Cloud points and phase separation of aqueous poly(N-vinylacetamide) solutions in the presence of salts

Aqueous poly(N-vinylacetamide) (PNVA) solution was found to exhibit the cloud point in the presence of salt. This cloud point was shown to correspond to a liquid-liquid phase separation, as confirmed when the PNVA-salt solutions were maintained at a temperature above the cloud point. The upper layer had a higher polymer concentration and a lower salt concentration than those in the lower layer. Thus interaction between PNVA and salts are repulsive. The lower critical solution temperatures were estimated to be 18±1°C for 1.25 molal (NH₄)₂SO₄ and 25±1°C for 0.76 molal Na₂SO₄. Divalent anions such as SO _2– ⁴ , SO _2– ³ , HPO _2– ⁴ and CO _2– ³ were effective in causing turbidity when examined at 25°C. Dependence of the effect on the cationic species was similar to but significantly different from that for acetyltetraglycine ethylester. The cloud points of PNVA decreased linearly with the increase of the polymer concentration at a fixed salt concentration or with the increase of the salt concentration at a fixed polymer concentration. A parameter analogous to the salting-out constant was empirically derived from the dependencies of the cloud points on the concentrations of polymer and salt.     

Viscosities and apparent molar volumes of some amino acids in water and in 6M guanidine hydrochloride at 25°C

Apparent molar volumes and viscosity B- and D- coefficients of amino acids glycine, valine, proline, serine and arginine have been determined in water and in aqueous 6M guanidine hydrochloride (GuHCl) solution at 25°C. Transfer volumes and transfer viscosity B-coefficients were evaluated for the amino acids studied in going from water to 6M GuHCl. These transfer properties which were all positive were interpreted in terms of strong interactions of GuHCl molecules with the charged centers of amino acid molecules. A comparison of results obtained in this work for GuHCl and those obtained from literature for urea has shown that GuHCl has stronger interactions than urea with amino acids. This finding explained the previous experimental observations on GuHCl being a stronger denaturing agent than urea for proteins.     

Surface antimicrobial modification of polyamide by poly(hexamethylene guanidine) hydrochloride

Antimicrobial polyamide (PA) received much attention for the demand of packaging and biomedical fields. In this paper, an antimicrobial PA6 membrane was prepared via a surface chemical reaction. A highly effective antibacterial component (PHMG‐E) with terminal epoxy group was firstly synthesized via a reaction between polyhexamethylene guanidine hydrochloride (PHMG) and ethylene glycol diglycidyl ether (EGDE). Then, PHMG‐E was bonded on the surface of PA6 membrane with secondary amine reduced by borane‐tetrahydrofuran (BH₃‐THF). The antimicrobial rates of surface‐modified PA6 membrane (PA6‐PHMG) against Escherichia coli and Staphylococcus aureus were both higher than 99.99%, and the PHMG was non‐leaching due to the chemical bonding. The hydrophilicity of antibacterial PA6 membrane was also significantly improved and the mechanical performance became better.     

Equilibrium and kinetic aspects of the pH-dependent swelling of poly(2-vinylpyridine-co-styrene) microgels

 Monodisperse, cationic microgels were synthesized by surfactant-free emulsion copolymerization of 2-vinylpyridine and styrene, using the cationic initiator 2,2′-azobis(2-amidinopropane) dihydrochloride. Low levels of divinylbenzene were employed as a cross-linking agent. The particle morphologies and diameters were characterized by a combination of TEM and photon correlation spectroscopy. At styrene contents less than 40% by weight, the particles were spherical with diameters of approximately 200 nm. The diameter decreased with increasing styrene content and the morphology changed from spherical to irregular. The pH-dependent swelling of the microgel particles was studied in constant ionic strength acetate buffers, as a function of styrene content and cross-link density. Particle diameters increased sharply below pH 4.6 due to ionization of the 2-vinylpyridine residues. At higher styrene levels, the transition pH is shifted to lower values and the extent of swelling is reduced. The pH at which swelling occurred was identical for the three cross-linker levels (0.25, 0.50 and 1.5 wt%), but the extent of swelling decreased in this order as expected. The rate of swelling of the particles was investigated by stopped-flow spectrophotometry; as microgels swell the turbidity of the dispersions decreases and this was followed as a function of time. Higher styrene contents not only reduce the extent of swelling, but also the rate at which maximum swelling is reached, whereas the level of cross-linker employed in this study has no effect on the rate of swelling. Received: 26 May 1997 Accepted: 16 July 1997     

