This study reports a reactive extrusion process leading to very high levels of anhydride grafting (2.5-3 wt %) along polypropylene backbone without recovering grafted PP waxes at the die exit. Such high graftings are attainable without excessive degradation of the PP chain by using a brominated reagent. Simultaneously, this brominated reagent allows the tuning of the grafted PP crystallinity via epimerization of the PP backbone. Indeed, the synthesis of a mainly isotactic/atactic stereoblock polymer containing high levels of grafted succinic anhydride moieties is demonstrated by NMR and melting enthalpies recorded by DSC are definitely observed depressed and broadened. Grafting levels of around 3 wt % have been achieved and ascertained by both chemical titration and NMR spectroscopy. In addition, FTIR spectroscopy reveals an unusual observation: for the first time, only one single pair of symmetric and asymmetric carbonyl stretching bands are observed on those grafted PP, while, in other processes of anhydride grafting, those symmetric and asymmetric bands were both split in at least two bands. This suggests, for the here reported process, the absence of interacting grafted anhydride rings, i.e., absence of closely grafted anhydride moieties and absence of poly(maleic anhydride). All those observations support that this ''bromine route'' brings a really new grafting process for PP.
Amorphous and low crystallinity polypropylenes were produced by reactive processing of commercial isotactic polypropylenes in the presence of a peroxide (2,5-dimethyl-2,5-di(tert-butylperoxy)hexane) and N-bromosuccinimide. Characterization of the modified polypropylene microstructures using 13 C NMR spectroscopy revealed that crystallinity loss is correlated with the epimerization of numerous methynes randomly along the polymer backbone, leading to decreasing isotacticities ([mmmm]) and average isotactic block lengths. Moreover, degradation usually induced by peroxide was shown to be comparatively limited in additional presence of N-bromosuccinimide. This fast and easy process therefore allows the production of polypropylene plastomers and elastomers with controlled and homogeneous crystallinities and isotacticities, and relatively low molecular weight distributions. V V C 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: [4505][4506][4507][4508][4509][4510][4511][4512][4513][4514][4515][4516][4517][4518] 2009
Polymeric materials based on epsilon-caprolactone (CL), 1,5-dioxepan-2-one (DXO), and trimethylene carbonate (TMC) were prepared and evaluated as possible candidates for polymer-on-multielectrode (PoM) applications. CL was copolymerized with either DXO or TMC in the presence of the diol initiator 1,4-benzenedimethanol (BDM). The ring-opening polymerization experiments, carried out in bulk and using tin(II) catalysis, yielded the desired low molecular weight random copolymer diols, as evidenced by NMR, IR, MALDI-ToF MS, and DSC techniques. Upon reaction with acryloyl chloride, the corresponding diacrylate end-capped copolymers were obtained. The latter were characterized by NMR and IR spectroscopy, and their photocross-linking (in the presence of a UV initiator) was followed by ATR-FTIR spectroscopy. Transparent and soft thin films of the copoly(ether-ester) and copoly(ester-carbonate) diacrylates were prepared and cured under UV irradiation. The resulting polymeric films showed good biocompatibility properties as far as in vitro neural stem cells proliferation and differentiation to neurons and astrocytes are concerned. Noteworthy are the beneficial effects obtained upon preconditioning the copolymers by means of the cell-culture medium and the excellent properties shown particularly by the CL-TMC copolymer. Moreover, preliminary results show that microchannel formation by photocuring is possible with the synthesized polymers.
This paper reports the flexible synthesis of 2,4,6,8,10-pentamethylundecane (PMU) as well as a chromatographic method for the separation of its diastereoisomers. This strategy offers a unique opportunity to accede to three model compounds of polypropylene (PP) of different tacticities (i.e., isotactic, syndiotactic, and atactic PP).Isotactic polypropylene modifications (i.e., grafting of polar monomers, racemization, etc.) are very challenging industrial processes and the underlying chemical reactions are barely established. 2 The very high molecular weights of the polymers and the low graft contents make the identification of reaction products and intermediates very delicate. As a consequence, small oligomers are commonly used as model compounds to shed light on the functionalization mechanisms through the analytical tools of the organic chemist. This paper describes a flexible synthesis of 2,4,6,8,10-pentamethylundecane (PMU) and a chromatographic method for the separation of its diastereoisomers as a route to polypropylene model compounds with controlled tacticities. PMU synthesis was initially described about 40 years ago and it has not been revisited since that time. 3 Reaction of 3,5-dimethylhexanal with the Grignard reagent from 1-bromo-2,4-dimethylpentane, followed by oxidation of the alcohol intermediate, led to 2,4,8,10-tetramethylundecan-6-one (Scheme 1). The central missing methyl group was then introduced by addition of methylmagnesium bromide, giving 2,4,6,8,10-pentamethylundecan-6-ol. Alcohol dehydration by distillation over iodine afforded a mixture of isomeric olefins that was hydrogenated in the presence of Raney nickel to yield PMU as a mixture of stereoisomers, separable by fractional distillation with low purity.In our hands, this PMU synthesis was hardly reproducible on a multigram scale, mainly because a competitive side reaction that occurred during the first organometallic coupling, auto-condensation of the alkyl bromide. We tried to replace the aldehyde partner by the corresponding Weinreb amide with a view to directly forming the ketone key intermediate, but without success. Therefore, we investigated another route to PMU based on Wittig-type coupling reactions and using a flexible intermediate, namely 2,4,8,10-tetramethyl-6-methyleneundecane, to furnish either a mixture of PMU stereoisomers, or the individual stereoisomers by chromatographic separation of more polar precursors.Scheme 2 depicts the overall synthetic route to 2,4,6,8,10-pentamethylundecane (PMU, 7) as a mixture of stereoisomers. The first two steps were performed according to known procedures. 4 The unsaturated ester 1 was synthesized from 4-methylpentan-2-one and triethyl phosphonoacetate, through a Horner-Wadsworth-Emmons (HWE) reaction, as a mixture of regio-and stereoisomers 1¢, all of them led to ethyl 3,5-dimethylhexanoate (2) upon catalytic hydrogenation; addition of methyl dimethylphosphonate in the presence of butyllithium led to the bketophosphonate 3. The enone 4 was synthesized through a second HWE reaction b...
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