Chain homopolymerisation

Chain reactions carried out on one type of monomer give rise to homopolymers when using two types of monomer the situation is more complicated. For example, polymerising mixtures of vinyl chloride with acrylate esters gives rise to a range of molecules, the first of which are relatively rich in acrylate molecules formed later, when the amount of acrylate monomer is relatively depleted, are richer in vinyl chloride. In a number of instances, reactions of this kind can be used to prepare polymers containing monomers which will not homopolymerise, e.g. maleic anhydride and stil-bene (vinylbenzene). 

In practice the amine curing reactions are often accelerated by the addition of Lewis acids, especially amine complexes of boron trifluoride. Such materials can also initiate epoxide homopolymerisation in which chain propagation occurs through a carbocation ... 

An analogous homopolymerisation can be initiated by strong bases, including for example tert-amines. In this case chain propagation probably proceeds through an oxyanion ... 

Similar behaviour to carbon monoxide is displayed by other heterounsatur-ated monomers of carbene-like structure, isocyanides, which homopolymerise in the presence of nickel-based catalysts, yielding polymers with a carbon-carbon main chain, poly(iminomethylene)s [60],... 

The same conclusion as in the case of propylene homopolymerisation has been drawn considering IR [396] and NMR [389,395] spectra of ethylene/propylene copolymers obtained with vanadium-based syndiospecific catalysts. The type of propylene insertion depends on the kind of last inserted monomer unit secondary insertion [scheme (40)] occurs more frequently when the last monomeric unit of the growing chain is propylene, while primary propylene insertion [scheme (39)] is more frequent when the last monomeric unit of the growing chain is ethylene [2]. The above explains the microstructure of ethylene/propylene copolymers obtained with vanadium-based Ziegler-Natta catalysts. These copolymers contain both m and r diads when the sequence of propylene units is interrupted by isolated ethylene units i.e. a propylene insertion after an ethylene insertion is substantially non-stereospecific [327,390,397], The existence of a steric interaction between the incoming monomer molecule and the last added monomer unit is also confirmed by the fact that the propagation rate for the secondary insertion of propylene in syndiospecific polymerisation is lower than for primary insertion in non-stereospecific polymerisation [398],... 

How can one explain the occurrence of steric defects in tactic poly(ot-olefin)s Explain why high-resolution nuclear magnetic resonance is the most convenient method for determining the chain micro structure in poly(a-olefin)s. Consider how 3H and 13C NMR spectroscopy can provide stereochemical information concerning a-olefin polymer chains on the diad level (m, r) and the triad level (mm, rr, mr). Explain why /1-olefins, which do not homopolymerise (without isomerisation) in the presence of Ziegler-Natta catalysts, undergo copolymerisation with ethylene in the presence of these catalysts. 

Telomerisation of hexafluoropropene may be achieved using fluoroalkyl iodides as telogens [218, 219] this is rather surprising, considering that it is very difficult to achieve homopolymerisation of hexafluoropropene (Figure 7.62). It has been suggested [218] that these reactions may not be radical-chain processes but could involve successive four-centre additions of fluorocarbon iodides to the olefin (Figure 7.63). 

In contrast to the requirements for homopolymerisation processes, the parameters needed to fully describe copolymerisation processes are more numerous. Molecular features such as the copolymer composition, composition distribution and chain sequence structure and their variation with conversion are compounded with those of copolymer MW and MWD. To understand copolymerisation processes, it is desirable to decouple as many of these molecular parameters as possible and study the influence of polymerisation reactor conditions on each. As yet there have been relatively few reports on the detailed behaviour of copolymerisation reactors (6-9 ). This work forms part of a wider range of investigations which are being carried out in our laboratories of control methods for the production of speciality polymers. 

The homopolymerisation and copolymerisation of vinylic monomers in liquid polyether polyols are typical chain reactions by radical mechanism and are characterised by initiation, propagation and termination steps [31] ... 

The monomers, obtained in near-quantitative yields, were submitted to free-radical homopolymerisation and copolymerisation with HEMA using 2-hydroxy-2-methyl-l-phenyl-propan-l-one as the photo-initiator. The interest of these materials (as opposed to the saturated counterparts reviewed above) is reactive C=C moieties within and at the end of their dangling chains. Their properties and chemical modifications are being investigated. 

The double bonds in bismalemide are highly electron-deficient due to two flanking carbonyl groups, and are reactive towards a bimolecular addition reaction. Hence the maleimide groups of a bismaleimide monomer or chain-extended prepolymer can undergo homopolymerisation to produce 3D network structures. To manipulate the structure and properties, different types of maleimide monomer or prepolymer can be used. The reactivity of such resins depends on their chemical structure and UPE. 

Copolymerisation of these macromonomers with norbomene or norbomene acetate has yielded a series of poly(norbomene)-graft-poly-(e-caprolactone) copolymers of well-defined structures. Furthermore, PCL macromonomers were also homopolymerised in high yield into high molecular weight comb chains of narrow molecular weight distribution MJM =1.10). Such copolymers have potential applications as surface modifiers, polymeric surfactants, compatibilisers in polymer blends, and dispersion stabilisers. 

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