Photosensitizer conjugate-functionalized poly(hexamethylene guanidine) for potentiated broad-spectrum bacterial inhibition and enhanced biocompatibility

Pathogen infection is the main cause of human morbidity and death. Traditional antibiotics usually sterilize bacteria in chemical ways, which tends to develop serious antibiotic resistance. Cationic polymers exhibit good bacterial inhibition with less resistance, but often face severe cytotoxicity toward normal cells. The optimization of polymeric antimicrobials for enhanced bactericidal capacity and improved biocompatibility is quite meaningful. In addition, photodynamic therapy (PDT) is a therapeutic modality with less susceptibility to develop resistance. Herein, a typical commercial polymeric antimicrobial, polyhexamethylene guanidine (PHMG) was selected for current proof-of-concept optimization due to its excellent bactericidal capacity but moderate biocompatibility. Eosin-Y (EoS) was copolymerized to afford EoS-labeled polymer conjugates, poly(2-(dimethylamino) ethyl methacrylate-co-eosin), P(DMAEMA-co-EoS), which was conjugated with PHMG to afford a novel polymeric antimicrobial, P(DMAEMA-co-EoS)-b-PHMG-b-P(DMAEMA-co-EoS), noted as PEoS-PHMG. It could efficiently kill broad-spectrum bacteria by physical damage and photodynamic therapy. Compared with PHMG, the bacterial inhibition of PEoS-PHMG was potentiated after the functionalization. Furthermore, PEoS-PHMG exhibited low cytotoxicity and minimal hemolysis, which was demonstrated by cell viability assays toward LO2 cells and RAW 264.7 cells as well as hemolytic assays against red blood cells. These results confirmed that the resultant PEoS-PHMG could act as promising alternative antibacterial materials with excellent broad-spectrum bacterial inhibition and favorable biocompatibility.     

Effect of temperature on the intrinsic viscosity of poly(ethylene glycol)/poly(vinyl pyrrolidone) blends in aqueous solutions

In this work the intrinsic viscosity of poly(ethylene glycol)/poly(vinyl pyrrolidone) blends in aqueous solutions were measured at 283.1–313.1 K. The expansion factor of polymer chain was calculated by use of the intrinsic viscosities data. The thermodynamic parameters of polymer solution (the entropy of dilution parameter, the heat of dilution parameter, theta temperature, polymer–solvent interaction parameter and second osmotic virial coefficient) were evaluated by temperature dependence of polymer chain expansion factor. The obtained thermodynamic parameters indicate that quality of water was decreased for solutions of poly(ethylene oxide), poly(vinyl pyrrolidone) and poly(ethylene oxide)/poly(vinyl pyrrolidone) blends by increasing temperature. Compatibility of poly(ethylene oxide)/poly(vinyl pyrrolidone) blends were explained in terms of difference between experimental and ideal intrinsic viscosity and solvent–polymer interaction parameter. The results indicate that the poly(ethylene glycol)/poly(vinyl pyrrolidone) blends were incompatible.     

