Facile preparation of poly(N-isopropylacrylamide)-based hydrogels via aqueous Diels-Alder click reaction

The study reports a facile method of preparing poly(N-isopropylacrylamide)- based hydrogels by means of the Diels-Alder reaction. First, polymeric dienes were synthesized by free radical copolymerization between N-isopropylacrylamide (NIPA) and furfuryl methacrylate (FM), with 2, 2′-azobisisobutyronitrile (AIBN) as an initiator, and polymeric dienophile was obtained by a coupling reaction of poly(ethylene glycol) (PEG) and N-maleoyl-l-leucine (LMI) under N, N′-dicyclohexylcarbodiimide (DCC). Afterwards, the resultant dienes and dienophiles were dissolved in water and put in a refrigerator remaining a temperature of 9 °C, gelation via Diels-Alder reaction was observed after some time. The samples obtained at different steps were characterized by FTIR, NMR, GPC, SEM, CD, etc. It was found that LCST of copolymers decreases with the increase of FM content in copolymers. And the disassembly time of the hydrogels is closely related to the temperature and the solvents used. The swelling behavior study by gravimetric measurement indicates the hydrogels possess thermosensitivity and exhibit considerable swelling in water. Due to the simplicity of synthesis and no need for initiator or catalyzer and organic solvent, the strategy described here could find a promising application in the preparation of hydrogels.     

Synthesis of hydrophilic cross-linker having phosphorylcholine-like linkage for improvement of hydrogel properties

As a novel cross-linking reagent, dimethacrylate having a phosphorylcholine-like linkage, called 2-(methacryloyloxy)ethyl-[N-(2-methacryloyloxy)ethyl]phosphorylcholine (MMPC), was synthesized by condensation between methacrylate having a cyclic phosphate and that with a tertiary amine group. The MMPC was copolymerized with 2-methacyloyloxyethyl phosphorylcholine (MPC) or 2-hydroxyethyl methacrylate (HEMA) to produce the polymer hydrogels. The polymerization initiated by a redox system in aqueous medium proceeded well and the hydrogel was formed. The swelling of the poly(MPC) hydrogel was regulated by the MMPC composition. For the poly(HEMA) gel cross-linked with MMPC, the swelling degree was almost the same in the MMPC composition range of 1.0-10 mol%. However, the transparency of the poly(HEMA) gel increased with an increase in the MMPC. The MMPC is a useful cross-linker to make hydrogels and control the swelling and property of the hydrogel.     

Thermosensitive nanospheres of low-density core - An approach to hollow nanoparticles

A novel strategy for the preparation of hollow core-shell nano- and microparticle is reported. Nanoparticle cores were created from poly(N-isopropylacrylamide) (PNIPAM) by controlled heating above the LCST of this polymer in the presence of a small amount of sodium dodecyl sulfate. Shells were formed by radical copolymerization of 2-hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol) dimethacrylate (PEG-DMA) as cross-linking agent. The PNIPAM particles were acting as nucleating agents so that core-shell colloidal particles of PNIPAM covered with cross-linked PHEMA resulted. Subsequent release of a part of the PNIPAM chains from the interior of the particles was obtained by dialysis. The sizes and the temperature behavior of obtained particles were measured by DLS, TEM and SEM. The semi-hollow particles showed reversible volume response to cyclic temperature changes.     

Swelling of and solute exclusion by poly(N-alkylacrylamide) gels

Temperature-sensitive hydrogels of poly(N-isopropylacrylamide) poly(N,N-diethylacrylamide), poly(N-N-propylacrylamide), copolymer of N-isopropylacrylamide and methylacrylamide, and copolymer of N,N-diethylacrylamide and N-tert-butylacrylamide were prepared. The swelling characteristics of the gels were studied and gel extraction of macromolecules, based on the solute exclusion by the gel network, were investigated. © 1995 John Wiley & Sons, Inc.     

Solute and penetrant diffusion in swellable polymers: X. Swelling of multiethylene glycol dimethacrylate copolymers

The swelling behavior of copolymers containing 2-hydroxyethyl methacrylate and various multiethylene glycol dimethacrylates was examined at 25°C. These highly crosslinked copolymers show some hydrophilic behavior due to the hydroxyl groups of HEMA. Analysis of the swelling data indicates and anomalous water transport in the network, which depends on the degree of crosslinking attained according to the dimethacrylate comonomer molar fraction in the copolymerization feed. Thermomechanical analysis data were used to further characterize the network structure.     

