Reactive homopolymers

A pair of vinyl or other unsaturated groups can also be linked by their direct reactions with free radicals. Similar end groups can be placed on siloxane chains by the use of an end blocker during polymerization,73,74 as mentioned earlier. Reactive groups such as vinyl units can, of course, be introduced as side chains by random copolymerizations involving, for example, methylvinylsiloxane trimers or tetramers.11 

Polysiloxanes have also been pyrolyzed to give ceramics, or organic-inorganic hybrid materials.238,239 This general topic is covered in Chapter 9. 

One of the most important uses of end-functionalized polymers is the preparation of block copolymers.73,74 The reactions are identical to the chain extensions already mentioned, except that the sequences being joined are chemically different. In the case of the -OSilCR Y chain ends mentioned above, R is typically (CH2)3 5 and Y can be NH2, OH, COOH, CH=CH2, and so on The siloxane sequences containing these ends have been joined to other polymeric sequences such as carbonates, ureas, urethanes, amides, and imides. 

There has long been interest in these peculiarly branched polymeric materials, and some of the most interesting species involve polysiloxane chains.240-244 

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In some cases, an end blocker such as YR SiR20SiR2R Y is used to give reactive -OSiR2R Y chain ends 16). Some of the uses of these materials are described in the section on reactive homopolymers. 

Reactive Homopolymers. Types of Reactions. In the typical ringopening polymerization mentioned previously see Preparation of Siloxane-Type Polymers), reactive hydroxyl groups are automatically placed at the ends of the chains (7, 13). Substitution reactions carried out on these chain ends can then be used to convert them into other functional groups. These functionalized polymers can undergo a variety of subsequent reactions (Table III). 

In order to distinguish the effect of F-C alkylation on blend MW from the effects of cross-linking and chain scission, the reaction was carried out onto PE and PS homopolymers. The same processing conditions and catalyst concentrations as in the reactive blends were used. These reactive homopolymers were also analyzed by SEC, and the results are summarized in Table 20.2 for different AICI3 concentrations. 

Table 20.2 Molecular Weight of Neat and Reactive Homopolymers. ...

In this binary blend, both PP and PS are susceptible to suffer degradation by chain scission. The presence of tertiary and benzyl carbon atoms in PP and PS, respectively, likely allows the event of (3-cleavage reactions that lead to chain scission (39,40). Consequently, certain amount of low MW PP and PS can be expected as by-products of the F-C reaction. In order to determine the possible occurrence of chain scission and/or cross-linking side reactions, a systematic study was performed in the same way as it was done for PE/PS in Section 20.3.1.1. Table 20.4 contains the MW of neat and reactive homopolymers. 

Fig.1 Different platforms for biomolecule immobilization or biosensor surface modifications a reactive ester-terminated SAM on gold b substrate-supported lipid bilayer on glass (structure of 1.2-dimyristoyl-sM-glycero-3-phosphatidylcholine, DMPC) c substrate-immobilized lipid vesicle d spin-coated thin film of a reactive homopolymer, such as poly(JV)-hydroxysuccinimidyl methacrylate (PNHSMA with tunable thickness dfiim the reactive groups are located in a region near the surface with depth the reactant molecules and reactive moieties in the film are schematically depicted as bars and dots, respectively)...

Fig. 3 Schematic of the different aspects of surface functionalization, patterning and analysis treated in this review. The topic is introduced and developed starting from the discussion of well-defined model systems (SAMs on Au). The determination of structure-reactivity relationships, and in particular the way conformational order affects the reactivity of NHS active esters will be discussed. Using iCFM, very localized information on surface reactions can be quantitatively measured in situ for SAM-based systems. The extension of the dimensionality to quasi-3D systems via the immobilization of den-drimers and the fabrication of thin reactive homopolymer films will be addressed, as well as micro- and nanopatterning approaches via soft and scanning probe lithography. Here we discuss SAM-based, as well as bilayer/vesicle-based systems...

Wong LJ, Sevimli S, Zareie HM, Davis TP, Bulmus V (2010) PEGylated functional nanoparticles from a reactive homopolymer scaffold modified by thiol addition chemistry. 

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