Crystallinity of poly(tetramethyl-p-silphenylenesiloxane) and (tetramethyl-p-silphenylenesiloxane)-(dimethyl siloxane) copolymers

An X-ray method is described for determining the degree of crystallinity of poly(tetramethyl-p-silphenylenesiloxane) (TMPS) homopolymers and copolymers of tetramethyl-p-silphenylenesiloxane (TMPS—DMS) of wt % TMPS—DMS ratio of $\text{48}\text{52}$, $\text{65}\text{35}$ and $\text{85}\text{15}$, respectively. The specimens had an average DMS block size of 30 monomeric units. Polymers ranging from 100 wt % TMPS to approximately 50 wt % of TMPS were studied. Over this composition range the crystallinities varied from 75 to 30% approximately. Crystallinity determinations were also made using a density gradient column and differential scanning calorimetric methods for comparison purposes to check the validity of the X-ray procedure described herein. The results of the three techniques were in satisfactory agreement although some refinements are still in order.     

Thermal properties of poly(tetramethyl-p-silphenylene siloxane) and (tetramethyl-p-silphenylene siloxane-dimethyl siloxane) copolymers

Some physical properties of poly(tetramethyl-p-silphenylene siloxane) homopolymer and random block copolymers of tetramethyl-p-silphenylene siloxane-dimethyl siloxane have been determined and correlated with polymer structure. Differential scanning calorimetry (d.s.c.), differential thermal analysis (d.t.a.), density gradient column measurements and optical hot stage melting point determination and diluent techniques were used. The thermodynamic melting temperature of the homopolymer was estimated to be 160°C and its heat of fusion, ΔH_u, found to be 54.4 J/g (13 cal/g or 2710 cal/mol of monomer repeat units). Its limiting glass transition temperature, T_g, was ?20°C. T_g of the copolymer was found to vary almost monotonically with increasing dimethyl siloxane (DMS) content ranging from ?20° (0% DMS) to just above ?123°C, for pure DMS polymer. The copolymer melting temperature was found to increase as the fraction of the crystalline (hard) TMPS constituent was increased. Based upon copolymer theory and extrapolated melting point data, it was estimated that the block size of soft DMS component in the copolymer most probably consists of twelve monomer units distributed amongst TMPS sequences of varying length.     

Studies of the chemical degradation of polysiloxanes by hydrofluoric acid: (2). Poly(tetramethyl-p-silphenylene siloxane-dimethyl siloxane) block copolymers

Block copolymers of tetramethyl-p-silphenylene siloxane (TMPS) and dimethyl siloxane (DMS) have been selectively degraded with hydrofluoric acid solution. The HF preferentially attacks the SiO bonds, particularly those of the non-crystalline DMS component. The copolymers which were precipitated by the self-seeding technique were etched with 48% HF at 30°C (established as suitable conditions for our work). The crystallinity change on etching these is largest for the sample of lowest TMPS content; it varies from about 20% at zero etching time to 98% after a period of 40 h approximately. The molecular weight, small-angle X-ray period, melting temperature, heat of fusion and degree of crystallinity were all determined as a function of etching time. The correlated results were found to be consistent with a two-phase model in which the DMS component was essentially excluded from the TMPS crystalline core. Some predictions, based on copolymer theories, were found to be consistent with the analysis of the experimental observations.     

Thermal and mechanical properties of tetramethyl-p-silphenylenesiloxanedimethylsiloxane block copolymer

