Side-chain Crystal Research Articles

Formation and elasticity of layer networks

Layer network formation of poly(styrene-alt-n-octadecylmaleimide) in dodecane is investigated. It is shown that the polymer in the bulk exhibits lamellar structures of alternated alkane side-chain and main-chain layers. Adding dodecane into the polymer separates the polymer layers, increases the mean distance between the layers, and results in a less orderly layered structure. Crystallization of the alkane side chains introduces linkages to staple the layers together and builds up a layer network. Dimensional analysis predicts that the modulus (G) of the layer network is simply related to the long period (L) of the layer network through a cubic power law, i.e., G ∼ L−3. This prediction is indeed observed experimentally. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 667–677, 1999

Poly(p-phenylene)s with Mesogenic Side Groups: A Potential Class of NII Side Chain Liquid Crystalline Polymers?

The synthesis and characterization of a series of n-[(4-cyano-4‘-biphenylyl)oxy]alkyl-2,5-dichlorobenzoate monomers containing from n = 2 to 12 methylenic groups in the alkyl spacer and their Ni(0)-catalyzed polymerization to produce poly(p-phenylene)s (PPP) containing mesogenic side groups are described. The resulting side chain liquid crystalline polymers (SCLCPs) have both a rigid rodlike mesogenic backbone and rigid rodlike mesogenic side groups. All polymers display only a broad enantiotropic nematic phase and no side-chain crystallization. The isotropization temperature of these SCLCPs exhibits a steeper increase with the degree of polymerization (DP) than that observed for polymers with flexible or semiflexible backbones. Therefore, above plateau DPs their isotropization temperature is higher than that of polymers with flexible or semiflexible backbones, although it displays a classic odd−even dependence on the spacer length. These unusual trends may indicate that the director of the nematic phase ...

Ordering in self-organizing comb copolymer-like systems obtained by hydrogen bonding between charged or noncharged polymers and amphiphiles

Mesomorphic structures and order–disorder transitions in comb copolymer-like systems obtained by hydrogen bonding of noncharged or charged homopolymers with amphiphiles are discussed. The amphiphiles consist of attractive and repulsive moieties and the emphasis will be on the situation without an additional solvent phase. Poly(4-vinyl pyridine), i.e. P4VP, hydrogen bonded to stoichiometric amounts of pentadecylphenol (PDP) is one of the characteristic examples. Small angle X-ray scattering and dynamic rheology demonstrate that this system forms a disordered melt at temperatures above the order-disorder temperature ( T ODT), whereas for T< T ODT a lamellar microphase separated structure is observed. Further cooling renders side chain crystallization. This phase behavior can be tailored by adjusting the attraction and the repulsion between the amphiphile and the polymer. Repulsion can be increased by making the alkyl chain longer or by adding charges to the backbone. Both lead in general to a higher T ODT. Order-disorder transitions can occur even in polyelectrolyte-amphiphile complexes as is demonstrated by first fully complexing P4VP with toluene sulphonic acid (TSA) to form a polymeric salt P4VP(TSA) 1.0 which is further hydrogen bonded to PDP. The presented results offer guidelines to apply the concepts to other polymers as well, with an example mentioned in relation to polyamide 6.

Diffusion of hexane vapour in a doped poly(3-tetradecyl thiophene) film

A poly(3-tetradecyl thiophene) (PTDT) film was synthesized and doped with iodine. Hexane vapour was used as a diffusional probe to study the doped polymer at temperatures from 30.3 to 45.5°C. Based on the results from sorption and diffusion measurements, morphological changes related to the side-chain crystals or ordered domains of doped PTDT appeared to occur between 30.3 and 40.2°C. Doping caused decreases in the diffusivity and solubility of doped PTDT in comparison to non-doped PTDT. However, the estimated sorption of hexane by the side-chain of doped PTDT was larger than that of non-doped PTDT, probably due to an enlargement in the spacing created by doping.

