Polymerization Of Propylene Sulfide Research Articles

Living polymerizations of propylene sulfide initiated with potassium xanthates characterized by unprecedentedly high propagation rates

In this paper we describe the original thiol-free approach towards the polymerization of propylene sulfide (PS) under various conditions (bulk, solution, and emulsion) initiated with potassium xanthates.

217. Synthesis and Characterization of a Smart Triblock Copolymer Carrier for siRNA

The ability to specifically down-regulate gene expression using the RNAi pathway in mammalian cells has tremendous potential as a therapeutic and as a tool in basic science. For example, after abdominopelvic surgery, the accumulation of fibrin between adjacent sides of the wound prevents the regeneration of healthy functional tissue, creating an adhesion between the two sites. Small interfering RNA (siRNA) targeted against key proteins in the blood clotting cascade that prevent the degradation of the accumulating fibrin could lead to a decrease of abdominal adhesions. However, a delivery system capable of efficiently and specifically delivering siRNA to the target cells is currently not available. Cationic polymers are some of the most widely studied and commonly utilized gene delivery vehicles, which can self-assemble with nucleic acids through electrostatic interacionts. Limitations of cationic-based gene delivery systems include toxicity, aggregation, and unpacking of the siRNA. The central hypothesis underlying our approach is that a triblock copolymer based on the self-assembling triblock copolymers of poly(ethylene glycol) (PEG45), poly(propylene sulfide) (PPSx) and CGGRKKRRQRRR (TAT, PEG-PPS-S-S-TAT)) can be tailored to complex siRNA via charge and hydrophilic/hydrophobic interactions; moreover, due to its reductive and pH sensitive character take advantage of chemical differences in the cell organelles and cellular pathways to achieve efficient delivery of siRNA. The polymer PEG45-PPSx-pyridyldithio was synthesized using anionic polymerization of propylene sulfide with AIBN as the radical initiator and dipyridine dithione as the end-capping agent. Triblock polymers with different PPS lengths (PEG45-PPS5-pyridyldithio and PEG45-PPS10-pyridyldithio) were synthesized to study the effect of hydrophobic character of the delivery system on complex formation, complex size and transfection efficiency. H-NMR was used to confirm the degree of polymerization of polypropylene sulfide showing a length of 5.056 and 9.648 for PEG45-PPS5-pyridyldithio and PEG45-PPS10-pyridyldithio respectively. The TAT peptide and a control CK12 peptide were bound to the PEG45-PPSx-pyridyldithio polymers using a disulfide exchange reaction between the free thiol of the N-terminal cysteine of the peptide and the disulfide of pyridyldithio of the triblock polymer. The reaction was complete after 2 hours as determined by monitoring the release of 2-pyridinethione at 343nm. The resulting triblock copolymer was purified using flow phase liquid chromatography (FPLC) with a cationic exchange column and 2mM sodium acetate as the liquid phase. Elution was achieved using 5M of salt and monitored using a UV detector. Gel electrophoresis analysis showed that the triblock polymers were able to complex plasmid DNA at a charge ratio (+/) of 2.52 and 2.3 for PEG45-PPS5-TAT and PEG45-PPS5-CK12 respectively. These studies have focused on the synthesis and characterization of a delivery system for siRNA that self-assembles not only based on charge but also based hydrophilic/hydrophobic interactions.

Novel sulfur‐containing ferrocene polymers

AbstractFerrocene‐containing polymers were synthesized via addition reaction of 1,1′‐dimercaptoferrocene (1) and 1,1′‐bis(2‐mercaptoethyl)ferrocene (2) to various diolefinic monomers such as dimethacrylates, divinyl ethers, divinyl sulfones and others. The dithiol 1 was also used as a monomer in condensation reactions with bifunctional acid chlorides. The polymerization of propylene sulfide in the presence of 1 as a bifunctional initiator was found to lead to polymers with a single central ferrocene unit.

NMR study of polypropylenesulphide and polypropylenedisulphide obtained by polymerization of propylenesulphide with organo-lithium catalysts

13C NMR data indicate that polypropylenesulphide prepared by polymerization of propylenesulphide by lithium thiolates (or alkyls) is atactic and contains up to 10% disulphide bonds and structurally irregular units. Their complexes with lithium alcoholates or lithium tert-butylate result mainly in the formation of structurally homogeneous disulphide polymers which are, however, stereo- and structurally irregular in view of the possibility of exchange reactions taking place. Taking account of the three-dimensional effect of substituents and results of the temperature dependence of spectra of the polymers obtained, enabled the signals to be assigned, which were found to be different from those previously proposed. Higher temperature coefficients Δδ/ ΔT of chemical shifts of CH 2-SS- and CH-SS-carbon atoms of the main chain, compared with Δδ/ ΔT of lateral CH 3 groups, indicate the significant effect of temperature on the conformation of disulphide groups of the macro-chain.

