Comparative study on water structures in polyHEMA and polyMEA by XRD‐DSC simultaneous measurement

We have found that poly(2‐methoxyethylacrylate) (polyMEA) has excellent blood compatibility and proposed that the property is due to freezing bound water in the polymer. This water is defined as that which cold‐crystallizes at around ?45°C in the heating process of differential scanning calorimetry (DSC). In addition, we have already reported that the water in polyMEA is classified into three types, nonfreezing, freezing bound, and free waters, whereas the water in other polymers is just classified into two types: free and nonfreezing waters. (J Biomed Mater Res 68A, 2004, 684) However, the phenomenon observed by DSC is the enthalpy change and is not a direct evidence for crystallization. To confirm cold‐crystallization, a comparative investigation of the thermal and crystallographical properties of water in hydrated polyMEA and poly(2‐hydroxyethylmethacrylate) (polyHEMA) as a control was carried out using simultaneous measurements by X‐ray diffractometer (XRD) and DSC. In addition, the effect of the water content in the polymers on the properties was studied. As for polyMEA, the finding that XRD crystalline peaks appearing in the heating process were assigned to hexagonal ice indicated cold‐crystallization. On the other hand, in the case of polyHEMA, the crystal due to ice was formed only in the cooling process, and during the heating process, the growth of crystal ice was not observed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Swollen behavior of crosslinked network hydrogels based on poly(vinyl alcohol) and polydimethylsiloxane

Poly(vinyl alcohol) (PVA) was dissolved in the water to make a 10 wt % aqueous solution, and polydimethylsiloxane (PDMS) was mixed with 1 wt % 2,2‐dimethyl‐2‐phenylacetophenone (DMPAP) and 0.5 mol % methylenebisacrylamide (MBAAm) in isopropyl alcohol. This mixture was added to a PVA aqueous solution and heated at 90°C for 7 h. Various crosslinked networks were prepared at different molar ratios of PVA/PDMS (1:1, 1:3, and 3:1). The characterization of PVA/PDMS crosslinked networks was determined by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), a universal testing machine (UTM), and the equilibrium water content (EWC). The DSC melting endotherms showed, at 219.49°C, a sharp endothermic peak of PVA, and PVA/PDMS crosslinked networks had melting peaks close to this point. The value of EWC increased with the content of PVA in the crosslinked networks, simultaneously depending on the temperature. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 957–964, 2002     

Enhanced crystallization of poly(lactide) stereocomplex by xylan propionate

The effect of xylan propionate (XylPr) as a novel biomass‐derived nucleating agent on the poly(lactide) sterecomplex was investigated. Addition of XylPr to an enantiomeric blend of poly(l ‐lactide) (PLLA) and poly(d ‐lactide) (PDLA) was performed in either the solution state or molten state. The solution blend of PLLA/PDLA with XylPr was prepared by mixing equal volumes of 1 wt% XylPr/PLLA and 1 wt% XylPr/PDLA solutions in chloroform and precipitating in methanol. The solution blend with XylPr showed shorter half‐time crystallization than the solution blend without XylPr in isothermal crystallization between 80 and 140 °C, although homocrystallization occurred. Enhanced stereocomplex crystallization in the solution blend with XylPr was observed at 180 °C, where no crystallization occurred in the solution blend without XylPr. Addition of XylPr to PLLA/PDLA blend in the molten state was performed at 240 °C. Thereafter, the melt blend of PLLA/PDLA with or without XylPr was either quenched in iced water or isothermally crystallized directly from the melt. Isothermal crystallization of the melt‐quenched blend with XylPr gave a similar result to the solution blend with XylPr. In contrast, the melt‐crystallized blend with XylPr formed only stereocomplex crystals after crystallization above 140 °C. Furthermore, the melt‐crystallized blend with XylPr showed a higher crystallinity index and melting temperature than the melt‐crystallized blend without XylPr. This shows that XylPr promotes stereocomplex crystallization only when the blend of PLLA/PDLA with XylPr is directly crystallized from the molten state just after blending. © 2016 Society of Chemical Industry     

