Copolymerization sequential

The use of a monolithium initiator and a three-stage sequential copolymerization, Eqs. (25)—(27), is straightforward and requires no further elaboration. However, for success, the dilithium, Eqs. (28) and (29), and coupling, Eqs. (30)-(32), approaches depend upon the proper choice of reagents. 

The experimental techniques followed are descrihed elsewhere (10). Sodium block was added to refluxing toluene under nitrogen and stirred to form small particles of the required size by controlling the stirrer speed. The monomer was added by syringe as rapidly as possible, with cooling if necessary to control the reaction. This step takes less than a minute, except for phenylmethyldichlorosilane, which was too reactive. In the sequential copolymerizations, enough time was left between the addition of the two monomers for >90% of the first monomer to react. The disappearance of the monomers was monitored by gas chromatography. 

Using of Terminal Silanolate Function for Building More Complex Macromolecular Structures by Macroinitiator and Macromonomer Techniques or by Sequential Copolymerization... 

All siloxane block copolymers may be synthesized by the sequential copolymerization of two cyclotrisiloxane monomers. For example, unsubstituted hexamethyicyclotrisiloxane, D3, was first polymerized, and, before full conversion of this monomer, 2,4,6-trivinyltrimetiiylcyclotrisiloxane, V3, was added to the polymerization system [11]. The obtained block copolymer showed a high topological purity and a low polydispersion, MJM = 1.1. 

Block copolymers with hydroxyl segments were prepared by various ways An example utilizes the copper-catalyzed sequential copolymerizations of nBA and 2-[(trimethylsilyl)oxy]ethyl acrylate by the macroinitiator method into B-31 to B-33. The copolymers were then hydrolyzed into amphiphilic forms by deprotection of the silyl groups.313 A direct chain-extension reaction of polystyrene and PMMA with HEMA also afforded similar block copolymers with hydroxyl segments (B-34 and B-35).241-243 In block polymer B-36, a hydroxy-functionalized acrylamide provides a hydrophilic segment.117 Block copolymers of styrene and p-acetoxystyrene (B-37 to B-39), prepared by iron... 

By sequential copolymerization of styrene and propylene using a modified Ziegler-Natta catalyst, MgCl2/TiCl4/NdClc(OR) //Al(iBu)3, which was developed in our laboratory, a styrene-propylene block copolymer is obtained. After fractionation by successive solvent extraction with suitable solvents, the copolymer was subjected to extensive molecular and morphological characterization using 13C-NMR, DSC, DMTA, and TEM. The results indicate that the copolymer is a crystalline diblock copolymer of iPS and iPP (iPS-fo-iPP). The diblock copolymer contains 40% iPS as determined by Fourier transform infrared spectroscopy and elemental analysis. 

Figure 1.31 Generali2ed schematic for formation of linear BCPs via different routes viz. (a) sequential copolymerization and (b) macro-reagent coupling method.

Carbon dioxide is an interesting synthetic feedstock, it can be copolymerized with heterocycles, such as epoxides, aziridines, and episulfides. In 1969, Inoue reported the zinc catalyzed sequential copolymerization of carbon dioxide and epoxides as a new route to polycarbonates (5,15). The reaction is shown in Figure 1.1. 

Reactor TPO Reactor TPOs made by sequential copolymerization of PP and EP copolymer Compounding with fillers and additives needed Excellent dispersion Lower need for rubber than compounded TPO Improved melt-flow Need special catalyst and reactor technologies Somewhat higher cost Reactor elastomer may not be quite as efficient as compounded TPO for low temperature toughness... 

The so-called palm tree-like copolymers consist in an arrangement of nB blocks with one A block of much larger size in a heteroarmed star architecture [8]. These architectures were obtained by sequential copolymerization of norbornenyl-PS macromonomers with a molecular comonomer, namely cyclooctadiene (COD), Scheme 6. Dumbbell-shaped copolymers can be viewed as double stars that are linked through a linear block. They are obtained upon using palm tree-like copolymers to trigger the polymerization of a new amount of PS macromonomers. Scheme 6. 

Iodine transfer (co)polymerization of fluoroalkenes has been reviewed [66,67,72, 73]. These processes have also involved TFE and have led to thermoplastic elastomers based on sequential copolymerization of fluoroalkenes that first yield a soft segment, followed a TFE (or VDF) monomer to enable the insertion of a hard PTFE or PVDF block as indicated in scheme 5.12 ... 

Bonnet has described photocurable, colored urethane - acrylate resins from sequential copolymerization of (XIl) with diisocyanates and multifunctional acrylates.Polyurethanes (XIIl) and polyureas (XIV) beaxing triphenylmethane and anthreiquinone dyes may be used for dyeing of natiaral and synthetic fibers or as electrophotographic toner materials. 3... 

Here, we report on the synthesis and characterization of PMMA-poly(/i-butylacrylate)-PMMA (MBuM) symmetric triblock copolymers, as a new family of thermoplastic elastomers. These compounds have be prepared by a novel route based on controlled radical polymerization [4]. Compared to classical anionic living polymerization [5], this new route, sketched in Scheme la, appears particularly appealing since the triblock copolymers are prepared in a two-step process instead of the usual three steps required in anionic polymerization. In the latter case, as butylacrylate cannot be polymerized via a living process, the MBuM symmetric triblocks have to be synthesized by sequential copolymerization of er butylacrylate (tBuA) and MMA followed by the transalcoholysis of the tBu esters with n-butanol... 

The sequential copolymerization of DTC and LLA revealed different polymer microstmctures, depending on the order in which the monomer was polymerized first. When LLA was polymerized first, a random copolymer was formed, whereas the addition of LLA to a living PDTC resulted in a block copolymer. The copolymerization of a mixture of LLA and DTC also resulted in a random copolymer. Based on these results, the following mechanism was proposed by the authors. The PLLA active centers are well stabilized by the adjacent carbonyl group (enol formation) and by the formation of a five-membered cyclic complex including the metallic species. After reaction of the PLLA active centers with DTC, the newly formed active site has a reduced capability of stabilization (Scheme 84). 

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.

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. " ... 

Figure 9 Classical examples of block copolymers by sequential copolymerization.

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