Poly(ethylene glycol)‐based amphiphilic model conetworks: Synthesis by RAFT polymerization and characterization

Poly(ethylene glycol) (PEG)‐containing quasi‐model amphiphilic polymer conetworks (APCNs) were prepared by reversible addition fragmentation chain transfer (RAFT) polymerization using α,ω‐bis(2‐cyanoprop‐2‐yl dithiobenzoate)‐PEG as a bifunctional RAFT macrochain transfer agent (macro‐CTA) and stepwise additions of a hydrophobic monomer and a crosslinker (crosslinker: macro‐CTA = 10:1, reaction time 24 h). Three different types of monomers, methyl methacrylate (MMA), n‐butyl acrylate and styrene, were employed as the hydrophobic monomers, whereas ethylene glycol dimethacrylate, ethylene glycol diacrylate and 1,4‐divinylbenzene served as the respective crosslinkers. PEG homopolymer hydrophilic quasi‐model networks were also prepared by RAFT‐polymerizing the three crosslinkers directly onto the two active ends of the PEG‐based macro‐CTA. From the three ABA triblock copolymers prepared, the MMA‐containing one was obtained at the highest polymerization yields. The crosslinking yields of the three ABA triblock copolymers with the corresponding crosslinkers were higher than those of the PEG‐based macro‐CTA with the same crosslinkers. The degrees of swelling (DSs) of all conetworks were measured in water and in tetrahydrofuran (THF). The DSs of the APCNs in THF were higher than those in water, whereas the reverse was true for the DSs of the hydrophilic homopolymer networks. Finally, the aqueous DSs of the APCNs were lower than those of the corresponding hydrophilic homopolymer networks. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7556–7565, 2008     

Synthesis and ring‐opening reactions of tetraphenyl‐substituted bisoxazoline monomers for preparing new thermosets and composites

To develop new monomers for formulating thermosetting composites, three new tetraphenyl‐substituted bisoxazoline monomers were synthesized via the direct reaction of 2‐(diphenylmethyl)oxazoline with bromoalkyls, using tert‐butyllithium. The structures were confirmed by Fourier transform infrared, nuclear magnetic resonance and mass spectrometry. These bisoxazolines have different melting points with varied molecular chain flexibility. They functioned well as crosslinkers when heated with phenolic resins or poly(acrylic acid), providing a path to new thermosetting materials with controlled glass transition temperature. To clarify the crosslinking reaction mechanism, the model reactions of these monomers with phenol and acetic acid were investigated. Copyright © 2000 John Wiley & Sons, Ltd.     

乳液聚合法制备聚合物与十二醇复合乳胶粒

通过乳液聚合法, 以苯乙烯、丙烯酸丁酯为主要单体, 以甲基丙烯酸为功能性单体, 以二乙烯基苯或二甲基丙烯酸乙二醇酯为交联剂, 制备了包覆有十二醇的聚合物复合颗粒. 通过动态光散射粒径仪和透射电镜观测乳胶粒粒径和形态, 气相色谱法测试了十二醇的包覆率, 并探讨了聚合过程中十二醇包覆率的变化情况. 结果表明十二醇的包覆率和十二醇与单体的质量比及单体转化率显著相关, 并且在聚合过程中包覆率存在先升后降的趋势. 实验发现十二醇包覆率的先升后降是由聚合物和十二醇的相容性不好引起的.     

Polyhydroxy and polyethyleneglycol (meth)acrylate polymers: physical properties and general studies for their use as electrophoresis matrices.

A new series of materials have been tested for their suitability as electrophoresis matrices. The mechanical and optical properties of gels composed of polyethyleneglycol (meth)acrylate esters or polyhydroxy (meth)acrylate esters in water and in various concentrations of organic solvents are described. Several crosslinkers including polyethyleneglycol and polyhydroxy di(meth)acrylates, piperazine diacrylate, and bisacrylamide were used in these studies. Electrophoretic migration and separation of a series of protein standards through polyethyleneglycol methacrylate (PEGM) 200, PEGM 400, and glyceryl methacrylate is demonstrated. Further, copolymerization of all of the monomers with acrylamide was performed and the distribution of monomer incorporation into the polymer network calculated. All monomers and copolymers that were examined by IR spectroscopy showed greater than 99% polymerization. These results justify their further study for biomolecule separations.     

