141 research outputs found
Stereoregulation, molecular weight, and dispersity control of PMMA synthesized via free-radical polymerization supported by the external high electric field
We show the remarkable effect of using static (DC) and alternating (AC) electric fields to control the free-radical polymerization of methyl methacrylate (MMA). The magnitude and/or frequency of the applied electric field (up to 154 kV cm−1) were found to control the molecular weight, dispersity, and stereochemistry of the produced polymers
Free-radical polymerization of 2-hydroxyethyl methacrylate (HEMA) supported by a high electric field
In macromolecular science, tuning basic polymer parameters like molecular weight (Mn) or molecular
weight distribution (dispersity, Đ) is an active research topic. Many prominent synthetic protocols concerning
the chemical modification of a polymerization mixture (adding additional reagents) and equipment
modification have been adopted for this purpose. On the other hand, less attention has been paid
to studying the impact of external stimuli such as pressure, light, and spatial restrictions on the properties
of resulting polymers. Here, we present a robust synthetic protocol in which a high electric field (an external
factor) supports the thermally-induced free-radical polymerization (FRP) of 2-hydroxyethyl methacrylate
(HEMA). The reactions were conducted with 0.1 wt% of 2’-azobisisobutyronitrile (AIBN) in the presence
of high dc (direct current) electric fields with various magnitudes ranging from 0 kV cm−1 to 140 kV
cm−1. By combining dielectric spectroscopy, nuclear magnetic resonance spectroscopy, exclusion
chromatography, and differential scanning calorimetry, we have explored the effect of an external electric
field on the progress of polymerization (via dielectric spectroscopy) and product characteristics. We
found that HEMA FRP supported by a high dc voltage results in charged macromolecules (polyelectrolytes)
with high conductivity ∼ 10−10 S cm−1 at a glass transition temperature, markedly reduced molecular
weight of Mn ≈41–58 kg mol−1 (E > 14 kV cm−1), and low/moderate Đ ∼ 1.1–1.3, which is an unexpected
finding for non-controlled free radical polymerization. In contrast, the polymer produced in the absence
of an electric field was characterized by Mn ≈ 103 kg mol−1 and much higher Đ = 1.73. Therefore, we
found that the electric field can be another efficient external factor such as a spatial restriction or compression
that allows for fine-tuning of polymer properties
Pressure-assisted solvent- and catalyst-free production of well-defined poly(1-vinyl-2-pyrrolidone) for biomedical applications
In this work, we developed a fast, highly efficient, and environmentally friendly catalytic systemfor classical freeradical
polymerization (FRP) utilizing a high-pressure (HP) approach. The application of HP for thermallyinduced,
bulk FRP of 1-vinyl-2-pyrrolidone (VP) allowed to eliminate the current limitation of ambientpressure
polymerization of ‘less-activated’ monomer (LAM), characterized by the lack of temporal control
yielding polymers of unacceptably large disperisites and poor result reproducibility. By a simple manipulation
of thermodynamic conditions (p ¼ 125–500 MPa, T ¼ 323–333 K) and reaction composition (twocomponent
system: monomer and low content of thermoinitiator) well-defined poly(1-vinyl-2-pyrrolidone)s
(PVP) in a wide range of molecular weights and low/moderate dispersities (Mn ¼ 16.2–280.5 kg mol 1, Đ ¼
1.27–1.45) have been produced. We have found that HP can act as an ‘external’ controlling factor that
warrants the first-order polymerization kinetics for classical FRP, something that was possible so far only for
reversible deactivation radical polymerization (RDRP) systems. Importantly, our synthetic strategy adopted for
VP FRP enabled us to obtain polymers of very high Mn in a very short time-frame (0.5 h). It has also been
confirmed that VP bulk polymerization yields polymers with significantly lower glass transition temperatures
(Tg) and different solubility properties in comparison to macromolecules obtained during the solvent-assisted
reaction
Ex-smokers with and without COPD: Investigating CT Pulmonary Vascular, Airway, Pulmonary Artery and Aorta Measurements
RATIONALE: Pulmonary hypertension is characterized by increased pressure in the pulmonary artery, and is a key contributor to worsening symptoms in individuals with chronic obstructive pulmonary disease (COPD). The pulmonary artery to aorta diameter ratio (PA:Ao), measured using computed tomography (CT), is a biomarker of pulmonary hypertension; however, longitudinal changes in this measurement and its relationship to pulmonary vascular and airway structural changes is not well understood. Our objective was to investigate longitudinal changes in PA:Ao and its relationship with CT pulmonary vascular and airway abnormalities, airflow limitation and exercise-capacity
The unique role of pore wall nanostructurization in the intrachannel photo-ATRP for fine-tuning PMMA tacticity
