional polystyrene has been synthesized in bulk polymerization method using atom transfer radical polymerization (ATRP) with Undecenyl-2-Bromopropionate (UnBP) and CuCl/bypyridine catalytic system. The polymerizations demonstrate an increase in molecular weight and conversion in direct proportion to the polymerization time by consumed monomer which exhibited first-order kinetics. This study concludes the simple kinetics of polystyrene synthesized by ATRP using initiator and ligand-to-copper(I) halide was found to be 1:2:1, which tentatively indicates that the coordination sphere of the active copper(I) center contains two bipyridine ligands. The propagation rate has been investigated for long range of time for ensuring that the rate of radical combination or disproportionation is sufficiently less.

Effects of molecular weight distribution on the self-assembly of end-functionalized polystyrenes

The molecular weight distribution of hydroxyl-end-functionalized polystyrenes shows effects on the self-assembly of patterned porous films and the mechanical strength.

Precise Synthesis and Surface Characterization of End‐Functionalized Polystyrene with Perfluoroalkyl Group via Ionic Bond Formation of Diethylamino End‐Group with Perfluoroalkylcarboxylic Acid

Well‐defined polystyrene end‐functionalized with N,N‐diethylamino group (PS‐NEt2) is prepared by a living anionic polymerization of styrene, followed by an end‐capping reaction with a 1,1‐diphenylethylene derivative bearing with the corresponding functional group. The PS‐NEt2 is applied for the reaction with C8F17COOH in order to introduce the ionic‐bonded C8F17 group, i.e., C8F17COO−N+H(C2H5)2 at the polymer chain end. Surface characterization of the resulting polymer film is performed by an X‐ray photoelectron spectroscopy and a contact angle measurement. These results clearly show that the C8F17COO−N+H(C2H5)2 end‐group concentrates at the top of film surface similar to the original C8F17 group. The ionic‐bonded C8F17COOH is found to be removed by a treatment of the film surface with methanol. Moreover, the C8F17COO−N+H(C2H5)2 end‐group that remained inside film appears at the top of film surface by annealing the methanol‐treated film, indicating the surface reconstruction by environmental changes. image

The architecture of the adsorbed layer at the substrate interface determines the glass transition of supported ultrathin polystyrene films.

To elucidate the mechanism underlying the effect of polymer/solid interfacial interactions on the dynamics of thin polymer films, the glass transition of thin end-functionalized polystyrene films supported on SiO2-Si, such as proton-terminated PS (PS-H), α,ω-dicarboxy-terminated PS (PS-COOH), and α,ω-dihydroxyl-terminated PS (PS-OH), was investigated. All the PS films exhibited a substantial depression in Tg with decreasing film thickness, while the extent of such depression was strongly dependent on the chemical structure of the end groups and molecular weights. It was found that T - T of the various PS films increased linearly with increasing hads/Rg, in which hads is the thickness of the interfacial adsorbed layer and Rg is the radius of gyration of PS. The hads/Rg is a direct reflection of the macromolecular chain conformation within the adsorbed layer which was affected by its end groups and molecular weights. These findings are in line with the work of Napolitano, and present direct experimental evidence.

Synthesis of Well-Defined Vinyl End-Functional Polystyrene Using Multifunctional Initiator by Atom Transfer Radical Polymerization

Atom Transfer Radical Polymerization (ATRP) has proven to be a powerful technique to obtain polymers with narrow polydispersities and controlled molecular weight. It also offers control over chain-ends. N-allyl-2-bromopropinamide (ABPN) was synthesized by one step reaction which involved on amidification of 2-bromo-propionyl bromide with allyl amine. 1H NMR has confirmed the structure of the ABPN. The well-defined polystyrene was synthesized by using ABPN as initiator in ATRP method. The results of the polymerization were significantly affected by reaction conditions. The vinyl end-functional polystyrene obtained was characterized by Gel Permeation Chromatography (GPC) and NMR analysis.

Interpenetration of chemically identical polymer onto grafted substrates

Interpenetrating interfaces between a deuterated polystyrene (dPS) and the grafted substrates with the same chemical identity were characterized using neutron reflectivity (NR) measurements, where the PS-grafted substrates were prepared using a grafting-to approach with hydroxyl end-functionalized polystyrene (PSOH) in a dry brush regime. The characteristic brush thickness (h) and grafting density (σ) of PS-grafted layers were determined based on the chain length (or molecular weight, Mn) of PSOHs. The experimental interpenetration length (ξ) was measured at the interfaces, and the limiting plateau in ξ above which the value was independent of film thickness shifted toward higher values as the Mn of PSOH increased. Normalization by the deformed brush thickness (hd) of PS-grafted layer after interpenetration revealed that the experimental value of ξ/hd in a short and dense PS-grafted substrate, prepared with a low-molecular-weight PSOH, deviated markedly from the theoretical value, indicating significant additional stretching of the grafted chains to accommodate inter-mixing with the dPS chains.

Preparation of polyethylene-graft-clay nanocomposites using Friedel–Crafts alkylation reaction as a new method

The main objective of this study was chemical grafting of polyethylene (PE) chains onto clay surfaces in PE/clay nanocomposites. Clay (Cloisite 30B) particles were successfully modified using a laboratory-synthesized carboxylic acid end-functionalized polystyrene (F-PS) and a commercial styrene–maleic anhydride copolymer (SMA). SMA showed higher grafting efficiency than F-PS. It is related to lower molecular weight and higher compatibility of SMA with Cloisite 30B particles. Both modified Cloisite 30B particles were used in preparation of PE nanocomposites where AlCl3 catalyst was used for chemical grafting of PE chains onto polystyrene (PS) or SMA chains, pendant from the clay particles surfaces. Using AlCl3 increased the storage modulus and decreased the damping factor, particularly at low-frequency ranges. It was related to the chemical grafting of the PE chains onto the PS segments of the SMA copolymer and the PS chains of F-PS on the clay particle surfaces via Friedel–Crafts alkylation reaction. Catalyzed nanocomposites showed better clay dispersion than those of the plain nanocomposites. It is believed that chemical grafting of PE chains onto clay particles surfaces provided effective stress transfer from PE matrix to clay tactoids resulting in delamination and higher degree of clay exfoliation.

Star polymers by photoinduced copper-catalyzed azide-alkyne cycloaddition click chemistry

Well-defined star polymers consisting of tri-, tetra-, or octa-arms have been prepared via coupling-onto strategy using photoinduced copper(I)-catalyzed 1,3-dipolar cycloaddition click reaction. An azide end-functionalized polystyrene and poly(methyl methacrylate), and an alkyne end-functionalized poly(ε-caprolactone) as the integrating arms of the star polymers are prepared by the combination of controlled polymerization and nucleophilic substitution reactions; whereas, multifunctional cores containing either azide or alkyne functionalities were synthesized in quantitatively via etherification and ring-opening reactions. By using photoinduced copper-catalyzed azide–alkyne cycloaddition (CuAAC) click reaction, reactive linear polymers are simply attached onto multifunctional cores to form corresponding star polymers via coupling-onto methodology. The chromatographic, spectroscopic, and thermal analyses have clearly demonstrated that successful star formations can be obtained via photoinduced CuAAC click reaction. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1687–1695