Effect of nucleating duality on the formation of γ‐phase in a β‐nucleated isotactic polypropylene copolymer

BACKGROUND: It is a challenge for polymer processing to promote the formation of γ‐phase under atmospheric conditions in isotactic polypropylene (iPP) copolymer containing chain errors. Incorporation of an α‐nucleator in iPP copolymer seems reasonable since it can enhance non‐isothermal crystallization. Up to now, however, the issue regarding a β‐nucleated iPP copolymer still remains unclear, which is the subject of this study. RESULTS: The results indicate that the γ‐phase indeed occurs in a β‐nucleated random iPP copolymer with ethylene co‐unit (PPR) sample and becomes predominant at slow cooling rates (e.g. 1 °C min^?1) where the formation of the β‐form is suppressed to a large extent. With detailed morphological observations the formation of γ‐phase in the β‐nucleated PPR sample at slow cooling rate is unambiguously attributed to the nucleating duality of the β‐nucleator towards α‐ and β‐polymorphs. The α‐crystals, induced by the β‐nucleator, serve as seeds for the predominant growth of the γ‐phase. Moreover, the presence of the β‐nucleator, acting as heterogeneous nuclei, promotes the formation of γ‐phase in the nucleated PPR sample, at least to some extent. CONCLUSION: The findings in this study extend our insights into the formation of γ‐phase in β‐nucleated iPP copolymer and, most importantly, provide an alternative route to obtain iPP rich in γ‐phase. Copyright © 2008 Society of Chemical Industry     

A novel highly efficient β‐nucleating agent for polypropylene using nano‐CaCO3 as a support

In order to increase the isotactic content of β‐nucleated polypropylene (β‐iPP) and decrease the cost of its production, the investigation and development of novel highly efficient β‐nucleators are important issues. Nano‐CaCO₃ was used as a support to prepare a supported β‐nucleator, nano‐CaCO₃‐supported calcium pimelate. Fourier transform infrared spectral analysis shows that an in situ chemical reaction takes place between nano‐CaCO₃ and pimelic acid. Differential scanning calorimetry results indicate that the crystallization and melting temperatures of β‐phase in supported β‐nucleator‐nucleated iPP are higher than those of calcium pimelate‐nucleated iPP. The β‐nucleating ability of the supported β‐nucleator is little influenced by the cooling rate and crystallization temperature over a wide range. The decreased content of pimelic acid in the supported β‐nucleator slightly decreases the crystallization temperature of iPP but it has no influence on the content of β‐phase in nucleated iPP. A novel supported β‐nucleator has been successfully synthesized via pimelic acid supported on the surface of CaCO₃. The crystallization temperature of iPP and melting temperature of β‐phase in iPP nucleated using the supported β‐nucleator are higher than those of iPP nucleated using calcium pimelate. The concept of a supported nucleator will provide a new way to increase the efficiency of polymer additives and to decrease the amounts of them that need to be used by using nanoparticles as supports. Copyright © 2010 Society of Chemical Industry     

A novel β‐nucleating agent for isotactic polypropylene

The nucleating ability of p‐cyclohexylamide carboxybenzene (β‐NA) towards isotactic polypropylene (iPP) was investigated by differential scanning calorimetry, X‐ray diffraction, polarized optical microscopy and scanning electron microscopy. β‐NA is identified to have dual nucleating ability for α‐iPP and β‐iPP under appropriate kinetic conditions. The formation of β‐iPP is dependent on the content of β‐NA. The content of β‐phase can reach as high as 96.96% with the addition of only 0.05 wt% β‐NA. Under non‐isothermal crystallization the content of β‐iPP increases with increasing cooling rate. The maximum β‐crystal content is obtained at a cooling rate of 40 °C min^–1. The supermolecular structure of the β‐iPP is identified as a leaf‐like transcrystalline structure with an ordered lamellae arrangement perpendicular to the special surface of β‐NA. Under isothermal crystallization β‐crystals can be formed in the temperature range 80–140 °C. The content of β‐crystals reaches its maximum value at a crystallization temperature of 130 °C. © 2012 Society of Chemical Industry     

