One-step RAFT synthesis of well-defined amphiphilic star polymers and their self-assembly in aqueous solution

Abstract

Multifunctional chain transfer agents for RAFT polymerisation were designed for the one-step synthesis of amphiphilic star polymers. Thus, hydrophobically end-capped 3-and 4-arm star polymers, as well as linear ones for reference, were made of the hydrophilic monomer N,N-dimethylacrylamide (DMA) in high yield with molar masses up to 150 000 g mol À1, narrow molar mass distribution (PDI # 1.2) and high end group functionality ($90%). The associative telechelic polymers form transient networks of interconnected aggregates in aqueous solution, thus acting as efficient viscosity enhancers and rheology modifiers, eventually forming hydrogels. The combination of dynamic light scattering (DLS), small angle neutron scattering (SANS) and rheology experiments revealed that several molecular parameters control the structure and therefore the physical properties of the aggregates. In addition to the size of the hydrophilic block (maximum length for connection) and the length of the hydrophobic alkyl chain ends (stickiness), the number of arms (functionality) proved to be a key parameter.

Synthesis and characterization of “Living” star‐shaped poly(N‐vinylcaprolactam) with four arms and carboxylic acid end groups

“…3(a)]. The OAH stretching of carboxylic acid peak in CTA-1 appears as a broad peak between 2459 and 3370 cm 21 . The bands at 1735 and at 1704 cm 21 can be ascribed to the stretching of carbonyl groups of the ester and carboxylic acid in the CTA structure.…”

“…The bands at 1735 and at 1704 cm 21 can be ascribed to the stretching of carbonyl groups of the ester and carboxylic acid in the CTA structure. The more characteristic bands in the spectrum of the CTA-1 corresponded to the moiety C@S at 1045 cm 21 and to the stretching of CAS at 819 cm…”

“…[8][9][10][11] The core-first strategy enables two distinct synthetic routes: the Z-group approach in which thiocarbonylthio groups are linked to the core via the "stabilizing" Z-group of the chain transfer agent (CTA), [8][9][10][11][12][13][14][15][16][17][18] and the R-group approach, in which the thio entity is attached to the core via the "leaving" R-group of the CTA. [19][20][21] On the other hand, over the last decade, particular attention has been given to temperature-sensitive polymers because of their potential applications. Two of the most studied thermosensitive polymers are poly(N-isopropylacrylamide) (PNIPAM) 22 and poly(N-vinylcaprolactam) (PNVCL) 23,24 ; both polymers are water-soluble below their LCST, are nonionic, and exhibit a LCST around the physiological range (Fig.…”

“…21,[39][40][41][42][43] The molar absorptivity of the CTA is used for polymer molar mass calculation. As an example, the thiocarbonylthio moiety in the trithiocarbonate have a molar absorptivity (e) well above 10,000 LÁmol…”

Well-Defined PDMAEA Stars via Cu(0)-Mediated Reversible Deactivation Radical Polymerization

“…[46][47][48][49][50] In comparison to their linear counterparts, star polymers possess additional properties thanks to their compact structures and high arm density. 47,51 The major challenge in the synthesis of well-defined star polymers is bimolecular termination due to starstar coupling.…”