Polymerization two-stage

We create polyurethanes from prepolymers by chain extension. In the case of hydroxyl-terminated prepolyraers the chain extender is an isocyanate. If we use a diisocyanate, Ae resulting polymer is linear. If we substitute some or all of the diisocyanate with a tri- or 

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Polymerization of raw feedstock. Aliphatic hydrocarbon resins. Raw feedstock contains straight-chain and cyclic molecules and mono- and diolefins. The most common initiator in the polymerization reaction is AICI3/HCI in xylene. The resinification consists of a two-stage polymerization in a reactor at 45°C and high pressure (10 MPa) for several hours. The resulting solution is treated with water and passed to distillation to obtain the aliphatic hydrocarbon resins. Several aliphatic hydrocarbon resins with different softening points can be adjusted. 

Single stage polymerization generates much more heat than the polymerization of a prepolymer in the chain extension stage of the two stage polymerization process. Why is this so, and what benefit is there in having a lower heat of polymerization ... 

Immobilized Mucor miehei lipase (lipase MM) induced the polycondensation of adipic acid and 1,4-butanediol in ether solvents [26]. A horizontal two-chamber reactor was employed to facilitate the use of the molecular sieves. A low disper-sity polyester with DP = 20 was obtained by two-stage polymerization. 

Fig.1. Two-stage polymerization of methyl methacrylate (MMA) in CH2CI2 at room temperature with the enolatealuminum porphyrin (2, R=Me)-methylaluminum bis(2,4,6-tri-tert-butylphenolate) (3f) (1.0 1.0) system. GPC profiles of the polymers formed at the first stage (I) [MMA]o/[l (X=Me)]o=50, 100% conversion Mn=7,000, Mw/Mn= 1.12 and the second stage (II) [MMA]o/[2]q=200, 100% conversion Mn=47,600,Mw/Mn= 1.05...

It is easy to show that for small t values, Eq. (2.29) transforms to Eq. (2.28). However, it is interesting to follow the pattern of P(t) dependence for the full range of p, from which it can be seen this dependence looks like a kinetic curve with self-acceleration. Thus the phenomenon of selfacceleration, which is observed in some cases, may be treated as a consequence of a two-stage polymerization reaction if the rate constants of both stages have values of the same order. The reaction rate at the initiation stage can be limited by various factors, and in this case, classification of activators as direct or indirect becomes meaningless.41... 

Figure 9.3 Typical temperature-time regime for a two-stage polymerization process...

In the polymerization of several cyclic acetals and ethers autoacceleration was observed. There might be a number of reasons for this behaviour, and some of these have already been discussed, namely the preinitiation equilibria and the inequality ki enhanced reactivity of the hydroxy end group in polyacetals toward active species (in comparison with acetal groups) is another, not yet considered, reason for induction periods. When the pol5mierization d ee increases with conversion the proportion of the active tertiary oxonium ions also increases, at the cost of the less reactive secondary oxonium ions (cf. Ref. 164), because the b k-biting or intermolec-ular transfer become more important than the end-biting. Thus, there b no need to make speculative assumptions about the nature of the active species and to propose the two stage polymerization of acetals in order to explain the induction... 

SYNTHETIC TECHNIQUES AND TYPES OF SYNTHESIS (a) Thermal two-stage polymerization... 

Ladder polymers can be produced batchwise in a two-stage polymerization process if the two polymerizable groups are activated by different catalysts (mechanism). Vinyl isocyanate, for example, responds differently to radical and anionic catalysts and can be polymerized first by one and then by the other mechanism ... 

SYNTHETIC TECHNIQUES AND TYPES OF SYNTHESIS (a) Thermal two-stage polymerization (ring-opening of hexachlorocyclotriphosphazene followed by nucleophilic substitution).(b) Mixed nucleophiles have also produced useful elastomers using the same two-step procedure, (c) Now better defined block and random polymers with elastomeric properties have been developed and characterized. ... 

PBOs are generally prepared by three general methods. The first method is a two-stage polymerization (Figure 5.23) that involves a low-temperature solution polycondensation of bis(o-aminophenol)s... 

A two-stage polymerization was carried out under argon. Owing to the high reactivity of the isocyanates, they polymerize first according to the following reaction scheme ... 

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