It is proverbial that the rheological properties of low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE) are disparate because of their different molecular microstructures due to the unlike methods of polymerization. In this work, multiple characterizations including Size-Exclusion Chromatography (SEC) coupled with low-angle light scattering and viscosmeter, 13C Nuclear Magnetic Resonance, Crystallization Elution Fractionation (CEF) and Differential Scanning Calorimetry (DSC) were conducted to get detailed information of branching on different LDPEs and LLDPEs. It was found that, in our case, LDPEs possessed higher molecular weight and greater amounts of long-chain branching (LCB) in comparison with LLDPEs. The Chemical Composition Distribution (CCD) of each LLDPE sample depends strongly on the catalyst used. LLDPE produced by Z-N catalyst exhibited broad short-chain branching (SCB) distribution (less uniform composition distribution), whereas LLDPE obtained by metallocene catalyst showed more uniform microstructure. Unlikely, the two LDPEs displayed wider but unimodal distribution corresponding to the free-radical polymerization mechanism. Both linear and nonlinear rheological results were strongly influenced by the presence of LCB. LDPEs in this work exhibited higher zero shear-viscosity, higher values of storage modulus, longer relaxation times, and higher activation energy comparing to LLDPEs. The presence of LCB leads to more pronounced strain hardening behavior in the elongational flow which is neglected in LLDPE. The molecular structures of linear and branched PEs were consistent with the rheological properties.

Azido β-cyclodextrins were attached to propiolate-functionalized polydimethylsiloxanes by metal-free click chemistry. The obtained telechelic copolymers spontaneously produced elastomeric gums. Demixing and supramolecular associations are the driving forces for the construction of these strongly associated (but reversible) physical networks.

A new and original method to recycle the PET into low molar masses di-alkyl functionalized oligomers is proposed. Ti(OnBu)4 and Ti(OnPr)4 used through alkoxide ligand exchange reactions, with a vertical twin-screw micro-extruder laboratory process, allow in a very short range of time around 10 min at high temperature to shorten the PET chains length. In homogeneous-like considered conditions fast decreases of molecular chains length and melting temperatures were observed. The structures of these oligomers were identified by 1H NMR, MALDI-ToF and SEC methods, and then correlated with physical properties determined by DSC and TGA analyses. Very useful tools are proposed to control the chemical reaction in order to scale up this process to reactive extrusion at relatively low temperatures.

A one-step process is reported to directly synthesize blends of poly(trimethylene carbonate) (PTMC) with a modified granular starch. Trimethylene Carbonate (TMC) ring-opening polymerization is performed in the presence of native starch particles in bulk conditions at 150 °C and the efficiency of metal-free organic catalysts (TBD and phosphazene superbases P1-t-Oct, P2-t-bu, and P4-t-bu) are investigated to replace the organo-metallic stannous octanoate initiator. TMC monomer is successively converted into PTMC and the robustness of organic catalysts is highlighted with significant activities at very low concentrations (<100 ppm), where stannous octanoate is inefficient. Reactivity of starch toward TMC ROP is deeply investigated by NMR techniques and a starch-graft-PTMC is indirectly evidenced. Starch substitution degree reaches 0.9% indicating that PTMC grafting only occurs at the surface of swollen granular starch. PTMC graft length from the starch surface remained low in the range 2–12 and model ROP reactions highlight the role of TMC hydrolysis on PTMC graft length. Despite low PTMC grafts, a fine dispersion of intact starch particles into the PTMC matrix is evidenced. Consequently, metal-free organic catalysts at low concentrations are promising candidates for synthesizing blends of PTMC with high loadings of surface-modified starch (32% by weight) in 2 min within a one-step process. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 493–503

The batch copolymerization of n-butyl acrylate (50 mol %) and acrylic acid (50 mol %)-two monomers with close reactivity but with very different water solubility-was performed under RAFT (reversible additionfragmentation chain transfer) control, in heterogeneous conditions in water or water/ethanol mixtures. The polymerizations were conducted in the presence of poly(acrylic acid) end-capped with a trithiocarbonate reactive group, serving as a control agent, a precursor for the in situ synthesis of amphiphilic block copolymers and a stabilizer for the formed particles. Good control over the polymerization and stable colloidal suspensions were achieved under such conditions. The kinetic study demonstrated that the polymerization rates of each monomer varied upon a change of the water/ethanol volumetric ratios and of the overall comonomer concentrations. The compositional microstructure of the copolymers was characterized by NMR analysis and by potentiometric titration. This work demonstrates that the distribution of the comonomer units in a copolymer formed under heterogeneous conditions can be controlled by the solubility of the monomers in the medium, hence leading to various types of compositional gradient structures.