Effects of salt on the temperature and pressure responsive properties of poly(N-vinylisobutyramide) aqueous solutions

 We examined the effects of salt on the lower critical solution temperature (LCST) and lower critical solution pressure (LCSP) of aqueous solutions of poly (N-vinylisobutyramide), polyNVIBA, and compared them with those on poly(N-isopropylacrylamide), polyNIPAAm. We found that the addition of salt (such as Na₂SO₄, NaCl, or KCl) decreased the LCST of aqueous polyNVIBA from 45 °C to below 20 °C, almost linearly with the salt concentrations and dependent on the type of salt. We observed a similar concentration-dependent decrease in LCST for polyNIPAAm. When KI or NaSCN was added to each aqueous polymer solution, some smaller increases in LCST were observed at relatively low salt concentrations; higher concentrations of salt gave an almost linear decrease in LCST. As for LCSP, the addition of most types of salt lowered the transition pressure, but the effects were much more dependent on the type and the valence of the salt (especially of anion) in both polymers. Salt with divalent anion showed a larger decrease in LCSP, but those with mono valent anion showed a relatively small decrease, even showed a slight increase at lower salt concentrations in the case of polyNVIBA. Salt with I^- or SCN^- showed evident increases in LCSP up to 1 M and was maintained higher than the control even at 2 M. We discuss the interactions of the amide group in the side chains of polymers and water and their perturbation by ions. Received: 13 November 1997 Accepted: 22 January 1998     

Relationships between ringed spherulitic morphology and miscibility in blends of poly(ɛ-caprolactone) with poly(benzyl methacrylate) versus poly(phenyl methacrylate)

 Ringed spherulites are an interesting phenomenon that is observed only in very few miscible systems. For the first time, the relationship between the state of chain intermixing and the ring-band pattern was demonstrated. Two previously demonstrated miscible blend systems, poly(ɛ-caprolactone) (PCL) with poly(benzyl methacrylate) (PBzMA) and PCL with poly(phenyl methacrylate) (PPhMA), were studied in order to understand the mechanism of ring-band formation in the spherulites and the relationships between the ring-band pattern and the state of miscibility. In both miscible PCL/PBzMA and PCL/PPhMA systems, extinction rings were observed within the PCL spherulites. In the PCL/PBzMA blend, the extinction rings are not as distinct (owing to distortion) as those in the PCL/PPhMA blend system. Analysis was performed and discussions were made to reveal relationships between miscibility, interaction strength, and the pattern of the ring bands in the PCL spherulites in polymeric mixtures. Received: 5 January 2000/Accepted: 14 March 2000     

Enzymatic hydrolysis of poly(D, L-lactide) spread monolayers by cutinase

 The enzymatic hydrolysis of a model poly(D,L-lactide) by cutinase was studied by using a barostat surface balance. A theoretical approach based on the adaptation of the Michaelis–Menten scheme at the interface and a process of random fragmentation of the macromolecules was developed. The role of the interfacial organisation of the reaction products was discussed. Hydrolysis rate constant values and the specific activity were estimated and compared with those obtained for the hydrolysis of lipid monolayers. The process of fragmentation of the interfacial polymer structures was visualised by using AFM imaging. Received: 19 August 1996 Accepted: 13 December 1996     

Influence of molecular weight on the microhardness of poly(ethylene terephthalate)

 Poly(ethylene terephthalate) (PET) was annealed in vacuum at different temperatures (190–260 °C) for different times (10 min–24 h) in order to examine the mechanical properties (microhardness) of PET samples with a wide range of molecular weights (10 000–120 000). Short annealing times result in a twofold decrease in mol. wt. due to hydrolytic decomposition. However, long annealing times give rise to a substantial molecular weight increase. It is found that microhardness (H) rises linearly with the degree of crystallinity obtained during up-grading of mol. wt. and its extrapolation leads to H-values of completely crystalline PET, H ^PET _c=405 MPa for samples with conventional mol. wt. and of 426 MPa for samples with mol. wt. higher than 30 000. It is shown that the increase of mol. wt. for each set of samples with a given range of degree of crystallinity also causes a slight increase of H. The influence of mol. wt. upon hardness is discussed in the light of the changes in the physical structure (crystallinity, crystal thickness) which is formed at given heat treatment conditions. Received: 29 April 1997 Accepted: 23 September 1997     

