Tetrafunctional initiator

Kinetic gelation simulations seek to follow the reaction kinetics of monomers and growing chains in space and time using lattice models [43]. In one example, Bowen and Peppas [155] considered homopolymerization of tetrafunctional monomers, decay of initiator molecules, and motion of monomers in the lattice network. Extensive kinetic simulations such as this can provide information on how the structure of the gel and the conversion of monomer change during the course of gelation. Application of this type of model to polyacrylamide gels and comparison to experimental data has not been reported. 

Figure 21. Atom transfer radical polymerization (ATRP) synthetic route to tetrafunctional initiators of a star polymer with adamantyl (adamantane core). Taken from Ref. [91] with permission.

The oxocarbenium perchlorate C(CH20CH2CH2C0+C104 )4 was employed as a tetrafunctional initiator for the synthesis of PTHF 4-arm stars [146]. The living ends were subsequently reacted either with sodium bromoacetate or bromoisobutyryl chloride. The end-capping reaction was not efficient in the first case (lower than 45%). Therefore, the second procedure was the method of choice for the synthesis of the bromoisobutyryl star-shaped macroinitiators. In the presence of CuCl/bpy the ATRP of styrene was initiated in bulk, leading to the formation of (PTHF-fc-PS)4 star-block copolymers. Further addition of MMA provided the (PTHF-fr-PS-fc-PMMA)4 star-block terpolymers. Relatively narrow molecular weight distributions were obtained with this synthetic procedure. 

PS-b-PEO) , n = 3, 4 star-block copolymers were synthesized by ATRP and anionic polymerization techniques [149]. Three- or four-arm PS stars were prepared using tri- or tetrafunctional benzylbromide initiators in the presence of CuBr/bipy. The polymerization was conducted in bulk at 110 °C. The end bromine groups were reacted with ethanolamine in order to generate the PS stars with hydroxyl end groups. These functions were then activated by DPMK to promote the polymerization of ethylene oxide and afford the desired well-defined products (Scheme 73). 

Fig. 8a, b. Snapshots of a homopolymerization of a tetrafunctional monomer in two dimensions on a 40 x 40 lattice a at 10% b at 25% conversion of double bonds. Initial species concentrations were 1.0 mol % initiator and 15% free volume. The initiator molecules are represented by, reacted double bonds by, free volume by, and unreacted double bonds by... 

Although the core-first method is the simplest, success depends on initiator preparation and quantitative initiation under living conditions. This method is of limited use in anionic polymerization because of the generally poor solubility of multifunctional initiators in hydrocarbon solvents [12]. Solubilities of multifunctional initiators are less of an issue in cationic polymerizations, and tri- and tetrafunctional initiators have been used to prepare well-defined three- and four-arm star polymers by this method [7] Except for two reports on the synthesis of hexa-arm polystyrene [27] and hexa-arm polyoxazoHne [26], there is a dearth of information in regard to well-defined multifunctional initiators for the preparation of higher functionality stars. 

Furthermore, by using the ATRP method with a tetrafunctional initiator, the star copolymers consisting of four PMMA-g-EPR graft copolymer arms were also synthesized (Fig. 22). These unique topologies of the obtained copolymers can be confirmed by GPC measurement and NMR analysis. From TEM observation, the morphologies of these graft and star copolymers were remarkably altered by changing EPR branch number and the structure of the... 

Using the tetrafunctional coupling agent 25, end-functionalized four arm po-ly(IBVE)s were synthesized [49]. End-functionalization was performed using functional initiators which were HC1 adducts of functionalized vinyl ethers bearing respectively acetoxy, styryl and methacryloyloxy groups (Scheme 5). 

Functionality of initiators 1, monofunctional 2, bifunctional 3, trifunctional. d F = tetrafunctional. 

In the development of the tetrafunctional initiator 24, the spatial shapes of initiator molecules turned out to be crucial for obtaining well-defined initiators [140]. As shown in Scheme 11, 24 is prepared from the corresponding tetrafunctional phenol via a reaction with 2-chloroethyl vinyl ether to attach vinyl ether moieties, followed by addition of trifluoro-acetic acid or hydrogen iodide. In this acid addition, the four vinyl ether groups should be well separated spatially. If the vinyl ether groups are located too close to each other, the treatment with the acid leads to intramolecular cyclization and other side reactions. 

More recent efforts investigating the kinetics and mechanism of cationic polymerization of oxazolines are aimed at the preparation of various types of functional polymers as described in a recent review [181] (cf., Section IV.D). One of the examples is the development of efficient di- and tetrafunctional initiators of oxazolines polymerization, allylic or benzylic dihalides and allylic tetrahalides [182], e.g. ... 

Linear (difunctional) and star-shaped (tetrafunctional) polyoxazolines with M up to 8000 and MJM < 1.3 were prepared using these initiators [182]. 

Recently, tetrafunctional initiators have also been introduced for styrenics. In 2001, Atofina Chemicals introduced a novel tetrafunctional initiator, Luperox JWEB50, developed specifically for the styrenics industry to produce high molecular weight, high-heat, crystal polystyrene with improved productivity in a cost-effective manner. JWEB50 is a room temperature stable, liquid peroxide with a half-life similar to those of currently used cyclic perketals, appropriate for use in mass polystyrene processes. A unique aspect of... 

Three- and four-arm star-shaped PEA (75 and 77) were synthesized by GTP with tri-and tetrafunctional initiators (74 and 76) according to equations 61 and 62 . ... 

Wnek and coworkers synthesized a four-arm star-shaped PMMA with a cyclic siloxane core, as shown in equation 63. Four ketene silylacetal units were first attached to 1,2,3,4-tetramethylcyclotetrasiloxane (78) to obtain the tetrafunctional core 79, which was used as an initiator of the GTP of MMA with formation of the targeted four-armed star-shaped PMMA (80). 

Another benzyl halide initiator (MI-37) with a cyclosiloxane core induced styrene polymerization (MJMn = 1.16).358 An ester-type initiator (MI-35) is effective in the copper-catalyzed radical polymerization of nBA.358 A tetrafunctional sulfonyl chloride... 

Another tetrafunctional ester (MI-36) is the smallest number of a series of dendrimer-type initiators such as MI-46 and MI-53 for 6- and 12-arm star polymers, respectively.414 419 420 These initiators induce the living radical polymerizations of MMA with Ni-2 to give the corresponding multiarmed polymers with controlled molecular weights although the arm number with MI-53 is slightly lower than 12 due to incomplete initiation from all the carbon—bromine bonds. 

Scorah, M.J. Experimental and Modelling Investigation of a Novel Tetrafunctional Initiator in 82. Free Radical Polymerization. Ph.D. Thesis, Department of Chemical Engineering, University of Waterloo, Waterloo, Canada, 2005. 

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