Crosslinkable micelles from diblock amphiphilic copolymers based on vinylbenzyl thymine and vinylbenzyl triethylammonium chloride

Polymeric micelles (PMs) composed of self‐assembled amphiphilic block copolymers were synthesized from vinylbenzyl thymine (VBT) and vinylbenzyl triethylammonium chloride (VBA) exhibiting improved physical stability. Three diblock copolymers of different chemical compositions and similar molecular weights (polydispersities below 1.5) were obtained via nitroxide mediated radical polymerization. Critical micelle concentration (CMC) was determined by dye micellization method, the shift of the absorption peak of the anionic (EY) due to the interactions with non‐assembled chains and auto‐assembled copolymers was followed. Polymeric systems exhibited good stability revealing that a higher proportion of cationic monomers in the diblock reduce the CMC. Furthermore, after the core of PMs was photocrosslinked by UV irradiation, the CMC decreases notably. Kinetic release studies using EY dye as probe demonstrated that both, higher VBA ratios in the polymer and higher UV‐irradiation, slow down the dye release. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41947.     

Synthesis of diblock and triblock copolymers from butyl acrylate and styrene by reverse iodine transfer polymerization

Well‐defined AB and BA diblock copolymers were obtained by a one‐pot two‐step sequential block copolymerization by reverse iodine transfer polymerization (RITP), A being a poly(styrene) block and B a poly(butyl acrylate) block. High monomer conversions during the formation of the first block avoided the purification steps before growing the second block. In a third sequential step, the diblock copolymers were further extended to synthesize ABA and BAB triblock copolymers. Furthermore, the synthesis of ABA and BAB copolymers in only two steps by RITP was investigated starting with the formation of the central block using 2,5‐di(2‐ethylhexanoylperoxy)‐2,5‐dimethylhexane as a difunctional initiator and then resuming the polymerization to grow the external blocks in a second step. The obtained copolymers were analyzed by size exclusion chromatography, transmission electron microscopy, and differential scanning calorimetry. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Emulsion polymerization of methyl methacrylate using the reverse iodine transfer polymerization (RITP) technique

The targeted molecular weight poly (methyl methacrylate) [PMMA] latex was successfully prepared in the presence of 4,4-azobis(4-cyanopentanoic acid) (ACPA) and various surfactants using the reversible iodine transfer polymerization (RITP)-emulsion polymerization at 85 °C for 7 h in the absence of light. The properties of PMMA particles upon the various ratios of ACPA to iodine within the concentration ranges of ACPA (1.0–2.0 mmol) and iodine (0.1–1.0 mmol) with various surfactants were investigated by means of GPC, SEM and particle analyzer. The weight-average molecular weight and the conversion increased with the ratio of [ACPA]/[I₂], but no correlation between the particle size and the [ACPA]/[I₂] ratio was obtained. The initiator, ACPA, was important in the formation of PMMA spherical particles, while molecular iodine dominated in controlling the molecular weight, inhibition period and the conversion. In overall, the appropriate concentration of ACPA, iodine and anionic or anionic with non-ionic surfactants controls the targeted molecular weight less than 100,000 g/mol and the enhanced conversion higher than 90% along with particle stability.     

Atom transfer radical coupling of polystyrene and poly(methyl acrylate) synthesized by reverse iodine transfer polymerization

Iodo-terminated polystyrene and poly(methyl acrylate) (PMA-I) were synthesized by reverse iodine transfer polymerization. The resulting polymers were coupled by atom transfer radical coupling using Cu(I)/linear amino-ligand catalysts in the presence of reducing Cu(0). The efficiency of the coupling reaction is discussed as a function of various factors, namely, the Cu(0) particle sizes, the number of nitrogen present in the ligand structure, the type of halogen associated with Cu(I) (CuX, X = I, Br, Cl), the nature of the polymer and the nature of the chain ends. In particular, a quantitative coupling (100%) was obtained with a CuBr/HMTETA system in the presence of nanosized Cu(0) for PMA-I, thus opening for the first time a facile route to telechelic and multiblock poly(acrylate)-based structures.     

