The amphiphilic block copolymers of 2-(dimethylamino)ethyl methacrylate and methyl methacrylate: Synthesis by atom transfer radical polymerization and solution properties

Amphiphilic di- and tri-block copolymers of poly(methyl methacrylate) (PMMA) and poly(2-dimethylamino)ethyl methacrylate (PDMAEMA) have been synthesized by atom transfer radical polymerization (ATRP) at ambient temperature (35 °C) in the environment-friendly solvent, aqueous ethanol (water 16 vol%) using CuCl/o-phenanthroline as the catalyst. The PDMAEMA blocks are contaminated with ethyl methacrylate (EMA) residues to the extent of 1-2 mol% of DMAEMA depending on the length of the PDMAEMA block. The EMA forms through the autocatalyzed ethanolysis of the DMAEMA monomer and undergoes random copolymerization with the latter. The rate of ethanolysis is unexpectedly greater in the aqueous ethanol than in neat ethanol, which has been attributed to the higher polarity of the former than of the latter. In contrast to the ethanolysis no hydrolysis of DMAEMA in the aqueous ethanol medium could be detected for 133 h. The block copolymers form micelles in water. Their solubility and CMC in neutral water have been studied. Dynamic light scattering (DLS) studies reveal that for a fixed degree of polymerization (DP) of the PMMA block the hydrodynamic diameter of the micelles in methanolic water (water 95 vol%) increases at a faster rate with the DP of the PDMAEMA block when it is much greater than that of the PMMA block compared to when it is less than or close to that of the latter.     

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.     

Synthesis and characterization of poly(dimethylamino ethyl methacrylate)–poly(ethylene oxide)–poly(dimethylamino ethyl methacrylate) triblock copolymers

Novel, monodispersed, and well‐defined ABA triblock copolymers [poly(dimethylamino ethyl methacrylate)–poly(ethylene oxide)–poly(dimethylamino ethyl methacrylate)] were synthesized by oxyanionic polymerization with potassium tert‐butanoxide as the initiator. Gel permeation chromatography and ¹H‐NMR analysis showed that the obtained products were the desired copolymers with molecular weights close to calculated values. Because the poly(dimethylamino ethyl methacrylate) block was pH‐ and temperature‐sensitive, the aqueous solution behavior of the polymers was investigated with ¹H‐NMR and dynamic light scattering techniques at different pH values and at different temperatures. The micelle morphology was determined with transmission electron microscopy. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Stereocomplex crystallization and spherulite growth behavior of poly(l-lactide)-b-poly(d-lactide) stereodiblock copolymers

The non-isothermally and isothermally crystallized stereodiblock copolymers of poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) with equimolar l-lactyl and d-lactyl units and different number-average molecular weights (M_n) of 3.9 × 10³, 9.3 × 10³, and 1.1 × 10⁴ g mol⁻¹, which are abbreviated as PLLA-b-PDLA copolymers, contained only stereocomplex crystallites as crystalline species, causing higher melting temperatures of the PLLA-b-PDLA copolymers compared to those of PLLA homopolymers. In the case of non-isothermal crystallization, the cold crystallization temperatures of the PLLA-b-PDLA copolymers during heating and cooling were respectively lower and higher than those of PLLA homopolymers, indicating accelerated crystallization of PLLA-b-PDLA copolymers. In the case of isothermal crystallization, in the crystallizable temperature range, the crystallinity (X_c) values of the PLLA-b-PDLA copolymers were lower than those of the PLLA homopolymers, and were susceptible to the effect of crystallization temperature in contrast to that of homopolymers. The radial growth rate of the spherulites (G) of the PLLA-b-PDLA copolymers was the highest at the middle M_n of 9.3 × 10³ g mol⁻¹. This trend is different from that of the PLLA homopolymers where the G values increased monotonically with a decrease in M_n, but seems to be caused by the upper critical M_n values of PLLA and PDLA chains as in the case of PLLA/PDLA blends (in other papers), above which homo-crystallites are formed in addition to stereocomplex crystallites. The disturbed crystallization of PLLA-b-PDLA copolymers compared to that of the PLLA/PDLA blend is attributable to the segmental connection between the PLLA and PDLA chains, which interrupted the free movement of those chains of the PLLA-b-PDLA copolymers during crystallization. The crystallite growth mechanism of the PLLA-b-PDLA copolymers was different from that of the PLLA/PDLA blend.     

