Macroinitiator method

Both methods require that the polymerization of the first monomer not be carried to completion, usually 90% conversion is the maximum conversion, because the extent of normal bimolecular termination increases as the monomer concentration decreases. This would result in loss of polymer chains with halogen end groups and a corresponding loss of the ability to propagate when the second monomer is added. The final product would he a block copolymer contaminated with homopolymer A. Similarly, the isolated macroinitiator method requires isolation of RA X prior to complete conversion so that there is a minimum loss of functional groups for initiation. Loss of functionality is also minimized by adjusting the choice and amount of the components of the reaction system (activator, deactivator, ligand, solvent) and other reaction conditions (concentration, temperature) to minimize normal termination. 

The one-pot sequential method has the disadvantage that the propagation of the second monomer involves a mixture of the second monomer plus unreacted first monomer. The second block is actually a random copolymer. The isolated macroinitiator method is the method of choice to avoid this contamination of the second block. The isolated macroinitiator... 

Another approach to block copolymers of the aromatic polyamide and coil polymer is the macroinitiator method the chain-growth condensation polymerization of 22a from a macroinitiator derived from coil polymer. A diblock... 

Block copolymers between alkyl acrylates such as B-4,358 B-5,202,203 and B-6,203 on the other hand, have been synthesized by the macroinitiator methods mostly with copper catalysts. Star block copolymers with a soft poly(MA) core and a hard poly(isobomyl acrylate) shell were synthesized by using multifunctional initiators.358 Poly(tBA) segments in B-5 and B-6 can be converted into hydrophilic poly(acrylic acid).203 Block copolymers between />methylstyrene and styrene (B-7) were also prepared by the rhenium-catalyzed living radical polymerization in conjunction with an alkyl iodide initiator.169... 

Block Copolymers between Different Families of Monomers. Block copolymers among different families of monomers (e.g., methacrylate/acrylate) can be efficiently prepared by metal-catalyzed radical polymerizations (Figure 17). Though widely feasible, the synthesis often calls for specific care, and in particular the initiating systems including terminal halogens, metals, and ligands should be carefully selected so that they are effective for both monomers in different families. For the macroinitiator method, in contrast, the catalysts for the first and the second polymerizations should not be necessarily the same. 

Most of the block copolymers consisting of methacrylates and acrylates (B-8 to B-12) have been prepared via macroinitiator methods. AB- and BA-type block copolymers of MMA and MA (B-876 135,359 and B-9359) were prepared with nickel, copper, and iron catalysts. Due to the higher activity of the carbon—halogen terminals in poly(methacrylate) s than in poly(acrylate)s, block copolymerization from PMMA is successfully performed via both sequential and macroinitiator methods, where the controllability seems better in the copper-based system. Similar... 

ABA-type block copolymers B-12 with a hard PMMA as the outer segment (A) and a soft poly(nBA) as the inner segment (B) are expected as all-acrylic thermoplastic elastomers. Examples of B-12 have been prepared with copper and nickel catalysts via bifunctional initiation.359-364 Unfortunately, the copolymers by R—Br/Ni-2 via the macroinitiator method were reported to be inferior as thermoplastic elastomers to those by living anionic polymerizations. A possible reason is the presence of short PMMA seg-... 

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... 

This polymer was synthesized via NMRP (Nitroxide Mediated Radical Polymerization) (Benoit et al. 1999) by sequential polymerization of 2VP and a mixture of NIPAAm and DMIAAm. Using the macroinitiator method, the preparation of well-defined linear block copolymers consisting of a homo polymer block P2VP (pH-sensitive) and a random copolymer block of PNlPAAm (temperamre sensitive) with DMIAAm (photo crosslinker) was possible. 

Dai, C.-A., Yen, W.-C., Lee, Y.-H. et al. (2007) Eacile synthesis of well-defined block copolymers containing regioregular poly(3-hexy 1 thiophene) via anionic macroinitiation method and their self-assembly behavior. Journal of the American Chemical Society, 129,11036-11038. 

Kim, S., Kakuda, Y., Yokoyama, A., and Yokozawa, T. (2007) Synthesis of controlled rod-coil block copolymers by a macroinitiator method chain-growth polycondensation for an aromatic polyamide from a polystyrene macroinitiator. Journal of Polymer Science Part A-Polymer Chemistry, 45,3129-3133. 

