The role of branching architecture in shape memory semi-IPNs: Shape memory effect and tube model analysis

The impact of branching architecture of one continuous uncrosslinked phase on properties of classic shape memory semi-interpenetrating polymer networks (semi-IPNs) was explored. Crosslinked poly (methyl methacrylate) (PMMA)/star-shaped polyethylene glycol (PEG) (PMMA/SPEG) semi-IPNs and PMMA/linear PEG (PMMA/LPEG) semi-IPNs were synthesized with the same PEG content. Mechanical properties, phase structure, thermal properties, dynamic mechanical properties, and shape memory properties of these two semi-IPNs systems were compared. Due to the better compatibility of SPEG in the PMMA network, which was derived from little crystallization compared with PMMA/LPEG semi-IPNs, PMMA/SPEG semi-IPNs exhibited a combination of large tensile strength and high elongation at break. PMMA/SPEG semi-IPNs, which had little crystallization exhibited superior shape recovery versus PMMA/LPEG semi-IPNs, which had more crystallization. Moreover, the higher the crystallinity in PMMA/PEG semi-IPNs was the worse long-term temporary shape retention. Based on tube model theory, the high shape recovery capacity of PMMA/SPEG semi-IPNs is mainly ascribed to the retraction of free PEG arms, which is entropically favorable and thermally activated due to the fluctuations of the path length. This result is supported by stress relaxation analysis and the influence of long shape fixity time on shape fixity ratio for these two systems.     

Water Sorption and Dye Uptake Studies of Highly Swollen AAm/AMPS Hydrogels and Semi-IPNs with PEG

A semi-interpenetrating network (semi-IPNs) hydrogel, composed of acrylamide (AAm) with 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) as co-monomer, with poly(ethylene glycol) (PEG) and two multifunctional cross-linkers such as 1,4-butanediol dimethacrylate (BDMA), and trimethylolpropane triacrylate (TMPTA) was prepared. AAm/AMPS hydrogels and AAm/AMPS/PEG semi-IPNs were synthesized by free radical solution polymerization. Swelling experiments were performed in water at 25°C, gravimetrically. For sorption of Toluidin Blue (Basic Blue 17, TB) into AAm/AMPS hydrogels and AAm/AMPS/PEG semi-IPNs was studied by batch sorption technique at 25°C. Dye removal capacity, removal effiency and partition coefficient of the hydrogels was investigated.     

Preliminary swelling and dye sorption studies of acrylamide/4-styrenesulfonic acid sodium salt copolymers and semi-interpenetrating polymer networks composed of gelatin and/or PEG

Semi-IPN hydrogels based gelatin (GEL) and/or poly (ethylene glycol) (PEG) were prepared with acrylamide (AAm) and 4-styrenesulfonic acid sodium salt, (SSS) as a water adsorbent for cationic dye (methyl violet, MV) sorption. For this, chemically crosslinked copolymer of AAm/SSS copolymer with GEL and/or PEG were prepared by polymerization of aqueous solution of AAm and SSS using ammonium persulfate (APS)/N,N,N′,N′-tetramethylethylenediamine (TEMED) as redox initiating pair in presence of poly(ethylene glycol)diacrylate (PEGDA) as crosslinker. FT-IR analysis was used to identify the presence of different repeating units in the semi-IPNs. Surface morphology was characterized by scanning electron microscopy (SEM). Some swelling and diffusion characteristics were calculated for different semi-IPNs and hydrogels prepared under various formulations. Water uptake, and dye sorption properties of the crosslinked polymeric systems such as AAm/SSS, AAm/GEL/SSS, AAm/PEG/SSS and AAm/GEL/PEG/SSS hydrogel systems were investigated as a function of chemical composition of the hydrogels. MV have used in sorption studies.     

