Preparation and polymerization of a water‐soluble,nonbonding crosslinking agent for a mechanically crosslinked hydrogel

A novel water‐soluble cyclic macromonomer based on a cyclic potassium polyacrylate was prepared. The radical polymerization of acrylamide in the presence of the cyclic macromonomer was carried out to obtain a mechanically crosslinked polyacrylamide. The terpolymerization of acrylamide, sodium acrylate, and the cyclic macromonomer gave a mechanically crosslinked polyelectrolyte with high swellability. The mechanically crosslinked polyelectrolyte exhibited large volume shrinkage in a water solution of Cu(II) salt. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5032–5040, 2005     

Synthesis of a thermoresponsive shell‐crosslinked 3‐layer onion‐like polymer particle with a hyperbranched polyglycerol core

A novel thermoresponsive shell crosslinked three‐layer onion‐like polymer particles were prepared using hyperbranched polyglycerol (PG) as parents compound, the periphery hydroxyl groups of PG were transformed into trithiocarbonates (? SC(S)S? ) first; then, it was used as chain transfer agent to prepare star‐like block copolymer of N‐isopropyl acrylamide (NIPA) and N,N‐dimethylaminoethyl acrylate (DMA) in sequence via reversible addition fragmentation chain transfer (RAFT) process. Thus, a three‐layer polymer, PG? [SC(S)S? (DMA)? b? (NIPA)]_n, was obtained. The middle layer of poly(DMA) was then crosslinked with 1,8‐diiodoctane, and the resulting onion‐like three‐layer polymer showed a lower critical solution temperature (LCST) in water because of the outer layer of poly(NIPA). The LCST value only slightly depended on the crosslinking degree. Finally, the ? SC(S)S? were transformed into thiols by sequential treating with sodium borohydride and formic acid; thus, the core molecule was chemically detached from the crosslinked shell and a novel shell crosslinked polymer particle was obtained. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5652–5660, 2005     

Synthesis of gold–poly(methyl methacrylate) core–shell nanoparticles by surface‐confined atom transfer radical polymerization at elevated temperature

Surface‐confined atom transfer radical polymerization was used to prepare gold nanoparticle–poly(methyl methacrylate) core–shell particles at elevated temperature. First, gold nanoparticles were prepared by the one‐pot borohydride reduction of tetrachloroaurate in the presence of 11‐mercapto‐1‐undecanol (MUD). MUD‐capped gold nanoparticles were then exchanged with 3‐mercaptopropyltrimethoxysilane (MPS) to prepare a self‐assembled monolayer (SAM) of MPS on the gold nanoparticle surfaces and subsequently hydrolyzed with hydrochloric acid. The extent of exchange of MUD with MPS was determined by NMR. The resulting crosslinked silica‐primer layer stabilized the SAM of MPS and was allowed to react with the initiator [(chloromethyl)phenylethyl] trimethoxysilane. Atom transfer radical polymerization was conducted on the Cl‐terminated gold nanoparticles with the CuCl/2,2′‐bipyridyl catalyst system at elevated temperature. The rates of polymerization with the initiator‐modified gold nanoparticles exhibited first‐order kinetics with respect to the monomer, and the number‐average molecular weight of the cleaved graft polymer increased linearly with the monomer conversion. The presence of the polymer on the gold nanoparticle surface was identified by Fourier transform infrared spectroscopy and transmission electron microscopy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3631–3642, 2005     

Local deformation in photo‐crosslinked polymer blends monitored by Mach‐Zehnder interferometry

Local deformation of a polymer mixture crosslinked by irradiation with ultraviolet light was in situ monitored by using a Mach‐Zehnder interferometer. In combination with the refractive index data obtained from independent measurements, the deformation in the nanometer scales of the crosslinked blends was calculated by using the difference in optical path length of the blend measured before and after irradiation. Upon varying the crosslink density of the blend by changing the light intensity, it was found that the local deformation well correlates with the crosslink density obtained from the reaction kinetics experiments. Furthermore, the strain relaxation of the blends was also monitored in situ and analyzed after irradiation over different time intervals. The results obtained in this study reveal the possibility of monitoring the nanometer‐scale deformation in polymers during radiation curing. These data also provide important information on the correlations between the irradiation‐induced elastic strain and the resulting morphology of reacting polymer blends. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2898–2913, 2005     

Influence of varying hard segments on the properties of chemically crosslinked moisture‐cured polyurethane‐urea