Poly-α-Olefins from Polypropene to Poly-1-eicosene Made with Metallocene Catalysts

ABSTRACT Linear α-olefins from propene to 1-eicosene have been polymerized using a zirconocene catalyst and a hafnocene catalyst. The resulting isotactic polymers were characterized by NMR, GPC and DSC analysis. Compared to the zirconocene products the molecular weights of the poly-α-olefins made with the hafnocene catalyst were higher. The molecular weight distribution was found to be narrow as expected for metallocene polymers. DSC measurements showed that side chain crystallization occurs for the polymers from poly-1-decene to poly-1-eicosene.

Side-Chain Crystallization in Alkyl-Substituted Semiflexible Polymers

A series of comblike semiflexible polymers, in which the alkyl side chains were located nonsymmetrically on the ring, were synthesized by reacting hydroxypropylcellulose (HPC) with hexyl, octyl, dodecyl, and octadecyl isocyanates. Side-chain melting was observed in DSC experiments for polymers with 12 and 18 carbons in the pendant groups (C12HPC and C18HPC). Wide-angle X-ray (WAXS) studies indicated that the alkyl groups in C12HPC crystallized in a form similar to the βT crystal of hydrocarbons but multiple crystalline forms coexisted in C18HPC. However, reorganization of the alkyl side chains was observed as the polymers underwent thermal transitions. A better packing of the alkyl side chains could be induced by shearing the samples in the molten state followed immediately by slow cooling. Quenching and annealing studies suggested that side-chain crystallization and reorganization could influence the packing of the semiflexible backbone. The interplay between the main chain and the side chain in order development is described.

Liquid Crystalline Side Chain Polysiloxanes with 4-Cyano- and 4-Alkoxy-Stilbene Mesogenic Units

Side chain homo- and copolysiloxanes with 4-cyano- and 4-alkoxy-4′-stilbene mesogens, spaced apart from the backbone by oligomethylene segments of variable lengths, were synthesized via a hydrosilylation coupling reaction of five stilbene-containing α-olefins with four commercial poly(methylhydrosiloxane)s and poly(methyl-hydro-∞-dimethylsiloxane)s. Broad smectic phases were observed for the polysiloxanes with cyanostilbene mesogens, whereas the homologous with alkoxy-terminated stilbenes displayed only narrow mesophases in the high temperature range. Preliminary room tem-perature X-ray diffraction studies on mechanically oriented samples evidenced the occurrence of side chain crystallization, microphase separation and indicated the interdigitated smectic A nature of the mesophases.

“Enabling Technology” Polymers

An area of polymer science that is of current and growing industrial importance is where the polymer is the enabling technology that makes a component, system, or process work. Without the special polymer, the technology simply does not operate in a useful manner. The characteristics of this arena are very different from high volume commodity or engineering polymers. Performance is the overwhelming concern and the material is likely to be highly specialized to achieve optimum performance. Cost is of minor concern because the material is used in small quantities and the value it adds to the end use is exceedingly high. Supply is an issue because even at ultra-high prices the sales dollars generated are too small to be of interest to a large polymer producer. In addition, these polymers are often developed by an end-user company which is not in the business of producing polymers and not eager to share the end-use value with a partner. One of the industrially important examples of polymers as enabling technology, is photoresists used in semiconductor chip manufacture. Within Raychem examples include: acrylic backbone polymers with crystallizable side chains; conductive, crystalline polymer composites; polymer-dispersed liquid crystal compositions; crosslinked fluorinated aromatic polymides or polyethers which will be discussed in detail.

Thermal behavior of poly(α-n-alkyl β-L-aspartate)s

A series of poly(α-n-alkyl β-L-aspartate)s (n being the number of carbon atoms in the linear alkyl side chain, withn=1, 2, 4, 6, 8, 12, 18 and 22), was studied by differential scanning calorimetry and thermogravimetric analysis. The effect of the length of the alkyl group on thermal properties such as stability, melting and crystallization of side chains, was investigated. For the polymers with n≥12, two endothermic peaks at T1 and T2 were detected separating three distinct phases A, B and C. The peak at T1 corresponds to the melting of the crystallized paraffinic side chains (transition A-B), and the peak: at T2 may be attributed to a transition (B-C), implying a liquid crystal phase.