Synthesis of amphiphilic poly(methyl methacrylate)‐block‐poly(methacrylic acid) diblock copolymers by atom transfer radical polymerization

Atom transfer radical polymerization (ATRP) of 1‐(butoxy)ethyl methacrylate (BEMA) was carried out using CuBr/2,2′‐bipyridyl complex as catalyst and 2‐bromo‐2‐methyl‐propionic acid ester as initiator. The number average molecular weight of the obtained polymers increased with monomer conversion, and molecular weight distributions were unimodal throughout the reaction and shifted toward higher molecular weights. Using poly(methyl methacrylate) (PMMA) with a bromine atom at the chain end, which was prepared by ATRP, as the macro‐initiator, a diblock copolymer PMMA‐block‐poly [1‐(butoxy)ethyl methacrylate] (PMMA‐b‐PBEMA) has been synthesized by means of ATRP of BEMA. The amphiphilic diblock copolymer PMMA‐block‐poly(methacrylic acid) can be further obtained very easily by hydrolysis of PMMA‐b‐PBEMA under mild acidic conditions. The molecular weight and the structure of the above‐mentioned polymers were characterized with gel permeation chromatography, infrared spectroscopy and nuclear magnetic resonance. Copyright © 2005 Society of Chemical Industry     

Synthesis of poly(ethylene glycol-b-styrene) block copolymers by reverse atom transfer radical polymerization

Reverse atom transfer radical polymerization (RATRP) of styrene (S) was carried out in bulk using polyazoester prepared by the reaction of polyethylene glycol with molecular weight of 3000 and 4,4′-azobis(4-cyanopentanoyl chloride) as initiator and CuCl₂/2,2′-bipyridine (bpy) catalyst system to yield poly(ethylene glycol-b-styrene) block copolymer. The block copolymers were characterized ¹H NMR, FT-IR spectroscopy and GPC. The ¹H NMR, and FT-IR spectra showed that formation of poly(ethylene glycol-b-styrene) block copolymer. The polydispersities of block copolymers were observed between from 1.49 and 1.98 GPC measurements.     

Synthesis of amphiphilic block copolymers based on poly(dimethylsiloxane) via fragmentation chain transfer (RAFT) polymerization

Dihydroxy terminated poly(dimethyl siloxane) (PDMS) was modified to form a di(trithiocarbonate) functional molecule capable of forming tri-block copolymers via the reversible-addition-fragmentation chain transfer (RAFT) process. Two statistical copolymer blocks were grown from the central PDMS block, comprising units of N,N-dimethyl acrylamide (DMA) and 2-(N-butyl perfluorooctanefluorosulfonamido) ethyl acrylate (BFA), to form A-B-A triblock macromolecules. The molecular weight of these block copolymers were found to increase with conversion while the polydispersity of the molecular weight distribution remains under 1.25. An unusual and interesting kinetic phenomenon was observed in that the copolymerization behaviour of DMA and BFA was influenced by the initial PDMS block. We surmise that this might be a direct observation of a ‘bootstrap’ effect.     

Synthesis and characterization of poly(n‐butyl methacrylate)‐b‐polystyrene diblock copolymers by atom transfer radical emulsion polymerization

Poly(n‐butyl methacrylate) (PBMA)‐b‐polystyrene (PSt) diblock copolymers were synthesized by emulsion atom transfer radical polymerization (ATRP). PBMA macroinitiators that contained alkyl bromide end groups were obtained by the emulsion ATRP of n‐butyl methacrylate with BrCH₃CHCOOC₂H₅ as the initiator; these were used to initiate the ATRP of styrene (St). The latter procedure was carried out at 85°C with CuCl/4,4′‐di(5‐nonyl)‐2,2′‐bipyridine as the catalyst and polyoxyethylene(23) lauryl ether as the surfactant. With this technique, PBMA‐b‐PSt diblock copolymers were synthesized. The polymerization was nearly controlled; the ATRP of St from the macroinitiators showed linear increases in number‐average molecular weight with conversion. The block copolymers were characterized with IR spectroscopy, ¹H‐NMR, and differential scanning calorimetry. The effects of the molecular weight of the macroinitiators, macroinitiator concentration, catalyst concentration, surfactant concentration, and temperature on the polymerization were also investigated. Thermodynamic data and activation parameters for the ATRP are also reported. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2123–2129, 2005     

Synthesis of amphiphilic diblock copolymers by direct radical polymerization of acrylic acid via DPE method

Amphiphilic diblock copolymers, poly(methyl methacrylate)-b-poly(acrylic acid) (PMMA-b-PAA) was prepared by 1,1-diphenylethene (DPE) method. First, free radical polymerization of methyl methacrylate was carried out with AIBN as initiator in the presence of DPE, giving a DPE-containing PMMA precursor with controlled molecular weight. Amphiphilic diblock copolymer PMMA-b-PAA was then prepared by radical polymerization of acrylic acid (AA) in the presence of PMMA precursor. The formation of PMMA-b-PAA was confirmed by ¹H NMR spectrum and gel permeation chromatography. Transmission electron microscopy and dynamic light scattering were used to detect the self-assembly behavior of the amphiphilic diblock polymers in methanol.     

