Thiol-lactam Initiated Radical Polymerization Research Articles

Thiol-Lactam Initiated Radical Polymerization (TLIRP): Scope and Application for the Surface Functionalization of Nanoparticles

: Controlled polymerization techniques make the possible fabrication of polymers with desired molecular weights, narrow dispersity, and tailor-making of advanced hybrid materials. Thiol- Lactam Initiated Radical Polymerization (TLIRP) was introduced in 2002 and developed during the last two decades. The thiol/lactam combination enables one to generate radicals that can initiate the polymerization of vinyl-based monomers. The study of the mechanism and kinetics of TLIRP revealed the characteristics of living polymerization for TLIRP. Moreover, TLIRP has been used successfully for the synthesis of homopolymers, block copolymers, and statistical copolymers with polydispersity below 2.0. Especially, TLIRP provides a very straightforward method for grafting polymer brushes on the surface of nanoparticles. We review herein the systems developed for TLIRP and their applications for macromolecular engineering, emphasizing the surface functionalization of nanoparticles via the grafting-from approach.

Effect of Silica Size and Content on Superamphiphobic Properties of Silica-Fluoropolymer Core-Shell Coatings.

We present a facile approach to fabricate superamphiphobic surfaces by spray coating silica-fluoropolymer core-shell particles without substrate pretreatment with an additional binder resin. A series of SiO2@poly(1H,1H,2H,2H-heptadecafluorodecyl methacrylate) (SiO2@PFMA) core-shell particles with core particles of different sizes were prepared via thiol-lactam initiated radical polymerization (TLIRP). The surface of each SiO2 particle with an average particle size of 12, 80, 150, and 350 nm was modified with (3-mercaptopropyl) trimethoxysilane and used as a seed for TLIRP. The SiO2@PFMA particles with various SiO2 sizes and contents were coated on aluminum substrates by a spray gun and then thermally treated to form a stable, rough composite layer. During the spray coating, the core-shell particles were aggregated by rapid evaporation of the solvent and then irregularly adhered to the substrate resulting in hierarchical structures. In the case of SiO2@PFMAs with low SiO2 contents, the roughness created mainly by the polymer shell disappeared during heat treatment. However, the substrates coated with SiO2@PFMAs with high SiO2 contents maintained the roughness even after heat treatment. The core-shell particles prepared with 12 nm SiO2 formed a stable superamphiphobic surface. The water/hexadecane contact and sliding angles on an aluminum plate coated with SiO2@PFMA, prepared using 12 nm silica at 46 wt% silica content (12 nm-SiO2(46)@PFMA), were 178.5°/159.2° and 1°/7°, respectively. The cross-cut tape test showed that adhesion between the 12nm-SiO2(46)@PFMA and the aluminum substrate was classified as 5B. A glass surface spray-coated with the core-shell composite particles exhibited transparent superhydrophobicity and translucent superamphiphobicity by controlling the concentration of the coating solution.

Robust and superomniphobic core-shell SiO2@poly(1H,1H,2H,2H-heptadecafluorodecyl methacrylate-co-methyl methacrylate) coating materials synthesized by thiol lactam initiated radical polymerization

Superomniphobic SiO2@poly(1H,1H,2H,2H-heptadecafluorodecyl methacrylate-co-methyl methacrylate) (SiO2@poly(FMA-co-MMA)) core-shell spheres were synthesized via a thiol lactam initiated radical polymerization (TLIRP). SiO2 and poly(FMA-co-MMA)s were used as they imparted both surface roughness and low surface energy for superhydrophobic surfaces. SiO2 particles were synthesized using the Stöber method, and their surface was subsequently modified with (3-mercaptopropyl) trimethoxysilane and used as seeds for polymerization in the presence of γ-butyrolactam. The CH2 peaks (4.26 and 2.56 ppm) from poly(FMA) and the CH3 peak (3.53 ppm) from poly(MMA) were observed in the 1H-NMR spectra, indicating successful preparation of SiO2@poly(FMA-co-MMA) by TLIRP. The maximum water and hexadecane contact angles of an aluminum plate coated with particles were 164.0° and 130.1°, respectively. The cross-cut tape test of the coated aluminum plate showed that adhesion between the coating material and the substrate was classified as 5B, without damage. Furthermore, the substrate maintained superhydrophobicity after 40 cycles of tape peeling, although the water contact angle slightly decreased (163.1°) and the sliding angle slightly increased (2° to 3°). The mechanical strength of the coated aluminum plate was enhanced by heat treatment above the Tg of SiO2@poly(FMA-co-MMA)s. The SiO2 content of SiO2@poly(FMA-co-MMA)s affected the wettability of the coating surface due to roughness generated by the core SiO2 particles.

