On the relevance of the 8‐chain model and the full‐network model for the deformation and failure of networks formed through photopolymerization of multifunctional monomers

Crosslinked networks were synthesized by copolymerization of mono‐functional tert‐butyl acrylate (tBA) with diethyleneglycol dimethacrylate (DEGDMA) or polyethylene glycol dimethacrylates (PEGDMA). By varying the chain length and concentration of the difunctional PEGDMA, we obtained tBA‐PEGDMA copolymer networks while by varying the concentration of difunctional DEGDMA, we obtained tBA‐DEGDMA crosslinked networks. The various materials were submitted to large deformations through uniaxial tension tests. For moderate weight percent of crosslinking agent, up to 20%, the networks showed standard S‐shape stress–strain curves, characteristic of rubber‐like elasticity. Two macromolecular models, the 8‐chain model and the full‐network model, were applied to fit the uniaxial tensile response of the materials. Both models provide good representations of the overall uniaxial stress–strain response of each material. After fitting to stress–strain data, the network models were employed to predict the shear modulus and the elongation at break. Neither the 8‐chain nor the full network model were capable of predicting the failure strain or shear modulus, indicating these models are best used to describe stress–strain relations rather than predict mechanical properties for the network polymers considered here. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1226–1234, 2008     

Styrene-PEG (600) DMA Crosslinked Polymers for Absorption of Oil Derivatives

In this work, styrene (St) based crosslinked polymers were prepared for removal of oil derivatives from aqueous solutions. Polyethylene glycol (600) dimethacrylate (PEG (600) DMA) was used as crosslinker in synthesis of styrene based crosslinked polymers, for the first time. The polymers were characterized by FTIR, SEM, elemental analysis and solvent (toluene, chloroform and fuel-oil) absorption capacities. The effects of different reaction parameters like crosslinker type, diluents amount and the presence of pore forming agent on the absorption properties of polymers were investigated. The polymers synthesized by using PEG (600) DMA have higher solvent absorption capacity than that of synthesized by using conventional crosslinker. Furthermore, the polymers synthesized in the presence of good diluents have higher absorption capacities. The addition of pore forming agent into the reaction medium has also improved the absorption rate of polymers. The absorption capacity of polymers in different solvents is in order of chloroform > toluene > fuel-oil. It was seen that oil derivatives can be removed efficiently from water by the St-PEG (600) DMA polymers.     

Characterization of well‐defined poly(ethylene glycol) hydrogels prepared by thiol‐ene chemistry

Considering the large number of applications for hydrogels, a better understanding of the relation between molecular structure and mechanical properties for well‐defined hydrogel is essential. A new library has been compiled of poly(ethylene glycol) polymers (PEG) of different length end functionalized with diallyl, dithiol, and dimethacrylate, and crosslinked with complementary trifunctional crosslinkers. In this study, the hydrogels were initially analyzed by FT‐Raman and NMR to study the conversion ratio of the functional groups. The effects of solvent type, solid content concentration, curing time and length of the PEG chains on the final leaching, swelling and tensile properties of the hydrogels were studied. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Diazonium salts for surface‐confined visible light radical photopolymerization

The surface chemistry of aryl diazonium salts has progressed at a remarkable pace in the last two decades, and opened many avenues in materials science. These compounds are excellent coupling agents for polymers to surfaces via several surface‐confined polymerization methods. For the first time, we demonstrate that diazonium salts are efficient for surface initiating radical photopolymerization in the visible light of methyl methacrylate (MMA) and 2‐hydroxyethyl methacrylate (HEMA) taken as model monomers. To do so, 4‐(dimethylamino)benzenediazonium salt was electroreduced on gold plates or flexible ITO sheets to provide 4‐(dimethylamino)phenyl (DMA) hydrogen donor layers; while excited state camphorquinone acted as the free hydrogen abstractor. In the same way, we co‐polymerized HEMA and MMA with ethylene glycol dimethacrylate in order to obtain crosslinked polymer grafts. We demonstrate by XPS that gold was efficiently screened by the polymer layers and that the wettability of the surfaces accounts for the hydrophilic or hydrophobic characters of the tethered polymers. Homo‐ and crosslinked PMMA grafts were found to resist removal by the paint stripper methyl ethyl ketone. The grafted DMA/camphorquinone system operating in the visible light holds great promises in terms of adhesion of in situ designed continuous or patterned polymer coatings on various substrates. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3506–3515     

