Isotactic-1,2-poly

The synthesis of isotactic polymers of higher a-olefins was discovered in 1955, simultaneously with the synthesis of isotactic PP (1,2) syndiotactic polymers of higher a-olefins were first prepared in 1990 (3,4). The first commercial production of isotactic poly(l-butene) [9003-29-6] (PB) and poly(4-methyl-l-pentene) [9016-80-2] (PMP) started in 1965 (5). 

Syntheses. Isotactic poly(methyl methacrylate) was synthesized by the method of Tsuruta et al. (9 ). Under a nitrogen atmosphere, a quantity of 6 mL (0.056 mole) of methyl methacrylate (MMA) dried over 4A molecular sieve was dissolved in 24 mL of similarly dried toluene. To the glass vial containing the reaction was added 0.65 mL of 1.6 M n-butyllithium, and the reaction was kept at -78°C in a dry ice/isopropanol bath. The polymerization was halted 24 hr later with the addition of hydrochloric acid and methanol (methanol/water 4.1 by volume). The polymer was dried in vacuo at 50°C, redissolved in methylene chloride, precipitated by being poured into water-containing methanol, and dried in vacuo at 50°C. Tacticlty and composition were verified with % NMR. Yield 47%. 

Isotactic poly(methyl methacrylate/methacrylic acid), a copolymer of methyl methacrylate and methacrylic acid, was synthesized by the partial hydrolysis of isotactic poly(MMA) according to the method of Klesper et al. (10-13). A hydrolyzing mixture of 8 mL dioxane and 4 mL methanolic KOH (10% by weight K0H) was mixed with 250 mg of polymer in closed vials at 85°C for 48 hr. Saponified polymer separated from the solution and adhered to the walls of the vial. The precipitated polymer was dissolved in water and then precipitated again with a few drops of HC1. The solution was warmed and the coagulated polymer removed, washed with water, and dried in vacuo at 50°C. The nmr spectrum indicated approxi-... 

Figure 3. NMR of isotactic poly(MMA) in CDCI3 at 300 K with 1% TMS. Upper trace is x8 vertical expansion.

Figure 6 Spherulites of isotactic poly-l-butene (a, during growth) and of polyethylene (b, after completion) by optical microscopy (OM) under crossed polars. Reproduced from Ref. [3] with permission of John Wiley Sons, Inc.

Figure 2 X-ray diffractograms recorded at room temperature, (a) Metallocene-synthesized isotactic poly(propylene), mmmm — 0.996 crystallized at 145°C. (b) Atactic poly(propylene). Reproduced with permission from Ref. [43], Copyright John Wiley Sons, Inc., 1999.

Table 1 Comparison of degree of crystallinity for metallocene isotactic poly(propylenes) from wide-angle X-ray scattering analyzed by different methods...

It has also been inferred that differences found between crystallinities measured by density and those from heat of fusion by DSC area determination, as given for polyethylenes in the example of Figure 4 [72], may be related to baseline uncertainties, or not accounting for the temperature correction of AHc. Given that similar differences in crystallinity from density and heat of fusion were reported for isotactic poly(propylene) [43] and polyfaryl ether ether ketone ketone), PEEKK [73], other features of phase structure that deviate from the two-phase model may be involved in the crystallinity discrepancy. 

Both vibrational spectroscopies are valuable tools in the characterization of crystalline polymers. The degree of crystallinity is calculated from the ratio of isolated vibrational modes, specific to the crystalline regions, and a mode whose intensity is not influenced by degree of crystallinity and serves as internal standard. A significant number of studies have used both types of spectroscopy for quantitative crystallinity determination in the polyethylenes [38,74-82] and other semi-crystalline polymers such as polyfethylene terephthalate) [83-85], isotactic poly(propylene) [86,87], polyfaryl ether ether ketone) [88], polyftetra-fluoroethylene) [89,90] and bisphenol A polycarbonate [91]. 

MHz, which determine the Tics, are the same for the non-crystalline region of isotactic poly(propylene) and for atactic poly(propylene). This in turn indicates that the disordered chain structure is the same for the two cases. 

Figure 11 Left Spherulites of a Ziegler-Natta isotactic poly(propylene) with Mw = 271,500 g/mol and mmmm — 0.95, isothermally crystallized at 148°C. Right Banded spherulites of a linear polyethylene with Mw = 53,600 g/mol slowly cooled from the melt.

Figure 17 Isothermal melting of Ziegler-Natta isotactic poly(propylene). (a) Spherulites with mixed birefringence at Tc = 148°C. The top middle figure displays the melting for the same thermal history, (b) Subsequent to crystallization, the temperature was raised to 171°C spherulites acquire negative birefringence, (c), (d) and (e) Isothermal melting at 171°C for 80, 200 and 300 min, respectively. Reproduced with permission from W.T. Huang, Dissertation, Florida State University, 2005. (See Color Plate Section at the end of this book.)...

Here m is the mode order (m — 1,3,5. .., usually 1 for polyethylenes), c the velocity of light, p the density of the vibrating sequence (density of pure crystal) and E the Young s modulus in the chain direction. The LAM band has been observed in many polymers and has been widely used in structural studies of polyethylenes [94—99,266], as well as other semi-crystalline polymers, such as poly (ethylene oxide) [267], poly(methylene oxide) [268,269] and isotactic poly(propylene) [270,271], The distribution of crystalline thickness can be obtained from the width of the LAM mode, corrected by temperature and frequency factors [272,273] as ... 

Further confirmation of the structure and tacticity of poly/5-methyl-l,4-hexadiene)was obtained from X-ray diffraction and u-NMR data of its hydrogenated polymer (Scheme 2). The hydrogenated polymer sample showed a highly crystalline pattern (Figure 7), with diffraction spots that were well defined. This pattern was identical to that of isotactic poly(5-methyl-l-hexene) as reported in the literature (26) (measured identity period, 6.2 A lit., 6.33 A). 

Syndiotactic and isotactic poly(methyl methacrylate) are crystalline and melt at 160 and 200 °C, respectively. 

Table 8. Isotactic poly(propylene) polymerized by bridged- and unbridged-metallocene catalysts... 

Scheme 1.1 Typical steric defects in a (mainly) isotactic poly-l-alkene chain (adapted Fisher projections) for (a) chain-end-stereocontrol (b) enantiomorphic site stereocontrol.

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