Several kinds of $\text{tetramethyl}\text{-p-}\text{silphenylenesiloxane}\text{dimethylsiloxane}$ (TMPS/DMS) block copolymers having various compositions and segment lengths were synthesized by the polycondensation of p-bis(dimethylhydroxysilyl)benzene and silanol-terminated DMS oligomers of different degrees of polymerization, which were 19, 43, 300, 380 and 540 DMS monomer units. The compositions ranged from TMPS/DMS wt% ratio of 100/0 to 24/76. For these copolymers, differential scanning calorimetry was carried out to determine the melting temperatures, the heat of fusion and the crystallinities. The melting temperatures and the crystallinities of the block copolymers were found to decrease as DMS contents were increased from 11 to 76 wt% and as DMS segment lengths were decreased from 540 to 19. The crystalline parts of TMPS segment would be increased according to the long TMPS sequences which were obtained from the copolymerizations by using DMS oligomers with high degrees of polymerization such as 300, 380 and 540. The stress-strain behaviour and the dynamic mechanical behaviour were also investigated for these copolymers. The tensile strength was decreased and the percentage elongation was increased with increasing DMS content and segment length. In the case of the copolymers for which the DMS contents remained constant at 26 wt%, two major transitions were observed at around ?120° and ?10°C for the copolymers having DMS block sizes of 300, 380 and 540. But for the copolymers having those of 19 and 43 the two transitions merged together at ?50°C. The relaxations at ?120°C corresponding to the glass transition of DMS component and those at ?10°C are due to the amorphous TMPS phase which is separated from the DMS phase owing to the longer sequence length. The relaxation observed around ?50°C is due to the shorter sequence length of TMPS in the main chain plus the presence of more flexible DMS component. It may be suggested that the long sequence length causes large domains of hard and soft phases which consist of TMPS and DMS blocks respectively.     

Crystallization kinetics and morphology of polymer blends of poly(tetramethyl-p-silphenylene siloxane) fractions

The crystallization behaviour of polymer blends or mixtures of the same system has been studied over a wide range of molecular weight and crystallization temperatures. Blends were made by mixing fractionated polymer samples. The spherulitic growth in these mixtures is dependent upon the number-average molecular weight of the system at the shorter chain lengths, but then becomes insensitive to molecular weight values when about 10⁵ to 10⁶ are reached. The growth rate kinetics of mixtures can be described by a kinetic model used for fractionated poly(tetramethyl-p-silphenylene siloxane) (TMPS) polymers. The crystal surface energies deduced from these rate data are molecular weight dependent as are the pre-exponential and transport factors in the rate equation. These parameters are explained in terms of the crystallite morphology. Mixtures (as well as fractions themselves) of all polymer fractions ranging from the monomer to the highest molecular weight (10⁶ approximately) have similar morphological features and form negatively birefringent spherulites. Although molecular weight segregation appears to play an important role in crystallization at comparatively small undercoolings, its influence seems to be minimal at large undercoolings (close to or below the growth rate maxima). Very low molecular weight additives significantly affect the overall crystallization kinetics. Compared to the undiluted sample, mixtures so formed have lower observed melting points and glass transition temperatures. Rates of crystallization are generally facilitated by the diluent with the peak in the growth rate being displaced to lower temperatures. The growth rates for diluted over the undiluted polymer at similar undercoolings are usually larger. At high molecular weights the log of the spherulitic growth rate varies as $\text{M}{}^{\mathrm{<mtext>?1</mtext><mtext>2</mtext>}}{}_{\mathrm{n}}$, over a considerable range, but at low molecular weight values the rate depends more strongly on M_n approaching a limit of M^?1.2_n as the monomeric state is approached.     

Characterization of siloxane copolymers by solution O NMR spectroscopy

Solution ¹⁷O NMR spectroscopy was used for structure elucidation of siloxane copolymers with the natural abundance of ¹⁷O, i.e. without any enrichment prior to spectroscopy. Homo, co, and terpolymers, as well as linear chains, cyclic oligomers, and graft polymers were investigated. All relevant chemical shifts and corresponding linewidths were reported for siloxane polymers substituted with methyl, phenyl, 3-cyanopropyl, 2-cyanoethyl, 3,3,3-trifluoropropyl, and polyethylene glycol ligands and with the backbone stiffening groups tetramethyl-p-silphenylene, tetramethyl-p,p′-sildiphenylene ether, and m-carborane. An increment system was extended to predict the chemical shifts of substituted siloxane copolymers. ¹⁷O NMR spectroscopy of polysiloxanes provided information concerning their chemical composition, average molecular weight, and microstructure.     

