Synthesis and properties of amphiphilic vinyl acetate triblock copolymers prepared by copper mediated living radical polymerisation

Polymerisation of vinyl acetate by conventional free radical polymerisation using a diazo initiator followed by copper mediated living radical polymerisation with a range of monomers was studied. This method led to the synthesis of triblock copolymers. We have thus successfully prepared several new ABA triblock copolymers where B is poly(vinyl acetate) and A is (dimethylamino)ethyl methacrylate (DMAEMA), (polyethylene glycol) methyl ether methacrylate (MeO(PEG)MA) or solketal methacrylate (SMA). The sequential conventional/living radical polymerisation approach provided an efficient route to synthesis of new block copolymers. The properties of these amphiphilic polymers have been subsequently investigated by ¹H NMR, fluorescence spectroscopy, tensiometry and dynamic light scattering to investigate their behaviour as potential surfactants.     

Photoinitiated cationic polymerisation of multifunctional systems

Different types of tridimensional polymer networks have been synthetised by photoinitiated cationic polymerisation of vinyl ether and epoxy-functionalised oligomers and polymers. The polymerisation kinetics was followed by real-time infrared (RTIR) spectroscopy, a technique that records directly conversion versus time profiles in a timescale as short as 1 s. The addition of a diacrylate monomer was shown to accelerate the ring-opening polymerisation of epoxidized polyisoprene, with formation of interpenetrating polymer networks having well contrasted properties. A dual polymer network has been generated by photocrosslinking of a polyisoprene functionalised with both epoxy and acrylate groups.     

Non-ideality in vinyl polymerisation—IX. Note on secondary dissociation of primary radicals

An extended mathematical analysis is proposed for free-radical polymerisation systems involving initiators which produce primary radicals that have quite long half-life and decompose to secondary radicals. Initiation and macroradical termination by both primary and secondary radicals have been considered. Data for styrene and vinyl chloride have been treated with the developed relationships; limitations of earlier treatments are discussed.     

Polymerisation of vinyl acetate in microemulsions with methanol

 The homogeneity domains for the system vinyl acetate – methanol – monomaleate of nonylphenol ethoxylated with 25 mol ethylene oxide as an aqueous solution (MEMNPEO25) (33%) have been studied; it has been shown that, due to the shorter chain of methanol, these domains are more reduced than in the case of ethanol. The changes in refractive indexes and electrical conductivities have shown the formation of microemulsions with different structures (water-in-oil, bicontinuous or oil-in-water). Ammonium persulphate is soluble only in oil-in-water or in bicontinuous microemulsions. The initial polymerisation rates as well as the decomposition rates for the initiator are apparently affected when the microemulsion structure is modified. The polymerisation rate of vinyl acetate is higher in the presence of methanol than in the presence of ethanol for similar compositions; this fact may be attributed to a higher degree of ionisation of the initiator in the presence of methanol. Also, in polymerisations initiated by benzoyl peroxide, the conversions are influenced by the microstructure; thus, the maximum corresponds to water-in-oil microemulsions. By measuring the amount of unreacted MEMNPEO25 (gel permeation chromatography) we were able to show that the copolymer formed consisted of vinyl acetate and reactive surfactant. Received: 9 March 1999/Accepted: 13 March 2000     

Poly(vinyl alcohol) star polymers prepared via MADIX/RAFT polymerisation

Poly(vinyl acetate) stars were prepared using MADIX/RAFT polymerisation mediated by xanthates. The polymerisation shows living characteristics with molecular weight increasing with conversion. The subsequent hydrolysis of these three and four arm stars led to the formation of poly(vinyl alcohol) stars.     

Synthesis of Telechelic Oligo(isobutyl vinyl ether)s via Alkylation of Silyl Enol Ethers by the Propagating Chain End in an Ab Initio Cationic Polymerisation

Telechelic oligomers prepared by cationic polymerisation of isobutyl vinyl ether were synthesised by an ab initio procedure, in which silyl enol ethers were alkylated by the propagating carbocationic chain end. In‐situ addition of a silyl enol ether to the propagating chain end in a cationic polymerisation yields functionalized oligomers during the polymerisation. Therefore, it is not necessary to operate under living conditions.     

Switching the mechanism of polymerisation from vinyl addition to metathesis using single‐site catalysts

Titanium/methylaluminoxane‐based catalyst systems polymerising norbornene by vinyl addition were modified to initiate ring‐opening metathesis polymerisation by interrupting the course of polymerisation with phenylacetylene. The products showed nearly 30% ring‐opened structures according to their ¹H NMR spectra. The change in mechanism of polymerisation after the addition of the reactivity transfer reagent is seen from the kinetic data.     

