Physical Cross-linking Points Research Articles

Biocompatible Tough Hydrogels via Micellar Copolymerization of NIPAM and Stearyl Acrylate: Synthesis and Characterization

Novel biocompatible tough hydrogels were prepared through free radical micellar polymerization of N-isopropylacrylamide (NIPAM) with ammonium persulphate (APS) as initiator, in which hydrophobic monomer stearyl acrylate (C18) underwent micellar polymerization in the presence of gelatin as emulsifier. FT-IR and DSC demonstrated the formation of co-polymer of NIPAM and C18. Swelling results indicated that hydrophobic polymer domains derived from C18 in aqueous medium acted as the physical crosslinking points by hydrophobic association. Uniaxial tensile test demonstrated the mechanical properties of hydrogels increased with increasing C18 and gelatin contents. The hydrogel exhibited low toxicity and promoted cell proliferation. The desirable toughness, low toxicity and the promoting effect of cell proliferation made the present hydrogels good candidates for tissue regeneration materials.

Regulating the crystallizing and rheological behaviors of poly(butylene succinate) by incorporating novel macromolecular ionomers

ABSTRACTWe designed a novel, facile, and mass‐producible strategy for regulating the crystallizing and rheological behaviors of poly(butylene succinate) (PBS) by incorporating segmented PBS urethane ionomers (PBSUI). These macromolecular ionomers contain two segments: one is an ionic enriched segment, which can spontaneously form inter‐ and intramolecular ionic aggregates in PBS to serve as physical crosslinking points to increase the crystallization rate and complex viscosity of the PBS matrix; the other one is a PBS segment, which can improve the compatibility between the PBSUI and PBS matrix. The results from differential scanning calorimetry, polarized optical microscopy, dynamic mechanical analysis, and rotational rheometry suggest that the performance tunability of PBS was easily achieved by adding a very low content of PBSUI (1–5 wt %). PBS containing 3 wt % PBSUI, in which the mass ratio of ionic groups in PBSUI is 7.4%, showed the fastest overall crystallization rate at 12 times faster than PBS to finish crystallization, due to the remarkably increased nucleating efficiency. The dynamic mechanical analysis indicates that for those samples with relatively high ionic concentrations, a cluster of glass‐transition temperatures occurred that was related to an aggregation of PBSUI. The complex viscosity and storage modulus G′ of PBS/PBSUI were also increased, due to the ionic aggregates formed by PBSUI. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45545.

Tough Supramolecular Hydrogel Based on Strong Hydrophobic Interactions in a Multiblock Segmented Copolymer

We report the preparation and structural and mechanical characterization of a tough supramolecular hydrogel, based exclusively on hydrophobic association. The system consists of a multiblock, segmented copolymer of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic dimer fatty acid (DFA) building blocks. A series of copolymers containing 2K, 4K, and 8K PEG were prepared. Upon swelling in water, a network is formed by self-assembly of hydrophobic DFA units in micellar domains, which act as stable physical cross-link points. The resulting hydrogels are noneroding and contain 75–92 wt % of water at swelling equilibrium. Small-angle neutron scattering (SANS) measurements showed that the aggregation number of micelles ranges from 2 × 102 to 6 × 102 DFA units, increasing with PEG molecular weight. Mechanical characterization indicated that the hydrogel containing PEG 2000 is mechanically very stable and tough, possessing a tensile toughness of 4.12 MJ/m3. The high toughness, processability, and ease of preparation make these hydrogels very attractive for applications where mechanical stability and load bearing features of soft materials are required.

Robust, tough and anti-fatigue cationic latex composite hydrogels based on dual physically cross-linked networks

Dual physically cross-linked hydrogels, which are triggered by cationic latexes as hydrophobic association and ionic crosslinking centers, were easily fabricated via a one-pot in situ polymerization method. First, the hydrophobic alkyl chains of hydrophobic monomers are adsorbed on the surface of latex microspheres and stabilized in the presence of surfactants, forming hydrophobic association centers as the first physical crosslinking points. Meanwhile, the anionic sulfate radicals dissociated by persulphate are attracted towards the cationic molecular chains of latex microspheres through ionic interactions, forming the secondary physical crosslinking centers, and initiate the copolymerization between acrylamide and hydrophobic vinyl monomers. The fabricated hydrogel exhibited high tensile strength of 1.32MPa, a remarkable toughness of 4.53MJm−3, excellent self-recovery properties and fatigue resistance. Therefore, the current work provides a promising strategy for designing novel hydrogels via multiple physical interactions and devoid of any chemical crosslinking. The novel design of hydrogels can enhance their mechanical properties and expand their biomedical applications.

