Ring-opening Polymerisation ROP

1 Thermodynamic Considerations. Most polymerisations are characterised by a reduction in entropy as a large number of monomer molecules with the freedom to move in three dimensions are joined together and ultimately constrained to a linear ID polymer chain, where motion is much more restricted. Hence, for a ROP to be thermodynamically favourable under such circumstances, ring strain is usually needed to provide an enthalpic driving force, A/Zrop, that overcomes the unfavourable TAArop term that contributes to AGrop [eqn (8.1)]. 

In the case of some cyclics, such as the thionylphosphazene six-membered ring [NS(0)Cl(NPCl2)2], the small degree of ring-strain makes the favourable A/Zrop and unfavourable TAArop terms finely balanced. In the presence of a catalyst such as GaCls, ROP can be favoured at high concentrations and depolymerisation to the cyclic monomer at low concentrations [eqn (8.2)]. 

A rare exception to the dominance of enthalpic driving force is provided by the unstrained eight-membered ring (Me2SiO)4, which undergoes ROP to give poly(dimethylsiloxane). For this process, A//rop is approximately zero but the remarkable skeletal flexibility of the polysiloxane backbone makes the TAArop term favourable and entropy provides the driving force for ROP. Exceptional behaviour occurs in the extremely rare cases of monomers where the polymerisation is driven by entropy and A7/rop is unfavourable. In these cases, the formation of polymer is favoured at elevated temperatures. For example, cyclo-Sg will polymerise above 150 °C (where the favourable TAArop term dominates), but slowly depolymerises back to the cyclic Sg monomer at room temperature.  

2 Mechanisms. A range of mechanisms has been either proposed or established for the ROP of inorganic rings depending on the nature of the highly 

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Beside the natural fermentation process, dextran can be synthesised chemically via a cationic ring-opening polymerisation (ROP) of levoglucosan (1,6-anhydro-/3-D-glucose), a pyrolysis product of polyglucans (Fig. 8, [83]). 

The gold(I) complexes of the hydroxycyclohexyl functionalised carbene ligands were tested for their ability in the ring opening polymerisation (ROP) of L-lactide under solvent-free melt conditions [177,178]. 

A methoxy-terminated PEG-/>-PLA copolymer (CHsO-PEG-fo-PLA) was synthesised using the anionic ring-opening polymerisation (ROP) of both ethylene oxide and D,L-lactide in anhydrous tetrahydrofuran (THE). A typical experimental procedure for the synthesis of CHsO-PEG-f -PLA is described below. 

In the last decade, very significant developments have been made in the fields of polymerisation (oligomerisation and telomerisation) using NHC complexes with metals. However, we want to pay special attention to those processes only catalysed by NHCs without the need of any metal. In this field, Hedrick et al. disclosed in 2002 a transesterification-ring opening polymerisation (ROP) in which imidazolinylidene carbenes catalyse the synthesis of biodegradable polyesters from cyclic esters (Seheme 2.24). More recently, Liu et al. have shown how a different imizadolium carbene is even able to promote the polymerisation of two different monomers in a controlled fashion. NHC-catalysed processes other than ROP have been described, such as the oxa-Michael addition polymerisation of acrylates recently reported by Matsuoka et al. ... 

Our studies are focused on synthesis and characterization of stannyloligosilanes [1-3]. Among these compounds ring systems find special interest because they are possible precursors for ring-opening polymerisation (ROP). Via this synthetic pathway it should be possible to produce polymeric stannylsilanes, a new and unexplored class of compounds. 

Chemical catalysis, which had failed in previous studies, was applied successfully recently to the ring-opening polymerisation (ROP) of PDL using cheap metal-based... 

Heise and co-workers [45] studied the thiol-ene functionalisation of a polyester synthesised by the enzymatic ring-opening polymerisation (ROP) of globalide (an unsaturated macrolactone prepared from hydroxyl fatty acids) (Scheme 6.15). Authors claimed that this was the first example of the thiol-ene fimctionalisation of a fatty acid-derived polymer. 

There are two main routes to synthesise aliphatic polyesters polycondensation of bifunctional hydroxy acids and ring-opening polymerisation (ROP) of cyclic ester monomers (Okada, 2002). 

PCL can be synthesised using two methods, namely by the condensation of 6-hydroxycaproic acid and by the ring-opening polymerisation (ROP) of the cycUc e-caprolactone. This monomer is typically produced by the Baeyer—ViUiger oxidation of cyclohexanone with acetyl hydroxyperoxide (Lecoq et al., 1988). 

PTMC synthesis is realised either by copolymerisation of epoxides with carbon dioxide or by the ring-opening polymerisation (ROP) of cyclic carbonate monomers. It is also possible to obtain aliphatic carbonates via polycondensation of dialkyl or diphenyl carbonate or chlorophormates and aliphatic diols. However, polycondensation usually leads to polymers with rather low molar masses (Hyon et al., 1997). Besides, side reactions often occur during polycondensation (Jerome and Lecomte, 2008). 

Synthesis of polyanhydrides is carried out through various methods such as melt polycondensation, solution polymerisation, and ring-opening polymerisation (ROP). 

The traditional and most widely used route to prepare high molecular weight poly(dichloro)phosphazene is the thermally induced ring-opening polymerisation (ROP) of hexachlorophosphazene [9]. This is most commonly carried out in the molten state under... 

In 2006, two NHC-phenoxide chelates 3 were prepared by Shen et al (Figure 7.1). One of them was an active initiator for the ring-opening polymerisation (ROP) of e-caprolactone, albeit with poor control over the chain length and molecular weight distribution. The same group went on with the synthesis of enolate complexes 4, which displayed higher reactivities but equally poor control. ... 

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