Characterization of Linear Poly(N-isopropylacrylamide) and Cloud Points in its Aqueous Solutions

Abstract

The second virial coefficient A 2 and intrinsic viscosity [] were determined in methanol at 25.0 C for poly(Nisopropylacrylamide) (PNIPA) samples synthesized by living anionic polymerization in the range of weight-average molecular weight M w from 4:91 Â 10 3 to 7:23 Â 10 4 , which are called L samples, and also for those by radical polymerization in tert-butanol and benzene by the use of azobis(isobutyronitrile) as an initiator in the range of M w from 1:23 Â 10 4 to 7:83 Â 10 4 , which are called T and B samples, respectively. It is found for both A 2 and [] that their values for the three kinds of samples agree well with each other in the range of M w. 3 Â 10 4 but deviate from each other as M w is increased from 3 Â 10 4 , the value for the L sample being the largest and that for the B sample the smallest. The result is consistent with the fact that the average chain dimension is the largest for the L sample having no branch point and the smallest for the B sample having the largest number of branch points. From a simultaneous analysis of A 2 and [] for the L samples on the basis of the Kratky-Porod wormlike chain with excluded volume, the stiffness parameter À1 is estimated to be 18 Å , which is almost the same as those determined for typical flexible polymers. For the L samples, the cloud point was also determined in their aqueous solutions in the range of the weight fraction w of PNIPA from ca. 0.5 to ca. 10%. It is found that the cloud point in the range of w & 2% decreases from ca. 32 C to ca. 18 C as M w is decreased from 7:23 Â 10 4 to 5:47 Â 10 3. Such behavior may be regarded as arising from effects of hydrophobic chain end groups of the L samples.

Multitemperature Responsive Self‐Folding Soft Biomimetic Structures

“…Literature LCST values of PDEGMA, POEGMA 300, and POEGMA 500 aqueous solution are ≈26, ≈64, and ≈90 °C, respectively. Our VTT values are lower and we note that the LCST is known to be affected by many factors, including polymer concentration and type of initiator. In addition, the LCST is generally measured with dilute polymer solutions (typically less than 1%), but our concentrations are estimated to be on the order of 10%.…”

Solid–liquid separations with a temperature-responsive polymeric flocculant: Effect of temperature and molecular weight on polymer adsorption and deposition

“…The point of incipient phase separation is a function of molecular weight, such that the LCST increases with decreasing molecular weight. The effect is only important for molecular weights below $5 Â 10 4 g/mol [9,16,[27][28][29]. When the molecular weight is very large, there is little influence of molecular weight so this factor is of little importance in the high-molecular weight polymers investigated in this study.…”

Temperature responsive flocculation and solid–liquid separations with charged random copolymers of poly(N-isopropyl acrylamide)

“…Even at 50°C, there is negligible settling observed for suspensions dosed with co-ionic PNIPAMs. The increase in settling rate that occurs when a suspension dosed with PNIPAM is heated above the LCST is a result of the phase separation attributed to the difference in free volume of the polymer and aqueous solvent [6,[31][32][33][34][35][36][37][38]. The polymer that has adsorbed on the surface at T below the LCST becomes insoluble as the temperature is raised and acts as a nucleation site for additional polymer deposition at T > LCST [4,39,40].…”