Chemically Modified Hydroxyapatite Nanocrystals by Temperature-Responsive Poly(N-isopropylacrylamide) via Surface Initiated Radical Polymerization

This article reports on application of surface-initiated thiol-lactam initiated radical polymerization (TLIRP) method to modify hydroxyapatite nanocrystals (HAP) with thermoresponsive poly(N-isopropylacrylamide) (PNIPAm) brushes through grafting from strategy. Initially, 3-mercaptopropyl trimethoxysilane possessing thiol groups was functionalized with the -OH species on the surface of hydroxyapatite through ligand-exchanging response to introduce thiol species on hydroxyapatite (hydroxyapatite-thiol). Subsequently, attaching polymerization of N-isopropylacrylamide from HAP-SH surface was accomplished in the attendance of butyrolactam to produce PNIPAAmg-HAP. Thermogravimetric analysis, Fourier transform infrared, X-ray photoelectron spectroscopy and their thermal phase transition behaviour were employed to confirm the grafting and to characterize the nanoparticle structure.

A Precised Surface Modification of Hydroxyapatite with Poly(methylmethacrylate) for Tissue Engineering & Regenerative Medicine

The poly(methylmethacrylate) (PMMA) grafted biocompatible hydroxyapatite nanocrystals (HAPs) hybrid nanocomposites (PMMA-g-HAPs) were synthesized by employing surface thiol-lactam initiated radical polymerization (TLIRP) through grafting from strategy. At first, the surface of HAPs was functionalized by 3-mercaptopropyl-trimethoxysilane in one-step process to prepare thiol immobilized HAPs (HAPs-SH). Subsequently, a controlled radical polymerization of MMA by using two component initiating system comprising of HAPs-SH and butyrolactam (BL) successfully afforded PMMA-g-HAPs nanocomposites. The resulting structure and morphological feature of nanocomposites was systematically characterized by FT-IR and XRD analyses. GPC studies of cleaved polymers from nanocomposites of different time revealed that the grafting polymerization from the surface of HAP was well controlled in nature. Moreover, the thermal property of the PMMA was found to be improved by incorporation of inorganic HAP nanoparticles in the polymer matrix as revealed by TGA and DSC studies. The colloidal stability of the synthesized nanocomposites was observed to be exceptionally good in organic solvents as suggested by the time dependent monitoring using UV-visible spectroscopy and captured digital photographs. The synthesized nanocomposites show a great promise for the safe application in tissue engineering and regenerative medicine.

β-cyclodextrin functionalized poly (5-amidoisophthalicacid) grafted Fe3O4 magnetic nanoparticles: A novel biocompatible nanocomposite for targeted docetaxel delivery

Thiol-lactam initiated radical polymerization (TLIRP) was successfully employed to prepare poly-N−5-acrylamidoisophthalicacid grafted onto Fe3O4 magnetic nanoparticles (MNPs@PAIP). β-Cyclodextrin (CD) was then conjugated to the carboxylic groups of the prepared MNPs via carbodiimide activation. Subsequently, tumor-targeting folic acid (FA) was attached to the hydroxyl groups of CD on the surface of the latter MNPs to increase the site-specific intracellular delivery. The prepared MNPs were fully characterized by FTIR, VSM, TGA, XRD, FE-SEM and TEM. Docetaxel (DTX) as hydrophobic anticancer drug was loaded via host-guest inclusion complexation with CD and the release profile of the system was studied at different pH. The effect of MNPs on the cell viability was evaluated for the human embryonic kidney normal cell line (HEK293) as well as HeLa and MDA-MB-231 cancerous cell lines and the results did not show any apparent cytotoxic effect. In comparison, DTX loaded MNPs reduced the growth of HeLa and MDA-MB-231 cells more than free DTX. Intracellular uptake ability of DTX loaded MNPs was also studied using fluorescent microscopy and showed cellular uptake about 90% after 4h treatment.

