Precursor copolymers, living polymerization

The counter radical method can also be used for graft copolymer synthesis. Solomon et al. propose two routes [51]. The first one involves copolymerization with a functional monomer such as methacrylate containing pendant al-koxyamine. In the second route, the alkoxyamine is grafted onto a polymer precursor used in a second step to initiate the living polymerization of a second monomer. PBd-g-PMA is prepared this way from PBd. 

The dormant polymer is living in the sense that it grows until the monomer is depleted, and that it can grow on after additional monomer feed as in an ionic living polymerization.3 The final degree of polymerization is determined by the initial concentrations of the monomer and of the radical precursor Ro Y, and the formation of block copolymers is possible. 

Similarly, stable macroanions obtained by the subsequent metalation of the proper end groups such as diphenylvinyl and diphenylmethoxy were used in the living polymerization of tBMA yielding PIB-l7-PtBMA block copolymers with almost quantitative efficiency (Scheme 35). Moreover, amphiphilic polymeric materials can be prepared by hydrolysis of ester moieties of the polymers obtained by this method for instance, amphiphilic PIB-I7-PMAA diblock was prepared by the hydrolysis of the acrylate segment of the suitable precursor copolymer. A series of linear and star copolymers consisting of PIB and PMMA were also prepared. ... 

The polydispersity index for precursor polymers prepared via the Durham route was only in the range of 1.8-2.8 [88]. Krouse and Schrock were able to improve on the metathesis ROMP method and prepared a series of acetylene block copolymers with success both in controlling the molecular weight and in achieving low polydispersity [82]. Compared to a living polymerization process, the well-controlled ROMP precursor polymers can be grown continuously... 

VSO can be used to form block copolymers with PS followed by VSO elimination to form EA-PS block copolymers [73,89,90]. th monomers can be polymerized anionical the s ene was initiated first and end-capped with 1,1-diphenyl ethylene (DPE). Vfith the addition of a few drops of DPE to the living styr solution, the styryl carbanions were converted to diphenyl methyl car-banions [91], which were bull, less reactive, and less nucleophilic than the styryl carbanions, thus minimizing any side reactions. The VSO monomer was then added to the DPE-capped styryl chains to generate a PS/PVSO copolymer. The resulting precursor copolymer had PDIs that were as low as 1.09. To thermally eliminate the benzenesulfenic acid moieties from the PVSO block, the copolymer was heated from room temperature to 80° C at l°C/min and then held at 80°C for 1 h [90]. It was then heated to 150°C at I°C/min to get the maximum amoimt of elimination (87-92%). Whereas the PS/PVSO precursor copolymer was soluble in many solvents, the PS/PA copolymer was soluble only when the PA content was less than 50 mol%. th 78 mol% PA content the conductivity of the copolymer was 8 x 10 S/cm after iodine doping. 

In conclusion, by overcoming the disadvantage of the previous synthetic methods for the preparation of hyperbranched polymers, we designed an all-new Seesaw-type macromonomer strategy to construct perfect hyperbranched model samples with uniform subchains. In onr stndy, we successfully prepared various kinds of Seesaw-type macromonomers, snch as homopolymers, triblock copolymers and diblock copolymers. Using these maCTomonomers as precursors, we have further prepared a series of perfect hyperbranched homopolymers, block copolymers, graft copolymers and hetero-snbchain copolymers by a combination of controlled/ living polymerization and click chemistry. Various solution properties of these novel hyperbranched (co) polymers in dilnte and semidilute solntions have been studied in detail. More specifically, the main achievements of this work are as follows ... 

The C-S bond of the sulfide end groups can be relatively weak and susceptible to thermal and photo- or radical-induced homolysis. This means that certain disulfides [for example 7-9] may act as iniferters in living radical polymerization and they can be used as precursors to block copolymers (Sections 7.5.1 and 9.3.2). 

A rather obvious method to synthesize block copolymers is to use a "living" precursor as the anionic Initiator for the polymerization of second monomer.22However, this method requires that the Initiation reaction be fast, quantitative and free of side reactions. This means that the nucleophlllclty of the carbanlonlc sites should be sufficient to attack the second monomer added In other words, the monomers have to be added In the order of Increasing electroaffinity. 

Another way of synthesizing B-A-B triblock copolymers is to use a coupling reaction.2 Monocarbanionic poly-B precursor is used to initiate the polymerization of A. The living two block copolymer is then reacted stoichiometrically with an efficient bifunctional coupling agent, such as dibromo-p-xylene or dimethyldichlorosilane, or even phosgene. This coupling reaction yields the triblock copolymers. 

The synthesis and purification of polystyrene methacryloyl macromonomers (PS-MA) in the molecular weight range Mn= 1000-2000 g mol 1 by living anionic polymerization of styrene (S), termination with ethylene oxide (EO), and subsequent reaction with methacrylic chloride has already been described in detail elsewhere [180] (see also Scheme 16). In this context it has to be emphasized that the hydroxyethyl-terminated PS-MA macromonomer precursor (PS-OH) as obtained after purification of the crude PS-OH by silica column chromatography (cyclohexane/dichloromethane 1/1 v/v) and as charged in the PS-MA synthesis still contains up to about 15 wt-% of non-functionalized polystyrene (PS-H). This PS-H impurity of the PS-MA macromonomer does not interfere with the PS-MA synthesis and the subsequent TBA/PS-MA copolymerization and is easily and conveniently removed from the resulting PTBA-g-PS graft copolymer (see below). 

One of the significant developments in living cationic polymerization has been the synthesis of telechelics and production of diblock copolymers. PIB based macromonomers are another class of functional precursors. Copolymerization of these... 

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