折叠链聚酯脲的合成与表征及其自组装行为研究

利用四甲基胍促进二羧酸与二溴代化合物的高效酯化聚合反应,设计、合成了一种新型手风琴式折叠链结构的聚酯脲.具有特殊结构的单体分别是4,4′-二羧基二苯基脲和3,5-二(溴代烷氧基)-苯甲酸酯,因此得到的聚酯脲具有类似接枝共聚物的结构.通过核磁氢谱(~1H-NMR)和傅里叶红外光谱(FTIR)对聚酯脲的结构及分子量进行了表征,结果显示,得到了分子量接近2×10~4的聚酯脲.通过核磁跟踪研究聚合反应动力学,结果表明,聚合反应速度与二溴单体的烷基链长度有关,二溴单体的烷基链较长时,聚合速率较慢.热重分析(TGA)结果显示,这种聚酯脲具有良好的热稳定性;由示差扫描量热(DSC)测试结果获知聚酯脲的熔融温度为57°C,表明它具有结晶性.脲基之间的氢键作用和苯环产生的π-π相互作用驱动这种聚酯脲在溶液中进行自组装.通过透射电子显微镜(TEM)研究聚酯脲的自组装行为,结果表明,该聚酯脲在氯仿和甲醇的混合有机溶剂中,静置4 h后,组装成片层结构;继续静置到3天后,形成了稳定的囊泡结构的聚集体,囊泡壁厚度约7 nm,接近折叠链宽度的预测值;小角X射线(XRD)测试结果表明聚酯脲是有序结构,进一步证实了合成的聚酯脲具有折叠链构象.     

Synthesis, polymerization, and dispersion copolymerization of poly(ethylene oxide) macromonomers carrying methacryloyloxyalkyl end groups

 Poly(ethylene oxide) macromonomers carrying methoxy group on the one (α-) end and methacryloyloxyhexyl or methacryloyloxydecyl group on the other (ω-) end were prepared, homopolymerized in water, and dispersion-copolymer-ized with styrene or methyl methacrylate in a methanol–water mixture. They were found to polymerize more rapidly and to produce stable polystyrene dispersions more effectively, as compared to the corresponding macromonomers carrying either α-methoxy and or α-dodecyloxy and ω-methacryloyloxy end groups. Thus, the amphiphilic constitution of the macromonomers such that favors the polymerizing methacrylate end groups to locally concentrate into the micelle core or to the particle surface while the poly(ethylene oxide) chains extending to the medium appears to be most important in enhancing their polymerizability and effectiveness as reactive steric stabilizers. On the other hand, stable poly(methyl methacry-late) particles with a number of craters or pleats on the surface were produced with a PEO macromono-mer with α-methoxy and ω-methacryl-oyloxy end groups. Received: 4 September 1996 Accepted: 18 October 1996     

DSC study of cold and heat denaturation processes of β-lactoglobulin A with guanidine hydrochloride

The cold and heat denaturations of bovine P-lactoglobulin A ((β-lg A) has been studied in solutions of guanidine hydrochloride (GuHCI) by differential scanning calorimetry (DSC). The experimental results are presented and discussed. It is shown that the number of protons bound by the monomeric molecules of β-lg A was unchanged before and after its heat denaturation below pH 3, and that the activation energy of the heat denaturation was depressed owing to the presence of GuHCI. In the solutions with 2.50 and 3.06 mol/L of GuHCI, both the cold and heat denaturations of P-lg A were observed. In comparison with the heat denaturation, the activation energy of cold denaturation was far lower and the number of GuHCl molecules bound by the unfolded polypeptide chains after culd denaturation increased a lot. The absolute value of the enthalpy of cold denaturation was larger than that of heat denaturation. It was found by the analysis that the contribution to the total denaturational enthalpy of conformational change itself of the monomeric molecules of β-lg A was the lowest among the globulins, according to the average of the number of heavy atoms. Project supported by the National Natural Science Foundation of China, and by the fund for excellent items under Director of the Institute of Chemistry.     