Impact of imidazolium-based ionic liquids on the curing kinetics and physicochemical properties of nascent epoxy resins
We investigated the influence of anion type (salicylate, [(MOB)MIm][Sal], vs chloride, [(MOB)MIm][Cl]) of imidazolium-based ionic liquid (IL) and its content on the curing kinetics of bisphenol A diglicydyl ether (DGEBA of molecular weight Mn = 340 g/mol). Further physicochemical properties (i.e., glass transition temperature, Tg, and conductivity, σdc) of produced polymers were investigated. The polymerization of the studied systems was examined at various molar ratios (1:1, 10:1, and 20:1) at different reaction temperatures (Treaction = 353–383 K) by using differential scanning calorimetry (DSC). Interestingly, both DGEBA/IL compositions studied herein revealed significantly different reaction kinetics and yielded materials of completely distinct physical properties. Surprisingly, in contrast to [(MOB)MIm][Cl], for the low concentration of [(MOB)MIm][Sal] in the reaction mixture, an additional step in the kinetic curves, likely due to the combined enhanced initiation activity of anion (salicylate)–cation (imidazolium-based), was noted. To thoroughly analyze the kinetics of all studied systems, including the two-step kinetics of DGEBA/[(MOB)MIm][Sal], we applied a new approach that relies on the combination of the two phenomenological Avrami equations. Analysis of the determined constant rates revealed that the reaction occurring in the presence of the salicylate anion is characterized by higher activation energy with respect to those with the chloride. Moreover, DGEBA/[(MOB)MIm][Sal] cured materials have higher Tg in comparison to DGEBA polymerized with [(MOB)MIm][Cl] independent of the IL concentration. This fact might indicate that, most likely, the products of hardening are highly cross-linked (high Tg) or oligomeric linear polymers (low Tg) in the former and latter cases, respectively. Such a change in the chemical structure of the polymer is also reflected in the dc conductivity measured at the glass transition temperature, which is much higher for DGEBA cured with [(MOB)MIm][Cl]. Herein, we have clearly demonstrated that the type of anion has a crucial impact on the polymerization mechanism, kinetics, and properties of produced materials
Correlation between locally ordered (hydrogen-bonded) nanodomains and puzzling dynamics of polymethysiloxane derivative
We examined the behavior of poly(mercaptopropyl)methylsiloxane
(PMMS), characterized by a polymer chain backbone of alternate
silicon and oxygen atoms substituted by a polar pendant group able to form
hydrogen bonds (−SH moiety), by means of infrared (FTIR) and dielectric
(BDS) spectroscopy, differential scanning calorimetry (DSC), X-ray diffraction
(XRD), and rheology. We observed that the examined PMMS forms relatively
efficient hydrogen bonds leading to the association of chains in the form of
ordered lamellar-like hydrogen-bonded nanodomains. Moreover, the recorded
mechanical and dielectric spectra revealed the presence of two relaxation
processes. A direct comparison of collected data and relaxation times extracted
from two experimental techniques, BDS and rheology, indicates that they
monitor different types of the mobility of PMMS macromolecules. Our
mechanical measurements revealed the presence of Rouse modes connected to
the chain dynamics (slow process) and segmental relaxation (a faster process),
whereas in the dielectric loss spectra we observed two relaxation processes related most likely to either the association−dissociation
phenomenon within lamellar-like self-assemblies or the sub-Rouse mode (α′-slower process) and segmental (α-faster process)
dynamics. Data presented herein allow a better understanding of the peculiar dynamical properties of polysiloxanes and associating
polymers having strongly polar pendant moieties
High pressure as a novel tool for the cationic ROP of γ-butyrolactone
In this study, we report the acid-catalyzed and high pressure assisted ring-opening polymerization (ROP) of
g-butyrolactone (GBL). The use of a dually-catalyzed approach combining an external physical factor and
internal catalyst (trifluoromethanesulfonic acid (TfOH) or p-toluenesulfonic acid (PTSA)) enforced ROP of
GBL, which is considered as hardly polymerizable monomer still remaining a challenge for the modern
polymer chemistry. The experiments performed at various thermodynamic conditions (T ¼ 278–323 K
and p ¼ 700–1500 MPa) clearly showed that the high pressure supported polymerization process led to
obtaining well-defined macromolecules of better parameters (Mn ¼ 2200–9700 g mol 1; Đ ¼ 1.05–1.46)
than those previously reported. Furthermore, the parabolic-like dependence of both the molecular
weight (MW) and the yield of obtained polymers on variation in temperature and pressure at either
isobaric or isothermal conditions was also noticed, allowing the determination of optimal conditions for
