One‐pot fabrication of robust interpenetrating hydrogels via orthogonal click reactions

Interpenetrating polymer network (IPN) hydrogels have been fabricated through a facile one‐pot approach from tetra/bifunctional telechelic macromonomers with epoxy, amine, azide, and alkyne groups by orthogonal double click reactions: epoxy‐amine reaction and copper‐catalyzed azide‐alkyne cycloaddition. Both the crosslinked networks are simultaneously constructed in water from the biocompatible poly (ethylene glycol)‐based macromonomers. The crosslinking density of each network was finely tuned by the macromonomer structure, permitting control of network molecular weights between crosslinks of the final gels. Compared to corresponding single network gels, the IPN gels containing both tightly and loosely crosslinked networks exhibited superior mechanical properties with shear moduli above 15 kPa and fracture stresses over 40 MPa. The synthetic versatility of this one‐pot approach will further establish design principles for the next generation of robust hydrogel materials. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1459–1467     

Free radical and thermal curing of terpyridine‐modified terpolymers

Terpolymers bearing terpyridine as well as (meth)acrylates as free radical curable groups (UV‐curing) or hydroxyl groups (thermal curing with bis‐isocyanates) were synthesized and characterized using ¹H NMR, IR and UV‐vis spectroscopy as well as GPC. Subsequently, the ability of covalent crosslinking via the UV‐initiated polymerization of the acrylate groups was investigated. Moreover, the thermal covalent crosslinking via the reaction of hydroxyl functionalized terpolymer and bis‐isocyanate compounds could be successfully achieved. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4028–4035, 2004     

Coordination Bonds and Diels–Alder Bonds Dual Crosslinked Polymer Networks of Self‐healing Polyurethane

A dual crosslinked self‐healing polyurethane was prepared with robust mechanical properties through the dynamic reversible pyridine‐Fe³⁺ coordination bonds and Diels–Alder (DA) covalent bonds dual crosslinking strategy. Moreover, the mechanical properties and self‐healing ability of polyurethane can be tuned readily by different ratio of the coordination bonds and DA bonds. Under external load, the coordination bonds serve as sacrificial bonds are broken to dissipate energy, the DA bonds can keep the shape of sample. With the coordination bonds participation, the damaged samples can be healed under moderate heating treatment or with the aid of FeCl₃ solution. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2228–2234     

Dynamic rheology and relaxation time spectra of oil‐based self‐degradable gels

In oil well treatments, such as matrix stimulations or water shut‐off, it is often necessary to temporary isolate or protect productive zones with chemical diverting agents. In this work, a solution of peroxide crosslinked styrene‐butadiene rubber (SBR) has been transformed to a self‐degradable gel system by adding hydroperoxide as a degradation agent to the formulation. This oil‐based self‐degradable gel has been characterized by linear oscillatory rheometry. In situ and ex situ experiments were performed to evaluate the evolution of crosslinking and degradation reactions, including the liquid‐solid transition. Relaxation time spectra were calculated from dynamic mechanical frequency sweeps. Structural changes in the polymer network were visible within the relaxation time spectra, since it qualitatively showed the contribution of local simple entanglements and chemical covalent bonds to the final rheological behavior. The influence of peroxide concentration, polymer concentration, hydroperoxide concentration, and temperature have been studied and described in terms of rheological changes. Finally, a hydrogen donor aromatic solvent was used as scavenger to retard both crosslinking and degradation reactions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 433–444     

IR spectra studies of core‐shell type waterborne polyacrylate‐polyurethane microemulsions

