Synthesis,characterization and thermal behaviors of polymers containing organosilicon groups

Various bis(silyl)ethenyl groups were attached to the aromatic ring of poly(α-methylstyrene) via Peterson olefination reaction of (RMe₂Si)₃CLi (R = H, Me and Ph) with formylated poly(α-methylstyrene) (Pα-MS-CHO) to give poly(α-methylstyrene)-co-[2,2-bis(silyl)ethenyl(α-methylstyrene)] as functionalized poly(α-methylstyrene) (Pα-MS-SiMe₂H, Pα-MS-SiMe₃ and Pα-MS-SiMe₂Ph). The trimethylsilyl groups of Pα-MS-SiMe₃ have been converted to 2,2-dibromoethenyl and epoxybis(silanes) groups via NBS-based bromodesilylation and MCPBA-based epoxidation respectively. The thermal degradation behaviors of the polymers were studied using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC).     

Synthesis and properties of new highly soluble poly(amide-ester-imide)s containing poly(ethylene glycol) as a soft segment

In this study, a new class of highly soluble poly(amide-ester-imide)s (PAEI)s contains poly(ethyleneglycol) (PEG) as hydrophilic and soft segment were prepared. Poly(ethylene glycol)-bis-(N-trimellitylimido-4-phenyl carboxylic acid) (3) as a novel diacid monomer was synthesized via two step. The reaction of poly(ethylene glycol) (PEG 6000) with trimellitic anhydride chloride yield poly(ethylene glycol)-bis-trimellitic anhydride (1). The reaction of dianhydride 1 with p-aminobenzoic acid (2) produces novel diacid monomer 3. The direct polycondensation technique of the diacid 1 with several aromatic diamines was carried out in pyridine/N-methyl-2-pyrrolidone/triphenylphosphite/CaCl₂ as condensing agent. The resulting novel PAEIs with inherent viscosities ranging between 0.21 and 0.42 dl g⁻¹, were obtained in good yield. This group of polymers exhibit excellent solubility in a variety of organic solvents and water. All of these polymers were characterized with FT-IR spectroscopy. Thermal properties, ¹H-NMR and XRD study of these PAEIs were also reported. The results demonstrate that this polymers show crystalline structure as well as high thermal stability. In addition the effect of PEG length on solubility and thermal properties of the polymers were also studied.     

Preparation and thermo-oxidative degradation of poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid)/poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid)-grafted SiO<Subscript>2</Subscript> nanocomposites

Poly(l-lactic acid)/poly(l-lactic acid)-grafted SiO₂ nanocomposites were prepared by in situ melt polycondensation, in which “free” poly(l-lactic acid) and poly(l-lactic acid)-grafted SiO₂ nanoparticles were formed simultaneously. The maximum values of grafting ratio and grafting efficiency of poly(l-lactic acid) were up to 37.67% and 26.60%, respectively. In the polycondensation system, SiO₂ content was a critical parameter of getting nanocomposites with uniformly dispersed SiO₂ nanoparticles. At lower SiO₂ content, Mn of grafted poly(l-lactic acid) was close to that of “free” poly(l-lactic acid), and poly(l-lactic acid)-grafted SiO₂ nanoparticles could be well dispersed in poly(l-lactic acid) matrix. While at higher SiO₂ content, Mn of “free” poly(l-lactic acid) and grafted poly(l-lactic acid) decreased seriously, especially GPC curves of “free” poly(l-lactic acid) exhibited two peaks due to the aggregation of SiO₂ nanoparticles during the polycondensation process. The grafting ratio and SiO₂ content exhibited a clear effect on the thermo-oxidative degradation of nanocomposites. The existence of poly(l-lactic acid)-grafted SiO₂ nanoparticles dramatically improved the thermo-oxidative stability of poly(l-lactic acid). Compared with that of pure poly(l-lactic acid), T _g, T _c, and T _m of nanocomposites varied slightly.     