Electrochemical characterization of hydrogels for biomimetic applications

Hydrogels are increasingly being recognized as having potential in bio‐compatible applications. In previous work, we investigated the feasibility of poly(ethylene glycol)‐dimethacrylate (PEG‐1000‐DMA) and poly(ethylene glycol)‐diacrylate (PEG‐400‐DA) polymerized using either a chemical initiator (C) or a photoinitiator (P) to encapsulate and stabilize biomimetic membranes for novel separation technologies or biosensor applications. In this paper, we have investigated the electrochemical properties of the hydrogels used for membrane encapsulation. Specifically, we studied the crosslinked hydrogels by using electrochemical impedance spectroscopy (EIS), and we demonstrated that chemically crosslinked hydrogels had lower values for the effective electrical resistance and higher values for the electrical capacitance compared with hydrogels with photoinitiated crosslinking. Transport numbers were obtained using electromotive force measurements and demonstrated that at low salt concentrations, both PEG‐400‐DA‐C and PEG‐400‐DA‐P hydrogels presented an electropositive character whereas PEG‐1000‐DMA‐P was approximately neutral and PEG‐1000‐DMA‐C showed electronegative character. Sodium transport numbers approached the bulk NaCl electrolyte value at high salt concentrations for all hydrogels, indicating screening of fixed charges in the hydrogels. The average salt diffusional permeability 〈P_s〉 and water permeability 〈P_w〉 were found to correlate with EIS results. Both PEG‐1000‐DMA‐C and PEG‐400‐DA‐C had higher 〈P_s〉 and 〈P_w〉 values than PEG‐1000‐DMA‐P and PEG‐400‐DA‐P hydrogels. In conclusion, our results show that hydrogel electrochemical properties can be controlled by the choice of polymer and type of crosslinking used and that their water and salt permeability properties are congruent with the use of hydrogels for biomimetic membrane encapsulation. Copyright © 2011 John Wiley & Sons, Ltd.     

Novel michael addition networks containing urethane hydrogen bonding

Covalently crosslinked networks based on poly(propylene glycol) bis(acetoacetate) with either neopentyl glycol diacrylate or hydroxyethyl acrylate derivatized bis(4‐isocyanatocyclohexyl)methane (HMDI) were prepared utilizing the Michael addition reaction in the presence of catalytic quantities of diazabicyclo[5.4.0]undec‐7‐ene (DBU). These networks were prepared in the absence of solvent at 23 °C without the formation of byproducts. Mechanical and thermal analyses of the networks were performed utilizing DMA, tensile testing, and TGA. Tensile analysis revealed that the introduction of hydrogen‐bonding urethane linkages in the diacrylate segment resulted in higher tensile strengths and elongation to break compared with nonhydrogen‐bonding analogs. All crosslinked products exhibited high gel fractions and excellent thermomechanical properties. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4118–4128, 2007     

UV‐curable bismaleimides containing poly(dimethylsiloxane): Use as hydrophobic agent

The synthesis and characterization of poly(dimethylsiloxanes) bearing maleimides end‐groups (PDMSM) were carried out through imidization of maleic anhydride with three poly(dimethylsiloxanes) diamines of different molecular weights. Self‐photopolymerization of PDMSM was studied by Real‐Time Fourier Transform infrared spectroscopy (RT‐FTIR) and was possible even without photoinitiator (Darocur 1173). The reaction was found to proceed within seconds upon exposure to ultraviolet (UV) radiation to generate highly crosslinked polymer networks. The results indicated that these polymerizations were less sensitive to oxygen inhibition than the radical processes carried out on conventional UV‐curable acrylate resins. The thermal and mechanical properties of these resulting materials were studied starting from PDMS precursors with different molecular weights. These materials exhibit a low glass transition temperature (相似文献   

