An investigation of influence of cryogenic treatment on extremely dilute aqueous solution of poly(vinyl alcohol) (PVA) was performed by viscometry. The solution was frozen in liquid nitrogen or in a freezer at-25℃, then thawed at ambient temperature and concentrated by evacuation. The viscosity of the solution was measured using the dilute method. The experimental results indicated that the viscosity of the solution is related to N, the times of the freezing and thawing cycle, and the temperature for freezing. Undergoing a treatment of freezing and thawing, the viscosity of the solution is decreased, while it can be recovered the value of before the treatment as the solution had been heated at a high temperature. Thus, a conclusion may be obtained; that is, for an extremely dilute aqueous solution of PVA, which concentration is below Cgel, threshold concentration for gelation, an intramolecular hydrogen bonding cohesional entanglement can be formed by freezing as N>5. However, in the case of N<5, it not only formed an intramolecular hydrogen bonding but also produced an intermolecular hydrogen bonding. At the same time, the abnormal behavior of reduced viscosity of the solution in extremely dilute concentration region has been explained.

A graft copolymer of oleic acid (OA) onto low-density polyethylene (LDPE) was prepared using dicumyl peroxide (DCP) as an initiator in the molten state. The grafting was carried out in a Haake rheometer. The effects of the reaction time and the amount of DCP and the monomer on the percentage of grafting were studied. The rheological behavior and the melt-flow rate of the graft copolymer (LDPE-g-OA) were also investigated. FTIR spectroscopy and a mass spectrum were used to characterize the structure of LDPE-g-OA. The experimental results showed that when the OA amount was 10 wt % and the DCP amount was 0.4 wt % based on the LDPE the percentage of grafting of LDPE-g-OA, prepared by maintaining the temperature at 170

Crosslinked sodium polyacrylate as a superabsorbent was prepared by inverse suspension polymerization with cyclohexane as the continuous phase and sorbite anhydride monostearic acid ester (span-80) as the dispersant. The crosslinking degree was regulated by NaOH. The distilled water absorbency (WA) of the polymer gel was about 700 times its own weight if the gel was allowed to swell at roomtemperature for 24 h. WA under various conditions, such as varying pH, temperature, reaction time, neutralization, and cyclohexane concentration, was investigated and optimized. Our results revealed that the optimal reaction conditions were 55

The intrachain and interchain hydrogen bonding of poly (N-isopropylacrylamide) (PNIPA) and intermolecular hydrogen bonding between PNIPA chains and the solvent molecules in the mixed solvent of methanol and water have been quantitatively investigated by using Fourier transform infrared (FTIR) spectroscopy at 25℃ In this spectroscopic system with curve fitting program, we found that in the C-H stretching region, both the N-isopropyl group and the backbone underwent conformational change upon the solvent composition. An analysis of the amide I band suggested that the amide groups of PNIPA were mainly involved in intermolecular hydrogen bonding with water molecules, and the polymer chains were flexible and disordered in the mixed solvent when the methanol volume fraction (Xv) was lower than 15%. While vv was in the range of 15-65%, about 30% of these intermolecular hydrogen bonding between the polymer and water were replaced by intrachain and interchain hydrogen bonding, consequently, PNIPA shrinked as aggregates. If Xv was above 65%, the interchain hydrogen bonding became predominant due to the solubility characteristics of amphiphilic methanol, and the PNIPA system was homogeneous solution again. We believe that the reentrant transition is related to the weaker interaction between PNIPA molecules and methanol–water complexes, (H2O)m(CH3OH)n (m/n=5/1, 5/2, 5/3, 5/4, 5/5) as compared to that between PNIPA and free water or free methanol.

Laser light scattering (LLS) was used to investigate the concentration dependence of intrachain and interchain associations of poly(vinyl alcohol) (PVA) in aqueous solution after different freezing-and-thawing cycles. Our results showed that if the PVA concentration (C) was much lower than its gelation concentration (Cgel), the average hydrodynamic size of the PVA chains became smaller after a cryogenic treatment, which was attributed to the change of the chain conformation from an extended coil to a compact globule because the static LLS results indicated that there was no change in the weight average molecular weight (Mw). This rules out a previously speculated degradation or scission of the PVA chains. When C was higher than Cgel, the apparent hydrodynamic size of the PVA chains was much larger and the scattering intensity became much stronger after the same cryogenic treatment, indicating the interchain association.