Nucleophilic comonomers

In another process for the synthesis of PPS, as well as other poly(arylene sulfide)s and poly(arylene oxide)s, a pentamethylcyclopentadienylmthenium(I) TT-complex is used to activate -dichlorobenzene toward displacement by a variety of nucleophilic comonomers (92). Important facets of this approach, which allow the polymerization to proceed under mild conditions, are the tremendous activation afforded by the TT-coordinated transition-metal group and the improved solubiUty of the resultant organometaUic derivative of PPS. Decomplexation of the organometaUic derivative polymers may, however, be compHcated by precipitation of the polymer after partial decomplexation. 

Synthesis of polyimides directly from perylene-3,4,9,10-tetracarboxylic acid dianhydride (DPTA) [4, 5] using diamines as the nucleophilic comonomers which leads to improved solubility for the target polymers. 

Propenylphenoxy compounds have attracted much research. BMI—propenylphenoxy copolymer properties can be tailored through modification of the backbone chemistry of the propenylphenoxy comonomer. Epoxy resins may react with propenylphenol (47,48) to provide functionalized epoxies that may be low or high molecular weight, Hquid or soHd, depending on the epoxy resin employed. Bis[3-(2-propenylphenoxy)phthalimides] have been synthesized from bis(3-rutrophthalimides) and o-propenylphenol sodium involving a nucleophilic nitro displacement reaction (49). They copolymerize with bismaleimide via Diels-Alder and provide temperature-resistant networks. 

We initiated our work by examining nucleophilic aromatic substitution, a somewhat difficult reaction to effect in other than activated aryl halides as substrates. It occurred to us that if polyhaloaromatics could be made to suffer disubstitution under mild solid-liquid PTC conditions, then they might be used as comonomers with a variety of bisnucliophiles to prepare halogenated polyaryl-ethers, sulfides, sulfone-ethers as well as other interesting polymers which are at present synthesized only with some difficulty. 

Dynamic polymeric systems utilizing the C=N exchange reaction have been reported by Lehn s group. They have suggested a polymerization system consisting of a fluorene-based dialdehyde monomer 4, cyclohexane diamine 5, and fluorene-based diamine 6 as a comonomer (Scheme 8.2) [20,21]. In principle, a 1 1 1 mixture of all monomers in ethanol was expected to yield the two-component polymers 7 and 8 together with all component-mixed polymers. However, polymer 7 was dominantly yielded (80%) due to the nucleophilicity of diamines. The nucleophilic-ity of aliphatic diaminocyclohexane is much higher than that of aromatic... 

Among the monomers given in Scheme 1, several possess sufficient nucleophilicity to undergo cationic polymerization (7,8), namely 2-vinyltetrahydrofiiran 1, the alkenylfiirans 2, the furfurylidene ketones 3, 2-furyl oxiranes 4 and the furfuryl vinyl ethers 6, Moreover, furfural and its 5-methyl derivative can act as comonomers in certain cationic copolymerizations. 

Ziegler-Natta (or Natta-Ziegler) catalyst (ZNC) Able to produce stereoregular pol5uners. zwitterionic polymerization Copolymerization between nucleophilic and electrophilic comonomers. 

Strongly electrophilic or nucleophilic monomers will polymerize exclusively by anionic or cationic mechanisms. However, monomers that are neither strongly electrophilic nor nucleophilic generally polymerize by ionic and free radical processes. The contrast between anionic, cationic, and free radical methods of addition copolymerization is clearly illustrated by the results of copolymerization utilizing the three modes of initiation (Figure 7.1). Such results illustrate the variations of reactivities and copolymer composition that are possible from employing the different initiation modes. The free radical tie-line resides near the middle since free radical polymerizations are less dependent on the electronic nature of the comonomers relative to the ionic modes of chain propagation. 

The maleimide group can undergo a variety of chemical reactions. The reactivity of the double bond is a consequence of the electron withdrawing nature of the two adjacent carbonyl groups which create a very electron-deficient double bond, and therefore is susceptible to homo- and copolymerizations. Such polymerizations may be induced by free radicals or anions. Nucleophiles such as primary and secondary amines, phenates, thiophenates, carboxylates, etc. may react via the classical Michael addition mechanism. The maleimide group furthermore is a very reactive dienophile and can therefore be employed in a variety of Diels Alder reactions. Bisdienes such as divinylbenzene, bis(vinylbenzyl) compounds, bis(propenylphenoxy) compounds and bis(benzocyclobutenes) are very attractive Diels Alder comonomers and therefore some are used as constituents for BMI resin formulations. An important chemical reaction of the maleimide group is the ENE reaction with allylphenyl compounds. The most attractive comonomer of this family is DABA particularly when tough bismaleimide resins are desired. 