Polymerization of propylene sulphide by the Zn(C 2H 5) 2-H 2O catalyst system

The hydrolysis of a complex of diethyl zinc (DEZ) with propylene sulphide (PS) in PS solution has been investigated. Suitable conditions have been found for the quantitative hydrolysis of DEZ with the formation of a catalyst system containing (ZO) n groups and ZnS bonds and effective for initiating the polymerization of PS. This polymerization was investigated and a tentative scheme for polymerization by a coordinate anionic mechanism is suggested. The structure of polypropylene sulphide (PPS) was investigated by high-resolution NMR spectroscopy and X-rays. The Zn(C 2H 5) 2—H 2O system prepared in situ is highly selective in the reactions of breaking the α-thioxide ring. Amorphous PS consists entirely of head-to-tail bonded units with equal content of iso- and syndiotactic diads. It was also shown that extremely high values of the molecular mass of PPS, the unusual dependence of [η] on conversion and the instability of polymer solutions are due to the presence of polymer aggregates formed in the polymerization of PS on complex associated active centres with a steric structure. Conditions were found for the stabilization of PS solutions containing zinc and for the purification of the polymer from traces of the catalyst system. It was shown that it is incorrect to use equations available in the literature to calculate M η for PPS obtained with the DEZ—H 2O system from viscometric data without thorough purification of the polymer. Osmometry and light scattering technique were used to estimate true values of the molecular mass of polymer aggregates and of linear PPS.

Polymerization of propylene sulphide by the catalytic system Zn(C 2H 5) 2H 2O

A study has been made of the diethyl zinc (DEZ) complex with propylene sulphide (PSu) in a PSu solution; conditions have been found for quantitative hydrolysis of DEZ and the formation of a catalytic system containing (ZnO) n groups and ZnS bonds, which effectively initiate the PSu polymerization. Some of the mechanisms of PSu polymerization over this system have been examined and the results used to suggest a reaction scheme which envisages the following steps 1) DEZ-Psu complex formation, 2) initiation of the polymerization which includes hydrolysis of the complex, ZnS bond formation during reaction of PSu with the hydrolysis products, and the association of the organic-zinc compounds, 3) the polymer chain propagation on the ZnS bonds by an anionic coordination mechanism. High resolution NMR spectroscopy and X-ray structural analysis have been used to study the structure of polypropylene sulphide (PPSu); the system Zn(C 2H 5) 2H 2O produced in situ has been found to be highly selective in the α-thiirane ring opening. Amorphous PPSu contains a complete “head-to-tail” structural type of arrangement containing equal numbers of iso- and syndiotactic diades.

Cationic polymerization of cyclic sulfides, 5 Polymerization of propylene sulfide with triethyloxonium tetrafluoroborate

AbstractTime‐conversion curves show that the polymerization of propylene sulfide (1) by triethyloxonium tetrafluoroborate (TEFB) in methylene chloride consists of an initial very fast, non‐stationary stage A and a much slower subsequent stage B which leads to quantitative conversion. The termination reaction of stage A is of first order with respect to initiator concentration and is independent of monomer concentration. The proposed mechanism for this termination is the formation of a (mainly) 12‐membered cyclic sulfonium salt at the end of the polymer chain. The ratio of the rate constant of propagation to the rate constant of termination at 0°C in CH2Cl2 is 9 dm3 mol−1. From the kinetics, it is concluded that stage B is initiated by slow formation of a three‐membered cyclic sulfonium salt by an intramolecular nucleophilic attack of the last sulfide function of the polymer chain on the α‐carbon next to the sulfonium salt. Further evidence for this kind of re‐initiation is obtained from the observation that simple trialkylsulfonium salts are very poor initiators or completely incapable of initiating the polymerization, whereas under identical conditions 2‐thia‐alkylsulfonium salts give polymerizations without stage A which are similar to the stage B of the TEFB‐initiated reactions. A backbiting reaction, similar to the termination reaction, is responsible for the degradation of polymer (mainly) into cyclic tetramer. The molecular weights of the polymers, measured by gel permeation chromatography, are in reasonable agreement with the proposed mechanism.