The hydrogen bonds in films of the polyurethane and the core‐shell type polyacrylate‐polyurethane microemulsions have been studied by FTIR spectroscopy in the regions of  NH absorption and CO absorption. The effects on hydrogen bonds of the composition, the core‐shell ratio were revealed. At the same time, the relationship between the hydrogen bonds and the crosslinked structures (Type A and Type B) was discovered. The shifts of the  NH and CO stretching bands to higher frequencies and the shift of  NH bending bands to lower frequencies, with the increase of acetone CO number in the core, mean that the hydrogen bonds between the soft and hard segments, and those in the short‐range order in the hard segment phase, are broken. The dipole/dipole interaction which is supposed to exist between the acetone CO groups in the core and the urethane CO in the shell can change the hydrogen bond distribution in the shell, and at the same time, lead to hydrogen bonds between acetone CO in the core and the urethane  NH in the shell. Type A and B crosslinked structure between the core and the shell located at the interface of the core and the shell can confine the acetone CO within the crosslinking network, and Type B crosslinked structure also decreases the acetone CO numbers. These weaken the dipole/dipole interaction between the acetone CO and the urethane CO, and lead to the decrease of the effect of the acetone CO groups on the hydrogen bond distribution in the shell. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2642–2650, 1999     

Pressure‐sensitive adhesive utilizing molecular interactions between thymine and adenine

A simple pressure‐sensitive adhesion (PSA) system incorporating noncovalent interaction between thymine and adenine is presented. A copolymer having thymine moieties is combined with a low‐molecular‐weight bifunctional adenine cross‐linker. Molecular interactions caused by multiple hydrogen bonds between the thymine and adenine units are evaluated by FT‐IR spectral measurement. Mechanical properties of the PSA are examined by stress–strain curves and dynamic mechanical analysis. As the number of adenine cross‐linkers increases, Young's modulus increases from 0.24 to 3.0 MPa, and the glass transition temperature increases. Furthermore, it is found that the PSAs have adequate adhesive property from their shear strength test. Heat treatment at 80 °C is effective for reinforcement because of interchange of the hydrogen bonds. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1332‐1338     

Macroscopic–microscopic mechanical relaxation behavior of hybrid organic–inorganic materials

The mechanical properties of transparent hybrid organic–inorganic nanocomposites made from siloxane and zirconium oxopolymers are investigated at two different length scales. The complex interface that associates the two phases is made of covalent Zr O Si bonds and hydrogen bonding. The rubbery properties studied by creep and recovery present specific behaviors in comparison with model elastomers. This is a result of the complex crosslinking units. The stress relaxation phenomenon has been studied at the molecular scale by ²H quadrupolar NMR. During stress relaxation, the anisotropy of the molecular motion decreases slowly. This study demonstrates the straightforward relationship existing between the macroscopic and microscopic relaxation phenomena. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 645–650, 2001     

Microstructural PALS study of regulated dimethacrylates: Thiol‐ versus β‐allyl sulfone‐based networks

Radical photocuring of multifunctional (meth)acrylates is lacking control over the irregular chain growth process yielding highly crosslinked, inhomogeneous networks. Chain transfer agents (CTAs, e.g., thiols or β‐allyl sulfones) have been widely used to modify this curing process, thus reducing shrinkage stress and increasing the toughness of the formed photopolymers. Resulting photopolymer networks exhibit higher bulk density, lower crosslinking density, and narrow glass transitions. Consequently, a more homogeneous network structure was postulated for those networks. Whereas macroscopic properties of the modified final materials have already been studied, herein the microstructural arrangement of such modified networks has also been evaluated with the help of positron annihilation lifetime spectroscopy (PALS). A more homogenous network structure with a decreased average free‐volume void size was confirmed for CTA‐based dimethacrylate networks. A sharper distribution of the ortho‐positronium (o‐Ps) lifetime, mainly for the β‐allyl sulfone‐based photopolymers, hints toward a more regulated network structure. Moreover, the combination of PALS, DMTA, density and swelling experiments elucidates relations between void formation, crosslinking density and macroscopic characteristics such as shrinkage stress and mechanical properties. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2476–2484     

Crosslinked PDMS elastomers and coatings from the thermal curing of vinyl‐functionalized PDMS and a diazide aliphatic crosslinker

