The Heck reaction allows the synthesis of monomers in a one-step reaction. Catalyzed by Pd, bromoarenes are reacted with ethylene to form substituted styrenes and symmetrical stilbenes. Unsymmetrical stilbenes are obtained from substituted bromoarenes and styrenes. Substituted hydroquinones and terephthalic acids are also available in high yields. Poly(l,4-phenylenevinylene) is obtained starting from 4-bromostyrene. Experimental partA typical procedure for the synthesis of a styrene and a stilbene derivative is given. Experimental conditions for other monomers are shown in Tab. 1.Reagents: DMF: distilled over 4,4 '-methylenedi(pheny1 isocyanate) and dibutyltin dilaurate as catalyst. Pd(OAc)2: used as received (Degussa). Tri-o-tolylphosphine: synthesized according to lit. '). Triethylamine, tributylamine: distilled over KOH. Styrene: used as received (stabilized with catechol). 4-Vinylbenzamide (6):A flame-dried pressure vessel of 100 ml volume was loaded under argon with 7 g (35 mmol) of p-bromobenzamide, 0,21 g (0,7 mmol) of tri-o-tolylphosphine, 0,078 g (0,35 mmol) of palladium acetate, 5,46 ml (40 mmol) of triethylamine, and a teflon@coated stir bar. 60 ml of DMF were added and a pressure of 72 bar ethylene (room temperature) applied. The autoclave was heated to 130°C for 24 h. The reaction mixture was precipitated with 400 ml of water and the solid dissolved in acetone. The filtered solution was concentrated and the residue was purified by sublimation. Yield: 3,7 g (72%), m.p. 176-177 "C, determined by DSC (lit.5): 170°C).

Summary: Several researches have dealt with the thermal initiation of methyl methacrylate (MMA) in the past. Some of them already discussed the presence of peroxide containing species that are formed from dissolved oxygen and the monomer itself as main reason for this initiation. However, a more detailed investigation as well as a kinetic description of this phenomenon is still due in literature. In this paper, the formation and decomposition of methyl methacrylate peroxides are described. MMA that has been in contact with air forms macromolecular peroxides at temperatures below 100 °C from physically dissolved oxygen. These peroxides have molecular weights of approximately 3 000–5 000 g · mol−1, depending on the temperature during formation. Above this temperature, these peroxides decompose quickly and initiate the radical polymerization. Depending on the reaction conditions, monomer conversions from 15 to 30% are obtained. In combination with additional initiators, the MMA peroxides provoke an acceleration of the reaction rate and can also lead to bimodal molecular weight distributions. An analytical method based on UV‐spectrophotometry was developed for the quantification of the peroxide content in the monomer. The kinetic rate constants for the formation were determined in batch experiments with purified, air‐saturated monomer to be kf,0 = 6.28 · 107 l2 · mol−2 · s and EA = 7.75 · 104 J · mol−1. The decomposition rate constants were determined from batch dead‐end polymerizations and found to be kd,0 = 4.73 · 107 l · mol−1 · s−1 and EA = 8.56 · 104 J · mol−1. magnified image

No abstract

Philipps-Universitat M a r b u r g , FB 1 4 Physikalische C h e m i e , I n s t i t u t f u r P o l y m e r e und Wis sens c h a f t l i c h e s Z e n t r u m fur M a t e r i a l wis s ens c h a ft en, H a n s -M e e r w e i n -S t raBe. D-3550 M a r b u r g , FRG S Y N T H E S I S OF MACROMONOMERS OF POLY(2.6-DIMETHYL-1.4-PHENYLENE O X I D E ) M i c h a e l W i c k e r , W a l t e r Heitz* D e d i c a t e d to Prof. D. B r a u n on t h e o c c a s i o n of his 6 0 t h birthday. S u m m a r y : Poly(2,6-dimethyl-l,4-phenylene o x i d e ) with e x a c t l y o n e functional endgroup was synthesized by o x i d a t i v e p o l y m e r i z a t i o n , halogen substitution polymerization, and by p h a s e t r a n s f e r c a t a l y s i s . Reaction with 4-vinylbenzoyl c h l o r i d e r e s u l t e d i n a q u a n t i t a t i v e conversion to a m a c r o m o n o m e r a s shown by G P C and endgroup analysis. The macromonomer is a g l a s s y m a t e r i a l with a Tg f r o m 150 t o 190 OC depending on t h e m o l e c u l a r weight.

Macromonomers of poly(2,6-dimethyl-l,4-phenylene oxide) (PPO) were synthesized by reacting the monofunctional polymer with 4-vinylbenzoyl chloride. The macromonomer was copolymerized with isoprene, butadiene, styrene, ethyl acrylate, and butyl acrylate. Reactivity ratios of 2,6-dimethylphenyl4-vinylbenzoate (2) as a model compound were determined with styrene (St) and butyl acrylate (BA). The values obtained are rSt = 0,504, rz = 1,233, and rBA = 0,123, rz = 4,070. Polystyrene-gruff-PPO is a one-phase system with a Tg between those of the homopolymers. Tg's of the polyacrylate and PPO fractions are not changed by the composition of the polyacrylate-gruff-PPO. DSC and dynamic mechanical measurements revealed that the polyacrylate-gruft-PPO copolymers are phase-separated if the molecular weight of the PPO macromonomer is high enough. In thermogravimetric analysis the polyacrylate-gruff-PPO shows a two-step weight loss, one due to the polyacrylate at 380-390°C and another due to the PPO at 440-460°C. In t r o d u c t i o nTelechelics and macromonomers can be used to modify polymers. Both types of materials can be considered as bifunctional segments. In telechelics the functional groups are located at the ends of the segment. In macromonomers 3, both functional groups are fixed at one end. The incorporation of telechelics and macromonomers into other polymers results in different materials. With telechelics block copolymers are obtained. The use of macromonomers results in graft copolymers. Many properties can be modified by the use of these segments. If we focus on the mechanical behavior, we can classify these segments into hard segments and soft segments. Soft segments have a glass transition temperature below the service temperature. Hard segments have either a high glass transition temperature or a high melting point. A high melting point is usually combined with low solubility, which restricts the use of bifunctional hard segments. By combination of hard and soft segments a variety of properties can be adjusted (Tab. 1).Incorporation of amorphous macromonomers with a high glass transition temperature into a matrix with a low glass transition temperature should result in thermoplastic elastomers. This property necessitates that phase separation occurs. Phase separation can only be expected if the molecular weight of the macromonomers exceeds a certain limit. 0 1991, Huthig & Wepf Verlag, Base1 CCC 0025-1 16X/91/$03.00