Polyurethane prepolymers are widely used in the reactive hot melt adhesives and moisture‐cured coatings. The chemically crosslinked moisture‐cured formulation based on PEG‐1000 and isophorone diisocyanate was prepared with NCO/OH ratio of 1.6:1.0. Trimethylol propane was used as a crosslinking agent. The excess isocyanate of the prepolymer was chain extended in the ratio of 2:1 (NCO/OH) with different aliphatic diols, and 4:1 with different aromatic diamines. The polymer network maturation during moisture cure was followed by dynamic mechanical thermal analyzer (DMTA) instrument. The thermal and dynamic mechanical properties of the crosslinked polymers were evaluated using thermogravimetric analysis, differential scanning calorimetric analysis and DMTA. Surface properties were evaluated through angle‐resolved X‐ray photoelectron spectroscopy. The present article discusses the physical properties of moisture‐cured polyurethane‐urea (MCPU) containing chemical crosslinks in the hard segment. The complete moisture‐cured polymers showed amorous results toward room temperature modulus, tensile strength, hardness, thermal stability, and transparency. The surface properties showed the enrichment of soft segments. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 102–118, 2006     

In situ fabrication of paclitaxel‐loaded core‐crosslinked micelles via thiol‐ene “click” chemistry for reduction‐responsive drug release

In this study, a facile method to fabricate reduction‐responsive core‐crosslinked micelles via in situ thiol‐ene “click” reaction was reported. A series of biodegradable poly(ether‐ester)s with multiple pendent mercapto groups were first synthesized by melt polycondensation of diol poly(ethylene glycol), 1,4‐butanediol, and mercaptosuccinic acid using scandium trifluoromethanesulfonate [Sc(OTf)₃] as the catalyst. Then paclitaxel (PTX)‐loaded core‐crosslinked (CCL) micelles were successfully prepared by in situ crosslinking hydrophobic polyester blocks in aqueous media via thiol‐ene “click” chemistry using 2,2′‐dithiodiethanol diacrylate as the crosslinker. These PTX‐loaded CCL micelles with disulfide bonds exhibited reduction‐responsive behaviors in the presence of dithiothreitol (DTT). The drug release profile of the PTX‐loaded CCL micelles revealed that only a small amount of loaded PTX was released slowly in phosphate buffer solution (PBS) without DTT, while quick release was observed in the presence of 10.0 mM DTT. Cell count kit (CCK‐8) assays revealed that the reduction‐sensitive PTX‐loaded CCL micelles showed high antitumor activity toward HeLa cells, which was significantly higher than that of reduction‐insensitive counterparts and free PTX. This kind of biodegradable and biocompatible CCL micelles could serve as a bioreducible nanocarrier for the controlled antitumor drug release. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 99–107     

Synthesis of siloxane‐crosslinked polysilylenemethylenes by chlorodephenylation

Thermally stable polysilylenemethylenes (PSMs) with siloxane crosslinking moieties were successfully synthesized by chlorodephenylation of preformed poly(methylphenylsilylenemethylene) (PMPSM) and subsequent in situ alcoholysis/hydrolysis/condensation reactions. The simplified process and mild reaction conditions are quite advantageous. The crosslink density of these materials can be adjusted by the degree of chlorodephenylation, although an alkoxysilyl group remains to some extent. The resulting crosslinked PSMs have well defined structures in which the backbone is composed of MePhSiCH₂ and Me(MeO)SiCH₂ as well as Me(O_1/2)SiCH₂ as a crosslinking moiety. The resulting crosslinked PSMs exhibited glass‐transition temperatures ranging from 15 to 20 °C, whereas that of linear PMPSM was 22 °C. The crosslinked PSMs remained unchanged in weight below 300 °C, suggesting that they are thermally stable up to that temperature. The good solvent resistance caused by crosslinking as well as high thermal stability of these materials allow us to design new PSM‐based polymer blends and preceramic polymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 416–422, 2002     

Photo‐crosslinked fluorinated thin films from azido‐functionalized random copolymers

Random copolymers of styrene, p‐azidomethylstyrene and 1H,1H,2H,2H‐perfluorodecyl methacrylate were prepared in two steps involving nitroxide‐mediated radical copolymerization and azidation reaction and further characterized by ¹H and ¹⁹F NMR, size exclusion chromatography, differential scanning calorimetry, and thermal gravimetric analysis. Ultrathin films of these azidomethyl‐functionalized fluorinated random copolymers, with thicknesses ranging from 20 to 100 nm, were spin coated onto Si substrates and then crosslinked by ultraviolet irradiation resulting in smooth and insoluble crosslinked fluorinated polymer mats. The surface properties of the supported thin films were investigated by X‐ray photoelectron spectroscopy and water contact angle measurements. These tailored photo‐crosslinked coatings afford a versatile control and homogenization of the wetting properties of different organic and inorganic substrates. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3888–3895, 2010     

