Functional terminator method

The functional terminator method in cationic polymerization calls for nucleophiles ( Nu-T) with functional groups (T). As required, the nucleophilic part of the terminator, but not the function Y, should combine with the living end (e.g., 11, Scheme 4) and thereby attach the function Y to the last repeat unit (the co-end or tail group) of polymer 12. The terminators should meet the following criteria ... 

The a,ft)-asymmetric polymers are available by the combination of the functional initiator and functional terminator methods. By the rational combination of haloboration-initiation and capping techniques, a series of a.w-asymmetrically functionalized PlBs have been prepared [139, 140]. Polymers prepared by haloboration-initiation invariably carry an alkylboron head group [42, 141, 142], which can easily be converted into a primary hydroxy [141] or a secondary amine group [139, 140]. To functionalize the (W-living ends, the functionalization strategy shown in Scheme 26.2 is applicable and has been used to incorporate methoxycarbonyl groups as w-functionahty [143]. 

A macromonomer is a macromolecule containing a (co)polymerizable end functional group. Macromonomers have been synthesized by living cationic polymerization using three different techniques by the functional initiator or functional terminator methods or by chain-end modification. 

In many cases, these cyclic siloxanes have to be removed from the system by distillation or fractionation, in order to obtain pure products. On the other hand, cyclic siloxanes where n = 3 and n = 4 are the two most important monomers used in the commercial production of various siloxane polymers or oligomers via the so-called equilibration or redistribution reactions which will be discussed in detail in Sect. 2.4. Therefore, in modern silicone technology, aqueous hydrolysis of chloro-silanes is usually employed for the preparation of cyclic siloxane monomers 122> more than for the direct synthesis of the (Si—X) functional oligomers. Equilibration reactions are the method of choice for the synthesis of functionally terminated siloxane oligomers. 

End-functional polymers were also synthesized by lipase-catalyzed polymerization of DDL in the presence of vinyl esters [103,104]. The vinyl ester acted as terminator ( terminator method ). In using vinyl methacrylate (12.5 mol % or 15 mol % based on DDL) and lipase PF as terminator and catalyst, respectively, the quantitative introduction of methacryloyl group at the polymer terminal was achieved to give the methacryl-type macromonomer (Fig. 12). By the addition of divinyl sebacate, the telechelic polyester having a carboxylic acid group at both ends was obtained. 

Prepolymer and Propellant Quality Control. Prepolymer Control. The characterization of the functionally terminated prepolymers was an important factor in the control of these materials required to assure satisfactory reproducibility of solid propellant properties. To characterize these materials adequately, it was necessary to develop new analytical methods or to improve existing methods to provide the desired level of control. It was ultimately demonstrated that (1) propellant mechanical... 

The utility of functionally terminated ( telechelic ) polymers, particularly difunctional materials, rests with the ability of such materials to be chain-extended to afford a high molecular weight and useful physical properties. In general, there are two organolithium-based methods for... 

While preparation of multilayers by the self-assembly method is less straightforward than that by the LB method, it still can be accomplished [11-13], The amphiphilic molecule should have a functionalized terminal group. In order to avoid either uncontrolled multilayer deposition or the simultaneous attachment of both head and terminal groups to the substrate, the terminal group should be protected. After the first monolayer is deposited, the sample should be removed from the solution, the terminal groups should be deprotected and the sample should be returned to the solution for deposition of the second layer. Subsequent deprotections and reimmersions allow one to coat the desired number of layers onto the substrate. 

A class of end-functionalized polymers with polymerizable terminal groups are generally called macromonomers. By both functional initiator and terminator methods, a variety of macromonomers have been synthesized in living cationic polymerization of vinyl ethers, styrenes, and isobutene, as summarized in Table 3 [16,31,147,149-151,155,158-171]. Some of these macromonomers are used in the synthesis of graft polymers (Section VI.C). 

Electrical conductivities for a series of sintered Sr RE TiOa-s (RE = Y, Yb, Gd, Sm, Nd, Pr, La) and Sri.xTii.yMyOj+s (M = Nb, Ta) perovskites were measured as a function of temperature using a D.C. current four-terminal method. The size of specimen used in the measurement was 5mm x 5 mm x 11 mm . Figure 3 shows the general view of the D.C. current four-terminal measurement. After the Pt-terminals were attached to the perovskite specimens using Ag-paste, electrical conductivity measurements were performed stepwise in air between 298 and 373 K under a vacuum condition. 

Another monomer frequently used is methyl methacrylate. Functional termination is the most common method for the preparation of macromonomers. MMA macromonomers with methacryloyl end groups were prepared [113] according to the following reaction series (Scheme 40). 

Poly(2-alkyl oxazoline)s having methacrylate or acrylate end groups were prepared by two methods [182]. a) Living polyoxazoline chains, prepared using methyl p-toluene sulphonate as initiator, were end-capped by reaction with metal salts or tetraalkylammonium salts of acrylic or methacrylic acid or a trialky-lammonium salt or trimethylsilyl ester of methacrylic acid (functional termination). b) The living polymers were terminated with water in the presence of Na2C03 to provide hydroxyl-terminated chains. Subsequent acylation with acry-loyl or methacryloyl chloride in the presence of triethylamine led to the formation of the macromonomers. The procedures are outlined in the following Scheme 51. 

Chemical crosslinks may be obtained by randomly joining segments in already formed chains, by random copolymerization, or by end-linking functionally-terminated chains. Sulfur cures, peroxide cures, and high-energy irradiations are familiar methods of random crosslinking. Copolymerization monomers where at least one type has three or more reactive sites also lead to randomly crosslinked networks. Formation of networks by end-linking... 

A common method to functionalize PCL is the functionalization of the polymer at the chain end, either via a functional initiator or via a functional terminating agent. Examples are... 

Thus, if the objective function can be well represented by a quadratic function, these methods find the minimum in ny one-dimensional searches as they have a quadratic termination. Moreover, it results in... 

The termination method using substituted silyl chloride provides a useful, general methodology for the synthesis of a wide variety of functional end groups. However, this methodology requires the use of protection and deprotection protocols for most functional groups of interest. In addition, the long-term stability of these protected, functionalized silyl chlorides has been found to be a problem. 

Functionalized poly(vinyl ether)s can be prepared by the functionalized initiator method by the use of a HI/I2 initiating system and a functionalized vinyl ether, resulting in a-functionalized polymers. Carboxylic add- and amine-terminated polymers were prepared by this method with high degrees of functionality as determined by H NMR. This method can be extended to the preparation of telechelic polymers by quenching the polymerization with the appropriate nucleophile. Methacrylate-functionalized poly(vinyl ether) s... 

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