Free radical grafting of polyethylene with vinyl monomers by reactive extrusion

The free radical grafting of polyethylene with vinyl monomers by reactive extrusion was studied numerically. Numerical computation expressions of key variables, such as the concentrations of the initiator and polymer, grafting degree, average molecular weight and apparent viscosity, were deduced. The evolutions of the above variables were predicted by means of an uncoupled semi-implicit iterative algorithm. The monomer conversion monotonically increases with decreasing throughput or increasing initial initiator concentration; with increasing barrel temperature, the monomer conversion first increases then decreases. The simulated results are nearly in good agreement with the experimental results.

Synthesis and properties of novel regioirregular polyimides from easily synthesized asymmetrical dichlorophthalimide monomers

New asymmetrical aromatic dichlorophthalimide monomers containing pendant groups (trifluoromethyl or methyl) were conveniently prepared from inexpensive and commercially available compounds. With these monomers, a new class of soluble polyimides with a regioirregular structure within the polymer backbone was obtained by the Ni(0)-catalyzed polymerization method. The structures of the polymers were confirmed by various spectroscopic techniques. The polyimides displayed better solubility and higher thermal stability than the corresponding regular polyimides. In addition, fluorinated polyimides in this study had low dielectric constants ranging from 2.52 to 2.78, low moisture absorptions of less than 0.59%, and low thermal expansion coefficients between 10.6 and 19.7 ppm/degrees C. The oxygen permeability coefficients and permeability selectivity of oxygen to nitrogen of the films were in the ranges of 2.99-4.20 barrer and 5.55-7.50, respectively. We have demonstrated that the synthetic pathway for polyimides provides a successful approach to increasing the solubility and processability of polyimides without sacrificing their thermal stability.

Electron-beam irradiation on poly(propylene carbonate) in the presence of polyfunctional monomers

Poly(propylene carbonate) (PPC) showed predominantly degradation under electron-beam irradiation, accompanied by deterioration of its mechanical performance due to sharp decrease of the molecular weight. Crosslinked PPC was prepared by addition of polyfunctional monomer (PFM) to enhance the mechanical performance of PPC. When 8 wt% of PFM like triallyl isocyanurate (TAIL) was added, crosslinked PPC with a gel fraction of 60.7% was prepared at 50 kGy irradiation dose, which showed a tensile strength at 20 degrees C of 45.5 MPa, whereas it was only 38.5 MPa for pure PPC. The onset degradation temperature (T-i) and glass transition temperature (T-g) of this crosslinked PPC was 246 degrees C and 45 degrees C, respectively, a significant increase related to pure PPC of 211 degrees C and 36 C. Therefore, thermal and mechanical performances of PPC could be improved via electron-beam irradiation in the presence of suitable PFM.

Reversible addition-fragmentation chain transfer mediated radical polymerization of asymmetrical divinyl monomers targeting hyperbranched vinyl polymers

Reversible addition-fragmentation chain transfer (RAFT) mediated radical polymerizations of allyl methacrylate and undecenyl methacrylate, compounds containing two types of vinyl groups with different reactivities, were investigated to provide hyperbranched polymers. The RAFT agent benzyl dithiobenzoate was demonstrated to be an appropriate chain-transfer agent to inhibit crosslinking and obtain polymers with moderate-to-high conversions. The polymerization of allyl methacrylate led to a polymer without branches but with five- or six-membered rings. However, poly(undecenyl methacrylate) showed an indication of branching rather than intramolecular cycles. The hyperbranched structure of poly(undecenyl methacrylate) was confirmed by a combination of H-1, C-13, H-1-H-1 correlation spectroscopy, and distortionless enhancement by polarization transfer 135 NMR spectra. The branching topology of the polymers was controlled by the variation of the reaction temperature, chain-transfer-agent concentration, and monomer conversion. The significantly lower inherent viscosities of the resulting polymers, compared with those of linear analogues, demonstrated their compact structure,

Facile synthesis and characterization of hyperbranched poly(ether amide)s generated from Michael addition polymerization of in situ created AB(2) monomers

A new straightforward strategy for synthesis of novel hyperbranched poly (ether amide)s from readily available monomers has been developed. By optimizing the reaction conditions, the AB(2)-type monomers were formed dominantly during the initial reaction stage. Without any purification, the AB(2) intermediate was subjected to further polymerization in the presence (or absence) of an initiator, to prepare the hyperbranched polymer-bearing multihydroxyl end-groups. The influence of monomer, initiator, and solvent on polymerization and the molecular weight (MW) of the resultant polymers was studied thoroughly. The MALDI-TOF MS of the polymers indicated that the polymerization proceeded in the proposed way. Analyses of H-1 NMR and C-13 NMR spectra revealed the branched structures of the polymers obtained. These polymers exhibit high-moderate MWs and broad MW distributions determined by gel permeation chromatography (GPC) in combination with triple detectors, including refractive index, light scattering, and viscosity detectors. In addition, the examination of the solution behavior of these polymers showed that the values of intrinsic viscosity [eta] and the Mark-Houwink exponent a were remarkably lower compared with their linear analogs, because of their branched nature.