Polymerization of adsorbed monolayers. III. Preliminary structure studies in dilute solution of the insertion polymers

Insertion poly(methyl acrylate) and poly(methyl methacrylate) were prepared from monomers adsorbed in monolayers on the surface of montmorillonite clay, both in the presence and in the absence of bifunctional crosslinkers (ethylene glycol dimethacrylate and tetramethylene glycol dimethacrylate). The insertion poly(methyl acrylate) and the crosslinked insertion poly(methyl methacrylate) and dilute-solution properties quite different from conventional polymers of these monomers, the differences including high light-scattering molecular weights combined with low viscosities, low values of the second virial coefficient, unusually large variations of the Huggins' constant k′ with the time-temperature history of the solutions, and low sedimentation velocities. These properties suggest that the insertion polymers have compact structures and are consistent with the postulate of sheetlike macromolecules. The dilute-solution properties of insertion poly(methyl methacrylate) made without crosslinker, unlike those of similarly prepared poly(methyl acrylate), were similar to those of conventional poly(methyl methacrylate). This difference in behavior is attributed to the different tendencies of the two monomers to undergo branching or crosslinking during radical polymerization.     

Nanocellulose Polymer Composites as Innovative Pool for (Bio)Material Development

Summary: Using a “never-dried” procedure (according to Figure 4) shaped bacterial nanocellulose (BC, 1% cellulose, 99% water) has been modified by the formation of BC-polymer composites. For this purpose, acrylate and methacrylate monomers and methacrylate crosslinkers were photopolymerized inside an ethanol-swollen nanofiber network. Using the ethanol as solvent and as confirmed by model reactions the synthetic polymer (SP) part of the composites is constructed of crosslinked polymers (number of repeating units in the range of 500). As part of ongoing work on the development of (bio)materials from the innovative pool of BC composites these investigations are recently directed towards the creation of collagen-like materials. Thus, for these purposes, mainly water absorption capacity, strength, and elasticity have to be controlled, whilst still retaining essential features of BC like shape, nanofiber network, pore system, and proved biocompatibility. Using acrylic acid, 2-ethylhexyl acrylate, 2-hydroxyethyl methacrylate, N-vinyl pyrrolidone as acrylate monomers and triethylene glycol dimethacrylate and 1,4-butandiol dimethacrylate as crosslinkers of different concentrations either a filling of the pores or a coating of the fibers in the BC nanocomposites could be achieved. The small cellulose content of the composites significantly increases the water absorption value and the strength of the material as well as the ability of re-swelling in the case of fiber coated composites. Sample 12 is an optimized BC-SP composite regarding important properties of hyaline cartilage like Young's modulus in the range of 5–20 MPa using the well-known Simplex-method.     

HIGH INDEX OPTICAL MATERIALS PREPARED BY COPOLYMERIZATION OF NOVEL BIFUNCTIONAL THIOMETHACRYLATES

Optical materials, such as ophthalmic lens, are thermosetting resins, which require crosslinking agents. An optical resin, having a high refractive index, is usually produced by radical copolymerization in which high index crosslinking monomers are significantly important. We provide here the resins prepared by radical polymerization of novel bifunctional thiomethacrylates as high index crosslinkers.     

Using hyperbranched macromers as crosslinkers of methacrylic networks prepared by photopolymerization

Hyperbranched polymers were modified with terminal methacryloyl groups to be used as crosslinkers. The photoinitiated polymerization of several methacrylic monomers was examined in the presence of the hyperbranched macromers and bis-(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (Irgacure 819^®) as a photoinitiator, upon UV irradiation. The photopolymerization kinetics was systematically studied by fluorescence and photoDSC in real time and in situ. Six types of monofunctional methacrylic monomers, two types of difunctional methacrylic monomers and four types of (meth)acrylate-modified hyperbranched macromers with different structures were employed for series of photopolymerization reactions. The incorporation of the hyperbranched macromers allows to increase the conversion at gelation and thus, final conversion. This behaviour is dependent on monomer and macromer nature and has been explained as due to an increase of the free volume fraction and confirmed by fluorescence. The results indicate that H-bonding and π-stacking induce self-assembly of hyperbranched macromers leading to reaction induced phase separation at the highest concentration of hyperbranched macromer used.     