Luminescent Poly(vinyl alcohol)/Carbon Quantum Dots Composites with Tunable Water-Induced Shape Memory Behavior in Different pH and Temperature Environments.

Luminescent water-induced shape memory polymer (SMP) composites with tunable shape recovery rate are developed by blending poly(vinyl alcohol) (PVA) and carbon quantum dots (CQDs). The oxygen and active hydrogen-rich CQDs can serve as extra physical cross-linking points in PVA via strong hydrogen bonding interaction, which largely improves the shape memory performances of PVA. At room temperature, water can successfully actuate the shape recovery of deformed PVA/CQDs composite. It is demonstrated that this water-induced shape recovery is mainly attributed to the plasticizing effect of water and its competitive hydrogen bonding. Furthermore, a quantitative bending test suggests that the shape recovery time of this water-induced SMP is tunable by altering the environmental pH value and temperature, and a relatively large shape recovery time window (from 20 to 200 s) can be achieved. In addition, the introduction of CQDs endows the PVA/CQDs SMP composites with excellent luminescent property, which makes the shape change of SMP visible under UV light. It should be noted that the mild stimulus condition and tunable shape recovery performances make the luminescent visible PVA/CQDs SMP feasible for diverse biological applications in smart medical devices, stimuli-responsive drug-release, and intelligent sensors in vivo and in vitro.

Toughening mechanism of nanocomposite physical hydrogels fabricated by a single gel network with dual crosslinking — The roles of the dual crosslinking points

A facile method to fabricate tough and highly stretchable polyacrylamide (PAM) nanocomposite physical hydrogel (NCP gel) was proposed. The hydrogels are dually crosslinked single network with the PAM grafted vinyl hybrid silica nanoparticles (VSNPs) as the analogous covalent crosslinking points and the reversible hydrogen bonds among the PAM chains as the physical crosslinking points. In order to further elucidate the toughening mechanism of the PAM NCP gel, especially to understand the role of the dual crosslinking points, the PAM hybrid hydrogels (H gels) and a series of poly(acrylamide-co-dimethylacrylamide) (P(AM-co-DMAA)) NCP gels were designed and fabricated. Their mechanical properties were compared with those of the PAM NCP gels. The PAM H gels are prepared by simply mixing the PAM chains with bare silica nanoparticles (SNPs). Relative to the poor mechanical properties of the PAM H gel, the PAM NCP gel is remarkably tough and stretchable and also generates large number of micro-cracks to stop notch propagation, indicating the important role of PAM grafted VSNPs in toughening the NCP gel. In the P(AM-co-DMAA) NCP gels, the P(AM-co-DMAA) chains are grafted on VSNPs and the polydimethylacrylamide (PDMAA) only forms very weak hydrogen bonds between themselves. It is found that mechanical properties of the PAM NCP gel, such as the tensile strength and the elongation at break, are enhanced significantly, but those of the P(AM-co-DMAA) NCP gels decreased rapidly with decreasing AM content. This result reveals the role of the hydrogen bonds among the grafted polymer chains as the physical crosslinking points in toughening the NCP gel.

Shape memory induced structural evolution of high performance copolyimides

ABSTRACTIn this work, two kinds of high temperature shape memory copolyimides were prepared and the shape memory cycles induced structural evolution of macromolecular chains was investigated in detail. The glass transition temperature (Tg) of poly(benzoxazole‐co‐imide) (PI1) and poly(benzimidazole‐co‐imide) (PI2) are 280 °C and 355 °C, respectively. The results show that PI1 could keep stable macromolecular chain structure under shape memory cycles and exhibit outstanding shape memory performance (Rf > 98%, Rr > 97%) under different stretch condition. Whereas, shape memory cycles induced orientation with more ordered macromolecular chains packing is formed for PI2 after several thermal mechanical cycles, which strongly affect physical crosslinking points, thermal mechanical properties as well as shape memory behaviors. The study on macroscopic property and microscopic structure evolution will promote a better understanding of the shape memory effect of polyimides and accelerate development of high performance polyimides for shape memory applications. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3858–3867