Swelling Characterization and Adsorptive Features of Acrylamide/Itaconic Acid Hydrogels and Semi-IPNs for Uranyl Ions

A novel semi-interpenetrating network (semi-IPNs) hydrogel, composed of acrylamide (AAm) with itaconic acid (ITA) as co-monomer, with poly (ethylene glycol)(PEG) and trimethylolpropane triacrylate (TMPTA) was prepared. Hydrogels and semi-IPNs were synthesized by free radical solution polymerization. Swelling experiments were performed in water and aqueous solutions of uranyl acetate. Diffusion behavior was investigated and their diffusion into hydrogels was found to be non-Fickian in character. Sorption of uranyl ion onto the polymeric system was studied by a batch sorption technique at 25°C. The sorption capacity, removal effiency and partition coefficient of the hydrogels were investigated.     

Effect of porosigen on the swelling behavior and drug release of porous N‐isopropylacrylamide/poly(ethylene glycol) monomethylether acrylate copolymeric hydrogels

A series of porous thermoreversible hydrogels were prepared from N‐isopropylacrylamide (90 mol %) and poly(ethylene glycol) methylether acrylate (10 mol %), which was derived from poly(ethylene glycol) monomethylether, N,N′‐methylenebisacrylamide, and porosigen, or poly (ethylene glycol) (PEG) with different molecular weights (MWs). The influence of pore volume in the gel on the physical properties, swelling kinetics, and solute permeation from these porous gels was investigated. The results show that the surface areas, pore volumes, and equilibrium swelling ratios for the porous gels increased with increasing MW of PEG, but the shear moduli and effective crosslinking densities decreased with increasing MW of PEG. The results from the dynamic swelling kinetics show that the transport mechanism was non‐Fickian. The diffusion coefficients of water penetrating into the gels increased with increasing pore volume of the gels. In addition, we also studied solute permeation through the porous gel controlled by temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5490–5499, 2006     

Nanofiltration membranes based on poly(vinyl alcohol) and ionic polymers

Nanofiltration membranes based on poly(vinyl alcohol) (PVA) and ionic polymers, such as sodium alginate (SA) and chitosan, were prepared by casting the respective polymer solutions. The membranes prepared from PVA or PVA–ionic polymer blend were crosslinked in a isopropanol solution using glutaraldehyde as a crosslinking agent. The membranes were characterized with Fourier transform infrared spectroscopy and X‐ray diffractometry and swelling test. The membranes crosslinked through the acetal linkage formation between the  OH groups of PVA and the ionomer and glutaraldehyde appeared to be semicrystalline. To study the permeation properties, the membranes were tested with various feed solutions [sodium sulfate, sodium chloride, poly(ethylene glycol) with 600 g/mol of molecular weight (PEG 600), and isopropyl alcohol]. For example, the permeance and the solute rejection of the 1000 ppm sodium sulfate at 600 psi of upstream pressure through the PVA membrane were 0.55 m³/m² day and over 99%, respectively. The effects of the ionomers on the permeation properties of the PVA membranes were studied using the PVA–SA and PVA–chitosan blend membranes. The addition of small amount of ionic polymers (5 wt %) made the PVA membranes more effective for the organic solute rejection without decrease in their fluxes. The rejection ratios of the PEG 600 and isopropanol were increased substantially. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1755–1762, 1999     

Shape-memory behavior of poly (methyl methacrylate-co –N-vinyl-2-pyrrolidone) / poly (ethylene glycol) semi-interpenetrating polymer networks based on hydrogen bonding

Based on hydrogen bonding interactions, Poly(methyl methacrylate-co-N-vinyl-2-pynolidone) (P(MMA-co-VP)) networks and linear poly(ethylene glycol) (PEG) can form semi-interpenetrating polymer networks (semi-IPNs), i.e. P(MMA-co-VP)/PEG semi-IPNs, which has shape memory behaviour; its maximum storage modulus ratio can be more than 400, and its shape recovery ratio could reach 99%. The morphology, thermal behaviors and dynamic mechanical properties of P(MMA-co-VP)/PEG semi-IPNs were studied by FTIR, TEM, DSC and DMA. When PEG with higher molecular weight was introduced into P(MMA-co-VP) networks, they possess higher glassy state modulus and higher recovering rate. In such a system, the maximum molecular weight of PEG required for the semi-IPN formation reaches 1000.     