The crosslinking of poly(dimethylsiloxane) elastomers and coatings by the thermal curing of poly(dimethylsiloxane‐co‐methylvinylsiloxane) and 1,12‐diazido‐dodecane was studied. This crosslinking pathway relies on the cycloaddition of azides and alkenes as well as the thermal generation of nitrene transient radicals, which react with alkenes, yielding respectively 1,2,3‐triazoline and aziridine crosslinking knots. The influence of temperature and the ratio of azide and vinyl functionalities has been investigated by rheological, swelling, and insoluble fraction measurements for materials crosslinked in bulk and by comparison of the thickness before and after extraction of the soluble materials by soxhlet extraction for the crosslinked coatings. The preparation of highly crosslinked PDMS‐based elastomers and coatings has been demonstrated, even if the fraction of elastically effective crosslinks in bulk remained below 160 mol/m³. Advantageously, this system does not require additional initiator or catalyst, is not sensitive to moisture or oxygen, and can be extended to a wide range of unsaturated polymers as well as different organic or inorganic solid substrates. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Hybrid ionic/covalent polymer networks derived from functional imidazolium ionomers

A new class of ionomers is described wherein ion‐pairs bear reactive functionality, thereby facilitating further chemical modification. Halide displacement from brominated poly(isobutylene‐co‐isoprene) by 1‐vinylimidazole is used to prepare ionomer derivatives that can be crosslinked by radical oligiomerization of pendant vinyl groups. The resulting thermosets contain a labile network of imidazolium bromide ion‐pair aggregates as well as a stable covalent network. As a result of their hybrid ionic/covalent composition, these thermoset elastomers provide a unique combination of rheological, tensile and stress relaxation properties that cannot be achieved from conventional covalent or ionic networks. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2438–2444     

利用聚乙烯醇结晶辅助制备多重交联的高强度聚丙烯酰胺水凝胶

在表面带有C=C双键的乙烯基杂化二氧化硅纳米颗粒(vinyl hybrid silica nanoparticle,VSNP)上接枝丙烯酰胺(AM),所得到的纳米刷状凝胶因子通过聚丙烯酰胺(PAM)间的氢键形成物理交联点,则多官能化的VSNP可作为拟共价交联点构筑双重交联的单一网络纳米复合物理水凝胶(nanocomposite physical hydrogel,NCP gel),表现出较高的强度和超拉伸性.为了进一步提高凝胶的强度和韧性,将少量PVA和PAM/VSNP纳米刷混合制成凝胶,通过冷冻-融化处理,使与PAM分子链相互缠绕并形成氢键作用的PVA结晶,形成新的交联点进一步交联PAM NCP gel,得到多交联的PAM NCP gel体系.通过拉曼光谱和示差扫描量热分析,证明凝胶中的PVA通过氢键既可以与PAM相互作用,又形成微晶为新交联点,大大增强了NCP gel的力学性能,与PAM NCP gel相比,凝胶的拉伸强度和断裂能分别从313 k Pa和1.41×104 J/m~2提高到了557k Pa和4.65×104 J/m~2.     

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     

Synthesis and characterization of novel biodegradable epoxy‐modified polyurethane elastomers

Biodegradable polyurethane elastomers with the potential for applications in medical implants were synthesized from the reaction of epoxy‐terminated polyurethane prepolymers (EUPs) with 1,6‐hexamethylenediamine as a curing agent. EUPs were themselves prepared from the reaction of glycidol and isocyanate‐terminated polyurethanes made from different molecular weights of poly(ε‐caprolactone) (CAPA) and 1,6‐hexamethylene diisocyanate. All materials were characterized by spectroscopic methods. The curing conditions were optimized by gel content measurements. The curing kinetic and kinetic parameters were determined from differential scanning calorimetry measurements. The effects of changing the crosslink density and crystallinity of elastomers via the alteration of the CAPA polyol molecular weight on the physical, mechanical, and degradation properties of the final elastomeric polymers were examined fully. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2985‐2996, 2005     

Syntheses and characterizations of bis(trialkoxysilyl)oligoimides. II. Syntheses and characterizations of fluorinated crosslinkable oligoimides with low refractive indices

