Carboxyla tion of Poly(2,tk?imethyl-l,4Phenylene Oxide) and Thermal Properties of Blends with Atactic Polystyrene
Poly(2,6-dimethyl-l,4phenylene oxide) (PPO) and atactic polystyrene (PSI form one of the best-known examples of thermodynamically miscible polymer blends. Thus a single, compositiondependent glass transition temperature Tg exists for all blend compositions,' and the segmental interaction parameter x between PPO and PS has been shown to be negative.2 Chemical modifications of either PPO or PS tend to decrease miscibility and, when carried far enough, will lead to incompatibility. This has been established through studies of various halogenated PS blends with PPO and brominated PPO blends with PS.3,4 Carboxylation of PPO has been reported using lithiation followed by treatment with C02? These polymers are interesting in their own right in that they can be modified to form various carboxylate derivatives such as esters, salts, amides, anhydrides, etc. It is also to be expected that such carboxylated PPO derivatives would exhibit partial miscibility with PS or perhaps complete immiscibility depending upon their compositions.
Here we report on the carboxylation of PPO through the aforementioned route, and we provide some preliminary information about the miscibility behavior of blends of PPO with differing concentrations of carboxylic acid (CPPO) and PS.
The PPO was carboxylated according to the method of Chalk and Hay.5 About 5 g PPO (z, 2.3 x lo4, sample provided by General Electric) were dissolved under nitrogen in 200 mL of freshly distilled THF. The solution was cooled to room temperature and the desired amount of BuLi (1.6Min hexane, Aldrich) was added dropwise. The reaction mixture was then poured over dry ice, acidified with dilute hydrochloric acid, and precipitated with hexane. The polymer was then purified further by washing in dioxane and hexane. The degree of carboxylation was assessed by titration in pyridine with alcoholic 0.1M KOH using phenanthrene-ethanol as indicator. Infrared spectra of KBr pellets of the polymers were obtained using a Perkin-Elmer IR-283 Spectrometer. The integrated absorbances of the carbonyl group stretching vibration at 1720 cm-I and the aromatic ring vibration at 1605 cm-I were measured, and the ratio of the two correlated well with the degree of carboxylation determined by titration. These data are collected in Table I.
The carboxylation reaction may be represented as follows:
In agreement with previous work, unit B represents the preferred carboxylation location. This is evident from 'H-NMR spectra, which showed a peak at 3.46-3.61 ppm in the various derivatives. This is assigned to a methylene proton on an aromatic ring. Peaks at 40.8 ppm and 168.5 ppm also appear in the 'W-NMR spectra of the derivatives and these are assigned to 4 H Z -and 4 0 -in unit B above.
Finally, the IR absorption at 1380 cm-1 due to the CH3 group on the aromatic ring showed a large decrease in magnitude in the C P P O s compared to unmodified PPO. 'H-NMR spectra were obtained on a Varian T-60 Instrument and W-NMR spectra were obtained on a Varian CFT-20 Instrument.