A highly active and selective β‐nucleating agent for isotactic polypropylene and crystallization behavior of β‐nucleated isotactic polypropylene under rapid cooling

Zinc adipate (Adi‐Zn) was observed to be a highly active and selective β‐nucleating agent for isotactic polypropylene (iPP). The effects of Adi‐Zn on the mechanical properties and the β‐crystals content of nucleated iPP were investigated. The impact strength of iPP nucleated with 0.2 wt % Adi‐Zn was 1.8 times higher than that of neat iPP. In addition, wide‐angle X‐ray diffraction analysis indicated that the content of β‐crystals in nucleated iPP (k_β value) reached 0.973 with 0.1 wt % Adi‐Zn, indicating that Adi‐Zn is a highly active and selective β‐nucleating agent for iPP. Furthermore, fast scanning chip calorimetry (FSC) studies using cooling rates from 60 to 13,800 °C min^?1 revealed that the formation of β‐crystals significantly depended on the cooling rates. At cooling rates below 3000 °C min^?1, only β‐crystals existed. However, at cooling rates above 6000 °C min^?1, β‐crystals failed to form. Moreover, a lower critical crystallization temperature that corresponded to the generation of β‐crystals was investigated using cooling‐induced crystallization, and the results are in good agreement with those of a previous study. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43767.     

Nonisothermal crystallization and melting behavior of β‐nucleated isotactic polypropylene and polyamide 66 blends

A highly novel nano‐CaCO₃ supported β‐nucleating agent was employed to prepare β‐nucleated isotactic polypropylene (iPP) blend with polyamide (PA) 66, β‐nucleated iPP/PA66 blend, as well as its compatibilized version with maleic anhydride grafted PP (PP‐g‐MA), maleic anhydride grafted polyethylene‐octene (POE‐g‐MA), and polyethylene‐vinyl acetate (EVA‐g‐MA), respectively. Nonisothermal crystallization behavior and melting characteristics of β‐nucleated iPP and its blends were investigated by differential scanning calorimeter and wide angle X‐ray diffraction. Experimental results indicated that the crystallization temperature (T) of PP shifts to high temperature in the non‐nucleated PP/PA66 blends because of the α‐nucleating effect of PA66. T of PP and the β‐crystal content (K_β) in β‐nucleated iPP/PA66 blends not only depended on the PA66 content, but also on the compatibilizer type. Addition of PP‐g‐MA and POE‐g‐MA into β‐nucleated iPP/PA66 blends increased the β‐crystal content; however, EVA‐g‐MA is not benefit for the formation of β‐crystal in the compatibilized β‐nucleated iPP/PA66 blend. It can be relative to the different interfacial interactions between PP and compatibilizers. The nonisothermal crystallization kinetics of PP in the blends was evaluated by Mo's method. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Structural characterization of α‐ and β‐nucleated isotactic polypropylene

Modification of isotactic polypropylene (iPP) with two nucleation agents, namely 1,3:24‐bis(3,4‐dimethylobenzylideno) sorbitol (DMDBS) (α‐nucleator) and N, N′‐dicyclohexylo‐2,6‐naphthaleno dicarboxy amide (NJ) (β‐nucleator), leads to significant changes of the structure, morphology and properties. Both nucleating agents cause an increase in the crystallization temperature. The efficiency determined in a self‐nucleation test is 73.4 % for DMDBS and 55.9 % for NJ. The modification with NJ induces the creation of the hexagonal β‐form of iPP. The addition of DMDBS lowers the haze of iPP while the presence of NJ increases the haze. Copyright © 2004 Society of Chemical Industry     

β‐Nucleation of pimelic acid supported on metal oxides in isotactic polypropylene