Effects of clay and POSS nanoparticles on the quiescent and shear‐induced crystallization behavior of high molecular weight poly(ethylene terephthalate)

The effects of organoclay and polyhedral oligomeric silsesquioxanes (POSS) nanoparticles on the crystallization behavior of high molecular weight poly(ethylene terephthalate) (HMWPET; inherent viscosity of 1.05) were investigated in terms of nanoparticle content and shear rate. Both nanoparticles played a role of nucleating agent for PET and increased the cold crystallization temperature by about 24°C. The half‐time of crystallization was also decreased with increasing the nanoparticle content. Clay proved to be more effective than POSS; a notable nucleating effect was observed at 0.3 wt% for clay and 2 wt% for POSS. Introducing 1 wt% of clay gave the highest crystallization rate among all PET nanocomposite samples examined. Isothermal crystallization of the nanocomposites under dynamic shear exhibited similar crystallization behavior. As in the DSC measurement, clay appeared to be more effective to promote the crystallization of PET under shear. The nucleating effects were more noticeable at higher shear rate. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers     

Characterization of hydrogels based on chitosan and copolymer of poly(dimethylsiloxane) and poly(vinyl alcohol)

Copolymers composed of poly(vinyl alcohol) (PVA) and poly(dimethylsiloxane) (PDMS) were crosslinked with chitosan to prepare semi‐interpenetrating polymer network (IPN) hydrogels by an ultraviolet (UV) irradiation method for application as potential biomedical materials. PVA/PDMS copolymer and chitosan was cast to prepare hydrogel films, followed by a subsequent crosslinking with 2,2‐dimethoxy‐2‐phenylacetophenone as a nontoxic photoinitiator by UV irradiation. Various semi‐interpenetrating polymer networks (semi‐IPNs) were prepared from different weight ratios of chitosan and the copolymer of PVA/PDMS. Photocrosslinked hydrogels exhibited an equilibrium water content (EWC) in the range of 65–95%. Swelling behaviors of these hydrogels were studied by immersion of the gels in various buffer solutions. Particularly, the PCN13 as the highest chitosan weight ratio in semi‐IPN hydrogels showed the highest EWC in time‐dependent and pH‐dependent swelling. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2591–2596, 2002     

Characterization of the water state of hyaluronic acid and poly(vinyl alcohol) interpenetrating polymer networks

Interpenetrating polymer networks (IPNs) composed of hyaluronic acid and poly(vinyl alcohol) hydrogels were prepared, and the influence of water and the drying kinetics were investigated. The IPN hydrogels were characterized with thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The glass‐transition temperatures of the IPN hydrogels decreased with increasing water content. The bound water was the sum of the nonfreezing bound water and freezing bound water. From the DSC melting curves, the values of the total water and freezing bound water were evaluated for IPN hydrogels containing large amounts of water. At the same time, the bound water value was estimated with TGA. In the TGA curves, one‐step and two‐step weight losses, corresponding to free water and nonfreezing bound water, were observed. The bound water of the hydrophilic polymers broke the hydrogen bonding between the hydroxyl groups of the polymers. The swollen IPN hydrogels exhibited relatively high bound water contents (43.04–59.17%) by DSC and TGA. The bound water contents of the dry IPN hydrogel films were 10.2–15.29% by TGA. The drying reaction rate constant of the IPN hydrogel increased with increasing temperature. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1467–1472, 2004     

pH‐ and thermal characteristics of graft hydrogels based on chitosan and poly(dimethylsiloxane)

Graft copolymerization of epoxy‐terminated poly(dimethylsiloxane) (PDMS) onto chitosan was reacted without using a catalyst. pH‐sensitive hydrogels were obtained that are based on two different components: a natural polymer and a synthetic polymer. These PDMS substitutents provide the basis for hydrophobic interactions that contribute to the formation of hydrogels. Various graft hydrogels were prepared from different weight ratios of chitosan and PDMS. Swelling behavior of these hydrogels was studied by immersion of the gels in various buffer solution. Photocrosslinked hydrogels exhibited a high equilibrium water content (EWC). Particularly, the sample CP31 of the highest chitosan–PDMS weight ratio showed the highest EWC in time‐dependent, temperature‐dependent, and pH‐dependent swelling behavior. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2661–2666, 2002     

