12 research outputs found
Poly(Sarcosine)-Based Nano-Objects with Multi-Protease Resistance by Aqueous Photoinitiated Polymerization-Induced Self-Assembly (Photo-PISA)
Poly(sarcosine)
(PSar) is a non-ionic hydrophilic polypeptoid with
numerous biologically relevant properties, making it an appealing
candidate for the development of amphiphilic block copolymer nanostructures.
In this work, the fabrication of poly(sarcosine)-based diblock copolymer
nano-objects with various morphologies via aqueous reversible addition–fragmentation
chain-transfer (RAFT)-mediated photoinitiated polymerization-induced
self-assembly (photo-PISA) is reported. Poly(sarcosine) was first
synthesized via ring-opening polymerization (ROP) of sarcosine N-carboxyanhydride, using high-vacuum techniques. A small
molecule chain transfer agent (CTA) was then coupled to the active
ω-amino chain end of the telechelic polymer for the synthesis
of a poly(sarcosine)-based macro-CTA. Controlled chain-extensions
of a commercially available water-miscible methacrylate monomer (2-hydroxypropyl
methacrylate) were achieved via photo-PISA under mild reaction conditions,
using PSar macro-CTA. Upon varying the degree of polymerization and
concentration of the core-forming monomer, morphologies evolving from
spherical micelles to worm-like micelles and vesicles were accessed,
as determined by dynamic light scattering and transmission electron
microscopy, resulting in the construction of a detailed phase diagram.
The resistance of both colloidally stable empty vesicles and enzyme-loaded
nanoreactors against degradation by a series of proteases was finally
assessed. Overall, our findings underline the potential of poly(sarcosine)
as an alternative corona-forming polymer to poly(ethylene glycol)-based
analogues of PISA assemblies for use in various pharmaceutical and
biomedical applications
Block Copolymers of Macrolactones/Small Lactones by a "Catalyst-Switch" Organocatalytic Strategy. Thermal Properties and Phase Behavior
Poly(macrolactones) (PMLs) can be considered as biodegradable alternatives of polyethylene; however, controlling the ring-opening polymerization (ROP) of macrolactone (ML) monomers remains a challenge due to their low ring strain. To overcome this problem, phosphazene (t-BuP_4), a strong superbase, has to be used as catalyst. Unfortunately, the one-pot sequential block copolymerization of MLs with small lactones (SLs) is impossible since the high basicity of t-BuP_4 promotes both intra- and intermolecular transesterification reactions, thus leading to random copolymers. By using ROP and the “catalyst-switch” strategy [benzyl alcohol, t-BuP_4/neutralization with diphenyl phosphate/(t-BuP_2)], we were able to synthesize different well-defined PML-b-PSL block copolymers (MLs: dodecalactone, ω-pentadecalactone, and ω-hexadecalactone; SLs: δ-valerolactone and ε-caprolactone). The thermal properties and the phase behavior of these block copolymers were studied by differential scanning calorimetry and X-ray diffraction spectroscopy. This study shows that the thermal properties and phase behavior of PMLs-b-PSLs are largely influenced by the PMLs block if PMLs components constitute the majority of the block copolymers
Block Copolymers of Macrolactones/Small Lactones by a "Catalyst-Switch" Organocatalytic Strategy. Thermal Properties and Phase Behavior
Poly(macrolactones) (PMLs) can be considered as biodegradable alternatives of polyethylene; however, controlling the ring-opening polymerization (ROP) of macrolactone (ML) monomers remains a challenge due to their low ring strain. To overcome this problem, phosphazene (t-BuP_4), a strong superbase, has to be used as catalyst. Unfortunately, the one-pot sequential block copolymerization of MLs with small lactones (SLs) is impossible since the high basicity of t-BuP_4 promotes both intra- and intermolecular transesterification reactions, thus leading to random copolymers. By using ROP and the “catalyst-switch” strategy [benzyl alcohol, t-BuP_4/neutralization with diphenyl phosphate/(t-BuP_2)], we were able to synthesize different well-defined PML-b-PSL block copolymers (MLs: dodecalactone, ω-pentadecalactone, and ω-hexadecalactone; SLs: δ-valerolactone and ε-caprolactone). The thermal properties and the phase behavior of these block copolymers were studied by differential scanning calorimetry and X-ray diffraction spectroscopy. This study shows that the thermal properties and phase behavior of PMLs-b-PSLs are largely influenced by the PMLs block if PMLs components constitute the majority of the block copolymers
Well-Defined Cyclic Triblock Terpolymers: A Missing Piece of the Morphology Puzzle
Two well-defined
cyclic triblock terpolymers, missing pieces of
the terpolymer morphology puzzle, consisting of poly(isoprene), polystyrene,
and poly(2-vinylpyridine), were synthesized by combining the Glaser
coupling reaction with anionic polymerization. An α,ω-dihydroxy
linear triblock terpolymer (OH-PI<sub>1,4</sub>-<i>b</i>-PS-<i>b</i>-P2VP-OH) was first synthesized followed by
transformation of the OH to alkyne groups by esterification with pentynoic
acid and cyclization by Glaser coupling. The size exclusion chromatography
(SEC) trace of the linear terpolymer precursor was shifted to lower
elution time after cyclization, indicating the successful synthesis
of the cyclic terpolymer. Additionally, the SEC trace of the cyclic
terpolymer produced, after cleavage of the ester groups, shifted again
practically to the position corresponding to the linear precursor.
