Syndiotactic poly copolymers

Preparation of Block Copolymers. Poly(styrene-b-methyl methacrylate) and poly(styrene-b-t-butyl methacrylate) were prepared by procedures similar to those reported for poly(styrene-b-methyl methacrylate (12,13). Poly(methyl methacrylate-b-t-butyl methacrylate) was synthesized by adaptation of the method published (14) for syndiotactic poly(methyl methacrylate) polymerization of methyl methacrylate was initiated with fluorenyllithium, and prior to termination, t-butyl methacrylate was added to give the block copolymer. Pertinent analytical data are as follows. 

Poly(vinyl alcohol) is typically obtained by alcoholysis of poly(vinyl esters), for example from polyfvinyl acetate) and methanol in the presence of NaOH. The process can be completed or only partially conducted. In this latter case a copolymer (alcohol/ester) is obtained. Other synthetic procedures are used, most of them also based on the hydrolysis of poly(vinyl esters). Poly(vinyl alcohol) is typically used in the atactic form, but isotactic or syndiotactic poly(vinyl alcohols) also are known. 

In the present study, syndiotactic polypropylene was supplied by FINA Chemical and Oil Company, having the reported weight-average and number-average molecular weights of sPP of 174,000 and 74,700 gmol , respectively, with a poly-dispersity (Mw/Mn) of 2.3 and 92.6% content of syndiotacticity. Poly(ethylene-octene) copolymer was provided by the Dow Chemical Company (Mw = 41,800 g mol , Mw/Mn = 2.26, and octene content = 10% by weight). 

This conclusion has been reached in the copolymerization of acrylic acid (AA) and methacrylic acid (MAA) with N-vinylpyrrolidone (34, 35) (a monomer noted for its thermal stability (36) and discussed in Chapter 9) and with acrylamide (37). The incorporation of the acid monomer in the copolymer decreases with increasing solution pH. The r values with MAA are particularly low at pH <5 because of hydrophobic associations of the methyl groups. Laser-Raman studies (38) have also indicated intramolecular association among the methyl groups of syndiotactic poly(methacrylic acid) (PMAA) in aqueous solution. The addition of NaCl, at a moderate pH, increases the amount of neutralized, weak acid monomer incorporated (Table III). A more gradual change is observed with pH in the MAA-AM combination than in the AA-AM pair because of the hydrophobic interactions cited. The relationships are nearly quantitative with the ionization of the acids as reflected by the pK of the monomer and polymer acid sequences. 

In toluene solution, syndiotactic block copolymers of methyl methacrylate (PMMA) and allyl methacrylate were formed using triphenylphosphine and triethylaluminum as initiator [76]. In acetone solution, syndiotactic poly(methyl methacrylate) forms a stereocomplex with other syndiotactic polymers. The complex formed with syndiotactic poly(allyl methacrylate), upon separation from the reaction mixture and drying had a melting point of 141.5°C by DSC thermogram. From X-ray powder patterns of this and related complexes of PMMA with other polymethacrylates, the authors postulate that a double-stranded helix may represent a model of the structure of these complexes [77]. 

Monomers Figure3.8 shows a small selection of cyclic monomers suitable for ROP [43]. Additionally, three different stereoisomers of lactide exist as a consequence of the presence of two stereocenters per monomer unit, namely meso-, L- and d-lactide, see Fig. 3.9. Further, racemic mixture of L- and D-lactide are commercially available. While ROP of either pure l- and D-lactide enables synthesis of highly crystalline poly(L-lactic acid) or poly(D-lactic acid), ROP of rac- or wcj< -lactide with adequate catalysts allows the synthesis of stereoblock copolymers, heterotactic and syndiotactic poly(lactic acid). Notably, stereoregular PLAs display much lower rates of degradation than the amorphous atactic polymer. 

Solvents influence the rate of free-radical homopolymerization of acrylic acid and its copolymerization with other monomers. Hydrogen-bonding solvents slow down the reaction rates. Due to the electron-withdrawing nature of the ester groups, acrylic and methacrylic ester polymerize by anionic but not by cationic mechanisms. Lithium alkyls are very effective initiators of a-methyl methacrylate polymerization yielding stereospecific polymers.Isotactic poly(methyl methacrylate) forms in hydrocarbon solvents. Block copolymers of isotactic and syndiotactic poly(methyl methacrylate) form in solvents of medium polarity. Syndiotactic polymers form in polar solvents, like ethylene glycol dimethyl ether, or pyridine. This solvent influence is related to Lewis basicity in the following order ... 

SMI Copolymer from styrene and maleimide SMM Styrene-methylmethacrylate copolymer SMMA Styrene methylmethacrylate sPhPS Syndiotactic poly(p-phenyl styrene) sPP Syndiotactic polypropylene sPS Syndiotactic polystyrene SSE Single-screw extruder TM Thio-rubber... 

Thus, it was not until 1990 that the group of Kaminsky and Arndt-Rosenau took a more detailed look at the homopolymerization of norbornene and the structures of the resulting polymers. Driven by the growing interest in copolymers with high norbornene contents and high glass transition (Tg) temperatures, as well as the unusual properties of PNBs, Arndt-Rosenau et al. used the hydrooligomerization technique to produce saturated model norbornene dimers and trimers with metallocene catalysts known to produce atactic, isotactic, and syndiotactic poly(a-olefins) (1-3, Table 16.1). 

Fig. 5.10 Plots of extrapolated equilibrium melting temperature of syndiotactic poly-(propylene)-l-octene copolymers as a function of comonomer concentration. Solid line calculated according to Eq. (5.42). (From Thomann, Kressler and Miilhaupt (71))...

Copolymers of syndiotactic poly(propylene) behave in a similar manner.(64) Here the copolymers with ethylene, 1-pentene, 1-hexene and 4-methyl-1-pentene as co-units obey the same melting temperature-composition relation. On the other hand, the copolymer with 1-butene gives higher melting temperatures than the others. This result will also be discussed further in the next section. 

Thermoreversible Gelation of Syndiotactic Poly(methyl methacrylate) Based Block Copolymers... 

Thermoreversible gelation has been studied in o-xylene for syndiotactic poly(methyl methacrylate) based block copolymers. The dynamic properties of solutions and gels have been analyzed and discussed on the basis of scaling assumptions. At the gel point, where the loss angle tan 5c=G 7G is independent of the probing frequency, the samples obey the typical power law G ((o) G (co) o... 

This paper is a discussion of the main results we have on the thermoreversible gelation of block copolymers of the MXM type in o-xylene, where M is syndiotactic poly(methyl methacrylate) (sPMMA) and X is either polybutadiene (PBD), hydrogenated PBD (PEB), poly(styrene-b-butadiene-b-styrene) (SBS) triblock or the hydrogenated version of this triblock (SEBS) (25-28). 

This behavior is probably related to the anomalous temperature dependence discussed in Section F2 of Chapter 11 and may be attributed to hyperentanglements with some kind of attraction between tactic regions in imperfectly atactic polymers. Such attractions can occur as evidenced by gel formation in solutions of mixed isotactic and syndiotactic poly(methyl methacrylate). " Similar effects might be expected in copolymer systems where hydrogen bonding can occur at widely separated points. ... 

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