Copolymerization bifunctional initiation

The first method, which is used in many instances, proceeds by anionic block copolymerization. In a first step styrene is anionically polymerized using an efficient bifunctional initiator. The polymer obtained has a well-defined molecular weight, it exhibits a rather narrow molecular weight distribution and it has carbanionic living sites at both ends of its linear chains7. ... 

Macromonomers with two methacrylate functionalities (MA-PIB-MA) at both ends of the PIB chain have also been synthesized, by a procedure essentially identical to that reported above, but starting with a bifunctional initiator in the polymerization of IB [103]. Free radical copolymerization of the resulting MA-PIB-MA with 2-(dimethylamino)ethyl methacrylate resulted in amphiphilic networks, with a wide range of mechanical and swelling properties. 

Besides the above-mentioned approaches varying the parameters governing the initiator decomposition, it is worth mentioning an interesting biphasic study based on the difference of solubility of monomers and the use an original amphiphilic bifunctional initiator, the palmitoyl (3-carboxy propionyl) sebacoyl diperoxide 3 [24], In such conditions, block copolymers of water soluble (acrylamide) and oil soluble (butylmethacrylate) monomers can be obtained by interfacial radical copolymerization as follows ... 

Problem 11.4 Suggest a scheme for preparing poly(styrene-fc-ethyleneimine) by a one-step, one-pot simultaneous block copolymerization using a bifunctional initiator for controlled/living polymerization pro-... 

These catalysts were used for random ester-carbonate bulk copolymerizations. Furthermore, by combining sequential polymerization techniques using bifunctional initiators, the mild polymerization conditions allow for the preparation of block copolymers. Hydrogen bond activation of monomer and initiator/propagating species was proposed as the underlying mechanism, which can be tuned to mitigate adverse side reactions (Scheme 36). 

ROP of functional cyclosiloxanes is a convenient route to all-siloxane copolymers. " " This may be realized in several ways. Sequential ring-opening copolymerization involves polymerization of one cyclosiloxane monomer to the desired chain length, then the second monomer is introduced, which adds to the growing chains. Diblock and triblock copolymers in the case of bifunctional initiator are produced provided the process is kinetically controlled. Otherwise, a copolymer with random or partly ordered sequencing is obtained. The kinetic control of the copolymerization process imposes the use of cyclotrisiloxanes as monomers. Thus, sequential copolymerization of two or more cyclotrisiloxanes is a good method for the precise synthesis of all-siloxane block copolymers. " ... 

The sequential copolymerization of cyclosiloxanes is particularly suitable for the synthesis of well-defined diblock and triblock all-siloxane functionalized copolymers. Using a monofunctional initiator leads to diblock copolymers, while triblock copolymers are formed with bifunctional initiators. Some typical examples of AB block copolymers are shown in Table 3.7. It is recommended that the less-reactive monomer be polymerized in the first step, and this is the case of the examples in which D3 and V4 are polymerized first. The comonomer should be introduced not later than at 90-95% of conversion of the first monomer, in order to avoid the processes that lead to chain randomization. Those monomers which have func-... 

Organic monoliths are based on copolymerization of a monofunctional and a bifunctional (uncommonly trifunctional) organic precursor in the presence of a suitable initiator and a porogenic solvent. During the last 15 years, a vast number of different monomers and cross-linkers have been introduced and copolymerized using different polymerization techniques and initiators. A general survey of the tremendous amount of scientific contributions can be gained from numerous reviews [25-32],... 

In a similar way as has been described for syntheses of type al, the majority of examples of type b involve polycondensation of a,ea bifunctional, small molecule reaction partners. Some examples are the reaction of AIBN or AIBN derivatives with 1,4-cyclohexane bismethyl diamine78), 1,2-ethylene diamine78), 1,6-hexamethylene diamine 78-80 , bisphenol A 78,81 and mono-, di- and tetraethylene glycol 55-64 . In almost all case using the AIBN derivative 4,4 -azobis(4-cyano valeryl chloride), an interfacial polymerization was employed. These polymeric azo compounds could be used as initiators for radical block copolymerizations. 

In contrast to the non-catalyzed reaction, the base-initiated copolymerization was found to be a specific reaction 35,36,39 -45) and the consumption of both monomers, epoxide and anhydride, is the same. The initiator not only affects the rate of copolymerization but also suppresses the undesirable homopolymerization of the epoxide. At equimolar ratio, epoxide and anhydride are strictly bifunctional. 

For chainwise polymerizations, the analysis of model systems implies consideration of the homopolymerization or copolymerization of bifunctional monomers. Kinetic results cannot be directly extrapolated to the case of networks, because very important features such as intramolecular cycliza-tion reactions are not present in the case of linear polymers. However, the nature of initiation and termination reactions may be assessed. For example, using electron spin resonance (ESR), Brown and Sandreczki (1990) identified different types of radicals produced during the homopolymerization of a monomaleimide (a model compound of bismaleimides). 

The value of Fn was determined by 1H NMR spectroscopy and found to be close to unity. By essentially the same method, bifunctional and trifunctional cyanoacrylate functional PIBs have also been prepared. Anionic polymerization of CA-PIB with N,N-dimethyl-p-toluidine as initiator in solution resulted in high MW product (Mn 35,000 gmol ) [107]. Anionic copolymerization of difunctional and trifunctional PIB yielded clear flexible films with low sol fraction. The... 

