End-group functionalization

In the course of quasi living carbocationic isobutylene polymerization it is possible to functionalize the polymer at their end groups by quenching with reactive compounds. The various possibilities are shown in Table 6.2. 

Poly(isobutylene)/Poly(methyl methacrylate) Poly(styrene)/Poly(isobutylene)/Poly(styrene)) Poly(isobutylene)/Thermoplastic poly(urethane) Poly(isobutylene)/Pivolactone (29,30) (4,31,32) (33) (34) 

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The relative propensity of radicals to abstract hydrogen or add to double bonds is extremely important. In radical polymerization, this factor determines the significance of transfer to monomer, solvent, etc. and hence the molecular weight and end group functionality (Chapter 6). It also provides one basis for initiator selection (Section 3.2.1). 

Thus alkyl radicals do not give unwanted end-group functionality and the kinetics of initiation arc comparatively uncomplicated. However, this situation can be perturbed by substitution at or near the radical center. 

Curtin SA, Deming TJ (1999) Initiators for end-group functionalized polypeptides via tandem addition reactions. J Am Chem Soc 121 7427-7428... 

The end group functionality of condensation polymers is typically defined by the monomers employed to make these materials. An example is shown below for a common polyamide polymer, namely nylon (see Figure 2). These polymers... 

Many ionic polymerisation routes (both cationic and anionic) are also used to make industrial polymers. The end group functionality typically depends on the initiator used to make the polymer. 

Di-hydroxyl end-capped PPG (18) is an intermediate in the formation of a common polyurethane prepolymer (20). End group functionality of this intermediate is important, as this hydroxyl functionality is modified to form the prepolymer. Any different end group structures could lead to the presence of prepolymer that will not form polyurethane of the desired structure. The desired reaction of the intermediate (18) to form the prepolymer (20) is described in Figure 21. Reaction of one unit of the intermediate (18) and two units of methylene diphenyl 4,4 -diisocyanate (MDI) results in the formation (nominally) of the prepolymer (20). 

Water soluble block copolymers consisting of N-isopropylacrylamidc, NIPA, and the zwitterionic monomer 3-[N-(3-methacrylamidopropyl)-N,N-dimethyl]ammoniopropane sulfonate, SPP, were prepared via the RAFT process [82] (Scheme 31). NIPA was polymerized first using AIBN as the initiator and benzyl dithiobenzoate as the chain transfer agent. To avoid the problem of incomplete end group functionalization the polymerization yield was kept very low (less than 30%). The block copolymerization was then performed... 

In this review, advances in the preparation of functionalized polysilanes by both pre- and post-polymerization functionalization and their properties will be reviewed. First, polymers with remote side-chain functionalities are covered, then those with the functionality directly attached to the main chain and finally those which are end group-functionalized. Chiral functionalization will be treated separately (see Section 3.11.6). 

Reactive impact modifiers are preferred for toughening of PET since these form a stable dispersed phase by grafting to the PET matrix. Non-reactive elastomers can be dispersed into PET by intensive compounding but may coalesce downstream in the compounder. Reactive impact modifiers have functionalized end groups. Functionalization serves two purposes - first, to bond the impact modifier to the polymer matrix, and secondly to modify the interfacial energy between the polymer matrix and the impact modifier for enhanced dispersion. Some examples of commercially available reactive impact modifiers for PET are shown in Table 14.3. An example of a non-reactive elastomer that can be used in combination with reactive impact modifiers is ethylene methyl acrylate (EMA), such as the Optema EMA range of ethylene methyl acrylates manufactured by the Exxon-Mobil Chemical Company (see Section 4.2). 

Amination. The synthesis of polymers with primary amine end-group functionality has been a challenge because the primary amine group can undergo rapid chain transfer and termination reactions with car-banionic chain ends (14). Schulz and Halasa (15) used a phenyllith-ium initiator with a bis(trimethylsilyl)-protected amine group to prepare amine-terminated polydienes. Nakahama and coworkers (16,17)... 

Amine, telechelic, synthesis, 139-145 Amine end-group functionality, primary, synthesis, 140-143... 

Fig. 3. Schematic illustration of the synthesis of metal nanoparticles within dendrimer templates. The composites are prepared by mixing of the dendrimer and metal ion, and subsequent chemical reduction. These materials can be immobilized on electrode surfaces where they serve as electrocatalysts or dissolved in essentially any solvent (after appropriate end-group functionalization) as homogeneous catalysts for hydrogenation and other reactions...

End-group functionalization in NMP can be achieved by using a functional radical initiator in combination with TEMPO. 

Chapter 3 focuses on the increased understanding in enzymatic strategies for the production of well-defined polymers. A wide variety of (co)polymers has been synthesised and explored in a variety of applications using lipase catalysts. On the other hand, detailed studies also revealed the limitations of the use of lipases as a result of the monomer-activation mechanism, polymers of low polydispersity and quantitative degree of end-group functionality are difficult to attain. 

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