Radical Polymerization of Highly Isotactic and Syndiotactic Poly(methyl methacrylate) Macromonomers

Abstract

ABSTRACT:Highly isotactic (iso-) and syndiotactic (syn-) poly( methyl methacrylate) (PMMA) macromonomers having styrene end group were prepared by the reaction of the corresponding PMMA living anions withp-vinylbenzyl bromide and their polymerizations were studied in toluene using 2,2'-azobisisobutyronitrile as an initiator. The rate of polymerization (Rp) of iso-PMMA macromonomer was slightly higher than that of syn-macromonomer. A similar tacticity dependence of the reactivity was also observed in the radical copolymerization of the macromonomers with styrene. Propagation rate constant (kp) for the homopolymerization of macromonomers was estimated from R", termination rate constant (k,) determined by ESR spectroscopy [K. Hatada et al., Makromol. Chern., Rapid commun., 11, 101 (1990)] and initiator efficiency (f) determined from end group analysis of polymacromonomer by means of NMR spectroscopy [T. Kitayama et al., Polym. Bull., 25, 205 (1991)]. Both the k, and k" values were much smaller than those for styrene polymerization, and the decrease of k, of the macromonomer was much more evident than the decrease of k". The kv and k, values for iso-macromonomer were much larger than the corresponding values for the syn-one. The results suggest that the higher segmental mobility of iso-PMMA chain than that of syn-PMMA chain brings about the larger rate constants for propagation and termination reactions.KEY WORDS PMMA Macromonomer I Stereoregularity I Tacticity I Propagation I Termination I Monomer Reactivity Ratio I Initiator Efficiency I Many papers have been published on the syntheses and applications of macromonomers.1-5 Especially, macromonomers of high purity and narrow molecular weight distribution (MWD) have been desired for the syntheses of graft or comb-like polymers which have well-defined structures. Characteristic features of the radical polymerization of macromonomers have been studied by kinetic experiments. 6 -14 However, little attention has been paid to the tacticity of the macromonomers. 15 -17 Poly(methyl methacrylate) (PMMA) is one of the typical polymers whose tacticity can be widely varied by changing the reaction conditions and whose properties in bulk and in solution depend strongly on the tacticity.18·19 Glass transition temperature (Tg) of PMMA is much lower for the iso-PMMA than for the syn-PMMA. 19 • 20 The 13 C NMR spin-lattice relaxation times of the carbons in iso-PMMA are larger than those of the corresponding carbons in syn-PMMA, indicating that the iso-polymer chains have greater segmental mobility than the syn-ones. 21 Therefore, control of stereoregularity of PMMA macromonomer will provide another means for controlling the properties of graft

Structurally controlled polymerizations of methacrylates and acrylates

“…End-capping reaction of a highly isotactic PMMA anion, prepared by t-C 4 H 9 MgBr with p-bromomethylstyrene (p-BMST) in the presence of hexamethylphosphric triamide (HMPA) or 1,8-diazabicyclo [5.4.0]undec-7-ene (DBU), gave an it-PMMA macromonomer containing one styrenic group at chain-end. 81,82 The number of styrene groups introduced at the terminating chainend was determined from the intensity measurement of the 1 H NMR signals due to the t-C 4 H 9 group and the vinyl group. The measurements indicated that most of the macromonomer molecules contained one styrene group at chain-end (eqn 13).…”

Reactivity in Radical Polymerization of Poly(2-oxazoline) Macromonomers

“…Decrease in polymerizability of MA-POcOZO macromonomers may be explained as follows: in MA-POcOZO macromonomers or their polymer radicals, linkages from vinyl groups or growing ends to POcOZO segments are wholly single bonds that are flexible in contrast to VB-POcOZO macromonomers or their radicals, and accordingly steric effect of the long acyl chains (pelargonoyl groups) seems highly exerted at reaction Figure 4. Relationship of surface tension ( i') to solution concentration in macromonomers; MA-PMeOZ0-32 (0), VB-PMcOZ0-34 (6). MA-PMeOZ0-15 (0).…”

“…8 It is essential to know the characteristics of macromonomer reactivity in polymerization to obtain well-defined polymers. Many studies on copolymerizations 6 • 9 and homopolymeriza-1 To whom correspondence should be addressed.…”

“…tions 2 b· 5 · 6 of macromonomers have been reported mainly in radical polymerization. The factor predominating polymerizability of macromonomers in copolymerization is primarily chemical reactivity of polymerizable end groups.2b.sab, lO Homopolymerization ofPROZO macromonomers has not been reported so far for radical and ionic polymerizations.…”

Synthesis of Graft Polymer with Controlled Stereoregularities in the Main Chain and in the Side Chains by Stereospecific Copolymerization of Isotactic Poly(methyl methacrylate) Macromonomer with Methacrylate Monomer

“…The procedure for the preparation of it-PMMA macromonomer is almost the same as that of st-macromonomer. 12 To it-PMMA living anions formed with t-C 4 H 9 MgBr in toluene at -78°C, 14 10 equivalents of allyl iodide were added slowly at -78°C to obtain it-PMMA with allyl end group (it-PM MA-CH 2 CH = CH 2 ). After l h, 5 equivalents of DBU in toluene were added to this mixture, and the reaction was continued for 24 h at -78°C and then for further 3 h at 0°C.…”