Syntheses and properties of tetramethyl-p-silphenylenesiloxanealkenylmethyl-siloxane copolymers and their derivatives

$\text{Tetramethyl}\text{-p-}\text{silphenylenesiloxane}\text{alkenylmethylsiloxane}$ (TMPS/AMS) copolymers were snyhtesized from p-bis-dimethylhydroxysilylbenzene and a series of alkenylmethyldichlorosilanes as the starting materials. The alkenyl groups of the copolymers were vinyl, allyl, 2-(3-cyclohexenyl)ethyl, methacryloxypropyl and 3-bicycloheptenyl groups. The composition ranged from TMPS/AMS mole% ratio of $\text{92}\text{8}$ to $\text{83}\text{17}$ and the molecular weights were in the range 10⁴ to 10⁵. These copolymers were confirmed to have two compositions, one a certain length of TMPS segment and the other an AMS monomer unit, and that they could form films on the basis of the crystallization character of the TMPS segment. The melting temperatures of these copolymers decreased as the TMPS mole content decreased and as the alkenyl group contents were increased. The epoxidation reactions of these copolymers with m-chloroperbenzoic acid were carried out and the proportions of conversions of the alkenyl groups into epoxy groups varied depending upon the types of alkenyl groups involved. Cyclic olefin groups such as the 2-(3-cyclohexenyl)ethyl or the 3-bicycloheptenyl group were more easily epoxidized than the vinyl or allyl groups. The TMPS/dimethylsiloxane (DMS) graft copolymer could also be synthesized by the reaction of TMPS/vinylmethylsiloxane copolymer with dimethylhydrosilyl-terminated DMS oligomer in the presence of chloroplatinic acid acting as the catalyst.     

Structural studies of polysiloxanes: crystal structure and fold conformation of poly(tetramethyl-p-silphenylene siloxane)

The crystal structure of poly(tetramethyl-p-silphenylene siloxane) has been determined using X-ray diffraction data from drawn fibres. The unit cell is tetragonal with dimensions a = b = 0.902 nm and c (fibre axis) = 1.543 nm. The space group is P4₃2₁2 and the unit cell contains four monomer units. Each chain adopts a 2₁ helical conformation so that two chains run through the unit cell. The crystallographic asymmetric portion of the molecule is one half of a monomer unit with the oxygen atom and the centre of mass of the phenyl group at special positions. The two halves of a monomer are symmetry related by a diad axis perpendicular to the fibre axis. In addition, this polymer [poly (TMPS)] can crystallize in the form of chain-folded lamellae, and detailed models for the fold structure have been examined using computer model building techniques. A unique conformational model was found for adjacent re-entry fold models and a stereochemically acceptable fold can be obtained using a single residue. The only acceptable models encompassing two or three residues in the fold turn out to be only small perturbations of the single residue adjacent re-entry fold.     

Synthesis of tetramethyl-p-silphenylenesiloxanedimethylsiloxane triblock copolymer by employing living anionic polymerization

Dimethylsiloxane-tetramethyl-p-silphenylenesiloxane-dimethylsiloxane (DMS-TMPS-DMS) triblock copolymer was synthesized by employing living anionic polymerization of hexamethylcyclotrisiloxane (D₃). Two synthetic methods were carried out for the polymerization. One of those methods was the anionic polymerization of D₃ initiated at the silanolate anion which was prepared from the terminal hydroxyl group of silanol-terminated TMPS prepolymer by reaction with n-butyllithium (method 1). The other was the coupling reaction of vinyl-terminated TMPS prepolymer with hydrosilyl-terminated DMS prepolymer obtained from the anionic polymerization of D₃ by using diphenylmethylsilanolate anion as initiator (method 2). In method 1, DMS contents of the copolymers ranged from 25.8 to 72.5 wt% and the values agreed with the ratio of D₃ to TMPS prepolymer. The weight-average molecular weights ranged from 1.36×10⁴ to 19.4×10⁴ and were close to the predicted values calculated from the $\text{M}\text{?}{}_{\mathrm{v}}$ of the TMPS prepolymer and the amount of D₃ added. In the case of method 2, weight-average molecular weights ranged from 19.5×10⁴ to 24.2×10⁴. The high molecular weight copolymer could thus be obtained by method 2. Intrinsic viscosity values of the triblock copolymers agreed with calculated values obtained by considering the copolymer as a binary mixture of these homopolymers. Differential scanning calorimetry and thermogravimetry were carried out on the triblock copolymers. The equilibrium melting temperatures of each of the copolymers were very close to that of poly-TMPS (160°C). The glass transition temperature and heat of fusion were decreased as the DMS content was increased. The thermogravimetric curves for the copolymers indicated that the thermal stability of the triblock copolymer was intermediate between the DMS and TMPS homopolymers.     