Poly(dimethylsiloxane‐b‐styrene) diblock copolymers prepared by reversible addition–fragmentation chain‐transfer polymerization: Synthesis and characterization

Well‐defined poly(dimethylsiloxane‐b‐styrene) diblock copolymers were prepared by reversible addition–fragmentation chain‐transfer (RAFT) polymerization. Monohydroxyl‐terminated polydimethylsiloxane was modified to form a functional polydimethylsiloxane/macro‐RAFT agent, which was reacted with styrene to form the diblock copolymers. The chemical compositions and structures of the copolymers were characterized by proton nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and gel permeation chromatography. The surface properties and morphology of the copolymers were investigated with static water contact‐angle measurements, X‐ray photoelectron spectroscopy, transmission electron microscopy, and atomic force microscopy, which showed a low surface energy and microphase separation surfaces that were composed of hydrophobic domains from polydimethylsiloxane segments. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and characterization of poly(ethylene glycol)-b-poly (l-lactide)-b-poly(l-glutamic acid) triblock copolymer

A biodegradable amphiphilic triblock copolymer of poly(ethylene glycol)-b-poly(l-lactide)-b-poly(l-glutamic acid) (PEG-b-PLLA-b-PLGA) was obtained by catalytic hydrogenation of poly(ethylene glycol)-b-poly(l-lactide)-b-poly(γ-benzyl-l-glutamic acid) (PEG-b-PLLA-b-PBLGA) synthesized by the ring-opening polymerization (ROP) of N-carboxyanhydride of γ-benzyl-l-glutamate (BLG-NCA) with amino-terminated MPEG-b-PLLA-NH₂ as a macroinitiator. MPEG-b-PLLA-NH₂ converted from MPEG-b-PLLA-OH first reacted with tert-Butoxycarbonyl-l-phenylalanine (Phe-^NBOC) and dicyclohexylcarbodiimide (DCC) and then deprotected the tert-butoxycarbonyl group. MPEG-b-PLLA-OH was prepared by ROP of l-lactide with monomethoxy poly(ethylene glycol) in the presence of stannous octoate. The triblock copolymer and its diblock precursors were characterized by ¹H NMR, FTIR, GPC and DSA (drop shape analysis) measurements. The lengths of each block polymers could be tailored by molecular design and the ratios of feeding monomers. The triblock polymer PEG-b-PLLA-b-PLGA containing carboxyl groups showed obviously improved hydrophilic properties and could be a good potential candidate as a drug delivery carrier.     

One-pot synthesis of poly(methacrylic acid)-b-poly(2,2,2-trifluoroethyl methacrylate) diblock copolymers via RAFT polymerization

In this work, the reversible addition-fragmentation chain transfer (RAFT) polymerization was utilized to synthesize the amphiphilic diblock copolymers of poly(methacrylic acid)-b-poly(2,2,2-trifluoroethyl methacrylate) (PMAA-b-PTFEMA) via one-pot two-step reaction protocol. The controlled radical polymerization of MAA monomer was first carried out in pure water by using 4-cyanopentanoic acid dithiobenzoate (CADB) as chain transfer agent. Subsequently, the as-synthesized PMAA homopolymers with dithiobenzoate end-groups were employed as macro-CTA and chain-extended in situ with the hydrophobic TFEMA monomer. The reactions were carried out in 1,4-dioxane/water medium. Both the polymerization of PMAA and PTFEMA blocks showed the well controllability on the molecular weighs and distributions. It was found that the amphiphilic diblock copolymers formed the stable spherical particles via the polymerization-induced self-assembly. Meanwhile, the effect of various parameters, such as the concentration ratio of TFEMA monomer over PMAA macro-CTA, the solvent condition (different ratio of 1,4-dixane/water), and the pH, on the RAFT polymerization of TFEMA monomer were investigated in detail. Their kinetic results suggested that the propagation of TFEMA monomer on the macro-CTA was performed at the particle/water interfaces. The concentration of chain transfer agents at the interfaces determined the polymerization rate. Finally, the stability of the fluorinated polymer dispersions was also evaluated in this work.     