Synthesis of syndiotactic polystyrene-graft-poly(ethylene glycol) copolymer by photochemical reaction

Syndiotactic polystyrene-graft-poly(ethylene glycol) (sPS-g-PEG) copolymer was prepared by photochemical attachment of poly(ethylene glycol) chains to the benzoylated syndiotactic polystyrene (BesPS) backbone. BesPS, a functional polymer bearing benzophenone moiety, was prepared in a heterogeneous process through Friedel-Crafts acylation reaction using benzoyl chloride as benzoylating agent. This substrate was then dispersed in o-dichlorobenzene at room temperature and mixed with poly(ethylene glycol) , which was reacted with the benzophenone moieties by illumination with UV light (λ > 340 nm). As a result of the photochemical reaction, the hydrophilic poly(ethylene glycol) was chemically attached to the hydrophobic syndiotactic polystyrene backbone. The resultant copolymer was characterized by FT-IR, NMR, and X-ray photoelectron spectroscopy. In addition, the thermal properties of graft copolymers were also studied by means of DSC.     

Effects of phenyl-based pendent groups on helical conformation of poly(<Emphasis Type="Italic">N</Emphasis>-propargylamides)

Five achiral N-propargylamide monomers with various phenyl-based substitutents, [HC ≡ CCH₂NHCOR, R for M1: C₆H₄CH₃; M2: C₆H₄CH₂CH₃; M3: C₆H₄(CH₂)₂CH₃; M4: C₆H₄(CH₂)₃CH₃; M5: C₆H₄C(CH₃)₃], were synthesized and polymerized with a rhodium catalyst, (nbd)Rh⁺B^-(C₆H₅)₄ (nbd = 2,5-norbornadiene). The corresponding five homopolymers were obtained in high yields of 90–95% and with moderate molecular weights (M _n ≥ 10 000). All the polymers possessed high cis contents (≥95%). Poly(1)–poly(3) exhibited UV-vis absorption peaks at approx. 350 nm, which indicates that the three polymers formed helical conformations, while no UV-vis absorption peaks could be observed in poly(4) and poly(5) in the wavelength range of 320–500 nm, demonstrating that these two polymers could not adopt helical structures under the examined conditions. To confirm the helical structures formed in poly(1)–poly(3), a chiral monomer, M6, was utilized to copolymerize with M2, which was used as the representative for M1−M3. M6 was utilized since its polymer could form stable helices under suited conditions. The resulting copolymers exhibited remarkable CD effects, however, the maximum wavelength in the copolymers varied remarkably, mainly depending on the composition of the copolymers. It is concluded that in the formation of ordered helical conformations, the substitutents of varied bulk led to different steric repulsion and varied synergic effects among the neighboring pendent groups.     

Asymmetric polymerization of N-substituted maleimides with organolithium — bisoxazolines complex

Asymmetric anionic polymerizations of achiral N-substituted maleimide (RMI) (N-cyclohexyl (CHMI), N-phenyl (PhMI), N-tert-butyl (TBMI)) by n-butyllithium (n-BuLi) or fluorenyllithium (FlLi) complexes of chiral bisoxazoline derivatives in toluene gave optically active polymers ([α]²⁵ ₄₃₅− 2.9° to − 8.2°). The polymers prerared with initiator of n-BuLi – 2,2′-bis(4,4′-isopropyl-,3-oxazoline) showed negative specific rotations (poly(RMI), [α]²⁵ ₄₃₅− 5.8° to − 8.2°) which were greater than those ([α]²⁵ ₄₃₅− 2.9° to − 5.9°) with other chiral 2,2′-bis(4,4′-alkyl-1,3-oxazoline) (alkyl group = iso-butyl and benzyl). Received: 29 July 1997/Revised: 27 August 1997/Accepted: 1 September 1997     

Synthesis of poly(ɛ-caprolactone-b-isobutylene) diblock copolymer and poly(ɛ-caprolactone-b-isobutylene-b-ɛ-caprolactone) triblock copolymer