To investigate the nucleation of metal pimelate for isotactic polypropylene (iPP) crystallization, iPP filled with a series of metal oxides with and without metal pimelate on their surface was prepared. There was a chemical reaction between pimelic acid (PA) and metal oxides MgO, CaO, BaO or ZnO, but not TiO₂. The corresponding metal pimelate formed by the chemical reaction between PA and MgO, CaO, BaO or ZnO had a different influence on the crystallization behavior and melting characteristics of iPP. Addition of metal oxides increased the crystallization temperature of iPP and mainly formed α‐phase due to the heterogeneous α‐nucleation of metal oxides. The α‐nucleation of CaO could be easily changed into β‐nucleation using CaO‐supported PA, and 90.1% β‐phase was obtained. The β‐nucleation of BaO could be markedly enhanced by barium pimelate formed using supported PA. However, no β‐phase was observed for iPP filled with MgO‐ or ZnO‐supported PA. The various metal oxides with supported PA had a different influence on the crystallization behavior and melting characteristics of iPP due to the different structure of metal pimelate formed by chemical reaction between PA and the metal oxides. Copyright © 2012 Society of Chemical Industry     

Isothermal crystallization and melting behavior of polypropylene with lanthanum complex of cyclodextrin derivative as a β‐nucleating agent

A novel highly active β‐nucleating agent, β‐cyclodextrin complex with lanthanum (β‐CD‐MAH‐La), was introduced to isotactic polypropylene (iPP). Its influence on isothermal crystallization and melting behavior of iPP was investigated by differential scanning calorimeter (DSC), wide‐angle X‐ray diffraction (WAXD), and polarized light microscopy (PLM). WAXD results demonstrated that β‐CD‐MAH‐La was an effective β‐nucleating agent, with β‐crystal content of iPP being strongly influenced by the content of β‐CD‐MAH‐La and the isothermal crystallization temperature. The isothermal crystallization kinetics of pure iPP and iPP/β‐CD‐MAH‐La was described appropriately by Avrami equation, and results revealed that β‐CD‐MAH‐La promoted heterogeneous nucleation and accelerated the crystallization of iPP. In addition, the equilibrium melting temperature (T) of samples was determined using linear and nonlinear Hoffman‐Weeks procedure. Finally, the Lauritzen‐Hoffman secondary nucleation theory was applied to calculate the nucleation parameter (K_g) and the fold surface energy (σ_e), the value of which verify that the addition of β‐CD‐MAH‐La reduced the creation of new surface for β‐crystal and then led to faster crystallization rate. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

A concise synthesis of single‐enantiomer β‐lactams and β‐amino acids using Rhodococcus globerulus

BACKGROUND: Pharmaceutical companies continue to evaluate β‐amino acids and β‐lactams in a range of drug candidates. The development of a highly efficient and selective bioresolution of cyclic β‐lactam substrates could yield enantiopure lactams and β‐amino acids with medicinal potential. The aim of this work was to discover and develop a biocatalyst capable of selectively hydrolysing β‐lactam substrates. RESULTS: Screening of our in‐house culture collection led to the discovery of a microorganism, Rhodococcus globerulus (NCIMB 41042) with β‐lactamase activity. Whole‐cell bioresolutions of the β‐lactams 1–4 were successfully carried out and in all cases enantiomeric excesses of the residual lactam and amino acid product were found to be greater than 98%. For one example, the bioresolution was optimised to operate at 60 g L^?1 substrate concentration with a 20% wt/wt cell paste loading. CONCLUSION: A microorganism, Rhodococcus globerulus (NCIMB 41042), capable of selectively hydrolysing a range of cyclic β‐lactams, has been discovered. A scalable whole‐cell bioresolution process has been developed, leading to the synthesis of multigram quantities of enantiomerically pure β‐lactams and β‐amino acids. Copyright © 2007 Society of Chemical Industry     

Variation of non‐isothermal crystallization behavior of isotactic polypropylene with varying β‐nucleating agent content