高强度水凝胶P(HEMA-co-NEVER)溶胀特性的研究

该文研究了酚醛环氧型乙烯基酯树脂(NEVER)/甲基丙烯酸-β-羟乙酯(HEMA)共聚水凝胶的溶胀性质。NEVER质量分数的增大,加强了水凝胶内部疏水基团间的相互作用,使平衡含水量EWC从39.7%下降到15.9%,聚合物体积分数φ2从0.5440上升到0.8085。溶胀介质离子强度增大,极性增强,形成了更加紧密的低溶胀水凝胶,导致产生盐出效应,水凝胶初始溶胀速率r0从0.189g水·g-1干胶·h-1下降到0.047g水·g-1干胶·h-1,理论最大吸水量S∞也从0.395g水·g-1干胶降到0.364g水·g-1干胶。水凝胶溶胀初期表现为Fickian行为,扩展溶胀符合Schott二级动力学方程。当温度由278K升至323K,水凝胶样品H/N3的r0从0.060g水·g-1干胶·h-1升高到0.287g水·g-1干胶·h-1,但S∞却从0.559g水·g-1干胶降到0.351g水·g-1干胶。热力学研究表明,水凝胶在水中的溶胀过程是放热过程。     

Crystallization behavior and morphology of double crystalline poly(trimethylene terephthalate)/poly(ethylene oxide terephthalate) copolymers

Double crystalline poly(trimethylene terephthalate)/poly(ethylene oxide terephthalate) copolymers (PTT/PEOT), with PTT content ranging from 16.5 to 65.5 wt%, were synthesized by melt copolycondensation. The morphological transformation of samples from microphase separation to macrophase separation was investigated by gel permeation chromatography and transmission electron microscopy. Differential scanning calorimetry and in situ wide‐angle X‐ray diffraction suggested that all copolycondensation samples displayed double crystalline behavior. The melt‐crystallization peak temperatures (T_{m, c} values) of PTT chains monotonously increased with increasing PTT content and were higher than that of homo‐PTT when the content of PTT was above 30.6 wt%. Interestingly, T_{m, c} values of PEOT chains were also increased with increasing PTT content. Polarized optical microscopy revealed that all copolycondensation samples studied could form ring‐banded spherulites and band spacing increased with increasing T_c values. In addition, band spacing decreased with increasing PTT content at a given T_c. Strangely, although PEOT was the main component in all copolycondensation samples, spherulitic morphology formed by the advance crystallization of PTT did not change after PEOT crystallization. Only a subtle change of quadrant tones was detected. © 2012 Society of Chemical Industry     

The effect of poly(ethylene glycol) mixed with poly(l‐lactic acid) on the crystallization characteristics and properties of their blends

The non‐isothermal and isothermal crystallizations of extruded poly(l ‐lactic acid) (PLLA) blends with 10, 20 and 30 wt% poly(ethylene glycol) (PEG) were investigated with differential scanning calorimetry. The formation of α‐form crystals in the blend films was verified using X‐ray diffraction and an increase in crystallinity indexes using Fourier transformation infrared spectroscopy. Crystallization and melting temperatures and crystallinity of PLLA increased with decreasing cooling rate (CR) and showed higher values for the blends. Although PLLA crystallized during both cooling and heating, after incorporation of PEG and with CR = 2 °C min^?1 its crystallization was completed during cooling. Increasingly distinct with CR, a small peak appeared on the lower temperature flank of the PLLA melting curve in the blends. A three‐dimensional nucleation process with increasing contribution from nuclei growth at higher CR was verified from Avrami analysis, whereas Kissinger's method showed that the diluent effect of 10 and 20 wt% PEG in PLLA decreased the effective energy barrier. During isothermal crystallization, crystallization half‐time increased with temperature (T_ic) for the blends, decreased with PEG content and was lower than that of pure PLLA. In addition, the Avrami rate constants were significantly higher than those of pure PLLA, at the lower T_ic. Different crystal morphologies in the PLLA phase were formed, melting in a broader and slightly higher T_m range than pure PLLA. The crystallization activation energy of PLLA decreased by 56% after the addition of 10 wt% PEG, increasing though with PEG content. Finally, PEG/PLLA blends presented improved flexibility and hydrophilicity. © 2019 Society of Chemical Industry     

