Tacticity of PMMA

Puzin et al.h] reported that the tacticity of PMMA prepared in bulk is influenced (slight increase in syndiotacticity) by very small amounts of titanoecnc diehloride (1 O 3 M). Selective complexation of the propagating radical was postulated. 

Table I shows the tacticities of PMMA samples which were prepared in counterion/solvent systems which so far have been investigated kinetically and in which the contribution of free anions was suppressed by the addition of a common ion salt. It is seen, that the degree of isotacticity as well as the persistence ratio decrease with decreasing solvation, exhibiting the following order Na/DME < Cs/DME Na/THF < Cs/THF.

TABLE 1. Tacticity of PMMA and PtBMA synthesized by anionic polymerization with a Li counter-ion in THF... 

It must be noted that LiCl has no effect on the tacticity of PMMA . In contrast, the isotacticity of PtBMA was increased from 9.9% to 25.5% when a threefold molar excess of LiCl was added to the initiator . ... 

The chain tacticity of PMMA synthesized by GTP catalyzed by nucleophiles at different temperatures was analyzed by Webster and coworkers The syndiotactic content increases from 50% at 60 °C up to 80% at —90°C in THF, using tris(dimethylamino)sulfonium bifluoride [(Me2N)3S+ HF2 ] as catalyst . In contrast to the anionic polymerization of MMA, the stereoselectivity of GTP is less sensitive to solvent. It must be noted that PMMA is less syndiotactic when the GTP is catalyzed by nucleophiles rather than by Lewis acids . GTP was extended to the living polymerization of many acrylates and methacrylates, such as nBuMA, glycidyl-MA, 2-ethylhexyl-MA, Me3SiOCH2CH2-MA, sorbyl-MA, allyl-MA, lauryl-MA), acrylates (EA, BuA), acrylonitrile, methacrylonitrile and Al,A-dimethylacrylamide . 

GTP of methacrylates. Tacticity of PMMA synthesized by either anionic polymerization or mucleophile-mediated GTP is very similar The same conclusion holds for the reactivity ratios in random copolymerization of methacrylates and acrylates for... 

Surprisingly or not, the tacticity of PMMA obtained with various metals including Ru,27 56 58 63... 

It has been reported that the tacticity of PMMA prepared with benzoyl peroxide (BPO) deviates slightly from Bernoullian statistics while that of PMMA... 

Table 12. Mean values of tacticity of PMMA determined from various NMR signals.

Table 13. Mean values (X) and standard deviations (a) of tacticity of PMMA determined by 1H and 13C NMR spectroscopy.

Fig. 6 (a) NMR spectra of Poly(methyl methacrylate) (PMMA) obtained from the nanochannels of [Cu2(L)2(ted)] and the bulk condition in nitrobenzene- / at 110°C. (b) Plot of nanochannel size effect on tacticity of PMMA... 

The most common acrylic, PMMA, shows limited miscibility with chlorinated hydrocarbons (e.g., PVDC, PVC, CPVC, or CPE). The miscibility depends on the type of chlorinated polymer, tacticity of PMMA, and molecular weights... 

I, H, and S = expected triad tacticities of the stereoblock polymer and = triad tacticities of PMMA homopolymer... 

Characterization tacticity of PMMA. Less soluble syndiotactic PMMA move with its initial solvents while better soluble isotactic PMMA elute in SEC mode. 

The majority of compositionally different poly(meth)acrylates are immiscible. Nevertheless, there are some examples noted in the literature of miscible combinations. One of the most interesting and well-studied cases involves isotactic PMMA (iPMMA) with syndiotactic PMMA (sPMMA).[149] The miscibility observed may be expected, but the formation of a stereocomplex offered an interesting system to study. The tacticity of PMMA blends with poly(vinyl pyrrolidone) (PVP) affected the blend phase behavior as atatic and syndiotactic PMMA were miscible with PVP, but isotactic PMMA was phase sepa-rated.[150,151] Miscibility with upper critical solution temperature (UCST) behavior was observed for PnBA blends with poly(propylene glycol) (linear and three arm star) oligomers.[152] Poly(vinyl buty-ral)/PMMA blends were found to be phase separated at high MW PMMA.[153] At low MW PMMA (2000-5000 g/mol), miscibility with UCST behavior was observed. The PMAA/PVAc miscibility was... 