Poly(ethylene glycol)-interpenetrated genipin-crosslinked chitosan hydrogels: Structure,pH responsiveness,gelation kinetics,and rheology

In the development of pH-responsive chitosan-based hydrogels, achieving reproducible porosity and swelling behavior is essential for the design of hydrogel networks. Herein, we enhance the level of control in hydrogel microarchitecture by incorporating poly(ethylene glycol) (PEG) into the chitosan–genipin matrix. Hydrogels, varied in composition, were synthesized under mild conditions (37°C, 1 atm, 24 hr), yielding microporous structures with a pore diameter ranging from 11 to 57 μm and an average cross-sectional porosity of approximately 40–64%. Compared to chitosan–genipin hydrogels without PEG, presence of PEG in concentrations up to 1.9 mM generated the same effect as would increase in genipin content, yielding structures with a smaller pore diameter, a lower swelling degree in pH 2 buffer and a higher elastic modulus. Considering cost effectiveness and scale-up, reducing genipin content by the addition of PEG is favorable. Importantly, hydrogel samples containing higher concentrations of PEG (2.9 mM and above) showed a sudden increase in the swelling degree accompanied with a decrease in the elastic modulus. Findings showcase the potential variation in the composition of these hydrogels has in yielding scaffolds with significantly different physico-chemical behaviors.     

Thermoreversible hydrogels. XVIII. Synthesis,swelling characteristics,and diffusion behaviors of porous,ionic, thermosensitive hydrogels

Porous, ionic, thermosensitive hydrogels were prepared from N‐isopropylacrylamide, a cationic monomer [trimethyl (acrylamido propyl) ammonium iodide (TMAAI)], an anionic monomer [acrylic acid (AA)], a zwitterionic monomer [N′,N′‐dimethyl (acrylamido propyl) ammonium propane sulfonate], or a nonionic monomer [poly(ethylene glycol) methyl ether acrylate], and a pore‐forming agent [poly(ethylene glycol) (PEG)] of different molecular weights. Some fundamental properties and dynamic swelling kinetic parameters and solute permeation for these porous gels were investigated. The results showed that the gel containing the cationic monomer TMAAI had a higher equilibrium swelling ratio. The diffusion coefficients showed that the swelling rates for the gels with the anionic monomer AA and PEG with a higher molecular weight (20,000) were faster. The results showed that the fast swelling–deswelling behavior for the porous structure gels was due to them being more available than the gels with long hydrophilic side chains. In addition, the interactive force between the solutes and gels and the solute permeation through the porous gels were investigated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2214–2223, 2003     

Poly(ethylene glycol)‐based poly(urethane isocyanurate) hydrogels for contact lens applications

Over the past few decades, the global use and market of contact lenses have expanded steadily. Due to the many demands on material properties (e.g. mechanical, optical and biological), the development of novel contact lens materials is challenging. Specifically, the ideal combination of high equilibrium water content, high toughness in the hydrated state and low protein adsorption is difficult to realize. In this work, poly(ethylene glycol)‐based poly(urethane isocyanurate) (PEG PUI) type hydrogels that combine the above important properties are presented as a new class of materials for contact lens applications. It is shown that these PEG PUI hydrogels demonstrate high toughness values in the hydrated state ranging from 98 to 226 kJ m^?3 and elastic moduli ranging from 0.8 to 17.2 MPa for networks with equilibrium water contents ranging from 76.3 to 16.1 wt%. These hydrogels also demonstrate transmittance values >90% across the visible spectrum, clarities close to 100% in most cases and refractive indices ranging from 1.48 to 1.36. Importantly, these hydrogels are non‐cytotoxic and demonstrate lower bovine serum albumin adsorption values than several commercial contact lenses of 0.24 to 0.65 mg g^?1 compared to 0.55 to 1.38 mg g^?1 after 24 h, respectively. This combination of high equilibrium water content, high toughness in the hydrated state and low protein adsorption is exceptional. These properties can be attributed to the PEG PUI network structure: the use of a PEG polymeric backbone provides hydrophilicity and chemical inertness while the PUI‐type crosslinking units provide high toughness in the hydrated state. © 2019 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Gamma radiation synthesis and swelling properties of hydrogels based on poly(ethylene glycol)/methacrylic acid (MAc) mixtures