Cold crystallization behavior of poly(lactic acid) in its blend with acrylic rubber; the effect of acrylic rubber content

Understanding the crystallization process of polymer blends is of great importance for designing their process conditions, especially when the crystallization occurs during heating, so‐called cold crystallization. In this paper, the cold crystallization behavior of poly(lactic acid) (PLA) in its blends with acrylic rubber (ACM) was studied as a function of ACM content, using various techniques including differential scanning calorimetry, polarized optical microscopy and rheological methods. It was found that the addition of 10 wt% ? 20 wt% ACM to the PLA accelerated its cold crystallization. However, on using a greater amount of ACM up to 30%, the rate of crystallization was not further increased. In the ACM‐rich blends, the crystallizable PLA domains were distributed inside the amorphous ACM matrix and consequently confined crystallization occurred. The observed effects are discussed in terms of the interplay between chain mobility enhancement and the influence of phase boundaries. © 2017 Society of Chemical Industry     

Synthesis and characteristics of the interpenetrating polymer network hydrogel composed of chitosan and polyallylamine

A temperature‐ and pH‐dependent hydrogel was studied with interpenetrating polymer network (IPN) hydrogels constructed with water‐insoluble chitosan and polyallylamine. Various IPNs were prepared from different weight ratios of chitosan–polyallylamine. Crosslinked‐IPN hydrogels exhibited relatively high equilibrium water content (EWC) in the range 80–83%. The EWC of IPN hydrogels depended on pH and the amount of complex, which is the content of chitosan and polyallylamine. The differential scanning calorimeter (DSC) thermogram of fully swollen IPN hydrogels appeared between 3 to 4 °C. The IPNs exhibited two glass‐transition temperatures (T_gs), indicating the presence of phase separation in the IPNs as exhibited by dielectric analysis (DEA). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 498–503, 2002     

Synthesis and characterization of an interpenetrating polymer network composed of poly(methacrylic acid) and poly(vinyl alcohol)

Temperature and pH‐responsive interpenetrating polymer network (IPN) hydrogels, constructed with poly(methacrylic acid) (PMAA) and poly(vinyl alcohol) (PVA), by a sequential IPN method, were studied. The characterization of IPN hydrogels was investigated by Fourier‐transform infrared spectroscopy, differential scanning calorimetry (DSC) and swelling under various conditions. The IPN hydrogels exhibited relatively high swelling ratios, in the range 230–380 %, at 25 °C. The swelling ratios of the PMAA/PVA IPN hydrogels were pH and temperature dependent. DSC was used for the quantitative determination of the amounts of freezing and non‐freezing water. The amount of free water increased with increasing PMAA content in the IPN hydrogels. Copyright © 2004 Society of Chemical Industry     

Cholesteryl moiety terminated amphiphilic polymethacrylates containing nucleic acid bases for drug delivery

