Comparing emulsion polymerization of methacrylate-monomers with different hydrophilicity

A comprehensive experimental study concerning the influence of various types of initiator-emulsifier systems on emulsion polymerization of methacrylate monomers (2-hydroxyethyl methacrylate (HEMA), methyl methacrylate (MMA) and butyl methacrylate (BMA)) reveals interesting relations between initiator and surfactant hydrophilicity on the one hand and the hydrophilicity of the monomers on the other hand. For the water-soluble HEMA stable latexes are only obtained if hydrophobic initiators such as 2,2′-azobisisobutyronitrile or dibenzoyl peroxide in combination with alkyl sulfate surfactants with carbon chain lengths greater than 10 or surface active initiators of the 2,2′-azobis(N-2′-methylpropanoyl-2-amino-alkyl-1)-sulfonate type with alkyl chain lengths greater than 8 are employed. Stable nano size range poly(2-hydroxyethyl methacrylate) (PHEMA) particles have been prepared also by batch emulsion polymerization using ionic surface active initiators (inisurfs). The results clearly show that the formation of stable latex particles requires a proper choice of the initiator-emulsifier system regarding its hydrophilic-hydrophobic balance. The PHEMA particles prepared with surface-active initiators keep their identity and spherical shape even in the dried state whereas in the case of the other initiator-emulsifier systems complete coagulation and coalescence occurs during drying.     

Facile atom transfer radical homo and block copolymerization of higher alkyl methacrylates at ambient temperature using CuCl/PMDETA/quaternaryammonium halide catalyst system

Controlled polymerization of higher alkyl methacrylates, e.g. lauryl methacrylate (LMA) and stearyl methacrylate (SMA) has been successfully achieved by atom transfer radical polymerization (ATRP) at ambient temperature using CuCl/N,N,N′,N′,N″-pentamethyldiethylenetriamine (PMDETA)/tricaprylylmethylammonium chloride (Aliquat^®336) as the catalyst system and ethyl 2-bromoisobutyrate or 2,2,2-trichloroethanol as the initiator. Although the bulk polymerization gives satisfactory control, the latter becomes better when anisole or THF is added into the system. Without AQCl the control was lost. A large deviation of molecular weight from theory has been observed which has been attributed to the very high-molecular weight of the dead polymers formed during the building-up of the persistent radical. The controlled polymers have been used as macroinitiators for block (di, tri and penta) ATR copolymerization with several methacrylates.     

Efficiency of ligands in atom transfer radical polymerization of lauryl methacrylate and block copolymerization with methyl methacrylate

Atom transfer radical polymerization of lauryl methacrylate (LMA) was carried out in the presence of various ligands using ethyl-2-bromoisobutyrate as initiator and CuBr as catalyst in toluene at 95 °C. The ligands used were 2,2′-bipyridyl,4,4′-dimethyl-2,2′-bipyridyl, N,N,N′,N′,N″-pentamethyldiethylenetriamine (PMDETA) and N-(n-propyl)-2-pyridylmethanimine (PPMI). Controlled polymerization was observed with PMDETA and PPMI ligands and poly(LMA)s with narrow molecular weight distribution (MWD) (M_w/M_n≤1.2) were obtained. The first-order time-conversion plot showed the presence of termination in the presence of PMDETA. A linear first-order time-conversion plot with a small induction period (∼10 min) was observed in the presence of PPMI ligand. Di-block copolymers of LMA and methylmethacrylate with controlled molecular weight and narrow MWDs were synthesized via sequential monomer addition.     

Preparation of functional poly(acrylates and methacrylates) and block copolymers formation based on polystyrene macroinitiator by ATRP