The non‐isothermal crystallization behavior, the crystallization kinetics, the crystallization activation energy and the morphology of isotactic polypropylene (iPP) with varying content of β‐nucleating agent were investigated using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The DSC results showed that the Avrami equation modified by Jeziorny and a method developed by Mo and co‐workers could be successfully used to describe the non‐isothermal crystallization process of the nucleated iPPs. The values of n showed that the non‐isothermal crystallization of α‐ and β‐nucleated iPPs corresponded to a tridimensional growth with homogeneous and heterogeneous nucleation, respectively. The values of crystallization rate constant showed that the rate of crystallization decreased for iPPs with the addition of β‐nucleating agent. The crystallization activation energy increased with a small amount (less than 0.1 wt%) of β‐nucleating agent and decreased with higher concentration (more than 0.1 wt%). The changes of crystallization rate, crystallization time and crystallization activation energy of iPPs with varying contents of β‐nucleating agent were mainly determined by the ratio of the content of α‐ and β‐phase in iPP (α‐PP and β‐PP) from the DSC investigation, and the large size and many intercrossing lamellae between boundaries of β‐spherulites for iPPs with small amounts of β‐nucleating agent and the small size and few intercrossing bands among the boundaries of β‐spherulites for iPPs with large amounts of β‐nucleating agent from the SEM examination. Copyright © 2010 Society of Chemical Industry     

Chemoenzymatic Preparation of Enantiopure Homoadamantyl β‐Amino Acid and β‐Lactam Derivatives

Racemic cis‐10‐azatetracyclo[7.2.0.1^2,6.1^4,8]tridecan‐11‐one was prepared from homoadamant‐4‐ene by chlorosulfonyl isocyanate addition. The transformation of the β‐lactam to the corresponding β‐amino ester followed by Candida antarctica lipase A‐catalyzed enantioselective (E>>200) N‐acylation with 2,2,2‐trifluoroethyl butanoate afforded methyl (1R,4R,5S,8S)‐5‐aminotricyclo[4.3.1.1^3,8]undecane‐4‐carboxylate and the (1S,4S,5R,8R)‐butanamide with>99% ee at 50% conversion. Alternatively, transformation of the β‐lactam to the corresponding N‐hydroxymethyl‐β‐lactam and the following Pseudomonas cepacia (currently Burkholderia cepacia) lipase‐catalyzed enantioseletive O‐acylation provided the (1S,4S,6R,9R)‐alcohol (ee=87%) and the corresponding (1R,4R,6S,9S)‐butanoate (ee>99%). In the latter method, competition for the enzyme between the (1R,4R,6S,9S)‐butanoate, 2,2,2‐trifluoroethyl butanoate and the hydrolysis product, butanoic acid, tended to stop the reaction at about 45% conversion and finally gave racemization in the (1S,4S,6R,9R)‐alcohol with time.     

Highly Enantioselective Phase‐Transfer Catalytic α‐Alkylation of α‐tert‐Butoxycarbonyllactams: Construction of β‐Quaternary Chiral Pyrrolidine and Piperidine Systems

A new enantioselective α‐alkylation of α‐tert‐butoxycarbonyllactams for the construction of β‐quaternary chiral pyrrolidine and piperidine core systems is reported. α‐Alkylations of N‐methyl‐α‐tert‐butoxycarbonylbutyrolactam and N‐diphenylmethyl‐α‐tert‐butoxycarbonylvalerolactam under phase‐transfer catalytic conditions (solid potassium hydroxide, toluene, −40 °C) in the presence of (S,S)‐3,4,5‐trifluorophenyl‐3,3′,5,5′‐tetrahydro‐2,6‐bis(3,4,5‐trifluorophenyl)‐4,4′‐spirobi[4H‐dinaphth[2,1‐c:1′,2′‐e]azepinium] bromide [(S,S)‐NAS Br] (5 mol%) afforded the corresponding α‐alkyl‐α‐tert‐butoxycarbonyllactams in very high chemical (up to 99%) and optical yields (up to 98% ee). Our new catalytic systems provide attractive synthetic methods for pyrrolidine‐ and piperidine‐based alkaloids and chiral intermediates with β‐quaternary carbon centers.     

