Search results for "End-group"
showing 10 items of 93 documents
Hyperbranched polyethylenimines as versatile precursors for the preparation of different type of unimolecular micelles
2007
Abstract Hyperbranched polyethylenimine (HPEI) was successfully employed as precursor for the preparation of unimolecular inverted and aqueous micelles. The unimolecular inverted micelles (UIMs) obtained by the amidation of HPEI with 1,1′-carbonyldiimidazole (CDI) activated palmitic acid exhibited high encapsulation efficiency for hydrophilic anionic dyes and the efficiency could be enhanced significantly by decreasing the degree of amidation or quaternizing the residual amines. The weight ratio of loaded guests to the amidated HPEIs was not dependent on the molecular weight of HPEI core when the degree of amidation was kept constant. Decreasing the length of the aliphatic chain from 16 to …
Mechanism of Anionic Polymerization of (Meth)acrylates in the Presence of Aluminium Alkyls IV. Formation of a Co-ordinative Polymer Network via the L…
1996
The polymerization of methyl methacrylate in the presence of aluminium alkyls in toluene deviates from conventional kinetics. This results predominantly from the formation and precipitation of a co-ordinative polymer gel or network. Due to the lower reactivity and accessibility of the living chains in the gel, they are regarded as ’dormant’ and thus the concentration of active species decreases during polymerization. The network formation occurs via co-ordination of the living aluminate chain end group with in-chain ester carbonyl groups. Part of the chains are deactivated by a termination process but they are free of cyclic β-ketoesters which would result from the common ’back-biting’ reac…
Ordering and mobility of ferroelectric liquid crystal dimer as studied by FT-IR spectroscopy with 2D-IR correlation analysis
1997
Both a conservative rapid-scan FT-IR technique and a novel step-scan FT-IR technique with 2D correlation analysis were used to study the orientation and the mobility ofa ferroelectric liquid crystal dimer during switching under an electric field. The detailed mutual arrangements of different molecular segments (mesogen, poly(methylene) chain, polysiloxane chain) in a smectic C* phase were derived from the static spectra. It was shown that the long mesogen axis, the average poly(methylene) and the average polysiloxane chain axes do not coincide with each other. The hindered rotation of the carbonyl group is confirmed. Time-resolved FT-IR technique was used to follow the segmental motion with…
Tetrazine- and trans -cyclooctene-functionalised polypept(o)ides for fast bioorthogonal tetrazine ligation
2020
The inverse electron demand Diets-Alder (IEDDA) reaction-initiated ligation between 1,2,4,5-tetra-zines (Tz) and trans-cyclooctenes (TCO) is one of the fastest bioorthogonal reactions known today and is therefore increasingly used for in vivo click chemistry. Described herein is the synthesis of Tz- and TCO-functionalised polypeptides, polypeptoids and polypeptide-block-polypeptoids (polypept(o) ides) by ring-opening polymerisation of the corresponding N-carboxyanhydrides using Tz- or TCO-functional amine initiators. Despite the reactivity of tetrazines, polymers with low dispersity and high end group integrity can be obtained as observed by gel permeation chromatography (GPC), nuclear magn…
Novel initiating systems for the living polymerization of acrylates and methacrylates
1998
The polymerization of methyl methacrylate with lithiated initiators in the presence of aluminium alkyls in toluene has living character but it deviates from conventional first-order kinetics and the polymers have fairly broad molecular weight distributions. This results from the formation and precipitation of a coordinative polymer network in which the lithium ions of the living chain ends are coordinated to the in-chain ester carbonyl groups. Thus, the network formation can be prevented by adding Lewis bases like methyl pivalate which coordinate to the living chain ends instead ofthe polymer. Alternatively, one can introduce tetraalkylammonium salts aiming at an exchange of the lithium ion…
Influence of End Groups on the Stimulus-Responsive Behavior of Poly[oligo(ethylene glycol) methacrylate] in Water
2010
The influence of the chemical structure of both end groups onto the lower critical solution temperature (LCST) of poly[oligo(ethylene glycol) monomethyl ether methacrylate] (POEGMA) in water was systematically investigated. POEGMA of Mn = 3550 g/mol and Mw/Mn = 1.14 prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization was equipped with two different functional end groups in a one-step postpolymerization reaction combining activated esters, functional amines, and functional methane thiosulfonates. As end groups, n-propyl, n-hexadecyl, di(n-octadecyl), poly(ethylene glycol)-550 (PEG), 1H,1H-perfluorononyl, azobenzene, and trimethylethylammonium groups were system…
Pyrene Containing Polymers for the Non-Covalent Functionalization of Carbon Nanotubes
2009
Pyrene containing diblock copolymers based on poly(methyl methacrylate) were synthesized and investigated regarding their adsorption on carbon nanotubes (CNT). The pyrene units were introduced using a reactive ester monomer for the build up of the second block which later on was reacted polymer-analogously with amine functionalized pyrene derivatives. As we started from the same reactive ester intermediate, full block length identity is given. We varied the length of the anchor block to find an optimal block length and used pyren-1-yl-methylamine as well as 4-pyren-1-yl-butylamine as anchor units. For both anchor units a maximal adsorption was found for 13 and 20 anchor units, respectively.…
Cyclodextrins in polymer synthesis: polymerization of methyl methacrylate under atom-transfer conditions (ATRP) in aqueous solution
2000
Host guest complexes of methyl methacrylate (MMA) and randomly methylated β-cyclodextrin (m-β-CD, 1 a) were polymerized in aqueous medium using atom-transfer radical polymerization. Ethyl 2-bromoisobutyrate (EBIB) was used as an initiator, copper(I) bromide as the catalyst, and bipyridine (bipy) or 4,4′-di-(5-nonyl)-2,2´-bipyridine (dNbipy) as ligands. The unthreading of m-β-CD during the polymerization led to water-insoluble poly(methyl methacrylate) (PMMA). It was found that using dNbipy resulted in higher monomer conversion than using bipy as the ligand under similar conditions. Furthermore, it is shown that the polymerization of MMA under these conditions has a living character. The pol…
Polypept(o)ides: Hybrid Systems Based on Polypeptides and Polypeptoids.
2015
Polypept(o)ides combine the multifunctionality and intrinsic stimuli-responsiveness of synthetic polypeptides with the "stealth"-like properties of the polypeptoid polysarcosine (poly(N-methyl glycine)). This class of block copolymers can be synthesized by sequential ring opening polymerization of α-amino acid N-carboxy-anhydrides (NCAs) and correspondingly of the N-substituted glycine N-carboxyanhydride (NNCA). The resulting block copolymers are characterized by Poisson-like molecular weight distributions, full end group integrity, and dispersities below 1.2. While polysarcosine may be able to tackle the currently arising issues regarding the gold standard PEG, including storage diseases i…
New phosphazene-based chain extenders containing allyl and epoxide groups
2003
In this paper we present the synthesis and the characterization of cyclophosphazenes substituted with allyl groups, their transformation in epoxide-containing cyclophosphazenes and the final utilization of these compounds as chain extenders in combination with polyamides. The reaction at high temperature of Nylon-6 with epoxy-functionalized cyclophosphazenes leads to the opening of the epoxy units by the action of both amino (--NH2) and carboxylic (--COOH) end-groups of the polymer to enhance the final molecular weight of this material. The consequences of this fact on the thermal, mechanical and visco-elastic properties of treated Nylon-6 have been also evaluated and compared to those of t…