The polymerization by ATRP of hydroxy and amino functional acrylates and methacrylates with tert-butyldimethylsilyl (TBDMS) or tert-butyloxycarbonyl (BOC) protective groups has been studied for the first time achieving high control over molecular weight and polydispersity. Detailed investigation of the ATRP of 2-{[tert-butyl(dimethyl)silyl]oxy}ethyl acrylate (M2b) in bulk and 2-[(tert-butoxycarbonyl)amino]ethyl 2-methylacrylate (M3a) in diphenyl ether (DPE) showed that the type of ligand plays an important role on either the polymerization rate or the degree of control of the polymerization. Among the ligands used, N,N,N,′N″N″-pentamethyl diethylenetriamine (PMDETA) was the most suitable ligand for ATRP of all functional acrylates and methacrylates. The kinetics of M2b and M3a polymerization using PMDETA as a ligand was reported and proved the living character of the polymerization. Well-defined block copolymers based on a halogen terminated polystyrene (Pst) macroinitiator and the functional acrylate and methacrylate monomers were successfully synthesized by ATRP, and subsequent deprotection of the protective groups from the acrylate or methacrylate segment afforded amphiphilic block copolymers with a specific solubility behavior.     

Synthesis of poly[dimethylsiloxane-block-oligo(ethylene glycol) methyl ether methacrylate]: an amphiphilic copolymer with a comb-like block

AB amphiphilic comb-like block copolymers of poly(oligo[ethylene glycol] methyl ether methacrylate) and polydimethylsiloxane were synthesised with a methodology based on atom transfer radical polymerization (ATRP). The anionic ring opening polymerisation of hexamethylcyclotrisiloxane followed by reaction with 3-(chlorodimethylsilyl) propyl 2-bromo-2-methylpropanoate propyldimethylchlorosilane gave suitable macroinitiators for the ATRP of oligo[ethylene glycol] methyl ether methacrylate. The latter synthetic procedure was optimised by performing a number of syntheses varying the reaction solvent, catalytic complex and the temperature used. Copolymers with relatively high polydispersity indices (M_w/M_n>1.3) could be synthesised at room temperature by employing a Cu(I)Br:N,N,N′,N′,N″-pentamethyldiethylenetriamine complex in n-propanol with Cu(II)Br. The optimum reaction conditions employed a Cu(I)Cl:N-(n-propyl)-2-pyridyl(methanimine) complex with an n-propanol/water mixture or toluene as solvent at 90 °C. This gave block copolymers of the desired molecular weights and polydispersity indices of less than 1.1. The block copolymers were characterised with ¹H NMR and ¹³C NMR spectroscopy and size exclusion chromatography.     

Novel carbazole phenoxy-based methacrylates to produce high-refractive index polymers

A novel, high-refractive index homopolymer was produced by incorporating carbazole and phenol into the methacrylate monomer structure. The reaction of phenol with 9-(2,3-epoxypropyl)-carbazole, followed by the reaction of the carbazole phenoxy-based intermediate with methacryloyl chloride or methacrylic anhydride, and recrystallization from methanol, produced a good yield of highly pure carbazole phenoxy functionalized methacrylate monomer. Subsequent free radical polymerization or UV photopolymerization of the functionalized methacrylate monomer, in addition to copolymerizations with methyl methacrylate, provided for high-refractive index materials well suited for lightweight optical applications. Unlike N-vinyl carbazole, the novel carbazole phenoxy-based methacrylate readily copolymerized with methyl methacrylate. Statistical copolymers of carbazole based methacrylates with methyl methacrylate were produced by free radical solution polymerization in DMAC or by photopolymerization in DMF. The carbazole phenoxy-based methacrylate monomer was characterized for molecular weight using gel permeation chromatography (GPC), for melting point and glass transition temperature using differential scanning calorimetry (DSC), for decomposition using thermal gravimetric analysis (TGA), and for chemical composition by one- and two-dimensional ¹H nuclear magnetic resonance (NMR) spectroscopy and by elemental analysis. The AIBN initiated carbazole phenoxy-based methacrylate polymerization was followed using in situ FTIR, which showed the reaction to be complete within 40 min in DMAC at 90 °C. Refractive indices of the carbazole based methacrylate homopolymers and copolymers ranged from 1.52 to 1.63. PhotoDSC was used to determine the heat of polymerization (ΔH_p) for the carbazole phenoxy-based methacrylate (ΔH_p=−39.4 kJ/mol). The carbazole phenoxy-based methacrylate homopolymer had a surprisingly high onset of decomposition temperature (T_onset=316 °C). ¹³C NMR spectroscopy experiments and molecular modeling were used to explore the configuration of the polymerized carbazole phenoxy-based methacrylate. The lack of head-to-head linkages due to steric considerations reasonably explains the high thermal stability observed for the carbazole phenoxy-based methacrylate polymer.     

