ABSTRACT:Crosslinked poly( N-isopropylacrylamide) (PNIPA) gels with different crosslink densities in the form of rods and beads were prepared by free-radical crosslinking copolymerization. Solution and inverse suspension polymerization techniques were used for the gel synthesis. The gels were utilized to concentrate dilute aqueous solutions of penicillin G acylase (PGA), bovine serum albumin (BSA), and 6-aminopenicillanic acid (6-APA). The discontinuous volume transition at 34ЊC observed in the gel swelling was used as the basis of concentrating dilute aqueous protein solutions. PNIPA gels formed below 18ЊC were homogeneous, whereas those formed at higher temperatures exhibited heterogeneous structures. The water absorption capacity of PNIPA gels in the form of beads was much higher, and their rate of swelling was much faster than the rod-shaped PNIPA gels. It was also found that the polymerization techniques used significantly affect the properties of PNIPA gels. The separation efficiency decreased when the protein molecules PGA or BSA in the external solution were replaced with small-molecular-weight compounds, such as 6-APA. The protein separation efficiency by the gel beads increased to 100% after coating the bead surfaces with BSA.

The time dependence of coil−globule collapse in atactic poly(methyl methacrylate) samples having molecular weights 6.5 × 106 and 3.3 × 106 g/mol dissolved in isoamyl acetate and n-butyl chloride were studied by dynamic light scattering. For example, a dilute solution of PMMA (6.5 × 106 g/mol) in isoamyl acetate was quenched from 61 °C (ϑ temperature) to 18.5 °C. As a result, the measured hydrodynamic radius (〈R h〉) was reduced from 42 ± 2 to 15 ± 2 nm. For the cells used in these DLS measurements the thermal equilibration time was found to be about 20 s. The transition from coil to globule in this cell was observed to take place in almost 35 s. We have found the coil-to-globule transition time to be inversely related to the depth of quench (ΔT) of the process. This transition time also increases with increase in molecular weight of the polymer chain.

The coil–globule transition for poly(methyl methacrylate) has been studied in the mixed solvent tert-butyl alcohol+water system. Two polymeric samples having molecular weights Mw=2.55×106 and Mw=4.73×106 were used. The contraction and expansion of the molecular chains were determined by viscometric measurements. The results were compared with light scattering data obtained recently for the same system. A smooth and continuous contraction was observed below the θ temperature (41.5 °C). The temperature dependence of [η] can be represented by a master curve in αη3|τ|Mw1/2 vs |τ|Mw1/2 plot, where αη3=[η(T)]/[η(θ)] is a viscosity expansion factor and τ=(T−θ)/T is the reduced temperature. A comparison of the observed globular radius with a theory for contracted coil confirmed the coil–globule transition for this system.