Synthesis of side chain liquid crystalline poly(vinyl ether)s containing 2,2′-dimethyl-4-methoxy-4′-[undecanyloxy-4-benzoyl]ester biphenyl side group

The synthesis and characterization of 2,2′-dimethyl-4-methoxy-[(11-vinyloxy)undecanyloxy-4-bezoyl]ester biphenyl (7), its cationic polymerization to side chain liquid crystalline polymers with relative number average degrees of polymerization (DP) of 2, 8 and 19 are presented. The mesogenic vinyl ether monomer displays an inverse monotropic nematic phase. The oligomers with DP=2 and DP= 8 display an enantiotropic nematic, while the polymer with DP=19 exhibits an inverse monotropic smectic A and an enantiotropic ncmatic phases. All the liquid crystalline polymers display only liquid crystalline phases and do not undergo side chain crystallization even though eleven methylenic units are used as the flexible spacer.

DSC and X-ray studies on side-chain crystallization of comb-like polymers

Thermal properties of acrylate and methacrylate monomers containing long-fluorocarbon chains (H(CF 2 ) n CH 2 OCOCH=CH 2 , (F n A) and H(CF 2 ) n CH 2 OCOC(CH 3 )=CH 2 , (F n MA), where n=6, 8, 10) and their comb-like polymers have been investigated by differential scanning calorimeter (DSC) and X-ray diffraction. The comb-like polymers (PF 10 A and PF 10 MA) with sufficiently long-fluorocarbon chains showed a simple melting and crystallizing behavior. For the fusion of PF 10 A in 1st heating, enthalpy change ΔH f was 18 kJ mol -1 and entropy change ΔS f was 45 J K -1 mol -1 , while for PF 10 MA the values ΔH f and ΔS f were 5.3 kJ mol -1 and 14 J K -1 mol -1 , respectively. Melted PF 8 A crystallized slowly, whereas PF 8 MA with same fluorocarbon chain and also both of PF 6 A and PF 6 MA with shorter fluorocarbon chains can hardly crystallize by the aggregation of side-chains. Effects of the length of side-chain and the flexibility of main chain on the side-chain crystallization of comb-like polymers are clear. Crystallization process of the methacrylate monomers was sensitively affected by the scanning rate of DSC measurement and the length of fluorocarbon chains.

Relationship between structure and conformation in liquid crystalline polymers

AbstractOur studies on the nematic phase of different kinds of thermotropic liquid crystalline polymers tend to focus on the following question: what about the anisotropy of the backbone conformation in the orientational medium imposed by its mesogenic groups ? By means of small angle neutron scattering (SANS) different features are qualitatively and quantitatively discussed. In the case of liquid crystal side chain polymers, the chain anisotropy is essentially driven by thermodynamical, structural and chemical considerations. In addition, in the case of liquid crystal main chain polymers, hairpin defects are observed for sufficiently long polymers.

Order−Disorder Transition in Comblike Block Copolymers Obtained by Hydrogen Bonding between Homopolymers and End-Functionalized Oligomers: Poly(4-vinylpyridine)−Pentadecylphenol

Dynamic mechanical spectroscopy (DMS) is used to further investigate the recently observed order-disorder transition (ODT) in comblike block copolymers obtained by hydrogen bonding between poly(4-vinylpyridine) and pentadecylphenol (P4VP-PDPx). For stoichiometric amounts of pyridine and phenol, i.e., z = 1.0, the ODT to a lamellar structure occurs at T similar or equal to 65 degrees C. The dynamic moduli G' and G '' simultaneously show a crossover from a liquidlike behavior (G' similar to omega(1.5) and G '' similar to omega) to a response intermediate between a Newtonian fluid and a solid (G' approximate to G'' similar to omega(1/2)). The behavior above T-ODT differs slightly from a homopolymer melt (G' similar to omega(2.0)) due to composition fluctuations, whereas the behavior below T-ODT is characteristic for quenched block copolymer lamellar phases with local uniaxial order and global isotropy. Near room temperature, a transition to solid behavior (G similar to omega(0)) takes place due to crystallization of the alkyl side chains. Larger amounts of PDP lower the T-ODT temperature, and for x = 2.0 the transition to solid response occurs directly from the disordered state. Small and wide angle X-ray scattering (SAXS and WAXS) experiments and differential scanning calorimetry (DSC) corroborate these findings. Furthermore, SAXS and WAXS demonstrate that the low-temperature state of P4VP-PDP2.0 is not stable and indicate that ultimately macrophase separation into a pure crystalline PDP phase and a microphase separated P4VP-PDP phase occurs.