Choi et al. [53] have successfully used both water-soluble and oil-soluble initiators in the miniemulsion polymerization of styrene. Alducin and Asua [119] have studied the MWD of polystyrene miniemulsion polymerized with oil-soluble initiators. Rodriguez et al. [61] have developed a mathematical model of seeded miniemulsion polymerization with oil-soluble initiator. Blythe et al. [ 120] have successfully carried out miniemulsion polymerization of styrene with AMBN (oil-soluble). Ghazaly et al. [117] have used AIBN for the miniemulsion copolymerization of a hydrophobic bifunctional macromer. The polymerization progressed much faster when KPS was used than when AIBN was used. This may be due to the tendency of oil-soluble initiator radicals to recombine before initiating polymerization, as discussed by Luo. 

Copolymerization of a bifunctional monomer with a polyfunctional comonomer produces branches which can continue to grow by addition of more monomer. An example is the use of divinylbenzene (4-9) in the butyl lithium initiated polymerization of butadiene (Section 9.2). The diene has a functionality of 2 under these conditions whereas the functionality of 4-9 is 4, The resulting... 

A series of ABA- and BAB-type triblock copolymers (B-22 to B-24) were obtained by two-step block copolymerization with bifunctional initiators202 or by three-step block copolymerization with monofunctional initiators.202 366 368 ABC-type block copolymers B-25203 and B-26202 consisting of styrene, MA, and tBA can be obtained by the latter method the tBA segment may be hydrolyzed to give amphiphilic triblock copolymers. 

Haloester-type trifunctional initiators are obtained from triols by a method similar to those for bifunctional haloesters. 3-arm star polymers of MMA are obtained with dichloroacetates MI-28 and MI-29, for which Ru-1 and Al(acac)3 are employed.228 The polymers have controlled molecular weights and narrow MWDs. Similarly, MI-30 and MI-31 with copper catalysts gave 3-arm star polymers of styrene, acrylates, and methacrylates suitable copper catalysts vary with each monomer.199,326 358 368 The obtained star polymers can be further transformed into star block copolymers comprised of hydrophilic/hydropho-bic368 or organic/inorganic326 segments by block copolymerizations of other monomers. 

The monomer 1 was copolymerized by free radical initiation in the presence of an inert solvent with a large amount of a bifunctional crosslinking agent. Under these conditions, macroporous polymers were obtained which possessed a permanent pore structure, a high inner surface area, and good accessibility. Additionally, low polymer swellability would imply limited mobility of the polymer chains. From a polymer of this type, 40 to 90% of template molecules can be split off by treatment with water or alcohol (see Figure 3 ). If this polymer is... 

The DB of branching can be modified by special synthetic approaches, as demonstrated by the NMR quantification of subunits. Copolymerization - for example, the addition of bifunctional monomers AB - resulted in an increase in linear units and, therefore, in a decrease of the DB [109-112]. An enhancement of DB was realized, for example, by employing a slow monomer addition technique [113], the polymerization of prefabricated dendron macromonomers [56, 114], and by a stepwise addition of the monomer mixture for the (A2 + B3) approach [92]. Whereas dendritic and terminal units are essential for a dendritic structure, in the case of hb polymers the content of the linear units can vary greatly. To date, few examples of AB2 hb polymerizations have been reported were the linear unit is a chemically labile structure that either breaks down to the initial educts, or reacts immediately with a further terminal unit to form the stabile dendritic unit. Thus, a hb polymer containing only T and D units is formed, with 100% DB [35,115-119]. 

Thermal and UV-initiated cyclo-polymerizations of mixed allyl-butenedioate monomers with both donor and acceptor unsaturations such as methyl allyl fumarate or maleate were recently described. Hyperbranched macromolecules were obtained by free radical alternating copolymerization of bifunctional monomers containing two polymerizable double bonds of allyl and vinylene type with styrene or maleic anhydride. Thanks to their original structure, this new class of liquid blends exhibit improved mechanical and physical properties useful for a wide range of coating applications. ... 

The dihydrocarvone can also be oxidized to an epoxy lactone, 7-methyl-4-(2-methyloxiran-2-yl)oxepan-2-one, with mCPBA and subsequently be used as bifunctional monomer and crosslinker in ROPs. Homopolymerizations using benzyl alcohol as the initiator and either diethyl zinc or tin(ll) 2-ethylhexanoate as the catalyst produce only low molecular weight polyesters (<2.5 kg/mol). Copolymerizations with s-caprolactone give flexible crosslinked materials [103]. 

Kricheldorfs group also proposed another approach to multiblock copolymers of TMC and LLA synthesis. Sequential copolymerizations of TMC and LLA were performed with 2,2-dibutyl-2-stanna-l,3-oxepane as a bifunctional cyclic initiator. The cyclic triblock copolymers were transformed in situ into multiblock copolymers by ring-opening polycondensation with sebacoyl chloride (Scheme 94). 

Scheme 94 Sequential copolymerizations of TMC and LLA with 2,2-dibutyl-2-stanna-1,3-oxepane as a bifunctional cyclic initiator.

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