Preparation and properties of semifluorinated block copolymers of 2-(dimethylamino)ethyl methacrylate and fluorooctyl methacrylates

Semifluorinated block copolymers of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and poly(fluorooctyl methacrylates) (PFOMA) were prepared using group transfer polymerisation via sequential monomer addition. Wide ranges of copolymers were obtained with good control over both molecular weight and composition by adjusting the monomers/initiator ratio. The micellar characteristics of the copolymers in water and chloroform were investigated by quasi-elastic light scattering and transmission electron microscopy. The size and morphologies of micelles were greatly influenced by copolymer composition, pH, and temperature. In addition, the solubility of copolymers and the formation of water-in-carbon dioxide (W/C) microemulsions were described in terms of the cloud points. The block copolymers exhibited the excellent ability of stabilizing W/C microemulsions.     

Synthesis of poly(trioctylammonium p-styrenesulfonate) homopolymers and block copolymers by RAFT polymerization

A method to prepare sulfonated polystyrene-containing block copolymers has been investigated by neutralizing styrene sulfonic acid with trioctylamine to produce the hydrophobic monomer trioctylammonium p-styrenesulfonate (SS-TOA). This monomer was polymerized by reversible addition fragmentation chain transfer (RAFT) polymerization to produce PSS-TOA homopolymers. A PSS-TOA homopolymer was then used as a macro-RAFT agent for the polymerization of styrene to prepare poly(trioctylammonium p-styrenesulfonate)-block-poly(styrene) (PSS-TOA-b-PS). These block copolymers could be ion-exchanged to produce either the hydrophilic sodium salt form of PSS or a hydrophobic quaternary ammonium salt. This approach will be useful for preparing PSS-containing block copolymers with a range of hydrophobic blocks for applications such as ion-exchange membranes.     

Selective betainization of 2-(dimethylamino)ethyl methacrylate residues in tertiary amine methacrylate diblock copolymers and their aqueous solution properties

2-(dimethylamino)ethyl methacrylate (DMA) was block copolymerized in turn with three other tertiary amine methacrylate comonomers, namely 2-(diethylamino)ethyl methacrylate (DEA), 2-(diisopropylamino)ethyl methacrylate (DPA) and 2-(N-morpholino)ethyl methacrylate (MEMA), using group transfer polymerization (GTP). The DMA residues of each of these diblock copolymers were selectively betainized using 1,3-propane sultone under mild conditions to yield a series of novel betaine diblock copolymers. These selectively betainized copolymers could be dissolved molecularly without co-solvents in aqueous media at room temperature, with micellization occurring reversibly on judicious adjustment of the solution pH, temperature or electrolyte concentration. In all three cases, stable block copolymer micelles were formed with betainized-DMA coronas and hydrodynamic diameters of 10-46 nm. The selective betainization of the DMA residues dramatically reduces the surface activity and increase the solubility of the tertiary amine methacrylate block copolymers (DMA-DEA, DMA-DPA and DMA-MEMA).     

Online monitoring of the copolymerization of 2-(dimethylamino)ethyl acrylate with styrene by RAFT. Deviations from reaction control

Kinetics of copolymerization reactions of 2-(dimethylamino)ethyl acrylate (DMAEA) and styrene by reversible addition fragmentation transfer (RAFT) in N,N-dimethylformamide (DMF) are reported. Novel approaches in the online monitoring of the synthesis of the amphiphilic copolymers by Automatic Continuous Online Monitoring of Polymerization reactions (ACOMP) are presented. Automatic withdrawal of separate reactor streams and their subsequent dilution throughout the reaction with organic and aqueous solvents, respectively, allowed different features to be captured. Thus, light scattering data combined with spectroscopic and viscometric measurements in DMF, together with conductivity measurements in aqueous medium provided in real time comonomer conversion, copolymer mass, reduced viscosity, and composition. Continuous data gathered allowed observing and quantifying the DMAEA-linked macroRAFT control agent decomposition, with significant effects on the reaction kinetics. Deviations from controlled behavior were investigated during (co)polymerization reactions under different conditions.Multi-detector Size Exclusion Chromatography (SEC) and NMR were used to bring additional information on the system investigated.     