Modified poly(3-hydroxybutyrate-co-3-hydroxyvalerate) using hydrogen bonding monomers

Properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) were significantly modified by a hydrogen bonding (H-bond) monomer-bisphenol A (BPA). BPA lowered the T-m of PHBV and widened the heat-processing window of PHBV. At the same time, a dynamic H-bond network in the blends was observed indicating that BPA acted as a physical cross-link agent. BPA enhanced the T, of PHBV and reduced the crystallization rate of PHBV. It resulted in larger crystallites in PHBV/BPA blends showed by WAXD. However, the crystallinity of PHBV was hardly reduced. SAXS results suggested that BPA molecules distributed in the inter-lamellar region of PHBV. Finally, a desired tension property was obtained, which had an elongation at break of 370% and a yield stress of 16 MPa. By comparing the tension properties of PHBV/BPA and PHBV/tert-butyl phenol blends, it was concluded that the H-bond network is essential to the improvement of ductility.

Kinetics study on melt grafting copolymerization of LLDPE with acid monomers using reactive extrusion method

Graft copolymerization in the molten state is of fundamental importance as a probe of chemical modification and reactive compatibilization. However, few grafting kinetics studies on reactive extrusion were carried out for the difficulties as expected. In this work, the macromolecular peroxide-induced grafting of acrylic acid and methyl methacrylate onto linear low density polyethylene by reactive extrusion was chosen as the model system for the kinetics study; the samples were taken out from the barrel at five ports along screw axis and analyzed by FTIR, H-1 NMR, and ESR. For the first time, the time-evolution of reaction rate, the reaction order, and the activation energy of graft copolymerization and homopolymerization in the twin screw extruder were directly obtained. On the basis of these results, the general reaction mechanism was tentatively proposed. It was demonstrated that an amount of chain propagation free radicals could keep alive for several minutes even the peroxides completely decomposed and the addition of monomer to polymeric radicals was the rate-controlled step for the graft copolymerization.

Synthesis and properties of three novel series of monomers containing para-methoxyazobenzene as the mesogenic group

Three novel series of monomers, namely n-1-bromo-[4-(4-methoxyphenylazo)phenyloxy]-alkanes (Bn, n = 3, 6, 10), n-[4-(4-methoxyphenylazo) phenyloxy]alkyloxy-4-methoxybenzene (Cn, n = 3, 6, 10) and n-[4-(4-methoxyphenylazo)phenyloxyl]alkyloxy-[4-methoxy-2,5-bis-(chloromethyl)] benzene (Dn, n = 3, 6, 10) were synthesized and characterized with FTIR, H-1 NMR, UV-visible and fluorescence spectroscopy. Their thermal behaviour was studied by different scanning calorimetry and polarizing optical microscopy. The results show that B3, B6 and C6 exhibit monotropic nematic liquid crystalline behaviour.

Synthesis and properties of two series of H-bonded and non-H-bonded thermotropic liquid crystal monomers

Two series of monomers, namely n-1-bromo-(4-(4-nitrophenylazo)phenyloxy]alkanes (Bn, n = 2, 3, 4, 5, 6, 8, 10) and N-n-[4-(4-nitrophenylazo)phenyloxy]alkyl diethanolamines (Cn, n = 3, 5, 6, 10), were synthesized and characterized. Their thermal behaviour was studied by differential scanning calorimetry (DSC), wide angle X-ray diffractometry (WAXD) and polarizing optical microscopy (POM) equipped with a hot stage. The results showed that the Bns (n greater than or equal to 6) exhibit monotropic nematic liquid crystalline behaviour; no liquid crystalline phase was found for the Bns (n < 6), while for the Cns, enantiotropic smectic liquid crystallinity for n = 5, 6, 10 was seen, and for n = 3 monotropic smectic phases were found. This different phase behaviour between Bn and Cn compounds is attributed to their different end groups. The FTIR analysis of Cn indicated that there exists an intermolecular hydrogen bond between hydroxy groups, so that more stable liquid crystalline phase are formed. The effect of the length of the flexible chain on the thermal behaviour is also discussed.

