One‐Reactant Photografting of ATRP Initiators for Surface‐Initiated Polymerization

Self‐initiated photografting polymerization is used to couple the polymerizable initiator monomer 2‐(2‐chloropropanoyloxy)ethyl acrylate to a range of polymeric substrates. The technique requires only UV light to couple the initiator to surfaces. The initiator surface density can be varied by inclusion of a diluent monomer or via selection of initiator and irradiation parameters. The functionality of the initiator surface is demonstrated by subsequent surface‐initiated atom transfer radical polymerization. Surfaces are characterized by x‐ray photoelectron spectroscopy (XPS), ellipsometry, and atomic force microscopy (AFM), and UV‐induced changes to the initiator are assessed by ¹H NMR and gel permeation chromatography (GPC). This is the first time this one‐reactant one‐step technique has been demonstrated for creating an initiator surface of variable density.

     

Palladium‐Mediated Surface‐Initiated Kumada Catalyst Polycondensation: A Facile Route Towards Oriented Conjugated Polymers

Palladium‐mediated surface‐initiated Kumada catalyst transfer polycondensation is used to generate poly(3‐methyl thiophene) films with controlled thickness up to 100 nm. The palladium initiator density is measured using cyclic voltammetry and a ferrocene‐capping agent, where the surface density is found to be 55% (1.1 × 10¹⁴ molecules per cm²). UV–Vis spectroscopy and AFM show increased aggregation in palladium‐initiated films due to the higher grafting density of palladium initiators on the surface. The anisotropy of the P3MT films is determined using polarized UV–Vis spectroscopy, which indicates a degree of orientation perpendicular to the substrate. Evidence that palladium can maintain π‐complexation even at elevated temperatures, is also shown through the exclusive intramolecular coupling of both a phenyl and thiophene‐based magnesium bromide with different dihaloarenes.     

Formation of Silica/Poly(p‐dioxanone) Microspheres by Surface‐Initiated Polymerization

A polymeric film of a biodegradable poly(p‐dioxanone) was grown from 490 nm silica particles by monolayer formation via self‐assembly of hydroxy‐terminated triethoxysilane and subsequent surface‐initiated ring‐opening polymerization of p‐dioxanone. The resulting silica/poly(p‐dioxanone) hybrid particles were characterized by means of ¹H NMR spectroscopy, IR spectroscopy, thermogravimetric analysis, field‐emission scanning electron microscopy, and energy‐dispersive X‐ray spectroscopy.

     

Hairy PEO‐Silica Nanoparticles through Surface‐Initiated Polymerization of Ethylene Oxide

Summary: The grafting of poly(ethylene oxide) (PEO) onto silica nanoparticles was performed in situ by the ring‐opening polymerization of the oxirane monomer initiated from the mineral surface using aluminium isopropoxide as an initiator/heterogeneous catalyst. Alcohol groups were first introduced onto silica by reacting the surfacic silanols with prehydrolyzed 3‐glycidoxypropyl trimethoxysilane. The alcohol‐grafted silica played the role of a coinitiator/chain‐transfer agent in the polymerization reaction and enabled the formation of irreversibly bonded polymer chains. Silica nanoparticles containing up to 40 wt.‐% of a hairy layer of grafted PEO chains were successfully produced by this technique.

The grafting of poly(ethylene oxide) (PEO) onto silica nanoparticles by in‐situ ring‐opening polymerization of the oxirane monomer.     

Factors Affecting Grafting Density in Surface‐Initiated ATRP: A Simulation Study

In surface‐initiated atom transfer radical polymerization, knowledge of grafting density is of significant interest because it is one of the determining properties of grafted polymer. It is well known that not all of the immobilized initiators can grow into polymer chains. However, little is known about why this happens and what affects the grafting efficiency. The lack of information is partly due to the difficulty in experimental determination of grafting density on flat substrates. To circumvent the problem, Monte Carlo simulation with bond fluctuation model is used in this study to investigate the effects of various reaction conditions on the grafting density. The simulation results show lower grafting density when less deactivator is present. In systems with lower deactivator concentration, the number of monomer added per activation cycle is higher. Coupling this with close proximity of immobilized initiators results in chains initiated at earlier time to shield their neighboring initiator moieties from adding mono­mers, thus lowering the grafting density in such a system. These simulation results also provide an explanation to the seemingly conflicting trend reported in the literatures.

     

Polymer‐Grafted Carbon Spheres by Surface‐Initiated Atom Transfer Radical Polymerization

Summary: In situ atom transfer radical polymerization techniques have been used to produce polymer‐grafted carbon spheres (CSs). The surfaces of as‐prepared CSs were functionalized in the presence of CS‐supported macroinitiators. The resulting materials were characterized by FTIR and NMR spectroscopy, TGA, SEM, TEM, and HRTEM. The amount of polymer grafted onto the surfaces of the spheres can be controlled by varying the monomer/initiator feed ratio. The wetting ability and dispersibility of the polymer‐grafted CSs were improved significantly, compared with crude CSs, enabling stable dispersions in organic solvents to be produced. SEM and TEM studies indicate that a uniform distribution of the carbon spheres in the continuous polymer phase can be produced.

SEM image (left) of poly(glycerol monomethacrylate) grafted carbon spheres, inset shows the structure. HRTEM image (right) of a polystyrene grafted carbon sphere, inset is the SAED pattern.     

