Tacticity Of Poly Research Articles

Radical polymerization behavior of vinyl phenylsufonylacetate

Vinyl phenylsulfonylacetate (VPSA) was prepared by the reaction of vinyl chloroacetate with sodium benzenesulfinate in acetone in the presence of a phase-transfer catalyst. VPSA showed a high radical homopolymerizability similar to vinyl acetate in spite of the fact that VPSA carries a phenyl group. The polymerization of VPSA with 2,2 ′-azobisisobutyrate (MAIB) was kinetically investigated in acetone. The overall activation energy of the polymerization was 27.6 kcal/mol. The polymerization rate ( R p) at 50 °C was expressed by R p= k[MAIB] 0.67[VPSA] 1.1. Poly(VPSA) showed exothermic (27 °C) and endothermic (57 °C) peaks in its DCS curve, corresponding to crystallization and melting. The tacticity of poly(VPSA) was estimated to be rr=29, mr=49, and mm=22.

Role of molecular weight of atactic poly(vinyl alcohol) (PVA) in the structure and properties of PVA nanofabric prepared by electrospinning

AbstractAtactic poly(vinyl alcohols) (a‐PVAs) having number‐average degrees of polymerization [(Pn)s] of 1700 and 4000 were prepared by the solution polymerization of vinyl acetate, which was followed by the saponification of poly(vinyl acetate) to investigate the effects of molecular weights of a‐PVA on the characteristics of electrospun a‐PVA nanofabrics. A‐PVA nanofabrics were prepared by electrospinning with controlling the process parameters including the electrical field, conductivity, tip‐to‐collector distance, and solution concentration. Through a series of characterization experiments, we identified that the molecular weight of a‐PVA had a marked influence on the structure and properties of nanofabrics produced. That is, the higher the molecular weight of PVA, the superior the physical properties of PVA nanofabric. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1638–1646, 2004

Controlled/Living Radical Polymerization of Methacrylic Monomers in the Presence of Lewis Acids: Influence on Tacticity

AbstractSummary: Atom transfer radical polymerization (ATRP) and reversible addition‐fragmentation transfer (RAFT) polymerization of N‐methyl methacrylamide and methyl methacrylate were investigated in the presence of rare‐earth triflates known to enhance polymer isotacticity. Poly(N‐methyl methacrylamide) with controlled molecular weight, low polydispersity, and enhanced isotacticity was prepared by ATRP and RAFT in the presence of catalytic amounts of yttrium trifluoromethanesulfonate or ytterbium trifluoromethanesulfonate. The tacticity of poly(N‐methyl methacrylamide) depends on the Lewis acid concentration: well‐defined polymers with predominantly either syndiotactic, atactic, or isotactic triads were prepared by adjusting the concentration of the Lewis acid. Simultaneous control of molecular weights, polydispersities, and tacticities in the polymerization of methyl methacrylate was less successful.Free radical propagation in the presence of a Lewis acid (LA) giving rise to chelate control.magnified imageFree radical propagation in the presence of a Lewis acid (LA) giving rise to chelate control.

Effect of tacticity of poly(methyl methacrylate) on the miscibility with poly(vinyl acetate)

The results of the miscibility between the chemically similar polymers poly(methyl methacrylate) (PMMA) and poly(vinyl acetate) (PVAc) published so far show inconsistent statements concerning miscibility. The problems may be due to differences in molecular weights, tacticity, and preparation methods of the polymers. This investigation was carried out by using either chloroform or tetrahydrofuran (THF) as solvent to prepare the blends, because to our knowledge, nobody has reported any tacticity effect of PMMA on the miscibility with PVAc. Therefore, in this article, different tactic PMMAs were used to mix with PVAc and their miscibility was studied calorimetrically. The results showed little effect of solvent and tacticity. PMMA and PVAc were determined to be almost completely immiscible because of the observation of two Tg's. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 35–39, 2004

Catalysts for the living insertion polymerization of alkenes: access to new polyolefin architectures using Ziegler-Natta chemistry.