The first exploratory results on morphology showed the tremendous
influence of the cyclic structure on the morphology of terpolymers
Anionic Polymerization of Styrene and 1,3-Butadiene in the Presence of Phosphazene Superbases
The anionic polymerization of styrene and 1,3-butadiene in the presence of phosphazene bases (t-BuP4, t-BuP2 and t-BuP1), in benzene at room temperature, was studied. When t-BuP1 was used, the polymerization proceeded in a controlled manner, whereas the obtained homopolymers exhibited the desired molecular weights and narrow polydispersity (Ð < 1.05). In the case of t-BuP2, homopolymers with higher than the theoretical molecular weights and relatively low polydispersity were obtained. On the other hand, in the presence of t-BuP4, the polymerization of styrene was uncontrolled due to the high reactivity of the formed carbanion. The kinetic studies from the polymerization of both monomers showed that the reaction rate follows the order of [t-BuP4]/[sec-BuLi] >>> [t-BuP2]/[sec-BuLi] >> [t-BuP1]/[sec-BuLi] > sec-BuLi. Furthermore, the addition of t-BuP2 and t-BuP1 prior the polymerization of 1,3-butadiene allowed the synthesis of polybutadiene with a high 1,2-microstructure (~45 wt %), due to the delocalization of the negative charge. Finally, the one pot synthesis of well-defined polyester-based copolymers [PS-b-PCL and PS-b-PLLA, PS: Polystyrene, PCL: Poly(ε-caprolactone) and PLLA: Poly(L-lactide)], with predictable molecular weights and a narrow molecular weight distribution (Ð < 1.2), was achieved by sequential copolymerization in the presence of t-BuP2 and t-BuP1
Core Cross-Linked Multiarm Star Polymers with Aggregation-Induced Emission and Temperature Responsive Fluorescence Characteristics
Aggregation-induced emission (AIE)
active core cross-linked multiarm
star polymers, carrying polystyrene (PS), polyethylene (PE), or polyethylene-<i>b</i>-polycaprolactone (PE-<i>b</i>-PCL) arms, have
been synthesized through an “arm-first” strategy, by
atom transfer radical copolymerization (ATRP) of a double styrene-functionalized
tetraphenylethene (TPE-2St) used as a cross-linker with linear arm
precursors possessing terminal ATRP initiating moieties. Polyethylene
macroinitiator (PE–Br) was prepared via the polyhomologation
of dimethylsulfoxonium methylide with triethylborane followed by oxidation/hydrolysis
and esterification of the produced PE–OH with 2-bromoisobutyryl
bromide; polyethylene-<i>block</i>-poly(ε-caprolactone)
diblock macroinitiator was derived by combining polyhomologation with
ring-opening polymerization (ROP). All synthesized star polymers showed
AIE-behavior either in solution or in bulk. At high concentration
in good solvents (e.g., THF, or toluene) they exhibited low photoluminescence
(PL) intensity due to the inner filter effect. In sharp contrast to
the small molecule TPE-2St, the star polymers were highly emissive
in dilute THF solutions. This can be attributed to the cross-linked
structure of poly(TPE-2St) core which restricts the intramolecular
rotation and thus induces emission. In addition, the PL intensity
of PE star polymers in THF(solvent)/<i>n</i>-hexane(nonsolvent)
mixtures, due to their nearly spherical shape, increased when the
temperature decreased from 55 to 5 °C with a linear response
in the range 40–5 °C
A Novel Poly(vinylidene fluoride)-Based 4‑Miktoarm Star Terpolymer: Synthesis and Self-Assembly
A well-defined
amphiphilic miktoarm polymer incorporating poly(vinylidene fluoride)
(PVDF), polystyrene (PS), and poly(ethylene glycol) (PEG) blocks was
synthesized via a combination of atom-transfer radical polymerization
(ATRP), iodine transfer radical polymerization (ITP), and copper-catalyzed
azide–alkyne cycloaddition (CuAAC). Morphology and self-assembly
of this star polymer were examined in organic solvents and in water.
The aggregates formed in water were found to possess unusual frustrated
topology due to immiscibility of PS and PVDF. The polymer was evaluated
for transport of small hydrophobic molecules in water