Synthesis of a novel polymeric surfactant by reductive N-alkylation of chitosan with 3-O-dodecyl-d-glucose

A novel chitosan-based polymeric surfactant, DG-chitosan, was prepared via reductive N-alkylation of chitosan with 3-O-dodecyl-d-glucose in acetate buffer (pH 4.3, 0.1 M)-methanol in the presence of sodium cyanoborohydride (NaBH₃CN). DG-chitosan was swelling in water, partly dissolvable in pyridine and DMF, and completely soluble in 0.1% aqueous acetic acid. ¹H and ¹³C NMR spectroscopic analyses in 2% acetic acid-d₄-methanol-d₄ together with elemental analysis showed the degree of substitution was 27%. Formation of polymeric micelles was observed by use of pyrene as a fluorescent probe, and the critical aggregation concentration (CAC) of DG-chitosan was marked equal to 28.1 mg/L.     

Syntheses of well-defined poly(siloxane)-b-poly(styrene) and poly(norbornene)-b-poly(styrene) block copolymers using functional alkoxyamines

Functional alkoxyamines, 1-[4-(4-lithiobutoxy)phenyl]-1-(2,2,6,6-tetramethylpiperidinyl-N-oxyl)ethane (2) and 1-[4-(2-vinyloxyethoxy)phenyl]-1-(2,2,6,6-tetramethylpiperidinyl-N-oxyl)ethane (3) were prepared, and well-defined poly(hexamethylcyclotrisiloxane)-b-poly(styrene)[poly(D₃)-b-poly(St)] and poly(norbornene)-b-poly(St) [poly(NBE)-b-poly(St)] were prepared using the alkoxyamines. The first step was preparation of poly(D₃) and poly(NBE) macroinitiators, which were obtained by the ring-opening anionic polymerization of D₃ using 2 as an initiator and the ring-opening metathesis polymerization of NBE using 3 as a chain transfer. The radical polymerization of St by the poly(D₃) and poly(NBE) macroinitiators proceeded in the ‘living’ fashion to give well-defined poly(D₃)-b-poly(St) and poly(NBE)-b-poly(St) block copolymers.     

Synthesis and characterization of dendritic-linear-dendritic triblock copolymers based on poly(amidoamine) and polystyrene

Dendritic-linear-dendritic triblock copolymers composed of linear polystyrene (PSt) and poly(amidoamine) dendrons have been successfully synthesized. Two bromines-terminated PSt with M_n = 13,000 was prepared by atom transfer radical polymerization (ATRP) using α,α′-dibromo-p-xylene as initiator. Then the terminal bromines at both ends of PSt chains were replaced by one imine group of piperazine (PZ), and further Michael addition reaction of terminal PZ with excess 1,3,5-triacryloylhexahydro-1,3,5-triazine (TT) produced the first generation (G₁) of the triblock copolymer. Continuous growth of dendrons from G1.5 to G4 at the both ends of PSt chains was carried out by the iterative Michael addition reactions with excess PZ and following TT. The ABA triblock copolymers composed of the G₁-G₄ dendrons and the linear PSt were obtained. Structures of the triblock polymers were characterized by GPC and ¹H NMR spectra. Thermal phase transitions of the polymers were studied by DSC measurements, and all of the copolymers displayed a glass transition temperature.     

Anionic polymerization of 2-(N-carbazolyl)ethyl methacrylate

The homopolymer, poly(CzMA), with controlled molecular weight (MW) and narrow molecular weight distributions (MWD) was successfully synthesized by using (1,1,4,4-tetraphenylbutanediyl)dipotassium and diethylzinc (Et₂Zn) in THF at various temperatures, 25, −45, and −78 °C, under high vacuum conditions. The Et₂Zn acted both as a protective group through the formation of coordination with ester enolate anion and as a scavenger to remove impurities. Block copolymers, poly(CzMA-b-styrene-b-CzMA) and poly(MMA-b-CzMA-b-MMA), with narrow MWD were also successfully synthesized by sequential anionic living polymerization.     