Poly[9‐(2‐methacryloyloxyethyl)adenine] and poly[1‐(2‐methacryloyloxyethyl)thymine] with one pendant cholesteryl moiety at the polymer end (PMEA‐Chol, PMET‐Chol) and with two pendant cholesteryl moieties at both polymer ends as terminal groups (PMEA‐2Chol, PMET‐2Chol) were prepared by radical polymerization of 9‐(2‐methacryloyl‐oxyethyl)adenine (MEA) and 1‐(2‐methacryloyloxyethyl)thymine (MET) initiated with 4,4′‐azobis[(3‐cholesteryl)‐ 4‐cyanopentanoate] in the presence of 2‐mercaptoethanol or thiocholesterol as chain transfer reagents, respectively. The copolymers [PNiPAAm‐co‐PMEA‐nChol (n = 1,2)] composed of N‐isopropylacrylamide (NiPAAm) and MEA were also prepared in a similar manner. The self‐organization of these polymers and copolymers was confirmed by a fluorescence measurement, and then their critical concentrations of micelle formation (CMC) were determined. The mixture of PMEA‐2Chol and cholesterol as a lipophilic drug model formed a lamella type of complex with an interplaner spacing of d = 35.3 Å. The hypochromism based on the formation of a 1 : 1 interaction of adenine and thymine moieties was found to appear in the mixed aqueous solution of PMEA‐Chol and PMET‐Chol. Complementary interactions were also confirmed in the system of PMET‐2Chol and adenosine as well as PMEA‐2Chol and uridine. Cis‐dichlorodiammine platinum(II) (CDDP) was bound to PNiPAAm‐co‐PMEA‐Chol through the adenine moiety by ligand substitution atoms of CDDP. The amount of CDDP loaded on the copolymer was found to be 0.143 g g^?1. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3064–3075, 2007     

Differential scanning calorimetry investigation of formation of poly(ethylene glycol) hydrate with controlled freeze–thawing of aqueous protein solution

The formation of poly(ethylene glycol) (PEG) hydrate during freeze–thawing of dilute lactate dehydrogenase solutions with the addition of 0.05–160 mg/mL PEG 6000 is investigated by differential scanning calorimetry and modulated temperature differential scanning calorimetry. The freeze–thawing process is performed with a controlled temperature history. A moderate cooling rate to a low freezing temperature in combination with a low heating rate seems to create the most stable PEG hydrate. The maximum amount and the most stable hydrate phase are obtained when the freezing temperature is at or below ?60°C. The enthalpy of melting for the hydrate at ?15°C is dependent on the heating rate but not on the cooling rate if the freezing temperature is ?60°C. The effect of the addition of reduced form nicotinamide adenine dinucleotide to the PEG and protein solution indicates that competing interactions with the protein can increase the stability of the PEG hydrate. The amount of bound water in the PEG hydrate can be calculated directly from the melting enthalpy of the hydrate if an adequate temperature history is used. For solutions with >10 mg/mL PEG there are 1.7–2.7 water molecules bound per PEG unit. The PEG protection of the protein at freeze–thawing can be an effect of the amount of available PEG hydrate in relation to the amount of ice surface. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1626–1634, 2004     

Crystallization behavior of PEO in blends of poly(ethylene oxide)/poly(2‐vinyl pyridine)‐b‐(ethylene oxide) block copolymer

The crystallization behavior of two molecular weight poly(ethylene oxide)s (PEO) and their blends with the block copolymer poly(2‐vinyl pyridine)‐b‐poly(ethylene oxide) (P2VP‐b‐PEO) was investigated by polarized optical microscopy, thermogravimetric analysis, differential scanning calorimetry, and atomic force microscopy (AFM). A sharp decreasing of the spherulite growth rate was observed with the increasing of the copolymer content in the blend. The addition of P2VP‐b‐PEO to PEO increases the degradation temperature becoming the thermal stability of the blend very similar to that of the block copolymer P2VP‐b‐PEO. Glass transition temperatures, T_g, for PEO/P2VP‐b‐PEO blends were intermediate between those of the pure components and the value increased as the content of PEO homopolymer decreased in the blend. AFM images showed spherulites with lamellar crystal morphology for the homopolymer PEO. Lamellar crystal morphology with sheaf‐like lamellar arrangement was observed for 80 wt% PEO(200M) and a lamellar crystal morphology with grain aggregation was observed for 50 and 20 wt% blends. The isothermal crystallization kinetics of PEO was progressively retarded as the copolymer content in the blend increased, since the copolymer hinders the molecular mobility in the miscible amorphous phase. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

