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- Linear and crosslinked copolymers of p-tert-butylcalix[4]arene derivatives and styrene: new synthetic approaches to polymer-bound calix[4]arenesPublication . Mendes, Ana R.; Gregório, Carla C.; Barata, Patrícia; Costa, Alexandra I.; Prata, José V.As an extension of our previous studies concerning the free radical copolymerisation of 25,26,27-tripropoxy-28-(4-vinyl-benzyloxy)-p-tert-butylcalix[4]arene (3) with styrylic monomers, we report herein on the synthesis and characterisation of new terpolymers derived from 3, styrene and divinylbenzene, having nominal crosslinking degrees ranging from 4% to 40% wt. The terpolymers exhibited good thermal stabilities (DSC) and were prepared in good yields. Depending on the reaction conditions (dilution degree and aqueous phase to porogen ratio), materials with identical nominal crosslinking but otherwise differentiated morphologies and swelling abilities were obtained. In a related study, the radical polymerisation of styrene was carried out in the presence of a novel calix[4]arene derivative 4, bearing two distal benzyl–vinyl groups in the lower rim. It is shown that, albeit the presence of two phenolic groups within the calixarene moiety which could have functioned as inhibitors of the free radical polymerisation, the macrocycle was able to take part in the copolymerisation reaction, yielding new soluble and crosslinked polymers. In both cases, no pendant vinyl groups were found in the polymeric materials. The probable mechanisms underlying their formation are discussed.
- The synthesis of novel polymer-bound calix[4]arenesPublication . Barata, Patrícia; Costa, Alexandra I.; Granja, Paulo; Prata, José V.Two simple and efficient procedures for the synthesis of linear and cross-linked polymers containing hydrophobic and hydrophilic lower rim derivatives of p-tert-butylcalix[4]arenes are described. The target polymers were prepared either through the direct attachment of 25,26,27,28-tetrahydroxy-p-tert-butylcalix[4]arene (1), or its tripropoxy (2) and tetracarboxymethoxy (4) derivatives, to light cross-linked Merrifield's resins (1–2% DVB) or via radical addition copolymerisation of 25,26,27-tripropoxy-28-(4-vinyl-benzyloxy)-p-tert-butylcalix[4]arene (11) with styrene and a cross-linking agent.
- Comparative study of the copolymerization kinetics of mono and divinylbenzyl p-tert-butylcalix[4]arene derivatives and styrenePublication . Costa, Alexandra I.; Barata, Patrícia; Prata, José V.A study of the copolymerization kinetics of 25,27-bis(4-vinyl-benzyloxy)-26,28-dihydroxy-p-tert-butylcalix[4]arene (1) and 25,26,27-tripropoxy-28-(4-vinyl-benzyloxy)-p-tert-butylcalix[4]arene (2) with styrene (St) was undertaken. The radical copolymerizations were carried outin THF in thepresence ofbenzoyl peroxideat 758C for a certain period. Six molar feed ratios, ranging from 1:1 to 1:20 (1 or 2 to St), were used to calculate the reactivity parameters. The copolymer composition was determined by FT-IR spectroscopy using a Beer’s law plot obtained from the corresponding homopolymers. The reactivity ratio calculations were performed with the linearization methods of Fineman-Ross (F-R) and Kelen-Tu ¨do ¨s (K-T), assuming the validity of the so-called terminal model. In the copolymerization of the monoene 2, similar reactivity ratios were found for the comonomers (ca. 1.2; K-T). On the other hand, the reactivity ratios calculated for the copolymerization of 1 with St yielded rSt 5 0.67 and rcalix 5 3.0 (K-T method). The higher reactivity of monomer 1 as compared to styrene is discussed in connection with our previously postulated cyclocopolymerization route.
- Studies towards the living polymerisation of phenylethynyl-calix[4]arene compounds with rhbased ternary catalytic systemsPublication . Costa, Alexandra I.; Prata, José V.The living polymerisation of mono and difunctional phenylethynylcalix[4]arene compounds 1 and 2 by Rh(I) ternary catalytic systems (TCS) was examined. Two TCS were tentatively prepared in situ, adapting known methodologies: (1) Rh(CuCPh)(norbornadiene)(PPh3) and (2) Rh(C(Ph)CvCPh2)(norbornadiene)(PPh3). Using the first TCS, the conjugated polymers poly 1 and poly 2 could be obtained in very good yields (77–86%), in short reaction times and freed from low-molecular-weight products, only when NEt3 was used as a co-catalyst. With the second TCS, excellent results were obtained. Indeed,thiscatalyticsystemprovedtobequiteefficientin thepolymerisation ofcalix[4]arenes 1and 2, affording the correspondent poly 1 and poly 2 essentially in almost quantitative yields (by GPC analysis), under appropriate conditions. The living nature of the polymerisation has been proved. For instance, in the case of calix[4]arene 1, the Mn of the polymer obtained at high monomer conversion increased proportionally with the [1]:[Rh] molar ratio in the feed, keeping [1]o constant, thus showing that irreversible chain transfer or termination reactions did not occur to a major extent. Under the most favourable conditions {[1]:[Rh] 5 50 and [2]:[Rh] 5 50}, the polydispersities of poly 1 and poly 2 were kept in a narrow range (1.16–1.30).