Fabrication of poly(methyl methacrylate)‐block‐poly(N‐isopropylacrylamide) amphiphilic diblock copolymer on silicon substrates via surface‐initiated reverse iodine transfer polymerization

Amphiphilic diblock copolymer on silicon substrates were synthesized via surface‐initiated reverse iodine transfer polymerization (RITP) technique. The silicon substrates (Si (111) surface) were modified with the azo groups, which were introduced by the treatment of Si (111) surface with 4,4′‐azobis (4‐cyanopentanoic acid). The poly(methyl methacrylate) (PMMA) were then prepared under RITP conditions from the Si (111) wafer. The synthesis of amphiphilic diblock copolymer was carried out on Si‐g‐PMMA substrate by sequential addition of monomer N‐isopropylacrylamide (NIPAM). The observed narrow molecular weight distributions (M_w/M_n), linear kinetic plots, and linear plots of molecular weight (M_n) versus monomer conversion indicate that the chain growth from the silicon substrates is a controlled process with a “living” characteristic. The ellipsometry and contact angle results indicated that the MMA had grafted from the surface of the silicon substrates successfully and the graft layer was well defined. The structure of the polymer and the ability to extend the chains were characterized and confirmed with the surface sensitive techniques such as X‐ray photoelectron spectroscopy and atomic force microscope. POLYM. ENG. SCI., 54:925–931, 2014. © 2013 Society of Plastics Engineers     

Synthesis and characterization of amphiphilic block copolymers of methyl methacrylate with poly(ethylene oxide) macroinitiators formed by atom transfer radical polymerization

Amphiphilic ABA triblock copolymers of poly(ethylene oxide) (PEO) with methyl methacrylate (MMA) were prepared by atom transfer radical polymerization in bulk and in various solvents with a difunctional PEO macroinitiator and a Cu(I)X/N,N,N′,N″,N″‐pentamethyldiethylenetriamine catalyst system at 85°C where X=Cl or Br. The polymerization proceeded via controlled/living process, and the molecular weights of the obtained block copolymers increased linearly with monomer conversion. In the process, the polydispersity decreased and finally reached a value of less than 1.3. The polymerization followed first‐order kinetics with respect to monomer concentration, and increases in the ethylene oxide repeating units or chain length in the macroinitiator decreased the rate of polymerization. The rate of polymerization of MMA with the PEO chloro macroinitiator and CuCl proceeded at approximately half the rate of bromo analogs. A faster rate of polymerization and controlled molecular weights with lower polydispersities were observed in bulk polymerization compared with polar and nonpolar solvent systems. In the bulk polymerization, the number‐average molecular weight by gel permeation chromatography (M_n,GPC) values were very close to the theoretical line, whereas lower than the theoretical line were observed in solution polymerizations. The macroinitiator and their block copolymers were characterized by Fourier transform infrared spectroscopy, ¹H‐NMR, matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry, thermogravimetry (TG)/differential thermal analysis (DTA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). TG/DTA studies of the homo and block copolymers showed two‐step and multistep decomposition patterns. The DSC thermograms exhibited two glass‐transition temperatures at ?17.7 and 92°C for the PEO and poly(methyl methacrylate) (PMMA) blocks, respectively, which indicated that microphase separation between the PEO and PMMA domains. SEM studies indicated a fine dispersion of PEO in the PMMA matrix. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 989–1000, 2005     

Synthesis and pH-dependent micellization of 2-(diisopropylamino)ethyl methacrylate based amphiphilic diblock copolymers via RAFT polymerization

The polymerization of 2-(diisopropylamino)ethyl methacrylate (DPA) by RAFT mechanism in the presence of 4-cyanopentanoic acid dithiobenzoate in 1,4-dioxane was studied. The DPA homopolymer was employed as a macro chain transfer agent to synthesize pH-sensitive amphiphilic block copolymers using poly(ethylene glycol) methyl ether methacrylate (PEGMA) as the hydrophilic block. ¹H NMR and GPC measurements confirmed the successful synthesis of these copolymers. Potentiometric titrations and fluorescence experiments proved that the copolymers underwent a sharp transition from unimers to micelles at a pH of ∼6.7 in phosphate buffered saline solutions. It was found that the hydrophilic/hydrophobic balance of these block copolymers had no apparent effect on their pH-induced micellization behaviors. The DLS investigation revealed that the micelles have a mean hydrodynamic diameter below 60 nm with a narrow size distribution.     