Thio-Pybox and Thio-Phebox complexes of chromium, iron, cobalt and nickel and their application in ethylene and butadiene polymerisation catalysis

A series of bis(thiazolinyl)- and bis(thiazolyl)pyridine Thio-Pybox ligands and their metal complexes of chromium(III), iron(II), cobalt(II) and nickel(II) has been prepared, as well as a nickel(II) complex containing a monoanionic bis(thiazolinyl)phenyl Thio-Phebox ligand. These new metal complexes have been characterised and used as catalysts, in combination with the co-catalyst MAO, for the polymerisation of ethylene and for the polymerisation of butadiene. In the case of ethylene polymerisation, the Thio-Pybox and Thio-Phebox metal complexes have shown relatively low polymerisation activities, much lower compared to the related bis(imino)pyridine complexes of the same metals. In the polymerisation of butadiene, several Thio-Pybox cobalt(II) complexes show very high activities, significantly higher than the other metal complexes with the same ligand. It is the metal, rather than the ligand, that appears to have the most profound effect on the catalytic activity in butadiene polymerisation, unlike in the polymerisation of ethylene, where bis(imino)pyridine ligands provide highly active catalysts for a range of 1st row transition metals.     

Surfactant-sensitive polymeric membrane electrodes

The development and testing is described of surfactant-sensitive electrodes in which the active element is a plasticised polymeric membrane containing a dissolved complex of a cationic and anionic surfactant. Electrodes made with poly(vinyl chloride) membranes plasticised with 40–60% tricresyl phosphate and containing cetyl trimethylammonium dodecyl sulphate are reasonably satisfactory for determining sodium dodecyl sulphate activities below and above the critical micelle concentration. A new class of membrane electrodes has been introduced in which ion-exchange groups are chemically bound to the ends of the poly(vinyl chloride) chains either through the use of an amine as chain transfer agent during polymerisation or by using the SO₃^? radical-anion as polymerisation initiator. The resulting electrodes are specific to anionic or to cationic surfactants but selectivity between different surfactants of the same charge sign is not high. The electrode lifetimes in micellar solutions are much higher than those of previously described electrodes because the electroactive material cannot be lost by solubilisation.     

Fonctionnalisation du polypropylene isotactique par le melange oxygene-ozone

Ozonisation of polypropylene in bulk causes chain scission through autooxidation processes at room temperature and produces mainly α-ω diketone polypropylene sequences. With poly(vinylchloride) or polyethylene, formation of α-ω diacid sequences has been observed. Hydroperoxides parallel ketone formation but they are grafted onto the polymer backbone. They may be used to initiate the polymerisation of vinyl monomers during the processing of the polypropylene.     

Thermal decomposition (STA and DSC) of PVC compounds under a variety of atmospheres and heating rates

Simultaneous thermal analyses (thermogravimetric, differential thermogravimetric and differential thermal analyses) have been performed on samples of five typical compounds based on poly(vinyl chloride). The analyses were performed at three heating rates and in atmospheres of nitrogen, air and oxygen. Differential scanning calorimetric analyses were additionally run on the same samples, in nitrogen. The materials used were a suspension-polymerised resin, a mass-polymerised resin, pipe material, wall covering material and wire jacketing material. All of them decompose in three main breakdown stages, the first accounting for over 60 wt% of the pure resins and for over 50 wt% of the other compounds. The values of T_1% and T_D have been determined under all conditions; T_1% is consistently less sensitive to these variations than T_D, particularly for the manufactured compounds. By analysing both the STA and the DSC data, it has been possible to distinguish between a pure resin prepared by suspension polymerisation and one prepared by mass polymerisation. Kinetic analyses have been carried out on all the data to determine the activation parameters. The first of the three breakdown stages is actually a composite of two stages, suggesting that the dehydrochlorination (by chain-stripping) cannot be complete at the end of this composite first stage. Furthermore, this stage must also involve some CC bond scission, contrary to what has traditionally been assumed.     