Polyketone materials: control of glass transition temperature and surface polarity by co‐ and terpolymerization of carbon monoxide with higher 1‐olefins

AbstractHighly soluble alternating 1‐olefin/carbon monoxide copolymers with olefin monomers (H2CCHR) containing 4, 5, 6, 10, 14, 16 and 18 C‐atoms in the R‐substituents were prepared by the use of dicationic palladium(II) phosphine catalysts and an optimized amount of methanol as activator. In terpolymerization experiments the influence of icosene‐CO or octadecene‐CO units, distributed randomly along a propene‐CO or ethene‐CO copolymer backbone, on molecular weight, glass transition temperature and on the surface polarity of films casted from solution has been investigated. As the length of the α‐olefin side chain increases, the glass transition temperature (Tg) of the copolymer is reduced from room temperature to almost −60°C. For octadecene‐CO and icosene‐CO copolymers side chain crystallization occurs, leading to elastic materials. Contact angle measurements, performed on water drops located on the surface of selected co‐ and terpolymer films demonstrate the wide range of surface polarity which can be covered by simple copolymerization of polar CO groups with apolar alkenes.

Crystallization of side chains in copolymers of ethylene and 1-alkenes

The phase structure of random copolymers of ethylene and ethylene-d4 with 1-octadecene and other 1-alkenes has been investigated. CPMAS 13C NMR spectra show that a fraction of the central sections of C16H33 side chains in ethylene-d4 copolymers are in ordered environments at 298 K. They give rise to resonances from 32.9 ppm to 33.8 ppm, which show that they are in trans conformations; T1C values for this group of resonances range from 1 s to 7 s. The remaining side chains are in an amorphous environment, the internal methylenes having a chemical shift of 30.8 ppm and a T1C close to 0.4 s. A Raman band at 1062 cm−1 in the spectrum of an ethylene-d4-1-octadecene copolymer is consistent with partial crystallization of side chains. Some side-chain crystallization also occurs in a 1-tetradecene copolymer. X-ray diffraction studies suggest that smaller side chains do not crystallize to a significant extent at 298 K. © 1996 John Wiley & Sons, Inc.

Synthesis and phase behaviour of new carbazole containing liquid crystal side chain polysiloxanes

AbstractA series of chiral mesogenic side chain polymers containing a carbazole unit have been synthesized and investigated with regard to their liquid crystal (1c) phase behaviour. The carbazole units are linked either via the 2‐position with a 1‐oxycarbonyl‐4‐alkoxylphenyl moiety (end‐on) or via the 9‐position with an alkyl chain (side‐on) to polymethylsiloxane. Only end‐on polymers with long spacers or a ratio bigger one of spacer length and the free lateral alkyl chain length exhibit stable or metastable smectic phases. The side‐on polymers are only isotropic or crystalline.

Blends of alkylated comb-like polyacrylates with copolymers with a controlled ethylene-vinyl acetate composition

The thermodynamic and morphological behaviors of poly(octadecyl acrylate) (PODA) with flexible ethylene-co-vinyl acetate copolymer (EVA) with a controlled amount of vinyl acetate units in the copolymer were investigated over the entire composition region by thermal analysis, Fourier transform infrared (FTIR) spectroscopy, x-ray diffraction, optical microscopy, and light scattering. Thermal analysis revealed that the EVA portion interferes with the side chain crystallization of PODA, as the number of crystallized methylene units in PODA was calculated from the heat of fusion of the paraffinic side chain crystals. The hexagonal packing of side chains was also confirmed by FTIR and x-ray diffraction. Optical microscope studies showed a homogeneous melt state beyond the melting temperature of EVA, but clearly showed two phases over the whole range of composition in EVA20, EVA40, and EVA50/PODA blends after the side chain crystallization of PODA. Light scattering showed the single circular halo as the evidence of phase separation when the samples were cooled to below the crystallization temperature. The changes in crystallization cannot be accounted for by the miscibility, because liquid-liquid phase separation competes with crystallization. © 1996 John Wiley & Sons, Inc.