Convenient synthesis of poly(2,6-dihydroxy-1,5-naphthylene) by Cu(II)-amine catalyzed oxidative coupling polymerization

A convenient synthesis of regiocontrolled poly(2,6-dihydroxy-1,5-naphthylene) (PDHN) with high molecular weights by oxidative coupling polymerization of 2,6-dihydroxynaphthalene (2,6-DHN) has been developed. Polymerizations were conducted in 2-methoxyethanol in the presence of di-μ-hydroxo-bis[(N,N,N′,N′-tetramethylethylenediamine)copper (II)] chloride (CuCl(OH)TMEDA) as the catalyst under air at 25 °C. To determine the optimum conditions, the effects of the amounts of the catalysts and the solvents were investigated. In the presence of 5 mol% of the catalyst to the monomer in 2-methoxyethanol, polymerization proceeded smoothly, giving PDHN with a number average molecular weight (M_n) of 52,000. PDHN was converted to poly(2,6-dibutoxy-1,5-naphthylene) (PDBN) to improve the solubility. The structure of PDBN was characterized by ¹H and ¹³C NMR spectroscopy and was estimated to consist completely of the 1,5-linkage. The average refractive indices (n_AV) of the PDHN and PDBN films were 1.6003 and 1.5815, respectively, and the dielectric constants (ε) estimated from the refractive indices were 2.82 and 2.75, respectively.     

Synthesis and characterizations of a polyimide containing a triphenylamine derivative as an interlayer in polymer light-emitting diode

Polyimide containing triphenylamine derivative (TPD-PI) was synthesized to prepare a polymer interlayer having insolubility in common nonpolar solvent for light-emitting polymers. N,N′-diphenyl-N,N′-bis(4-aminophenyl)-1,1-biphenyl-4,4′-diamine, as a new triphenylamine-containing diamine monomer, was synthesized by the palladium-catalyzed amination reaction between 4-nitrodiphenylamine and 4,4′-dibromobiphenyl and subsequent reduction of the nitro-intermediate. The TPD-PI was prepared from the synthesized diamine monomer and 4,4′-(hexafluoropropylidene)-diphthalic anhydride by the standard two-step polymerization method, which involved ring-opening polymerization and subsequent cyclodehydration. The structures and properties of the monomer and the resulting polyimide were characterized with ¹H and ¹³C NMR, elemental analysis, gel permeation chromatography, UV-visible spectroscopy, etc. The TPD-PI is readily soluble in aprotic polar solvents such as N-methyl-2-pyrrolidinone and N,N-dimethylformamide and insoluble in nonpolar solvents such as toluene and xylene. The highest occupied molecular orbital (HOMO) level of the TPD-PI was measured to be 5.5 eV by a photoelectron spectrometer in air, and the band gap was calculated as 3.1 eV from the onset of UV-vis spectrum. The polymer light-emitting diode with the thin TPD-PI layer between a hole injection layer and an emitting polymer layer was fabricated to examine the performance of the polyimide as an polymer interlayer. Although the luminous efficiency of the device is lowered by the introduction of the TPD-PI interlayer, the lifetime of the device is improved.     

Synthesis and characterization of perfluorocyclobutyl aryl ether-based amphiphilic diblock copolymer

Perfluorocyclobutyl aryl ether-based amphiphilic diblock copolymer containing hydrophilic poly(ethylene glycol) segment was synthesized by atom transfer radical polymerization (ATRP). Perfluorocyclobutyl-containing methacrylate-based monomer, 4-(4′-p-tolyloxyperfluorocyclobutoxy)benzyl methacrylate, was prepared firstly, which can be polymerized by ATRP in a controlled way to obtain well-defined homopolymers with narrow molecular weight distributions (M_w/M_n ≤ 1.30). The molecular weights increased linearly with the conversions of monomer and the apparent polymerization rate exhibited first-order relation with respect to the concentration of monomer. ATRP of 4-(4′-p-tolyloxyperfluorocyclobutoxy)benzyl methacrylate was initiated by PEG-based macroinitiators with different molecular weights to obtain amphiphilic diblock copolymers with narrow molecular weight distributions (M_w/M_n < 1.35) and the number of perfluorocyclobutyl linkage can be tuned by the feed ratio and the conversion of the fluorine-containing methacrylate monomer. The critical micelle concentrations of these amphiphilic diblock copolymers in water and brine were determined by fluorescence probe technique. The morphologies of the micelles were found to be spheres by TEM.     