Waterborne POSS-silane-urethane hybrid polymer and the fluorinated films

Abstract A feasible co-endcapping strategy has been developed for the synthesis of monofunctional polyhedral oligomeric silsesquioxanes (POSS) modified waterborne polyurethane (WPU). The work starts from the synthesis of di-isocyanate terminated PU prepolymer from isophorone di-isocyanate (IPDI), poly (1,4-butylene adipate) end-capped diol (PBAD), and 2,2-bis(hydroxymethyl) butyric acid (DMBA). The two kinds of modifiers of monofunctional aminopropyl isobutyl POSS (AIPOSS) and with (3-aminopropyl) triethoxysilane (APTES) were used together to block the PU chains. The hybrid dispersions of curable silane-co-modified WPU with 2–8 wt% of AIRPOSS could form continuous and homogenous films under ambient conditions. The morphology and structure of the dispersed particles and the films were characterized, as well as the mechanical property and surface performance. The results indicate that the incorporation of POSS moieties into the silane-modified PU can significantly improve the mechanical property of the films and the formation of additional physical crosslinking points upon the chemical crosslinking networks. Moreover, both the surface hydrophobicity and the dielectric performance have been promoted by the incorporation of POSS. Furthermore, fluorinated groups were introduced on the films by the treatment of the fluorosilane coupling agent. The fluoro-POSS-PU hybrid films exhibit notable surface hydrophobicity as well as low dielectric constant and loss.

Comparative study of in situ polymerized waterborne polyurethane/nano-silica composites and polyethersiloxanediol-modified polyurethane

The waterborne polyurethane/nano-silica composites (WPU/nano-silica, WPUS) and WPU composites modified by polyethersiloxanediol (WPUPES) were prepared, respectively. The properties of WPUS and WPUPES were investigated by various characterizations. The results showed both WPUS and WPUPES had better waterproof property and thermal stability than neat WPU. However, WPUPES has a lower elongation at break due to the higher micro-phase separation. This is ascribed to migration and aggregation of siloxane segments during the film formation. The tensile strength of WPUS was higher than that of neat WPU. This is attributed to the WPUS chain restriction caused by the network and physical cross-link points of nano-silica particles. Moreover, the glass transition temperature of WPUS shifted to higher temperature region while that of WPUPES shifted to lower temperature region.

Thermally Reversible Physically Cross-Linked Hybrid Network Hydrogels Formed by Thermosensitive Hairy Nanoparticles.

This Article reports on thermally induced reversible formation of physically cross-linked, three-dimensional network hydrogels from aqueous dispersions of thermosensitive diblock copolymer brush-grafted silica nanoparticles (hairy NPs). The hairy NPs consisted of a silica core, a water-soluble polyelectrolyte inner block of poly(2-(methacryloyloxy)ethyltrimethylammonium iodide), and a thermosensitive poly(methoxydi(ethylene glycol) methacrylate) (PDEGMMA) outer block synthesized by sequential surface-initiated atom transfer radical polymerizations and postpolymerization quaternization of tertiary amine moieties. Moderately concentrated dispersions of these hairy nanoparticles in water underwent thermally induced reversible transitions between flowing liquids to self-supporting gels upon heating. The gelation was driven by the lower critical solution temperature (LCST) transition of the PDEGMMA outer block, which upon heating self-associated into hydrophobic domains acting as physical cross-linking points for the gel network. Rheological studies showed that the sol-gel transition temperature decreased with increasing hairy NP concentration, and the gelation was achieved at concentrations as low as 3 wt %.