Coordination-insertion polymerization systems have long been superior to their anionic, cationic, and radical polymerization counterparts with regard to stereochemical control. However, until five years ago, these metal-based insertion methods were inferior to ionic and radical mechanisms in the category of living polymerization, which is simply a polymerization that occurs with rapid initiation and negligible chain termination or transfer. In the last half decade, the living insertion polymerization of unactivated olefins has emerged as a powerful tool for the synthesis of new polymer architectures. Materials available today by this route range from simple homopolymers such as linear and branched polyethylene, to atactic or tactic poly(alpha-olefins), to end-functionalized polymers and block copolymers. This review article summarizes recent developments in this rapidly growing research area at the interface of synthetic and mechanistic organometallic chemistry, polymer chemistry, and materials science. While special emphasis is placed on polymer properties and novel polymeric architectures, most of which were inaccessible just a decade ago, important achievements with respect to ligand and catalyst design are also highlighted.

Miscibility of block copolymers of poly(ε‐caprolactone) and poly(ethylene glycol) with poly(3‐hydroxybutyrate) as well as the compatibilizing effect of these copolymers in blends of poly(ε‐caprolactone) and poly(3‐hydroxybutyrate)

AbstractAtactic poly(3‐hydroxybutyrate) (a‐PHB) and block copolymers of poly(ethylene glycol) (PEG) with poly(ε‐caprolactone) (PCL‐b‐PEG) were synthesized through anionic polymerization and coordination polymerization, respectively. As demonstrated by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) measurements, both chemosynthesized a‐PHB and biosynthesized isotactic PHB (i‐PHB) are miscible with the PEG segment phase of PCL‐b‐PEGs. However, there is no evidence showing miscibility between both PHBs and the PCL segment phase of the copolymer even though PCL has been block‐copolymerized with PEG. Based on these results, PCL‐b‐PEG was added, as a compatibilizer, to both the PCL/a‐PHB blends and the PCL i‐PHB blends. The blend films were obtained through the evaporation of chloroform solutions of mixed components. Excitingly, the improvement in mechanical properties of PCL/PHB blends was achieved as anticipated initially upon the addition of PCL‐b‐PEG. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2600–2608, 2001

Poly(phenyl methacrylate) and poly(1-naphthyl methacrylate) prepared in microemulsions

Phenyl methacrylate and 1-naphthyl methacrylate were polymerized in microemulsions using stearyltrimethylammonium chloride, cetyltrimethylammonium bromide, and a mixture of nonionic Triton surfactants to form latexes that were 20–30 nm in diameter. A temperature of 70 °C was needed to obtain polymers using thermal initiation. The tacticities of poly(phenyl methacrylate) (PPhMA) (55% rr) and poly(1-naphthyl methacrylate) (P-1-NM) (47% rr) were the same as those of the polymers prepared in toluene solutions. The weight average molecular weights were 1 × 106 and 5 × 105 g/mol for PPhMA and P-1-NM prepared in microemulsions with very broad distributions. PPhMA samples from microemulsions and solution had the same Tg = 127 °C. P-1-NM from microemulsions had Tg = 145–147 °C compared with Tg = 142 °C for P-1-NM from solution. The molecular weights and the glass-transition temperatures of both PPhMA and P-1-NM from microemulsions are substantially higher than any previously reported. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 519–524, 2001

Phase Behavior of Ternary Blends of Tactic Poly(methyl methacrylate)s and Poly(vinylidene chloride-co-acrylonitrile)

Previously, isotactic and atactic poly(methyl methacrylate)s (PMMAs) were found to be miscible with poly(vinylidene chloride-co-acrylonitrile) (Saran F) because all the prepared films were transparent and showed composition dependent glass transition temperatures (Tgs). However, the syndiotactic PMMA/Saran F blends were immiscible because most of the cast films were translucent and had two glass transition temperatures. Atactic PMMA is known to be miscible with syndiotactic PMMA according to literature. So atactic PMMA is miscible with both Saran F and syndiotactic PMMA but Saran F and syndiotactic PMMA are immiscible. It will be interesting to study the miscibility of ternary blends of atactic and syndiotactic PMMAs and Saran F. Therefore an investigation based on this is reported in this article. Calorimetry was used as the principal tool to study miscibility. A blend composed of atactic and syndiotactic PMMAs was prepared previously and confirmed to be miscible. An approximate phase diagram of the ternary blends was established based on differential scanning calorimetry data. The results indicated that for all the studied compositions, the thernary blends were determined to be miscible. Most of the blend Tg values were fitted well by the Fox equation. For the syndiotactic PMMA/Saran F (wt ratio=1) blend, adding of at least 12.5 wt% of atactic PMMA was sufficient to cause the immiscible blends to be miscible.