Synthesis of methacrylated hyaluronic acid with tailored degree of substitution

The aim of this work was to develop a new method to derivatize hyaluronic acid (HyA) with polymerizable methacrylate residues with precise control over the substitution degree. The synthesis of methacrylated HyA (HyA-MA) was performed in dimethyl sulfoxide (DMSO) using glycidyl methacrylate (GMA) and 4-(N,N-dimethylamino)pyridine as a catalyst. HyA was rendered soluble in DMSO by exchanging the Na⁺ ions by the more lipophilic tetrabutylammonium ions. HyA-MA with a fully controlled degree of substitution (DS, defined as the number of methacrylate groups per 100 disaccharide units), ranging from 5 to 30, was obtained at 50 °C after 48 h. Hydrogels were obtained upon radical polymerization of aqueous solutions of HyA-MA using potassium peroxodisulfate (KPS) as initiator and N,N,N′,N′-tetramethylethylenediamine (TEMED) as catalyst. Almost complete methacrylate conversion (95%) was achieved for hydrogels obtained by polymerization of HyA-MA with a degree of substitution of 15. At lower DS (DS 8.5 and 5) the methacrylate conversion was 82% and 68%, respectively. Rheological characterization showed that with increasing DS the storage modulus of these HyA-MA hydrogels increased. Swelling experiments showed that HyA-MA gels with a DS of 15 or above were dimensionally stable, whereas HyA-MA gels with DS 5 and DS 8.5 swelled 1.6 and 1.4 times their initial weight, respectively. In conclusion, this paper shows that the DS of HyA-MA can be tailored by the reaction conditions and that consequently HyA-MA hydrogels with different characteristics can be prepared.     

One-step synthesis of pegylated cationic nanogels of poly(N,N′-dimethylaminoethyl methacrylate) in aqueous solution via self-stabilizing micelles using an amphiphilic macroRAFT agent

Cationic nanogels of Pegylated poly(N,N′-Dimethylaminoethyl methacrylate) (PEG-PDAEMA) have been synthesized in aqueous solution by a one-step surfactant-free reversible addition-fragmentation transfer (RAFT) process. A Pegylated amphiphilic macroRAFT agent (mPEG₅₅₀-TTC) with a hydrophobic dodecyl chain was utilized to stabilize the micelles and control the polymerization and crosslinking of DMAEMA in aqueous solution. ¹H NMR, GPC, Elemental analysis, Dynamic light scattering (DLS), Zeta potential and Atomic force microscopy (AFM) measurements confirmed the formation of the cationic nanogels in size of about 20 nm with a narrow distribution. It also revealed that the concentration of monomer and the kinds of crosslinker are the key factors to control the formation of nanogel. This cationic nanogel has potential application in gene delivery.     

Vinyl polymerization: 414. Polymerization of vinyl monomer initiated by poly(N,N,N-trimethyl-N-2-methacryloxyethyl)ammonium chloride

The polymerization of vinyl monomer initiated by an aqueous solution of poly(N,N,N-trimethyl-N-2-methacryloxyethyl)ammonium chloride (poly(Q-DMAEM-CI) has been carried out at 85°C. The effects of the amounts of vinyl monomer, poly(Q-DMAEM-CI) and water on the conversion of vinyl monomer have been studied. The overall activation energy in the polymerization of MMA is estimated as 41.9 kJ mol^?1. The polymerization proceeds through a radical mechanism. The location in which the polymerization occurs is discussed. The selectivity for vinyl monomer is explained by ‘the concept of hard and soft hydrophobic areas and monomers’.     

