Telechelic polymers block copolymers

Kennedy and co-workers 2 117) used the changing effect of the initiation ability of the Lewis acids according to Eq. (17) and the termination tendency of the anion formed according to Eq. (18) in order to obtain telechelic polymers , block copolymers and graft copolymers in a controlled manner. Quantum chemical calculations provide the possibility to discuss structural influences which work on the equilibrium Eq. (19) and therefore on the stability of the two adjacent ions. 

Advantages of end-group transformation include the ability to incorporate functionality incompatible with the polymerization procedure, to prepare halogen-free materials for subsequent reactive processing, to allow characterization of the initial copolymer prior to further functionalization, and an ability to prepare telechelic polymers, block copolymers, and materials that can be immobilized to surfaces, by a full range of substitution and addition chemistry. The use of a difunctional initiator allowed for the first time in a radical process preparation of functional homo-telechelic polymers with almost any desired chain end functionality (Scheme 33). ... 

Synthesis of Well Defined Copolymer Structures Starting from Ozonized Polymers Block Copolymers, Graft Copolymers, Telechelic Oligomers... 

Investigations were mainly devoted to the synthesis of telechelic polymers and copolymers rather than to living radical polymerization. In particular, from 1960, Imoto et al. [234] started surveys on the synthesis of block copolymers from this method. Thus, polystyrene-i>-poly(vinyl alcohol) diblock copolymer... 

There have been other types of approaches also for the synthesis of hybrid polymers. Block copolymers containing polysiloxane segments and polyphosphazene segments have been synthesized by the reaction of hydride-terminated polysiloxane H-[Si(Me2)-0]n-SiMe2H with the telechelic polyphosphazene containing an amino end-group (Fig. 6.28) [33]. 

The quantum yield of polymerization is 6.72 and for photoinitiation < / = 2.85 x 10 . The polystyrene produced with this initiator shows photosensitivity when irradiated with UV light (A = 280 nm). This polymer, which carries two photosensitive end groups of - SC(S) N(CH3)2, behaves as a telechelic polymer and it is useful for production of ABA block copolymer. 

Depending on the choice of transfer agent, mono- or di-cnd-functional polymers may be produced. Addition-fragmentation transfer agents such as functional allyl sulfides (Scheme 7.16), benzyl ethers and macromonomers have application in this context (Section 6.2.3).212 216 The synthesis of PEG-block copolymers by making use of PEO functional allyl peroxides (and other transfer agents has been described by Businelli et al. Boutevin et al. have described the telomerization of unsaturated alcohols with mercaptoethanol or dithiols to produce telechelic diols in high yield. 

ADMET is quite possibly the most flexible transition-metal-catalyzed polymerization route known to date. With the introduction of new, functionality-tolerant robust catalysts, the primary limitation of this chemistry involves the synthesis and cost of the diene monomer that is used. ADMET gives the chemist a powerful tool for the synthesis of polymers not easily accessible via other means, and in this chapter, we designate the key elements of ADMET. We detail the synthetic techniques required to perform this reaction and discuss the wide range of properties observed from the variety of polymers that can be synthesized. For example, branched and functionalized polymers produced by this route provide excellent models (after quantitative hydrogenation) for the study of many large-volume commercial copolymers, and the synthesis of reactive carbosilane polymers provides a flexible route to solvent-resistant elastomers with variable properties. Telechelic oligomers can also be made which offer an excellent means for polymer modification or incorporation into block copolymers. All of these examples illustrate the versatility of ADMET. 

In one of their notable examples, the hydroboration polymerization of low molecular weight allyl-telechelic polyisobutylene with tripylborane (trip = 2,4,6-triisopropylphenyl) was found to yield air-stable organoboron segmented block copolymers. These boron main-chain polymers (8) (Fig. 8), unlike the general ones, were stable to air. The stability was due to the steric hindrance of the bulky tripyl groups preventing oxygen attack of the borons.28... 

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. 

Difunctional Iniferter X-X > X-QA X Telechelic polymer, AB- or ABA-type block copolymer... 

Anionic and cationic living polymerizations offer routes to block copolymers, star polymers, telechelic polymers, and other polymers [Charleux and Faust, 1999 Hadjichristidis et al., 2002],... 

Block copolymers of isobuylene with styrene, isoprene, and vinyl ethers have been synthesized, often requiring an appropriate adjustment of reaction conditions for the second stage, as described above for styrene-MVE. Another approach is the use of a telechelic polymer (containing the first block) as the initiator for polymerization of the second monomer (Sec. 5-4b). 