Starch-based tunable amphiphilic copolymers are easily obtained by grafting polycaprolactone chains via 1,3 dipolar Copper-Catalyzed Azide-Alkyne Cycloaddition (click chemistry CuAAC), starting from propargylated starch and azido oligocaprolactones with different chain lengths as the precursors. The copolymers are characterized by (1)H and (13)C NMR, from which a degree of substitution of starch can tentatively be deduced. Besides these bulk characterizations, the surface of the functionalized starch is also characterized by XPS which confirms the triazole formation, particularly through the deconvolution of the N 1s peak, and by ToF-SIMS which, not only confirms the surface modification, but also highlights the disappearance of the Cu(+) cations. The solubility and swelling behaviours of these copolymers have been investigated, which clearly show the dependence both on the solvent and the PCL chain length. These investigations highlight the swelling dependence on the δd component of the Hansen solubility parameter of solvents. Finally, at low concentration, they present the capacity to organize themselves in aggregates in aqueous solutions, as seen from TEM and DLS investigations.

Enhanced spin capturing polymerization (ESCP)—a recent and versatile technique in the field of controlled radical polymerization—achieves control over molecular weights and the synthesis of complex copolymer structures for a wide range of monomers. In the present work, the use of ESCP was extended to the radical polymerization of ethylene under mild conditions (low temperature and medium ethylene pressure) using a nitrone as spin trapping agent. It was demonstrated that the evolution of polyethylene (PE) molecular weight can be accurately described by classical ESCP kinetic equations. A PE bearing a midchain alkoxyamine function was thus obtained with high selectivity (90%). A more complex structure was produced from the radical polymerization of ethylene in the presence of a midchain alkoxyamine-functionalized polystyrene (PS) synthesized by ESCP in the form of ABA triblock copolymer (where A is polystyrene and B polyethylene).

Hydridosilazane compounds containing Si–N and Si–H bonds can be used as precursors of SiOx materials. The hydrolysis-condensation reactions of tetramethyldisilazane, as a polyhydridosilazane model compound, were investigated by 1H and 29Si liquid NMR spectroscopy. These reactions were carried out at room temperature for up to 120 min in presence of water. The identified products are short linear siloxane species (hydride terminated polydimethylsiloxanes MHDxMH) and cyclosiloxanes. Silicon hydride persistence in the reactional mixture suggested that silazane group is more sensitive to hydrolysis reaction than silicon hydride group. Moreover, additional experiments evidenced that the low steric hindrance of the silicon hydride influences the silazane hydrolysis kinetic. Hence the presence of ammonia released during silazane hydrolysis reaction was demonstrated to be a catalyst of the silicon hydride hydrolysis reaction.

A new ethylene vinyl acetate (EVA)-based hybrid material containing silicon and phosphorus has been developed in order to improve fire retardancy of EVA. The preparation of the hybrid material was based on exchange reaction between acetoxy groups from EVA and ethoxysilane groups from diethyl-phosphatoethyltriethoxysilane (SiP). The exchange reaction was characterized by NMR spectroscopy, showing the presence of silicon in the crosslinking bridges bonded to unreacted phosphonate groups. The formation of the crosslinked network was characterized by rheology and TGA-GC-MS. The influence of silicon and phosphorus on the thermal behaviour and the flame retardancy of EVA was investigated by thermogravimetric analysis (TGA) and cone calorimeter. The results showed a synergistic effect between silicon and phosphorus on the fire properties for low charge contents (1.3 wt% of silicon and 1.4 wt% of phosphorus). The peak heat release rate (PHRR) measured in a cone calorimeter decreased by 35% for EVA hybrid materials compared to pure EVA due to the formation of a compact charred layer. The charred residue was analysed by NMR spectroscopy and showed the presence of silicophosphorated complexes. (C) 2012 Elsevier Ltd. All rights reserved.

The reaction in bulk at high temperature of α,ω-aminopropyl oligodimethylsiloxane and thermoplastic polyurethane (TPU) allowed observing interesting behavior. Mixing at 200 °C first involved dissociation of urethanes and splitting of polyurethane chains followed by reaction of the released isocyanates with amino end-groups of the oligosiloxane. At this stage, a copolymer was formed which morphology consisted of a very fine dispersion of the polysiloxane domains at the nanoscale (20 nm) with a narrow size dispersity. The polymer blend was perfectly transparent. Increasing the reaction time resulted in a significant coarsening of the morphology and a consequent loss of transparency. The reason for such a morphology evolution has been elucidated. The progressive formation of alkyl–alkyl urea linkages at the expense of aryl–alkyl bonds obtained earlier in the process caused an increase in the average number of successive polydimethylsiloxane (PDMS) blocks that organized in larger domains. The average number of consecutive polysiloxane segments was found to evolve from ∼1.5 in the first 10–15 min to a value of 3–5 at the end of the reactive process.

