Highly Branched Poly(N-isopropylacrylamide)s with Imidazole End Groups Prepared by Radical Polymerization in the Presence of a Styryl Monomer Containing a Dithioester Group

Abstract

Highly branched poly(N-isopropylacrylamide) (PNIPAM) compounds were prepared by copolymerization of 3H-imidazole-4-carbodithioic acid 4-vinylbenzyl ester, 1, with N-isopropylacrylamide (NIPAM) using reversible addition−fragmentation chain transfer (RAFT) polymerization. The polymerizations proceeded well with few side reactions. An increase in the content of 1 in the monomer feed appears to increase the number of branch chains, and at the same time no evidence was obtained for the presence of substituted acrylamide chain ends that may potentially result via elimination of the dithioate group. The polymer products show a clear tendency to increased molecular weight as the extent of conversion of monomer increases, while size exclusion chromatography (SEC) profiles indicate a complex distribution of molecular weights compared to linear polymers obtained with a non-RAFT carboxylate monomer. Both NMR and viscometry indicate that, as expected, increasing the amount of 1 in the feed has the effect of increasing the degree of branching in the final product. This increase in branching reduces the intrinsic viscosity of the solutions of the highly branched polymers compared to similar linear polymers. Poly(N-isopropylacrylamide) displays a lower critical solution temperature (LCST) in aqueous solutions, and cloud point data indicate a clear effect of chain architecture on the temperature at which this transition occurs. Thus, a set of linear analogous copolymers have LCST's that, for equivalent mole fractions of imidazole content, are higher than the similar highly branched polymers. However, on complexation of copper by the imidazole groups the LCSTs of the linear and highly branched sets cannot be differentiated.

Living Radical Polymerization by the RAFT Process—A First Update

“…35 [93] NIPAM [93] 36 [94],C 37 [95],C A First reference after compound number (where given) provides a synthesis of the RAFT agent. An asterisk indicates the RAFT agent is mentioned in our previous review or has been previously described.…”

“…[227] (c) Self-condensing vinyl polymerization involves (co)polymerization of a monomer that also contains RAFT agent functionality. A recent example is hyperbranched PNIPAM prepared by copolymerization of NIPAM with 112 (Scheme 20) [93,228] and used in protein separation. [228] There have also been further studies on network formation by RAFT polymerization.…”

Thermoresponsive Poly(2-oxazoline) Block Copolymers Exhibiting Two Cloud Points: Complex Multistep Assembly Behavior

“…The temperature-induced phase transition is an entropically driven process, which is based on the increased mobility of the water molecules that are released into the bulk water upon dehydration. The cloud point temperature generally depends on various factors such as polymer concentration, 11−15 molecular weight of the polymer, [12][13][14]16 grafting 17 or branching 18 of the polymer, copolymerization with other monomers, 2,12,13,16,19−23 the architecture of the resulting copolymers, 19 and the addition of cosolvents 24,25 or cosolutes such as salts 11,26 or surfactants. 11,26 The decreased transmittance of the samples is due to the self-assembly of the partially dehydrated polymers into large, compact aggregates.…”

Multifunctional Nanostructured Polymers for Improved 19F MRI

“…Carter et al 208 RAFT SCVP, which utilises polymerisable CTAs to prepare HBPs in the absence of crosslinkers, seems to be a promising way to avoid gelation and obtain HBPs with relatively narrow Đ M . Carter et al present the earliest work on the synthesis of HBPs via RAFT SCVP.…”

“…Carter et al present the earliest work on the synthesis of HBPs via RAFT SCVP. [208][209][210] As shown in Figure 1-14, a polymerisable CTA, 4-vinylbenzylimidazole dithioate was designed and copolymerised with NIPAM to form highly-branched polymers with low Đ M value. The characteristics of HBPs could be easily tuned by using different polymerisation parameters in particular NIPAM/CTA ratio.…”