Promoting effect of crystallization on the foaming behavior in polypropylene homopolymer/polypropylene block copolymer blends

Polypropylene (PP) is a kind of semi-crystalline polymer so it is hard to foam with supercritical carbon dioxide (SCCO2). We used polypropylene block (PP-B) copolymer as a modifier to improve the crystallization behaviors and foaming performance of polypropylene homo polymer (HPP). HPP, PP-B, and a series of HPP/PP-B blends were characterized by differential scanning calorimeter (DSC), X-ray diffraction, and polarized optical microscope. Results show that both the crystallization behaviors and melt strength have influence on the cell structure. The crystallization temperature of PP-B is about 7°C higher than that of HPP and that the crystallization behavior of HPP/PP-B blends is similar to that of PP-B. Much denser and smaller size spherulites are observed in PP-B and HPP/PP-B blends than in HPP, and the crystal structure is unchanged after blending. Scanning electron microscope results show that much more uniform, smaller cells can be obtained for the HPP/PP-B blends. The crystal nuclei formed earlier can act as physical cross-link points, increasing the melt strength and improving dramatically the cell structure and morphology of the HPP/PP-B blends. Furthermore, the best cell structure and morphology was achieved for HPP/PP-B blends with the ratio of 70/30 under the same foaming conditions. POLYM. ENG. SCI., 2016. © 2016 Society of Plastics Engineers

Enhanced toughness and strength of poly (d‐lactide) by stereocomplexation with 5‐arm poly (l‐lactide)

ABSTRACTThe enhancement of mechanical properties were achieved by solution blending of poly(d‐lactide) (PDLA) and 5‐arm poly(l‐lactide) (5‐arm PLLA). Differential scanning calorimetry (DSC) and wide‐angle X‐ray diffraction (WAXD) results indicated almost complete stereocomplex could be obtained when 5‐arm PLLA exceeded 30wt %. Tensile test results showed that the addition of 5‐arm PLLA in linear PDLA gave dramatically improvement both on tensile strength and elongation at break, which generally could not be increased simultaneously. Furthermore, this work transformed PDLA from brittle polymer into tough and flexible materials. The mechanism was proposed based on the TEM results: the stereocomplex crystallites formed during solvent evaporation on the blends were small enough (100–200 nm), which played the role of physical crosslinking points and increased the interaction strength between PDLA and 5‐arm PLLA molecules, giving the blends high tensile strength and elongation at break. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 132, 42857.

Hydrophilic nanofiber of bacterial cellulose guided the changes in the micro-structure and mechanical properties of nf-BC/PVA composites hydrogels

Hydrophilic nanofibers derivate from bacterial cellulose (nf-BC) were compounded with PVA colloidal sol to form physical crosslinking hybrid hydrogels. With the hydrophilic and hydrogen bonding interaction between the groups of PVA and nf-BC during the composite gel phase transformation process, a regular and uniform distributed porous structure was formed which interconnected through fibrous funicular cords composed of PVA gel along nf-BC orientation by controlling the content of nf-BC and gel transition condition. The micro-morphology, chemical structure, crystallinity and mechanical properties of the nf-BC/PVA hydrogels changed with the different proportion and distribution of nf-BC. It has been verified that hydrophilic nf-BC acts as “crosslinking agent” and reinforced phase which can guide the composite hydrogels to form more ordered and compact porous structure, via enhancing the interaction of hydrogen bonds and physical crosslinking points between nf-BC and PVA macromolecule, finally resulted in the enhancement of their mechanical performances. The composite hydrogels have broad application prospects in the field of medicine, such as artificial cartilage, blood vessel, wound dressing and so on.

Permeability of hydrated poly(vinyl alcohol): Effect of relaxation behaviors and hydrogen bonds in supramolecular structure

The particular permeability of hydrated poly(vinyl alcohol) (PVA) was investigated from the point of polymeric relaxation behavior, and the more essential effect of hydrogen bonds in supramolecular structure was further analyzed as well. The permeability measurement showed that various hydrated PVA samples all had lower permeability to non-polar solvents, and the permeability was affected by relaxation state, which can be controlled by water content. Dynamic mechanical analysis measurements indicated that, in PVA with lower water content the relaxation motion benefiting permeation almost became frozen in glassy amorphous region, due to high activation energy of conformation transition, which then induced the slower permeation to occur. Solid-state 1H and 13C NMR spectra of hydrated PVA samples allowed to analyze the effect of hydrogen bonds. It was found that in PVA with lower water content conformation transition in amorphous region was restricted by more intermolecular and intramolecular hydrogen bonds, especially by the former. Also relatively added crystalline regions, which can affect permeability as physical cross-linking points, were mainly constructed by chain segments with no intramolecular hydrogen bonds. Above results suggest that intermolecular and intramolecular hydrogen bonds via conformation transition control relaxation behavior. Consequently, the relaxation behavior affects the permeability of hydrated PVA, in which water play an important role.