Cationic polymerization of cyclic sulfides

AbstractThe mechanism of the cationic polymerization of cyclic sulfides, initiated with triethyloxonium salts is reported. Differences due to changing the counter‐ion from BF to SbCl are discussed. Initiation consists of the alkylation of monomer forming a cyclic sulfonium ion which is the active species in the propagating step. A generally occurring termination reaction is the formation of non‐strained (linear or cyclic) sulfonium ions. In the case of epithiopropane (propylene sulfide) these can slowly re‐initiate the polymerization by an intramolecular reaction forming the 3‐membered cyclic sulfonium salt. This re‐initiation is not possible with the thietanes because of the greater difficulty to form 4‐membered cyclic sulfonium salts. When SbCl is the counter‐ion, an additional, more drastic termination can occur most probably by reaction of the growing chain with the counter‐ion, thereby forming an alkyl chloride and SbCl5. After the polymerization of propylene sulfide with BF as the counter‐ion, the polymer degrades to low molecular weight oligomers, predominantly the cyclic tetramer. This degradation is a back‐biting reaction occuring via sulfonium salts. With SbCl as the anion, the sulfonium salts are destroyed by the termination reaction and degradation does not occur.It was possible to follow the concentration of the growing species (4‐membered cyclic sulfonium salt) during the polymerization of 3,3‐dimethylthietane by means of 300 MHz NMR spectroscopy. By measuring the rate constants of propagation for different initiator concentrations or in the presence of different amounts of an indifferent electrolyte, it was possible to calculate separate rate constants for propagation via free ions (k) and via ion‐pairs (k). The ratio k/k was about 60 when BF was the anion and 35 when it was SbCl.

Anionic polymerization of cyclic sulfides initiated by metal complexes of aromatic nitriles and ketones

AbstractThe capacity of metal complexes of aromatic nitriles and ketones to initiate the polymerization of ethylene sulfide, propylene sulfide and styrene sulfide is studied by means of spectral and chemical methods. The results indicate that the polymerization of styrene sulfide initiated by anion‐radicals of the used nitriles and ketones proceeds via electron transfer from the initiator to the monomer, while ethylene sulfide polymerizes by way of valence bond formation between the initiator and the monomer. The polymerization of propylene sulfide is a multistage reaction linked with the formation of propylene and initiator species. The polymerization of all three monomers initiated by aromatic nitrile dianions proceeds by electron transfer.

Isolation and identification of oligomers formed during cationic polymerization of propylene sulfide

Isolation and identification of oligomers formed during cationic polymerization of propylene sulfide

Reactive liquid polymers of propylene sulphide

Liquid polymers of desired molecular weight can be prepared by polymerization of propylene sulphide by thiolate compounds of alkali metals, zinc or cadmium in the presence of thiol compounds as transfer agents. The molecular weight is controlled by the ratio of monomer to that of initiator plus the transfer agent. The initiator may be formed in situ by the reaction of alkali metal hydroxide or zinc and cadmium carbonate with thiol compounds. Polyfunctionality of the liquid polymer is achieved by using polythiol compounds as transfer agent. The reactive thiol groups are easily converted to other functional groups such as hydroxyl, epoxy, amine, etc. The thiol-tipped polymers can be compounded directly to give resilient, elastic sealants with excellent resistance to swelling in hydrocarbons. Polyurethane films prepared from the dihydroxyl tipped prepolymers are tough, transparent and resist swelling in most common solvents. The liquid polypropylene sulphide exhibits useful properties in adhesive and coating compositions, especially with aluminium and zinc metals.

Polysulphide linkages in polypropylene sulphide prepared using zinc and cadmium thiolate initiators

In the polymerization of propylene sulphide using zinc thiolate initiators, substantial amounts of propylene are produced. This reaction is accompanied by the incorporation of sulphur as di- or polysulphide linkages in the polymer chain. Up to 15 per cent of the monomer has been found to participate in this side reaction and up to one in ten of the linkages to be polysulphidic. No elemental sulphur is formed. The polymers are cleaved by n-butane thiol/piperidine and by tri n-butyl phosphine/water to give low mol. wt. thiol terminated products. Substantial amounts of sulphur can be removed by treatment with triphenyl phosphine. Polymerization using cadmium thiolates was accompanied by very small amounts of propylene, difficult to distinguish from that present in monomer as an impurity. The polymers produced with these catalysts are essentially monosulphide but probably contain a small proportion of polysulphide linkages.

Asymmetric‐selection polymerization of propylene sulfide

Asymmetric‐selection polymerization of propylene sulfide