Synthesis of β-cyclodextrin-Based Star Block Copolymers with Thermo-Responsive Behavior

Abstract

Star polymers are one example of three-dimensional macromolecules containing several arms with similar molecular weight connected to a central core. Due to their compact structure and their enhanced segment density in comparison to linear polymers of the same molecular weight, they have attracted significant attention during recent years. The preparation of block-arm star copolymers with a permanently hydrophilic block and an "environmentally" sensitive block, which can change its nature from hydrophilic to hydrophobic, leads to nanometer-sized responsive materials with unique properties. These polymers are able to undergo a conformational change or phase transition as a reply to an external stimulus resulting in the formation of core-shell nanoparticles, which further tend to aggregate. Star-shaped copolymers with different cores were synthesized via atom transfer radical polymerization (ATRP). The core-first method chosen as synthetic strategy allows good control over the polymer architecture. First of all the multifunctional initiators were prepared by esterification reaction of the hydroxyl groups with 2-chloropropionyl chloride. Using β-cyclodextrin as core molecules, which possess a well-defined number of functional groups up to 21, allows defining the number of arms per star polymer. In order to prepare stimuli-responsive multi-arm copolymers, containing a stimuli-responsive (poly(N-isopropylacrylamide) (PNIPAAm)) and a non-responsive block (poly(N,N-dimethylacrylamide) (PDMAAm)), consecutive ATRP was carried out. The polymers were characterized intensively using NMR spectroscopy OPEN ACCESSPolymers 2015, 7 922 and size exclusion chromatography (SEC), whereas the temperature-depending aggregation behavior in aqueous solution was determined via turbidimetry and differential scanning calorimetry (DSC).

Pyrene‐functional star polymers as fluorescent probes for nitrophenolic compounds

“…The tetra‐armed star‐shaped styrenic copolymers having pyrene side groups [ (S1‐S3)‐Pyr ] were prepared using core‐first approach (Scheme ), by which the number of arms of the star polymer could be clearly defined and would be equal to the number of the functional units on the polymerization‐initiating compound . Besides, this method provides good control on the macromolecular architecture . The tetra‐functional initiator ( 2 ) was synthesized via facile esterification and atom transfer radical addition reactions.…”

Natural cyclodextrins and their derivatives for polymer synthesis

“…Cyclodextrin allows for unusually high grafting densities as for typical well-defined multiarm initiators. Primarily, 7, 58,109 Fig . 6 The two most common approaches in preparation of CD-based monomers.…”

“…B: Copper mediated azide-alkyne coupling. Polymer Chemistry Review 14 58,110 or 21 23,64 sites are accessible but intermediate numbers were also reported. 111,112 Arms not directly involved in the polymerisation can be further modified to tailor the solubility of the initiator or attach various pendants such as sugars.…”

Dual pH‐Sensitive DOX‐Conjugated Cyclodextrin‐Core Star Nano‐Copolymer Prodrugs

“…More importantly, it is easy to form unimolecular micelle, which demonstrates a micellar behavior as a single molecule, avoiding dissociation of the micelle under dilution. Among multiarmed star copolymers, cyclodextrin (CD)‐core star copolymers are very interesting and important candidate drug carriers for drug delivery . This is because a CD‐core star polymer shows a designable and well‐defined molecular architecture, but its synthesis procedures is less tedious compared with that of a dendritic polymer.…”

“…[9,10,[16][17][18][19][20][21][22][23][24][25][26][27][28] This is because a CD-core star polymer shows a designable and well-defined molecular architecture, but its synthesis procedures is less tedious compared with that of a dendritic polymer. Through structure control, β-CD-core star polymers with 7, 14, or 21 arms could be synthesized accurately, especially after controlled/living radical polymerization and click reaction techniques were used, [9,10,[16][17][18][19][20][21][22][23][24][25][26][27][28] However, so far drug delivery systems based on CD-core star copolymers were obtained by multimolecular selfassembly, [16][17][18][19][20][21] or formation of unimolecular micelles with the help of an organic solvent. [9,10,28] There are few reports on drug-encapsulated CD-core star polymeric system, which could directly dissolve in aqueous solution without the help of an organic solvent.…”