Synthesis of well‐defined three‐armed polystyrene having thiourethane–isocyanurate as the core structure derived from trifunctional five‐membered cyclic dithiocarbonate

The synthesis of a three‐armed polymer with an isocyanurate–thiourethane core structure is described. Monofunctional reversible addition–fragmentation chain transfer (RAFT) agent 2 and trifunctional RAFT agent 5 were prepared from mercapto‐thiourethane and tris(mercapto‐thiourethane), which were obtained from the aminolysis of mono‐ and trifunctional five‐membered cyclic dithiocarbonates, respectively. The radical polymerization of styrene in the presence of 2,2′‐azobis(isobutyronitrile) and RAFT agent 2 in bulk at 60 °C proceeded in a controlled fashion to afford the corresponding polystyrene with desired molecular weights (number‐average molecular weight = 3000–10,100) and narrow molecular weight distributions (weight‐average molecular weight/number‐average molecular weight < 1.13). On the basis of the successful results with the monofunctional RAFT agents, three‐armed polystyrene with thiourethane–isocyanurate as the core structure could be obtained with trifunctional RAFT agent 5 in a similar manner. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5498–5505, 2005     

Improvement of the thermal stability of cluster‐crosslinked polystyrene and poly(methyl methacrylate) by optimization of the polymerization conditions

The polymerization conditions for polystyrene and poly(methyl methacrylate) crosslinked by 0.5 mol % of the cluster Zr₆O₄(OH)₄(methacrylate)₁₂ were optimized by applying a step polymerization procedure. The onset of thermal decomposition was thus increased up to about 50° for polystyrene and about 110° for poly(methyl methacrylate). The increase in thermal stability correlated with a higher char yield. The glass transition temperatures were also increased by about 15°. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6586–6591, 2005     

Dual‐responsive crosslinked micelles of a multifunctional graft copolymer for drug delivery applications

A novel multifunctional amphiphilic graft copolymer has been synthesized consisting of a biodegradable poly(l ‐aspartic acid) backbone that was decorated by water‐soluble poly(ethylene glycol) (PEG) and pH‐responsive poly(N,N‐diethylaminoethyl methacrylate) (PDEAEMA) side‐chains as well as thiol pendant groups. This graft copolymer together with doxorubicin (DOX) formed micelles in water at pH = 10.0 with PDEAEMA and DOX acting as the core and PEG serving as the micellar corona. Upon oxidation, the thiol groups dimerized to form disulfide bonds, thus “locking in” the micellar structure. These crosslinked micelles expanded as the pH was decreased from 7.4 to 5.0 or upon the addition, at pH = 7.4, of glutathione (GSH), a thiol‐containing oligopeptide that is present in cancerous cells and cleaves disulfide bonds. At pH = 5.0, GSH addition triggered the disassembly of the micelles. The expansion and disassembly of the micelles have been determined via in vitro experiments to evaluate their DOX release behavior. More importantly, the graft copolymer micelles could enter cells by means of endocytosis and deliver DOX to the nuclei of ovarian cancer BEL‐7402 cells. Thus, this polymer and its micelles are promising candidates for drug delivery applications. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1536–1546     

Synthesis of crosslinked poly(butyl methacrylate‐co‐pentaerythritol triacrylate) gel by single electron transfer‐living radical polymerization and its oil‐absorbing properties

A novel high oil‐absorbing crosslinked gel was synthesized by copolymerization of butyl methacrylate (BMA) with a small amount of pentaerythritol triacrylate (PETA) crosslinker using single electron transfer‐living radical polymerization (SET–LRP) initiated with carbon tetrachloride (CCl₄) and catalyzed by Cu(0)/hexamethylenetetramine (HMTA) in N, N‐dimethylformamide (DMF). The polymerization followed first‐order kinetics as indicated by linear increase of monomer concentration with reaction time. Effects of reaction temperature, crosslinker, initiator, and catalyst on the oil‐absorbing properties of the crosslinked gel were investigated in detail. The oil absorptions of the crosslinked gel to chloroform, toluene could reach 51.9, 34.5 g/g, respectively. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Infrared and Raman spectroscopic investigation of crosslinked polystyrenes and radiation‐grafted films