Novel pH-responsive multilayer magnetic nanoparticles for controlled drug delivery

A multifunctional nanocarrier with multilayer core–shell architecture was prepared by chemical modification of Fe3O4 magnetic nanoparticle (MNPs) with acrolein–styrene–polyethyleneimine (AL–St–PEI) via covalent bonding. MNPs were prepared by co-precipitation method, and then, thiol functionalized (MNPs-SH) were synthesized by treating MNPs with the (3-mercaptopropyl) trimethoxysilane. Subsequently, the copolymerization of St and AL was performed in the presence of the MNPs-SH and butyrolactam by thiol-lactam initiated radical polymerization. Finally, PEI was covalently bounded to the aldehyde groups on the surface of AL–St copolymer. The AL–St–PEI MNPs were investigated by FTIR, XRD, TGA, SEM and TEM. The drug release from AL–St–PEI MNPs was evaluated using doxorubicin as the model anticancer. Furthermore, to determine the effect of drug structure in the release profile from the modified MNPs, some lipophilic model drugs were studied in loading and release study. It was found that the nature of the drugs affect the release profile. The in vitro release modeling demonstrated that doxorubicin release is described by zero-order mechanism while release of lipophilic model drugs is controlled by fickian diffusion.

A Facile Route Towards the Synthesis of Nanocomposites for the Application as Solid Electrolytes via Grafting Polymer from TiO2 Nanoparticles

Poly(acrylic acid)/TiO2 (PAA-g-TiO2) nanocomposites were synthesized by the surface thiol-lactam initiated radical polymerization (TLIRP) technique. The synthetic strategy involved the modification of TiO2by a one-step direct anchoring of thiol groups via reaction between the hydroxyl groups on the surface of TiO2 and triethoxysilane groups of (3-mercapto)propyltrimethoxysilane (MPTMS). The modified TiO2nanoparticles (NPs) were dispersed in acrylic acid monomers and subsequently polymerized by TLIRP to yield PAA-g-TiO2nanocomposites. FT-IR spectra, XPS, EDS, UV-Vis spectroscopy and SEM images provided direct and clear evidence for the coordination of MPTMS and the presence of PAA on TiO2 NPs. The immobilization of PAA onto TiO2 NPs significantly improved their dispersibility in organic solvents. Additionally, laser diffraction spectroscopy of the TiO2 NPs was examined in order to get the size distribution of nanocomposites.

Encapsulation of TiO2 Nanoparticles with Poly(4-vinylpyridine) Using Surface Functionalized Thiol-Lactam Initiated Radical Polymerization

A nanocomposite of TiO2 nanoparticle with an electroactive poly(4-vinylpyridine) (PVP) was synthesized via a simple surface thiol-lactam initiated radical polymerization upon grafting from protocol. This can be achieved through the primary modification of the TiO2 surface with a silane coupling agent leading to thiol functionalized TiO2 (TiO2-SH). Subsequently, a controlled radical polymerization of 4-vinylpyridine in the presence of TiO2-SH and butyrolactam afforded PVP-g-TiO2 nanocomposites. The grafting of PVP on the surface of TiO2 was confirmed by FT-IR, TGA, XPS, EDX, TEM and SEM analyses. The UV-vis studies of the synthesized PVP-g-TiO2 nanocomposite demonstrated an exceptionally good dispersibility in organic solvents.

A Facile Route Towards the Synthesis of Polystyrene/Zinc Oxide Nanocomposites

ZnO nanoparticles were covalently wrapped by polystyrene (PS) through surface thiol-lactam initiated radical polymerization using the grafting from approach. The surface of ZnO nanoparticles was initially modified by 3-mercapto propyltrimethoxysilane to afford thiol functionalized ZnO nanoparticles (ZnO-SH). The controlled radical polymerization of styrene (St) was subsequently accomplished by using an initiating system of ZnO-SH and butyrolactam. FT-IR, XPS, XRD, TGA, DSC, TEM and DLS were employed to investigate the chemical structure, morphology, thermal properties, the size and size distribution of nanocomposites. The dispersibility of ZnO nanoparticles was observed to be significantly improved upon functionalization by PS brushes. The controlled nature of the surface initiated thiol-lactam aided polymerization of St from the ZnO nanoparticles surface was confirmed by GPC analysis.

