Polymers from Substituted Styrenes

Many derivatives of styrene can be readily synthesized. Some are commercially available. One of them is a-methyl styrene. It is formed from propylene and benzene by a process that is very similar to styrene preparation:

Due to the allylic nature of a-methyl styrene it cannot be polymerized by free-radical mechanism. It polymerizes readily, however, by an ionic one. Resins based on copolymers of a-methyl styrene are available commercially. Other styrene derivatives that can be obtained commercially are:

1. Alkyl or aryl substituted styrenes,

where R1 and R2 are alkyl or aryl groups.

2. Halogen derivatives,

where X1 and X2 = F, Cl, Br, or I.

3. Polar-substituted styrenes,

where R = CN, CHO, COOH, OCOCH₃, OH, OCH₃, NO₂, NH₂, and SO₃H. Vinyl toluene polymerizes readily by free-radical mechanism at 100C. The absolute rate at that temperature is greater than for styrene. The activation energy for vinyl toluene polymerization is 17–19 kcal per mole while that for styrene is 21 kcal mole. This monomer can also be polymerized by ionic and coordination mechanisms. Earlier attempts at polymerization of a-methyl styrene with Ziegler–Natta catalysts were not successful [187, 188]. Later, however, it was shown that polymeri zation does take place with TiCl₄/Al(C₂H₅)₃ at 78C. The activity of the catalyst and the DP depend on the ratio of aluminum to titanium, the nature of the solvent, and on the aging of the catalyst [189]. The optimum ratio of the aluminum alkyl to titanium chloride is 1.0–1.2. Mixing and aging of the catalyst must be done below room temperature, and the valence of titanium must be maintained between 3 and 4 [189]. This led Sakurada to suggest that the reaction actually proceeds via a cationic rather than a coordinated anionic mechanism [189]. Various reports in the literature describe cationic polymerizations of a-methyl styrene with Lewis acids [190–192]. The products are mostly low molecular weight polymers, some containing unsaturation with pendant phenylindane groups. A high molecular weight polymer can be prepared from a-methyl styrene by cationic polymerization at 90 to 130C with AlCl₃ in ethyl chloride or in carbon disulfide [193]. The product has a narrow molecular weight distribution. Some Tg and Tm values of polystyrene-like materials, including isotactic polystyrene, are presented in Table 6.11.

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

Thermoplastic and Thermoset Acrylic Resins

Acrylic Elastomers

Polymerizations of Acrylic and Methacrylic Esters

Polymers of Acrylic and Methacrylic Esters

ABS Resins

High-Impact Polystyrene

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