Poly addition Reactions

When poly(ethylene glycol) of molecular weight 1000 was used as the starting material for this poly addition reaction, polymers of molecular weight more than 20000 were obtained. As the functional groups are located in equidistant order, neighbouring effects can be excluded in this copolymer. 

In our particular type of step-addition polymerisation, monomers, dimers, trimers, oligomers and polymers are the reactive species which participate in the chain growth. Initially, the monomers react with monomers and give dimers, dimers react with monomers and dimers and give trimers and tetramers, respectively. The high MW polymer is formed only in the last stages of the poly addition reaction, at high conversion rates. Chain transfer and termination reactions are absent. 

Because hydrazine hydrate contains water, after the poly addition reaction 6.21 it is necessary to eliminate water by vacuum distillation. The reaction between hydrazine and TDI is very exothermic and the temperature increases rapidly in a short time, for example from room temperature to 50 °C to the reflux temperature ( 100 °C or more) [7, 8, 67-73]. 

The synthesis of monomers derived from fatty acids incorporating end-functions susceptible to classical poly addition reactions has been revived recently and yielded interesting results. Vinyl oleate (VO) and vinyl linoleate (VL) were synthesised by a transvinylation reaction of the corresponding fatty acids with an excess of vinyl acetate (VAc) in bulk using a safe iridium-based catalyst instead of previously used mercury-based counterparts (which are not acceptable today because of safety concerns) [91]. Scheme 4.21 summarises this synthesis in the case of OA. 

Step-growth polymerizations in extruders, both polycondensations and polyadditions, are far less investigated than chain growth reactions. Because the polymer has to remain thermoplastic, only bifunctional monomers should be used, and the molecular weight can be controlled by the addition of a small amount of monofunctional monomers. For both polycondensation and poly-addition reactions the feeding should be very accurate and stochiometrically correct, because otherwise the conversion and therefore pressure built up will be seriously restricted. 

The second category of polymerization reactions does not involve a chain reaction and is divided into two groups poly addition and poly condensation [4]. In botli reactions, tire growth of a polymer chains proceeds by reactions between molecules of all degrees of polymerization. In polycondensations a low-molecular-weight product L is eliminated, while polyadditions occur witliout elimination ... 

Diacyl peroxides are used in a broad spectmm of apphcations, including curing of unsaturated polyester resin compositions, cross-linking of elastomers, production of poly(vinyl chloride), polystyrene, and polyacrjlates, and in many nonpolymeric addition reactions. 

Poly(phenylene oxide)s undergo many substitution reactions (25). Reactions involving the aromatic rings and the methyl groups of DMPPO include bromination (26), displacement of the resultant bromine with phosphoms or amines (27), lithiation (28), and maleic anhydride grafting (29). Additional reactions at the open 3-position on the ring include nitration, alkylation (30), and amidation with isocyanates (31). 

Sulphones - see also Acetoxysulphones, /1-Acyloxysulphones, a-Alkoxysulphones, a-Aminosulphones, Azidosulphones, Azosulphones, Azoxysulphones, co-Cyanosulphones, Dialkoxysulphones, a-Diazosulphones, Disulphones, Episulphones, Epoxysulphones, a-Halosulphones, Hydroxysulphones, / -Iminosulphones, Ketosulphones, a-Lithiosulphones, a-Nitrosulphones, /1-Oxosulphones, Poly(olefin suphonejs, Polysulphones, y-Siloxysulphones, Tetrahalosulphones, Trisulphones addition reactions of 642-649, 774-809 alkadienyl - see Alkadienyl sulphones alkenyl - see Alkenyl sulphones alkyl aryl - see Alkyl aryl sulphones alkylthiomethyl - see Alkylthiomethyl sulphones... 

Successive 1,4 units in the synthetic polyisoprene chain evidently are preponderantly arranged in head-to-tail sequence, although an appreciable proportion of head-to-head and tail-to-tail junctions appears to be present as well. Apparently the growing radical adds preferentially to one of the two ends of the monomer. Which of the reactions (6) or (7) is the preferred process cannot be decided from these results alone, however. Positive identification of both 1,2 and 3,4 units in the infrared spectrum shows that both addition reactions take place during the polymerization of isoprene. The relative contributions of the alternative addition processes cannot be ascertained from the proportions of these two units, however, inasmuch as the product radicals formed in reactions (6) and (7), may differ markedly in their preference for addition in one or the other of the two resonance forms available to each. We may conclude merely that structural evidence indicates a preference for oriented (i.e., head-to-tail) additions but that the 1,4 units of synthetic polyisoprene are by no means as consistently arranged in head-to-tail sequence as in the naturally occurring poly-isoprenes. 

Polymers can be formed from compounds containing a c=c double bond. Alkenes, such as ethene, can undergo addition polymerisation to form a polymer. A polymer is a compound consisting of very long chain molecules built up from smaller molecular units, called monomers. The polymerisation of ethene, to form poly(ethene), is a free radical addition reaction. 

