Unexpected reactivity for the RAFT copolymerization of oligo(ethylene glycol) methacrylates

Homo‐ and copolymers of di(ethylene glycol) methyl ether methacrylate (DEGMA) and oligo(ethyleneglycol) methyl ether methacrylate (OEGMA₁₁₀₀) were synthesized with various chain lengths via reversible addition fragmentation chain transfer (RAFT) polymerization in ethanol using [M]/[RAFT] ratios of 100 and 200. Kinetic investigations on the homo‐ and copolymerization of these monomers were performed using a parallel synthesizer resulting in well‐defined polymers with polydispersity indices mostly below 1.3. The polymerization kinetics are presented and discussed in detail surprisingly revealing that the DEGMA homopolymerization is slower than the OEGMA₁₁₀₀ homopolymerization. Transfer coefficients c were estimated to be ～0.5 for the RAFT polymerization of both DEGMA and OEGMA₁₁₀₀ resulting in hybrid behavior at the beginning of the polymerizations. Subsequent copolymerization also revealed fast incorporation of the OEGMA₁₁₀₀ and relatively slow incorporation of DEGMA resulting in well‐defined copolymers with a molecular weight up to 100 kDa and polydispersities around 1.20. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2811–2820, 2009     

Block copolymerization of methyl methacrylate with poly(ethylene oxide) radicals formed by high-speed stirring

A block copolymer of methyl methacrylate with poly(ethylene oxide) was synthesized by initiation with poly(ethylene oxide) radicals formed by high-speed stirring. The effects of the concentration of the monomer, the concentration of the polymer, the degree of polymerization, the rotation speed, and the solvent on the rate of copolymerization were studied. It was found that the rate of copolymerization was proportional to the concentration of the monomer and to the square root of the rate of scission of the polymer chain. The block copolymerization of methyl methacrylate monomer and styrene monomer (1 : 1 mole ratio) with poly(ethylene oxide) radicals was also carried out by the same method and it was found that the block copolymerization was a radical one.     

Crosslinked copolymers with degradable oligo(lactide) branches

Methods for preparation of oligo(lactone) macromonomers end-capped with methacrylate groups are summarized. The conversion of C=C double bonds during the crosslinking copolymerization of the macromonomers has been studied by means of Laser Raman spectroscopy at room temperature. Glass transition, mechanical properties and the degradation rate of composite materials prepared by copolymerization in the presence of hydroxylapatite may systematically be influenced both by the type of lactone monomer, e.g. D,L- or L,L-dilactide, diglycolide, and the comonomer, e.g. 2-hydroxyethyl methacrylate, tetrahydro-furfuryl methacrylate, tri(ethylene glycol) dimethacrylate. The composites should be useful as bone implant materials with lower polymerization exotherm and better biocompatibility than conventional materials based on methyl methacrylate.     

Libraries of methacrylic acid and oligo(ethylene glycol) methacrylate copolymers with LCST behavior

Homopolymers of methacrylic acid (MAA), monoethyleneglycol methyl ether methacrylate (MEOMA), diethyleneglycol methyl ether methacrylate (MEO₂MA), oligo(ethyleneglycol) methyl ether methacrylate (OEGMA₄₇₅ and OEGMA₁₁₀₀) and oligo(ethyleneglycol) ethyl ether methacrylate (OEGEMA₂₄₆) were synthesized with various chain lengths via reversible addition fragmentation chain transfer (RAFT) polymerization. The homopolymers of MAA, MEOMA and OEGMA₁₁₀₀ did not show any cloud point (CP) in the range of 0–100 °C, whereas at a pH value of 7, the CPs were found to be 20.6, 93.7, and 20.0 °C for p(MEO₂MA), p(OEGMA₄₇₅) and p(OEGEMA₂₄₆), respectively, with an initial monomer to initiator ratio of 50. Furthermore, statistical copolymer libraries of MAA with OEGMA₄₇₅ and OEGMA₁₁₀₀ were prepared. The cloud points of the random copolymers of MAA and OEGMA₄₇₅ were found to be in the range of 20–90 °C; surprisingly, even though the homopolymers of MAA and OEGMA₁₁₀₀ did not exhibit any LCST behavior, the copolymers of these monomers at certain molar ratios (up to 40% OEGMA₁₁₀₀) revealed a double responsive behavior for both temperature and pH. Finally, the cloud points were found to be in the range of 22–98 °C, measured at pH values of 2, 4, and 7, while no cloud point was detected at pH 10. © Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7138–7147, 2008     