Summary Poly(isobutylene-b-ɛ-caprolactone) diblock and poly(ɛ-caprolactone-b-isobutylene-b-ɛ-caprolactone) triblock copolymers have been prepared and characterized. The synthesis involved the living cationic polymerization of IB, followed by capping with 1,1-diphenylethylene or 1,1-p-ditolylethylene and end-quenching with 1-methoxy-1-trimethylsiloxy-2-methyl-propene to yield methoxycarbonyl functional PIB. Hydroxyl end-functional PIB polymers were quantitatively obtained by the subsequent reduction of methoxycarbonyl end-functional PIB with LiAlH₄. The structure of hydroxyl end-functional PIBs was confirmed by ¹H NMR and IR spectroscopy. Poly(ɛ-caprolactone-b-isobutylene) diblock copolymers and poly(ɛ-caprolactone-b-isobutylene-b-ɛ-caprolactone) triblock copolymers were synthesized by the living cationic ring-opening polymerization of ɛ-caprolactone with hydroxyl end-functional PIB as macroinitiator in the presence of HCl•Et₂O via the “activated monomer mechanism”. The block copolymers exhibited close to theoretical M_ns and narrow molecular weight distributions. Received: 30 January 2002/Revised version: 19 February 2002/ Accepted: 19 February 2002     

Radical polymerization of (trimethylsilylethynyl)styrene and thermal properties of polystyrene with ethynyl group

The radical polymerizations of 2-, 3-, and 4-(trimethylsilylethynyl)styrenes (1 a – c) and copolymerizations of 1 a – c (M₁) with styrene (M₂) have been studied. Copolymerization parameters were determined as r₁ = 1.22 and r₂ = 0.54 for 1 a, ₁ = 1.10 and r₂ = 0.90 for 1 b, and r₁ = 1.42 and r₂ = 0.38 for 1 c. The deprotection of the trimethylsilyl groups in poly[(trimethylsilylethynyl)styrene] (2 a – c) and poly[(trimethylsilylethynyl)styrene-co-styrene] (4 a – c) using (C₄H₉)₄NF smoothly proceeded to yield poly(ethynylstyrene) (3 a – c) and poly(ethynylstyrene-co-styrene) (5 a – c), respectively, which underwent curing reactions at elevated temperature to form crosslinking polystyrenes. Received: 31 March 1997/Revised: 2 June 1997/Accepted: 3 June 1997     

Synthesis and characterization of ethylene-xylene-based polysulfide block-copolymers using the interfacial polymerization method

Copolymers of linear and aromatic polysulfide blocks are synthesized using interfacial polymerization of dichloro-xylene-based aromatic and ethylene-dichloride-based non-aromatic organic monomers. Synthesized copolymers consist of poly(ethylene sulfide) as well as ploy (xylene sulfide) blocks. Fascinating properties of linear and aromatic polysulfide species are gathered in the structure of synthesized polysulfide copolymers. Ethylene dichloride and α,α′-dichloro-p-xylene are used as the non-aromatic and aromatic organic monomers, respectively. To investigate the influences of sulfur contents in the backbone of the polymer on the thermal stability of synthesized copolymers, poly(ethylene-xylene disulfide) (PEXDS), poly(ethylene-xylene trisulfide) (PEXTRS) and poly(ethylene-xylene tetrasulfide) (PEXTS) copolymers are synthesized using, respectively, sodium disulfide, sodium trisulfide and sodium tetrasulfide, as aqueous monomers. Compared to both linear and nonlinear homopolymers, synthesized copolymers exhibit improved thermal stability. Moreover, the thermal degradation temperatures of synthesized copolymers improve by decreasing the number of sulfur atoms in the backbone of copolymers. These results reveal that thermal degradation of polysulfide copolymers can be tailored by controlling the polysulfide chain’s sulfur contents. Structural characteristics of synthesized polysulfide copolymers are also investigated using Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy and X-ray diffraction analysis.     

