Cover Picture: Macromol. Rapid Commun. 9/2006

Abstract

Cover: Quartz crystal microbalance with dissipation monitoring is used to probe the effect of salt concentration on the phase transition behavior of thermoresponsive surface-grafted poly(N-isopropylacrylamide) (PNIPAM) brushes brushes. The phase transition temperature of grafted polymer is found to decrease as the concentration of salt is increased. This depression in phase transition temperature is similar to that observed for free polymer and is attributed to unbinding of the water molecules from the PNIPAM by the presence of ions. Further details can be found in the article

Swelling Behavior of Multiresponsive Poly(methacrylic acid)‐block‐‐poly(N‐isopropylacrylamide) Brushes Synthesized Using Surface‐Initiated Photoiniferter‐Mediated Photopolymerization

“…Although the LCST behavior of free PNIPAM chains in water is distinguished by a relatively sharp transition at $32 8C, in agreement with reports by Genzer et al [29] we observe a broadening of the transition, and a lower transition temperature due to added ions. (As noted in Section 4, the ionic strength of the buffer solutions is 154 mM.)…”

“…Similarly, as shown in Figure 6b, the swelling ratio decreases slightly at 40 8C and substantially at 28 8C and 30 8C as the ionic strength of the pH ¼ 5 buffer solutions is increased from 40 mM to 200 mM. The decreases in swelling ratios at 28 8C and 30 8C (around the LCST of PNIPAM) are primarily indicative of depression of the LCST of PNIPAM with increasing ionic strength, which is consistent with the observations of Genzer et al [29] On the other hand, the decreases in swelling ratios at 40 8C could be a combined effect of ionic strength impacting both the PMAA and PNIPAM blocks. However, at this stage it is not possible to speculate on the relative contribution of each individual block to overall swelling.…”

“…of PNIPAM. [29] Also, added salts play a complex and crucial role in the swelling behavior of weak polyelectrolytes: at low ionic strength (the so-called ''osmotic brush'' regime) and as salt is added, a weak PE brush will increase its height until the internal salt concentration equals the external salt concentration. When the ''salted brush'' regime is reached, the weak PE brush will shrink as the ionic strength is increased.…”

“…Polymer brushes have been widely used as well-defined model systems to study structure-property relationships because tethering the chain to the surface provides the opportunity to study chain stretching as a function of tethering density, molecular weight, solvent quality, pH, salt concentration (ionic strength) and temperature. [1,2,8,[19][20][21][22][23][24][25][26][27][28][29][30] In this work, we report the use of surface-initiated, photoiniferter-mediated photopolymerization (SI-PMP) to create homopolymer and block copolymer brushes of poly(methacrylic acid) (PMAA) and poly(N-isopropylacrylamide) (PNIPAM). SI-PMP has certain advantages over other surface-initiated controlled radical polymerization techniques, such as atom transfer radical polymerization (ATRP), nitroxide-mediated free-radical polymerization (NMP) and reversible addition fragmentation transfer (RAFT), because SI-PMP can be carried out at room temperature and is amenable to lithographic methods for readily creating FULL PAPER Surface-initiated photoiniferter-mediated photopolymerization (SI-PMP) in presence of tetraethylthiuram disulfide is used to directly synthesize surface-grafted poly(methacrylic acid)-block-poly(N-isopropylacrylamide) (PMAA-b-PNIPAM) layers.…”

“…These studies indicate that the LCST of homo-PNIPAM brushes depends upon the molecular weight and grafting density of chains: [27,30] the swollencollapsed transition is more pronounced for PNIPAM brushes of higher molecular weight and grafting density. Genzer et al [29] showed that the LCST of PNIPAM brushes decreases as the concentration of salt in solution increases.…”