Random, Defect-Free Ethylene/Vinyl Halide Model Copolymers via Condensation Polymerization

Abstract

The synthesis of ethylene vinyl halide (EVH) copolymers containing fluorine, chlorine, and bromine via the ADMET copolymerization of halogen containing R-ω-dienes with 1,9-decadiene is presented. The statistically random nature of the copolymers was established from their 13 C NMR spectra. Thermal analysis via differential scanning calorimetry points to a distinct difference in the crystallization behavior of these random copolymers when compared to their compositionally matched precise analogues. In this case, sharp melting peaks typical of homopolymer-like crystallization of the precise analogues are no longer observed in Cl-and Br-based random copolymers and are replaced by broader peaks indicating a mechanism based on the selection of long crystallizable sequences. The results presented herein thus point to the utility of these random ADMET copolymers as suitable models for industrially relevant PE copolymers based on the perfectly linear, defect-free, and statistically random copolymer composition.

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.…”

“…Differences observed in the melting behavior are consistent with this crystalline pattern. 16 For instance, while the melting of precisely substituted polymers is very sharp, typical of homopolymers, random analogues melt in a broad temperature range due to the changing melt composition and lead to higher final melting temperatures because the initially formed less defected crystals melt at this final stage. This comparative behavior demonstrates that the placement of the substituent has a major impact on the crystallization behavior of substituted polyethylenes.…”

“…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.…”

“…In addition, the crystallization behavior and crystalline morphology of precision vinyl chloride polymers are compared with data for analogous systems with a matched composition but random chlorine distribution that were synthesized using an analogous ADMET approach. 16 …”

Long‐chain branched random polyethylene via acyclic diene metathesis (ADMET) copolymerization

“…The branch of interest is incorporated in the polymer via the symmetrical α,ω‐diene, and the overall branch content can be controlled by varying the feedstock ratio of the two monomers. Using this procedure, the properties of such copolymers can be systematically studied as a function of branch content …”