Effect of composition on molecular alignment in polyethylene terephthalate copolymers

In this study molecular alignment in copolymers of polyethylene terephthalate (PET) and p-hydroxybenzoic acid (PHB) was examined by means of differential radial distribution function (DRDF) analysis of wide angle X-ray scattering data. The study was carried out using two representative copolymers with the PHB content of 30 and 60 mol%. The DRDF curves for the amorphous and the partially crystalline samples of these copolymers showed periodic intermolecular peaks up to various radial distances. The appearance of these peaks at $\text{～5}\text{A}\text{?}$ periodicity suggested the existence of more-or-less parallel chain segments in the copolymers. The extent of the lateral molecular organization was $\text{～15}\text{and}\text{30}\text{A}\text{?}$ for the amorphous copolymers containing 30 and 60 mol% PHB, respectively. A substantial structural difference was therefore shown for the copolymers in this composition range. The DRDF curve for the amorphous copolymer with 30 mol% PHB was found to be very similar to that for the previously reported glassy PET with 0 mol% PHB, indicating that the two materials had almost the same intermolecular structure. The structural information revealed by these DRDF results was in agreement with the various property changes caused by varying PHB contents of the copolymers.     

Improved synthetic method and conformation studies of polymers and copolymers of l-β-3,4-dihydroxyphenyl-α-alanine with l-glutamic acid

Eight different copolymers of l-β-3,4-dihydroxyphenyl-α-alanine (l-Dopa) and l-glutamic acid with high degrees of polymerization have been synthesized by the treatment of a series of $\text{copoly}\text{(O,O′-}\text{dimethyl-}\text{l}\text{-Dopa}$, γ-benzyl-l-glutamate) with boron tribromide in chloroform. The conformation of poly(l-Dopa) has been established to be a right-handed helix in trimethyl phosphate on the basis of the following observations. The [θ]₂₂₂ and b₀ values of the copolymers were almost linear with composition in trimethyl phosphate. The linear relationship between the rotation properties and composition indicates that poly(l-Dopa) has the same helical sense as that of poly(l-glutamic acid) which is a right-handed α-helix.     

Synthesis and characterization of poly(ester ether siloxane)s

A series of novel thermoplastic elastomers based on ABA‐type triblock prepolymers, poly[(propylene oxide)–(dimethylsiloxane)–(propylene oxide)] (PPO‐PDMS‐PPO), as the soft segments, and poly(butylene terephthalate) (PBT), as the hard segments, was synthesized by catalyzed two‐step melt transesterification of dimethyl terephthalate (DMT) with 1,4‐butanediol (BD) and α,ω‐dihydroxy‐(PPO‐PDMS‐PPO) (M?_n = 2930 g mol^?1). Several copolymers with a content of hard PBT segments between 40 and 60 mass% and a constant length of the soft PPO‐PDMS‐PPO segments were prepared. The siloxane‐containing triblock prepolymer with hydrophilic terminal PPO blocks was used to improve the compatibility between the polar comonomers, i.e. DMT and BD, and the non‐polar PDMS segments. The structure and composition of the copolymers were examined using ¹H NMR spectroscopy, while the effectiveness of the incorporation of α,ω‐dihydroxy‐(PPO‐PDMS‐PPO) prepolymer into the copolyester chains was controlled by chloroform extraction. The effect of the structure and composition of the copolymers on the transition temperatures (T_m and T_g) and the thermal and thermo‐oxidative degradation stability, as well as on the degree of crystallinity, and some rheological properties, were studied. Copyright © 2006 Society of Chemical Industry     

Crystallographic changes characterizing the Curie transition in three ferroelectric copolymers of vinylidene fluoride and trifluoroethylene: 2. Oriented or poled samples