Mathematical Analysis of the Formation of Molecule Sizes on a Spinning Disc Reactor

A mathematical analysis of the behaviour of the molecular weights of addition polymers during a polymerisation process is described. Spinning disc reactor (SDR) technology has been shown to yield significant improvements in terms of polymerisation rates whilst retaining close control of the molecular weights and the molecular weight distributions^[1,2]. However, understanding of the kinetics of the polymerisation process on a SDR remains unresolved. One of the questions to be addressed concerns the sizes of the macromolecules preferably formed during the polymerisation process. To address this question, a mathematical analysis of the observed trends in number and weight average molecular weight, monomer concentration and polydispersity during the polymerisation process on a SDR has been undertaken. To validate the results, experimental data obtained from benzoyl peroxide initiated free radical polymerisation of styrene on a SDR^[2] was used. It was concluded that most of the monomers consumed are in the growth of smaller size chains.     

Ultra-porous hollow particles

Hollow particles with porous shells have been prepared by a simple modification to the surfactant-free polymerisation of styrene by the incorporation of water-soluble natural polymers and the use of high stirring speeds. The particle morphology has been characterised by scanning electron microscopy (SEM). When styrene is polymerised in the presence of either carboxymethyl cellulose (CMC) or sodium alginate at high stirring speeds, small homogeneous (solid) particles (diameter ~200 nm) and large porous particles (diameter~10 m) are both formed. However, at low stirring speeds only the small homogeneous (solid) particles are formed. Further, only the small homogeneous (solid) particles are formed when non-adsorbing polymers such as starch and poly(vinyl alcohol) are present. In contrast, polymers that strongly adsorb onto polystyrene particles cause the polymerising mixture to flocculate. It is proposed that the porous character is a direct result of the polymerisation of a multiple emulsion in the presence of a depletion interaction. Moreover, addition of a high concentration of surfactant to the CMC system simply results in the spherical homogenous particles, suggesting that the surfactant removes the depletion effect.     

Preparation of ion-imprinted polyvinyl sulfonate-grafted silica particles for trace enrichment of Th(IV) prior to determination by inductively coupled plasma-mass spectrometry

Grafting from polymerisation technique has been used to prepare Th(IV) ion-imprinted polyvinyl sulfonate (IIPVS)-bonded silica particles. The graft polymerisation of vinyl sulfonate (VS) on the surface of silica particles was achieved in aqueous medium through thermal decomposition of surface-bound azo initiators (60°C) in the presence of thorium ion. The prepared material was characterised by Fourier transform infrared spectroscopy, differential scanning calorimetry and thermogravimetric analysis. The entrapped template ion was then removed using 2 M HCl. The experimental batch rebinding data were successfully described by the Langmuir–Freundlich model. The prepared material was then packed to a PTFE micro-column (20 mm × 3.0 mm, id) to evaluate its efficiency in column operations prior to determination by inductively coupled plasma-mass spectrometry (ICP-MS). The limit of detection of the method and breakthrough capacity of the column was evaluated as 0.074 µg L^?1 and 0.83 mg g^?1, respectively. The selectivity of the prepared polymer towards Th(IV) ion was investigated in the presence of some foreign competitor ions, including U(VI). Finally, the proposed method has been used to determine Th(IV) ion in real samples.     

Near- and Mid-Infrared Spectroscopy of Sol-Gel Derived Ormosil Films for Photonics from Tetramethoxysilane and Trimethoxysilylpropylmethacrylate

Ormosil dipped thin films and cast films were prepared using tetramethoxysilane and trimethoxysilylpropylmethacrylate (TMSPM). Structural changes during thermally induced polymerisation of the organic groups were investigated using near- and mid-infrared (IR) spectroscopy. IR spectra of the ormosil dipped thin films, dried at 60°C, have shown that further heat-treatment of the films at 160°C leads to the free radical polymerisation of C=C bonds in TMSPM. In the mid-infrared spectra, the intensity of the band at around 3500 cm^–1, due to O–H bonds, increased with the progress of polymerisation of vinyl groups. Near-infrared spectra of the cast films showed that this increase in intensity of the O–H band is due to the increase of monomeric water molecules hydrogen bonded to silanols. We suggest that optical loss measurements must be made in a dry atmosphere or, with a cover coating to protect the ormosil from adsorption of water, to reduce this source of optical loss for waveguides based on TMSPM.     

The synthesis and X-ray structure of a phenoxyimine catalyst tailored for living olefin polymerisation and the synthesis of ultra-high molecular weight polyethylene and atactic polypropylene

A phenoxyimine catalyst (bis-(N-(3′,5′-diiodo-salicylidene)-2,6-difluoroaniline)-titanium(IV)-dichloride has been synthesised. The ligand as well as the complex have been fully characterised. An X-ray structure of the titanium complex was obtained. After activation with MAO, it was used as highly active catalyst in living olefin polymerisation of ethylene and propylene. Ultra-high molecular weight polyethylene and atactic polypropylene of low polydispersity were obtained. The living character of the polymerisation was shown by online polymerisation kinetics and linear growth of number-average molar mass with polymerisation time. In addition, the influence of hydrogen as a chain transfer agent was studied in living olefin polymerisation.     