Novel crosslinkable fluorinated oligoimides were prepared in two steps. The first involved the synthesis of oligoimides terminated with nadic or allylic double bonds, and the second step was materialized either by a radical addition of mercaptotrialkoxysilane derivatives onto nadic double bonds or a hydrosilylation reaction of hydrogenotrialkoxysilane derivative onto allylic double bonds. Three kinds of crosslinking of the trialkoxysilane end groups were studied. The first kind entailed a thermal self‐crosslinking of trialkoxysilane groups. The second process of crosslinking incorporated a bicomponent system—the crosslinked agent was 1,1,1‐tris(4‐hydroxyphenyl)ethane (TRIOH). The trialkoxysilane groups reacted with the hydroxyl–phenol groups of TRIOH to give thermally stable phenoxysilane bonds as well as a crosslinking network. The last method was also a bicomponent system; the oxalic acid was added into an oligoimide solution where by thermal treatment water was created. The water molecules hydrolyzed the trialkoxysilane groups into silanol groups that polycondensed into a crosslinked network following a sol–gel process. The mechanism of the different crosslinking reactions was investigated by Fourier transform infrared spectroscopy and solid‐state ²⁹Si NMR. The self‐crosslinked material prepared from precursor α,ω‐trimethoxysilyl fluorinated oligomer (M_n = 5500 g · mol^?1) exhibited a 10 wt % loss temperature under air higher than 420 °C and a low birefringence (Δn = 0.008) at 1.300 μm. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2602–2619, 2001     

Phase structure and thermomechanical properties of primary and tertiary amine‐cured epoxy/silica hybrids

Several kinds of organic–inorganic hybrids were synthesized from an epoxy resin and a silane alkoxide with a primary amine‐type curing agent or tertiary amine curing catalyst. In the hybrid systems cured with the primary amine‐type curing agent, the storage modulus in the high‐temperature region increased, and the peak area of the tan δ curve decreased. Moreover, the mechanical properties were improved by the hybridization of small amounts of the silica network. However, these phenomena were not observed in the hybrid systems cured with the tertiary amine catalyst. The differences in the network structures of the hybrid materials with the different curing processes were characterized with Fourier transform infrared (FTIR). In the hybrid systems cured with the primary amine‐type curing agent, FTIR results showed the formation of a covalent bond between silanol and hydroxyl groups that were generated by the reaction of an epoxy group with an active hydrogen of the primary amine. However, this phenomenon was not observed in the hybrids cured with the tertiary amine. The hybrids with the primary amine showed a homogeneous microstructure in transmission electron microscopy observations, although the hybrids cured with the tertiary amine showed a heterogeneous structure. These results mean that the differences in the interactions between the organic and inorganic phases significantly affect the properties and microstructures of the resultant composites. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1071–1084, 2001     

Conductivity,proton percolation,and gelation during the network growth in a flexible chain diepoxide and diamine mixture

The conductivity of a stoichiometric mixture of diglycidyl ether of 1,4‐butanediol and 1,6‐hexamethylene diamine has been studied during its polymerization at several temperatures where the ultimate product is a crosslinked gel. The decrease in the dc conductivity, σ₀, with the polymerization time, t, fits an equation for bond percolation, σ₀ ∼ [(t_gel‐t)/t_gel]^p, and yields a gelation time, t_gel which agrees with the t_gel determined from the viscosity and shear modulus measurements. It is proposed that as one covalent bond forms on chemical reaction, an indeterminable number of intermolecular H‐bonds in the structure vanish, and protonic conduction is disrupted. Thus, as the original H‐bond network gives way to a covalently bonded network, the mechanical rigidity increases, and protonic conductivity decreases. The gel point is reached when the increase in the number of covalent bonds brings the liquid's state up to its rigidity percolation threshold, and the decrease in the number of H‐bonds brings it down to its electrical percolation threshold. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 122–126, 2000     