Coil-to-globule-type transition of poly(N-isopropylacrylamide) adsorbed on colloidal silica particles

 The temperature dependence of the dimensions of poly(N-isopropylacrylamide) (PNIPAM) adsorbed on two different colloidal silica particles was studied with dynamic light scattering. The hydrodynamic diameter was measured when the temperature was varied stepwise from 10 to 60 °C. PNIPAM molecules free in solution undergo a conformational transition at the θ temperature. We have found that PNIPAM adsorbed onto silica particles also undergoes a transition below the θ temperature. When a small amount of polymer was adsorbed the coil-to-globule transition at the θ temperature did not occur. Potentiometric titrations showed that the surface charge of the silica particles was not affected by the polymer adsorption. Sodium dodecyl sulfate (SDS) (100–1200 mg/l) was added to improve the stability. The particles with a higher zeta potential required a smaller addition of SDS to prevent coagulation compared to the particles with a smaller surface potential. For low additions of SDS the transition curves of adsorbed PNIPAM were unaffected. For larger additions of SDS the collapse of PNIPAM was shifted to higher temperatures. When as much as 1200 mg/l SDS was added, two regions with weak transitions were observed before the collapse. It was also observed that the presence of SDS results in a smaller adsorption of PNIPAM onto the particles. The addition of SDS strongly increased the magnitude of the electrophoretic mobility of the polymer–particle unit. From the electrophoretic measurements an electrokinetic layer thickness was calculated and it was found to be smaller than the corresponding hydrodynamic layer thickness, as obtained by dynamic light scattering. Received: 14 December 1999/In revised form: 22 February 2000/Accepted: 6 March 2000     

The miscibility of poly(vinyl alcohol)/poly(N-vinylpyrrolidone) blends investigated in dilute solutions and solids

Poly(vinyl alcohol) (PVA) (polymer A) and poly(N-vinylpyrrolidone) (PVP) (polymer B) are known to form a thermodynamically miscible pair. In the present study the conclusion on miscibility of PVA/PVP solid blends, confirmed qualitatively (DMTA, FTIR) and quantitatively (DSC, χ_AB = − 0.69 at 503 K) is compared with the miscibility investigations of PVA/PVP solution blends by the technique of dilute solution viscometry. The miscibility of the ternary (polymer A/ polymer B/ solvent) system is estimated on the basis of experimental and ideal values of the viscosity parameters k, b and [η]. It is found that the conclusions on miscibility or nonmiscibility drawn from viscosity measurements in dilute solution blends depend: (i) on the applied extrapolation method used for the determination of the viscosity interaction parameters, (ii) on the assumed definition of the ideal values and (iii) on the thermodynamic quality of the solvent, which in the case of PVA depends on its degree of hydrolysis. Hence, viscometric investigations of dilute PVA/PVP solution blends have revealed that viscometry, widely used in the literature for estimation of polymer-polymer miscibility can not be recommended as a sole method to presume the miscibility of a polymer pair.     

Complexation of poly(ethylene oxide) and urea

The complexation of ultrahigh-molecular-weight poly(ethylene oxide) (PEO) with urea in both the solid and molten states was studied by infrared spectroscopy. Information about the temperature dependences of the absorption bands in the 3600–2600 and 1300–600 cm^?1 region on heating and cooling was obtained. Some conclusions concerning the interaction between PEO and urea were also made. The formation of a high temperature, metastable molecular complex between PEO and urea, which is susceptible to undercooling, was confirmed spectroscopically. Heating to 85–90°C resulted in a molecular complex stable at room temperature.© 1994 John Wiley & Sons, Inc.     