Synthesis of Oil Spill Sorbents Based on Cellulose Derivatives

In this work, hydroxypropyl cellulose (HPC) was used to synthesize hydroxypropylcellulose acrylate (HPCA) macromonomer by esterification of HPC with acryloyl chloride in homogenous solution of DMF. Then the produced HPCA monomer was copolymerized with ethylhexyl acrylate (EHA) in presence of two types of crosslinkers to produce oil gel. Several parameters were considered, namely, monomers feed ratio, type and concentration of the applied crosslinkers. The chemical structures of both HPC and HPCA were confirmed by using FTIR and ¹H NMR spectroscopic analyses. Also, the thermal properties of the crosslinked oil absorbents were investigated by using TGA. Furthermore, morphological propoeries of these crosslinked sorbers were studied through SEM and their swelling efficiency was thoroughly investigated in heavy and light oil.     

Synthesis and polymerizations of phosphonated‐bis(methacrylamide)s for dental applications

Novel phosphonate and phosphonic acid‐containing bis(methacrylamide)s were synthesized. The phosphonate‐containing monomers ( 1a and 1b ) were synthesized by amidation of 2‐(2‐chlorocarbonyl‐allyloxymethyl)‐acryloylchloride with diethyl 2‐aminoethylphosphonate and diethyl 1‐aminomethylphosphonate. The phosphonic acid‐containing monomers ( 2a and 2b ) were synthesized by hydrolysis of 1a and 1b with trimethylsilyl bromide (TMSBr). All monomers were liquids and dissolved in water and ethanol. Thermal homopolymerization of 1a and 1b in bulk and solution using 2,2′‐azobis(isobutyronitrile) (AIBN) at 80 °C gave crosslinked polymers indicating low cyclization tendencies of these monomers. They were also homopolymerized using photo‐DSC with 2,2′‐dimethoxy‐2‐phenyl acetophenone (DMPA) as photoinitator, and their maximum rates of polymerization were found to be higher than commercial monomers 2,2‐bis[4‐(2‐hydroxy‐3‐methacryloyloxy propyloxy) phenyl] propane (Bis‐GMA) and 2‐hydroxyethyl methacrylate (HEMA), indicating their potential as reactive diluents or crosslinkers in dental materials. In fact, copolymerization with monomer 1a resulted in improvements in photopolymerization kinetics of both Bis‐GMA and HEMA. The acidic nature of the aqueous solutions (pH of 2a : 1.42, 2b : 1.53), stability under aqueous conditions after 1 month of study at 37 °C, interaction of 2a with hydroxyapatite (HAP) as representative of both monomers, and copolymerizability of the same with HEMA make these monomers suitable as adhesive monomers in dental adhesives, although their low observed reactivities may present a drawback. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Controlled preparation of nanometer‐sized supramolecular cylinders of poly(ethylene oxide) embedded in methacrylate matrices

Semi‐interpenetrating networks of poly(ethylene oxide) (PEO) and highly crosslinked poly(methacrylate)s were generated from solutions of PEO in mixtures of methacrylate monomers and dimethacrylate crosslinkers. The deep quenching of the solutions into the unstable region resulted in microphase separation via a spinodal decomposition mechanism. Through the crystallization of the PEO inside the polymer‐rich phase, the domain size was reduced below the Cahn–Hilliard limit. The microstructure was permanently preserved by subsequent UV‐initiated polymerization of the monomers well below the PEO melting temperature. The semi‐interpenetrating networks were characterized by differential scanning calorimetry, small‐angle X‐ray scattering, NMR spin‐diffusion measurements, and electron microscopy. Morphologies based on networks of cylindrical PEO aggregates with diameters of 10 ± 2 nm were observed, nearly independent of the molecular weight of the used PEO. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2041–2056, 2000     

Swelling and Network Parameters of 1-Hexadecene-Co-Trimethylolpropane Distearate Monoacrylate Sorbers

Linear and crosslinked copolymers with different compositions of 1-hexadecene and trimethylolpropane distearate monoacrylate monomers were synthesized and evaluated for oil-absorbency application. Different concentrations of ethylene glycol diacrylate (EGDA) and ethylene glycol dimethacrylate (EGDMA) crosslinkers were used. The concentration of both crosslinkers was varied from 0.5% to 2%. Copolymer compositions were determined from ¹H NMR spectroscopy. Monomer reactivity ratios were calculated using Fineman-Ross and Kelen-Tudos techniques at low conversions. The oil absorbency and swelling rate constant were measured and influenced mainly by the degree of crosslinking and the hydrophobicity of copolymer units. The final equilibrium oil content, volume fraction of polymer and swelling capacity were determined at 298 K. The effective crosslinking density V_e, theoretical crosslink density V_t, the average molecular weight between the crosslinks M_c and the polymer-toluene interaction parameter χ were determined from swelling measurements. The efficiencies of EGDA and EGDMA crosslinking agents toward copolymers were determined.     