The effects of uniaxial drawing or poling on the structural changes involved in the ferroelectric-to-paraelectric phase transition in copolymers of vinylidene fluoride and trifluoroethylene were examined and compared to the behaviour of as-crystallized films. The compositions studied were $\text{65}\text{35}$, $\text{73}\text{27}$ and $\text{78}\text{22}\text{mol}\text{\%}$ vinylidene fluoride/trifluoroethylene, all of which crystallize from the melt with a molecular conformation and packing analogous to those of the common piezoelectric β-phase of poly(vinylidene fluoride). Contrary to the previously described behaviour of a $\text{52}\text{48}\text{mol}\text{\%}$ copolymer, orientation did not induce any significant changes in the structure of these copolymers or in its variation with temperature, primarily because these already crystallize directly from the melt in well-ordered, compact unit cells. On the other hand, electrical poling caused the all-trans chains of the ferroelectric phase to be packed more compactly and to survive to higher temperatures, thus shifting the Curie transition closer to the melting points of these copolymers. As a result, competition from melting interfered with the later stages of this solid-state transformation in the $\text{73}\text{27}\text{mol}\text{\%}$ composition, and aborted it at a very early point in the $\text{78}\text{22}\text{mol}\text{\%}$ samples. The Curie temperature was found to exhibit hysteresis between heating and cooling parts of the thermal cycle, to extend over a broad range of temperatures, and to involve intramolecular changes to the same disordered conformation found in melt-crystallized samples. Our results have allowed reasonable implications to be made concerning the existence and nature of a Curie transition in the piezoelectric β-phase of poly(vinylidene fluoride).     

Poly(2,2-dimethyltrimethylene carbonate)-block-poly(dimethylsiloxane)-block-poly(2,2-dimethyltrimethylene carbonate). Synthesis and thermal properties

Lithium salts of hydroxytelechelic poly(dimethylsiloxane) [poly-(DMS)] were used as initiators for the anionic ring-opening polymerization of 2,2-dimethyltrimethylene carbonate (DTC). Triblock copolymers were obtained in high yields. Complexation of the active site in DTC polymerization by the poly(DMS) chain leads to a decrease in polymerization rate. The thermal properties of the copolymers of different compositions were determined. Catalysed thermal degradation of the block copolymers leads to cyclic oligomers D_n and DTC upon ring-closing depolymerization.     

Morphology and properties of crystalline polyester-siloxane block copolymers

A new series of crystalline (AB)_n type multiblock copolymers based on crystalline poly(hexamethylene sebacate) (HMS) and amorphous poly(dimethylsiloxane) (DMS) has been prepared, and their solid state properties have been examined. The copolymers range from 0-69 wt percent DMS, and they crystallize in spherulitic textures when cast in films from solution or the melt. As the DMS concentration in the copolymers increases, the spherulite sizes decrease, but only a very small melting point depression is observed. Available evidence suggests extensive microphase separation in the bulk of the solid state. Surface characterization of the copolymers indicates that phase separation is also prevalent at the polymer-air interface. The block copolymers and polyblends have critical surface tensions of wetting very similar to DMS homopolymer.     

Non-aqueous polymer dispersions: dimensions of adsorbed AB block copolymers of polystyrene and poly(dimethyl siloxane) by small-angle neutron scattering

Poly(methyl methacrylate) and polystyrene particles stabilized in n-heptane, Freon 113 (1,1,2-trichloro-1,2,2-trifluoroethane) and silicone fluid by AB block copolymers of polystyrene and poly(dimethyl siloxane) have been studied using small angle neutron scattering. Particle sizes calculated from the scattering intensity are in reasonable agreement with particle diameters estimated from electron micrographs. The intensity of scattering from poly(methyl methacrylate) particles stabilized with copolymers containing A blocks prepared from perdeuterostyrene was much higher than from polystyrene particles stabilized with the same block copolymers. It is proposed that the polystyrene blocks are molecularly dispersed in polystyrene particles and cluster into domains in poly(methyl methacrylate) particles. Scattering arising from the poly(dimethyl siloxane) blocks has been detected but could not be simply interpreted.     

