Controlled polymerisation

Polyolefins. The most common polyolefin used to prepare composites is polypropylene [9003-07-0] a commodity polymer that has been in commercial production for almost 40 years following its controlled polymerisation by Natta in 1954 (5). Natta used a Ziegler catalyst (6) consisting of titanium tetrachloride and an aluminum alkyl to produce isotactic polypropylene directly from propylene ... 

Controlled polymerisation of ethylene oxide under alkaline conditions will produce a range of polymers marketed under the trade name Carbowax. These have molecular weights in the range 1500-20000 and are greases or waxes according to their degree of polymerisation. Lower molecular weight polymers... 

A temperature-controlled polymerisation process is estimated to have a transfer function of ... 

Hydrothermal synthesis of the non-uniform silica gel used for preparative chromatography proceeds in a different fashion. Sodium silicate (IMa2Si03),1 obtained by alkaline fusion of very pure sand, is acidified to yield orthosilicic acid (Si(0H)4). This unstable acid initially dimerises then condenses further to yield a gel with a hydroxylated surface. Under conditions of controlled polymerisation, a hydrogel is obtained which is further calcinated to yield a very dense silica gel (xerogel). Some of the processes involved here are of the same type as those used to produce microspheres for analytical chromatography. 

In this chapter, three topics of research will be described in which textile fibres and structures are used as electrodes to detect and determine chemical compounds, concentration to optimise the detection conditions and to use such systems to follow and control polymerisation reactions. 

The cleavage of C-I bond can be achieved from various methods [373-375]. However, according to well chosen monomers, two main ways have been developed in order to control telomerisation from alkyl iodides iodine transfer polymerisation (ITP) and degenerative transfer. ITP can be easily applied to fluorinated monomers whereas degenerative transfer concerns the controlled polymerisation of methyl methacrylate, butyl acrylate [376] or styrene [377] and will not be discussed in this chapter. 

The polymer displays narrow molecular weight distributions characteristic of living polymerisation systems. Among catalysts exhibiting an ability to perform such controlled polymerisations of dicyclopentadiene according to scheme (40), titanacycles and Mo or W alkylidenes are representative [142, 143] ... 

These are produced in a two-step process from glycerol and fatty acids [41 ]. The first step is a controlled polymerisation of glycerol into a polymeric form by heating the glycerol in the presence of an alkaline catalyst, such as 1% caustic soda, at a temperature of 260-270°C ... 

Through the use of controlled polymerisation techniques it is possible to synthesise polymers, based on existing monomers, which have different properties when compared against conventional random processes. Extended aspects of control include ... 

The design and the realisation of well-defined polymer architectures has become an important goal in macromolecular science. The prerequisite for achieving this goal is the availability of controlled polymerisation reactions. Living anionic polymerisation was the first reaction fulfilling these requirements. Cationic polymerisation only came into play when it was realised that it was possible to create an equilibrium between active and dormant species with the fraction of the dormant species being far superior to that of active ones. 

Thus, the polymerisation of methyl methaciylate in toluene was investigated using an initial eatalyst/initiator/monomer molar ratio of 1 2 800 with ethyl 2-bromo-2-methyl-propionate as the initiator. Under these experimental eonditions, all the criteria of living polymerisation were fulfilled. Indeed, the plot of hi([M o/[Af]t) versus time followed a linear relationship, which is typical for a controlled polymerisation. Furthermore, a linear evolution... 

When the polymerisation of MM A was carried out at 35 °C instead of 85 °C with complex 6, the semilogarithmic plot of ln([A7]c/[M t) versus time remained linear, but high molecular weight polymers were formed from the very beginning of the reaction and A/ as well as MJM remained almost constant 76 kg.mol and 1.60, respectively) throughout the entire run. This behaviom sharply contrasts with the results reported for complex 5 at 35 °C that met all the criteria of controlled polymerisation (77). With the NHC-based complex 6, the decrease of temperatrrre most likely induced a switch of mechanism, from controlled ATRP to a redox-initiated free-radical process (7), although further investigations are needed to fully clarily this point. 

Figure 10.5 Controlled polymerisation of methylacetylenes in the pores of the coordination polymer Cu2(pzdc)2(pyz) gives r 5 -polyacetylene due to the steric restrictions. [Reproduced from reference 33 with permission. Copyright 2006, Wiley-VCH Verlag GmbH Co. KGaA.]...

