Copolymerization random

Random copolymerization is rather unusual. Sometimes a monomer which does not easily form a homopolymer will readily add to a reactive group at the end of a growing polymer chain. In turn, that monomer tends to make the other monomer much more reactive. 

GopolymeriZation Initiators. The copolymerization of styrene and dienes in hydrocarbon solution with alkyUithium initiators produces a tapered block copolymer stmcture because of the large differences in monomer reactivity ratios for styrene (r < 0.1) and dienes (r > 10) (1,33,34). In order to obtain random copolymers of styrene and dienes, it is necessary to either add small amounts of a Lewis base such as tetrahydrofuran or an alkaU metal alkoxide (MtOR, where Mt = Na, K, Rb, or Cs). In contrast to Lewis bases which promote formation of undesirable vinyl microstmcture in diene polymerizations (57), the addition of small amounts of an alkaU metal alkoxide such as potassium amyloxide ([ROK]/[Li] = 0.08) is sufficient to promote random copolymerization of styrene and diene without producing significant increases in the amount of vinyl microstmcture (58,59). 

For instance, the temperature of the solid-solid transition at room temperature of PTFE is lowered of nearly 40 °C for the random copolymerization of 5% by mol of hexafluoropropylene with tetrafluoroethylene [97,98],... 

Random copolymerization occnrs between butadiene and styrene [15]. There are no appreciable differences in the nncleophilic and electrophilic abilities between the radical centers with the vinyl and phenyl groups at the end of the growing polymer chain or in the donor/acceptor properties between the monomers. 

The results agreed well with the kinetic B, assuming random copolymerization and similar reactivities of the initiating vinyl sites of the inimer, calculated from the following equation ... 

The living nature of the system has been utilized to prepare a range of block copolymers, including PEO-b-PPO,938 939 P(Et-EO)-b-PEO, P(Et-EO)-b-PPO and the triblock P(Et-EO)-b-PEO-b-PPO.936 Random copolymerization of EO and PO also affords narrow molecular weight distributions.940 However, for the copolymerization of PO with slower monomers, such as ECH, the more active PO incorporates preferentially to afford block-like materials. 

Random copolymerization of propylene oxide with ethylene oxide proceeded smoothly with the Nd(2-EP)3/AlEt3/H20 system at 80 °C [59]. From... 

The living radical polymerization of some derivatives of St was carried out. The polymerizations of 4-bromostyrene [254], 4-chloromethylstyrene [255, 256], and other derivatives [257] proceed by a living radical polymerization mechanism to give polymers with well-controlled structures and block copolymers with poly(St). The random copolymerization of St with other vinyl... 

Cao and coworkers synthesized three series of copolymers 348 [426], 349 [427], 350 [428], and 351 [429], exploiting random copolymerization of fluorene fragments with dibromo-derivatives of Se,N and S,N heterocycles (Scheme 2.55). Fluorene-benzoselenadiazole... 

Peduoropolyethers, which constitute special class of fluoropolymer, are useful as lubricants,1 elastomers,2 and heat-transfer fluids under demanding conditions. Several commerical products are available, which are generally prepared by ring-opening polymerization of hexafluoropropylene oxide or by the random copolymerization oftetrafluoroethylene and hexafluoropropylene with oxygen under ultraviolet irradiation.3 Direct fluorination of hydrocarbon ethers has been reported4 but must be done very slowly under carefully controlled... 

The alternating tendency of the copolymers is advantageous in that the polymerizations can be carried out to high conversions with little or no compositional drift. For random copolymerizations in which there is preferential incorporation of one monomer due to a mismatch in reactivity ratios, the compositional variations with conversion can be substantial. Such compositional heterogeneities in resist materials can lead to severe problems during image development. 

Random copolymerization of one or more additional monomers into the backbone of PET is a traditional approach to reducing crystallinity slightly (to increase dye uptake in textile fibers) or even to render the copolymer completely amorphous under normal processing and use conditions (to compete with polycarbonate, cellulose propionate and acrylics in clear, injection molded or extruded objects). 

Scheme 8.12 Preparation of the diblock copolymer 57 by random copolymerization of PMMA block prepared by ATRP, methacrylic esters containing alkoxyamine nnits 55 and 56 [44],...

This high extent of polymerization usually accentuates deviations from random copolymerization using this protocol, but none was seen even after 3 hours (data not shown). 

The synthesis of biopolymers in vivo leads to macromolecules with a defined sequence of units. This effect is very important for living organisms and is different in comparison with random copolymerization in which sequences of units are distributed according to stochastic rules. On the other hand, the predicted sequence of units can be achieved by a set of successive reactions of respective monomer molecule addition. In template copolymerization, the interaction between comonomers and the template could pre-arrange monomer units defining sequence distribution in the macromolecular product. 

The Tg values may also be reduced by random copolymerization with a monomer which produces more-flexible polymers. This lowering of Tg values by copolymerization is sometimes called internal plasticization. 

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