Synthesis of PS-g-TiO2 Nanocomposites through a Simple Method of Surface Initiated Radical Polymerization

Hybrid nanocomposites of polystyrene (PS) and TiO2 were prepared by the facile surface thiol-lactam initiated radical polymerization (TLIRP). At first, the surface of TiO2 nanoparticles was modified by 3-mercaptopropyl-trimethoxysilane to prepare TiO2-SH. Subsequently, a radical polymerization of styrene was accomplished in the presence of TiO2-SH and butyrolactam to afford PS-g-TiO2 nanocomposites. The nanocomposites were investigated by 1H-NMR, FT-IR, GPC and XPS. The morphology of the nanocomposites was captured on TEM images, showing the encapsulation of TiO2 with PS. The TGA data suggest that the thermal stability of PS was enhanced upon inclusion of TiO2 nanoparticles. The dispersability of TiO2 nanoparticles was improved significantly after functionalization of PS chains.

Synthesis of P(MMA-co-MAA)/TiO2 Nanocomposites via Surface Thiol-Lactam Initiated Radical Polymerization

Poly(methylmethacrylate-co-methacrylic acid) were covalently wrapped onto TiO2 nanoparticles through surface thiol-lactam initiated radical polymerization via grafting from approach. Initially, the surface of TiO2 nanoparticles was modified by (3-mercapto)propyl trimethoxysilane to get thiol functionalized TiO2 nanoparticles (TiO2-SH). A radical polymerization of methylmethacrylate and methacrylic acid was subsequently conducted to afford chemically bonded copolymer with TiO2 nanoparticles by employing two component initiating system consisting of TiO2-SH and butyrolactam. The TiO2 nanocomposites were identified by taking advantage of FT-IR, XPS, and EDX. The physical structure of the nanocomposites was studied by using XRD. The morphology of the nanocomposites was investigated by TEM and SEM analyses. TGA scan showed that the inclusion of TiO2 nanoparticles improved the thermal stability of the copolymer to a certain extent. Additionally, dynamic laser light scattering measurement of the TiO2 nanocomposites was carried out in order to get the size distribution of nanocomposites.

A Facile Synthesis of PMMA-SiO2 Nanocomposites via Surface Initiated Radical Polymerization

Well-defined core–shell structured poly(methyl methacrylate) grafted silica nanocomposites (PMMA-g-SiO2) were synthesized via thiol-lactam initiated radical polymerization by employing a grafting from protocol. Spherical SiO2 nanoparticles were reacted with 3-mercaptopropyl-trimethoxysilane in order to prepare thiol functionalized SiO2 nanoparticles (SiO2-SH). Subsequently, the surface initiated polymerization was accomplished by using two component initiating system comprising SiO2-SH and butyrolactam. The anchoring of PMMA onto the surface of SiO2 nanoparticles was ascertained by FTIR and XPS analyses. A uniform and spherical core-shell structure of PMMA-g-SiO2 was revealed from TEM and SEM images. The GPC analysis demonstrated that the molecular weight of PMMA was a function of both monomer conversion and polymerization time. DLS also confirmed that the hydrodynamic diameter of the nanocomposites was directly related to the polymerization time. An improved thermal property of the polymer matrix with incorporating SiO2 nanoparticles was revealed by TGA study.

Synthesis and Characterization of Poly(oxyethylene methacrylate) Coated TiO2 Nanoparticles via Surface Thiol-Lactam Initiated Radical Polymerization

Poly(oxyethylene methacrylate) (POEM) anchored TiO2 nanoparticles were synthesized via the surface thiol-lactam initiated radical polymerization of POEM in the presence of thiol functionalized TiO2 nanoparticles. The grafting of POEM onto the surface of TiO2 nanoparticles was investigated by FT-IR, XPS, EDX, TGA, XRD, and TEM analyses. The experimental findings suggested that a strong interaction prevailed between grafted POEM and TiO2 nanoparticles. The TEM image of POEM-g-TiO2 showed that the agglomeration propensity of TiO2 nanoparticles was reduced significantly upon the functionalization of POEM. Moreover, an improved thermal property of the POEM in the POEM-g-TiO2 nanocomposites was observed by TGA.

Synthesis and Characterization of TiO2/Poly(methyl methacrylate) Nanocomposites via Surface Thiol-Lactam Initiated Radical Polymerization

An approach to the surface modification of TiO2 nanoparticles was described based on the thiol functionalization of TiO2 followed by thiol-lactam initiated radical polymerization (TLIRP) of methyl methacrylate (MMA). FT-IR, XRD and XPS analyses confirmed the grafting of the polymer on the TiO2 surface. TGA analysis revealed superior thermal stability of PMMA-g-TiO2 compared with PMMA. TEM measurements and time-dependent phase monitoring suggested much higher colloidal stability of PMMA-g-TiO2 than TiO2 in toluene. The controlled nature of the TLIRP of MMA from the surface of TiO2 was determined by GPC analysis.