The crosslinking of functionalized polystyrene resins is often of critical importance in determining resin properties and performance in the application of these materials as membranes and supports. In this investigation model systems are developed for quantifying the infrared and Raman spectroscopic properties of copolymers based on poly(styrene‐co‐divinylbenzene). Analytical curves appropriate for the quantification of para‐ and metasubstituted species and pendant double bonds are reported, and corrections to previously reported spectroscopic assignments and analytical methods are made. The usefulness of these two analytical methods in characterizing radiation‐grafted films and commercial copolymers is compared, and typical characterization results are given. The relative concentrations of the species found in the grafted films are quite different from their concentrations in the grafting solution, and empirical relationships between the two are developed. In addition, the graft composition varies as a function of the base polymer film thickness and type and the penetration depth in the grafted film. Radiation‐grafted films are more highly crosslinked in their near surface regions, and thinner films are more extensively crosslinked. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 59–75, 2004     

Selective retention of some polyaromatic hydrocarbons by highly crosslinked polymer networks

Highly crosslinked polymer networks were characterized in terms of structural differences based on the crosslinked network structures with their chromatographic molecular retentivity for some polyaromatic hydrocarbons (PAHs). Because PAHs and some sterically bulky solutes were used in the chromatographic characterization, tiny differences in the crosslinked polymer networks were observed in terms of the chromatographic molecular retentivity. Ethylene dimethacrylate afforded molecular retentivity for anthracene, and this recognition ability changed with the polymerization time. In addition, 1,4‐butanediol dimethacrylate afforded molecular retentivity for pyrene, and this retentivity was larger than that for anthracene. The polymerization methods also affected the resulting polymer networks drastically. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2556–2566, 2005     

Molecular layer‐by‐layer deposition of highly crosslinked polyamide films

A molecular layer‐by‐layer (mLbL) deposition process is demonstrated to synthesize conformal coatings of crosslinked polyamide. This process controls the rapid reaction of trimesoyl chloride and m‐phenylene diamine, unlike interfacial polymerization techniques which produce rough films and poorly defined network structure. Layer‐by‐layer polyamide films appear structurally similar to interfacially polymerized films with a linear film growth rate of ≈0.9 nm per cycle. Films made by mLbL deposition show a 70‐fold decrease in surface roughness as compared to a commercial, interfacially polymerized polyamide. Surface chemistry could be controlled based on which reaction step was performed last, leading to amine or carboxylic acid rich surfaces. With the ability to control chemical structure throughout the crosslinked network, this technique provides new routes to build polyamide films and improve analysis techniques for commercial applications such as reverse osmosis membranes. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Role of molten fraction on the structural evolution in stretching and cooling of crosslinked low‐density polyethylene: Real‐time mechano‐optical measurements

We investigated the uniaxial deformation behavior of crosslinked low‐density polyethylene in partially and substantially molten states using a real‐time true stress–strain birefringence system. The stress–birefringence behavior exhibits a multiregime behavior during stretching and holding process. The details of this regime behavior are primarily governed by the degree of unmelted crystallinity as it has a dominant role in the long‐range structural connectivity. When the long‐range physical connectivity is present, a three‐regime nonlinear stress–optical behavior was observed. When the long‐range connectivity is substantially eliminated at higher temperatures, the regime I behavior disappears. Structural studies including cooling process reveal that the lower the proportion of molten material during stretching, the higher the concentration of fibrillar structure and the shorter are the lengths of the kebabs that exhibit twisted lamellae after solidification. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1825–1841, 2005     

Photo‐induced thiol‐ene polysulfide‐crosslinked materials with tunable thermal and mechanical properties

Photo‐induced thiol‐ene crosslinked polymeric networks have been extensively explored in constructing a variety of new materials with enhanced mechanical properties for optical, biomedical, and sensing applications. Toward the broad applications, however, tunable mechanical properties are greatly desired. Here, an effective approach utilizing high‐molecular‐weight methacrylate copolymers having pendant thiol and vinyl groups (MCPsh and MCPenes) to modulate thermal and mechanical properties of photo‐induced thiol‐ene crosslinked materials is reported. The MCP copolymers are synthesized by an industrially friendly polymerization method, followed by post‐modification including either a facile coupling reaction or reductive cleavage. Upon UV irradiation, thiol‐ene reactive blends of MCPsh and MCPenes yield highly crosslinked materials through the formation of flexible sulfide linkages. These polysulfide‐crosslinked materials based on rigid MCP backbones exhibit enhanced mechanical properties. Further, their thermal and mechanical properties are tuned by modulating monomer compositions of MCPs as well as varying numbers of pendant SH or vinyl groups (i.e., extent of crosslinking densities). This approach is versatile and effective for development of high performance polymeric materials. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3060–3068     