SET‐RAFT of MMA mediated by ascorbic acid‐activated copper oxide

In this work, cupric oxide (CuO) or cuprous oxide (Cu₂O) was used as the catalyst for the single electron transfer‐reversible addition‐fragmentation chain transfer (SET‐RAFT) polymerization of methyl methacrylate in the presence of ascorbic acid at 25 °C. 2‐Cyanoprop‐2‐yl‐1‐dithionaphthalate (CPDN) was used as the RAFT agent. The polymerization occurred smoothly after an induction period arising from the slow activation of CuO (or Cu₂O) and the “initialization” process in RAFT polymerization. The polymerizations conveyed features of “living”/controlled radical polymerizations: linear evolution of number‐average molecular weight with monomer conversion, narrow molecular weight distribution, and high retention of chain end fidelity. From the polymerization profile, it was deduced that the polymerization proceeded via a conjunct mechanism of single electron transfer‐living radical polymerization (SET‐LRP) and RAFT polymerization, wherein CPDN acting as the initiator for SET‐LRP and chain transfer agent for RAFT polymerization. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Novel antifouling oligo(ethylene glycol) methacrylate particles via surfactant-free emulsion polymerization

The use of particle formulations with antifouling surface properties attracts increasing interest in several biotechnological applications. Majority of these studies utilize a poly(ethylene glycol) coating to render the corresponding surface nonrecognizable to biological macromolecules. Herein, we report a simple way to prepare novel antifouling colloids composed of oligo(ethylene glycol) backbones via surfactant-free emulsion polymerization. Monodisperse cross-linked poly(ethylene glycol) ethyl ether methacrylate particles were characterized by dynamic light scattering and transmission electron microscopy. The effects of monomer, cross-linker and initiator on particle characteristics were investigated. More importantly, a prominent blockage of bovine serum albumin adsorption was obtained for the poly(ethylene glycol)-based sub-micron (~200 nm) particles when compared with similar-sized poly(methyl methacrylate) counterparts.     

Radical copolymerization of 2-vinyl pyridine and oligo(ethylene glycol) methyl ether methacrylates: Monomer reactivity ratios and thermal properties

Statistical copolymers of 2-vinylpyridine (VP) with oligo(ethylene glycol) methyl ether methacrylates of two different molecular weights (300 g/mol (OEGMA₃₀₀) and 1100 g/mol (OEGMA₁₁₀₀)), were prepared by free radical polymerization. The reactivity ratios of these two sets of monomers were estimated using the Finemann–Ross, the inverted Finemann–Ross and the Kelen–Tüdos graphical methods. Structural parameters of the copolymers were obtained by calculating the dyad monomer sequence fractions and the mean sequence length. The effect of the length of the oligo(ethylene glycol) group on the copolymer structure is discussed. The glass-transition temperature (T_g) values of the VP copolymers with OEGMA₃₀₀ were measured and examined in the frame of several theoretical equations, allowing the prediction of these T_g values. The copolymers of VP with OEGMA₁₁₀₀ exhibited the characteristic melting endotherm, due to the crystallinity of the methacrylate sequences and glass transition temperatures attributed to the PVP sequences.     

Synthesis of superparamagnetic and thermoresponsive hybrid nanoparticles via surface‐mediated RAFT polymerization of di(ethylene glycol) ethyl ether acrylate and (oligoethylene glycol) methyl ether acrylate

A reversible addition‐fragmentation chain transfer (RAFT) agent was directly anchored onto superparamagnetic Fe₃O₄ nanoparticles (SPNPs) in a simple procedure using a ligand exchange reaction of 2‐[(dodecylsulfanylcarbonylthiolsulfanyl) propionic acid] (DCPA) with oleic acid initially present on the surface of Fe₃O₄ nanoparticles. The DCPA‐modified SPNPs were then used for the surface‐mediated RAFT polymerization of di(ethylene glycol) ethyl ether acrylate and (oligoethylene glycol) methyl ether acrylate to fabricate structurally well‐defined hybrid SPNPs with temperature‐responsive poly[di(ethylene glycol) ethyl ether acrylate‐co‐(oligoethylene glycol) methyl ether acrylate] shell and magnetic Fe₃O₄ core. Evidence of a well‐controlled surface‐mediated RAFT polymerization was gained from a linear increase of number‐average molecular weight with overall monomer conversions and relatively narrow polydispersity indices of the copolymers grown from the SPNPs. The resultant hybrid nanoparticles exhibited superparamagnetic property with a saturation magnetization of 55.1–19.4 emu/g and showed a temperature‐responsive phenomenon as the temperature changed between 25 and 40 ^°C. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3420–3428     