The effect of graphene nanofiller on the crystallization behavior and mechanical properties of poly(vinyl alcohol)

The effect of graphene on the crystallization behavior of graphene/poly(vinyl alcohol) (PVA) nanocomposites is investigated in terms of the heterogeneous nucleation effect using Fourier transform infrared spectroscopy and differential scanning calorimetry. Nanometer‐sized graphenes with disc‐type shape are successfully fabricated by transversal cutting of platelet carbon nanofibers, and the graphene/PVA nanocomposites are prepared by varying the concentration of graphene using a solution‐casting method. The graphene/PVA nanocomposites exhibit an enhanced degree of crystallization, increasing to 18.8% at a graphene concentration of 0.5 wt%. The graphene acts as an effective nucleating agent during the crystallization process, enhancing the degree and rate of crystallization. In addition, the graphene/PVA nanocomposites with a high graphene content have markedly improved mechanical properties. Mechanical properties, including hardness and elastic modulus, of the prepared graphene/PVA nanocomposites are analyzed using an atomic force microscopy nanoindentation method. The graphene plays a key role in increasing the crystallinity by acting as an effective nucleating agent at low concentrations (<1.0 wt%) and in enhancing the mechanical properties by acting as a nanofiller at high concentrations (>1.0 wt%).     

Structure of Microemulsion Formulated with Monoacylglycerols in the Presence of Polyols and Ethanol

The influence of polyols as cosurfactants (propylene glycol PG; glycerol G) and short chain alcohol as a cosolvent (ethanol EtOH) on the formation and solubilization capacity of the systems: hexadecane/monoacylglycerols (MAG)/polyol/water:EtOH, at 60 °C, was investigated. Electrical conductivity measurement, and the DSC method were applied to determine the structure and type of microemulsions formed. The dimension of the droplets was characterized by DLS. It has been stated that concentration of EtOH has a strong influence on the shape and extend the microemulsion areas and helps to avoid rigid structures such as gels, precipitates, and liquid crystals. It was found that, depending on the concentration of five‐component systems, it was possible to obtain fully diluted microemulsions with dispersed particles size distribution ranging from 5 to 30 nm. Studied systems are changing the w/o structure into a bicontinuous system. The results of electrical conductivity showed that the electrical percolation threshold is dependent on the hydration of polar head groups in the whole system and the less rigid interfacial film due to the intercalation of ethanol. In addition, the surfactant/alcohol/polyol can strongly bind water in the inner phase so that it freezes below ?10 °C and acts in part as ‘bound’ water. In the systems containing more than 50 mass% of polyols, with respect to the water, the all the water was non‐freezable. Propylene glycol and glycerol are cryoprotectants protecting biological systems from massive ice crystallization, since they lower the freezing point of water.     

Crystallization of poly(3‐hydroxybutyrate) with stereocomplexed polylactide as biodegradable nucleation agent

Crystallization kinetics behavior and morphology of poly(3‐hydroxybutyrate) (PHB) blended with of 2–10 wt% loadings of poly(L ‐ and D ‐lactic acid) (PLLA and PDLA) stereocomplex crystallites, as biodegradable nucleating agents, were studied using differential scanning calorimetry, polarizing‐light optical microscopy (POM), and wide‐angle X‐ray diffraction (WAXD). Blending PLLA with PDLA at 1:1 weight ratio led to formation of stereocomplexed PLA (sc‐PLA), which was incorporated as small crystalline nuclei into PHB for investigating melt‐crystallization kinetics. The Avrami equation was used to analyze the isothermal crystallization of PHB. The stereocomplexed crystallites acted as nucleation sites in blends and accelerated the crystallization rates of PHB by increasing the crystallization rate constant k and decreasing the half‐time (t_1/2). The PHB crystallization was nucleated most effectively with 10 wt% stereocomplexed crystallites, as evidenced byPOM results. The sc‐PLA complexes (nucleated PHB crystals) exhibit much small spherulite sizes but possess the same crystal cell morphology as that of neat PHB based on the WAXD result. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers