Synthesis and Characterization of Star-Shaped Poly(ethylene-co-propylene) Polymers Bearing Terminal Self-Complementary Multiple Hydrogen-Bonding Sites

Synthesis of telechelic polyolefins

A comprehensive review of all the methodologies developed for the synthesis of telechelic polyolefins is reported.

Physically cross-linked polyethylene via reactive extrusion

Ureidopyrimidinone (UPy) is introduced into various polyethylenes (PEs) bearing hydroxyl groups by solution grafting, affording physically cross-linked PE via multiple H-bonding.

Self-assembly of magnetically functionalized star-polymer nano-colloids

We explore the potential of star-polymers that carry super-paramagnetic nano-particles as end-groups with respect to the single-molecule self-assembly process. With the aid of molecular dynamics simulation, the configurations of these macromolecules are analyzed as a function of functionality, magnetic interaction strength, and the length of the polymeric arms. By means of an external magnetic field the nano-particles can be controlled to form static or dynamic dipolar chains, resulting in conformations of isolated stars that can be characterized by the average number of chains and length. The single-molecule conformation diagram in the plane of magnetic interaction strength vs. the star-functionality is obtained. Further, the molecules are characterized by means of various shape and size order parameters.

Heteromer Nanostars by Spontaneous Self-Assembly

Heteromer star-shaped nanoparticles have the potential to carry out therapeutic agents, improve intracellular uptake, and safely release drugs after prolonged periods of residence at the diseased site. A one-step seed mediation process was employed using polylactide-co-glycolic acid (PLGA), polyvinyl alcohol (PVA), silver nitrate, and tetrakis(hydroxymethyl)phosphonium chloride (THPC). Mixing these reagents followed by UV irradiation successfully produced heteromer nanostars containing a number of arm chains attached to a single core with a high yield. The release of THPC from heteromer nanostars was tested for its potential use for breast cancer treatment. The nanostars present a unique geometrical design exhibiting a significant intracellular uptake by breast cancer cells but low cytotoxicity that potentiates its efficacy as drug carriers.

Association of star-shaped poly(D,L-lactide)s containing nucleobase multiple hydrogen bonding

A new family of associating polymers based on four-arm, star-shaped poly(D,L-lactide) (PDLLA) containing peripheral complementary hydrogen-bonding sites is described. Hydroxy-terminated, four-arm, star-shaped PDLLAs of controlled molar mass were functionalized with complementary DNA base pairs, adenine (A) and thymine (T), to obtain PDLLA-A and PDLLA-T, respectively. 1H NMR spectroscopy confirmed quantitative functionalization and the subsequent formation of PDLLA-A and PDLLA-T hydrogen-bonded complexes. Job's analysis revealed a 1:1 optimal stoichiometry for the hydrogen-bonded complexes, and the association constant (Ka) that was determined using the 1H NMR-based Benesi-Hildebrand treatment was 84 M(-1) for the low molar mass complementary polymers. Furthermore, the PDLLA-based hydrogen-bonded complexes exhibited higher solution viscosities compared to the corresponding non-hydrogen-bonded precursors, which further confirmed strong complementary multiple-hydrogen-bonding associations between the star-shaped polymers with terminal adenine and thymine groups. Moreover, variable-temperature 1H NMR studies demonstrated the thermoreversibility of the hydrogen-bonded PDLLA-based complexes in solution.

Synthesis and self-assembly behavior of four-arm poly(ethylene oxide)-b-poly(2-(diethylamino)ethyl methacrylate) star block copolymer in salt solutions

A well-defined block copolymer consisting of four-arm poly(ethylene oxide)-b-poly(2-(diethylamino)ethyl methacrylate) (four-arm PEO56-b-PDEAEMA74) was synthesized by atom transfer radical polymerization. The pH-responsive self-assembly behavior was examined by potentiometric titration, surface tensiometry, laser light scattering, and transmission electron microscopy over the course of dissociation by the addition of a base or acid. The apparent hydrodynamic radius (Rh) of the micelle increased from 21 to 56 nm when the degree of protonation of the amine groups was increased from 0 to 0.5 in 0.01 M NaCl solution. In higher concentration NaCl solution, the micelle shrank due to the electrostatic charge screening of the protonated DEAEMA groups. At low pH, the micelles dissociated into unimers.