Room‐temperature RAFT copolymerization of 2‐chloroallyl azide with methyl acrylate and versatile applications of the azide copolymers

A new vinyl azide monomer, 2‐chlorallyl azide (CAA), has been synthesized from commercially available reagent in one step. The reversible addition fragmentation chain transfer (RAFT) copolymerization of CAA with methyl acrylate (MA) was carried out at room temperature using a redox initiator, benzoyl peroxide (BPO)/N,N‐dimethylaniline (DMA), in the presence of benzyl 1H‐imidazole‐1‐carbodithioate (BICDT). The polymerization results showed that the process bears the characteristics of controlled/living radical polymerizations, such as the molecular weight increasing linearly with the monomer conversion, the molecular weight distribution being narrow, and a linear relationship existing between ln([M]₀/[M]) and the polymerization time. Chain extension polymerization was performed successfully to prepare block copolymer. Furthermore, the azide copolymers were functionalized by Cu^I‐catalyzed “click” reaction with alkyne‐containing poly(ethylene glycol) (PEG) to yield graft copolymers with hydrophilic PEG side chains. Surface modification of the glass sheet was successfully achieved via the crosslinking reaction of the azide copolymer under UV irradiation at ambient temperature. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1348–1356, 2010     

Efficient synthesis of monodisperse,highly crosslinked,and “living” functional polymer microspheres by the ambient temperature iniferter‐induced “living” radical precipitation polymerization

The facile and efficient one‐pot synthesis of monodisperse, highly crosslinked, and “living” functional copolymer microspheres by the ambient temperature iniferter‐induced “living” radical precipitation polymerization (ILRPP) is described for the first time. The simple introduction of iniferter‐induced “living” radical polymerization (ILRP) mechanism into precipitation polymerization system, together with the use of ethanol solvent, allows the direct generation of such uniform functional copolymer microspheres. The polymerization parameters (including monomer loading, iniferter concentration, molar ratio of crosslinker to monovinyl comonomer, and polymerization time and scale) showed much influence on the morphologies of the resulting copolymer microspheres, thus permitting the convenient tailoring of the particle sizes by easily tuning the reaction conditions. In particular, monodisperse poly(4‐vinylpyridine‐co‐ethylene glycol dimethacrylate) microspheres were prepared by the ambient temperature ILRPP even at a high monomer loading of 18 vol %. The general applicability of the ambient temperature ILRPP was confirmed by the preparation of uniform copolymer microspheres with incorporated glycidyl methacrylate. Moreover, the “livingness” of the resulting polymer microspheres was verified by their direct grafting of hydrophilic polymer brushes via surface‐initiated ILRP. Furthermore, a “grafting from” particle growth mechanism was proposed for ILRPP, which is considerably different from the “grafting to” particle growth mechanism in the traditional precipitation polymerization. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis and characterization of novel degradable photocrosslinked poly(ether‐anhydride) networks

New degradable poly(ether‐anhydride) networks were synthesized by UV photopolymerization. Dicarboxylated poly(ethylene glycol) (PEG) or poly(tetramethylene glycol) (PTMG) was reacted with an excess of methacrylic anhydride to form dimethacrylated macromers containing anhydride linkages. The percent of conversion for the macromer formation was more than 80% at 60 °C after 24 h. ¹H NMR and IR spectroscopies show the presence of anhydride linkages in the macromer. In vitro degradation studies were carried out at 37 °C in PBS with crosslinked polymer networks formed by UV irradiation. All PEG‐based polymers degraded within 2 days, while PTMG‐based polymers degraded by 50% of the initial weight after 14 days. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1277–1282, 2000     

