Techniques of Polymer Preparation

Many step-growth polymerizations are carried out by mass or bulk type polymerization. This is widely done not only due to convenience, but also because it results in minimum contamination. Few step- growth reactions are highly exothermic, so thermal control is not hard to maintain. Because equilibrium considerations are very important, the reactions are usually carried out in a way that allows continuous removal of the by-product. Occasionally, the polymerizations are carried out in dispersion in some convenient carriers. Solution polymerizations are sometimes used as a way of moderating the reactions. Step-growth polymerizations can also be carried out with certain monomers at low temperature by a technique known as interfacial polymerization or interfacial polycondensation [28]. The reactions (applicable only to fast reactions) are conducted at the interface between two immiscible liquids. Usually one of the liquids is water and the other one an organic solvent. An example may by a Schotten-Baumann polarization reaction. In such an interfacial polymerization, the diamine would be in the aqueous phase and the diacid chloride in the organic phase. The strong reactivity of acid chloride groups with amines allows the reaction to be carried out at room temperature:

Addition of a base to the aqueous phase removes the hydrochloric acid that forms and catalyzes the reaction. The choice of the organic solvent is important, because it appears that the reaction occurs on the organic side of the interface [28]. There are several important differences between interfacial polymerizations and high temperature condensations. Much higher molecular weight products form from polymerizations at the interface. This is probably due to the high speed of the reactions between the diamines that diffuse into the organic phase and the diacid chloride chain ends [28]. Exact stoichiometry is not necessary to attain high molecular weights in interfacial polycondensation. The opposite is true in high temperature polymerizations.

Interfacial polycondensation is an interesting procedure that is often used in demonstrations in polymer chemistry courses. Polyamides are prepared rapidly, in front of the class from diacid chlorides and diamines. The products are removed quickly as they form, by pulling them out as a string from the interface [47]. Polyesters can also be prepared from diacid chlorides and bisphenols. On the other hand, preparation of polyesters from glycols and diacid chlorides is usually unsuccessful due to low reactivity of the dialcohols. The diacid chlorides tend to undergo hydrolysis instead. Commercially, this proce- dure is so far confined mainly to preparations of polycarbonates.

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بيان صادر عن العتبة العباسية المقدسة

قسم التطوير يقيم دورة تدريبية عن الهندسة النفسية لملاكاته

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قسم الصناعات ينهي أعمال صيانة منظومة التهوية في مجمع أبي الفضل العباس (عليه السلام)

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

Synthetic Methods

Linear Saturated Polyesters

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)