The miscibility between several (meth)acrylate polymers and phenoxy (PHE) has been reported.[155,156] PEMA was noted to be partially miscible and PBMA to be phase separated in PHE blends. [155] An investigation of the effect of PMMA s tacticity on the phase behavior of PMMA/PHE blends showed aPMMA, sPMMA and iPMMA to all exhibit miscibility with PHE. [156] The miscibility of PMMA with a vinylidene chloride-acrylonitrile (20 wt% AN) copolymer was shown to be a function of the PMMA tacticity (aPMMA and iPMMA miscible with the copolymer and sPMMA immiscible). [157] Hsu et fl/.[158] reported the effect of tacticity of PMMA on the miscibility with PVAc. This study showed a limited effect of tacticity and solvent choice on the phase behavior of PMMA/PVAc blends and all blends were analyzed as being immiscible based on the observation of two Tgs. Modest areas of miscibility were established for MA, EA, nBA, and 2-ethylhexyl acrylate based acrylate-acrylic acid in the respective copolymers. No miscible combinations were found for MMA-AA or acrylate-MAA copolymers with vinyl acetateethylene (VAE) or PVAc. 

Blends of PMMA and polycarbonate based on hexafluoroBisphenol A (HFPC) were noted to be miscible as well as blends of PC copolymers based on HFBisphenol A and Bisphenol A PC [437]. Additionally, HFPC exhibited miscibility with PEMA and PnPMA. Bisphenol chloral polycarbonate (BCPC) exhibited miscibility only with PMMA. The effect of tacticity of PMMA was reported [438] on phase behavior with PC blends. Miscibility was shown to increase in PC blends in the order of atactic, isotactic, syndiotactic, with syndiotactic PMMA/PC showing no thermally induced phase separation up to 300 °C. 

The Wilkinson complex Rh-1 was examined for styrene in the hulk at 130 ° C coupled with sulfonyl chloride as the initiator hy Percec et al. in 1996. The obtained polystyrene had broader MWDs (Mw/Mn= 1.7) than those with the mthenium or copper catalysts. Meanwhile, it induced faster polymerizations of MMA in the presence of CCI4 or CHCl2COPh in a mixture of THF and water at 60 °C, in which the conversion reached 90% in 4h to give PMMA with relatively narrow MWDs (M /Mn= 1.3-1.7). The effects of galvinoxyl and the tacticity of PMMA agreed again with that for the free radical polymerization. A bromide complex (Rh-3) in conjrmction with a bromide initiator afforded PMMA with narrower... 

Wu [49] proposed estimating G° as the storage modulus at the frequency where tan 5= minimum, but often there is no minimum in the data. Using this method, Fuchs et al. [38] reported a modest effect of the tacticity of PMMA on the plateau modulus. They also found that Eq. 5.4 fitted their viscosity data with a = 3.4 but that the constant K depended on tacticity. Plazek et al. [50] studied the effect of tacticity on the creep behavior of PMMA and noted that absorbed water is always a problem in making measurements on polar polymers. Wu [51] later proposed an empirical equation between the ratio (G Gq) of the plateau modulus to the crossover modulus, G, (where G = G") and the polydispersity index. 

The diad tacticity determined from the relative peak intensities of the diastereomeric tetramers in the programs was consistent with that obtained by pNMR, suggesting that no appreciable thermal isomerisation occurred during the pyrolysis. The thermal degradation mechanisms yield the diastereomeric tetramers from PMMA without isomerisation and this opens up, the possibility of estimating the triad tacticity of PMMA from the distribution of diastereomeric pentamers. 

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