On the crystallization behavior of syndiotactic-b-atactic polystyrene stereodiblock copolymers, atactic/syndiotactic polystyrene blends, and aPS/sPS blends modified with sPS-b-aPS

International audienceCrystallization and morphological features of syndiotactic-b-atactic polystyrene stereodiblock copolymers (sPS-b-aPS), atactic/syndiotactic polystyrene blends (aPS/sPS), and aPS/sPS blends modified with sPS-b-aPS, with different compositions in aPS and sPS, have been investigated using differential scanning calorimetry (DSC), polarized light optical microscopy (POM) and wide angle X-ray diffraction (WAXRD) techniques. For comparative purposes, the properties of parent pristine sPS samples were also studied. WAXRD analyses revealed for all the samples, independently from their composition (aPS/sPS ratio) and structure (blends, block copolymers, blends modified with block copolymers), the same polymorphic β form of sPS. The molecular weight of aPS and sPS showed opposite effects on the crystallization of 50:50 aPS/sPS blends: the lower the molecular weight of aPS, the slower the crystallization while the lower the molecular weight of sPS, the faster the crystallization. DSC studies performed under both isothermal and non-isothermal conditions, independently confirmed by POM studies, led to a clear trend for the crystallization rate at a given sPS/aPS ratio (ca. 50:50 and 20:80): sPS homopolymers > sPS-b-aPS block copolymers ∼sPS/aPS blends modified with sPS-b-aPS copolymers > sPS/aPS blends. Interestingly, sPS-b-aPS block copolymers not only crystallized faster than blends, but also affected positively the crystallization behavior of blends. At 50:50 sPS/aPS ratio, blends (Blend-2), block copolymers (Cop-1) and blends modified with block copolymers (Blend-2-mod) crystallized via spherulitic crystalline growth controlled by an interfacial process. In all cases, an instantaneous nucleation was observed. The density of nuclei in block copolymers (160,000−190,000 nuclei mm−3) was always higher than that in blends and modified blends (30,000−60,000 nuclei mm−3), even for quite different sPS/aPS ratio. At 20:80 sPS/aPS ratio, the block copolymers (Cop-2) preserved the same crystallization mechanism than at 45:55 ratio (Cop-1). On the other hand, the 20:80 sPS/aPS blend (Blend-4) and blend modified with block copolymers (Blend-4-mod) showed a spinodal decomposition

Ring-opening metathesis polymerization of cyclooctene derivatives with chain transfer agents derived from glycerol carbonate

International audienceThe synthesis of a variety of mono- and di-(glycerol carbonate) telechelic polyolefins has been achieved upon ruthenium-catalyzed ring-opening metathesis polymerization (ROMP) of cyclooctene (COE) derivatives in the presence of a vinyl or acryloyl derivative of glycerol carbonate (GC) acting as a chain-transfer agent (CTA). Reaction monitoring based on SEC and 1H NMR analyses suggested that the ROMP proceeds through the formation of first the α-GC,ω-vinyl-poly(cyclooctene) (PCOE) intermediate, which eventually evolves over time into the α,ω-di(GC)-PCOE. The nature of the solvent was shown to have a significant impact on both the reaction rates and the eventual selectivity for the mono-/di-telechelic PCOE. ROMP of 3-alkyl (methyl, ethyl, n-hexyl)-substituted COEs (3-R-COEs) afforded only the α-GC,ω-vinyl-poly(3-R-COE)s, as a result of the steric hindrance around the active intermediate, while a 5-ethyl substituted COE (5-Et-COE) enabled access to the corresponding α,ω-di(GC)-poly(5-Et-COE). The ROMP of 5,6-epoxy-, 5-hydroxy- and 5-oxo-functionalized COEs in the presence of acryloyl-GC as the CTA has also been achieved, affording from the first two monomers polymers with GC end-groups at both extremities, while a 60 : 40 mixture of mono- and di-GC terminated P(5-O[double bond, length as m-dash]COE) was observed in the latter case

α,ω-Di(glycerol carbonate) telechelic polyesters and polyolefins as precursors to polyhydroxyurethanes: an isocyanate-free approach

