Multifunctional Poly(ethylene glycol): Synthesis, Characterization, and Potential Applications of Dendritic–Linear–Dendritic Block Copolymer Hybrids

Abstract

Emerging dendritic−linear−dendritic (DLD) hybrids that possess synergetic properties of linear and highly functional branched dendritic polymers are becoming important macromolecular scaffolds in fields ranging from biomedicine to nanotechnology. By exploiting pseudo-one-step polycondensation reactions, a facile and scalable synthetic methodology for the construction of highly functional DLDs has been developed. A library of three sets of DLDs exhibiting a hydrophilic linear PEG core with covalently attached hyperbranched bis-MPA blocks was synthesized up to the seventh generation with 256 reactive peripheral hydroxyl groups. The degree of branching for the hybrids was found between 0.40 and 0.59 with dispersities ranging from 1.03 to 1.88. The introduction of hyperbranched components resulted in control over or even full disruption of the crystallinity of the PEG. Postfunctionalizations of the peripheral hydroxyl groups with azides, allyls, and ATRP initiators yielded reactive intermediates. These intermediates were successfully assessed through UV-initiated thiol−ene coupling reactions for the synthesis of charged hybrids. ATRP of styrene from the pheriphery afforded amphiphilic macromolecules. Finally, their scaffolding capacity was evaluated for the fabrication of 3D networks, i.e., novel dendritic hydrogels and highly ordered breath figures.

Synthesis, nanoprecipitation and pH sensitivity of amphiphilic linear–dendritic hybrid polymers and hyperbranched-polydendrons containing tertiary amine functional dendrons

“…S28); however, hyp-polydendron synthesis using the G 1 -Br and G 2 -Br initiators propagated noticeably slower than their analogous linear-dendritic polymer reactions. S28); M w values up to 1.02 Â 10 6 g mol À1 were observed, suggesting significant contributions to the physical mass of each sample from complex branched structures containing on average 480 primary chains (18), 465 primary chains (19), 445 primary chains (20) and 417 primary chains (21). Linear semilog plots were observed within the branched polymerisations using each of the initiators, confirming first order kinetics (ESI, † Fig.…”

“…1B). When using the G 0 -Br, G 1 -Br and G 2 -Br initiators 11-13, gel formation was seen within the HPMA/EGDMA copolymerisations at this ratio but soluble hyp-polydendrons (19,20,21) were achieved at lower brancher : initiator ratios (0.90 : 1) again suggesting a lower initiator efficiency, as poor initiation will lead to fewer propagating polymer chains and a higher effective brancher : chain ratio within each reaction. When using the G 0 -Br, G 1 -Br and G 2 -Br initiators 11-13, gel formation was seen within the HPMA/EGDMA copolymerisations at this ratio but soluble hyp-polydendrons (19,20,21) were achieved at lower brancher : initiator ratios (0.90 : 1) again suggesting a lower initiator efficiency, as poor initiation will lead to fewer propagating polymer chains and a higher effective brancher : chain ratio within each reaction.…”

“…Molecular weight analyses were enabled by determining average dn/dc values (ESI, † Table S2). Each primary chain of the hyp-polydendrons 19, 20 and 21 contains a dendron initiator end group, therefore the weight average branched architectures contain approximately 65 tertiary amines (19), 90 tertiary amines (20) or 68 tertiary amine (21) chain-end functional groups. S28); M w values up to 1.02 Â 10 6 g mol À1 were observed, suggesting significant contributions to the physical mass of each sample from complex branched structures containing on average 480 primary chains (18), 465 primary chains (19), 445 primary chains (20) and 417 primary chains (21).…”

“…[10][11][12][13] In contrast, divergent growth leads to large increases in both the molecular weight of the material and its physical sample mass but an exponentially increasing number of reactions are required at the periphery of growing macromolecule, leading to difficulty in accurate attainment of each generation; 14,15a recent application of ''click'' chemistries have been shown to present options to overcome many of these synthetic issues. These include the introduction of dendrons as pendant side chains, 16,17 to produce dendronised polymers, and the placement of dendrons at linear polymer chain-ends, [18][19][20] to form linear-dendritic polymer hybrids. These include the introduction of dendrons as pendant side chains, 16,17 to produce dendronised polymers, and the placement of dendrons at linear polymer chain-ends, [18][19][20] to form linear-dendritic polymer hybrids.…”

Hyperbranched Polydendrons

“…Various DLD hybrids have been reported since and have been utilised in applications such as self-assembly to form aggregates around 200 nm [90], cell internalisation for drug delivery [91] and the formation of isoporous films and 3D networks [92].…”