Very few heterogeneous alkoxide Ti-based catalysts were reported for the ROP of e-CL. Among the examples, the aforementioned catalysts used for the ROP of LA, i.e. Ti-supported onto (un)modified MCM-41 7-9 and Ti-MOF 10, were also investigated, resulting in a more controlled polymerisation process than the other titanium alkoxide/aryloxide complexes.Only catalyst 7 was tentatively recycled after complete conversion of s-CL (after 15 min) was observed, showing a diminished activity (75% after 2.5 h) due presumably to the catalyst being altered during the recovery procedure. ... 

As stated above, the use of bullqr ancillary ligands has been shown to improve the control over polymerisation, yield polymers with narrow PDIs and control M . For the ROP of LAs, the series of acetylacetonates 17-19 (Scheme 6.2), were tested and displayed a moderate activity with a narrow PDIs (1.07-1.99) indicating a controlled polymerisation. 

The controlled polymerisation of higher alkyl methacrylates and stearyl methacrylate has also been successfully achieved by the bulk atom transfer radical polymerisation technique at ambient temperature in the presence of CuCl/PMDETA/tricaprylyl methyl ammonium chloride (Aliquatw336)... 

The phenomenological rate constant kin(, 7 ) describes the overall chemically controlled polymerisation reaction and is incorporating an increase in value due to auto-catalysis. Combining Eq. (11) and Eq. (14) results in... 

Gibson VC, Marshall EL, Liobet DN, White AJP, Williams DJ. A well-defined Iron(II) alkoxide initiator for the controlled polymerisation of lactide. J Chem Soc Dalton Trans 2002 4321-2. 

Polymers can be produced by applying the various types of polymerisation mechanism described above, i.e. all radical polymerisations including controlled polymerisation and ionic polymerisation. In addition to producing polymers with well-defined characteristics, polymerisation in heterogeneous systems can be used to produce well-defined polymer particles including very well-structured composite nanoparticles. For instance, particles with a magnetic core and nanoparticles showing a core-shell-type nanostructure can be... 

Synthesis of block copolymers with well-defined structure has received considerable attention, as their properties are potentially of great interest (see Section 4.1). Until recently, the possibilities were limited to the use of either sequential addition of monomers in living anionic polymerisation systems, or coupling of polymers possessing reactive ends, e.g. telechelic polymers. Advances in radical controlled polymerisation have opened new perspectives. 

Latent initiators that are activated photochemically or by heating, such as benzylpyrazinium salts, enable controlled polymerisations. In fact, the activity of pyrazinium salts can be controlled by electronic modifications of benzyl and pyrazine groups [5]. Epoxidised soybean and castor oils have been polymerised by cationic means in the presence of the latent initiator N-benzylpyrazininm hexaflnoroantimonate [6]. Cationic resins prepared from epoxidised castor oil display higher glass transition temperature (Tg) values and lower coefficients of thermal expansion than counterparts prepared from epoxidised soybean oil (ESO) because of increased intermolecnlar interactions in the former materials when compared with the latter polymer [6]. 

The development of well-defined ROMP initiators has expanded the scope of the metathesis reaction, permitting the controlled polymerisation of highly functionalised monomers. Schrock s well-defined olefin metathesis initiators became available in the mid 1980s and they were based on alkoxy imido complexes of tungsten and molybdenum of general... 

The key to controlled polymerisation of fluorinated bicyclic olefins such as bis(trifluoromethyl) norbomadiene, BTFMND using the well defined Schrock initiators is that while they are inactive towards double bonds in the polymer chain, they react rapidly with the strained double bonds in the monomer to give ring-opening and a linear polymer, see Figure 2. The living nature of these polymerisations can be conveniently... 

However, the structure and composition of microdroplets in which the reaction takes place are not the only parameters controlling polymerisation. We shall see later that particles in the initial microemulsion cannot be considered as independent reactors since interparticle interactions play an important role. Small angle light and neutron scattering experiments have shown that these interactions are attractive [6.20]. There is a clear increase in these attractive interparticle forces as the proportion of acrylamide is raised. In particular, this has two consequences the second virial coefficient of osmotic pressure takes negative values the peak in the structure factor which characterises a hard sphere system is no longer present. 

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