In this work, gamma radiation was used to prepare hydrophilic hydrogels based on different mass ratios of poly(ethylene glycol) (PEG) and methacrylic acid (MAc) monomer. The thermal stability of hydrogels was characterized thermogravimetric analysis (TGA). The effect of temperature and pH, as external environments, on the equilibrium swelling of PEG/MAc hydrogels was also studied. The results showed that the gel fraction of PEG/MAc hydrogels is lower than that of PMAc hydrogel, in which the gel fraction of PMAc hydrogel was decreased greatly with increasing the mass ratio of PEG polymer in the initial solutions. The results showed that PEG/MAc hydrogels reached the equilibrium swelling state in water after 6 hours. It was found that the equilibrium swelling of PEG/MAc hydrogels displayed a transition change within the temperature range 30–40°C. This change in equilibrium swelling was illustrated by differential scanning calorimetry (DSC). However, it was observed that the equilibrium swelling of PEG/MAc hydrogels increases progressively with increasing the pH value from 4 up to 8. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Solute diffusion through degradable semicrystalline polyethylene glycol/poly(l-lactide) copolymers

Summary The diffusion of C.I. direct orange 34(MW=299) and benzoic acid(MW=122) through degraded semicrystalline polyethylene glycol(PEG)/poly(L-lactide)(PLLA) block copolymers with various PEG contents and PEG segment lengths at 37°C was studied by UV-visible spectroscopy, differential scanning calorimetry(DSC), wide angle X-ray diffractometer (WAXS) and scanning electron microscopy(SEM). The influences of the PEG contents, PEG segment lengths and hydrolytic degradation of PEG/PLLA copolymers on the solute diffusion coefficient and mode for transport were investigated. It is concluded that the diffusion rate increases with the increase of PEG contents and PEG segment lengths in PEG/PLLA copolymers. This is understandable that the increase of PEG content and PEG segment length both make the degree of crystallinity decrease. The steady state of mass flux could not be reached at the diffusion times up to 1000 h, because the copolymers underwent hydrolysis reaction during this period. Furthermore, it is understood that the characteristic time of diffusion as defined by the square of film thickness at an instant of time over the diffusion coefficient of solute through polymer decreases with the increasing diffusion time.     

Hydrophilicity,crystallinity and electrostatic dissipating properties of poly(oxyethylene)-segmented polyurethanes

Plaques of poly(oxyethylene)-segmented polyurethanes prepared from isophorone diisocyanate (IPDI) and polyethylene glycol (PEG) were used to probe the structure/property relationships with regard to hydrophilicity, crystallinity and electrostatic dissipating (ESD) ability. The prepared urethane polymers or oligomers consistently exhibited lower surface resistivities than their corresponding PEG-1000, 2000 and 8000 starting materials. The magnitude of the decrease in surface resistivity (ohm/sq) was correlated with heat of crystallinity, measured by differential scanning calorimetry. Surface resistivity as low as 10^7.5 ohm/sq for PEG-1000/IPDI polyurethane, a decrease by 2.5 orders of magnitude from pure PEG-1000, was observed and attributed to the differences in crystallinity. Polyurethanes containing PEG, polypropylene glycol (PPG) and mixed PEG/PPG were also prepared for comparison. The mixed PEG/MDEA (N -methyl diethanolamine) polyurethanes further demonstrated the importance of the nature and mobility of the hydrophilic groups for lowering the polymer surface resistivity. To account for these observations, an electron conducting mechanism via association and mobility of the hydrogen-bonded water molecules with hydrophilic poly(oxyethylene) groups is suggested. © 1999 Society of Chemical Industry     

