Syndiotactic copolymers

For the syndiotactic copolymer, highly extended conformations with c values of 7.5-7.6 A can be obtained for a glide plane symmetry when... 

Figure 1. Compositional distribution of a predominantly syndiotactic copolymer bearing COCHiSOsN(CHs)t units (DPn = 650, DSm = O 366) from precipitation fractionation data. System 1 (6) CHCls—Et2C) system II (O) DMF—Hs0 + O, 5% NH4Cl cross fractionation ( ) intermediate fractions obtained from system II are further fractionated according to System I.

The experimental results of the two methods a) and b) applied to copolymers bearing COCI SC CH and COd SC frKCH-j) 2 8rouPs are in fairly good agreement 7 as shown in Figure 2 for isotactic copolymers the distribution of B units is nearly bernouillian, as expected from the kinetics kQ=kj for syndiotactic copolymers B units tend to be isolated between A blocks, and their distribution is quite compatible with that calculated taken into account the corresponding autoretarded kinetics (ko>k] k - 0). 

Turning to propylene, cis addition was found also for syndiotactic polymers (4(X), 401). This result deserves additional comment. It is known that only one disyndiotactic polymer is obtained from a CHA=CHB olefin (see Sect. II-B) but this is no longer true when one considers the syndiotactic copolymers between two differently labeled monomers. The syndiotactic copolyriKr between perdeuteropropylene and propylene-l-d, can have either of the two structures 99 Ot 199. Hew 9ve motvomet mil deti ixv% from Ihe second mononvei (present in small quantity) can be clearly identified as to its stereochemistry. 

The NMR proton spectra of the syndiotactic copolymers obtained from perdeuteropropylene with the l-d,-cis or the l-dj-trans monomer present a doublet around 16 attributed to the methylene proton of the r dyad coupled to the methine proton. In the two polymers the vicinal coupling constants are different, 4.8 Hz... 

For the first experiments aiming to achieve isotactic copolymerization, optically active 2-pyridinecarboxaldehyde(l-phenylethyl)imine was used as the ligand (58) nevertheless, a prevailingly syndiotactic copolymer (ww H-triads 56 20 20 4)... 

The methods of calculation described above were used for the evaluatimi of triad composition of products of the l drol of syndiotactic copolymers of methylmethacrylate and meth a ic add in condi His corresponding to the accel-mting and retarding ndf dxirit -groups effect. Hie probabilities of different triads calculated with constants being found from kinetic data (ko k k2= 1 3 and 1 0,2 0,05 were compared with the residts of NMR study The satis-... 

Isotactic or syndiotactic homopolymer, or isotactic/syndiotactic copolymer Good good spin-stretch, easy processing... 

PMMA analogous to the preparation of the syndiotactic copolymers. The NMR spectrum in Fig. 5, trace I, has been recorded from isotactic PMMA used as the starting material for hydrolysis. Trace II to VI are due to the isotactic copolymers... 

As may be derived from Figs. 3 and 4, the syndiotactic copolymer triads are positioned in DMF as shown in Table 2. The assignment of PMMA in DMF was anticipated to be analogous to the well known assignments in other solvents, while that of PMAA in DMF had still to be found [74]. In Fig. 8, trace I, the spectrum... 

The inequality of the average vicinal coupling constants between methynic and methylenic protons (J = 4.8 cps, = 8.3 cps) suggests that the macromolecules in solution predominantly assume a planar zig zag conformation [i]. By considering this fact, it is possible to prepare syndiotactic copolymers of per-deuteropropylene with cis Id propylene and with trans d propylene and to foresee, for the two copolymers, trans-syndiotactic and awc/z -syndiotactic structures (Fig. 3) differing for the relative positions of the vicinal methynic and methylenic protons. 

The coupling constant (8.3 cps) will be characteristic of the trans syndiotactic copolymer and the constant J is (4-8 cps) will be characteristic of the gauche syndiotactic copolymer. 

Fig. 4 shows the NMR spectrum of a syndiotactic copolymer of perdeutero-propylene with 20 mole- % of trans 1 propylene and Fig. 5 the NMR spectrum of a syndiotactic copolymer of perdeuteropropylene with 20 mole-% of cis Id propylene. 

On the contrary, the alternating distribution in syndiotactic copolymers indicates the existence of steric interactions, which are important for the addition, between monomer and last unit of the growing chain end. Hence, in the case of syndiospecific polymerization, it seems logical to attribute, at least in part, the steric control to the last unit in the chain. These assumptions seem confirmed by the examination of the microstructure of homopolymers of propylene having a partial steric regularity. 

On this regard we are completing the above data by studying syndiotactic copolymers of propylene with ethylene, and model compounds. Our... 

Natta et al. (63% Miyazawa cr al. (64) and Zambelli et cd. (65) determined the structure of isotactic polymers of cis and treats 1-dj propylene and of syndiotactic copolymers of dg-propylene with cis and trans 1-di-propyIene. In so doing, they succeeded in establishing that cis addition is common to both isotactic and syndiotactic propagation. 

Loffredo, E, Pranzo, A., Venditto, V., Longo, P., Gnerra, G. Clathrate phases of styrene/p-methylstyrene co-syndiotactic copolymers. Macromol. Chem. Phys., 204, 859-867 (2003). 

Turek, D. A. Sununary of the physical properties of continuous melt-spun fibers formed from syndiotactic polystyrene and syndiotactic copolymers of styrene and paramethylstyrene. Dow Internal Report, September 1994. 

Ethylene and ar-2-butene form a syndiotactic copolymer in a reaction catalyzed by a vanadium catalyst. Draw a representation of the polymer. 

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