Miscibility studies of binary and ternary mixtures of tactic poly(methyl methacrylates) with poly(vinylidene chloride-co-acrylonitrile)

Isotactic, atactic, and syndiotactic poly(methyl methacrylates) (i, a, and s PMMAs) were mixed with poly(vinylidene chloride-co-acrylonitrile) (Saran F) separately in tetrahydrofuran to make three polymer blend systems. Differential scanning calorimetry (DSC) was used mainly to study the miscibility of these blends. iPMMA and aPMMA were found to be miscible with Saran F based on the transparency and a single glass transition temperature (T g ) of the films. However, sPMMA was immiscible with Saran F because of the observation of two T g s and opacity in most compositions of the blend. aPMMA is known to be miscible with sPMMA. Therefore aPMMA is both miscible with Saran F and sPMMA but Saran F and sPMMA are immiscible. Preliminary results of the effect of adding of aPMMA to immiscible sPMMA and Saran F mixtures were also reported. First, binary mixtures of atactic and syndiotactic PMMAs were also prepared and confirmed to be miscible. Elevation of T g of the aPMMA/ sPMMA blend above weight average was observed probably due to stereocomplexation occurred between aPMMA and sPMMA. Then ternary blends of atactic and syndiotactic PMMAs and Saran F in the weight ratios of about 3/1/4, 2/2/4, and 1/3/4 were also measured calorimetrically. A single T g was observed for these three compositions different from two T g s detected in the sPMMA/Saran F (50.0/50.0, i.e., 4/4) blend. Obviously, the composition of Saran was fixed in the ternary blends. When the other half of the blends was changing from pure sPMMA to sPMMA and aPMMA mixture, the blends became miscible because of the addition of aPMMA.

Polymerization of methyl methacrylate using a metallocene catalyst system

Methyl methacrylate was polymerized with Cp2YCl(THF) or IVB group metallocene compounds (i.e., Cp2ZrCl2 and Cp2HfCl2, etc.), in the presence of a Lewis acid like Zn(C2H5)2. The Lewis acid was complexed with methyl methacrylate, which avoided the metallocene compounds being poisoned with a functional group. A living polymerization was promoted through the use of metallocene/MAO/Zn(C2H5)2, which gave tactic poly(methyl methacrylate) with a high molecular weight. The polymer yield increases with polymerization time, which indicates that the propagation rate is zero in order in the concentration of the monomer. The polymer yield increases also with the concentration of Cp2YCl(THF), which indicates the yttrocene to be the real catalyst. When the polymerization temperature exceeds room temperature, the poly(methyl methacrylate) cannot be synthesized by the Cp2YCl(THF) catalyst. When the reaction temperature reachs −60 °C, the poly(methyl methacrylate) is high syndiotatic and molecular weight by the Cp2YCl(THF)/MAO catalyst system. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1184–1194, 2000

Effect of tacticity of poly(methyl methacrylate) on the miscibility with poly(styrene-co-acrylonitrile)

