End-reactive oligomers

By controlled thermal degradation of PIB, end-reactive oligomers can be prepared (53). For example, the resulting end-reactive polymers having one or two tertiary chloro groups can be converted to terminal-unsaturated polymers bearing an isopropenyl group by dehydrochlorination... 

T. Sawaguchi and M. Seno, Preparation and characterization of end-reactive oligomers by thermal degradation of polyisobutylene, Polymer, 37(16) 3697-3706, August 1996. 

The scope of MACROMER has been extended to generally designate the end-reactive oligomers of various monomers. A variety of MACROMERS have been reported. Hydroxy end-reactive oligomers were esterified with methacroyl chloride to yield methacrylate end-reactive MACROMERS 41,43) ... 

Another type of one-end reactive oligomers are oligomeric initiators which have an end group capable of initiating the polymerization of other monomers. Polymeric azo compounds of the type 52 and 53 were prepared by reaction of anionic living polymers with azo-bis-isobutyronitrile 9) ... 

The model networks are general prepared with end-reactive oligomers 62 and cross-linking moleailes Af of functicmality f [the (Af + B2) system]. A perfect network is obtained for a theoretical value of unity for the composition ratio... 

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. 

It can be arranged that these oligomers contain a reactive end group, e.g., hydroxyl, carboxyl, allowing subsequently further polymerisation with a different reactant monomer to take place. These reactive oligomers are called macromers. 

There is a current drive in microlithography to define submicron features in bilevel resist structures. The introduction of organometallic components, most notably organosilicon substituents, into conventional resists is one promising approach. To this end, organosilicon moieties have been primarily utilized in starting monomers (1-4) or in post-polymerization functionalization reactions on the polymer (5,6). Little work has been done on the reaction of preformed reactive oligomers to synthesize block copolymer systems. 

To improve the processability of PI and to alleviate or eliminate volatiles, work began in the late 1960 s under NASA Lewis sponsorship (23), to end-cap oligomers with reactive groups. The first report involved the use of 3,6-endomethylene-l,2,3,6-tetrahy-drophthalic anhydride (5-norbornene-2,3-dicarbo ylic anhydride, nadic anhydride) and alkyl derivatives thereof (e.g. citraconic anhydride) and 1,2,3,4-tetrahydrophthalic anhydride (4-cyclohexene-1, 2-dicarboxylic anhydride) as the reactive end group on imide oligomers (23-25). This initial effort led to the development of P13N [with T for polyimide, 13 for Mn of 1300g/mole and N for nadic end cap] whose structure is shown below. 

The literature on thermally reactive oligomers contains only one example of a polymer containing styrene chain ends, i.e., p,p -di-vlnylbenzyl end-capped phenylquinoxaline oligomers (11). 

Table I also presents the temperature at which this exothermal process starts (as Tg) and at which it ends (as Tg). The difference Tg- T can be considered as being the processing window of the thermally reactive oligomers, and is also listed in Table I.

The telechelica,(i -bis(2,6-dimethylphenol)-poly(2,6-dimethylphenyl-ene oxide) (PP0-20H) [174-182] is of interest as a precursor in the synthesis of block copolymers [175] and thermally reactive oligomers [179]. The synthesis has been accomplished by five methods. The first synthetic method was the reaction of a low molecular weight PPO with one phenol chain end with 3,3, 5,5 -tetramethyl-l,4-diphenoquinone. This reaction occurred by a radical mechanism [174]. The second method was the electrophilic condensation of the phenyl chain ends of two PPO-OH molecules with formaldehyde [177,178], The third method consists of the oxidative copolymerization of 2,6-dimethylphenol with 2,2 -di(4-hydroxy-3,5-di-methylphenyl)propane [176-178]. This reaction proceeds by a radical mechanism. A fourth method was the phase transfer-catalyzed polymerization of 4-bromo-2,6-dimethylphenol in the presence of 2,2-di(4-hy-droxy-3,5-dimethylphenyl)propane [181]. This reaction proceeded by a radical-anion mechanism. The fifth method developed was the oxidative coupling polymerization of 2,6-dimethylphenol (DMP) in the presence of tetramethyl bisphenol-A (TMBPA) [Eq. (57)] [182],... 

Chain propagation by addition of molecules starts with the reactive dimer molecules DR2 and AC2. Below about 80 K addition of molecules is possible photochemically only upon excitation of the perturbed monomer molecules adjacent to the reactive chain ends of the intermediates. The photoaddition reactions are defined by the reaction Eq.(lOa-c). The generation and decay rates G = d[RO]/dtandD = —d[RO]/ dt of the individual reactive oligomer molecules RO = DR, AC, DC of lengths n are given by ... 

Other less reactive monomers were incorporated into chain ends of oligomers, including divinyl benzene for MMA [138] and maleic anhydride for styrene [139] (Scheme 21) and methacrylates [140]. The method for the synthesis of maleic anhydride terminated PS is based on the fact that maleic anhydride cannot be homopolymerized under normal conditions [141]. These maleic anhydride terminated PSs were used for the compatibilization of the nylon 6-PS binary system in the melt by reaction with NH2-terminated polyamide. 

When p-nadimidochlorobenzene as a monofunctional dichloro compound is added to the reaction mixture of sulfide and aromatic dichloro compound, an end capped oligomer with a pendant double bond is obtained. Further, a trifunctional compound, such as trichlorobenzene, may be added to compensate the monofunctional compound with respect to molecular weight. OUgomers with a molecular weight of 1,000-6,000 Dalton can be readily obtained. The oligomerization is achieved at 225-260 C. At this temperature, the double bonds are still not reactive. 

Functionality refers to the moieties chemically distinct from the repeating units of polymer chains. It can be the terminal groups at chain ends or the functional groups deliberately added to a polymer chain. Determination of functionality type distribution of reactive oligomers (telechelics) is an old problem in polymer characterization. The classical method is the combination of SEC separation and functionality sensitive detection. Recent advances of the detection methods such as FT-NMR and MALDl-TOF MS have brought about big improvements in the precision of functionality characterization [12]. 

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