Synthesis of lanthanide-alkylaluminium bimetallic complexes and studies on their catalytic activities for polymerization of some polar monomers

Three new lanthanide (Ln)-alkylaluminium (Al) bimetallic complexes with the formula [(mu-CF3CO2)(2)Ln(mu-CF3CHO2)AIR(2) . 2THF](2) (Ln = Nd, Y, R=i-C4H9 (i-Bu); Ln=Eu, R=C2H5(Et); THF=tetrahydrofuran) were synthesized by the reaction of Ln(CF,CO,), (Ln=Nd, Y) with HAI (i-Bu)(2) and of Eu(CF3CO2)(3) with AlEt(3), respectively. Their crystal structures were determined by X-ray diffraction at 233 K. [(mu-CF3CO2)(2)Nd (mu-CF3CHO2)Al(i-Bu)(2) . 2THF](2) (Nd-Al) and [(mu-CF3CO2)(2)Y(mu-CF3CHO2)Al(i-Bu)(2) . 2THF](2) (Y-Al) are isomorphous and crystallize in space group with a=12.441(3) Angstrom [12.347(5) Angstrom for Y-Al], b=12.832(3) Angstrom [12.832(4) Angstrom], c=11.334(3) Angstrom [11.292(8) Angstrom], alpha=104.93 (2)degrees [104.45(4)degrees], beta=98.47(2)degrees [98.81(4)degrees], gamma=64.60(2)degrees [64.30(3)degrees], R=0.519 [0.113], R(w)=0.0532 [0.110], Z=1 and [(mu-CF3CO2)(2)Eu(CF3CHO2)AlEt(2) . 2THF](2)(Eu-Al) in space group P2(1)/n with a=11.913(6) Angstrom, b=14.051(9) Angstrom, c=17.920(9) Angstrom, alpha=101.88(11)degrees, beta=gamma=90 degrees, R=0.0509, R(w)=0.0471 and Z=2. The six CF3CO2- (including CF3CHO2-) of each complex, among which pairs are equivalent, coordinated to Ln and Al in three patterns: (A) the two oxygen atoms in one of the three CF3CO2- type coordinated to two different Ln; (B) the two oxygen atoms in the second of CF3CO2- type coordinated to Ln and Al, respectively; (C) one of the two oxygen atoms in the third CF3CO2- type bidentately coordinated to two Ln and another oxygen coordinated to Al and one of the two Ln, respectively. Unlike types A and B, in type C the carboxyl carbon with a hydrogen atom bonded to it was found to appear as an sp(3)-hybridized configuration rather than an sp(2)-one. 1D and 2D NMR results further confirmed the existence of such a disproportionated CF3CHO2- ligand. Methyl methacrylate (MMA) and epichlorohydrin (ECH) could be polymerized by Y-Al or Eu-Al as a single-component catalyst and highly syndiotactic poly(MMA) was obtained. THF could also be polymerized by Y-Al in the presence of a small amount of ECH.

SYNTHESES AND CHARACTERIZATION OF [(MU-CF3CO2)(2)LN(MU-CF3CHO2)ALR(2)CENTER-DOT-2THF](2) AND THEIR CATALYTIC ACTIVITIES FOR POLYMERIZATION OF SOME POLAR MONOMERS

Three new bimetallic complexes were synthesized and crystalized by reactions of (CF3CO2)(3)Ln With R(1) AlR(2)(Ln=Nd and Y, R(1)=H, R=i-C4H9; Ln=Eu, R=R(1)=C2H5) in tetrahydrofuran solution, and their crystal structures were determined using a X-ray diffraction method. The structures and the questions on valence state and noncoplanarity in the structures were confirmed and cracked by means of H-1 NMR and C-13 NMR spectra, especially by C-13-H-1 COSY 2D NMR technique. A general formula of molecules of the three rare earth complexes was defined as follows: [(mu-CF3CO2)(2)Ln(mu-CF3CHO2)AlR(2) . 2THF](2) A mechanism on the formation of the new complexes was also proposed through the following five steps: alkylating, beta-elimination (or hydrogenation), hydrogen transfer, linkage and association. Both Y-Al and Eu-Al complexes function as a catalyst in polymerization of MMA and ECH. The polymer obtained from the first monomer is mainly syndiotactic chain structure and the polymerization of the last monomer shows higher catalytic activity. The Y-Al complex also capable of ring-opening polymerization of THF in case of adding-vary small amount of ECH and a oxonium ion mechanism of THF polymerization was suggested from the analysis of THF polymer terminal.

New cocktail functional monomers in making molecule imprinting polymer with high chiral selectivity

in order td produce molecule imprinting polymer (MIP) with high chiral selectivity against N-c-protected amino acid, new cocktail functional monomers acrylamide (AM) + 2-vinylpyridine (2-VP) and AM + methacrylic acid (MAA) were investigated. AM + 2-VP was found to be more efficient in improving the selectivity and resolution of the molecule imprinting polymer.