The nucleophilic halo displacement reaction was employed to synthesize 2,6-bis(o-propenylphenoxy)pyridine (80). This comonomer was combined with Compimide 353 to provided a system with excellent room temperature tack and therefore is suited for prepreg tape. 

Similarly, the same catalysts that promote the syndiospecific polymerisation of styrene also polymerise ethylene and a-olefins [106,107], ring-substituted styrenes [6] and conjugated dienes [44,74,108-110], These monomers can also be copolymerised with each other [111-114], Substituted styrenes, which yield syndiotactic polymers by polymerisation run with syndiospecific catalysts, form copolymers with styrene the polymerisation rate increases with increasing nucleophilicity of the comonomer. The random copolymers formed are co-syndiotactic [6,111,112]. 

Since oxiranes are representative heterocyclic monomers containing an endo-cyclic heteroatom, and the most commonly polymerised of such monomers, they have been subjected to copolymerisations with heterocyclic monomers containing both an endocyclic and an exocyclic heteroatom. Coordination copolymerisations of heterocyclic monomers with different functions are focused on oxirane copolymerisation with cyclic dicarboxylic acid anhydride and cyclic carbonate. However, the statistical copolymerisation of heterocyclic monomers with an endocyclic heteroatom and monomers with both endocyclic and exocyclic heteroatoms have only a limited importance. Also, the block copolymerisation of oxirane with lactone or cyclic dicarboxylic acid anhydride is of interest both from the synthetic and from the mechanistic point of view. Block copolymerisation deserves special interest in terms of the exceptionally wide potential utility of block copolymers obtained from comonomers with various functions. It should be noted, however, that the variety of comonomers that might be subjected to a random, alternating and block polymerisation involving a nucleophilic attack on the coordinating monomer is rather small. 

With the purpose of increasing the range of available block copolymers, comonomers other than methacrylates and acrylates can also be involved in sequential polymerization, provided that they are susceptible to anionic polymerization. Dienes, styrene derivatives, vinylpyridines , oxiranes and cyclosiloxanes are examples of such comonomers. The order of the sequential addition is, however, of critical importance for the synthesis to be successful. Indeed, the pX a of the conjugated acid of the living chain-end of the first block must be at least equal to or even larger than that of the second monomer. Translated to a nucleophilicity scale, this pK effect results in the following order of reactivity dienes styrenes > vinylpyridines > methacrylates and acrylates > oxiranes > siloxanes. 

In the preceding section we have disscussed the influence of monomer nucleophilicity on copolymerization behaviour. Only monomers of similar nucleophilicities can be randomly copolymerized. Attempted simultaneous copolymerization of e.g. amines with ethers, and sulfides or oxazolines with ethers gives homopolymers of the more nucleophilic monomer. However, stepwise addition of a more basic comonomer to a living polymer derived from the less nucleophilic heterocycle yields block copolymers (cf. Sect. 15.3.1.2). 

Table 15.8, gives examples of copolymerization above Tc (depending on monomer concentration) and shows regular 1 1 or 1 2 copolymers under suitable conditions. When THF reacts with comonomer of similar or higher nucleophilic reactivity, an excess of THF is required to form the corresponding regular polymers (oxetanes,... 

Nearly all the reported attempts at ionic copolymerization of vinyl ketones led to polymers containing very high ketone content, even when the comonomer was known to homopolymerize under the conditions. Copolymerization of phenyl vinyl ketone and styrene in bulk or in tetrahydrofuran initiated with n-butyllithium produced only poly(phenyl vinyl ketone) [341]. The non-incorporation of styrene in the anionic copolymerization was due to the phenyl vinyl ketone enolate anion being sufficiently nucleophilic to add the phenyl vinyl ketone monomer but not the styrene. 

Method of synthesis cationic polymerization of high purity Isobutylene and isoprene is used to produce butyl rubber in the presence of complex systems of catalysts polymerization is terminated by irreversible destruction of the propagating carbenium ion by the collapse of the ion pair, by hydrogen abstraction from the comonomer, by formation of stable allylic carbenium ions, or by reaction with nucleophilic species such as alcohols or amines ... 

Schemes 64 and 65 outline the synthesis of bifunctional telechelic macromolecules using methylene chloride as a comonomer or chain extender. In the first procedure, the phenolic polymer chain ends are end capped with an electrophilic compound containing a functional group such as p-chloromethylstyrene. The order of the rate constants shown in Scheme 64 is self-explanatory. In the second procedure, the chloromethyl ether chain ends are end capped with a nucleophilic compound containing a functional group such as 2-(p-hydroxyphenyl)-2-oxazoline. " ...

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