Esters terminal chains

The authors concluded that the side reactions normally observed in amine-initiated NCA polymerizations are simply a consequence of impurities. Since the main side reactions in these polymerizations do not involve reaction with adventitious impurities such as water, but instead reactions with monomer, solvent, or polymer (i.e., termination by reaction of the amine-end with an ester side chain, attack of DMF by the amine-end, or chain transfer to monomer) [11, 12], this conclusion does not seem to be well justified. It is likely that the role of impurities (e.g., water) in these polymerizations is very complex. A possible explanation for the polymerization control observed under high vacuum is that the impurities act to catalyze side reactions with monomer, polymer, or solvent. In this scenario, it is reasonable to speculate that polar species such as water can bind to monomers or the propagating chain-end and thus influence their reactivity. 

Nitro compounds, like quinones, terminate chains in oxidizing compounds where hydroperoxyl radicals are formed. This was proved for the oxidation of polyatomic esters [37] and PP [38], Nitrobenzene retards the initiated oxidation of the following esters tetrapropionate of pentaerythritol, propionate of 2,2-dimethylbutanol, and dipropionate of 2,2-dimethylpro-panediol terminating chains by the reaction with peroxyl radicals [37]. The hydroperoxyl radicals were supposed to be formed as a result of the following reactions ... 

Fig. 9. HREELS spectra of functionalized silicon surfaces prepared via photochemical reactions with H/Si(lll). In each case R represents a saturated alkyl chain (9 or 10 carbon atoms long) covalently attached to the Si surface. The methyl and acid terminated surfaces were prepared via reactions with decene and undecylenic acid respectively while the thienyl terminated surface was prepared by reaction of thienyl Li with an ester terminated surface. The dashed line at 1500 cm-1 represents the typical low frequency cut-off for ATR-FTIR measurements on silicon.

Similar effects have been found for /ra 5-4- -alkylcyclohexyl trans-4-n-alkylcyclohexanoates and the corresponding esters with one or two trans carbon-carbon double bonds in the terminal chain.However, the ester with two terminal alkenyl chains only possesses a nematic phase over a temperature range of Related bicyclohexanes with an additional... 

Although carboxylic acids generally form 1 1 adducts with alkenes, the resulting esters are easily ionized in the presence of either Lewis or protonic acids. The higher efficiency of chlorinated acetic acids relative to hydrogen halides is ascribed to the ability of their 1 1 adducts to coordinate with excess acid. Alkyl halides are eventually formed when carboxylic acids are used to initiate polymerization in the presence of a Lewis acid due to migration of the carboxylate moiety to the Lewis acid [Eq. (25)]. Similarly, styrene and isobutene polymerizations initiated by preformed alkyl acetate adducts in the presence of BC13 always produce Cl-terminated chains [104,105]. 

The apparent partial reversion of the polymerizing mixture after torque peaking, its dependence on shortstop concentration, and its ultimate decline with polymerization time are interesting phenomena. The desired shortstopping chemistry is pictured in Equation 3. It involves the reaction of the hydroxyl group of the added 1-propanol shortstop molecules with the unreacted terminal isocyanate groups on the poly(ester-urethane) chains. This permanently stops chain growth as desired. 

Poly(2-alkyl oxazoline)s having methacrylate or acrylate end groups were prepared by two methods [182]. a) Living polyoxazoline chains, prepared using methyl p-toluene sulphonate as initiator, were end-capped by reaction with metal salts or tetraalkylammonium salts of acrylic or methacrylic acid or a trialky-lammonium salt or trimethylsilyl ester of methacrylic acid (functional termination). b) The living polymers were terminated with water in the presence of Na2C03 to provide hydroxyl-terminated chains. Subsequent acylation with acry-loyl or methacryloyl chloride in the presence of triethylamine led to the formation of the macromonomers. The procedures are outlined in the following Scheme 51. 

---