Polymerizable Gd(iii) building blocks for the synthesis of high relaxivity macromolecular MRI contrast agents

A new synthetic strategy for the preparation of macromolecular MRI contrast agents (CAs) is reported. Four gadolinium(iii) complexes bearing either one or two polymerizable methacrylamide groups were synthesized, serving as monomers or crosslinkers for the preparation of water-soluble, polymeric CAs using Reversible Addition–Fragmentation Chain Transfer (RAFT) polymerization. Using this approach, macromolecular CAs were synthesized with different architectures, including linear, hyperbranched polymers and gels. The relaxivities of the polymeric CAs were determined by NMR relaxometry, revealing an up to 5-fold increase in relaxivity (60 MHz, 310 K) for the linear polymers compared with the clinically used CA, Gd-DOTA. Moreover, hyperbranched polymers obtained from Gd(iii) crosslinkers, displayed even higher relaxivities up to 22.8 mM⁻¹ s⁻¹, approximately 8 times higher than that of Gd-DOTA (60 MHz, 310 K). A detailed NMRD study revealed that the enhanced relaxivities of the hyperbranched polymers were obtained by limiting the local motion of the crosslinked Gd(iii) chelate. The versatility of RAFT polymerization of Gd(iii) monomers and crosslinkers opens the doors to more advanced polymeric CAs capable of multimodal, bioresponsive or targeting properties.

A new synthetic strategy for the preparation of efficient macromolecular MRI contrast agents is reported.     

Diffusive Adhesives for Water-Rich Materials: Strong and Tunable Adhesion Beyond the Interface

It is notoriously difficult to adhere water-rich materials, such as hydrogels and biological tissues. Existing adhesives usually suffer from weak and nonadjustable adhesion strength, in part because the contact between the adhesive and substrate is largely restrained to the adhesive/substrate interface. In this study, we have attempted to overcome this shortcoming by developing a class of diffusive adhesives (DAs) that can extend adhesion deep into the substrate to maximize the adhesive/substrate contact. The DAs consist of hydrogel matrices and preloaded water-soluble monomers and crosslinkers that can diffuse extensively into the water-rich substrates after adhesive/substrate contact. Polymerization and crosslinking of the monomers are then triggered leading to a bridging network that interpenetrates the DA and substrate skeletons and topologically binds them together. This kind of adhesion, in the absence of adhesive/substrate covalent bonding, is of high strength and toughness, comparable to those of the best-performing natural and artificial adhesives. More importantly, we can precisely tune the adhesion strength on demand by manipulating the diffusion profile. It is envisioned that the DA family could be extended to include a large pool of hydrogel matrices and monomers, and that they could be particularly useful in biological and medical applications.     

Crosslinker Copolymerization for Property Control in Inverse Vulcanization

Sulfur is an underused by-product of the petrochemicals industry. Recent research into inverse vulcanization has shown how this excess sulfur can be transformed into functional polymers, by stabilization with organic crosslinkers. For these interesting new materials to realize their potential for applications, more understanding and control of their physical properties is needed. Here we report four new terpolymers prepared from sulfur and two distinct alkene monomers that can be predictively tuned in glass transition, molecular weight, solubility, mechanical properties, and color.     

Photocaged Quinone Methide Crosslinkers for Light‐Controlled Chemical Crosslinking of Protein–Protein and Protein–DNA Complexes

Small‐molecule crosslinkers are invaluable for probing biomolecular interactions and for crosslinking mass spectrometry. Existing chemical crosslinkers target only a small selection of amino acids, while conventional photo‐crosslinkers target almost all residues non‐specifically, complicating data analysis. Herein, we report photocaged quinone methide (PQM)‐based crosslinkers that target nine nucleophilic residues through Michael addition, including Gln, Arg, and Asn, which are inaccessible to existing chemical crosslinkers. PQM crosslinkers were used in vitro, in Escherichia coli, and in mammalian cells to crosslink dimeric proteins and endogenous membrane receptors. The heterobifunctional crosslinker NHQM could crosslink proteins to DNA, for which few crosslinkers exist. The photoactivatable reactivity of these crosslinkers and their ability to target multiple amino acids will enhance the use of chemical crosslinking for studies of protein–protein and protein–DNA networks and for structural biology.     

