Polycondensation, functional

However, the chain-end functionality remained an iodine atom. Further investigations to replace the iodine atom by an interesting polycondensable function were undertaken by various authors. 

Unlike vinyl-type macromonomers, studies concerning macromonomers bearing two polycondensable functions are rather rare. This may be due to the rather complex syntheses of such macromonomers. In the following sections, we will describe the different methods for synthesizing both vinyl-type and polycondensable-type macromonomers. 

Material produced by the reaction of relatively simple molecules with functional groups that allow their combination to proceed to high-molecular weights under suitable conditions formed by polymerization or polycondensation. Chemical reaction that takes place when a resin is activated. 

Recently, the above mentioned model reaction has been extended to polycondensation reactions for synthesis of polyethers and polysulfides [7,81]. In recent reports crown ether catalysts have mostly been used in the reaction of a bifunctional nucleophile with a bifunctional electrophile, as well as in the monomer species carrying both types of functional groups [7]. Table 5 describes the syntheses of aromatic polyethers by the nucleophilic displacement polymerization using PTC. 

Interfacial polycondensation between a diacid chloride and hexamethylenediamine in the presence of small amounts of ACPC also yield polymeric azoamid, which is a macroazo initiator.[27] In this manner, azodicarbox-ylate-functional polystyrene [28], macroazonitriles from 4,4 -azobis(4-cyano-n-pentanoyl) with diisocyanate of polyalkylene oxide [29], polymeric azo initiators with pendent azo groups [3] and polybutadiene macroazoinitiator [30] are macroazoinitiators that prepare block and graft copolymers. 

In conclusion, the self-condensation of 2-furaldehyde promoted by heat occurs with the formation of di- and trifurylic intermediates. The functionality of the growing chain increases after each oligomerization step until gelation and precipitation of the resin occurs. Thus, the process is non-linear from the onset since the condensation product 4 possesses three sites for further attack, namely the free C-5 position and the two formyl groups. It is interestering to note that while the polycondensation of 2-furfuryl alcohol is essentially linear and cross-linking is due to side reactions, the thermal resinification of 2-furaldehyde is intrinsically non-linear and gel formation occurs at earlier conversions. 

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... 

Block copolymers containing polysiloxane segments are of great interest as polymeric surfactants and elastomers. Polycondensation and polyaddition reactions of functionally ended prepolymers are usually employed to prepare well-defined block copolymers. The living polystyrene anion reacts with a,co-dichloropoly(dimethyl-siloxane) to form multiblock copolymers398. ... 

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. 

Example 13.2 Determine PD as a function of chain length for binary polycondensations that go to completion. 

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. 

When making theoretical considerations of polycondensation processes it is necessary to distinguish chemically identical functional groups if they differ in reactivity. Examples are primary and secondary hydroxyls in a molecule of glycerine, SA2j A2, which belong to kinetically distinct types Ax and A2. 

Monomers employed in a polycondensation process in respect to its kinetics can be subdivided into two types. To the first of them belong monomers in which the reactivity of any functional group does not depend on whether or not the remaining groups of the monomer have reacted. Most aliphatic monomers meet this condition with the accuracy needed for practical purposes. On the other hand, aromatic monomers more often have dependent functional groups and, thus, pertain to the second type. Obviously, when selecting a kinetic model for the description of polycondensation of such monomers, the necessity arises to take account of the substitution effects whereas the polycondensation of the majority of monomers of the first type can be fairly described by the ideal kinetic model. The latter, due to its simplicity and experimental verification for many systems, is currently the most commonly accepted in macromolecular chemistry of polycondensation processes. 

Noteworthy that all the above formulated results can be applied to calculate the statistical characteristics of the products of polycondensation of an arbitrary mixture of monomers with kinetically independent groups under any regime of this process. To determine the values of the elements of the probability transition matrix of corresponding Markov chains it will suffice to calculate only the concentrations Q()- of chemical bonds (ij) at different conversions of functional groups. In the case of equilibrium polycondensation the concentrations Qy are controlled by the thermodynamic parameters, whereas under the nonequilibrium regime of this process they depend on kinetic parameters. 

Let us address first the processes of irreversible polycondensation of an arbitrary mixture of monomers. The functional groups A1,...,Ai,...,Am act here as kineti-cally independent elements, and the scheme of the elementary reactions of condensation between them... 

The rate constants in the reactions (29) may be conveniently envisaged as elements of symmetric matrix k. In order to calculate the statistical characteristics of a particular polycondensation process along with matrix k parameters should be specified which characterize the functionality of monomers and their stoichiometry. To this end it is necessary to indicate the matrix f whose element fia equals the number of groups A in an a-th type monomer as well as the vector v with components Vj,... va,..., v which are equal to molar fractions of monomers M1,...,Ma,...,M in the initial mixture. The general theory of polycondensation described by the ideal model was developed more than twenty years ago [2]. Below the key results of this theory are presented. 

Fig. 1. The dependence of weight fraction of gel on conversion of functional groups A under irreversible polycondensation of monomer SA3 described by the simplified FSSE model with kinetic parameters K k k0 and K2=k2/k0. The curves are depicted proceeding from the results of calculations at values of these parameters equal to kx=1, k2=0.1 (a), and kx=1, 2=10 (b)...

The results reported above have been extended to the general case of irreversible polycondensation of an arbitrary mixture of monomers (characterized by arbitrary matrix of functionalities f and the composition vector v) under the conditions of the applicability of the FSSE model [26]. 

Polycondensation of difunctional oligomeric cyclodisilazanes with a,co-dihydroxypolysiloxanes proved to be another successful attempt to synthesize silazane modified polysiloxanes of improved thermostability. The cyclodisilazane oligomers IHa (see scheme below) are readily available from common and cheap materials, dichlorodimethylsilane and ammonia (fi). The chlorine atoms in these compounds can be easily exchanged to other functional groups, such as amino, hydroxyl, etc. 

---