Cononsolvency-induced micellization of pyrene end-labeled diblock copolymers of N-isopropylacrylamide and oligo(ethylene glycol) methyl ether methacrylate

Pyrene end-labeled double hydrophilic diblock copolymers, poly(N-isopropylacrylamide)-b-poly(oligo(ethylene glycol) methyl ether methacrylate) (Py-PNIPAM-b-POEGMA), were synthesized via consecutive reversible addition-fragmentation chain transfer polymerization using a pyrene-containing dithioester as the chain transfer agent. These diblock copolymers molecularly dissolve in pure methanol and water, but form well-defined and nearly monodisperse PNIPAM-core micelles in an appropriate mixture of them due to the cononsolvency of PNIPAM block. 1H NMR, laser light scattering, fluorescence spectroscopy, and transmission electron microscopy were employed to characterize the cononsolvency-induced PNIPAM-core micelles. When the volume fraction of water, phi water, in the methanol/water mixture is in the range of 0.5-0.8, the sizes of micelles are in the range of 20-30 nm in radius for Py-PNIPAM50-b- POEGMA18. At phi water = 0.5, the formed micelles possess the highest overall micelle density and the largest molar mass. The effects of varying the block lengths of Py-PNIPAM-b-POEGMA diblock copolymers on the structural parameters of PNIPAM-core micelles have also been explored. Although we can observe the immediate appearance of bluish tinge upon mixing the diblock copolymer solution in methanol with equal volume of water (phi water = 0.5), which is characteristic of the formation of micellar aggregates, the whole micellization process apparently takes a relatively long time to complete, as revealed by monitoring the time dependence of fluorescence emission spectra. The excimer/monomer fluorescence intensity ratios, IE/IM, continuously decrease with time and then reach a plateau value after approximately 20 min. The decrease of IE/IM after the initial formation of pseudo-equilibrium micelles should be ascribed to the structural rearrangement and further packing of PNIPAM segments within the micelle core, restricting the mobility of pyrene end groups and decreasing the probability of contact between them. Compared to the conventional cosolvent approach employed for the micellization of block copolymers in selective solvents, the reported cononsolvency-induced unimer-micelle-unimer transition of Py-PNIPAM-b-POEGMA in methanol/water mixtures has been unprecedented.     

Conventional free-radical and RAFT copolymerization of poly(ethylene oxide) containing macromonomers

Conventional free-radical and RAFT copolymerization of poly(ethylene oxide) substituent containing methacrylate macromonomers, PEO₅MEMA and PEO₄₅MEMA, was studied by the use of ¹H NMR spectroscopy for an analysis of residual monomers. From the monomer consumption curves, several parameters including monomer conversion, instantaneous copolymer composition and reactivity ratios of the monomers were evaluated. Reactivity ratios of PEO₅MEMA and MAA estimated by non-linear approach of error-in-variables model and presented as joint confidence regions were constant during conventional free-radical and RAFT copolymerizations of the above monomers but were slightly affected by the RAFT process. Reactivity ratio of PEO₄₅MEMA was found to be lower than that of PEO₅MEMA and varied during copolymerization: increased with conversion in conventional free-radical copolymerization and slightly (without confidence) decreased in the RAFT process. RAFT copolymerization of PEO₄₅MEMA and MAA enabled to synthesize comb copolymers with low composition distribution and more homogeneous distribution of PEO side chains along the mainchain. Under copolymerization with MAA, PEO₄₅MEMA behaved like typical macromonomer with appropriate steric hindrance while the behavior of PEO₅MEMA was similar to that of a low-molecular methacrylate.     