On the Contributions to the Materials Science Aspects of Phosphazene Chemistry by Professor Christopher W. Allen: The One-Pot Synthesis of Linear Polyphosphazenes

Summary The wide range of applications for the phosphazene compounds has stimulated a major research effort involving several industrial, academic, and national laboratories over the past 40 years. One of Professor Allen’s research areas was to establish fundamental synthetic methods for the commercial preparation of phosphazene polymers, investigate their properties, and develop useful products. In this paper we review some of the materials science aspects of Professor Allen’s research including recent advances on the preparation and polymerization of Cl₃PNP(O)Cl₂. This work, in particular, has led to a route for the “one-pot” synthesis of stable linear poly(organophosphazenes) as demonstrated through the formation of poly[bis-(2-methoxyethoxyethoxy)phosphazene] (MEEP) and a phosphazene heteropolymer (HPP) containing a balance of hydrophilic and hydrophobic components that allow for control and molecular affinities. The authors would like to dedicate this paper to Professor Christopher W. Allen in honor of his significant contributions to phosphazene chemistry. Furthermore, the authors thank him for his counsel and friendship in the development of the “one pot” phosphazene synthesis discussed in this paper.     

Easy one-pot method to control the morphology of polyethylene/carbon nanotube nanocomposites using metallocene catalysts

An easy one pot method is demonstrated for the controlled periodical surface coating of polyethylene over multiwalled carbon nanotubes (MWCNT) by insitu polymerization of ethylene using highly active metallocene catalysts (Cp₂ZrCl₂ and Cp₂TiCl₂) in combination with methylalumoxane. The crystallinity of the nanocomposite was increased and its morphology could be tuned from “sausage” like to “shish-kebab” in the presence of CNT depending on the experimental condition and choice of metal atom.     

Thermal characteristics of high-strength and thermostable aromatic fibres

The thermal characteristics of para-aramid, polyoxadiazole, and polyimide fibres were comparatively investigated by dynamic thermogravimetric analysis, differential scanning calorimetry, and thermomechanical analysis. It was shown that thermooxidative degradation of these types of fibres began at 400–450 °C and intensified at higher temperatures. The fibres investigated are characterized by size stability up to the initial temperature of thermooxidative processes (400–450 °C). With respect to thermal stability, these fibres are in the following order: polyimide > polyoxadiazole, and carbocyclic para-aramid fibres. The correlation of the “hydrogen index” I_H and “aromaticity index” I_Ar for thermostable fibres with their thermal stability was demonstrated. Translated from Khimicheskie Volokna, No. 3, pp. 72–74, May–June, 2008.     

Lipase Catalyzed Synthesis and Thermal Properties of Poly(dimethylsiloxane)–Poly(ethylene glycol) Amphiphilic Block Copolymers

Resin immobilized lipase B from Candida antarctica (CALB) was used to catalyze the condensation polymerization of two difuctional siloxane and poly(ethylene glycol) systems. In the first system, 1,3-bis(3-carboxypropyl)tetramethyldisiloxane was reacted with poly(ethylene glycol) (PEG having a number-average molecular weight, M_n = 400, 1000 and 3400 g mol⁻¹, respectively). In the second system, α,ω-(dihydroxy alkyl) terminated poly(dimethylsiloxane) (HAT-PDMS, M_n = 2500 g mol⁻¹) was reacted with α,ω-(diacid) terminated poly(ethylene glycol) (PEG, M_n = 600 g mol⁻¹). All the reactions were carried out in the bulk (without use of solvent) at 80 °C and under reduced pressure (500 mmHg vacuum gauge). The progress of the polyesterification reactions was monitored by analyzing the samples collected at various time intervals using FTIR and GPC. The thermal properties of the copolymers were characterized by DSC and TGA. In particular, the effect of the chain length of the PEG block on the molar mass build up and on the thermal stability of the copolymers was also studied. The thermal stability of the enzymatically synthesized copolymers was found to increase with increased dimethylsiloxane content in the copolymers.     