Well-defined diblock copolymers of poly(tert-butyldimethylsilyl methacrylate) and poly(dimethylsiloxane) synthesized by RAFT polymerization

We report the application of reversible addition-fragmentation chain transfer (RAFT) polymerization using poly(dimethylsiloxane) (PDMS) chain transfer agents toward the synthesis of a variety of diblock copolymers containing tert-butyldimethylsilyl methacrylic (MASi) monomer units. The methodology relies on the synthesis of PDMS monofunctional chain transfer agents easily available in one synthetic step from commercially available hydroxylated PDMSs. The RAFT process enables access to polymer chains with narrow molar mass distributions and high conversions. Data from differential scanning calorimetric measurements revealed that the diblock copolymers exhibited two glass transition temperatures, corresponding to the PDMS- and PMASi-enriched phases, respectively. Copolymerizations of MASi and butyl methacrylate (BMA) within the second block led to immiscible phases with lower glass transition temperatures than PDMS-block-PMASi copolymers.     

Synthesis and surface properties of amphiphilic fluorine-containing diblock copolymers

Amphiphilic diblock copolymers (DCs) of 2,3,4,5,6-pentafluorostyrene (PFS) and 2-hydroxyethyl methacrylate (HEMA) of different composition and molecular weights were prepared by two-step reversible addition–fragmentation chain transfer (RAFT) polymerization and first used for preparation of superhydrophobic coatings for cotton/polyester fabrics. The transition from hydrophobic to superhydrophobic coatings is controlled by the ratio between poly(2,3,4,5,6-pentafluorostyrene) (PPFS) block and poly(2-hydroxyethyl methacrylate) (PHEMA) block lengths (P_n^PFS/P_n^HEMA). The increase in P_n^PFS/P_n^HEMA is accompanied by a significant increase in water (θ^Н₂^О) and diiodomethane (θ^CH₂^I₂) contact angles, which reach the plateau at P_n^PFS/P_n^HEMA = 3.5 and remains almost constant up to P_n^PFS/P_n^HEMA = 6.2. Surface modification of the cotton/polyester fabric with the DC having P_n^PFS/P_n^HEMA = 6.2 produced superhydrophobic surface with θ^Н₂^О = 158 ± 4° and contact angle hysteresis CAH = 5 ± 2°, and θ^CH₂^I₂ = 107 ± 3°.     

Synthesis of poly(styrene-co-isopropenyl acetate) -g-polyisobutylene graft copolymers via combination of radical polymerization with cationic polymerization

Random copolymers of poly(styrene-co-isopropenyl acetate) (SIPA) with an average number of 9 initiating sites per chain were synthesized by free radical copolymerization of styrene with a small amount of isopropenyl acetate using 2,2′-azo-bis-(isobutyronitrile) as an initiator at 70 °C. SIPA copolymer could be further used as macroinitiator for the grafting cationic polymerization of isobutylene (IB) from SIPA chain in CH₂Cl₂ at ?40 °C to produce graft copolymers of SIPA-g-PIB. The effect of SIPA concentration ([SIPA]), TiCl₄ concentration ([TiCl₄]) and IB concentration ([IB]) on initiation efficiency of macroinitiator, grafting efficiency of initiating sites, average length of PIB branches of the resulting graft copolymers were investigated. It can be found that almost all of the initiating sites of IPAc units on SIPA chains were active for the cationic polymerization of IB and both initiation efficiency and grafting efficiency were close to 100% at sufficient molar ratio of TiCl₄/IPAc. This synthetic route presents quantitative grafting efficiency and possibility to control length of PIB branches. The graft copolymers of SIPA-g-PIB with average 9-branched PIB chains having terminal functional tert-chlorine groups could be successfully obtained. The average molecular weight of PIB branches in SIPA-g-PIB graft copolymers could be mediated from 3900 to 47,300 g mol^?1 by changing the ratios of macroinitiator to monomer and concentration of TiCl₄.     

Nanostructures from photo-cross-linked amphiphilic poly(ethylene oxide)-b-alkyl diblock copolymers

Poly(ethylene oxide) monomethylether was functionalized by alkyl chains of various lengths (l=10-19 methylene groups) bearing a polymerizable methacrylate moiety. Each synthesis step on the polymer gives quantitative functionalization rates. The self-assembly of the amphiphilic polymers in water was studied by light scattering for various end-groups. Sterical and polar effects were shown to influence the micellization step. The cores of the micelles formed by PEO-C_l-methacrylate were irreversibly cross-linked by UV irradiation. Star polymers that are stable under dilution in good solvent are obtained after 1-min irradiation. The hydrodynamic radius and the molar mass of the nanoparticles depend on the amount of photoinitiator introduced in the cores.     