Characterization of molecularly imprinted polymers employing crosslinkers with nonsymmetric polymerizable groups

Crosslinking monomers have been developed with a combination of methacrylamide and methacrylate or vinyl ketone polymerizable groups that provide molecularly imprinted polymers (MIPs) with improved binding and selectivity. The differential reactivity rates of the polymerizable groups prompted an investigation into the time‐dependent behavior of the crosslinkers, which suggests a new mechanism for MIP formation. The mechanism involves the formation of long sections of linear poly(vinyl ketone) with pendant methacrylamide groups that form a highly crosslinked network in a subsequent step. This has implications for the sequence morphology of polymers, affecting the structure and improving the binding properties of MIPs. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3668–3675, 2004     

不同交联剂对甲基丙烯酸-β-羟乙酯/E-51双甲基丙烯酸酯聚合物水凝胶性能的影响

以水溶性单体甲基丙烯酸-β-羟乙酯(HEMA)与大分子交联剂E-51双甲基丙烯酸酯(E-51-DMA)(质量比HEMA/E-51-DMA=90/10)为主要原料,分别引入了5种小分子交联剂:N,N′-亚甲基双丙烯酰胺(MBA)、二乙烯基苯(DVB)、双甲基丙烯酸乙二醇酯(EDMA)、1,1,1-三(丙烯酰氧甲基)丙烷(TAP)和2,2,2-三(丙烯酰氧甲基)乙醇(TAE),采用本体聚合方法合成了5个系列的聚合物水凝胶.研究了小分子交联剂的类型及用量对水凝胶溶胀性能、杨氏模量以及有效交联密度ve和聚合物-水相互作用参数χ的影响,并比较了不同交联剂的交联效率.结果表明,随着小分子交联剂用量的增大,水凝胶平衡含水量EWC逐渐降低,聚合物体积分数2逐渐增大,反映聚合物网络结构的有效交联密度ve以及热力学参数聚合物-水相互作用参数χ值也随之增大.通过理论交联密度和有效交联密度的线性拟合,得到所选用的5种小分子交联剂在E-51-DMA10/HEMA90水凝胶体系中的交联效率,其顺序为DVB>EDMA>TAE>MBA≈TAP.     

Comparative study on the separation behavior of monolithic columns prepared via ring-opening metathesis polymerization and via electron beam irradiation triggered free radical polymerization for proteins

Monolithic columns have been prepared via ring-opening metathesis polymerization using different monomers and crosslinkers, i.e. norborn-2-ene, 1,4,4a,5,8,8a-hexahydro-1,4,5,8-exo,endo-dimethanonaphthalene, cyclooctene and tris(cyclooct-4-en-1-yloxy)methylsilane. 2-Propanol and toluene were used as macro- and microporogens. Alternatively, monolithic supports were realized via electron beam triggered free radical polymerization using trimethylolpropane triacrylate and ethylmethacrylate. Here, 2-propanol, 1-dodecanol and toluene were used as porogens. The three monolithic supports were structurally characterized by inverse size exclusion chromatography and investigated for their separation capabilities for a series of proteins. Separation efficiencies are discussed within the context of the different structural features of the monolithic supports and are compared to the separation data obtained on a commercial silica-based Chromolith RP-18e column.     

Preparation of waterborne polyurethane nanocomposites: Polymerization from functionalized hydroxyapatite

We report the preparation and characterization of waterborne polyurethane (WBPU)/hydroxyapatite (HAp) nanocomposites through in situ polymerization from functionalized HAp. The HAp nanoparticles (HAp NPs) were urethanated with 3-isocyanatemethyl-3,5,5-trimethyl-cyclohexylisocyanate (isophorone diisocyanate) to obtain grafted HAp NPs containing isocyanate groups (HAp-g-NCO) as crosslinkers and then the HAp-g-NCO is further polymerized with WBPU monomers to form the WBPU/HAp nanocomposites. The HAp NPs were homogeneously dispersed in the polyurethane matrix at low loading levels (?2.0 wt%), thus the mechanical strength and the elongation at break of the WBPU/HAp nanocomposites were significantly improved. Thermal stability and water resistance of the WBPU/HAp nanocomposites are also enhanced. These results suggest that the WBPU/HAp nanocomposites prepared by in situ polymerization hold the potential as new materials with improved mechanical properties, thermal stability and water resistance.