Diblock copolymer of polystyrene and polyamide was synthesized by the macroinitiator method (Scheme 25). First, polystyrene with a terminal carboxyl group was prepared by anionic living polymerization of styrene, followed by quenching with dry ice, and then the carboxyl group was converted to the phenyl ester by using phenol and a condensation agent. From this terminus, CGCP of 14a... 

Since the number of monomers, and thus the resulting polymer structures, are limited by any of the specific living polymerization techniques, appropriate combination of different polymerization mechanisms can lead to a variety of new and useful polymeric materials. Therefore combinations of controlled radical polymerizations and other polymerizations applied to synthesize block copolymers have been developed. Generally, polymers with active sites, such as carbon-halogen or nitroxide or dithioester terminal groups, are synthesized by other living polymerizations, and the product is further used to initiate the controlled radical polymerization. In many cases, this method is essentially a variant of the macroinitiator method discussed above. However, in some cases, these kinds of macromolecules do not act as initiators, and may act as transfer agents. For example, an AB-type amphiphilic block copolymer, CLB-2 was prepared by RAFT polymerization of 2-(N-dimethylamino)ethyl methacrylate... 

Polymers prepared with the trichloromethyl-functional initiators648 or with chloroform or carbon tetrachloride as a transfer agent649 have been used as macroinitiators for ATRP. The method has been used to make PVAc-block-PS... 

The transformation of the chain end active center from one type to another is usually achieved through the successful and efficient end-functionalization reaction of the polymer chain. This end-functionalized polymer can be considered as a macroinitiator capable of initiating the polymerization of another monomer by a different synthetic method. Using a semitelechelic macroinitiator an AB block copolymer is obtained, while with a telechelic macroinitiator an ABA triblock copolymer is provided. The key step of this methodology relies on the success of the transformation reaction. The functionalization process must be 100% efficient, since the presence of unfunctionalized chains leads to a mixture of the desired block copolymer and the unfunctionalized homopolymer. In such a case, control over the molecular characteristics cannot be obtained and an additional purification step is needed. 

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. 

In a different approach, Hedrick et al. have studied multifunctional dendritic initiators for the synthesis of multiarm star-shaped copolymers [102]. Several dendritic initiators with hydroxyl functionality ranging from 2 to 48 have been prepared according to the method developed by Hult et al. [120]. The bulk polymerization of sCL initiated by these multifunctional macroinitiators and acti-... 

By taking advantage of the simultaneous enzyme inhibition by nickel, the nickel-catalyzed ATRP, and the stereoselectivity of the enzyme, Peters et al. obtained chiral block copolymers by this method from 4-methyl-e-caprolactone (4-MeCL) by [27], The polymerization of racemic 4-MeCL showed good enantioselectivity and produced a chiral macroinitiator with ATRP endgroup by selectively polymerizing only the (5 )-4-MeCL. Macroinitiation was then started by adding the nickel catalyst and methyl methacrylate (MMA) to the reaction mixture, which simultaneously inhibited the enzyme and activated the ATRP process. Chiral poly[MMA-fe-(5 )-4-MeCL] was successfully obtained in this synthesis. 

The synthesis of poly(MMA-fr-IB-fr-MMA) triblock copolymers has also been reported using the site-transformation method, where a,site-transformation technique provides a useful alternative for the synthesis of block copolymers consisting of two monomers that are polymerized only by two different mechanisms. In this method, the propagating active center is transformed to a different kind of active center and a second monomer is subsequently polymerized by a mechanism different from the preceding one. The key process in this method is the precocious control of a or co-end functionality, capable of initiating the second monomer. Recently a novel site-transformation reaction, the quantitative metalation of DPE-capped PIB carrying methoxy or olefin functional groups, has been reported [90]. This method has been successfully employed in the synthesis of poly(IB-fr-fBMA) diblock and poly (MMA-fc-IB-fo-MMA) triblock copolymers [91]. 

Controlled radical polymerization (CRP) is an attractive tool, because of the resultant controllability of polymerization, and because of it being a versatile method to synthesize of well-defined polymer hybrids. The three main radical polymerization techniques, ATRP, NMP, and RAFT polymerization, have thus been employed. Other techniques, such as the oxidation of borane groups, have also been studied. In general, using CRP techniques, block copolymers can be synthesized from terminally functionalized PO as PO macroinitiator, and block copolymers can be prepared from functionalized PO produced by the copolymerization of olefins with functional monomers. 

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