- Novel fluorescent (p-Phenylene ethynylene)-Calix[4]arene- based polymer: design, synthesis, and propertiesPublication . Costa, Alexandra I.; Ferreira, Luís F. V.; Prata, José V.A novel fluorescent (p-phenylene ethynylene)-calix[4]arene-based polymer (CALIX-PPE) has been successfully synthesized by cross-coupling polymerization of bis-calix[4]arene 1 with 1,4-diethynylbenzene. The polycondensation was carried out in toluene/NEt3 at 35 8C for 24 h, using PdCl2(PPh3)2/CuI as the catalytic system, furnishing CALIX-PPE in excellent isolated yields (higher than 95%, several runs). The yellow polymer is freely soluble in several nonprotic organic solvents. The GPC trace of the isolated polymer showed a monomodal distribution and a number-average molecular weight of 23,300 g mol-1 (Mw/Mn¼ 2.05). No evidence was found in the structural analysis (FTIR and 1H/13C NMR) regarding the formation of alkyne homocoupled segments along the polymer chain. For comparative purposes, the syn- thesis of an analogous poly(p-phenylene ethynylene) containing p-t-butyl-phenoxy- methyl side chains (TBP-PPE) was also undertaken. A great similarity was found between the photophysical properties of CALIX-PPE and TBP-PPE in solution (UV–vis and laser induced luminescence), clearly demonstrating their unique de- pendence on the structure and conformation of the conjugated PPE backbone. The fluorescence spectra of polymers are of nearly identical shape, displaying their maxi- mum emission around 420 nm. The calculated solution photoluminescence quantum yields of CALIX-PPE and TBP-PPE are of similar magnitude (Ø/F(CALIX-PPE) = 0.43; Ø/F(TBP-PPE) = 0.51).
- Radical cyclopolymerization of a divinylbenzyl-p-tert-butylcalix[4]arene derivativePublication . Costa, Alexandra I.; Barata, Patrícia; Prata, José V.The synthesis and characterization of a new homopolymer (poly 1), obtained in the course of the radical polymerization of 25,27-bis-(4-vinyl-benzyloxy)-26,28-dihydroxy-p-tert-butylcalix[4]arene (1), is described. Homopolymerization of 1 in THF, using BPO or thermal initiation, afforded soluble polymers in good isolated yields (60–90%). Gel permeation chromatography (GPC) profiles showed unimodal distributions for all the analyzed polymers, which is indicative that chain branching reactions did not occur to a major extent. Molecular weights (Mn) ranging from 30,000 to 60,000 g mol−1 were reached within a 8 h period, when the reactions were conducted at 0.06–0.5 mol% of BPO or thermally initiated, showing relatively narrow polydispersity indexes (1.5–2.0). The structure of the polymers was deduced upon analysis of their 1H NMR and FT-IR spectra, which, in conjunction with GPC and solubility data led to their formulation as cyclopolymers.
- Synthesis and Rh(I)‐catalyzed polymerization of 1,3‐diphenylyne–calix[4]arene compounds: novel conjugated, calixarene‐based polymersPublication . Costa, Alexandra I.; Prata, José V.The synthesis of two 1,3‐bis(4‐ethynylbenzyloxy)calix[4]arenes, 5,11,17,23‐tetrakis(1,1‐dimethylethyl)‐25,27‐bis(4‐ethynylbenzyloxy)‐26,28‐dihydroxycalix[4]arene (1 ) and 25,27‐bis(4‐ethynylbenzyloxy)‐26,28‐dihydroxycalix[4]arene (2 ), was accomplished through Sonogashira coupling of appropriate calixarene derivatives. Methods for the polymerization of these bifunctional building blocks with Rh(I) as a catalyst, leading ultimately to conjugated polymers having calix[4]arene units incorporated into the main chain, were explored. Calixarenes 1 and 2 were efficiently polymerized with rhodium‐based initiators and afforded the conjugated polymers poly{5,11,17,23‐tetrakis(1,1‐dimethylethyl)‐25,27‐bis(4‐ethynylbenzyloxy)‐26,28‐dihydroxycalix[4]arene} (poly 1 ) and poly{25,27‐bis(4‐ethynylbenzyloxy)‐26,28‐dihydroxycalix[4]arene}. Depending on the conditions, high conversions and good yields were obtained. The effects of adding cocatalysts (NHEt2 and/or PPh3) were studied in connection with the number‐average molecular weight and the molecular weight distribution of the resultant polymer (poly 1 ) and tentatively correlated with the formation of low‐molecular‐weight materials. A catalytic system containing triphenylphosphine as the sole additive ([Rh(nbd)Cl]2; [Rh]/[PPh3] = 0.5) proved to be the best for the polymerization of p ‐tert ‐butylcalixarene compound 1 . Linear polymers having high number‐average molecular weights (up to 1.1 × 105 g mol−1) with low polydispersities were produced under these conditions. For debutylated homologue 2 , its polymerization was best carried out in the absence of any added cocatalyst. A cyclopolymerization route, comprising the intramolecular ring closing of the calix[4]arene pendant ethynyl groups followed by an intermolecular propagation step, is advanced to explain the results.