Temperature-dependent structure and dynamics of highly-branched poly(N-isopropylacrylamide) in aqueous solution

Abstract

Small-angle neutron scattering (SANS) and neutron spin-echo (NSE) have been used to investigate the temperature-dependent solution behaviour of highly-branched poly(N-isopropylacrylamide) (HB-PNIPAM). SANS experiments have shown that water is a good solvent for both HB-PNIPAM and a linear PNIPAM control at low temperatures where the small angle scattering is described by a single correlation length model. Increasing the temperature leads to a gradual collapse of HB-PNIPAM until above the lower critical solution temperature (LCST), at which point aggregation occurs, forming disperse spherical particles of up to 60 nm in diameter, independent of the degree of branching. However, SANS from linear PNIPAM above the LCST is described by a model that combines particulate structure and a contribution from solvated chains. NSE was used to study the internal and translational solution dynamics of HB-PNIPAM chains below the LCST. Internal HB-PNIPAM dynamics is described well by the Rouse model for non-entangled chains.

Long‐Chain Hyperbranched Polymers: Synthesis, Properties, and Applications

“…Furthermore, this kind of regular LCHBP via RAFT‐based SCVP process could be efficiently engineered with high‐density and hetero‐functional groups on the whole scaffold via a collection of click chemistry, making multifunctionalization and novel architecture building readily accessible . Rimmer and coworkers prepared thermoresponsive poly( N ‐isopropylacrylamide)s‐based LCHBPs via RAFT‐based SCVP and their temperature‐dependent structure and dynamics in solution were recently studied . Sumerlin et al.…”

“…Although LCHBPs now remain in a nascent stage when compared with well‐developed conventional HBPs with short subchains, many synthetic approaches have been developed . In situations where “living” or controlled polymerizations such as anionic polymerization, ring opening polymerization (ROP), nitroxide mediated polymerization (NMP), atom transfer radical polymerization (ATRP), or reversible addition‐fragmentation chain transfer (RAFT) polymerization are usually utilized to afford AB x ( x ≥ 2) or A x (B x , x ≥ 3) macromonomers bearing various reactive functional groups.…”

“…Therefore, only the specific methods that will result in LCHBPs are included herein, and are primarily categorized into two different methods (Figure ). The one is copolymerization of a small molecular inimer with comonomers, where the additional comonomers are utilized for producing linear polymeric subchains. The other is direct homopolymerization of a macromolecular inimer or abbreviated macroinimer …”

“…Moreover, LCHBPs can also be easily afforded through certain copolymerizations by using high molecular weight macromonomers or small molecular monomers, or simultaneously both, as building blocks via A 2 + B x ( x ≥ 3) or AB + AB x ( x ≥ 2) copolymerization process . Additionally, the famous self‐condensing vinyl polymerization (SCVP) usually affording conventional HBPs with short subchains has been adjusted for the preparation of LCHBPs through copolymerization of the traditional small molecular inimer with an additional comonomer, or direct homopolymerization of a macroinimer …”

Highly-ordered onion micelles made from amphiphilic highly-branched copolymers

“…It is generally accepted that a deterioration of solvent quality leads to the formation of aggregates. [42][43][44] Indeed onion micelles are formed under specific conditions and only for branch-poly(butyl methacrylate)-[ poly(butyl methacrylate)-block-poly(acrylic acid)], which is abbreviated here as HB-PBMA-PAA. (The nomenclature used here is extended to the other PnMA highly-branched cores: HB-PMMA-PAA and HB-PLMA-PAA.)…”