the polymerization process. However, most importantly, this strategy allowed to significantly reduce the
reaction time (just 3 h at room temperature) and increase the yield of obtained polymers (up to 0.62
gPGBL/gGBL). Moreover, despite using a strongly acidic catalyst, synthesized polymers remained non-toxic
and biocompatible, as proven by the cytotoxicity test we performed in further analysis. Additional
investigation (including MALDI-TOF measurements) showed that the catalyst selection affected not only
MW and yield but also the linear/cyclic form content in obtained macromolecules. These findings show
the way to tune the properties of PGBL and obtain polymer suitable for application in the biomedical
industry
Sugar decorated star-shaped (co)polymerswith resveratrol-based core – physicochemicaland biological properties
Star-shaped glycopolymers due to the attractive combination of the physicochemical, morphological, self-assembly properties along with biological activity have gained increased attention as innovative agents in novel cancer therapies. Unfortunately, the production of these highly desirable biomaterials remains a challenge in modern macromolecular chemistry. The main reason for that is the low polymerizability of ionic glycomonomers originated from their steric congestion and the occurrence of ionic interactions that generally negatively influence the polymerization progress and hinder controllable reaction pathway. In this work, the new ionic sugar monomer was (co)polymerized for the first time via Activator Generated by Electron Transfer Atom Transfer Radical Polymerization (AGET ATRP) using a three-arm resveratrol-based core to obtain star-like (co)polymers. The obtained products were examined in terms of their physicochemical properties and morphology. Aside from the synthesis of these new glycopolymers, also a thorough description of their thermal properties, ability to self-assembly, the formation of stable superstructures was studied in detail. It was found that examined (co)polymers did not show any heterogeneities and phase separation, while their variation of glass transition temperature (Tg) was strictly related to the change in the number of glycomonomer. Also, the stability and shapes of formed superstructures strictly depend on their composition and topology. Finally, we have shown that synthesized carbohydrate-based polymers revealed high antiproliferative activity against several cancer cell lines (i.e., breast, colon, glioma, and lung cancer). The cytotoxic activity was particularly observed for star-shaped polymers that were systematically enhanced with the growing concentration of amine moieties and molecular weight. The results presented herein suggest that synthesized star-shaped glyco(co)polymers are promising as drug or gene carriers in anticancer therapies or anti-tumor agents, depending on their cytotoxicity.
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Synthetic strategy matters : the study of a different kind of PVP as micellar vehicles of metronidazole
Poly(1-vinyl-2-pyrrolidone) (Povidone, PVP) is one of the most interesting and versatile synthetic polymers utilised in the pharmaceutical and cosmetic industries. Its large-scale commercial production offers an assortment of products in a wide range of molecular weights but poorly-controlled (macro)structural parameters (i.e., dispersity, functionality) limiting the efficiency of PVP-based drug delivery systems (DDS). In this work, synthesised linear and star-shaped PVPs with a strictly defined structure and functionality were compared with the linear, commercially-supplied product and explored as potential vehicles for physical entrapment of metronidazole (MTZ). Here, a question is addressed how differences in their macromolecular properties affect the amorphisation of MTZ, drug encapsulation, the stability of drug-loaded micellar structures and their in vitro release from the carrier. The X-ray diffraction studies and calorimetric measurements revealed that MTZ crystallises in all investigated herein systems reducing the glass transition temperature of the binary mixture significantly. Transmission electron microscopy and dynamic light scattering analysis revealed that MTZ-loaded DDS are able to form ultrasmall regular nanocarriers with an increasing effect of regularity and sphericity from star-shaped DDS to linear-based ones. We founded that synthesised linear-based DDS is the most effective for MTZ entrapment (PVP:MTZ = 1:1 weight ratio) due to their smallest hydrodynamic radius dh = 14.7 nm, the highest stability of micellar structures −2.37 mV, and the highest values of loaded drug 76.5%. Moreover, all applied PVP-based DDS revealed an initial burst release effect of MTZ (pH = 7.4) reaching up to 60% of drug released within the first 5 h (the first-order release model fits). The marked efficiency of MTZ-loaded DDS of strictly defined structural parameters indicates the great importance of polymer preparation strategy in the targeted therapy
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