Prevention of surgical adhesions with barriers of carboxymethylcellulose and poly(ethylene glycol) hydrogels synthesized by irradiation

Biocompatible and biodegradable hydrogels based on carboxymethylcellulose (CMC) and poly(ethylene glycol) (PEG) were prepared as physical barriers for preventing surgical adhesions. These interpolymeric hydrogels were synthesized by a γ‐irradiation crosslinking technique. Sections (1.5 cm × 1.5 cm) of the cecal serosa and an adjacent abdominal wall were abraded with a bone burr until the serosal surface was disrupted and hemorrhagic but not perforated, and the serosa of the cecum was sutured to the abdominal wall 5 mm away from the injured site. The denuded cecum was covered with either CMC/PEG hydrogels or a solution from a CMC/PEG hydrogel. A control rat serosa was not covered. Two weeks later, the rats were killed, and the adhesions were scored on a 0–5 scale. No treatment showed a significantly higher incidence of adhesions than the CMC/PEG hydrogels or solutions from the CMC/PEG hydrogels. This study demonstrated that CMC/PEG hydrogels could prevent intra‐abdominal adhesion in a rat model. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1138–1145, 2005     

Analysis of molecular interactions in poly(methacrylic acid-g-ethylene glycol) hydrogels

Molecular and structural changes of the P(MAA-g-EG) hydrogels were investigated in their hydrated state using attenuated total reflectance Fourier transform infrared spectroscopy. FTIR studies identified the formation of hydrogen-bonded complexes at low pH and polyelectrolyte complexes at high pH. Hydrogen bonding and electrostatic repulsion were not affected by the grafted PEG molecular weight in the hydrogels. Additionally, investigation of the macroscopic swelling properties showed that the presence of the grafted PEG chain in the P(MAA-g-EG) hydrogels contributed to the formation of hydrogen bonds.     

Permeation of solutes through interpenetrating polymer network hydrogels composed of poly(vinyl alcohol) and poly(acrylic acid)

The swelling behaviors of poly(vinyl alcohol)–poly(acrylic acid) (PVA–PAAc) interpenetrating networks (IPN) hydrogels in the presence of electrolytes were studied. The ionized carboxylic group within IPN hydrogels at pH 7 strongly interacted with electrolytes in the medium and caused anomalous swelling pattern. The permeabilities of 5 representative solutes were regulated as a function of temperature, pH, ionic strength, solute size, and ionic properties of solutes. The permeation of nonionic solutes followed the swelling behaviors dependent on external stimuli, including the above factors. However, the ionic solutes showed different trends in their permeation through IPN hydrogels. © 1998 John Wiley & Sons, Inc. J Appl Polm Sci 69: 479–486, 1998     

Glycerol-modified poly(vinyl alcohol)/poly(ethylene glycol) self-healing hydrogel for artificial cartilage

Poly(vinyl alcohol) (PVA) hydrogels have shown potential applications in bionic articular cartilage due to their tissue-like viscoelasticity, good biocompatibility and low friction. However, their lack of adequate mechanical properties is a key obstacle for PVA hydrogels to replace natural cartilage. In this study, poly(ethylene glycol) (PEG) and glycerol were introduced into PVA, and a PVA/PEG–glycerol composite hydrogel was synthesized using a mixing physical crosslinking method. The mechanical properties, hydrophilicity and tribological behavior of the PVA/PEG–glycerol hydrogel were investigated by changing the concentration of glycerol in PEG. The results showed that the tensile strength of the hydrogel reached 26.6 MPa at 270% elongation at break with 20 wt% of glycerol plasticizer, which satisfied the demand of natural cartilage. In addition, the excellent hydrophilicity of glycerol provides good lubricating properties for the composite gel under dry friction. Meanwhile, self-healing and cellular immunity assays demonstrated that the composite gel could have good self-healing ability and excellent biocompatibility even in the absence of external stimuli. This study provides a new candidate material for the design of articular cartilage, which has the potential to facilitate advances in artificial joint cartilage repair. © 2022 Society of Industrial Chemistry.     

