Search results for "Plastics"
showing 10 items of 2724 documents
Effect of core-forming molecules on molecular weight distribution and degree of branching in the synthesis of hyperbranched polymers
1998
The polydispersity index, the molecular weight distribution (MWD), and the degree of branching ( ) are calculated for hyperbranched polymers obtained in self-condensing vinyl polymerization of AB* monomers in the presence of a core-forming molecule (i.e. a multifunctional initiator, Bf*). Two cases are considered: (a) batch polymerization, i.e., with all components mixed together; (b) semibatch polymerization, i.e., slow addition of the monomer to the core-forming molecule. The results obtained for the latter case are also valid for polycondensation of AB2 monomers. The presence of core-forming molecules leads to a considerable narrowing of the MWD's, the polydispersity index decreasing wi…
Synthesis of Defined Poly(silsesquioxane)s: Fast Polycondensation of Trialkoxysilanes in a Continuous-Flow Microreactor
2009
The polycondensation of trialkoxysilanes to PSSQs in a microreactor setup is demonstrated. While continuous-flow processes involving microreactors found various applications in chain growth polymerization, their influence on step-growth polymerization is less explored, and the polycondensation of multifunctional monomers has not been studied in detail. We found significantly increased yields and a decreased polydispersity of the obtained polymers in comparison to the batch process. By variation of the residence time molecular weights could be adjusted reproducibly ranging from M n =1900 to 11000 g · mol -1 . Thus, the microreactor setup offers for the first time the possibility to synthesiz…
New ferrocene-containing copolyesters
1995
We have synthesized four new ferrocene monomers (three diols and one diester). The redox potential of these ferrocene derivatives varies between 0 mV and 230 mV due to different degrees of ring alkylation. Amorphous and liquid crystalline copolyesters were prepared with these monomers in the polymer main chain. Cyclovoltammetric measurements show that the redox potential of the ferrocene units is increased by about 40 mV upon polymer formation (esterification). Since the ester group is 4 to 6 σ-bonds away from the ferrocene unit this increase is probably caused by some charge-transfer interaction through space. First rheological measurements show an unusual rubber-like behaviour of the ferr…
Redox Materials by the Covalent Entrapment of Redox-Active Dirhodium(II,II) Species in a Siloxane Network
2004
Hydrolysis and polycondensation of the coupling agent (aminopropyl)triethoxysilane (APS), axially coordinated to the redox-active complex [Rh 2 (form) 2 (CH 3 COO) 2 -(APS) 2 ], lead to the insertion of redox-active inorganic microdomains into a siloxane network; the new polymers undergo cyclic redox reactions indicating that dirhodium(II,II) centres retain their redox activity even when incorporated into siloxane networks.
Synthesis of Oxetane-Functional Aliphatic Polyesters via Enzymatic Polycondensation
2012
Synthesis, characterization, and thermal properties of a series of oxetane-functional aliphatic polyesters are investigated. The incorporation of the acid-sensitive 3,3-bis(hydroxymethyl)oxetane (BHMO) into polymers is achieved by using the enzyme CALB (Candida antarctica Lipase B) as a catalyst. This mild synthetic strategy provides well-defined, oxetane-functional polyesters. The enzymatic polycondensation allows for the synthesis of a series of aliphatic polyesters containing various ratios of the difunctional monomers sebacic acid, 1,8-octanediol, and BHMO with molecular weights between 5000–9800 g mol−1 and polydispersity indices (Mw/Mn) in the range of 1.25 and 1.92. Furthermore, cros…
Vitamin C Loaded Polyethylene: Synthesis and Properties of Precise Polyethylene with Vitamin C Defects via Acyclic Diene Metathesis Polycondensation
2020
A polyethylene-like polymer with an in-chain vitamin C group was synthesized by olefin metathesis polymerization. Here, we describe both the synthesis and a comprehensive physical characterization. Because of the olefin metathesis synthesis, the vitamin C groups are equidistantly arranged in the polyethylene (PE) main chain. Their separation was adjusted to 20 CH2 units. After hydrogenation, a semicrystalline polymer is obtained that is soluble in polar solvents. Because of its size and steric effect, the vitamin C acts as a chain defect, which is expelled from the crystal lattice, yielding a lamellar crystal with a homogeneous thickness corresponding to the interdefect distance. The physic…
On what terms and why the thermodynamic properties of polymer solutions depend on chain length up to the melt
2003
Theoretical considerations based on chain connectivity and conformational variability of polymers have lead to an uncomplicated relation for the dependence of the Flory-Huggins interaction parameter, chi, on the volume fraction of the polymer, phi, and on its number of segments, N. The validity of this expression is being tested extensively by means of vapor pressure measurements and inverse gas chromatography (complemented by osmotic and light scattering data from literature) for solutions of poly(dimethylsiloxane) in the thermodynamically vastly different solvents n-octane (n-C8), toluene (TL), and methylethylketone (MEK) over the entire range of composition for at least six different mol…
Self-organized nanostructures of poly(4-vinylpyridine), polyaniline and polyamides due to metal complexation
2002
Comb-shaped supramolecules are constructed using flexible polymers and semi-rigid conjugated undoped or doped conjugated polymers upon complexing Zinc dodecyl benzene sulphonate, Zn(DBS) 2 . Self-organized nanostructures are formed in the bulk due to competing attractive interactions (coordination or water mediated hydrogen bonding) and repulsive polar/nonpolar interactions, showing characteristic long periods of ca. 30 A.
Light-induced demixing of hole or electron transporting moieties
2004
This paper describes the synthesis of two tri-phenylamine monomers (hole conducting) and one triazine monomer (electron conducting) which differ in their copolymerization parameters because of their styrene and vinyl ester nature. A blend of triphenylamine monomer and poly-(ethylene glycol) and mixtures of both types of monomers (triphepylamine and triazine) were illuminated through a line mask, creating laterally modulated radicals, thus leading to lateral demixing. The experiments with mixtures of triphenylamine and triazine monomers show that the concentration of p- or n-type polymers can be modulated laterally in a controlled way.
In-situ synthesis of thiophene-based multifunctional polymeric networks with tunable conductivity and high photolithographic performance
2017
Abstract Design of novel multifunctional polymeric materials combining electrically conducting properties with patterning capability is a significant challenge in materials science. Herein, we report on the synthesis of multifunctional interpenetrating polymer networks (IPN) by the in-situ oxidative polymerization of thiophene-based monomers with Cu(ClO 4 ) 2 inside a novolac-based photoresist. The resulting IPNs show conductivities up to 20 S/cm depending on the monomer properties. Among them, 3,3‴-Dihexyl-2,2’:5′,2’’:5″,2‴-quaterthiophene (DH4T) is chosen because it has the largest conjugation length and excellent solubility in organic solvents. Moreover, it renders a low percolation thre…