Highly active thermally stable β‐nucleating agents for isotactic polypropylene

Calcium salts of suberic (Ca‐Sub) and pimelic (Ca‐Pim) acids were synthesized and implemented as in different grades of isotactic polypropylene (iPP). Propylene homopolymer, as well as random and block copolymers containing these additives, crystallized iPP into pure or nearly pure β modification in the isothermal and nonisothermal crystallization experiments. Recently, Ca‐Sub proved to be the most effective β‐nucleating agent of iPP. The Ca‐Sub nucleating agent widens the upper crystallization temperature range of pure β‐iPP formation up to 140°C. In this study the effect of the these additives on the crystallization, melting characteristics, and structure of the PP were studied. The degree of crystallinity of β‐iPP was markedly higher than that of α‐iPP. A widening in the melting peak of the samples crystallized in a high temperature range was first observed and discussed in regard to literature results of the same phenomenon for α‐iPP. The morphology of the β‐iPP samples was revealed by scanning electron microscopy. Independent of the type of polymer or nucleating agent, hedritic structures were found in the early stages of growth of the β‐spherulites. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2357–2368, 1999     

Effect of α‐ and β‐nucleating agents on the fracture behavior of polypropylene‐co‐ethylene

The effect of α‐ and β‐nucleating agents (NA) of various amounts on the fracture behavior of polypropylene‐co‐ethylene (CPP) was evaluated using the essential work of fracture (EWF) method. The specific EWF values of CPPs incorporated with α‐NA of different amount were all lower than that of pure CPP, while the specific nonessential work of fracture was the highest at relative low α‐NA loading (0.1 wt %), and then decreased with further increasing amount of α‐NA. Similar trend of variation was observed with increasing amount of β‐NA in CPP, and it was found that the variation of K_β for β‐NA nucleated CPP versus NA content accorded well with the EWF versus NA content, which indicated that the addition of β‐NA could lead to effectively increased β‐crystal content and consequently improved fracture resistance of CPP. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Structural elucidation and iron oxidation states in situ formed β‐Ca3(PO4)2/α‐Fe2O3 composites

A detailed structural analysis on the in situ synthesized β‐Ca₃(PO₄)₂/α‐Fe₂O₃ composites is demonstrated. Compositional ratios, the influence and occupancy of iron at the β‐Ca₃(PO₄)₂ lattice, oxidation state of iron in the composites are derived from analytical techniques involving XRD, FT‐IR, Raman, refinement of the powder X‐ray diffraction and X‐ray photoelectron spectroscopy. Iron exists in the Fe³⁺ state throughout the investigated systems and favors its occupancy at the Ca²⁺(5) site of β‐Ca₃(PO₄)₂ until critical limit, and thereafter crystallizes as α‐Fe₂O₃ at ambient conditions. Fe³⁺ occupancy at the β‐Ca₃(PO₄)₂ lattice yields a Ca₉Fe(PO₄)₇ structure that is isostructural with its counterpart. A strong rise in the soft ferromagnetic behavior of β‐Ca₃(PO₄)₂/α‐Fe₂O₃ composites is obvious that depends on the content of α‐Fe₂O₃ in the composites. Overall, the diverse level of iron inclusions at the calcium phosphate system with a Ca/P ratio of 1.5 yields a structurally stable β‐Ca₃(PO₄)₂/α‐Fe₂O₃ composites with assorted compositional ratios.     

Acid hydrolysis of glycosidic bonds in oat β‐glucan and development of a structured kinetic model

Homogeneous acid‐catalyzed hydrolysis of oat β‐glucan, which contains β‐(1,4) and β‐(1,3) glycosidic bonds in a nonrandom order, was studied at 353 K using HCl and H₂SO₄. A new structured kinetic model was developed that takes into account the difference in the reactivity of β‐(1,4) and β‐(1,3) glycosidic bonds as well as their positions in the polysaccharide chain. To minimize the correlation of adjustable parameters in the new model, the reactivities of these bonds were studied independently (T = 313…363 K; c_H+ = 0.1…2 mol/L) using cellobiose and laminaribiose. The difference in kinetic parameters (e.g., T = 338 K: k_β‐(1,4) = 0.693 × 10^?3 L/mol/min, k_β‐(1,3) = 1.027 × 10^?3 L/mol/min) was found to be statistically significant (P < 0.0001), which emphasizes the need for the structured model for oat β‐glucan hydrolysis. The simulation of β‐glucan hydrolysis with the new model was in good agreement with the experimental data and shows improvement over existing nonstructured models. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2570–2580, 2018     