Physical properties of glycosaminoglycan hydrogels

The chemical composition of glycosaminoglycan (GAG) hydrogels was found to have a profound effect on the physical properties of gels. Hyaluronan (HA) and chondroitin sulfate (CS) were each modified with adipic dihydrazide (ADH) with carbodiimide chemistry. The resulting polymer was crosslinked with various concentrations of poly(ethylene glycol) dialdehyde (PEG‐diald) to produce a series of hydrogels. The physical properties of these GAG hydrogels varied in a concentration‐dependent fashion. Maximal crosslinking was observed at a theoretical crosslinking of 50% for the HA‐ADH‐PEG‐diald hydrogels and 75% for the CS‐ADH‐PEG‐diald hydrogels. Adding PEG‐diald beyond the optimum for crosslinking prolonged the in vitro enzymatic degradation time of the hydrogels. The swelling of the crosslinked GAG hydrogels was correlated with the amount of PEG‐diald used rather than with the crosslinking density. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4344–4356, 2004     

Complex amphiphilic networks derived from diamine‐terminated poly(ethylene glycol) and benzylic chloride‐functionalized hyperbranched fluoropolymers

Amphiphilic copolymer networks were prepared from hyperbranched fluoropolymer (HBFP*, M_n = 38 kDa, by atom transfer radical‐self condensing vinyl copolymerization) and linear diamine‐terminated poly(ethylene glycol) (DA‐PEG, M_n = 1,630 Da). Model studies found that the crosslinking mechanism occurred at ambient temperature as a result of reaction between DA‐PEG and the benzylic chlorides of HBFP*. These networks underwent covalent attachment to glass microscope slides derivatized with 3‐aminopropyltriethoxysilane, whereupon gel percent studies at various weight percentages of DA‐PEG to HBFP* found that curing could be achieved at lower temperatures and shortened time periods relative to the previously reported parent HBFP–PEG system. Thermogravimetric analysis revealed that the crosslinked materials gave no evident mass loss up to 250 °C. Differential scanning calorimetry of the complex amphiphilic networks showed a suppressed glass transition temperature, relative to that observed for neat HBFP*, and multiple melting DA‐PEG endotherm(s) near 30 °C. The films possessed a topographically‐complex surface with features that increased in tandem with an increase in the ratio of DA‐PEG to HBFP*, as detected by atomic force microscopy and quantified by increased rms roughness values. Internal reflection infrared imaging revealed a heterogeneous surface composition and confirmed that the domain sizes increased as the weight percent of DA‐PEG increased. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4782–4794, 2006     

Viscoelastic characteristics of UV polymerized poly(ethylene glycol) diacrylate networks with varying extents of crosslinking

The viscoelastic relaxation characteristics of ultraviolet crosslinked networks based on poly(ethylene glycol) diacrylate [PEGDA] have been investigated by dynamic mechanical methods. Effective crosslink density in the networks was varied via the use of PEGDA prepolymers of different molecular weight, or by the introduction of controlled amounts of water in the reaction mixture. In all cases examined, fully amorphous networks were obtained. Time–temperature superposition was applied to obtain master curves of storage modulus versus frequency across the glass transition, and these could be satisfactorily described using the Kohlrausch–Williams–Watts relaxation function. The glass transition temperature (T_g), relaxation breadth, and fragility of the segmental relaxation were correlated with the effective crosslink density obtained in the networks. Gas permeation measurements on the PEGDA/water networks indicated only a very modest variation in gas transport properties, despite the sizeable variation in apparent crosslink density achieved in these materials. This result suggests that the controlling structural factor for gas transport in the networks is not simply crosslink density, and that attempts to correlate gas transport to network structure must necessarily consider the broader relationships between crosslink density, segmental mobility, and fractional free volume. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2058–2070, 2006     

Phase behavior,crystallization, and morphology in thermosetting blends of a biodegradable poly(ethylene glycol)‐type epoxy resin and poly(ϵ‐caprolactone)