Cu(0) Wire-mediated Single-electron Transfer-living Radical Polymerization of Oligo(ethylene oxide) Methyl Ether Acrylate by Selecting the Optimal Reaction Conditions

The efficient Cu(0) wire-catalyzed single-electron transfer-living radical polymerization (SET-LRP) in organic solvents and mixtures of the organic solvents with water has been thoroughly investigated.Oligo(ethylene oxide) methyl ether acrylate was used as an exemplar oligomer monomer to determine the optimum polymerization conditions for rapid,controlled,and quantitative production of well-defined polymers.The effects of Cu(0)-wire length (12.5 or 4.5 cm),ligand type (tris(dimethylaminoethyl)amine,Me6-TREN,or tris(2-aminoethyl)amine,TREN),and solvent type (dipolar aprotic solvents,cyclic ethers,alcohol,or acetone) on the polymerization have been evaluated.Kinetic experiments were performed for all polymerizations to assess the "living" behavior of each system employed.Importantly,TREN could be used as a replacement for Me_6-TREN in Cu(0) wire-catalyzed SET-LRP of oligomer monomer,which probably provides the most economical and efficient methodology since TREN is 80 times less expensive than Me6-TREN.The high chain-end fidelity of resulting polymer was experimentally verified by thiol-Michael addition reaction at the a-Br chain end and subsequent chain extension with methyl acrylate.     

Macromolecular Architecture Based on Anionically Prepared Poly(ethylene oxide) Macromonomers

Synthesis of poly(ethylene oxide) (PEO) macromonomers carrying a methacyloyl group in one end, and N, N-dimethyl amino, thiophene, styryl and vinyl ether functional groups in the other end was desribed. The general synthetic strategy is based on the living anionic polymerization of ethylene oxide initiated with functional potassium alcoholates, followed by reaction with methacyloyl chloride. These macromonomers were further utilized in various macromolecular architectures through via concurrent or selective thermal free radical, oxidative and photoinitiated free radical and cationic polymerization methods. The use of this synthetic route to prepare graft copolymers possessing completly and perfectly alternating PEO side chains using charge-transfer-complex polymerization was also demonstrated.     

Synthesis of oligo(ethylene glycol) methacrylate polymer brushes

Here we report a study into controlling the polymerization of mono-hydroxy and mono-methoxy terminated oligo(ethylene glycol) methacrylates (HOEGMA and MeOEGMA, respectively) from functionalised, planar surfaces via atom transfer radical polymerization (ATRP). The effects of initiator structure, initiator density, temperature, and monomer ratios have been investigated for these polymerizations. The polymer brushes grown in this way were found to convey protein resistance to the underlying inorganic substrates, prone to facile protein adsorption in their native state.     

Temperature responsive copolymers of N‐vinylcaprolactam and di(ethylene glycol) methyl ether methacrylate and their interactions with drugs

Poly(N‐vinylcaprolactam) (PVCL) and poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) are well known for their thermoresponsive behavior in aqueous solutions. Indeed, they display lower critical solution temperatures (LCST) in the physiological range, which makes them interesting for biomedical devices and use in drug delivery systems. Homopolymers of N‐vinylcaprolactam and di(ethylene glycol) methyl ether methacrylate as well as copolymers thereof were synthesized by solution and direct miniemulsion polymerizations. The cloud points of the copolymers in aqueous solution were investigated as a function of temperature, comonomer ratio, and in the presence of model pharmaceutical ingredients. By variation of the comonomer ratio, it was possible to control the cloud point temperature between 26 and 35 °C, which was found to be beneficial to attenuate the effect of the drugs that also altered the cloud points. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3308–3313     

Block and star block copolymers by mechanism transformation X. Synthesis of poly(ethylene oxide) methyl ether/polystyrene/poly(l-lactide) ABC miktoarm star copolymers by combination of RAFT and ROP

Poly(ethylene oxide) methyl ether/polystyrene/poly(l-lactide) (MPEO/PSt/PLLA) ABC miktoarm star copolymers were synthesized by combination of reversible addition-fragmentation transfer (RAFT) polymerization and ring-opening polymerization (ROP) using bifunctional macro-transfer agent, MPEO with two terminal dithiobenzoate and hydroxyl groups. It was prepared by reaction of MPEO with maleic anhydride (MAh), subsequently reacted with dithiobenzoic acid and ethylene oxide. RAFT polymerization of St at 110 °C yielded block copolymer, MPEO-b-PSt [(MPEO)(PSt)CH₂OH], and then it was used to initiate the polymerization of l-lactide in the presence of Sn(OCt)₂ at 115 °C to produce ABC miktoarm star polymers, s-[(MPEO)(PSt)(PLLA)]. The structures of products obtained at each synthetic step were confirmed by NMR and gel permeation chromatography data.     

