Vinyl polymerisation branching

Van der Waals radii, 8 Vibrational modes, 342 Vinyl ethers, polymerisation, 189 Vinyl polymerisation, 320 branching in, 321 chain length in, 321 coordination, 322 induction period in, 321... 

In SMM methodology, AB or latent AB , monomers are polymerised to obtain hyperbranched polymers. In general, in accordance with the reaction mechanism, there are two different routes (i) poly-condensation of AB , monomers and (ii) self-condensation vinyl polymerisation (SCVP). However, this methodology is not popular in the preparation of vegetable oil-based polymers, but as these approaches are significant in obtaining highly branched polymer and can also be used for this purpose, they are briefly described here. 

Dow catalysts have a high capabihty to copolymetize linear a-olefias with ethylene. As a result, when these catalysts are used in solution-type polymerisation reactions, they also copolymerise ethylene with polymer molecules containing vinyl double bonds at their ends. This autocopolymerisation reaction is able to produce LLDPE molecules with long-chain branches that exhibit some beneficial processing properties (1,2,38,39). Distinct from other catalyst systems, Dow catalysts can also copolymerise ethylene with styrene and hindered olefins (40). 

Investigation has shown that chain transfer to polymer occurs predominantly on the acetate methyl group in preference to the chain backbone one estimate of the magnitude of the predominance is 40-fold (92,93). The number of branches per molecule of poly(vinyl acetate) polymerised at 60°C is ca 3, at 80% conversion. It rises rapidly thereafter and is ca 15 at 95% conversion and 1-2 x lO" number-average degrees of polymerisation. 

It has been shown that intramolecular chain transfer to polymer occurs during the polymerisation of vinyl acetate, lea ding to short-chain branching (81,235—238). The number of short-chain branches has been estimated by nmr to be in the range of 0.12—1.7 mol % (81). The number of short-chain branches increases significantly at low monomer concentration. 

In this chapto we have reviewed recent developments in the technology dealing with the emulsion polymerisation of VAc and its copolymers. In particular, we have examined problems peculiar to VAc, such as reactivity and water solubility, and the resulting consequences regarding particle formation, growth and stabilization options. In addition, the development of particle structure and its effect on the film formation ttnd ultimate film properties were discussed. Finally, a family of branched vinyl esters for the production of higher performance vinyl copolymers was described as one possible path of future development in this area. 

RAFT polymerisation has also been used in conjunction with CuAAC for the preparation of highly branched, hyperbranched and neo-glycopolymers [134, 135]. For instance, Stenzel and co-workers reported the synthesis of a new class of glycomonomer (4-vinyl-l, 2,3-triazole), followed by its RAFT polymerisation in water/methanol at 60 C (Scheme 1.9) [135]. 

Another important feature is the sequence [3] by which butadiene polymerises it is called a microstructure , resulting from different ways of addition. A typical value for E-SBR is 13% cis-1,4, 69% trans-l,A and 18% 1,2 addition. The 1,2 addition results in vinyl pendent group. A pendent group is a small side group, which usually has a different chemical composition from that of the main chain, e.g., the phenyl-group in SBR. If the composition is the same and it has a polymeric sequence it will be called a branch in this book. 

BR is made with similar polymerisation systems as SBR. The molecular architecture of the anionic BR is essentially the same as that described for the anionic SBR. The microstructure is also the same and some high vinyl BR is also made. This system gives well-defined polymers, for example monodispersed linear and equal-arm star molecules. The equal arm star molecule is a branched polymer with equal branch-lengths. These samples have been extensively investigated to obtain scientific information. 

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