Composite membranes from polyacrylonitrile with poly(N,N-dimethylaminoethyl methacrylate)-grafted silica nanoparticles as additives

Polyacrylonitrile (PAN)-based composite membranes were prepared by immersion precipitation method by using poly(N,N-dimethylaminoethyl methacrylate)-grafted silica (PDMAEMA@SiO₂) nanoparticles as hydrophilic additives. The molecular weight of PDMAEMA were controlled by the surface initiated atom transfer radical polymerization of N,N-dimethylaminoethyl methacrylate on SiO₂ nanoparticles. The synthesized nanoparticles have a typical core–shell structure as characterized in detail by FT-IR, TEM, DLS and GPC. The prepared PAN-based composite membranes have higher porosity and water permeation flux than those of the pure PAN membranes. They also show high rejection (⩾90%) to bovine serum albumin and high flux recovery ratio (⩾90%) to water permeation. These improved performances are attributed to the good hydrophilicity of PDMAEMA@SiO₂ nanoparticles. The results suggest that PDMAEMA@SiO₂ nanoparticles are suitable for the property optimization of PAN-based composite membranes.     

Synthesis and characterization of novel fluoropolymers containing sulfonyl and perfluorocyclobutyl units

A novel sulfonyl-containing monomer, 4,4′-sulfonyl-bis(trifluorovinyloxy)biphenyl, and the resulting fluoropolymers with good thermal stability have been prepared. The monomer was synthesized by two steps using 4,4′-sulfonyldiphenol as starting material and characterized by FT-IR, ¹H NMR, ¹³C NMR, ¹⁹F NMR and element analysis in detail. Fluoropolymers containing sulfonyl and perfluorocyclobutyl units were prepared by different polymerization methods. A series of fluoropolymers with higher molecular weights were obtained by solution polymerization in diphenyl ether. The molecular weight is dependent on the polymerization time, polymerization temperature and the concentration of the monomer. The resulting polymers show excellent solubility in conventional solvents and good thermal stability with a high decomposition temperature about 500 °C measured by TGA.     

Emulsion atom transfer radical polymerization of 2-ethylhexyl methacrylate

The emulsion atom transfer radical polymerization (ATRP) of 2-ethylhexyl methacrylate (EHMA) was carried out with ethyl 2-bromoisobutyrate (EBiB) as an initiator and copper bromide (CuBr)/4,4′-dinonyl-2,2′-bipyridyl (dNbpy) as a catalyst system. The effects of surfactant type and concentration, temperature, monomer/initiator ratio, and CuBr₂ addition on the system livingness, polymer molecular weight control, and latex stability were examined in detail. It was found that the polymerization systems with Tween 80 and Brij 98 as surfactants at 30 °C gave the best latex stability. The polymer samples prepared under these conditions had narrow molecular weight distributions (M_w/M_n=1.1-1.2) and linear relationships of number-average molecular weight versus monomer conversion.     

Synthesis of novel mono-substituted polyacetylenes bearing functional urea groups in side chains

Novel mono-substituted polyacetylenes bearing urea groups in side chains, i.e. poly(N-propargylureas), were successfully synthesized for the first time. The solubility of the resulting three polymers (poly(1)–poly(3)) was examined, and it was found that the solubility of them largely depended on the pendent groups; the polymer with benzene cycle (poly(2)) showed high solubility in polar solvents including DMF and DMSO. The effects of polymerization temperature, solvents, and the ratio of monomer concentration to the catalyst concentration ((nbd)Rh⁺B⁻(C₆H₅)₄ (nbd = norbornadiene)) on the polymerization of monomer 2 were investigated. Poly(2) could be obtained with moderate molecular weights (20,100–29,200) in high yields (⩾90%), and the cis content of the polymer backbones was quite high (⩾96%).     

Synthesis of water-soluble homo- and block-copolymers by RAFT polymerization under γ-irradiation in aqueous media

