Smart materials are capable of varying their physical properties in response to environmental changes or stimuli. Such stimuli include temperature, pH, solvent composition, and electric field strength. In particular, smart hydrogels, which change their shrinking and swel領(lǐng) characteristics in response to external stimuli, have been studied for use in engineering and biomedical applications, such as controlled drug release. Poly(n-isopropylacrylamide) (PNIPAM) gel is an important smart hydrogel that responds to temperature changes. PNIPAM gels exhibit negative thermosensitivity, meaning that they undergo a significant level of shrinkage with increasing temperature. Precise control over a hydrogels shrinking and swel領(lǐng) characteristics is desirable since this may lead to control over its drug release/ uptake properties. Among other important properties that affect the thermosensitivity of PNIPAM, such as particle structure and size, a key characteristic is the molecular weight distribution. The molecular weight distributions of two PNIPAM polymers were accurately measured by means of GPC with online viscometry, allowing application of the universal calibration technique. This method permits an accurate calibration of the GPC system based upon molecular size in solution (using the relationship between the viscosity of the eluting polymer and its molecular weight). This in turn allows accurate molecular weights to be calculated even though the polymer standards used are not chemically identical to the polymer under investigation, as the column is separating on size not molecular weight. As a result, the molecular weight data usually obtained via this technique are very accurate, in contrast to conventional GPC employing a concentration detector only (eg UV, RI), which provides molecular weight data relative to the polymer calibration standards used. The 390-MDS can be used to provide accurate molecular weights for polymers of unusual structure by employing differen Agilent 1260 Infinity II 液相色譜系統(tǒng)