Polymerization reaction conditions

In anionic and coordination polymerizations, reaction conditions can be chosen to yield polymers of specific microstructurc. However, in radical polymerization while some sensitivity to reaction conditions has been reported, the product is typically a mixture of microstructures in which 1,4-addition is favored. Substitution at the 2-position (e.g. isoprene or chloroprene - Section 4.3.2.2) favors 1,4-addition and is attributed to the influence of steric factors. The reaction temperature does not affect the ratio of 1,2 1,4-addition but does influence the configuration of the double bond formed in 1,4-addition. Lower reaction temperatures favor tram-I,4-addition (Sections 4.3.2.1 and 4.3.2.2). 

In the context of ROMP chemistry, living polymerization reaction conditions have only been observed when well-defined carbene complexes are used as the catalysts. The first catalyst to behave in this fashion was the titanocene complex (4), while more recently, complexes containing Ta, W, and Mo have been shown to be catalysts for the living ROMP of a variety of cyclic alkenes. The Mo complex (5b) is an especially promising catalyst since it is compatible with a number of functional groups and thus can be used to synthesize a variety of functionalized polymers. 

The polycondensation of BHET to PET proceeds in the melt at temperatures of 270-305 °C, under vacuum (< 1 mbar absolute pressure) and in the presence of Lewis acid metal compounds, such as titanium alkoxides, dialkyltin oxide, gallium oxide, germanium oxide, thallium oxide, lanthanide salts, and most commonly, antimony oxide [1,2, 22-26]. Under polymerization reaction conditions, these catalysts are generally converted to their alkoxides with ethylene glycol. Typical of such alkoxides is antimony(III) glycolate, the active catalyst for the majority of the world s PET production [27] (cf. Structure 1). 

Type of reaction Polymerization Reaction condition solid-state... 

Just as the comparatively weak metal-metal bonds pose problems for the synthesis of the difunctional dimers, they cause similar problems in the synthesis of the polymers. The relative weakness of the metal-metal bonds makes them more reactive than the bonds found in standard organic polymers thus, under many standard polymerization reaction conditions, metal-metal bond cleavage would result. For example, metal-metal bonds react with acyl halides to form metal-hahde complexes. Therefore, the synthesis of polyamides using metal-metal bonded diamines and diacyl chlorides would simply lead to metal-metal bond cleavage rather than polymerization. Likewise, metal-metal bonded complexes are incompatible with many Lewis... 

Bases were used as polymerization catalyst since early days of polymerizalion studies, but showed limited usefulness due to the encountered low extent of polymerization. Reaction conditions are adjusted to enhance living anionic polymerization as applied to styrene in liquid ammonia through initiation by K NH2. Addition of the NH2 to olelinic part of the monomer generates the intermediate carbanion which propagates until termination is attained by abstraction of proton by the anion from the ammonia. If this type of termination occurred fast, then a limited polymerization process would be attained as shown in Scheme 3.8. 

An example of the first-order measurement approach of combinatorial materials is illustrated in Figure 5.3. Measurements of fluorescence spectra of solid polymerized materials were performed directly in individual microreactors. A view of the 96-microreactor array is shown in Figure 5.3A. Several chemical parameters in the combinatorial samples were identified from these measurements. The spectral shape of the fiuorescence emission with an excitation at 340 nm provided the information about the concentration of the branched product in the polymer and the selectivity of a catalyst used for the melt polymerization. A representative fiuorescence spectrum (along with an excitation line at 340 nm) from a single microreactor in the array is illustrated in Figure 5.3B. The first-order measurements were used for the optimization of melt-polymerization reaction conditions as described in Section 5.1. 

Figure 6. Real-time ATR-FTIR monitoring of a living IB polymerization. Reaction conditions [1B] = 2 M, [TMPCI], = 4x10 M, [TiCIJ, = 4x10 M, [D/BP]=...

Metal complexes bearing initiator functionalities in their ligand periphery may act as multifunctional metalloinitiators according to the core-first approach. This method is less sensitive to steric restrictions and the products can be easily purified from the unreacted monomer by precipitation. Limitations of the method include the difficulties concerning the synthesis of the metalloinitiator, which often bears sensitive functionalized ligands, and the compatibility problems of the metal complex with the polymerization reaction conditions. Furthermore, decomposition of the complex has to be avoided during... 

Reynhout XEE, Beckers M, Meuldijk A, Drinkenburg BAH (2005) Electrosteric stability of styrene/acrylic acid copolymer latices under emulsion polymerization reaction conditions. J Polymer Sci Part Polymer Chem 43(4) 726... 

In anionic and coordination polymerizations, reaction conditions can be chosen to yield polymers of specific miaostracture. However, in radical polymerization, while... 

The nature of the formed polymer structure depends on the type of the diene monomer and of the initiator as well as on the polymerization reaction conditions. In general, lowering the reaction temperature leads... 

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