Search results for "Degree of polymerization"

Acid‐Cleavable Poly(ethylene glycol) Hydrogels Displaying Protein Release at pH 5

2020

Abstract PEG is the gold standard polymer for pharmaceutical applications, however it lacks degradability. Degradation under physiologically relevant pH as present in endolysosomes, cancerous and inflammatory tissues is crucial for many areas. The authors present anionic ring‐opening copolymerization of ethylene oxide with 3,4‐epoxy‐1‐butene (EPB) and subsequent modification to introduce acid‐degradable vinyl ether groups as well as methacrylate (MA) units, enabling radical cross‐linking. Copolymers with different molar ratios of EPB, molecular weights (M n) up to 10 000 g mol−1 and narrow dispersities (Đ<1.05) were prepared. Both the P(EG‐co‐isoEPB)MA copolymer and the hydrogels showed pH‐…

The use of utraviolet-visible spectrophotometry in the determination of average properties of nonylphenol ethylene oxide condensates

1983

Ultraviolet spectrophotometry is usd in the determination of average molecular weight (M), average degree of polymerization (X), the hydrophilic-lipophilic balance (HLB) and ethylene oxide percentage of nonylphenol ethylene oxide condensates. The method is based on determination of the absorptivity a, expressed in g lt-1 cm−1, from the absorbances measured at 275 nm for a series of dilutions of an aqeuous ethanolic solution (60:40, v/v/) of a given product, followed by numerical interpolation of this value in the expression a = f(HLB), log a = f(log M), and log a = f(log X). These expressions are obtained from reference samples or samples previously analyzed. The proposed method gives relat…

Synthesis of monodisperse oligomers of ɛ-aminocaproic acid up to a degree of polymerization of 25 by the Merrifield method (1)

1967

Poly(glycolide) multi-arm star polymers: Improved solubility via limited arm length.

2010

Due to the low solubility of poly(glycolic acid) (PGA), its use is generally limited to the synthesis of random copolyesters with other hydroxy acids, such as lactic acid, or to applications that permit direct processing from the polymer melt. Insolubility is generally observed for PGA when the degree of polymerization exceeds 20. Here we present a strategy that allows the preparation of PGA-based multi-arm structures which significantly exceed the molecular weight of processable oligomeric linear PGA (&lt;1000 g/mol). This was achieved by the use of a multifunctional hyperbranched polyglycerol (PG) macroinitiator and the tin(II)-2-ethylhexanoate catalyzed ring-opening polymerization of gly…

Üuber eine abgekürzte Fraktioniermethode zur Bestimmung von Molekulargewichtsverteilungen

1950

Es wird ein Verfahren beschrieben, welches die Breite und ungefahre Gestalt der Verteilungskurve cines polymolekularen Stoffs auf Grund folgender experimenteller Daten zu bestimmen erlaubt: 1 Mittlerer Polymerisationsgrad (z. B. durch eine osmotische Bestimmung). 2 Gewichtsanteil und mittlerer Polymerisationsgrad einer obersten Fraktion. 3 Gewichtsanteil und mittlerer Polymerisationsgrad einer untersten Fraktion. Anwendungsbereich und Grenzen des neuen Verfahrens werden experimentell ermittelt. A method is described permitting to determine latitude and approximate shape of the distribution curve of a polymolecular substance by means of the following experimental data: 1 Average degree of po…

Hierarchical Self-Organization of Perylene Bisimide–Melamine Assemblies to Fluorescent Mesoscopic Superstructures

2000

A series of three perylene tetracarboxylic acid bisimide dyes 3a-c bearing phenoxy substituents at the four bay positions of the perylene core were synthesized and their complexation behavior to complementary ditopic dialkyl melamines 8a-c was investigated. Binding constants and Gibbs binding energies for the hydrogen bonds between the imide and the complementary melamine moiety have been determined in several solvents by NMR and UV/Vis titration experiments with monotopic model compounds 5 and 9. The effects of the solvent polarity and specific solvent-solute interactions on the degree of polymerization of (3 x 8)n are discussed, and a general formula to estimate the chain length of [AA-BB…

Molecular parameters of hyperbranched polymers made by self-condensing vinyl polymerization. 1. Molecular weight distribution

1997

The molecular weight distribution (MWD) and its moments are calculated for hyperbranched polymers formed by self-condensing vinyl polymerization (SCVP) of monomers (“inimers”) with the general structure AB*, where A is a vinyl group and B* is an initiating group. The calculated MWD is extremely broad, the polydispersity index (PDI) being equal to the number-average degree of polymerization:  Pw/Pn = Pn. It is twice as broad as that for the polycondensation of AB2 type monomers. If the fraction of unreacted monomer is not taken into account, the MWD becomes somewhat narrower, P‘w/P‘n ≈ 0.40P‘n. The kinetics of the polymerization process are first order with respect to the concentration of vi…

Dielectric and mechanical assessment of cellulosic insulation during transformer manufacturing

2021

Due to the impact of cellulose of paper insulation on transformer life, it is imperatire to remove moisture from the oil and the solid insulation. Several techniques have been implemented during manufacturing of power transformers to reduce water content in transformers. These drying processes can involve different costs and time, and they can damage the insulation paper. In this work, a drying process has been implemented in the laboratory trying to simulate the most aggressive conditions that can be suffered by the paper in transformer manufacturing in a real industry. Once the moisture content of papers was lower than 0.5%, the effect of the drying process on paper degradation was evalua…

Hologram development by diffusion in a polymer glass

2003

Thick rigid polymer media with diffusive development of gratings are suitable for archive information storage, and especially for 3D holographic optical elements. Diffusion of unreacted molecules of photosensitive dye ensures postexposure growth of diffracted light, which can be followed either by secondary growth, or by some decay caused by displacement of chromophore groups photochemically attached to polymer chains (photoproduct). In a long run, extremely slow, though still finite, diffusion of macromolecules leads to destruction of a holographic grating. Not only the rate, but also the shape of postexposure kinetics noticeably depends on the choice of particular polymer, its degree of p…

1992

The kinetics and the molecular weight distributions (MWD) in the anionic polymerization of tert-butyl acrylate (tBuA) in tetrahydrofuran at 23 ± 3°C were investigated. Tert-butyl α-lithioisobutyrate (tBiB-Li) was used as the initiator in the absence and presence of the additives lithium chloride and lithium tert-butoxide (tBuOLi). A flow tube reactor was used which allowed very rapid mixing of reagents, within milliseconds. The polymerization is extremely fast, half-lives being 0,01 s for the system without additive, 0,05 s for LiCl and 3 s for tBuOLi as an additive. The rate of termination was estimated from the strong UV absorption of the enolized β-oxoester end group formed. The number-a…