Production of β‐galactosidase from recombinant Saccharomyces cerevisiae grown on lactose

Improved productivity and costs reduction in fermentation processes may be attained by using flocculating cell cultures. The production of extracellular heterologous β‐galactosidase by recombinant flocculating Saccharomyces cerevisiae cells, expressing the lacA gene (coding for β‐galactosidase) of Aspergillus niger under the ADHI promotor and terminator in a bioreactor was studied. The effects of lactose concentration and yeast extract concentration on β‐galactosidase production in a semi‐synthetic medium were analysed. The extracellular β‐galactosidase activity increased linearly with increasing initial lactose concentrations (5–150 g dm^?3). β‐Galactosidase production also increased with increased yeast extract concentration. During the entire fermentation, no accumulation of the hydrolysed sugars, glucose and galactose, was observed. The catabolic repression of the recombinant strain when cultured in a medium containing equal amounts of glucose and galactose was confirmed. In complete anaerobiosis, the fermentation of lactose resulted in a very slow fermentation pattern with lower levels of β‐galactosidase activity. The bioreactor operation together with optimisation of culture conditions (lactose and yeast extract concentration) led to a 21‐fold increase in the extracellular β‐galactosidase activity produced when compared with preliminary Erlenmeyer fermentations. Copyright © 2004 Society of Chemical Industry     

Diaryl‐Substituted Azolylthioacetamides: Inhibitor Discovery of New Delhi Metallo‐β‐Lactamase‐1 (NDM‐1)

The emergence and spread of antibiotic‐resistant pathogens is a global public health problem. Metallo‐β‐lactamases (MβLs) such as New Delhi MβL‐1 (NDM‐1) are principle contributors to the emergence of resistance because of their ability to hydrolyze almost all known β‐lactam antibiotics including penicillins, cephalosporins, and carbapenems. A clinical inhibitor of MBLs has not yet been found. In this study we developed eighteen new diaryl‐substituted azolylthioacetamides and found all of them to be inhibitors of the MβL L1 from Stenotrophomonas maltophilia (K_i<2 μM ), thirteen to be mixed inhibitors of NDM‐1 (K_i<7 μM ), and four to be broad‐spectrum inhibitors of all four tested MβLs CcrA from Bacteroides fragilis, NDM‐1 and ImiS from Aeromonas veronii, and L1 (K_i<52 μM ), which are representative of the B1a, B1b, B2, and B3 subclasses, respectively. Docking studies revealed that the azolylthioacetamides, which have the broadest inhibitory activity, coordinate to the Zn^II ion(s) preferentially via the triazole moiety, while other moieties interact mostly with the conserved active site residues Lys224 (CcrA, NDM‐1, and ImiS) or Ser221 (L1).     

Structure and properties of a β‐nucleated polypropylene impact copolymer

The effect of a β‐nucleating agent (β‐NA) on the properties and structure of a commercial impact polypropylene copolymer (IPC) was investigated. The effect of selected β‐NAs on the impact resistance, stress and strain behaviour of the IPC is reported. In addition, the IPC was fractionated according to crystallinity by preparative temperature rising elution fractionation. Fractions with varying chemical composition and crystallinity were treated with a two‐component β‐NA to investigate the effect of the β‐NA on the various fractions. The results indicate that the efficacy of the β‐NA is dependent on the chemical composition of the polymer that crystallises, more specifically on the sequence length of crystallisable propylene units. The effect of the addition of β‐NAs on the overall morphology of the IPC was also investigated, and in particular the size and distribution of the rubbery particles in these complex reactor blends were probed. © 2014 Society of Chemical Industry