Structure and phase behaviour of polyazomethines having flexible (n-alkyloxy)methyl side chains

Structure and phase behaviour of a series of thermotropic polyazomethines having ( n -alkyloxy)methyl side chains (-CH 2 O- n -C m H 2m+1 , m = 4, 6, 8, 12) have been studied by wide-angle X-ray scattering, differential scanning calorimetry (d.s.c.) and polarizing optical microscopy. In d.s.c. thermograms the samples showed basically three transitions. The first transitions were ascribed to solid-solid transitions resulting from a large increase in disorder of the side chains. The second ones were assigned to crystal-mesophase transitions arising from melting of the side chain crystals. The third ones were attributed to mesophase-isotropic melt transitions. All the samples showed layered structures in the mesophase as well as in the crystalline phase, in which the side chains were fully interdigitated. In the crystalline phase the repeat units of rigid main chain were found not to align parallel with those of neighbouring main chains, but slipped by 49°. In the mesophase the side chain crystals were molten and the layer spacings increased proportionally with increasing side chain length. The structural regularity in the slipped repeat unit disappeared in the polymers bearing long side chains, whereas it was retained in those having short side chains. A unidirectional shearing made the layer plane align parallel on the surface.

Effect of solvent on aggregation structure and responsive properties of copolymeric gel with side chain crystals

The copolymeric gel films were prepared by a radical copolymerization of stearyl acrylate(SA), acrylic acid(AA) and N,N′-methylenebisacrylamide (MBAA) as a cross-linking agent. The copolymeric (molar ratio SA/AA/MBAA: 24.7/74.3/1.0) gel films with crystalline side chains were swollen in three different kinds of solvent and their aggregation structure and responsive properties have been investigated. In order to control the SA side chains-solvent interaction and to dissociate carboxyl groups in AA, solvents such as dimethyl sulfoxide (DMSO), (1-hexanol/DMSO) mixed solvents and water with different pH values were used. The responsive behaviors of the (SA/AA/MBAA) gel film swollen in different solvents were discussed on the basis of the weight swelling ratio. The X-ray diffraction study of the gel film revealed that the long period corresponding to a layer distance for the (SA/AA/MBAA) gel film swollen in DMSO increased with temperature or the swelling ratio, and the interchain distance of alkyl side chains remained constant with the variation of temperature up to the melting temperature of SA side chain crystals. The swelling ratio of the gel film in (1-hexanol/DMSO) mixed solvent exhibited an abrupt increase in the case of about 40wt% of 1-hexanol, because the SA side chain crystals of the gel film in the mixed solvents were dissolved due to an increase in SA-solvent interaction. On the other hand, the gel film in the water with different pH values showed a sharp increase in the swelling ratio above pH = 11, because the ionic repulsive force among the AA groups became greater than the aggregation one among alkyl side chains. These results indicate that the swelling ratio of the (SA/AA/MBAA) gel film can be controlled by temperature, pH and the magnitude of solubility parameter of swelling solvent.

Fluorinated Poly(α,l-glutamate)s

Poly(α,l-glutamate)s carrying C8, C10, and C12 fluorinated side chains were synthesized by polymerization of the corresponding amino acid N-carboxyanhydrides. Contact angle measurements with water were used to assess the effects of fluorination on the surface energies of films of the resulting polypeptides. The wettability of the polymers was found to decrease with increasing fluorine content, as expected. A remarkably high contact angle (121°) was measured for the homopolymer carrying C12 fluorinated side chains, indicating a surface consisting of closely packed trifluoromethyl groups. Side chain crystallization, consistent with the formation of such a surface, was suggested by the results of X-ray diffraction and calorimetric measurements.