Fabrication of Micropatterned Gold Nanoparticle Arrays as a Template for Surface‐Initiated Polymerization of Stimuli‐Responsive Polymers

Summary: This paper demonstrates a new, reliable, and simple method for fabricating micropatterned nanoparticle arrays that can serve as templates for the surface‐initiated polymerization of polymer brushes. As a proof of concept, we micropatterned gold nanoparticles (Au‐NPs, ≈10 nm) onto glass, silicon, polystyrene, and gold surfaces by a simple three‐step process: (1) microcontact printing of soluble polymer, (2) incubation with a solution of Au‐NPs, and (3) lift‐off of the template in a mixture of ethanol and deionized water. 40 µm wide features were successfully fabricated without any significant defects or nonspecific adsorption on the background. To demonstrate the utility of these Au‐NP templates, we subsequently polymerized N‐isopropylacrylamide by surface‐initiated polymerization, using a surface‐bound initiator.

Synthesis of PNIPAAm brushes from micropatterned Au‐NP.     

Superhydrophobic Polypropylene Surfaces Prepared with TiO2 Nanoparticles Functionalized by Dendritic Polymers

Hybrid inorganic–organic nanomaterials have received increasing interest due to the possibility of implementing different functions and characteristics within a single material. Their functionalities are a consequence of the synergy of the properties of distinct building blocks and are related to their varied natures and spatial locations. In this work, we present the development of superhydrophobic properties on polypropylene (PP) surfaces using hybrid nanomateriales from TiO₂ nanoparticles (NPs) and dendronized polymers. The dendron acryl Behera's amine was successfully grafted on the TiO₂ NP surfaces by Surface‐Initiated Atom Transfer Radical Polymerization (SI‐ATRP) and a core‐brush material was obtained. Finally, PP substrates were coated with NP hybrids to produce superhydrophobic surfaces with water contact angles of over 158 degrees. Controlling the organic silane concentration on the TiO₂ NPs allowed the dendronized process to be driven and thereby permitted the selection of specific wettability properties on PP substrate surfaces with high water adhesion or self‐cleaning conditions. This dendronized effect with consequent steric congestion of the polymeric brushes on the NPs changed their behaviors from Wenzel to the Cassie Baxter state. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2019–2029     

Bio‐Inspired Renewable Surface‐Initiated Polymerization from Permanently Embedded Initiators

Herein, we describe a simple and robust approach to repeatedly modify surfaces with polymer brushes through surface‐initiated atomic transfer radical polymerization (SI‐ATRP), based on an initiator‐embedded polystyrene sheet that does not rely on specific surface chemistries for initiator immobilization. The surface‐grafted polymer brushes can be wiped away to expose fresh underlying initiator that re‐initiates polymerization. This strategy provides a facile route for modification of molded or embossed surfaces, with possible applications in the preparation of fluidic devices and polymer‐embedded circuits.     

The Synthesis of Magnetic Core‐Shell Nanoparticles by Surface‐Initiated Ring‐Opening Polymerization of ε‐Caprolactone

Summary: The synthesis of core‐shell particles with a poly(ε‐caprolactone) (PCL) shell and magnetite (Fe₃O₄) contents of between 10 wt.‐% and 41 wt.‐% proceeds by surface‐initiated ring‐opening polymerization of ε‐caprolactone to give surface‐immobilized oligomers with between 1 400 g · mol⁻¹ and 11 500 g · mol⁻¹. The particles are dispersable in good solvents for the PCL shell. Magnetization experiments on the resulting superparamagnetic ferrofluids give a core‐size distribution with an average diameter, d_v, of about 9.7 nm.

TEM image of Fe₃O₄/PCL core‐shell particles cast from CHCl₃ dispersion.     

Surface‐Initiated Polymerization for Amplification of Self‐Assembled Monolayers Patterned by Microcontact Printing

Patterned polymer brushes can be prepared by a novel strategy that combines surface‐initiated polymerization and microcontact printing (see picture; μCP SAM indicates the self‐assembled monolayer formed by microcontact printing). The living nature of the polymerization process permits the thickness of the polymer brush and its physical properties to be accurately controlled.     

Fabrication of Chemically Tethered Binary Polymer‐Brush Pattern through Two‐Step Surface‐Initiated Atomic‐Transfer Radical Polymerization

Summary: The communication provides a novel and alternative route to generate chemically tethered binary polymer‐brush pattern through two‐step surface‐initiated atomic‐transfer radical polymerization (SI‐ATRP). Polymer brush‐1 was prepared by SI‐ATRP, passivated by a reaction with NaN₃, and etched with UV irradiation through a transmission electron microscopy grid to create exposed sites for the subsequently attached initiator on which polymer brush‐2 was grown.

Schematic representation of the resultant binary polymer brush patterns.     

Silica/Poly(1,5‐dioxepan‐2‐one) Hybrid Nanoparticles by “Direct” Surface‐Initiated Polymerization

Summary: Biodegradable poly(1,5‐dioxepan‐2‐one) (PDXO) was grown directly from Si OH groups of a silica nanoparticle by surface‐initiated, ring‐opening polymerization (SI‐ROP) of 1,5‐dioxepan‐2‐one (DXO). The direct SI‐ROP of DXO was achieved by heating a mixture of Sn(Oct)₂, DXO, and the silica nanoparticles (316 nm in diameter) in anhydrous toluene. The resulting silica/PDXO hybrid nanoparticles were characterized by means of ¹H NMR spectroscopy, IR spectroscopy, thermogravimetric analysis, and field‐emission scanning electron microscopy.

The procedure for the surface‐initiated, ring‐opening polymerization of 1,5‐dioxepan‐2‐one on silica nanoparticles reported here.