Synthetic Methods

The synthetic methods that are in general use for the preparations of linear polyesters [15] can be summarized as follows: 1. Dibasic acids are reacted with glycols. Stoichiometric balance is strictly maintained. When low boiling glycols are used, however, they are often added in a slight excess and the excess gradually removed by vacuum [6] or by sweeping an inert gas over or through the reaction mixture [6, 8]. This procedure is useful with dicarboxylic acids that otherwise require high temperatures and strong catalysts. Running the reaction at high temperatures can cause the glycols to condense into ethers and the dicarboxylic acids to decompose.

2. Diesters or half esters of dicarboxylic acids or amine salts of the acids are reacted with glycols [19]:

The above transesterification reaction is practical for use with high melting and poorly soluble dicarboxylic acids. In addition, less energy is needed to remove alcohol than water.

3. Hydroxy acids, like p-hydroxyethoxybezoic acid or o-hydroxydecanoic acid, are capable of self-condensation to form polyesters [10]:

4.Although not practical commercially, polyesters can be prepared in the laboratory by reacting aliphatic dibromides with silver salts of dibasic acids [6]:

5. Polyesters also form reactions of dicarboxylic acid anhydrides with glycols [10]:

6.Glycol carbonates undergo ester interchange reactions with dibasic acids[11]:

7. Ester interchange reactions between glycol acetates [12, 13] or diphenol diacetates [12] and dicarboxylic acids:

8.Acidchlorides react with diphenols to form polyesters. The reaction is quite efficient when scavenger of HCl is added to the aqueous phase. Such scavengers can be tertiary amines [15]:

When in place of dicarboxylic acid chlorides phosgene is used, polycarbonates form:

9. Polyesters also form in ring opening polymerizations of lactones. This is discussed in Chap. 5.

Many modifications of the above-described reactions are known. For instance, poly (propylene phthalate) can be prepared from phthalic anhydride and propylene oxide [14]. The reaction is catalyzed by tertiary amines that probably form carboxylate ion intermediates:

This produces a low molecular weight polyester. A modification is a reaction of a dianhydride with a glycol:

In all esterification reactions, catalysts increase the speed of condensations. Such catalysts are either acids or bases.

Beyond the above, there are many other polyester syntheses that can be found in the literature, but arenot in common use. For instance, polyesters form from additions of carboxylic acids to divinyl ethers [29]:

Polyesters also form by the Tischenko reaction from dialdehydes [26,27].The intramolecular hydride transfer reaction is typically catalyzed by bases:

Another reported procedure consists of condensations of nitriles with glycols. The resultant poly (iminoether hydroxide) s hydrolyze to polyesters [32].

Carbon suboxide condenses with glycols to form polyesters [26]:

Also, an alternating free-radical addition copolymerization of cyclohexene and formic acid, perhaps via charge transfer, donor–acceptor complexes, yields polyesters [30]:

Cyclic carbonates, oxalates, and glycolates polymerize by ring opening polymerizations to yield polyesters. An example is a conversion of a cyclic carbonate into a low molecular weight polymer (about4,000) [39,40]:

Another example is a ring opening polymerization of an oxalate [39]. Again, only low molecular weight polymers result:

Lactides, on the other hand, when subjected to ring opening polymerization with Lewis acids yield high molecular weight polymers [41]:

Also, a-hydroxycarboxylic acids can polymerize to high molecular weight polymers through formation of anhydrosulfides [42]:

In addition, it was reported [49] that polyesterification reactions are possible at room temperature. High molecular weight polyesters form directly from carboxylic acids and phenols. These solution polymerization reactions proceed under mild conditions, near neutral pH. Equimolar mixtures of acids and alcohols condense as the reactions are being driven by additions of water across carbodiimide groups. Substituted ureas form as by-products:

The reaction is useful in preparations of isoregic ordered chains with translational polar symmetry. It can also be applied in polymerizations of functional or chiral monomers.

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المزيد

الآخبار الصحية

عادات يومية تدمر قلبك بصمت.. خبراء يطلقون التحذير

خبراء تغذية يكشفون "أفضل وقت لتناول الإفطار"

أطعمة تزيد فرص وفاة مرضى السرطان 60 بالمئة.. ما هي؟

اختبار ثوري جديد يكشف مبكرا عن سرطان البنكرياس

المزيد

الآخبار التكنلوجية

الذكور أم الإناث؟ دراسة "تنسف الشائع" بشأن التوحد

خبير يكشف عن اقتراب العلماء من فك شفرات "لغات الحيوانات" !

دراسة تدفعك لشراء ساعة ذكية "فورا".. هذا ما تقوله عن قلبك

علماء حاصلون على "نوبل": الذكاء الاصطناعي لن يستبدل الإنسان

المزيد

مواضيع ذات صلة

Linear Unsaturated Polyesters

Copolyesters

Linear Saturated Polyesters

Techniques of Polymer Preparation

Ring Formation in Step-Growth Polymerizations

Kinetic Considerations

Reactions of Functional Groups

Poly (vinyl alcohol) and Poly (vinyl acetal) s

Poly (vinyl acetate)

Poly (vinylidine chloride)

Copolymers of Vinyl Chloride

Poly (vinyl chloride)