Detailed microstructure and concentration of the chlorinated n-butyl branches in poly(vinyl chloride)

Summary The -¹³C NMR spectra of reductively dehalogenated samples of poly(vinyl chloride) (PVC) have provided conclusive evidence for the presence of 2,4-dichloron-butyl branches in the original polymer. These branches are contained in a-CHCl-CH₂-CCl(CH₂-CHCl-CH₂-CH₂Cl)-CH₂-CHCl-arrangement which is formed as the result of a radical backbiting reaction. For a series of polymers prepared in conventional ways at temperatures of 43 to 100 °C, the 2,4-dichloro-n-butyl branch concentration ranges from about 0.6 to 1.0/(1000 C).     

Synthesis and thermal characterization of poly(ester-ether urethane)s based on PHB and PCL-PEG-PCL blocks

A series of block poly(ester-ether urethane)s, poly(PHB/PCL-PEG-PCL), based on poly(3-hydroxybutyrate) (PHB-diol), as hard segments, and poly(ε-caprolactone)-b-poly(ethylene glycol)-b-poly(ε-caprolactone), (PCL-PEG-PCL) triblock copolydiol, as soft segments, were prepared using 1,6-hexamethylene diisocyanate (HDI), as non-toxic connecting agent. Polyurethanes block copolymer was synthesized from bacterial PHB and PCL-PEG-PCL blocks. The chemical structure and molecular weights of polymers prepared were characterized by FTIR, ¹H NMR and GPC. The effect of chemical structure on the thermal and mechanical properties was studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and tensile testing. The DSC results revealed that poly(PHB/PCL-PEG-PCL) urethanes are semi-crystalline with two crystallizable PHB and PCL-PEG-PCL blocks. The thermal stability of the urethanes is less than neat PHB. The results of tensile testing showed that the extensibility of PHB is largely enhanced by the incorporation of PCL-PEG-PCL soft segments. Activation energy E _a , as a kinetic parameter of thermal decomposition, was estimated by each of the Ozawa and Kissinger methods. Close values of activation energy were obtained by both methods. The swelling behaviour of the copolymers was also investigated.     

Copolymerization of 4-cyanophenyl acrylate with methyl methacrylate: synthesis, characterization and determination of monomer reactivity ratios

A novel acrylic monomer, 4-cyanophenyl acrylate (CPA) was synthesized by reacting 4-cyanophenol dissolved in methyl ethyl ketone with acryloyl chloride in the presence of triethylamine as a catalyst. Copolymers of CPA with methyl methacrylate (MMA) at different composition was prepared by free radical solution polymerization at 70 ± 1 °C using benzoyl peroxide as an initiator. The copolymers were characterized by FT-IR, ¹H-NMR and ¹³C-NMR spectroscopic techniques. The solubility tests were checked in various polar and non polar solvents. The molecular weight and polydispersity indices of the copolymers were estimated by using gel permeation chromatography. The glass transition temperature of the copolymers increases with increases MMA content. The thermal stability of the copolymer increases with increases in mole fraction of CPA content in the copolymer. The copolymer composition was determined by using ¹H-NMR spectra. The monomer reactivity ratios determined by the application of linearization methods such Fineman–Ross (r ₁ = 0.535, r ₂ = 0. 0.632), Kelen–Tudos (r ₁ = 0.422, r ₂ = 0.665) and extended Kelen–Tudos methods (r ₁ = 0.506, r ₂ = 0. 0.695).     