The ambient temperature (20 °C) reversible addition fragmentation chain transfer (RAFT) polymerization of several water-soluble monomers conducted directly in aqueous media under γ-initiation (at dose rates of 30 Gy h⁻¹) proceeds in a controlled fashion. Using functional trithiocarbonates, i.e., S,S-bis(α,α′-dimethyl-α″-acetic acid) trithiocarbonate (TRITT), 3-benzylsulfanyl thiocarbonylsulfanyl propionic acid (BPATT), and dithioester, i.e., 4-cyanopentanoic acid dithiobenzoate (CPADB), as chain transfer agents, fully water-soluble polymers of monomers such as N,N-dimethylacrylamide, 2-hydroxyethyl acrylate, acrylamide or oligo(ethylene glycol) methacrylate and stimuli-responsive polymers of monomers such as acrylic acid, N-isopropylacrylamide, 2-(dimethylamino)ethyl methacrylate or 2-acrylamido-2-methylpropane sulfonic acid can be obtained over a wide range of degrees of polymerization up to 10,000 with low polydispersity (typically ) to near quantitative conversions. Well-defined block copolymers between these monomers, based on several asymmetric macro-RAFT agents, can be obtained, suggesting that the RAFT agents are stable throughout the polymerization process so that complex and well-defined architectures can be obtained.     

Preparation of hyperbranched copolymers of maleimide inimer and styrene by ATRP

Novel hyperbranched copolymers were prepared by the atom transfer radical copolymerization of N-(4-α-bromobutyryloxy phenyl) maleimide (BBPMI) with styrene in 1-methyl-2-pyrrolidone (NMP) using the complex of CuBr/2,2′-bipyridine as catalyst. The copolymerization behavior was investigated by comparison of the conversion of double bond of BBPMI determined by ¹H NMR with that of styrene. The hyperbranched structure of resulting copolymers was verified by gel permeation chromatography (GPC) coupled with multi-angle laser light scattering (MALLS). The influences of dosage of catalyst and monomer ratio on the polymerization rate and structure of the resulting polymers were also investigated. The glass transition temperature of the resulting hyperbranched copolymer increases with increasing mole fraction of BBPMI, f_BBPMI. The resulting copolymers exhibit improved solubility in organic solvents; however, they show lower thermal stabilities than their linear analogues.     

UV-assisted grafting of polymers: A method towards biocompatible carbon nanotubes

A strategy for covalent grafting of biocompatible polymers onto sidewalls of multi-walled carbon nanotubes (MWNTs) via UV-initiated free-radical polymerization is presented. The effects of the irradiation doze(time) and monomer/MWNTs ratio on the stability of the corresponding aqueous dispersions were investigated. It was found that stable dispersions of MWNTs modified with polyacrylamide, poly(N-isopropylacrylamide), poly[poly(ethylene glycol) methacrylate] and poly(sodium methacrylate) can be obtained by irradiation with UV light for at least 5 min at an irradiation dose rate of 5.7 J/cm² min at a minimum monomer/CNTs ratio of 200:1. Biocompatibility of polymer-modified MWNTs was assessed using the standard MTT-dye reduction assay and compared to pristine MWNTs. As a rule, all polymer-functionalized nanotubes examined in this study were non-cytotoxic up to concentration 150 μg/mL and, remarkably, MWNTs-g-PNIPAAm did not exhibit cytotoxicity even at the highest concentration studied (300 μg/mL). MWNTs modified with stimuli-sensitive polymers underwent a reversible transition from well-dispersed nanotubes in water to precipitate triggered by changes in temperature or pH.     

A readily modified polyethersulfone with amino-substituted groups: Its amphiphilic copolymer synthesis and membrane application

An amino-substituted polyethersulfone (PES) was synthesized by the polycondensation of a functional monomer bis(3-amino-4-hydroxyphenyl) sulfone with bis(4-fluorophenyl) sulfone. The amine groups incorporated into PES were employed as anchors to immobilize the chain transfer agents of reversible addition-fragmentation polymerization (RAFT). The resultant macro chain transfer agent was used to initiate the polymerization of the hydrophilic monomers N-isopropyl acrylamino (NIPAAm) and N, N-dimethylamino-2-ethyl methacrylate (DMAEMA), respectively. The gel permeation chromatography (GPC) results confirmed the successful synthesis of the amphiphilic copolymers PES-g-PNIPAAm and PES-g-PDMAEMA, and these two copolymers were perhaps the few examples of amphiphilic copolymer synthesized via a radical polymerization from PES main chains. The amino-substituted PES seemed a versatile precursor that showed a potential of functionalization via various strategies including click chemistry, atom transfer radical polymerization and RAFT polymerization. The synthesized amphiphilic copolymers were finally used as additives to improve the hydrophilicity and the filtration performances of PES membranes.