Gradient copolymers can exhibit physical properties that are different than their block polymer analogues. Property variations should depend upon differences in the molecular arrangement of individual comonomers in the polymer chain and in the gradient zone of each chain as well as the morphological arrangement of those chains in space. Here we describe experimental approaches based on fast and slow magic-angle spinning (MAS) NMR, which reveal the amount of rigid and soft phases in styrene− butadiene gradient copolymers with component specific resolution. In addition, we introduce a spin-counting strategy that quantitatively and directly determines the amount of the low-T g , or "soft", butadiene component that is incorporated into the rigid domains and also the amount of high-T g , or "hard", styrene component that is incorporated into the mobile domains. In total, the experiments provide bulk rigidity, amount of polybutadiene partitioned in both soft and hard phases and the amount of polystyrene partitioned in each phase. We show that the synthesis conditions can be changed to vary the partitioning of each gradient copolymer component in a systematic way and propose that the interphase between the hard and soft domains is responsible for differential partitioning.

The distribution of polyethylene (PE) chain segments between the crystalline, noncrystalline, and interfacial morphological regions is an old question that continues to intrigue the polymer science community. Simple solid state NMR experiments described here reveal that even in the case of linear PE, four distinct chain components may be resolved and reliably quantified. The amounts of rigid crystalline chains in all-trans conformations, amorphous chains with increased equilibrium gauche conformer content undergoing essentially isotropic reorientation, mobile all-trans chains (termed mobile trans), and less mobile noncrystalline chains (termed constrained amorphous) can be quantified by simple 13C NMR experiments on solid polymer samples. A version of the EASY background suppression pulse sequence [ Jaeger Hemmann Solid State Nucl. Magn. Reson.201457–5822], modified to eliminate transient Overhauser effects, is used to obtain all of the data in a single experimental acquisition. Using a broad range of well-characterized linear metallocene PE’s, the method reveals that the constrained amorphous and the mobile all-trans fractions, i.e., the total interface content, increases essentially linearly with increasing M w. Topologically modified PE’s, at similar M w’s, that contain short-chain branches (SCB), long-chain branches (LCB), or long-chain branches with SCB’s (LCB + SCB) have significantly larger interfacial content per unit molecular weight and most significantly so for the LCB + SCB polymers.

Jute fabrics such as reinforced polyvinyl chloride (PVC), polypropylene (PP), and a mixture of PVC and PP matrices-based composites (50 wt% fiber) were prepared by compression molding. Tensile strength (TS), bending strength (BS), tensile modulus (TM), and vbending modulus (BM) of jute fabrics' reinforced PVC composite (50 wt% fiber) were found to be 45 MPa, 52 MPa, 0.8 GPa, and 1.1 GPa, respectively. The effect of incorporation of PP on the mechanical properties of jute fabrics' reinforced PVC composites was studied. It was found that the mixture of 60% PP and 40% PVC matrices based composite showed the best performance. TS, BS, TM, and BM for this composite were found to be 65 MPa, 70 MPa, 1.42 GPa, and 1.8 GPa, respectively. Degradation tests of the composites for up to six months were performed in a soil medium. Thermo-mechanical properties of the composites were also studied.

Electrochemical dehalogenation of polyhalogenated compound is an inefficient process as the working electrode is passivated by the deposition of short-chain polymers that form during early stages of electrolysis. Herein, we report use of 1,1,1,3,3,3-hexaflouroisopropanol (HFIP) as an efficient reagent to control C–H formation over radical association. Debromination of 1,6-dibromohexane was examined in the presence of Ni(II) salen and HFIP as the electrocatalyst and hydrogen atom source, respectively. Electrolysis of 10 mM 1,6-dibromohexane and 2 mM Ni(II) salen in the absence of HFIP yields 50% unreacted 1,6-dibromohexane and ~40% unaccounted for starting material whereas electrolysis with 50 mM HFIP affords 65% n-hexane. The mechanism of hydrogen atom incorporation was examined via deuterium incorporation coupled with high-resolution mass spectrometry, and density functional theory (DFT) calculations. Deuterium incorporation analysis revealed that the hydrogen atom originated from the secondary carbon of HFIP. DFT calculations showed that the deprotonation of hydroxyl moiety of HFIP, prior to the hydrogen atom transfer, is a key step for C-H formation. The scope of electrochemical dehalogenation was examined by electrolysis of 10 halogenated compounds. Our results indicate that through the use of HFIP, formation of short-chain polymers is no longer observed and monomer formation is the dominant product.