Thermosetting blends of a biodegradable poly(ethylene glycol)‐type epoxy resin (PEG‐ER) and poly(?‐caprolactone) (PCL) were prepared via an in situ curing reaction of poly(ethylene glycol) diglycidyl ether (PEGDGE) and maleic anhydride (MAH) in the presence of PCL. The miscibility, phase behavior, crystallization, and morphology of these blends were investigated. The uncured PCL/PEGDGE blends were miscible, mainly because of the entropic contribution, as the molecular weight of PEGDGE was very low. The crystallization and melting behavior of both PCL and the poly(ethylene glycol) (PEG) segment of PEGDGE were less affected in the uncured PCL/PEGDGE blends because of the very close glass‐transition temperatures of PCL and PEGDGE. However, the cured PCL/PEG‐ER blends were immiscible and exhibited two separate glass transitions, as revealed by differential scanning calorimetry and dynamic mechanical analysis. There existed two phases in the cured PCL/PEG‐ER blends, that is, a PCL‐rich phase and a PEG‐ER crosslinked phase composed of an MAH‐cured PEGDGE network. The crystallization of PCL was slightly enhanced in the cured blends because of the phase‐separated nature; meanwhile, the PEG segment was highly restricted in the crosslinked network and was noncrystallizable in the cured blends. The phase structure and morphology of the cured PCL/PEG‐ER blends were examined with scanning electron microscopy; a variety of phase morphologies were observed that depended on the blend composition. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2833–2843, 2004     

Synthesis and characterization of thermoresponsive poly(ethylene glycol)‐based hydrogels and their magnetic nanocomposites

Temperature‐responsive hydrogels are one of the most widely studied types of stimuli‐responsive hydrogel systems. Their ability to transition between their swollen and collapsed states makes them attractive for controlled drug delivery, microfluidic devices, and biosensor applications. Recent work has shown that poly(ethylene glycol) (PEG) methacrylate polymers are temperature‐responsive and exhibit a wide range of lower critical solution temperatures based on the length of ethylene glycol units in the macromer chain. The addition of iron oxide nanoparticles into the hydrogel matrix can provide the ability to remotely heat the gels upon exposure to an alternating magnetic field (AMF). In this work, diethylene glycol (n = 2) methyl ether methacrylate and PEG (n = 4.5) methyl ether methacrylate copolymers were polymerized into hydrogels with 5 mol % PEG 600 (n = 13.6) dimethacrylate as the crosslinker along with 5 wt % iron oxide nanoparticles. Volumetric swelling studies were completed from 22 to 80 °C and confirmed the temperature‐responsive nature of the hydrogel systems. The ability of the gels to collapse in response to rapid temperature changes when exposed to an AMF was demonstrated showing their potential use in biomedical applications such as controlled drug delivery and hyperthermia therapy. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3229–3235, 2010     

“Kick‐Starting” oxetane photopolymerizations

In the presence of small amounts of 2,2‐dialkyl‐, 2,2,3‐trialkyl‐, or 2,2,3,3‐tetraalkyl substituted epoxides such as isobutylene oxide, 1,2‐limonene oxide, and 2,2,3,3,‐tetramethyl oxirane, the photoinitiated cationic ring‐opening polymerizations of 3,3‐disubstituted oxetanes are dramatically accelerated. The acceleration affect was attributed to an increase in the rate of the initiation step of these latter monomers. Both mono‐ and disubstituted oxetane monomers are similarly accelerated by the above‐mentioned epoxides to give crosslinked network polymers. The potential for the use of such “kick‐started” systems in applications such as coatings, adhesives, printing inks, dental composites and in three‐dimensional imaging is discussed. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2934–2946     