Telechelic polymers, containing one or more end groups with the capacity to react with other molecules, are useful for synthesizing block and other copolymers [Fontanille, 1989 Hsieh and Quirk, 1996 Nuyken and Pask, 1989 Pantazis et al., 2003 Patil et al., 1998 Quirk et al., 1989, 1996 Rempp et al., 1988]. Living anionic polymers can be terminated with a variety of electrophilic reagents to yield telechelic polymers. For example, reaction with carbon dioxide, ethylene oxide, and allyl bromide yield polymers terminated with carboxyl, hydroxyl, and allyl groups, respectively. Functionalization with hydroxyl or carboxyl groups can also be achieved by reaction with a lactone or anhydride, respectively. Polymers with amine end... 

Most of the methods for synthesizing block copolymers were described previously. Block copolymers are obtained by step copolymerization of polymers with functional end groups capable of reacting with each other (Sec. 2-13c-2). Sequential polymerization methods by living radical, anionic, cationic, and group transfer propagation were described in Secs. 3-15b-4, 5-4a, and 7-12e. The use of telechelic polymers, coupling and transformations reactions were described in Secs. 5-4b, 5-4c, and 5-4d. A few methods not previously described are considered here. 

A series of interesting block copolymer architectures has also been prepared by Zhang et al. In a first paper, the synthesis of H-shaped triblock copolymers was demonstrated from enzymatically obtained PCL diol after end-functionalization with a difunctional ATRP initiator [40]. This allowed the growth of two PS chains from each end of the telechelic PCL. When methanol instead of glycol was used as the initiator in the initial enzymatic CL polymerization, a PCL with one hydroxyl endgroup was obtained. Functionalization of this endgroup with the difunctional ATRP initiator and subsequent ATRP of styrene or GMA resulted in Y-shaped polymers (Scheme 3) [41, 42]. 

These results indicate that if polydienes and similar polymers can be prepared quantitatively with tertiary amine terminal groups, then they can be combined with other halogen functional polymers using established techniques to create interesting new block copolymer systems. For example, consider the reaction between telechelic pyridine terminated polybutadiene and monofunctional bromine terminated polystyrene (equation 4) -the latter has been prepared in 95% yield. >it The product would be an ABA... 

Functionally terminal polymers are valuable material intermediates. The di- and polyfunctional varieties (telechelic polymers) have found theoretical (e.g., model network) and commercial (e.g., liquid rubber) applications (1, ). On the other hand, macromolecules with a functional group at one chain end (semitelechelic polymers) have been used to prepare novel macromolecular monomers (Macromers ), as well as block and graft copolymers ( -8). 

Reed 332) has reported that reaction of ethylene oxide with the a,(a-dilithiumpoly-butadiene in predominantly hydrocarbon media (some residual ether from the dilithium initiator preparation was present) produced telechelic polybutadienes with hydroxyl functionalities (determined by infrared spectroscopy) of 2.0 + 0.1 in most cases. A recent report by Morton, et al.146) confirms the efficiency of the ethylene oxide termination reaction for a,ta-dilithiumpolyisoprene functionalities of 1.99, 1.92 and 2.0j were reported (determined by titration using Method B of ASTM method E222-66). It should be noted, however, that term of a, co-dilithium-polymers with ethylene oxide resulted in gel formation which required 1-4 days for completion. In general, epoxides are not polymerized by lithium bases 333,334), presumably because of the unreactivity of the strongly associated lithium alkoxides641 which are formed. With counter ions such as sodium or potassium, reaction of the polymeric anions with ethylene oxide will effect polymerization to form block copolymers (Eq. (80) 334 336>). 

Under such chromatographic conditions it is possible to determine the heterogeneities of the polymer chain selectively and without any influence of the polymer chain length. LC-CC has been successfully used for the determination of the functionality type distribution of telechelics and macromonomers [104-109], for the analysis of block copolymers [111-114], macrocyclic polymers [115], and polymer blends [116-118]. 

Moreover, in situ polyurethane formation was performed by irradiation of the polymeric pyridinium salt in THF containing toluene diisocyanate and catalyst. It is clear that alkoxy pyridinium terminated polymers are useful materials as precursors for block copolymers and hydroxy functional telechelics. The latter are particularly attractive in photoinduced polycondensation and in applications where hydroxyl groups are needed to be protected. 

A series of at least 14 papers [200-208] have been published dealing with the synthesis of telechelic polymers or block copolymers from the radical polymerization of various vinyl monomers with substituted 1,1,2,2-tetraphenyl ethanes. These aromatic compounds, known for over a century [209], are efficient in radical polymerization [201,210], They behave as both initiators and terminating agents [200] that can be involved in living radical polymerization as illustrated in the following reaction ... 

The quantitative character of initiation and the living character of active species permits the preparation of functional polymers (telechelic oligomers) as well as block copolymers (cf., Section IV.A.). 

Telechelic polymers are defined as macromolecules with reactive sites on the polymer chain, usually as endgroups on linear polymers [106]. This macro-molecular architecture has successfully produced a wide variety of block copolymers using macroinititated polymerizations. Living anionic polymeriza-... 

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