Dual crosslinked phenylethynyl end‐capped sulfonated polyimides via the ethynyl and sulfonate groups promoted by PEG

Typically, phenylethynyl (PE) end‐capped oligomides require a temperature of 370 °C for 1 h to develop a crosslinked system. A published method using poly(ethylene glycol)s (DM‐PEG‐250 and PEG‐400) as cosolvents with NMP was effective in crosslinking the ethynyl end‐caps at 250 °C/3 h in nonsulfonated oligomides. The application of this novel crosslinked method to PE end‐capped sulfonated oligomides was effective but caused a secondary crosslinked network via the sulfonic acid groups and ethylene glycol solvents. The solid‐state ¹³C NMR spectral data on ¹³C‐labeled end‐caps in the PE‐3F‐SPI‐3 oligomide provide evidence for the ethynyl to ethynyl and ethylene oxide sulfonate ester dual crosslinked structure. Infrared spectroscopy of model compounds also provides evidence for the presence of crosslinked sulfonate ester and appended sulfonate ester side chains. ¹³C NMR also provided quantitative data on the extent of the ethynyl to ethynyl crosslinking reaction and sulfonate ester crosslinks and side chains. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Bioreducible and core‐crosslinked hybrid micelles from trimethoxysilyl‐ended poly(ε‐caprolactone)‐S‐S‐poly(ethylene oxide) block copolymers: Thiol‐ene click synthesis and properties

Bioreducible and core‐crosslinked hybrid micelles were for the first time fabricated from biodegradable and biocompatible trimethoxysilyl‐terminated and disulfide‐bond‐linked block copolymers poly(ε‐caprolactone)‐S‐S‐poly(ethylene oxide), which were prepared by combining thiol‐ene coupling reaction and ring‐opening polymerization. The molecular structures, physicochemical, self‐assembly, and bioreducible properties of these copolymers were thoroughly characterized by means of FTIR, ¹H NMR, gel permeation chromatography, differential scanning calorimetry, wide‐angle X‐ray diffraction, dynamic light scattering (DLS), and transmission electron microscopy. The core‐crosslinking sol‐gel reaction was confirmed by ¹H NMR, and the core‐crosslinked hybrid micelles contained about 3 wt % of silica. The bioreducible property of both uncrosslinked and core‐crosslinked micelles in 10 mM 1,4‐dithiothreitol (DTT) solution was monitored by DLS, which demonstrated that the PEO corona gradually shedded from the PCL core. The anticancer doxorubicin drug‐loaded micelles showed nearly spherical morphology compared with blank micelles, presenting a DTT reduction‐triggered drug‐release profile at 37 °C. Notably, the core‐crosslinked hybrid micelles showed about twofold drug loading capacities and a half drug‐release rate compared with the uncross‐liked counterparts. This work provides a useful platform for the fabrication of bioreducible and core‐crosslinked hybrid micelles potential for anticancer drug delivery system. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Zwitterionic shell‐crosslinked micelles from block‐comb copolymer of PtBA‐b‐P(PEGMEMA‐co‐DMAEMA)

Through reversible addition‐fragmentation chain transfer (RAFT) polymerization of t‐butyl acrylate (tBA) and RAFT copolymerization of 2‐dimethylaminoethyl methacrylate (DMAEMA) with poly(ethylene glycol) methyl ether methacrylate (PEGMEMA), block‐comb copolymer of PtBA‐b‐P(PEGMEMA‐co‐DMAEMA) was prepared. After the self‐assembly of PtBA‐b‐P(PEGMEMA‐co‐DMAEMA) into core‐shell spherical micelles, P(PEGMEMA‐co‐DMAEMA) segments of the shell was crosslinked with 1,2‐bis(2‐iodoethoxy)ethane and the core of PtBA was selectively hydrolysized with trifluoroacetic acid. Thus, zwitterionic shell‐crosslinked micelles with positively charged outer shell and negatively charged inner core were obtained. Dynamic light scattering, transmission electron microscope, Zeta potential measurement, and nuclear magnetic resonance were used to confirm the formation of the zwitterionic shell‐crosslinked micelles. They showed the excellent resistance to the variation of pH value and possessed the positive values throughout the whole range of pH range even if the carboxylic groups of the micelles was much more than ammonium groups. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011