Poly(ethylene oxide) gel as a novel polymerization medium anionic polymerization of methyl methacrylate

Crosslinked poly(ethylene oxide)-(PEO-N) is used as a novel medium for the anionic polymerization of methyl methacrylate (MMA) initiated by t-BuOK and ethyl-α-lithioisobutyrate (α-LiEtIB) in toluene. Comparative studies with linear poly(ethylene oxide)-(PEO-L) are performed as well. It is found that PEO-N effectively binds both initiators, and the polymerization process takes place mainly in the gel phase. PEO-N accelerates the polymerization process initiated by t-BuOK enabling the formation of high-molecular-weight polymers with high yields. Part of poly(methyl methacrylate)-(PMMA) remains in the gel particles yielding semi-interpenetrating networks with amphiphilic properties. PEO additives do not influence profoundly the course of the polymerization, initiated by α-LiEtIB. The influence of PEO-N on the proceeding of the polymerization is discussed in some detail.     

Radiation-grafting of 2-hydroxyethylmethacrylate and oligo (ethylene glycol) methyl ether methacrylate onto polypropylene films by one step method

Polypropylene films were modified with 2-hydroxyethylmethacrylate (HEMA) and oligo (ethylene glycol) methyl ether methacrylate (OEGMA) using the pre-irradiation method with gamma-rays (one step method). The effect of absorbed dose from 10 to 100 kGy, temperature (50, 60, and 70 °C), monomer concentration between 12.5% and 62.5%, monomers ratio from 10% to 90% and reaction time from 5 to 50 h; on the degree of grafting was determined. The grafted samples were analyzed by FTIR-ATR, TGA, DSC, swelling, and contact angle. Grafts onto polymeric films between 3% and 109% were obtained at doses from 10 to 100 kGy and a dose rate around 7.4 kGy/h. The graft percent increased with the content in HEMA in the HEMA:OEGMA feed mixture, which indicates a lower reactivity of OEGMA compared to HEMA. The hydrogel layer grafted on the polypropylene substrate increases the hydrophilicity of the surface and also provides certain temperature-responsiveness, which may be of interest for biomedical applications.     

Grafting of poly(ethylene oxide) on poly(methyl methacrylate) by transesterification

The grafting of the potassium alkoxide derivative of poly(ethylene oxide) on poly(methyl methacrylate) in homogeneous solution in toluene was studied. The alkoxide was prepared by reaction with potassium metal with methanolic potassium methoxide, or with potassium naphthalene. The last was the most suitable for the systematic investigation of the grafting process. Soluble graft polymers were formed, and essentially the initial poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) participated in the production of graft polymer. The composition of the graft polymers and the frequency of grafting of the side chains were determined by NMR. The solubility of the graft polymers in methanol and water increased with increasing PEO contents, while the melting ranges decreased. Fractionation of the crude graft polymers showed that the grafting reaction was random, and graft polymers containing one PEO side chain per about 10–170 MMA units were obtained.     

Synthesis of novel biodegradable poly(ethylene glycol) analogue:Water-soluble aliphatic polyester with pendant oligo(ethylene glycol) chains

A novel poly(ethylene glycol)(PEG) analogue composed of aliphatic polyester backbone and pendant oligo(ethylene glycol) short chains is reported.The PEG analogue is a copolymer synthesized by ring-opening alternating copolymerization of succinic anhydride with 2-((2-(2-metho xyethoxy)ethoxy)methyl)oxirane.The structure of the copolymer was confirmed by ~1H NMR spectrum.The effects of the monomer feed ratio on the copolymerization were studied and the polymerization mechanism was given.The PEG analogue di...     

Thermoresponsive oligo(ethylene glycol) methacrylate colloids with antifouling surface properties

Thermoresponsive polymeric colloids attract great attention in several biotechnological applications owing to their ability to manipulate drug release characteristics in a controlled manner. Majority of these applications utilized N‐isopropylacrylamide (NIPAM)‐based particles for controlled drug release. Despite its advantages, such as easy chemical modification and well‐documented literature, a potentially important bottleneck for NIPAM in biological applications is its tendency for nonspecific protein adsorption. Herein, we report a simple way to prepare novel thermoresponsive colloids composed of oligo(ethylene glycol) side chains via precipitation polymerization technique. In addition to displaying highly reversible thermal response, these particles also have considerably low nonspecific protein adsorption when compared with NIPAM counterparts. These crosslinked poly(ethylene glycol) ethyl ether methacrylate particles were characterized using dynamic light scattering and transmission electron microscopy. The effects of co‐monomer, crosslinker and initiator on particle characteristics were investigated. Finally, particle toxicity studies were carried out using 3T3 fibroblast cell lines in MTT cytotoxicity assay. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011