Polydienes method

Of particular interest to us was to find a method to surface modify elastomers. G. B. Butler and co-workers have demonstrated that 4-substituted-l,2,4-triazoline-3,5-diones, RTDs, readily undergo ene reactions with polydienes at ambient temperatures (13). They found that the solubility and solution properties of the modified... 

Comparison of chemiluminescence isothermal runs with oxygen uptake and DSC measurements has been at the centre of interest since practical industrial applications of the chemiluminescence method were attempted. It is a fact that the best comparison may be achieved when studying polymers that give a distinct induction time of oxidation typical for autoaccelerating curves of a stepwise developing oxidation. This is the particular case of polyolefins, polydienes and polyamides. The theoretical justification for the search of a mutual relationship between the oxidation runs found by the various methods follows directly from the kinetic analysis of the Bolland-Gee scheme of polymer oxidation. 

This PSH technique was later utilized as an effective method of reductive modification for the unsaturated polymers such as polydiene rubbers and polypentenamer by Mango (2) and Samui et al ( ) ... 

Hydrolysis procedures have been, developed for the removal of the acetal protecting groups without accompanying crosslinking of polydiene backbones. Dilute solution hydrolyses are preferred over bulk methods ( ). (Eq. 6-9). 

This method was applied to synthesize various networks, with elastic chains of different nature polystyrene, polymethacrylates, polyvinylpyridine, and more recently polydienes. In some cases ethylene dimethacrylate is used to achieve cross-linking9, because of its higher electrophilicity. 

THe network structure of these block polymers can also be altered by actually crosslinking the elastomeric polydiene chains, thus introducing a chemical network. In this approach it was necessary to use a crosslinking method which would not result in any measurable chain scission. Dicumyl peroxide (Dicup) was chosen for crosslinking an SIS polymer since this peroxide is known to accomplish exclusive crosslinking without any observable chain scission (3). The Dicup was dissolved in a THF solution of the polymer, and a cast film was prepared which was then vulcanized in a press at 155 °C for 35 min. A control sample, without Dicup was treated in the same way. 

Asymmetric polyisoprene (PI) three-arm stars with variable length of the third arm were synthesized using the same method [8]. The reaction of the living PI chains with excess methyltrichlorosilane was performed at 5 °C. This low temperature was selected in an effort to minimize the coupled byproduct. Nevertheless the reduced steric hindrance of the PILi chain end in association with the low molecular weight of the polydienes used (Mn=5500 and 1100) led to the formation of an appreciable amount of the coupled byproduct, which was later separated by fractionation, with the excess of the last coupled arm, using a sol-vent-precipitant system. Pure products were finally isolated as evidenced by the molecular characterization techniques used (SEC, MO, SLS). 

The crucial point of the procedure is the control of the stoichiometry of the reaction between the living A chains and the DPE derivative, otherwise a mixture of stars is produced. A major problem is the fact that the rate constants for the reaction of the first and second polymeric chain with the DPE derivative are different. This results in bimodal distributions because of the formation of both the monoanion and dianion. In order to overcome this problem polar compounds have to be added, but it is well known that they affect dramatically the microstructure of the polydienes that are formed in the last step. However the addition of lithium sec-butoxide to the living coupled DPE derivative, prior to the addition of the diene monomer, was found to produce monomodal well defined stars with high 1,4 content. Finally another weak point of the method is that, as in the case of the DVB route, the B arms cannot be isolated from the reaction mixture and characterized separately. It is therefore difficult to obtain unambiguous information about the formation of the desired products. 

The x,x -azobis(x-cyano-alkanol)s are prepared by the Strecker synthesis followed by oxidation of the hydrazo intermediate. The same method was also used for 4,4 -azobis(4-cyano-n-pentanol) and 5,5 -azobis(5-cyanohexane-2-ol). The former one was a good initiator for secondary hydroxyl-terminated polydienes. Similar results were reported by Reed (see Sect. 1.1.2. a) for hydroxytelechelic polybutadienes (the functionality was 1.9 to 2.5, generally higher than 2, M < 5000). 

Isomerism in diene polymers can be measured by infrared and nuclear magnetic resonance spectroscopy. Some of the polymerization methods described in Chapter 9 allow the production of polydienes with known controlled constitutions and geometrical configurations. 

Finally, an original method to obtain telechelic polydienes is also possible — it can be associated to the telomerization of allylic alcohol with butadiene. 

Several star polymers have been prepared by reacting living polymers with DVB. The method has been applied in the past for the synthesis of PS48-49 and polydiene50 stars. Rather narrow molecular weight distribution PS stars were obtained when the [DVB] [PSLi] ratio was varied from 5.5 to 30 and the corresponding functionality was between 13 and 39. Similar behavior was obtained for polydiene stars when the [DVB] [PDLi] ratio was from 5 to 6.5 and the functionality of the star was varied between 9 and 13. In other cases, broad distributions were observed, caused by the large distribution of the functionalities of the stars prepared by this method. 

It is fairly well understood that alkyl lithiums form rather stable aggregates in which carbon-lithium bond order is maximized by the utilization of all valence orbitals of lithium.(1) Polystyryl lithium molecules are mostly dimeric in solution.(1.3,4) This has been generally accepted by all the investigators.TlT However, association numbers of two(6) and four(Z T has been reported for polydienes. Two methods were used in determining these values, viz., light scattering measurements (in vacuo) and viscosity measurements. 

Anionic polymerization frequently has been used to prepare well-defined living polymers such as polystyrene, poly(a-methylstyrene), polydienes, which may be transformed by two methods into block copolymers with cationically polymerizable monomers. When a living anionic polymer is mixed with a stoichiometric amount of a living cationic polymer the cationic and anionic species may couple. For example, anionic living polystyrene (St) or poly (a-methylstyrene) (MSt) were reacted with living cationic polytetrahydrofuran (THF). In the latter system the coupling efficiency was low, probably because of proton or hydride transfer 132) ... 

Block Copolymer Synthesis by Three-Step Sequential Monomer Addition The preparation of block copolymers by sequential addition of monomers using living anionic polymerization and a monofunctional initiator is the most direct method for preparing well-defined block copolymers. Detailed laboratory procedures for anionic synthesis of block copolymers are available [37, 230], Several important aspects of these syntheses can be illustrated by considering the preparation of an important class of block copolymers (Scheme 7.22), the polystyrene-fe-polydiene-( -polystyrene triblock copolymers. 

It is generally accepted that, in the polymerisation of dienes on lanthanide catalysts, the growing chain is attached to the transition metal by an 7t-allyl bond and that the chain growth occurs by incorporation of the monomer via the metal-carbon o-bond. In the case of neodymium catalysts, the delocalised 7t-allyl type structure of the terminal unit has been observed by spectroscopic methods [8, 26, 28, 58-60]. The results reported in these papers show that the relative contents of cis-l,A- and tri2ns-1,4-units in polydienes depend on the type of solvent used, the polymerisation temperature, structure of diene monomer, and the composition of lanthanide-based catalysts. These data can be interpreted in terms of the concept of isomerisation equilibrium between anti- and syn-forms of n-allyl terminal unit. One of the arguments in favour of the existence of this isomerisation... 

This is still the most popular method for graft copolymerization of elastomers via free radicals. Free radicals (I) are generated from the same types of initiators which are used for free radical polymerization and copolymerization (see Section 2.4). In general, these radicals are formed in the presence of a polydiene elastomer and a monomer therefore, there are several possible reactions of these initiator-derived radicals which can occur as shown in Eqs. (2.93)-(2.96). The competition between initiation of monomer polymerization (Eq. 

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