Combination of magnetic and enhanced mechanical properties for copolymer-grafted magnetite composite thermoplastic elastomers.

Composite thermoplastic elastomers (CTPEs) of magnetic copolymer-grafted nanoparticles (magnetite, Fe3O4) were synthesized and characterized to generate magnetic CTPEs, which combined the magnetic property of Fe3O4 nanoparticles and the thermoplastic elasticity of the grafted amorphous polymer matrix. Fe3O4 nanoparticles served as stiff, multiple physical cross-linking points homogeneously dispersed in the grafted poly(n-butyl acrylate-co-methyl methacrylate) rubbery matrix synthesized via the activators regenerated by electron transfer for atom transfer radical polymerization method (ARGET ATRP). The preparation technique for magnetic CTPEs opened a new route toward developing a wide spectrum of magnetic elastomeric materials with strongly enhanced macroscopic properties. Differential scanning calorimetry (DSC) was used to measure the glass transition temperatures, and thermogravimetric analysis (TGA) was used to examine thermal stabilities of these CTPEs. The magnetic property could be conveniently tuned by adjusting the content of Fe3O4 nanoparticles in CTPEs. Compared to their linear copolymers, these magnetic CTPEs showed significant increases in tensile strength and elastic recovery. In situ small-angle X-ray scattering measurement was conducted to reveal the microstructural evolution of CTPEs during tensile deformation.

2次元小角X線散乱と応力-ひずみ同時測定によるエラストマー特性を有するブロックコポリマーフィルムの一軸延伸にともなう構造と物性の変化の研究

Simultaneous measurements of small-angle X-ray scattering with stress-strain tests were conducted to reveal changes in microphase-separated structures being correlated with changes in the mechanical properties upon the uniaxial stretching of an elastomeric block copolymer film containing glassy spherical microdomains embedded in the rubbery matrix. For this purpose, high brilliant synchrotron X-ray source was utilized at SPring-8, Japan, and cycled stretching-and-reversing process was conducted three times. While the tensile modulus decreased to be less than the half for the second cycle of the stretching, affine deformation for the changes in the microphase-separated structures was confirmed not only for the second but also for the third cycles. The Mullins effect (stress-induced softening) may be attributed to stress-induced disentangling of the soft-segment chains between two adjacent glassy spherical microdomains (as physical crosslinking points). It was found that the number density of the active network chain (νe ) is more than 22-times higher than that of the soft-segment chains between two adjacent glassy spherical microdomains (νe°) in the virgin sample. Such a big number of the active network chain suggests that the soft-segment chains between two adjacent glassy spherical microdomains are heavily entangled. Furthermore, it was found that the ratio νe /νe° is still around 10 for the second and third stretching cycles, suggesting that appreciable number of entanglements can be relaxed while comparable number of entanglements cannot be. The latter is so referred to as “trapped entanglement due to crosslinking”.

Synthesis and Characterization of Nanostructured Copolymer-Grafted Multiwalled Carbon Nanotube Composite Thermoplastic Elastomers toward Unique Morphology and Strongly Enhanced Mechanical Properties

Considering that multiwalled carbon nanotubes (MWCNTs) can be used as anisotropic and stiff nano-objects acting as minority physical cross-linking points dispersed in soft polymer grafting matrixes, a series of copolymer-grafted multiwalled carbon nanotube composite thermoplastic elastomers (CTPEs), MWCNT-graft-poly(n-butyl acrylate-co-methyl methacrylate) [MWCNT-g-P(BA-co-MMA)], with minor MWCNT contents of 1.2–3.8 wt % was synthesized by the surface-initiated activators regenerated by electron transfer for atom-transfer radical polymerization (ARGET ATRP) method. Excellent dispersion of the MWCNTs in the CTPEs was demonstrated by SEM and TEM, and the thermal stability properties and glass transition temperatures of the CTPEs were characterized by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), respectively. Mechanical property test results demonstrated that the CTPEs exhibit obviously enhanced mechanical properties, such as higher tensile strength and elastic recovery, as c...

