Block copolymers from radical polymerisation

However, despite considerable progress, the truly living character is far from being attained and it seems preferable to use the term controlled process rather than living process. Recently, various methods to synthesise block copolymers by radical polymerisation or telomerisation were reviewed [349]. But, to our knowledge, the literature does not mention any investigation of controlled radical polymerisation of fluorinated polymers. 

In this section, we review the properties of a series of PNIPAM-b-PEO copolymers with PEO blocks of varying length, with respect to the PNIPAM block. Key features of their solutions will be compared with those of PNIPAM-g-PEO solutions. PNIPAM-b-PEO copolymers were prepared by free-radical polymerisation of NIPAM initiated by macroazoinitiators having PEO chains linked symmetrically at each end of a 2,2/-azobis(isobutyronitrile) derivative [169,170]. The polydispersities of PEOs were low, enabling calculations of the number-average molar mass for each PNIPAM block from analysis of their H-NMR spectra (Table 2). 

Figure 8 Schematic representation of (a) branched-block copolymers which could be available by statisticallpragmatic modification of free-radical polymerisation. (b) represents a controlled structure available from living free-radical polymerisation...

In this century it has been shown that mastication of rubber produces free radicals with high chemical reactivity. Thus, for example, macroradicals from cis-polyisoprene initiate vinyl polymerisation when oxygen is rigorously excluded from a high shear mixer, giving rise to block copolymers, typically containing rubber and methyl methacrylate (Scheme 3.2). In the presence of oxygen this process is inhibited and the... 

Near-IR spectroscopy (10000-4000/cm) was successfully used to monitor conversion dining conventional, anionic solution polymerisation of styrene and isoprene to homopolymers and block copolymers. The conversion of the vinyl protons in the monomer to methylene protons in the polymer was easily monitored under conventional (10-20% solids) solution polymerisation conditions. In addition to the need for an inert probe, high sampling frequencies were required since polymerisation times ranged from 5s in tetrahydrofuran to 20 minutes in cyclohexane. Preliminary data indicate that near IR is capable of detecting sequence distribution for tapered block copolymers, geometric isomer content, and reactivity ratios for free-radical copolymerisation. 20 refs. USA... 

Polymers with more than one type of repeating unit are referred to as copolymers, and they are important in that they have properties different from either homopolymer. One example of a copolymer is polyethylene-vinylacetate which is widely used as a hot melt adhesive. Another is acrylic fibre where a small amount of comonomer added to acrylonitrile makes it easier to spin and to dye. In both these examples the monomers are mixed together and then polymerised by a free radical process the resulting copolymer has a random arrangement of the two units along the chain. Using more specific methods of polymerisation it is possible to prepare block and graft copolymers. 

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