Functionally-terminated oligomers

Segmented or multiblock copolymers can be made by combining a functionally terminated oligomer or prepolymer with at least two monomers. To form a... 

Synthesis of ot,td-Organofunction ally Terminated LMsiloxanes Precursors for the Functionally Terminated Oligomers... 

K. (1984) Synthesis of functionally-terminated oligomers by free radical ring-opening polymerization. J. Macromol. ScL Part A Pure Appl. Chem., 21 (8), 979. 

The common synthetic route to bismaleimides or maleimide functionalized oligomers is the condensation of diamines or amino-terminated oligomers with maleic anhydride. Another possibiUty is the use of an AB-type monomer of the following general formula to build the polymaleimide, where X represents a functional group that can be employed in condensation reactions. 

Newer silicone adhesives having solids levels up to 97% are also commercially available [109]. Instead of using silanol condensation reactions, they rely on addition chemistry between vinyl functional silicone oligomers and silicon hydride terminated silicones. This addition reaction is typically facilitated with platinum derived catalysts. This hydrosilation process can be run at reduced oven temperatures, but the finished products typically do not yield the same balance of properties as seen for condensation cure materials. 

Liquid organic rubbers with reactive functionality can be prepared by several methods. End-functional oligomers are preferred. Chains attached to the network at only one end do not contribute as much strength to the network as those attached at both ends [34], Urethane chemistry is a handy route to such molecules. A hydroxy-terminated oligomer (commonly a polyester or a polyether) can be reacted with excess diisocyanate, and then with a hydroxy methacrylate to form a reactive toughener [35]. The methacrylate ends undergo copolymerization with the rest of the acrylic monomers. The resulting adhesive is especially effective on poIy(vinyl chloride) shown in Scheme 2. 

Poly (ary lene ether sulfone)s and poly(arylene ether ketone) have been employed to prepare block and graft copolymers. Generally, the block copolymers can be prepared by reacting functional-group-terminated oligomers with other functional oligomers and monomers. 

Preparation of Functionally Terminated Siloxane Oligomers via Controlled Hydrolysis of Organo-silanes... 

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. 

The Major Route to the Functionally Terminated Siloxane Oligomers... 

An important advantage in the preparation of a,eo-functionally terminated siloxane oligomers, over the other telechelic systems, is the flexible polymerization chemistry of cyclic organosiloxane monomers and intermediates. This is mainly due to the partial... 

Unfortunately, there have been very few studies on the synthesis and characterization of functionally terminated siloxane oligomers with a mixed siloxane backbone. 

Acetylene-terminated oligomers, incorporation of isoimide functionality, 462 Acid functionalities, block copolymers, 258... 

If the polyester synthesis is performed with equimolar amounts of diol and diacid, then, in addition to hydroxy, carboxy-terminated oligomers, dihydroxy- and dicarboxy-terminated oligomers are formed, as shown below. In a thermodynamic equilibrium, the molar ratios of the three functionality fractions should be 2 1 1, respectively. 

C-termini and a large glycosylated extracellular loop between transmembrane domains 3 and 4. The proteins show the most homology in their transmembrane spanning domains, particularly domains 1, 2, and 4-8, which may be involved in moving the transmitter across the membrane. The transporters are substrates for PKC-dependent phosphorylation, which reduces their activity. The dopamine transporter is phosphorylated on the extreme end of the N-terminal tail, and consensus phosphorylation sites for various other kinases are present in the intracellular loops and domains [20-22] (Fig. 12-4). The dopamine and norepinephrine transporters form functional homo-oligomers, although it is not known if this is required for transport activity, and the transporters also interact with many other membrane proteins that may control their cell-surface expression or other properties. 

As it is well known, the (Si-0) bond in organosiloxanes may be considered to be polar or partially ( 50%) ionic.(12) Therefore, it can be cleaved by the attack of strong acids or bases. This is the main rationale behind the "equilibration" route to the synthesis of a wide variety of functionally terminated siloxane oligomers(12-14) from cyclic siloxanes and a.ordifunctional disiloxanes as shown in Scheme 3. 

These type of reactions are generally named as "equilibration" or "redistribution" reactions due to the nature of the processes. During the reactions the catalyst can only cleave the (Si-0) bonds in the cyclic or linear species including that of the "end blocker" and growing chains. However, the (Si-R) or (R-X) bonds are stable. Therefore at the end of the reactions the linear oligomers are functionally terminated and the minority (10-15%) cyclic side products are nonfunctional. After elimination of catalyst, the cyclic side products can usually be removed from the system by... 

---