International audienceα,ω-Di(glycerol carbonate) telechelic poly(propylene glycol) (PPG), poly(ethylene glycol) (PEG), poly(ester ether) (PEE), and poly(butadiene) (PBD) have been synthesized through chemical modification of the corresponding α,ω-dihydroxy telechelic polymers (PPG-OH2, PEG-OH2, PEE-OH2 and PBD-OH2, respectively). Tosylation of the polymer diols with 4-tosylmethyl-1,3-dioxolan-2-one (GC-OTs) afforded, in high yields, the desired PPG, PEG, PEE and PBD end-capped at both termini with a five-membered ring cyclic glycerol carbonate (4-hydroxymethyl-1,3-dioxolan-2-one, GC). The GC-functionalization of the polymers at both chain-ends has been confirmed by NMR (1H, 13C, 1D and 2D) and FTIR spectroscopies. Using PPG-GC2 to demonstrate the concept, the corresponding polyhydroxyurethanes (PHUs/non-isocyanate polyurethanes (NIPUs)) have been subsequently prepared following a non-isocyanate method upon ring-opening catalyst-free polyaddition of the PPG-GC2 with JEFFAMINEs (Mn = 230-2000 g mol−1). The effect of various additives introduced during the polyaddition reaction has been studied at different temperatures. In particular, addition of LiBr (5 mol%) to the reaction medium was found to slightly promote the cyclocarbonate/amine reaction. The polymerization process was supported by FTIR and SEC analyses

Living Ring-Opening Homo- and Copolymerization of epsilon-Caprolactone and L- and D,L-Lactides by Dimethyl(salicylaldiminato)aluminum Compounds

ABSTRACT: The dimethylaluminum compounds {3-tBu-2-(O)C6H3CH=N-R}AlMe2 [R=C6H5 (1); 2,6- iPr2C6H3 (2); C6F5 (3)] were used as initiators in the ring-opening polymerization (ROP) of ε-capro- lactone, L-lactide, and D,L-lactide. Compound 3, in combination with 1 equiv of methanol, exhibited a living behavior in the ROP of the cyclic esters. Such a feature allowed the preparation of poly(D,L-lactide-block- ε-caprolactone) and poly(L-lactide-block-ε-caprolactone) copolymers. Random copolymers of ε-caprolactone and L-lactide and of ε-caprolactone and D,L-lactide were also synthesized by compound 3. NMR and DSC characterization confirmed a highly random structure of these copolymers, even in the absence of transesterification reactions. All the materials, characterized by GPC, showed high molecular weight and narrow molecular weight distributions

Chain Growth Polymerization of Isoprene and Stereoselective Isoprene-Styrene Copolymerization Promoted by an ansa-Bis(indenyl)allyl-Yttrium Complex

International audienceThe ability of rac-[{Me2C(Ind)2}Y(1,3-(SiMe3)2C3H3)] (Ind = 9-indenyl) (1) to catalyze isoprene polymerization, either as a single-site component or in combination with an alkyl-metal as a chain transfer agent (CTA) via coordinative chain transfer polymerization (CCTP), has been investigated. Complex 1 alone catalyzes the highly 1,4-trans-stereoselective polymerization of isoprene with moderate activity. The addition of ZnEt2 provides an efficient catalytic system for the reversible CCTP of isoprene with retention of the 1,4-trans stereoselectivity. By contrast, in the presence of Mg(nBu)2, with increasing amounts of CTA, the 1,4-trans specificity gradually decreases at the advantage of the 3,4-polymer. The copolymerization between isoprene and styrene has been also studied, resulting in the formation of materials with unprecedented architecture. Simultaneous copolymerization of isoprene and styrene with 1 provides copolymers with a wide range of compositions (χS = 0.30-0.98) and a stereospecific blocky distribution of the monomers in the copolymer chain. The reactivity ratios (average values: r1,Ip = 2 and r2,St = 18) determined by NMR spectroscopy confirmed the propensity to form multiblock materials. Microstructural 13C NMR analysis showed the presence of stereoregular 1,4-trans-polyisoprene and isotactic polystyrene segments. The copolymerization via sequential monomer addition allowed the synthesis of well-defined 1,4-trans-polyisoprene-block-isotactic polystyrene, which contains two crystalline blocks. The authenticity of these new di- or multiblock copolymer materials was assessed by combined NMR, GPC, and DSC characterizations

Isotactic-Specific Polymerization of Propene by a C-s-Symmetric Zirconium(IV) Complex Bearing a Dianionic Tridentate [-NNN-] Amidomethylpyrrolidepyridine Ligand

ABSTRACT: The synthesis and characterization of a new tridentate amidomethylpyrrolidepyridine ligand (LigH2) and of the corresponding LigZr(NMe2)2 complex (1) are described. Characterization of 1 by single-crystal X-ray diffraction analysis showed a slightly distorted square-pyramidal geometry. Variable-tempera- ture NMR analysis suggested that 1 adopts a Cs-symmetric structure in solution. Complex 1 in combination with AliBu2H and methylalumoxane afforded a highly active single-site catalyst for the polymerization of ethylene and propene, producing ultrahigh molecular weight linear polyethylene and isotactic polypropylene via an “enantiomorphic sites” mechanism of steric control