Polymer Brushes on Carbon Nanotubes by Thiol-Lactam Initiated Radical Polymerization of 2-Hydroxyethyl Methacrylate

Water-soluble polymer brushes with multi-walled carbon nanotubes (MWNTs) as backbones were synthesized by grafting 2-hydroxyethyl methacrylate (HEMA) from surface functionalized MWNTs via in situ surface thiol-lactam initiated radical polymerization. MWNTs were functionalized with 2-mercaptoethanol and used as initiators in the polymerization of HEMA in the presence of butyrolactam. FT-IR, XPS, 1H NMR, GPC and TGA were used to determine chemical structure and the grafted polymer quantities of the resulting product. The covalent bonding of PHEMA to the MWNTs dramatically improved the water dispersibility of MWNTs. The average thicknesses of the polymer brushes in the functionalized MWNTs were detected with electron microscopy (SEM and TEM) and images indicated that the nanotubes were coated with polymer layer.

Encapsulation of Fe3O4 magnetic nanoparticles with poly(methyl methacrylate) via surface functionalized thiol-lactam initiated radical polymerization

Poly(methyl methacrylate) (PMMA) was grafted onto Fe3O4 magnetic nanoparticles (MNPs) by using a thiol-lactam initiated radical polymerization (TLIRP) via grafting from approach. The surface of the MNPs was treated with the (3-mercaptopropyl)trimethoxysilane coupling agent to give thiol functionalized MNPs (MNPs-SH). Subsequently, the polymerization of MMA performed in the presence of the MNPs-SH and butyrolactam efficiently afforded PMMA-g-MNPs. The grafting of PMMA on the surface of the MNPs was investigated by FT-IR, 1H NMR, TGA, XPS, and EDX analyses. The morphology of the core/shell type PMMA-g-MNPs was confirmed by HR-TEM. GPC analysis showed that the molecular weight of PMMA and monomer conversion increased with the reaction time. The amount of the grafted polymer on the surface of the MNPs was found to be ca. 82.5% as estimated from TGA analysis. The MNPs and PMMA-g-MNPs were subjected to magnetic property investigation by SQUID, and the PMMA-g-MNPs showed relatively high saturated magnetization (53.3emu/g) without any remanence or coercivity, which made the nanocomposites easily separable from solid–liquid phases suggesting their superparamagnetic character. The magnetic nanocomposites had an exceptionally good dispersibility in organic solvents as demonstrated by UV–Vis spectroscopy as well as time-dependent digital photographic monitoring.

Synthesis of Well-Dispersed Multiwalled Carbon Nanotubes-Polystyrene Nanocomposites via Surface Thiol-Lactam Initiated Radical Polymerization

A fascinating nanoobject, possessing a hard core of multi-walled carbon nanotubes (MWNTs) and a relatively soft shell of brushlike polystyrene (PS) was chemically synthesized by thiol lactam initiated radical polymerization. FT-IR and X-ray photoelectron spectroscopy were employed to characterize the nanocomposites and electron microscopic methods were used to investigate the morphologies of the as-prepared hybrid nanocomposites. The MWNT-PS nanocomposites possess good dispersibility in common organic solvents. Transmission electron microscopic images of the samples provide direct evidence for the formation of a core-shell nanostructure, i.e., the MWNTs coated with the PS layer.

Synthesis of silica–polystyrene core–shell nanoparticles via surface thiol-lactam initiated radical polymerization

This paper reports the synthesis of structurally well-defined silica–polystyrene (SiO 2@PS) hybrid nanoparticles using a thiol-lactam-initiated, radical-polymerization technique. The surface of silica particles, 80 nm in size, were functionalized with (3-mercaptopropyl) trimethoxysilane and used as seeds in the polymerization of styrene in the presence of butyrolactam. 1H nuclear magnetic resonance and X-ray photoelectron spectroscopy showed that the thiol groups on the SiO 2 surface could initiate polymerization with the aid of butyrolactam. Transmission electron microscopy showed that the hybrid particles had uniform core–shell morphologies. The molecular weight of grafted PS increased with increasing polymerization time.