Gelation of Solvate Ionic Liquid by Self-Assembly of Block Copolymer and Characterization as Polymer Electrolyte

We report a new class of polymer electrolytes that exhibit high Li+-ionic conductivity and thermal stability up to 200 °C. The polymer electrolyte consists of a solvate ionic liquid ([Li(G4)][TFSA]), comprising an equimolar mixture of lithium bis(trifluoromethanesulfonyl)amide (Li[TFSA]) and tetraglyme (G4), and a well-defined ABA-triblock copolymer, polystyrene-b-poly(methyl methacrylate)-b-polystyrene (PSt-b-PMMA-b-PSt, SMS). The electrolyte is formed by the self-assembly of SMS, where the solvatophobic PSt segments serves as physical cross-linking points, and the solvatophilic PMMA segment with preferentially dissolved [Li(G4)][TFSA] forms ion-conduction paths. In the electrolyte, the preservation of the complex cation [Li(G4)]+ in the PMMA phase was demonstrated by pulsed-field gradient spin–echo (PGSE) NMR, Raman spectra, and thermogravimetric analysis. Because of the preservation of [Li(G4)]+, which hinders the direct interaction of Li+ with the polymer segment and the coupling of the ionic transport from the segmental motion, the room temperature ionic conductivity of the electrolyte reached an appreciable level (10–4–10–3 S cm–1).

Influences of polyhedral oligomeric silsesquioxanes (POSSs) containing different functional groups on crystallization and melting behaviors of POSS/polydimethylsiloxane rubber composites

In this article, three kinds of polyhedral oligomeric silsesquioxanes (POSSs)—octamethylsilsesquioxane (OMS), octaphenylsilsesquioxane (OPS) and heptaphenylhydrogensilsesquioxane (H-POSS)—were successfully synthesized. Then, POSSs were incorporated into polydimethylsiloxane (PDMS) rubber through solution blending followed by open two-roll mill blending with curing agent. Finally, the blends were cured with a plate vulcanizing press and the effects of POSSs on crystallization and melting behaviors of PDMS were investigated. DSC tests indicated that crystallinity (Xc) of the OMS/PDMS composite was lowered, while Xc and the melting temperature (Tm) of the OPS/PDMS composite could be significantly enhanced when 20 wt% OPS was incorporated. OPS was proved to play a role as a nucleating agent in the crystallization of PDMS, but its nucleation mechanism was different from H-POSS which was previously studied by us. The crystals of OPS were flake-like with huge surfaces which provide templates for PDMS crystals to grow. However, due to the grafting of H-POSS onto PDMS chains, H-POSS played a role as physical crosslinking points to reduce the mobility of the PDMS chain segments.

Microdynamics mechanism of thermal-induced hydrogel network destruction of poly(vinyl alcohol) in D2O studied by two-dimensional infrared correlation spectroscopy.

Microdynamics mechanism of thermal-induced hydrogel network destruction of poly(vinyl alcohol) (PVA) in D2O at heating (25-62 °C) was studied by in situ Fourier transform infrared (FTIR) spectroscopy combining with moving-window two-dimensional (MW2D) technique and two-dimensional (2D) correlation analysis. The temperature range of hydrogel destruction was determined within 34-52 °C by dynamic rheological test at first, and then also monitored by MW2D FTIR spectra. The motion of vs(-C-O-, microcrystals) was important in the entire hydrogel destruction process. The microdynamics mechanism of PVA molecular chains can be elaborated as follows: At 32 °C, the number of D2O molecules in the swollen amorphous remains unchanged. At 32-37 °C, more D2O molecules enter into the swollen amorphous region, and the groups of -C-O-, together with -CH2-, are partially hydrated. At 37 °C, the intramolecular or intermolecular hydrogen bonds of PVA are dissociated. The physical cross-linking points of hydrogel are broken due to the melting of PVA microcrystals. At 42 °C, the dissociated hydroxyls from PVA microcrystals rapidly integrate solid hydrogen bonds with D2O molecules. The groups of -C-O- and -CH- are completely hydrated by D2O simultaneously. At 45-55 °C, PVA molecules are surrounded by more D2O molecules. The partially hydrated -CH2- is completely hydrated, and all of the PVA molecules are fully dissolved in D2O.