Synthesis of diblock copolymer poly(10-hydroxydecanoic acid)/polystyrene by combining enzymatic condensation polymerization and ATRP

Summary The diblock copolymers poly(10-hydroxydecanoic acid)-block-polystyrene (PHDA-b-PSt) were synthesized by combining enzymatic condensation polymerization of 10-hydroxydecanoic acid (HDA) and atom transfer radical polymerization (ATRP) of styrene (St). PHDA was firstly obtained via enzymatic condensation polymerization catalyzed by Novozyme-435. Subsequently one end of poly(10-hydroxydecanoic acid) (PHDA) chains was modified by reaction with α-bromopropionyl bromide and the other was protected by chlorotrimethylsilane (TMSCL), respectively, the resulting monofunctional macroinitiator was used in the ATRP of St using CuCl/2,2^′-bipyridine (bpy) as the catalyst system to afford the diblock copolymers including biodegradable PHDA blocks and well-defined PSt blocks.     

Synthesis and polymerization ofgem-methyl-(vinylbenzyl)tetrachlorocyclotriphosphazene

A new styrene-substituted chlorocyclotriphosphazene,gem-methyl(vinylbenzyl) tetrachlorocyclotriphosphazene, has been prepared from vinylbenzylmagnesium chloride and hexachlorocyclotriphosphazene. The organosubstituted chlorocyclotriphosphazene has been used in radical homo- and copolymerization with methyl methacrylate. The reactivity ratios for the MMA copolymerization show a small effect of the phosphazene ring on the olefin reactivity. All these polymers exhibit flame-retardant properties.     

Synthesis of poly(vinyl acetate) by degenerative transfer polymerization in the presence of iodine

A new curing agent containing maleimide and biphenyl moieties (MIBP) was synthesized by the condensation polymerization of 4,4′-bismethoxymethylbiphenyl and N-(4-hydroxyphenyl)maleimide (HPM). The chemical structure was characterized with Fourier transform infrared (FTIR) spectroscopy, and the molecular weight of the new curing agent was determined by gel permeation chromatography. Curing reactions of O-cresol formaldehyde epoxy (CNE) resin with MIBP were investigated under nonisothermal differential scanning calorimetry, and the exotherm exhibited two overlapping exothermic peaks during the curing process; this was demonstrated by FTIR traces. The Flynn–Wall–Ozawa and Friedman methods were used to examine the kinetic parameters and the kinetic models of the curing processes of the CNE/MIBP mixtures. Both reactions turned out to be nth-order curing mechanisms. Values of the reaction order (n) = 1.42 and activation energy (E_a) = 91.2 kJ/mol were obtained for the first reaction of the curing of the CNE/MIBP system, and values of n = 1.11 and E_a = 78.7 kJ/mol were obtained for the second reaction. The thermal properties of the cured resin were measured with thermogravimetric analysis, and the results show a high glass-transition temperature (T_g = 155°C), good thermal stability (temperature at 10% weight loss, under nitrogen and in air, ≈ 400 and 408°C, respectively), and high char yield (temperature = 800°C, char residue = 44.5% under nitrogen). These excellent thermal properties were due to the introduction of the maleimide and biphenyl groups of MIBP into the polymer structure. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis of comb-shaped copolymers by combination of reversible addition-fragmentation chain transfer polymerization and cationic ring-opening polymerization

Comb-shaped graft copolymers with poly(methyl acrylate) as a handle were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization and ring-opening polymerization (ROP) techniques in three steps. First, copolymers of poly(styrene-co-chloromethyl styrene), poly(St-co-CMS), were prepared by RAFT copolymerization of St and CMS using 1-(ethoxycarbonyl)prop-1-yl dithiobenzoate (EPDTB) as RAFT agent. Second, the polymerization of MA using poly(St-co-CMS)-SC(S)Ph as macromolecular chain transfer agent produced block copolymer poly(St-co-CMS)-b-PMA. Third, cationic ring-opening polymerization of THF was performed using poly(St-co-CMS)-b-PMA/AgClO₄ as initiating system to produce comb-shaped copolymers. The structures of the poly(St-co-CMS), poly(St-co-CMS)-b-PMA and final comb-shaped copolymers were characterized by ¹H NMR spectroscopy and gel permeation chromatography (GPC).