Synthesis of well‐defined comb‐like amphiphilic copolymers with protonizable units in the pendent chains: 2. Poly(2‐(dimethylamino)ethyl methacrylate) grafted poly(methyl methacrylate‐co‐2‐hydroxyethyl methacrylate) copolymers and their association behavior in aqueous solution

Narrow‐distribution, well‐defined comb‐like amphiphilic copolymers are reported in this work. The copolymers are composed of poly(methyl methacrylate‐co‐2‐hydroxyethyl methacrylate) (P(MMA‐co‐HEMA)) as the backbones and poly(2‐(dimethylamino)ethyl methacrylate) (PDMAEMA) as the grafted chains, with the copolymer backbones being synthesized via atom‐transfer radical polymerization (ATRP) and the grafted chains by oxyanionic polymerization. The copolymers were characterized by gel permeation chromatography (GPC), Fourier‐transform infrared (FT‐IR) spectroscopy and ¹H NMR spectroscopy. The aggregation behavior in aqueous solutions of the comb‐like amphiphilic copolymers was also investigated. ¹H NMR spectroscopic and surface tension measurements all indicated that the copolymers could form micelles in aqueous solutions and they possessed high surface activity. The results of dynamic light scattering (DLS) and scanning electron microscopy (SEM) investigations showed that the hydrodynamic diameters of the comb‐like amphiphilic copolymer aggregates increased with dilution. Because of the protonizable properties of the graft chains, the surface activity properties and micellar state can be easily modulated by variations in pH. Copyright © 2004 Society of Chemical Industry     

Poly(dimethylsiloxane‐b‐styrene) diblock copolymers prepared by reversible addition‐fragmentation chain transfer polymerization: Kinetic model

Well‐defined polydimethylsiloxane‐block‐polystyrene (PDMS‐b‐PS) diblock copolymers were prepared by reversible addition‐fragmentation chain transfer (RAFT) polymerization using a functional PDMS‐macro RAFT agent. The RAFT polymerization kinetics was simulated by a mathematical model for the RAFT polymerization in a batch reactor based on the method of moments. The model described molecular weight, monomer conversion, and polydispersity index as a function of polymerization time. Good agreements in the polymerization kinetics were achieved for fitting the kinetic profiles with the developed model. In addition, the model was used to predict the effects of initiator concentration, chain transfer agent concentration, and monomer concentration on the RAFT polymerization kinetics. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Solvent and oxygen effects on the free radical polymerization of 6-O-vinyladipoyl-d-glucopyranose

The vinyl ester-type glycomonomer 6-O-vinyladipoyl-d-glucopyranose was polymerized in water and alcohol solutions. In all cases, long polymerization times were necessary to achieve reasonable conversions. Depending on the nature of the solvent, polydisperse glycopolymers were obtained possessing a molecular weight ranging between 10,000 and 122,000 Da (PS equivalent). Higher alcohols appeared to act as chain transfer agents and oligomers with DP_n between 2 and 6 were indeed obtained when 2-propanol was the solvent. Also, thorough oxygen removal from the reaction mixture proved to be essential for the success of the experiment, plain nitrogen sparging being ineffective in most cases.     

Synthesis and characterization of A-B-A triblock copolymers derived from chloro-telechelic poly(l-lactide): combining ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP)

Ring-opening polymerization (ROP) of l-lactide was combined with atom transfer radical polymerization (ATRP) to produce well-defined linear block copolymers. Poly(l-lactide) (PLLA) was synthesized via ROP using ethylene glycol as an initiator and stannous octoate as a catalyst. The isolated hydroxy-telechelic PLLA was reacted with thionyl chloride and pyridine in toluene to afford chloro-telechelic PLLA (Cl-PLLA-Cl). The latter was employed as a macroinitiator in the synthesis of A-B-A triblock copolymers having either tert-butyl acrylate or benzyl acrylate outer blocks. Outer-block molecular weight was targeted by the mole ratio of monomer (acrylate) to the PLLA chloride initiating sites. The actual incorporation of acrylate into the triblock copolymer was lower than the molar feed ratio as the copolymer became increasingly less soluble upon conversion of acrylate in all cases.