The early work of Wessely suggested the occurrence of some side reactions which led to the formation of diketopiperazines (77) or hydan-toins (27). These reactions may put an upper limit to the degree of polymerisation which may be obtained in poly-additions of NCA s but it is more probable that these products arise from an unsuccessful initiation (see p. 40) rather than from a termination. Their participation in the process decreases the yield of C02 evolved in the polymerisation. 

The discovery of high molecular-weight synthetic polypeptides came as a result of systematic studies by Blout and his co-workers of the conditions which limit the degree of polymerisation of products formed by polymerisation of NCA. Contrary to previous beliefs, it was found that the polymerisation initiated by n-hexyl amine in dry dioxane yields polypeptides of higher molecular weights than expected from the monomer-to-initiator ratio, provided M/I < 100. It should be stressed again that this observation demonstrates that some additional modes of propagation contribute to the reaction, i. e. the "simple poly-addition mechanism cannot account in toto even for the polymerisation initiated by primary amines in dioxane. 

An example for a synthesis of a poly(siloxane) network is shown in Fig. 37b. In a one-step reaction the mesogenic moieties as well as the crosslinking agent are coupled via an addition reaction to the reactive linear poly(methylhydrogensiloxane) backbone 92). Because of similar reactivity of the crosslinking agent and mesogenic molecules, a statistical, disordered addition to the backbone has to be expected. 

In the following we will discuss the corresponding polymer By addition reaction to a poly(hydrogenmethylsiloxane) (r = 95), the m-l.c. is attached to the backbone... 

Addition polymer A polymer formed by an addition reaction. For example, poly(ethene) is formed from ethene. 

In Chapter 14 (p. 226) you studied the different addition polymers produced from alkenes. Not all polymers are formed by addition reactions, though. Some are produced as a result of a different type of reaction. In 1935 Wallace Carothers discovered a different sort of plastic when he developed the thermoplastic, nylon. Nylon is made by reacting two different chemicals together, unlike poly(ethene) which is made only from monomer units of ethene. Poly(ethene), formed by addition polymerisation, can be represented by ... 

Quantitative conversion is one of the essential preconditions to achieve a significant molecular weight in stepwise polymerization process. Consequently, an iron-catalyzed Michael reaction would be a suitable elementary step for a polyaddition. Bis-donor 24c and bis-acceptor 41b, readily accessible from common starting materials [69], were converted with FeCl3-6H20 to yield a poly-addition product... 

In peroxyl-free-radical chemistry, H02702 " elimination reactions play a major role (Chap. 8.4). In polymer free-radical chemistry, these reactions are of special interest, because they lead to a conversion of slowly diffusing polymer-derived radicals into the readily diffusing HCV/CV radicals. The H02 /02 "-elimina-tion typically proceeds from an a-hydroxyalkylperoxyl radical [reaction (22)]. In poly(vinyl alcohol), for example, such an structural element is formed by H-abstraction and subsequent 02 addition [reactions (18) and (19)]. The same structural element may also be formed during the bimolecular decay of peroxyl radicals which carry an H-atom in [3-position [reactions (20) and (21)]. 

A third variant on the polyphosphazene skeletal structure is represented by the poly(thionylphosphazenes) (reactions (65) and (66)) in which every third phosphorus along the chain is replaced by a sulfur VI atom.266-272 These species are more hydrolytically stable than their sulfur IV analogues, probably because the presence of two side groups on sulfur provides additional protection for the main chain. 

For poly silanes made by Wurtz reaction, the presence of functional groups in polysilane polymers is limited by the vigorous conditions of the sodium condensation reaction. Any substituents that react with molten sodium metal must therefore be introduced after the polymer is synthesized. Halogen atoms can be introduced into alkenylpolysilanes by HBr or HC1 addition reactions, as shown for the 3-cyclohexenyl-ethyl polymers in equation (21).37 Chlorine atoms have also been introduced into arylpolysilanes by chloromethylation, in which -CH2C1 groups are substituted onto phenyl rings in the polymer.38... 

Terminally brominated PE as PE macroinitiator can be produced by other methods. It has been reported that vinyl terminated PE produced by a bis(phenoxy-imine)metal complex and MAO catalyst system (Mn = 1800, Mw/Mn = 1.70) was converted to terminally 2-bromoisobutyrate PE through the addition reaction of 2-bromoisobutyric acid to the vinyl chain end. Polyethylene-Wodc-poly( -bulyl acrylate) (PE-fo-PnBA) from terminally brominated PE by ATRP procedure has also been produced [68]. It was reported that degenerative transfer coordination polymerization with an iron complex can be used to prepare terminally brominated PE as a macroinitiator [69]. A Zn-terminated PE prepared using an iron complex and diethylzinc,... 

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