Rapid pH‐dependent phase transition and elasticity of stimuli‐responsive cationic poly(N,N‐dimethylaminoethyl methacrylate) hydrogels prepared with a dimethacrylate crosslinker

Stimuli‐responsive hydrogels prepared from poly(N,N‐dimethylaminoethyl methacrylate) (PDMAEMA) and its copolymers have attracted much interest to serve in biomedical and pharmaceutical applications. To investigate pH‐dependent swelling and elasticity, a series of cationic hydrogels based on N,N‐dimethylaminoethyl methacrylate were prepared by free radical crosslinking copolymerization at 60 °C in the presence of tetraethylene glycol dimethacrylate as the crosslinker. The equilibrium swelling and the mechanical properties of the PDMAEMA hydrogels were investigated as a function of the gel preparation concentration. To explain the effect of pH on the equilibrium swelling of the hydrogels, pH‐dependent swelling studies were carried out in solutions of pH ranging from 2.1 to 10.7. It was found that the PDMAEMA hydrogels exhibit a rapid pH‐dependent phase transition in aqueous solutions; that is, the gels first remain in the swollen state at acidic pH then collapse in a very narrow range of pH. The results showed that the volume of PDMAEMA hydrogels in acidic conditions is about 10‐ to 40‐fold larger than that in the basic pH region. By using the Flory–Rehner theory, the characteristic network parameters of the PDMAEMA hydrogels were calculated and good agreement obtained between the swelling equilibria of hydrogels and their mechanical properties over the whole range of gel preparation concentration. © 2012 Society of Chemical Industry     

Temperature- and solvent-sensitive hydrogels based on N-isopropylacrylamide and N,N-dimethylacrylamide

Summary The swelling behaviour in water-dioxane mixtures of hydrogels containing N-isopropylacrylamide (NIPAM) and N,N-dimethylacrylamide (DMAM) is investigated as a function of dioxane content and temperature. The composition of the hydrogels, reported as the mol percentage of DMAM units, x, varies from 0 up to 100. It is found that the hydrogel containing only NIPAM units, GPNIPAM, deswells significantly in the water-rich region, while the hydrogel containing only DMAM units, GPDMAM, presents a pronounced deswelling in the dioxane-rich region. This deswelling becomes less significant with decreasing the DMAM content x, when using the hydrogels of the copolymers GP(NIPAM-co-DMAMx). This swelling behaviour of the hydrogels results from a combination of the lower critical solution temperature-type cononsolvency behaviour of poly(N-isopropylacrylamide) with the upper critical solution temperature-type cononsolvency behaviour of poly(N,N-dimethylacrylamide) in water-dioxane mixtures.     

Poly(vinyl alcohol) Based pH Responsive Semi-IPN Hydrogels: A Comparative Swelling Investigation

The semi-interpenetrating polymer network (IPN) hydrogels composed of poly(vinyl alcohol) (PVA) and random copolymers of poly(acrylamide-co-sodium methacrylate), poly(AAm-co-NMA); poly(acrylamide-co-potassium methacrylate), poly(AAm-co-KMA); poly(acrylamide-co-maleic acid), poly(AAm-co-MA) were prepared by conventional co-polymerization employing ammonium persulphate (APS)/N,N,N¹,N¹-tetraethylmethylenediamine (TMEDA) as redox initiating system in presence of N,N¹-methylenebisacrylamide (MBA) as a crosslinker. The swelling behavior of these semi-IPN hydrogels were compared in detail in various swelling media, including different pH, salt, and biological fluids.     

Effect of the crosslinking agent on porous networks formation of hema-based copolymers

New copolymers of ethylene glycol dimethacrylate/2-hydroxyethyl methacrylate [poly(EGDMA-co-HEMA)],2,2′,2″-nitrilotriethyl triacrylate/2-hydroxyethyl methacrylate [poly(NTETA-co-HEMA)] and pentaerythritol tetraacrylate/2-hydroxyethyl methacrylate [poly(PETA-co-HEMA)] were obtained by suspension polymerization at 70 or 85 °C, using cyclohexane (Cyc) as porogen. In this work, the influence of the crosslinking agent (di, tri, or tetravinyl monomer) on the morphology of the polymeric networks was investigated. Swelling studies, Fourier Transform Infrared (FTIR) and mercury intrusion porosimetry, demonstrated that when both the vinyl groups number and molecular chain length between double bonds of the crosslinking agent decreased, networks with high porosity and crosslinking degree were generated.     

Properties of n‐butyl methacrylate copolymer latex films derived from crosslinked latex particles

Films obtained from copolymer latexes of n‐butyl methacrylate (BMA) with a series of crosslinking monomers [i.e., a macromonomer crosslinker (Mac), ethylene glycol dimethacrylate (EGDMA), and aliphatic urethane acrylate] exhibited differences in their tensile properties and swelling behaviors. For P(BMA‐co‐EGDMA) copolymer, a dependence on the initiator type was obtained. It is postulated that the network microstructures for the various copolymers evolved as the result of the copolymerization reactions between the monomer pairs during the synthesis in the miniemulsion free‐radical copolymerization. These network microstructures are, therefore, hypothesized to influence the mechanical properties of the resultant films. Copolymers prepared with Mac were tough in comparison with copolymers made with EGDMA. The presence of longer linear or lightly crosslinked poly(n‐butyl methacrylate) (PBMA) chains and the looseness of the crosslinked network structures in the PBMA‐co‐Mac copolymers appear to be the factors responsible for the differences. All of the copolymer films disintegrated into swollen individual microgels when they were immersed in tetrahydrofuran. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 42–49, 2003     

Disparate polymerization facilitates the synthesis of versatile block copolymers from poly(trimethylene carbonate)

A disparate polymerization technique is utilized for preparing versatile block copolymers from poly(trimethylene carbonate) (poly(TMC)). In this study, 4-(chloromethyl)benzyl alcohol (CBA) is used for the disparate polymerization. The hydroxyl group of CBA is involved in ring-opening polymerization and the benzyl chloride group is involved in incorporating dithiocarbamate for pseudo-living radical polymerization. First, TMC is polymerized from the hydroxyl group of CBA by using an organocatalyst. The benzyl chloride group in CBA is modified using a dithiocarbamate, and then vinyl and methacrylate monomers are polymerized by photo-driven pseudo-living radical polymerization. The resulting block copolymers are versatile and the molecular weight distribution is reasonably narrow. In the present study, N-isopropylacrylamide, acrylamide glycolic acid, and 2-hydroxyethyl methacrylate are used for the disparate polymerization. The resulting block copolymers could be well dissolved in water by incorporation of hydrophilic segment into hydrophobic poly(TMC). The solution property is characterized in terms of hydrophobic domain formation and phase transition under ambient conditions. Moreover, enzymatic degradation is evaluated by using a copolymer-coated substrate. The block copolymer synthesis technique is considerably versatile, and the resulting polymer function can be freely designed. The disparate polymerization technique is a promising approach that provides universal materials for integrating biodegradable polyesters and functional polymers.     

Swelling and mechanical behavior of charged poly(<Emphasis Type="Italic">N</Emphasis>-isopropylmethacrylamide) and poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide) networks in water/ethanol mixtures. Cononsolvency effect

Summary Swelling and mechanical behavior of negatively (ionic comonomer-sodium methacrylate) and positively (ionic comonomer-(2-acrylamidoethyl)trimethyl ammonium chloride) charged networks of poly(N-isopropylmethacrylamide) (PIPMAm) and poly(N-isopropylacrylamide) (PIPAAm) was investigated in water/ethanol mixtures at room temperature. Strong cononsolvency effect was observed for uncharged and negatively charged gels of both systems; while for neat solvents high degree of swelling Q was observed, for solvent mixtures pronounced minima in swelling were found. Swelling minima are connected with the coil-to-globule transition of network chains and their characteristic parameters-concentration of ethanol at the minimum, c_eth,m, and corresponding swelling degree, Q_m, were determined. With increasing amount of negatively charged ionic comonomer the minimum in swelling shifts to higher c_eth,m values and Q_m increase. On the other hand, positively charged networks of both systems exhibit roughly constant Q values practically independent of solvent mixtures compositions. For all four systems it was found that mechanical behavior is predominantly determined by the degree of swelling regardless of charge concentration.     

Preparation of hydrophilic polymer networks by post-curing reaction

Hydrophilic gels are a very important class of polymeric materials with extensive applications as biomedical products. The critical properties of hydrogels, such as sorption and desorption, mechanical behavior, swelling properties, etc., are controlled by network characteristics, i.e. degree of crosslinking and the density, distribution and length of crosslinks. Hydrogels prepared by copolymerization of 2-hydroxyethyl methacrylate (HEMA) with ethylene glycol dimethacrylate (EGDMA) have already been studied in detail. In this work, hydrophilic networks were prepared by crosslinking HEMA with EGDMA, and poly(2-hydroxy-ethyl methacrylate) (PHEMA) with diphenylmethane-4,4′-diisocyanate (MDI). The swelling properties of both types of networks were studied and the differences in behavior were attributed to the different techniques applied for network formation.     

Effects of experimental variables on the synthesis of porous matrices

Macroporous beads, poly(ethylene glycol dimethacrylate‐co‐acrylic acid) [poly(EGDMA‐co‐AAc)], and poly(ethylene glycol dimethacrylate‐co‐hydroxyethyl methacrylate) [poly(EGDMA‐co‐HEMA)] were prepared by the suspension polymerization technique in the presence of a porogen agent. Different experimental conditions such as amount of initiator, porogen type, and temperature were studied to optimize the polymerization systems. These hydrophilic copolymers were characterized by IR spectroscopy, scanning electron microscopy, specific surface area, and swelling in water. A new parameter, H, defined as the ratio between the equilibrium weight swelling ratio (q_w) and equilibrium volume swelling ratio (q_v), allowed to select the reaction conditions from which matrices with high capacity of water sorption and low stretching degree were reached. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 920–927, 2001     

Synthesis,characterization, and antimicrobial properties of novel quaternary amine methacrylate copolymers

A novel amine methacrylate monomer trimethylolpropane trimethacrylate–piperazine–ethyleneglycol dimethacrylate (TMPTMA‐PPZ‐EGDMA) was synthesized by amination of trimethylolpropane trimethacrylate (TMPTMA) with excess of piperazine (PPZ) followed by reaction with ethyleneglycol dimethacrylate (EGDMA). Copolymerization of TMPTMA‐PPZ‐EGDMA with 2‐hydroxyethyl methacrylate (HEMA) was carried out by free radical polymerization using ammonium persulfate (APS) and N,N,N′,N′‐tetramethyl ethylenediamine (TEMED) as a redox initiator. The copolymers obtained were then quaternized with 1‐iodooctane. The monomers were characterized by FTIR and ¹H NMR spectral studies. The molecular weights and polydispersity values of the monomers were determined with gel permeation chromatography. Quaternized copolymers containing more than 20% amine methacrylate monomer showed microporosity in the range of 9.9–10.4 μm. The antibacterial activity of the quaternized copolymers against Escherichia coli and Staphylococcus aureus was studied using UV–vis spectrophotometer and scanning electron microscopy. Quaternized copolymers showed broad‐spectrum contact‐killing antibacterial properties without releasing any active agent as checked by iodide selective ion meter. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Influence of copolymer composition on non-fickian water transport through glassy copolymers

The dynamic swelling behavior of poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) and poly(2-hydroxyethyl methacrylate-co-N-vinyl-2-pyrrolidone) in water was followed at 37°C. The results were analyzed in terms of a simple non-Fickian transport equation, which expresses the fractional penetrant uptake as an exponential function of the diffusion time. The exponent n, which indicates Fickian or non-Fickian transport mechanism, was correlated to the content of the more hydrophilic component of the copolymer. Photomicrographs obtained with polarized light offer new information about the position and movement of the penetrant front in glassy, hydrophilic polymers.     

Preparation of iodine containing quaternary amine methacrylate copolymers and their contact killing antimicrobial properties

A novel quaternary amine methacrylate monomer (QAMA) was synthesized by amination of dimethacrylate with piperazine followed by its quaternization using an alkyl iodide. Copolymerization of QAMA with 2‐hydroxyethyl methacrylate was carried out by free radical bulk polymerization technique at room temperature using ammonium persulfate and N,N,N′,N′‐tetramethyl ethylenediamine as a redox initiator. The monomer as well as copolymers was characterized by FTIR and ¹H NMR spectral studies. Thermal and physical characteristics of copolymers of varying compositions of QAMA were evaluated by thermogravimetric analysis, differential calorimetry, contact angle and scanning electron microscopy. The antibacterial activity of the synthesized quaternary amine dimethacrylate copolymers against Escherichia coli and Staphylococcus aureus was studied by zone of inhibition and colony count method. QAMA copolymers showed broad‐spectrum contact killing antibacterial properties without releasing any active agent as checked by iodide‐selective ion meter. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1038–1044, 2006     

Effect of degree of crosslinking on water transport in polymer microparticles

The water transport in microparticles of poly(2-hydroxyethyl methacrylate) crosslinked with small amounts of ethylene glycol dimethacrylate was investigated as a function of time. Dynamic swelling curves were obtained and analyzed with a simple, empirical, exponential expression, where the exponent n indicates the mechanism of water transport. It was determined that the mechanism changed from Fickian to non-Fickian transport as the nominal crosslinking ratio increased from X = 0.007 to X = 0.124 mol EGDMA/mol HEMA. Smaller particles attained their equilibrium swelling value faster. The velocity of the penetrant front was determined with optical microscopy, and it was found to decrease from 22.2 to 11.2 μm/min as the crosslinking ratio increased.     

Architecture of rod–brush block copolymers synthesized by a combination of coordination polymerization and atom transfer radical polymerization

A combination of coordination polymerization and atom transfer radical polymerization (ATRP) was applied to a novel synthesis of rod–brush block copolymers. The procedure included the following steps: (1) the monoesterification reaction of ethylene glycol with 2-bromoisobutyryl bromide (BIBB) yielded the bifunctional initiator monobromobutyryloxy ethylene glycol and (2) a trichlorocyclopentadienyl titanium (CpTiCl₃; bifunctional initiator) catalyst was prepared from a mixture of CpTiCl₃ and bifunctional initiator. The coordination polymerization of n-butyl isocyanate initiated by such a catalyst provided a well-defined macroinitiator, poly(n-butyl isocyanate)–bromine (PBIC–Br). (3) The ATRP method of 2-hydroxyethyl methacrylate initiated by PBIC–Br provided rod [poly(n-butyl isocyanate) (PBIC)]–coil [poly(2-hydroxyethyl methacrylate) (PHEMA)] block copolymers with a CuCl/CuCl₂/2,2′-bipyridyl catalyst. (4) The esterfication of PBIC-block-PHEMA with BIBB yielded a block-type macroinitiator, and (5) ATRP of methyl methacrylate with a block-type macroinitiator provided rod–brush block copolymers. We found from the solution properties that such rod–brush block copolymers formed nanostructured macromolecules in solution. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Novel flexible network polymers consisting of oligomeric primary polymer chains originated in the mechanistic discussion of multiallyl crosslinking polymerization

Summary It is well known that allyl monomers polymerize only with difficulty and yield polymers having low molecular weights, i.e., oligomers. Inevitably, free-radical multiallyl crosslinking polymerization provides network polymers consisting of oligomeric primary polymer chains, i.e., having abundant dangling chains. This led to the development of novel flexible network polymers such as amphiphilic network polymers (I) consisting of short primary polymer chains and long crosslink units with opposite polarities, simultaneous interpenetrating networks (II) consisting of both polyurethane (PU) and polymethacrylate (PM) networks with oligomeric primary polymer chains, and network polymers (III) consisting of centipede-type primary polymer chains. Thus, the solution copolymerizations of benzyl methacrylate with tricosaethylene glycol dimethacrylate in the presence of lauryl mercaptan yielded I consisting of nonpolar, short primary polymer chains and polar, long crosslink units. The opposite type of I was prepared by the copolymerization of 2-hydroxyethyl methacrylate, a polar monomer having a hydroxyl group, with heneicosapropylene glycol dimethacrylate, a nonpolar monomer having a poly(oxypropylene) unit. The equimolar polyaddition crosslinking reaction of poly(methyl methacrylate-co-2-methacryloyloxyethyl isocyanate) with tri(oxytetramethylene) glycol, leading to PU networks, and the free-radical crosslinking copolymerization of methyl methacrylate with tri(oxytetramethylene) dimethacrylate in the presence of CBr₄, leading to PM networks, were progressed simultaneously, providing II formed via the topological crosslink between PU and PM network structures. The post-copolymerizations of oligomeric allyl methacrylate/alkyl methacrylate precopolymers, having different amounts of pendant allyl groups and different molecular weights, with allyl benzoate/vinyl benzoate monomer mixtures were conducted to give III.