gem‐Dimethyl Effects in the Thermal Behavior of Polyethylene

Abstract

Summary: Polyethylene can be rendered completely amorphous via the insertion of regularly spaced gem‐dimethyl defects along its backbone, where frequency of insertion is the deciding factor in achieving the totally amorphous state. Accurate placement of defects along polyethylene's backbone is achieved with step polymerization metathesis chemistry (the ADMET reaction) rather than using chain polymerization techniques. These gem‐dimethyl polyethylene macromolecules, when compared with other ADMET ethylene‐based model materials, demonstrate that steric bulk, frequency, and distribution of the defect along the polymer backbone are more important than stereoregularity (tacticity) when the defects are spaced nine carbon atoms or more apart. Comparisons are made between gem‐dimethyl “defects” and methyl “defects” in a polyethylene backbone.

Synthesis of Amorphous Hydrophobic Telechelic Hydrocarbon Diols via ADMET Polymerization

“…2 100. The hydrogenation method was successful here, despite difficulties encountered previously when this heterogeneous catalyst was used to hydrogenate a high molecular weight ADMET polymer,30 possibly due to the higher solubility of the low molecular weight telechelic polymers.…”

“…Scheme was developed with the goal of preparing a difunctional, completely amorphous telechelic hydrocarbon diol with a number average molecular weight ($\overline M _{\rm n}$ ) between 1 000 and 2 000. ADMET polymerization of a previously reported30 monomer ( 2 ) in the presence of a diacetate CTR (either 3a or 3b , where y = 1 and 3, respectively) forms the unsaturated diacetate telechelic polymer ( 4a or 4b , respectively), which is then quantitatively hydrogenated to give the saturated diacetate telechelic polymer ( 5a or 5b , respectively). Subsequent hydrolysis of the acetate end groups gives the desired telechelic diol ( 1a or 1b , respectively).…”

“…1,4‐bisacetoxy‐2‐butene (CTR 3a ) was purchased from Aldrich and distilled from CaH 2 (63 °C at 0.1 mmHg) and acetic acid 4‐pentenyl ester was purchased from TCI and distilled from CaH 2 (66–68 °C at 53 mmHg). The monomer ( 2 ) was prepared by a previously reported procedure 30. All other reagents were used as received.…”

“…The present work entails the synthesis of several difunctional, completely amorphous hydrophobic telechelic hydrocarbon diols using ADMET chemistry. These hydroxyl telechelics, shown in Figure 1, are based on an ADMET ethylene/isobutylene (EIB) model copolymer reported previously 30. The molecular structures of the three telechelic diols ( 1a–c ) differ by the number of methylene “spacers” at the chain ends, which is a direct result of the identity of the chain termination reactant (CTR) used to end‐cap the polymer chains during the ADMET reaction.…”

Facile synthesis of ethylene–propylene fully alternating copolymer and comparison with random copolymer of similar composition

“…[22][23][24][25][26][27] Wagener and coworkers have done a lot of work on the synthesis and characterization of ethylene-propylene copolymer models using step polymerization namely acyclic diene metathesis (ADMET) polymerization rather than chain polymerization techniques. [28][29][30][31][32][33][34][35][36][37] ADMET polymerization of symmetric a,x-diolefin monomers followed by exhaustive hydrogenation offers a new viable method to synthesize PE backbone with precisely distributed methyl branches, for instance, PEs containing methyl on every 5,7,9,15,21, and 39 carbons along the backbone respectively were successfully prepared. Wilke and coworker have successfully synthesized ethylene-propylene copolymer with five methylene between the two methyl branches.…”