Thermal and rheological properties of poly(vinyl alcohol) and water‐soluble chitosan hydrogels prepared by a combination of γ‐ray irradiation and freeze thawing

Poly(vinyl alcohol) (PVA)/water‐soluble chitosan (ws‐chitosan) hydrogels were prepared by a combination of γ‐irradiation and freeze thawing. The thermal and rheological properties of these hydrogels were compared with those of hydrogels prepared by pure irradiation and pure freeze thawing. Irradiation reduced the crystallinity of PVA, whereas freeze thawing increased it. Hydrogels made by freeze thawing followed by irradiation had higher degrees of crystallinity and higher melting temperatures than those made by irradiation followed by freeze thawing. ws‐Chitosan disrupted the ordered association of PVA molecules and decreased the thermal stability of both physical blends and hydrogels. All the hydrogels showed shear‐thinning behavior in the frequency range of 0.2–100 rad/s. Hydrogels made by freeze thawing dissolved into sol solutions at about 80°C, whereas those made by irradiation showed no temperature dependence up to 100°C. The chemical crosslinking density of the hydrogels made by irradiation followed by freeze thawing was much greater than that of hydrogels made by freeze thawing followed by irradiation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermo‐responsive polyurethane hydrogels based on poly(ethylene glycol) and poly(caprolactone): Physico‐chemical and mechanical properties

In this work, we present the synthesis and characterization of chemically crosslinked polyurethanes (PU) composed of poly(ethylene glycol) (PEG) and poly(caprolactone) diol (PCL‐diol), as hydrophilic and hydrophobic segments respectively, poly(caprolactone) triol (PCL‐triol), to induce hydrolysable crosslinks, and hexamethylene diisocyanate (HDI). The syntheses were performed at 45 °C, resulting in polyurethanes with different PEG/PCL‐diol/PCL‐triol mass fractions. All the PUs are able to crystallize and their thermal properties depend on the global composition. The water uptake capacities of the PU increase as the PEG amount increases. The water into hydrogels is present in different environments, as bounded, bulk and free water. The PU hydrogels are thermo‐responsive, presenting a negative dependence of the water uptake with the temperature for PEG rich networks, which gradually changes to a positive behavior as the amount of poly(caprolactone) (PCL) segments increases. However, the water uptake capacity changes continuously without an abrupt transition. Scanning electron microscopy (SEM) analyses of the hydrogel morphology after lyophilization revealed a porous structure. Mechanical compression tests revealed that the hydrogels present good resilience and low recovery hysteresis when they are subject to cycles of compression–decompression. In addition, the mechanical properties of the hydrogels varies with the composition and crosslinking density, and therefore with the water uptake capacity. The PU properties can be tuned to fit for different applications, such as biomedical applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43573.     

Synthesis and characteristics of interpenetrating polymer network hydrogel composed of chitosan and poly(acrylic acid)

Interpenetrating polymer network (IPN) hydrogels composed of chitosan and poly(acrylic acid) (PAAc) were synthesized by UV irradiation method, and their structure, crystallinity, swelling behavior, thermal property, and mechanical property were investigated. Chitosan/PAAc IPNs exhibited relatively high equilibrium water content and also showed reasonable sensitivity to pH. From the swelling behaviors at various pH's, Fourier transform infrared spectra at high temperature and thermal analysis confirmed the formation of polyelectrolyte complex due to the reaction between amino groups in chitosan and carboxyl groups in PAAc. For this reason, even at a swollen state, the present chitosan/PAAc IPNs possess good mechanical properties. Particularly, the CA‐2 sample (with a weight ratio of chitosan/PAAc = 50/50, molar ratio [NH₂]/[COOH] = 25/75) showed the lowest equilibrium water content and free water content, attributed to the more compact structure of the polyelectrolyte than CA‐1 or CA‐3 due to the high amount of interchain bond within the IPN. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 113–120, 1999