Isotactic, atactic, and syndiotactic poly(methyl methacrylates) (PMMAs) (designated as iPMMA, aPMMA, and sPMMA) with approximately the same molecular weight were mixed separately with poly(styrene-co-acrylonitrile) (abbreviated as PSAN) containing 25 wt % of acrylonitrile in tetrahydrofuran to make three polymer blend systems. Differential scanning calorimetry (DSC) was used to study the miscibility of these blends. The results showed that the tacticity of PMMA has a definite impact on its miscibility with PSAN. The aPMMA/PSAN and sPMMA/PSAN blends were found to be miscible because all the prepared films were transparent and showed composition dependent glass transition temperatures (Tgs). The glass transition temperatures of the two miscible blends were fitted well by the Fox equation, and no broadening of the glass transition regions was observed. The iPMMA/PSAN blends were found to be immiscible, because most of the cast films were translucent and had two glass transition temperatures. Through the use of a simple binary interaction model, the following comments can be drawn. The isotactic MMA segments seemed to interact differently with styrene and with acrylonitrile segments from atactic or syndiotactic MMA segments. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2894–2899, 1999

Phase Behavior of Ternary Blends of Tactic Poly(methyl methacrylate)s and Poly(styrene-co-acrylonitrile)

Previously, atactic and syndiotactic poly(methyl methacrylate)s (PMMAS) were found to be miscible with poly(styrene-co-acrylonitrile) (PSAN) because all the prepared films were transparent and showed composition dependent glass transition temperatures (Tgs). However, the isotactic PMMA/PSAN blend was immiscible because most of the cast films were translucent and had two glass transition temperatures. Isotactic PMMA is known to be miscible with atactic PMMA according to literature. Atactic PMMA is miscible with both PSAN and isotactic PMMA but PSAN and isotactic PMMA are immiscible. It will be interesting to study the miscibility of ternary blends of isotactic and atactic PMMAs and PSAN. An investigation based on this is reported in this article. Calorimetry was used as the principal tool to study miscibility. A blend composed of isotactic and atactic PMMAs was also prepared and confirmed to be miscible. Tg of this blend seemed to vary linearly with composition. An approximate phase diagram of the ternary blends was established based on differential scanning calorimetry data. The results indicated that the ternary blends rich in isotactic PMMA and with a low PSAN concentration were found to be immiscible. One possible cause is attributed to more repulsive MMA-styrene interaction and/or MMA-acrylonitrile (AN) interaction between isotactic PMMA and PSAN.

Distance and orientation factor of fluorescence labels in complexed tactic and atactic poly(methyl methacrylate)s

Isotactic, syndiotactic and atactic poly(methyl methacrylate)s (i-, s- and a-PMMA) labeled with a donor (carbazole) or an acceptor (anthracene) were prepared. The distance between the donor and acceptor fluorophores in complexed tactic PMMA was measured using Forster's energy transfer method and compared with that found for atactic PMMA. The measured average distance of the fluorophores in the stereocomplex (˜3.7 nm) was found to be shorter than that in atactic systems where stereocomplexation does not take place. The upper and lower boundaries for the dipole-dipole orientation factor (K2) in Forster's theory were determined by time-resolved emission anisotropy. The orientational freedom of the fluorophores was found to be restricted for tactic PMMA in N,N-dimethylformamide as a result of stereocomplex formation but for tactic PMMA in 1,4-dioxane and atactic PMMA in 1,4-dioxane and N,N-dimethylformamide, the dynamic average value of 〈K2〉 = 2/3 was used.

Distance and orientation factor of fluorescence labels in complexed tactic and atactic poly(methyl methacrylate)s

Distance and orientation factor of fluorescence labels in complexed tactic and atactic poly(methyl methacrylate)s

Study of Poly(methyl methacrylate) Stereocomplex Formation by Nonradiative Energy Transfer and by Time-Resolved Fluorescence Spectroscopy

Poly(methyl methacrylate)s labeled with a fluorophore donor, carbazole (C), or acceptor, anthracene (A), have been prepared by free radical, anionic, and coordination polymerization, yielding atactic (a), isotactic (i), and syndiotactic (s) polymers. Nonradiative energy transfer (NET) was used to study polymer association in solutions. The efficiency of NET for mixtures of labeled tactic poly(methyl methacrylate)s (CPOL = 5.00 g L-1; CC = 2.61 × 10-4 M; CA = 6.00 × 10-4 M) in dimethylformamide and dioxane was 0.20 and 0.10, respectively. For a mixture of atactic polymers, the efficiency of NET in the same solvents under similar conditions is much lower. The efficiency of NET for a mixture of labeled atactic poly(methyl methacrylate)s increases with increasing polymer concentration and is nearly independent of concentration for a mixture of labeled tactic polymers. The time-dependent decays of fluorescence anisotropy show that stereocomplexation causes an increase in rotational correlation times of carbazole and anthracene fluorophores. The rotational correlation time of carbazole fluorophore as a part of a stereocomplex is 25.5 and 19.1 ns in dimethylformamide and dioxane, respectively, and shorter than 2 ns in noncomplexing solvents.

