Thermoplastic and Thermoset Acrylic Resins

Among methacrylic ester polymers, poly (methyl methacrylate) is the most important one industrially. Most of it is prepared by free-radical polymerizations of the monomer and a great deal of these polymerizations are carried out in bulk. Typical methods of preparation of clear sheets and rods consist of initial partial polymerizations in reaction kettles at about 90C with peroxide initiators. This is done by heating and stirring for about 10 min to form syrups. The products are cooled to room

temperature and various additives may be added. The syrups are solutions of about 20% polymer dissolved in the monomer. They are poured into casting cells where the polymerizations are completed. The final polymers are high in molecular weight, about 1,000,000. Poly(methyl methacrylate) intended for surface coatings is prepared by solution polymerization. The molecular weights of the polymers are about 90,000 and the reaction products that are 40–60% solutions are often used directly in coatings. A certain amount of poly(methyl methacrylate) is also prepared by suspension polymerization. The molecular weights of these polymers are about 60,000 and they are used in injection molding and extrusion. Thermosetting acrylic resins are used widely in surface coatings. Both acrylic and methacrylic esters are utilized and the term is applied to both of them. Often such resins are terpolymers or even tetra polymers where each monomer is chosen for a special function [214]. One is selected for rigidity, surface hardness, and scratch resistance; another for the ability to flexibilize the film, and the third one for cross-linking it. In addition, not all comonomers are necessarily acrylic or methacrylic esters or acids. For instance, among the monomers that may be chosen for rigidity may be methyl methacrylate. On the other hand, it may be styrene instead, or vinyl toluene, etc. The same is true of the other components. Table 6.12 illustrates some common components that can be found in thermoset acrylic resins. The choice of the cross-linking reaction may depend upon desired application. It may also simply depend upon price, or a particular company that manufactures the resin, or simply to overcome patent restrictions. Some common cross-linking reactions will be illustrated in the remaining portion of this section. If the functional groups are carboxylic acids in the copolymer or terpolymer, cross-linking can be accomplished by adding a diepoxide.

Other reactions can also cross-link resins with pendant carboxylic acid groups. For instance, one can add a melamine formaldehyde condensate:

A diisocyanate, a phenolic, or a melamine–formaldehyde resin can be used as well. Resins with pendant hydroxyl groups can also be cross-linked by these materials. A diisocyanate is effective in forming urethane linkages:

When the pendant groups are epoxides, like glycidyl esters, cross-linking can be carried out with dianhydrides or with compounds containing two or more carboxylic acid groups [241]. Aminoplast resins (urea–formaldehyde or melamine–formaldehyde and similar ones) are also very effective [242]. Pendant amide groups from terpolymers containing acrylamide can be reacted with formaldehyde to form methylol groups for cross-linking [243]:

The product of the above reaction can be thermoset like any urea–formaldehyde resin . Many cross-linking routes are described in the patent literature, because there are many different functional groups available.

اخر الاخبار

اخبار العتبة العباسية المقدسة

شعبة الحرم الشريف تستعد لاستقبال زائري النصف من شهر شعبان

العتبة العباسية المقدسة تنشر لافتات الفرح بمناسبة ذكرى ولادة الإمام المهدي (عجّل الله فرجه)

العتبة العباسية المقدسة تفتتح التسجيل لتأدية الزيارة بالنيابة في ليلة النصف من شعبان

قسم المقام يعلن جاهزيّته لاستقبال زائري النصف من شعبان

المزيد

الآخبار الصحية

الصحة العالمية تكشف حقيقة انتشار فيروس نيباه خارج الهند

متى يصبح محيط الخصر "مؤشر خطر"؟

دراسة تكشف دور "العوامل الوراثية" في تحديد عمر الإنسان

رائحة كريهة في الجسم.. "علامة خفية" أخطر مما تتصور

المزيد

الآخبار التكنلوجية

مايكروسوفت تكشف عن الجيل الثاني من شرائحها للذكاء الاصطناعي

خرافة "ثمانية أكواب يوميا".. كم من الماء يحتاج جسمك فعليا؟

هل توجد حياة خارج كوكبنا؟.. اكتشاف جديد يثير اهتمام العلماء

اكتشاف الخلايا المسؤولة عن فقدان ذاكرة الطفولة

المزيد

مواضيع ذات صلة

Acrylic Elastomers

Polymerizations of Acrylic and Methacrylic Esters

Polymers of Acrylic and Methacrylic Esters

ABS Resins

High-Impact Polystyrene

Polymers from Substituted Styrenes

Polystyrene Prepared by Ionic Chain-Growth Polymerization

Preparation of Polystyrene by Free-Radical Mechanism

GR-N Rubber

GR-S Rubber

Cyclopolymerization of Conjugated Dienes

Special Polymers from Dienes