Densely crosslinked polycarbosiloxanes. II: Thermal and mechanical properties

The thermal and mechanical properties of two densely crosslinked polycarbosiloxane systems were investigated in relation to the molecular structure. The networks were prepared from functional branched prepolymers and crosslinked via a hydrosilylation curing reaction. The prepolymers having only vinyl functionalities (poly[phenylmethylvinyl]siloxanes) were crosslinked by using crosslinking agents with reactive silicon–hydrogen groups. In prepolymers having both silicon–vinyl and silicon–hydrogen groups (poly[phenylmethylvinylhydro)]siloxanes crosslinking took place intermolecularly. The thermal and mechanical properties of the polymer networks were found to be dependent on the phenyl  Si O_3/2 (branches) content in the prepolymer, the number of elastically effective crosslinks, the elastically effective network chain density and molecular weight between crosslinks, length of the chain segments introduced by the hydrosilylation crosslinking reaction, and the number of dangling ends. As a consequence of the dense crosslinking, the mechanical properties were also strongly dependent on the glass transition temperature. A tough–brittle transition was observed around the glass transition temperature of the polymer networks. The properties of the poly(phenylmethylvinylhydro)siloxane networks were found to be superior to those of the poly(phenylmethylvinyl)siloxane networks. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1311–1331, 1997     

Molecularly templated reaction for forming poly(dimethyl siloxane)–graphene oxide composite elastomers

This study explores the molecularly templated reaction of pyrene‐terminated telechelic poly(dimethyl siloxane) (PDMS) with graphene oxide (GO) to produce composite elastomers. These materials undergo chemical crosslinking between secondary amides near PDMS chain ends and epoxies on the surface of GO as confirmed by infrared spectroscopy, rheology, gel content, and mechanical property measurements. The incorporation of pyrene end groups introduces π–π interactions with GO surfaces that enhance the reaction efficacy of the nearby secondary amide groups. As a comparison, methoxy‐terminated telechelic PDMS containing the same secondary amides near the chain ends did not exhibit appreciable crosslinking with GO. Depending on the concentration of the amide groups, the pyrene‐terminated PDMS/GO elastomer can be highly crosslinked (e.g., up to 96 wt % gel) but highly extensible (e.g., extensional strains of more than 200%). This general strategy could be implemented using other amide containing polymers to produce a wide range of high‐performance thermosets and elastomers. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1406–1413     

Dynamic covalent polymers

This Highlight presents an overview of the rapidly growing field of dynamic covalent polymers. This class of polymers combines intrinsic reversibility with the robustness of covalent bonds, thus enabling formation of mechanically stable, polymer‐based materials that are responsive to external stimuli. It will be discussed how the inherent dynamic nature of the dynamic covalent bonds on the molecular level can be translated to the macroscopic level of the polymer, giving access to a range of applications, such as stimuli‐responsive or self‐healing materials. A primary distinction will be made based on the type of dynamic covalent bond employed, while a secondary distinction will be based on the consideration whether the dynamic covalent bond is used in the main chain of the polymer or whether it is used to allow side chain modification of the polymer. Emphasis will be on the chemistry of the dynamic covalent bonds present in the polymer, in particular in relation to how the specific (dynamic) features of the bond impart functionality to the polymer material, and to the conditions under which this dynamic behavior is manifested. © 2016 The Authors. Journal of Polymer Science Part A: Polymer Chemistry Published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3551–3577.     

Mechanical mapping and morphology across the length scales unveil structure–property relationships in polycaprolactone based polyurethanes

Segmented polyurethane elastomers for biomedical applications were synthesized and studied at macroscopic (by mechanical testing) and meso/nanoscopic length scales (by atomic force microscopy, AFM). The polyurethanes are composed of 4,4'‐methylenebis(phenyl isocyanate), 1,4‐butanediol and an ε‐polycaprolactone diol. The stoichiometric ratio of the isocyanate and hydroxyl groups is constant, but the polymer diol to total diol—varies from 0 to 100 %. We show the representative features of the morphology from phase separation to mixed phases, how this is related to the mechanical properties in the bulk and locally, at exposed free surfaces and at the nanoscale. We propose a morphological model considering the molecular structure, the length of hard segments, and the dimensions of both the soft and the hard phases, respectively. Understanding such structure–property relations is pivotal to establishing designer materials and controlling the performance of the final product to achieve optimal properties in polyurethane based medical devices. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2298–2310.