Synthesis of Polyvinylacetate‐Sodium Montmorillonite Hybrids by Emulsion Polymerization in the Presence of Anionic Surfactants

The emulsion polymerisation of vinyl acetate (VAc) in presence of sodium dodecylsulphate (SDS) and sodium montmorillonite (NaMMT) is used in order to achieve polymer‐clay hybrids. The influence of the polyvinylacetate (PVAc), SDS, and PVAc‐SDS complex on the NaMMT structure also was investigated. The VAc emulsion polymerization rate exhibits a maximum as the NaMMT concentration increases. The XRD patterns correspond to hybrids with intercalated structure. If a water soluble comonomer, ammonium sulphato ethylmethacrylate (ASEMA) is used for copolymerization with VAc, a exfoliated hybrid structure (from XRD spectra) is obtained. The solid materials were analysed by TGA, FTIR, XRD, SEM, and TEM.     

Development of Amino–Oxazoline and Amino–Thiazoline Organic Catalysts for the Ring‐Opening Polymerisation of Lactide

The ring‐opening polymerisation of lactide by a range of amino–oxazoline and amino–thiazoline catalysts is reported. The more electron‐rich derivatives are demonstrated to be the most highly active and polymerisation is well controlled, as evidenced by the linear relationship between the molecular weight and both the monomer conversion and the monomer‐to‐initiator ratio. Mechanistic studies reveal significant interactions between the monomer, initiator and catalyst and that the polymerisation is first order with respect to each of these components. These observations indicate that the polymerisation operates by a general base/pseudo‐anionic mechanism.     

Double UV polymerisation with variable temperature-controllable selective reflection of polymer-stabilised liquid crystal (PSLC) composites

In this study, a method of preparing wide-band reflection cholesteric liquid crystals (CLCs) films by UV-radical polymerisation in combination with UV-cationic polymerisation is proposed. Because the helical twisting power (HTP) of the chiral dopant decreases with increasing temperature and the polymerisation rate of UV-initiated free radical polymerisation is faster than UV-initiated cationic polymerisation, by adjusting the temperature, broadband reflective films with non-uniform pitch distribution are obtained. The fractured surface of the polymer network of the broadband reflective films is observed by scanning electron microscopy (SEM), which reveals the presence of non-uniform pitch distribution. In addition, the influences of monomer concentration, UV light intensity and UV curing time on the consequent non-uniform pitch distribution have been studied.     

Homochiral oligopeptides via a lattice-controlled polymerisation in racemic crystals of valine N-carboxyanhydride suspended in aqueous solutions

As part of our program on the biochirogenesis of homochiral peptides, we report the formation of racemic parallel (p) beta sheets composed of alternating R and S chains of up to 14-15 repeat units of the same handedness through the polymerisation of (R,S)-valine N-carboxyanhydride (NCA) crystals suspended in aqueous solutions of a primary amine as the initiator. The occurrence of such a lattice-controlled reaction accompanied by a reduction in volume implies the operation of a mechanism that differs from that of the common solid-state polymerisation in vinyl systems. The topotacticity of the reaction is explained through the operation of a multistep nonlinear process comprising lattice control coupled with an asymmetric induction in the formation of homochiral short peptides followed by their self-assembly into racemic p beta sheets, which operate as efficient templates in the ensuing process of enantioselective chain elongation at the polymer/crystal interface. The composition of the diastereoisomeric libraries of oligopeptides was determined by MALDI-TOF and MALDI-TOF-TOF MS analyses of the products obtained from monomers enantioselectively labelled with deuterium. The structure of the p beta sheets could be determined by initiating the polymerisation reaction with water-soluble esters of enantiopure alpha-amino acids or short peptides. The same reaction performed with the monomer crystals suspended in hexane yielded a complex mixture of diastereoisomeric oligopeptides, thus highlighting the indispensable role played by water in controlling the stereoselectivity of the reaction. By contrast, polymerisation of (R,S)-leucine NCA crystals, with a different packing arrangement that presumably does not endorse the formation of periodic peptide templates, yielded, both in aqueous and hexane suspensions, libraries of peptides dominated by heterochiral diastereoisomers.