Polymerization interchange

The addition of alcohols to form the 3-alkoxypropionates is readily carried out with strongly basic catalyst (25). If the alcohol groups are different, ester interchange gives a mixture of products. Anionic polymerization to oligomeric acrylate esters can be obtained with appropriate control of reaction conditions. The 3-aIkoxypropionates can be cleaved in the presence of acid catalysts to generate acrylates (26). Development of transition-metal catalysts for carbonylation of olefins provides routes to both 3-aIkoxypropionates and 3-acryl-oxypropionates (27,28). Hence these are potential intermediates to acrylates from ethylene and carbon monoxide. 

Glycol Titanates. Primary diols (HOGOH), such as ethylene glycol and 1,3-propanediol, react by alkoxide interchange at both ends, yielding insoluble, white soflds that are polymeric in nature (18,61—63) ... 

When a mixture of alkenes 1 and 2 or an unsymmetrically substituted alkene 3 is treated with an appropriate transition-metal catalyst, a mixture of products (including fi/Z-isomers) from apparent interchange of alkylidene moieties is obtained by a process called alkene metathesis. With the development of new catalysts in recent years, alkene metathesis has become a useful synthetic method. Special synthetic applications are, for example, ring-closing metathesis (RCM) and ring-opening metathesis polymerization (ROM) (see below). 

This section describes polymerizations of monomer(s) where the initiating radicals are formed from the monomer(s) by a purely thermal reaction (/.e. no other reagents are involved). The adjectives, thermal, self-initialed and spontaneous, are used interchangeably to describe these polymerizations which have been reported for many monomers and monomer combinations. While homopolymerizations of this class typically require above ambient temperatures, copolymerizations involving certain electron-acceptor-electron-donor monomer pairs can occur at or below ambient temperature. 

Although the term RAFT (an acronym for Reversible Addition-Fragmentation chain Transfer)38" is sometimes used in a more general sense, it was coined to describe, and is most closely associated with, the reaction when it involves thiocarbonylthio compounds. RAFT polymerization, involving the use of xanthates, is also sometimes called MADIX (Macromolccular Design by Interchange of Xambate) 96 The process has been reviewed by Rizzardo et [Pg.502]

Olefin metathesis, an expression coined by Calderon in 1967,1 has been accurately described in Ivin and Mol s seminal text Olefin Metathesis and Metathesis Polymerization as the (apparent) interchange of carbon atoms between a pair of double bonds (ref. 2, p. 1). This remarkable conversion can be divided into three types of reactions, as illustrated in Fig. 8.1. These reactions have been used extensively in the synthesis of a broad range of both macromolecules and small molecules3 this chapter focuses on acyclic diene metathesis (ADMET) polymerization as a versatile route for the production of a wide range of functionalized polymers. 

Polymers like those in the poly aniline family interchange protons and anions with the solution, allowing a local modulation of pH. Composites that interchange cations allow the modulation of any cation concentration. Efforts are being devoted to the synthesis of polymer or polymeric derivatives having great cationic specificity. 

The polymerization of a ring compound usually proceeds by an interchange reaction, induced either catalytically or by the presence of small amounts of end-group-producing substances. For example, the polymerization of lactide, the cyclic dimer of lactic acid, is accelerated by small amounts of water. The water undoubtedly hydrolyzes the lactide to lactyllactic acid, which may then react with other lactide molecules by ester interchange. This reaction scheme can be represented as follows ... 

The counterpart of reaction (III) in polyesters, i.e., ester-ester interchange, probably does not take place to any appreciable degree. Polymeric polysulfide rubbers ( Thiokor type)... 

Polyanhydrides are susceptible to interchange reactions with carboxyl groups in analogy to (I) and (II). Polymeric dimethylsiloxanes readily interchange in the presence of sulfuric acid by a mechanism which may be presumed to involve cations. In some polymers the interunit linkage is too stable to enter readily into interchange reactions. Such an example is polyethylene oxide... 

The conditions essential for the formation of this exceptionally sharp distribution are the following (1) growth of each polymer molecule must proceed exclusively by consecutive addition of monomers to an active terminal group, (2) all of these active termini, one for each molecule, must be equally susceptible to reaction with monomer, and this condition must prevail throughout the polymerization, and (3) all active centers must be introduced at the outset of the polymerization and there must be no chain transfer or termination (or interchange). If new active centers are introduced over the course of the polymerization, a much broader distribution will be produced for the obvious reason that those introduced late in the process will enjoy a shorter period in which to grow. If the chains suffer transfer, or if termination occurs with constant replenishment of the active centers by one... 

If a polymer formed initially by the addition of monomers to a fixed number of centers is subjected to conditions permitting interchange processes to occur, either during polymerization or subsequent thereto, the distribution will broaden. Polymerization of a lactone, for example, according to the mechanism... 

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