Differential refractometry and light scattering on nylon-6 and poly(methyl acrylate) in mixed solvents

Investigations have been made of solvent systems for potential use in characterizing nylon-6/poly (methyl acrylate) copolymers. To this end, measurements involving differential refractometry (at constant composition and also constant chemical potential of solvents) and light scattering have been conducted on solutions of nylon-6, poly(methyl acrylate) and a mixture of these two polymers. From refractometric and solubility considerations the most suitable solvents are binary mixtures of o-chlorophenol (o-CP) and 2, 2′, 3, 3′-tetrafluoropropanol. In particular, the binary solvent containing 73% (by volume) of o-CP yields the molecular weight of the nylon-6 constituent of the polymer mixture directly, since the light scattering from the other polymer constituent is thereby eliminated. Preferential adsorption of o-CP occurs to both polymers, the maximum extents corresponding to 1 mol $\text{o-}\text{CP}\text{1.4}$ segments nylon and 1 mol $\text{o-}\text{CP}\text{5.7}$ segments poly(methyl acrylate). This is attributed to a breakdown of intramolecular hydrogen-bonding in o-CP and subsequent formation of hydrogen bonds with the carbonyl groups in the polymers.     

LCST behaviour in blends of poly(vinylidene fluoride) and isotactic poly(ethyl methacrylate)

Blends of poly(vinylidene fluoride) (PVF₂) with isotactic, atactic or syndiotactic poly(ethyl methacrylate) (it-, at- or st-PEMA) were studied by calorimetry and light microscopy. The occurrence of single glass transitions over a broad composition, as well as the lowering of the crystallization temperature upon cooling from the melt, indicate a complete compatibility in the amorphous state in blends of PVF₂ with at- and st-PEMA up to high temperatures. With it-PEMA, however, phase separation took place when the temperature was raised, sugesting LCST behaviour. Cloud points appeared in the temperature range of 150–200°C, making this system suitable for phase separation studies. The occurrence of double glass transitions as well as double crystallization exotherms in some $\text{PVF}{}_2\text{it-PEMA}$ blends could be explained from the phase diagram and the slowness of phase mixing upon cooling.     

Studies of polymers and copolymers of O,O′-dicarbobenzoxy-l-β-3,4-dihydroxyphenyl-l-alanine with γ-benzyl-l- and d-glutamates

The synthesis of ten different copolymers of $\text{O,O′-}\text{dicarbobenzoxy-}\text{l}\text{-β-3,4,-}\text{dihydroxyphenyl}\text{-α-}\text{alanine}$ ($\text{O,O′-}\text{dicarbobenzoxy-}\text{l}\text{-Dopa}$) and γ-benzyl-l- and d-glutamates with degree of polymerization of 40–270 is described. It has been concluded that $\text{poly}\text{(O,O′-}\text{dicarbobenzoxy-}\text{l}\text{-Dopa}\text{)}$ and poly(γ-benzyl-l-glutamate) exist as helices with the opposite sense of twist in dioxane on the basis of the following observations. The copolymers of $\text{O,O′-}\text{dicarbobenzoxy-}\text{l}\text{-Dopa}$ with γ-benzyl-l-glutamate show a linear variation of circular dichroism properties with composition in methylene dichloride, whereas the copolymers do not in dioxane. The results for the copolymers with γ-benzyl-d-glutamate are the reverse in dioxane and methylene dichloride.     

The morphology of poly(aryl-ether-ether-ketone)

The morphology and related properties are described for the aromatic thermoplastic poly(aryl-ether-ether-ketone) (PEEK) [C₆H₄OC₆H₄OC₆H₄CO]_n. Topics covered include crystallinity, crystallization and melting behaviour, Iamellar thickness and spherulitic structure. The data are used to derive the following material parameters $\text{T1}{}_{\mathrm{<mtext>m</mtext>}}\text{= 395°}\text{C}$, σ_e = 49 erg cm^?2, σ_s = 38 erg cm^? and ΔH_F = 130 kJ kg^?1. PEEK is closely analogous to poly(ethylene terephthalate) in its crystallization behaviour except that the main transitions occur about 75°C higher.