Thermal degradation behaviour of poly(vinyl chloride) in the presence of poly(N′-acryloyl benzhydrazide)

The thermal degradation behaviour of poly(vinyl chloride), PVC, in the presence of poly(N′-acryloyl benzhydrazide), PABH, has been studied using continuous potentiometric determination of the evolved hydrogen chloride gas from the degradation and by measuring the extent of discoloration of the degraded samples. Blending this polymeric additive with dibasic lead carbonate, DBLC, reference stabilizer in different ratios had synergistic effects on both the thermal stability and the extent of discoloration of PVC.     

Structure–property relationships of anionic poly(urethane–urea) dispersion cross-linked with partially methylated melamine formaldehyde

An anionic poly(urethane–urea) dispersion (PUD) was cross-linked with different amount of partially methylated melamine formaldehyde (PMMF). The isothermal curing behavior was observed by a rigid-body pendulum rheometer. The test results showed that cure response of PUD cross-linked with PMMF was a function of the concentration of PMMF. Also, PMMF self-condensation could take place during the curing process. In this experiment, the anionic poly(urethane–urea) dispersion has a large number of >N–H cross-linking or branching sites in urethane and urea groups per molecule that allow a large number of PMMF to couple into elastic PUD backbone to form branched structure with partial cross-linking. The dynamic mechanical properties of PUD cross-linked with PMMF were affected by the concentration of PMMF. It was further shown that the tensile properties were strongly influenced by the concentration of PMMF and curing temperature.     

Morphology and mechanical properties of poly(vinyl alcohol) and starch blends prepared by gelation/crystallization from solutions

 In an attempt to produce biodegradation materials, poly(vinyl alcohol) (PVA)–starch (ST) blends were prepared by gelation/crystallization from semidilute solutions in dimethyl sulfoxide (Me₂SO) and water mixtures and elongated up to 8 times. The content of mixed solvent represented as Me₂SO/H₂O (volume percent) was set to be 60/40 assuring the greatest drawability of PVA homopolymer films. The PVA/ST compositions chosen were 1/1, 1/3, and 1/5. The elongation up to 8 times could be done for the 1/1 blend but any elongation was impossible for blends whose ST content was beyond 50%. When the blends were immersed in water at 20 or 83 °C, the solubility became considerable for an undrawn blend with 1/5 composition and a drawn 1/1 blend with λ=8. To avoid this phenomenon, cross-linking of PVA chains was carried out by formalization under formaldehyde vapor. Significant improvement could be established by the cross-linking of PVA chains. For the 1/1 blend, the amount of ST dissolved in water at 23 °C was less than 3% for the undrawn state and 25% for the drawn film. The decrease in the ST content was enough for use as biodegradation materials. Namely, the water content relating to the biodegradation in soil is obviously different from such a serious experimental condition that a piece of blend film was immersed in a water bath. At temperatures above 0 °C, the storage modulus of the formalization blends became slightly higher than those of the nonformalization blends. The Young's modulus of the drawn films with a draw ratio of 8 times was 2 GPa at 20 °C. Received: 23 June 2000 Accepted: 30 October 2000     

Characterization of cross-linked poly(N-isopropylmethacrylamide) microgel latexes

 This article reports the colloidal and physicochemical characterization of crosslinked poly (N-isopropylmethacrylamide) (poly[NIPMAM]) latexes. The latex particles were first characterized by determining the lowest critical solubility temperature by measuring the optical density variation as a function of temperature. In addition, the electrophoretic mobility behaviors of all latexes were examined as a function of pH and temperature. Finally, the colloidal stability was investigated by determining the critical coagulation concentration and the critical flocculation temperature, and the corresponding results were discussed by taking into account both the effect of salinity and temperature on the solvency of poly[NIPMAM]. Received: 25 March 1999 Accepted: 5 May 1999