Heteroarm H‐shaped terpolymers through click reaction

Heteroarm H‐shaped terpolymers, (polystyrene)(poly(methyl methacrylate))‐ poly(tert‐butyl acrylate)‐(polystyrene)(poly(methyl methacrylate)), (PS)(PMMA)‐PtBA‐(PMMA)(PS), and, (PS)(PMMA)‐poly(ethylene glycol)(PEG)‐(PMMA)(PS), through click reaction strategy between PS‐PMMA copolymer (as side chains) with an alkyne functional group at the junction point and diazide end‐functionalized PtBA or PEG (as a main chain). PS‐PMMA with alkyne functional group was prepared by sequential living radical polymerizations such as the nitroxide mediated (NMP) and the metal mediated‐living radical polymerization (ATRP) routes. The obtained H‐shaped polymers were characterized by using ¹H‐NMR, GPC, DSC, and AFM measurements. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1055–1065, 2007     

Amphiphilic and hydrophobic surface patterns generated from hyperbranched fluoropolymer/linear polymer networks: Minimally adhesive coatings via the crosslinking of hyperbranched fluoropolymers

Hyperbranched fluoropolymers (HBFPs), based on benzyl ether linkages and having a large number of pentafluorophenyl chain ends, were crosslinked by a reaction with diamino-terminated poly(ethylene glycol) (PEG) or diamino-terminated poly(dimethyl siloxane) (PDMS) to form hyperbranched–linear copolymer networks of different compositions, structures, and properties. The crosslinking reactions involved the nucleophilic aromatic substitution of the pentafluorophenyl para-fluorines of HBFP by the amine functionalities of the respective telechelic linear segments. The contact angles, differential scanning calorimetry, thermogravimetric analysis, tensile measurements, and atomic force microscopy (AFM) were used to characterize the resulting network film samples. The surface wettability of the crosslinked materials was affected by the nature and amount of the linear polymer crosslinking agent employed. Amphiphilic polymer networks were formed by the incorporation of diamino-terminated PEG as a crosslinker, whereas diamino-terminated PDMS produced polymer networks of a hydrophobic character. The mechanical properties improved upon crosslinking, as measured by tensile testing. The mechanical integrity of the films was also found to improve upon crosslinking, as measured by AFM machining protocols. The AFM images revealed topographical morphologies that appeared to be the result of phase segregation of HBFP from PEG or PDMS; the dimensions of the phase-segregated domains were dependent on the stoichiometry of HBFP to the linear polymer and the thickness of the coating. As the content of PEG increased, fouling by human fibrinogen, used as a model protein, decreased. Further studies are in progress to determine the effects of the surface composition, morphology, and topography on the biofouling characteristics. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3531–3540, 2003     

Free radical initiated low temperature crosslinking of phenylethynyl (PE) end‐capped oligomides

A relatively low‐temperature crosslinking method for phenylethynyl (PE) end‐capped oligomides was developed. PE end‐capped oligomides are typically cured into crosslinked polyimides at 370 °C for about 1 h. The addition of a low viscosity mixed‐solvent of N‐methylpyrrolidinone (NMP)/dimethyl ether of polyethylene glycol (M = 250 g/mol), NMP/DM‐PEG‐250, or NMP/polyethylene glycol (M = 400 g/mol), NMP/PEG‐400, as film forming medium for PE‐end‐capped oligomides was investigated. Fourier transform infrared spectroscopy and ¹³C NMR showed that the mixed solvent addition was effective for achieving low‐temperature crosslinking of the ethynyl end‐caps over the temperature range 200–250 °C. The low temperature crosslinking process was explained by thermolysis of the PEG molecules over this temperature range forming free radical species such as ～CH₂CH₂O· or ～CH₂CH₂^· which initiate cure of the ethynyl groups resulting in a cross linked polyimide membrane. The PEG solvents also provide a radical source for the degradation polymerization of the solvents to a water and NMP insoluble polymer, which formed a miscible blend with the crosslinked membrane. Glass transition temperature (differential scanning calorimetry) data and thermo gravimetric analysis data provide evidence for the miscible blend. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3950–3963, 2010.