In this article, the hydrosilylation reaction of carbonyl groups of acetate derivatives and SiH groups of hydride-terminated polydimethylsiloxane at high temperature (100-130 degrees C) are described. Triruthenium dodecacarbonyl, Ru-3(CO)(12), was used as effective catalyst for hydrosilylation reaction. The hydrosilylation reactions with octyl acetate and 4-heptyl acetate were investigated by multinuclear NMR spectroscopy (H-1, C-13, and Si-29). This work provides evidence of the addition reaction of SiH groups onto carbonyl groups. The influence of the nature of the acetate structure on the reaction kinetics was shown and the slight contribution of side reactions at high temperature highlighted. Hydrosilylation reaction was extent to the crosslinking of ethylene-vinyl acetate (EVA) copolymer in the same range of temperature. The formation of EVA chemical network was demonstrated by HR-MAS NMR spectroscopy and by measuring the gel fraction of EVA chains in hot toluene. From Flory theory, the crosslinking density of elastic strand was calculated to be 80 mol m (3) in agreement with the measurements from swelling ratio (VA/SiH molar ratio: 11.8). (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 2899-2907, 2011

An α-[Cu(II)-porphyrin]-polyethylene was synthesized for the first time using copper catalyzed 1,3-dipolar azide-alkyne Huisgen cycloaddition yielding highly colored moiety-substituted polyethylene.

Novel thermoresponsive biohybrid guar-based grafted copolymers were prepared in aqueous medium by copper catalyzed 1,3-dipolar Huisgen cycloaddition between an alpha-butoxy-omega-azido-PEO-co-PPO derivative, characterized by LCST behavior, and guar gum bearing alkyne functionalities randomly distributed along the chain. The chemical pathway gives well-defined guar-g-(PEO-co-PPO) copolymers with tunable chemical compositions. The resulting grafted copolymers were shown to exhibit a reversible thermo-induced association leading to elastic physical network-like behaviors. It has been shown that the rheological properties are intimately related to the molecular weight and to the degree of substitution of guar. The temperature of association of the grafted copolymer is controlled by the cloud point of the grafted polyoxyalkylene and the salt concentration variation appeared as a very convenient manner to tune the thermoresponsive character without changing the chemical nature of the side-chains. Finally, in relation with macroscopic properties, the thermoassociative effect was monitored by NMR analysis.

Metallocene borohydride complexes {(Me2Si(Cl3H8)(2))Nd(mu-BH4)[(mu-BH4)Li(THF)]}(2) (1) and (Me2Si(2,7-tBu(2)Cl(3)H(6))(2))Nd(BH4)(mu-BH4)Li(ether)(3) (2) were prepared by reaction of the dilithium salts of silylene-bridged bis(fluorenyl) ligands with the borohydride precursor Nd(BH4)(3)(THF)(3). The solid state structures of dimeric 1 and monomeric 2 ate complexes were established by X-ray diffraction studies. We showed that these complexes used in combination with (nBu)(nOct)Mg are highly efficient for cyclocopolymerization of ethylene with butadiene leading to a new class of elastomers. Catalyst 1/(nBu)(nOct)Mg provided elastomers with a polyethylene skeleton incorporating unsaturated groups (trans double bond and pendant vinyl units) and 1,2-cyclohexane rings. These rings are formed via an intramolecular cyclization which occurs with a high trans selectivity. The investigation of catalyst 2/(nBu)(nOct)Mg has revealed that the tertio-butyl substitution in positions 2 and 7 of fluorenyl ligands influenced the microstructure of copolymers since in addition to 1,2-cyclohexane rings, 1,4-cyclohexane rings were formed. This original microstructure was characterized using 2D NMR H-1-H-1 and H-1-C-13 with direct and long-range correlations. Mechanisms of stereoselective formation of trans-1,2-cyclohexane and trans-1,4-cyclohexane rings were fully investigated.

A means to an end: Polyethylene chains obtained by catalyzed chain growth on magnesium and exhibiting molar masses up to 5000 g mol−1 have been end-functionalized in high yield with iodide, azide, and amine reactive end groups (see scheme). The functionalized polyethylenes can be used to generate a range of reactive polyolefins; for example, the azide-functionalized chain can undergo "click" reactions to afford macromonomers. Detailed facts of importance to specialist readers are published as "Supporting Information". Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.