Polymers with Terminal Functional Groups

POLYMERS WITH TERMINAL FUNCTIONAL GROUPS A. General Methodology and Scope 

Before the development of living cationic polymerization in the 1980s, Kennedy and his co-workers devised another way to synthesize end-functionalized polymers, which uses special reagents called inifer, or initiator-chain transfer agents [129]. The method is primarily for the synthesis of polyisobutene with a tertiary chlorine terminal, which is, however, a synthon for a variety of other functional groups. These developments have been reviewed extensively [1,3,130] and fall outside the scope of this chapter. 

Rather interestingly, most of the end-functionalized polyisobutenes have been prepared by the inifer method, in sharp contrast to that those 

The terminators for vinyl ether polymerizations include the sodium salt of ethyl malonate [sodiomalonic ester Na CH(C02C2H5)2] [131], 

As pointed out already, rather few end-functionalized poly isobutenes have been obtained from isobutene via living cationic polymerization, whereas abundantly via the inifer method followed by various chemical reactions to convert the resulting tertiary chloride terminal (Section IV.A.3) [3], 

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Another important role of the pendant-functionalized vinyl ethers is that they can be precursors of initiators for living cationic polymerization of other vinyl ether and styrene derivatives, from which polymers with terminal functional groups can be prepared (see Section IV). 

Dendrimers with terminal functional groups represent mode compact precursors that are spherical and almost monodisperse, with reactive groups placed on their periphery. Their synthesis, structure and properties have been reviewed in monographs and review articles often together with hyperbranched polymers (cf., e.g. [15-20]), as well as in this book. Application of dendrimers as precursors for conventional materials is limited at this time by their relatively high cost. 

The free radical polymerization of HPMA in the presence of mercaptans involves two different initiation mechanisms (Scheme 2) [26]. One is the initiation by RS radicals from chain transfer agent the other appears to be the direct initiation by the primary isobutyronitrile (IBN) radicals formed by the decomposition of AIBN [27]. The RS are formed by either the free radical transfer reaction of alkyl mercaptans with the IBN radicals or the chain transfer reaction of an active polymer chain with the mercaptans. The initiation by the RS radicals produces the ST polymers with a functional group at one end of the polymer chain. The initiation by IBN radicals leads to nonfunctional polymer chains with an IBN end group. The presence of the polymers with IBN end groups effects the purity and the functionality of ST polymers. As expected, the production of nonfunctionalized polymer chains is affected by reaction conditions. The polymerization is mainly terminated by chain transfer reaction with the mercaptans, but other termination mechanisms, such as disproportionation and recombination, take place depending on the reaction conditions [26]. 

Another approach is to use an initiator for ATRP that produces a polymer with a functional group capable of initiating a non-ATRP polymerization. ATRP polymerization of methyl methacrylate with 2,2,2-tribromoethanol produces an HO-terminated poly(methyl methacrylate). The hydroxyl group acts as an initiator in the presence of triethyl aluminum for the ring-opening polymerization of caprolactone. 

L-24 as a ligand, up to 85—90% yield. The linking reaction of a poly(tBA) with a bromide terminal was also possible with divinylbenzene, whereas the other two divinyl compounds led to side reactions.328 The yield of star polymers can be increased up to 95% with the use of additives. The a-end-functionalized linear polymers afford surface-functionalized star polymers with various functional groups such as alcohols, amines, epoxides, and nitriles. 

An acetal-protected lithium initiator was used to polymerize styrene followed by linking with 1,3,5-triallyloxy-2,4,6-triazine to produce three-arm star polystyrenes.73 The protective acetal group was cleaved by weak acidic treatment in THF to give star polymers with terminal OH groups. These functional groups were coupled with toluene-2,4-diisocyanate to give randomly cross-linked products. Unfortunately, few characterization data were provided in this study. 

Oligomers and polymers with reactive functional groups have been used extensively to prepare a great variety of polymeric materials. In many cases the behavior of these functional homopolymers is largely dependent on the nature and number of functional groups. In a number of important applications the functional groups are located at the end of the polymer chain macromolecules with terminal functional groups are usually termed telechelics or macromonomers . To characterize them it is necessary to have information not only about their molar mass but also on their functionality. 

Ferret et al. (1996) have encapsulated a third polymer within a PO phase dispersed in a PEST matrix the third polymer was PA-66, having higher Tm than the matrix. In this ternary blend, the epoxy-functionalized PO was capable of reacting with terminal functional groups on both of the other two polymers. The blend was formed either by preextrusion of PO with PA, followed by extrusion with PEST, or by feeding PO and PA to the feed throat of an extrader, then adding PEST downstream. The morphology showed a PEST matrix in which shells of PO... 

Polythiophenes present a multitude of color contrasts. These polymers, with a functional group terminal to a flexible alkyl chain at the 3-position of the ring, are used for many specialized applications. One such candidate of this class is poly(3-[12-(/7-methoxyphenoxy)dodecyl]thiophene [poly(12-MPDDT)], synthesized by Ribeiro et al., which exhibited a deposition charge of ca. 65 mCcm" presented greater stability over a large number of redox cycles (> 1000), a chromatic contrast of 40 % at 725 nm, a Coulombic efficiency of 80 % and good optical memory in the neutral state (E = 0.0 V) [15]. 

Diblock copolymers are known to be the most effective compatibilizers for improving the interfacial interactions between two polymers that are immiscible. This is particularly interesting for iPP, since its lack of functionality and the poor compatibility between iPP and other materials have imposed limitations for iPP applications in many areas, including polymer blends and composites. The synthesis of iPP with terminal functional groups (OH, NH2, etc.) offers a good opportunity to carry out chain extensions through simple coupling reactions with suitable polymers. These may be carried out in solution or in the polymer melt. Reactive extrusion of two chain-end reactive polymers... 

Living polymers can also react with the appropriate chemical reagents (XY) to give polymers containing terminal functional groups, such as macromeres ... 

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