Polycondensation, functional polymers

Interest in anionic polymerizations arises in part from the reactivity of the living carbanionic sites4 7) Access can be provided to polymers with a functional chain end. Such species are difficult to obtain by other methods. Polycondensations yield ro-functional polymers but they provide neither accurate molecular weight control nor low polydispersity. Recently Kennedy51) developed the inifer technique which is based upon selective transfer to fit vinylic polymers obtained cationically with functions at chain end. Also some cationic ring-opening polymerizations52) without spontaneous termination can yield re-functional polymers upon induced deactivation. Anionic polymerization remains however the most versatile and widely used method to synthesize tailor made re-functional macromolecules. 

An alternative strategy to obtain silica immobilised catalysts, pioneered by Panster [23], is via the polycondensation or co-condensation of ligand functionalised alkoxysilanes. This co-condensation, later also referred to as the sol-gel process [24], appeared to be a very mild technique to immobilise catalysts and is also used for enzyme immobilisation. Several novel functional polymeric materials have been reported that enable transition metal complexation. 3-Chloropropyltrialkoxysilanes were converted into functionalised propyltrialkoxysilanes such as diphenylphosphine propyltrialkoxysilane. These compounds can be used to prepare surface modified inorganic materials. Two different routes towards these functional polymers can be envisioned (Figure 3.4). One can first prepare the metal complex and then proceed with the co-condensation reaction (route I), or one can prepare the metal complex after the... 

There are however many other examples of reactions between -functional polymers, yielding two-block, triblock-or multiblock copolymers, depending upon the functionality of both precursors. Functionalization can be achieved anionically, or by polycondensation, or by using transfer reactions. However, the anionic techniques are the only method to achieve an adequate molecular weight control and a low polydispersity. 

Another demonstration of the independence of the reactivity of functional groups with chain length was given by determining the degree of polycondensation for polymers derived from a homologous series of acids, each acid reacting with 1,6-hexanediol under identical conditions [32]... 

Various piperidine-functionalized polymers were obtained by polyaddition or polycondensation and contain ether, ester, siloxane, carbonate, amine, amide, urea or urethane construction units [8], Oligomeric siloxane 36 having n = 4 and analogous HAS-functionalized siloxanes [291] or polymers like 189 obtained by... 

Homopolymers, as well as random and block copolymers with PDMS, were created by a combination of polycondensation and anionic ring-opening polymerization. To convert the chlor-opropyl side groups into quaternary ammoniums, the polymer was first treated with lithium bromide to replace the chlorine with bromine. The polymer was dissolved with (3-hydroxypro-pyl)dimethylamine to create the amphiphilic quaternary amine-functionalized polymer. Bactericidal assays of statistical and block copolymers gave MIC values of 6-25 pgmr against E. coli and S. aureus, with somewhat better activity against S. aureus. 

Polyaddition and polycondensation reactions usually lead to functional polymers, since the polymers produced are terminated with reactive functional groups. A higher degree of functionality is easily affordable if monomers with additional reactive groups are used that do not participate in the step-growth polymerization. In emulsion polymerizations, neither polyaddition nor polycondensation reactions can be carried out consequently, the miniemulsion technique is of special interest as no diffusion of the monomers takes place. The first polyaddition in miniemulsion were performed in 2000, with the reaction of polyepoxides and hydrophobic diamines, bisphenols, and dimercaptanes [105]. Stable latexes of epoxy resins could be obtained, and apparent molecular weights of up to 20 000 g mol were measured. 

ADMET polymerization represents a versatile technique for the synthesis of unique, complex, and functional polymer stractures. ADMET is a step-growth polycondensation reaction that proceeds under mild conditions, whereby any molecule that can be functionalized with two terminal olefin groups has the potential to become an ADMET monomer. This, in turn, allows an almost Hmitless possibility to create interesting and useful polymer structures. Recently, ADMET has been used to synthesize functionalized PEs, silicon-containing elastomers, conductive polymers, and many other exotic and interesting macromolecules. Yet, this area of research is by no means exhausted rather, this simple and elegant reaction will continue to provide the means to explore the basic stracture-property relationships of complex functional materials. 

Polymer— A compound formed by the reaction of simple molecules having functional groups which permit their combination to proceed to higher molecular weights under suitable conditions. Polymers may be formed by polymerization (addition polymers) or polycondensation (condensation polymers). When two or more different monomers are involved, the product is a copolymer. 

Figure 7.16 Design and synthesis of a chemically functional polymer membrane by an interfacial polycondensation reaction and multilayer flow inside a microchannel.

Abstract In vitro synthesis of polyesters by polycondensation using isolated enzymes as catalyst via nonbiosynthetic pathways is reviewed. In most cases, lipase was used as catalyst and the polyesters were obtained from oxyacids, their esters, and dicarboxylic acid derivatives/glycols. Enzymatic polymerization proceeded under mild reaction conditions in comparison with chemical processes. By utilizing characteristic properties of lipases, regio- and enantioselective polymerizations proceeded to give functional polymers, most of which are difficult to synthesize by conventional methodologies. 

Another definition, taking into account polymerization conversion, has been more recently proposed.192 Perfect dendrimers present only terminal- and dendritic-type units and therefore have DB = 1, while linear polymers have DB = 0. Linear units do not contribute to branching and can be considered as structural defects present in hyperbranched polymers but not in dendrimers. For most hyperbranched polymers, nuclear magnetic resonance (NMR) spectroscopy determinations lead to DB values close to 0.5, that is, close to the theoretical value for randomly branched polymers. Slow monomer addition193 194 or polycondensations with nonequal reactivity of functional groups195 have been reported to yield polymers with higher DBs (0.6-0.66 range). 

Tractable polymers can be prepared when amino and anhydride functions are not located on the same aromatic ring, and different strategies were employed to obtain soluble polymer. AB benzhydrol imide was prepared by polycondensation of 4-(3-amino-l-hydroxymethylene) phtlialic acid monomethyl ester in NMP. The polymer soluble in NMP has been used as adhesive and coating.56 A second approach was based on an ether imide structure. AB aminophenylether phthalic acids (Fig. 5.34) were prepared by a multistep synthesis from bisphenols.155 The products are stable as hydrochloride, and the polycondensation takes place by activation with triphenylphosphite. The polymers are soluble in an aprotic polar... 

The DB obtainable in SCVP is DB=0.465 for r=kjk =l and reaches its maximum, DB=0.5, for r=2.6 [70,78]. This value is identical to that obtained in AB2 polycondensation when both B functions have the same reactivity [70,78]. Thus, hyperbranched polymers prepared by bulk polycondensation or polymerization contain at least 50% linear units, making this approach less efficient than the synthesis of dendrimers. 

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