Influence of tacticity of poly(methyl methacrylate) on the compatibility with poly(vinyl phenol)

Isotactic, atactic, and syndiotactic poly(methyl methacrylate) (PMMA) were mixed with poly(vinyl phenol) (PVPh) separately in tetrahydrofuran to make three polymer blend systems. Differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy were used to study the miscibility of these blends. Isotactic PMMA was found to be more miscible with PVPh than atactic or syndiotactic PMMA.

Stereochemical Configuration of Poly(maleic acid) as Studied by 13C NMR

The tacticity of poly(maleic acid) has been resolved by 150-MHz 13C NMR spectroscopy in 0.1 N HCl solution at 60 °C by using the chemical shifts from the backbone carbon atoms and the carboxyl carb...

The effect of benzyl alcohol on pulsed laser polymerization of styrene and methylmethacrylate

The homo- and copolymerizations of styrene (STY) and methylmethacrylate (MMA) have been studied in the presence of several levels of benzyl alcohol (BA). From pulsed laser polymerizations it has been found that the apparent propagation rate constant increased with increasing BA for all systems. In copolymerization it has been found that the reactivity ratios for STY decrease somewhat, but those for MMA change little with increasing BA. The tacticity of poly(MMA) formed in the presence of BA is affected, the amount of mm diads increasing with increasing BA. The results are interpreted as supporting the hypothesis that BA forms a strong complex with radical chain ends terminating in MMA and a weak complex with those terminating in STY. © 1997 John Wiley & Sons, Inc.

The effect of benzyl alcohol on pulsed laser polymerization of styrene and methylmethacrylate

The homo- and copolymerizations of styrene (STY) and methylmethacrylate (MMA) have been studied in the presence of several levels of benzyl alcohol (BA). From pulsed laser polymerizations it has been found that the apparent propagation rate constant increased with increasing BA for all systems. In copolymerization it has been found that the reactivity ratios for STY decrease somewhat, but those for MMA change little with increasing BA. The tacticity of poly(MMA) formed in the presence of BA is affected, the amount of mm diads increasing with increasing BA. The results are interpreted as supporting the hypothesis that BA forms a strong complex with radical chain ends terminating in MMA and a weak complex with those terminating in STY. © 1997 John Wiley & Sons, Inc.

Fluorescence lifetime of terbium(III) as a probe for the ion-binding properties of tactic poly(methacrylic acids)

The binding properties of trivalent metal ions to polyelectrolytes were investigated through the use of terbium [Tb(III)] in fluorescence studies. The fluorescence intensity and lifetimes of the lanthanide ions are directly dependent upon the number of water molecules bound to their inner coordination sphere. The more efficiently a ligand coordinates to a lanthanide ion, the more water molecules are expelled and consequently, the greater the fluorescence intensity and lifetime. This effect was used to probe for differences in the complexation behavior of tactic polymers. Aqueous solutions of isotactic and syndiotactic poly(methacrylic acid) (PMA) were neutralized and complexed with Tb(III) ions. The fluorescence intensity of the 286 nm hypersensitive excitation band was monitored and the lifetimes were measured using several excitation wavelengths. It was found that the isotactic PMA/Tb(III) complex exhibited a six times greater fluorescence intensity than the syndiotactic PMA complex. Lifetime measurements gave the number of water molecules coordinated by Tb(III) in the isotactic complex to be 2.4 while 3.4 waters remained bound to the Tb(III) ion in the syndiotactic PMA complex. These results indicate that isotactic PMA has the greater binding affinity towards Tb(III) ions.