Precision Ethylene/Vinyl Chloride Polymers via Condensation Polymerization

Abstract

A family of precision ethylene/vinyl chloride polymers synthesized via acyclic diene metathesis (ADMET) followed by exhaustive hydrogenation is described in which chlorine atoms are present on each and every ninth, 15th, and 21st carbons, respectively, in the series. Detailed 1H NMR and 13C NMR experiments are used to establish the precise nature of the polymers and assign absolutely the observed NMR signals to the corresponding atoms in the precise repeat unit. Thermal analysis via TGA and DSC is also presented. Decomposition behavior measured by TGA indicates a distinct mechanism for decomposition for these precise polymers relative to PVC and random EVC polymers, highlighted by an enhanced stability to thermal HCl loss induced by inhibition of the cooperative zipper mechanism for HCl found in PVC. A homopolymer-like crystallization and melting behavior is inferred from sharp DSC peaks, indicative of a precise polymer structure in which long chain segments, incorporating the halogens, build the core crystal, as opposed to the sequence selection mechanism that operates in random EVC polymers.

Crystallization of Polyethylenes Containing Chlorines: Precise vs Random Placement

“…These results fully support a drastically different crystallization mechanism between substituted polyethylenes with precision or random placement, which was previously inferred from their different melting behavior. 13,15,16 The equivalence in the distribution of Cl between crystalline and amorphous regions in the precision systems gives evidence of a crystallization drive led by packing continuous chain segments that accommodate the substituent as a defect. In reference to linear PE, distortions to the lattice by the Cl substituent cause first a change in the crystallographic packing from the orthorhombic to a triclinic cell, and second, the formation of conformationally disordered, but structurally more ordered, crystallites when the distance between substituents decreases to e8 methylenes.…”

“…A feature unique to the ADMET synthesis used is the absence of vicinal chlorination and of blocky substituted structures which are characteristic of ethylene vinyl chloride copolymers made by chlorination of polyethylene in suspension or from the bulk. [24][25][26] In the latter, multiple stereo sequences define the environment of the methine region, resulting in broad 13 C NMR CH resonances not suitable to determine the distribution of Cl between crystalline and noncrystalline regions. 8 The precise and isolated nature of the CHCl group in the ADMET polymers studied here allows a resolved difference in the CHCl chemical shift between crystalline (∼66 ppm) and noncrystalline phases (∼64 ppm) in all samples, as clearly seen in the expanded insets of Figure 4.…”

“…As expected, there is also a clear resolution of the more abundant crystalline (∼33 ppm) and amorphous (∼30 ppm) CH 2 as well as for R-CH 2 (39-41 ppm) in most of the spectra. All observed 13 C NMR chemical shifts are listed in Table 3. The most significant chemical shift difference between orthorhombic (random) and triclinic (precision) polymers corresponds to the crystalline CH 2 .…”

“…DD-MAS solid-state 13 C NMR spectra were obtained in a Bruker DMX300 spectrometer operating at 75.5 MHz for 13 C. The experiments were conducted at room temperature using a Bruker solid-state probe for 4 mm rotors under a MAS frequency of 4000 Hz. The small quantities available for these polymers were placed in the center of the zirconium rotors and the empty spaces filled with Teflon tape.…”

“…AFM micrographs were obtained using the environmental JEOL 4210 scanning probe microscope operating at ambient conditions with Olympus single side coated silicon cantilevers (spring constant of ∼40 N/m and a c Crystallization peak (Tc), second melting peak (T m), and observed heat of fusion (∆Hm) obtained by DSC at 10°C/min. 13,16 tip radius of less than 10 nm) at a resonant frequency of ∼300 kHz. Topographic and phase images were simultaneously collected under ambient conditions in noncontact AC mode at 256 × 256 pixel resolution.…”