Preparation,characterization and degradation characteristics of polyanhydrides containing poly(ethylene glycol)

Poly(ethylene glycol) (PEG) segments were introduced into a polyanhydride main chain by copolymerization of terminal-carboxylated poly(ethylene glycol) with diacidic monomers (sebacic acid and trimellitylimidoglycine). IR and ¹H NMR spectroscopy confirmed the copolymer structures. DSC analysis showed that these polyanhydrides have low T_g and low crystallinity. In vitro degradation tests indicated that introducing PEG segments accelerated the degradation rate of these polymers and the degradation duration could be manipulated from 3 days to 3 weeks. The pH of the environment caused by the polymer degradation was lower than 5.0; therefore, the polyanhydrides could be used as components of a newly designed pulsed-release device for peptide and protein delivery. © 1999 Society of Chemical Industry     

Concurrent physical aging and degradation of crosslinked coating systems in accelerated weathering

Coating degradation is a combination of both chemical and physical processes; however, physical processes have not received much attention. Physical aging has a non-negligible effect on coatings’ mechanical properties and permeability etc. through the densification that continues as a polymer approaches its thermodynamic equilibrium below the glass transition temperature, T _g. Observations in recent work showed that physical aging affects coatings’ mechanical property response during accelerated weathering and is, itself, affected by the associated chemical degradation. Two crosslinked coating systems were studied in order to compare different chemical compositions, their T _g, and their thermal response in accelerated weathering. During thermal cycling, physical aging measured by enthalpy recovery exhibited different trends in the two coatings. A “rejuvenation” mechanism was observed in the coating with a T _g between the top and bottom limits of the exposure cycle; continued aging was observed for the coating with a high T _g. Stress relaxation tests detected aging and “memory” behavior over periods comparable with accelerated weathering cycles. Both thermal and mechanical responses changed in complicated and different ways as the coatings degraded. Different degrees of coating thickness reduction were observed in both isothermal relaxation and degradation. When various coatings are evaluated, simply judging their performance under the same weathering environment is not reliable since polymer relaxation behavior depends on the relationship between the exposure temperatures and the T _g of each polymer. This paper was awarded First Place in the 2007 Gordon Awards technical paper competition, held as part of the FutureCoat! conference, sponsored by the Federation of Societies for Coatings Technology, in Toronto, ON, Canada, on October 3–5, 2007.     

Synthesis and properties of highly branched poly(urethane–imide) via A2 + B3 approach

A series of highly branched poly(urethane–imide) (HBPUI) were synthesized via A₂ + B₃ approach using isophorone diisocyante (IPDI), polycarbonatediol (PCDL), 3,3′,4,4′-Benzophen-onetetracarboxylic dianhydride (BTDA), and poly(oxyalkylene) triamine (ATA) as materials. The structure of the products was characterized by FT-IR and ¹³C-NMR. The molecular weights were characterized by gel permeation chromatograph (GPC). The solution viscosity, thermal, and mechanical properties were measured by rotational rheometer, differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), tensile tests, and dynamic mechanical analysis (DMA), respectively. The HBPUI showed lower viscosity than that of linear poly(urethane–imide) (LPUI), nevertheless T _g of HBPUI was higher than that of LPUI. TGA indicated that the thermal degradation of poly(urethane–imide) occurred above 300 °C, which was higher than conventional polyurethane. The tensile strength of HBPUI was obviously improved by increasing the content of BTDA and the molar ratio of [A₂]/[B₃]. The effects of the content of BTDA and the molar ratio of [A₂]/[B₃] on the storage modulus of the polymers were also studied.     

Effects of Thickness,Deformation Rate and Energy Partitioning on the Work of Fracture Parameters of uPVC Films

Summary Unplasticised poly(vinyl chloride) (uPVC) films have been tested using the essential work of fracture (EWF) method. Influence of loading rate and film thickness on the tensile properties and work of fracture parameters was evaluated. In addition, energy partition analyses were carried out applying two different approaches (“yielding” and “initiation”), which differ in the treatment of the stored elastic energy. Results showed less effect of the film thickness and deformation rate (<l00 mm/min) on the EWF terms. On the other hand, the specific essential work of fracture (w _e) at high load rate (1.2 m/s) approached the yielding-related term (w _e,y) obtained at static loading rates (<l00 mm/min). Received: 16 July 2002/Revised version: 31 March 2003/Accepted: 29 April 2003 Correspondence to M. Ll. Maspoch