Crystallinity Of Copolymers Research Articles

Correlation between ferroelectric phase transition and crystallization behaviour of ferroelectric polymers

Abstract The degree of crystallinity of ferroelectric copolymers of vinylidene fluoride and trifluoroethylene was measured as a function of annealing temperature. It increased remarkably at the ferroelectric phase transition temperature. The increase was attributed to the growth of crystallites by the thermodynamical consideration, where a concept of “sliding diffusion was introduced as a growth mechanism of the crystallite.

The Genetic Production of Synthetic Crystalline Protein Polymers

AbstractGenetic and protein engineering are components of a new polymer chemistry which provide the tools for producing macromolecular polyamide copolymers of diversity and precision far beyond the current capabilities of synthetic polymer chemistry. The genetic machinery allows molecular control of chemical and physical chain properties. Nature utilizes this control to formulate protein polymers into materials with extraordinary mechanical properties such as the strength and toughness of silk and the elasticity and resilience of mammalian elastin. The protein chains which make up these fibers consist of extensive repeating oligopeptide sequences. By producing synthetically designed protein chains containing many tandem repeats of only one repetitive sequence block (homoblock polymers), we are able to evaluate the inherent contribution of each repeat to the overall material properties. Using biotechnology, we produced homoblock protein polymers consisting exclusively of silklike crystalline blocks in quantities sufficient for material evaluation studies (10–100 grams). Silk-like homoblock polymers, as produced by microbial fermentation, exhibited measurable crystallinity both in solution and in solid state. The chain properties of the homoblock polymer were changed by adding blocks of amino acids designed to contribute different structural or functional properties. We produced alternating copolymers of various amounts of silk-like and elastin-like blocks ranging from a ratio of 1:4 to 2:1, respectively. The crystallinity of each copolymer varied with the extent of crystalline block interruption. The substitution of the elastin block with one containing the amino acids from human fibronectin responsible for mammalian cell attachment, produced a highly active silk-like copolymer with biological activity. The ability to specifically engineer the mechanical and functional properties of a fiber material is a potential outcome of this technology.

Polyvinyl alcohol-methyl acrylate copolymers as a sustained-release oral delivery system.

Low crystalline and crystalline polyvinyl alcohol-methyl acrylate (PVA-MA) copolymers were examined, because of their excellent flow and compressibility properties, as matrices for sustained-release tablets using phenylpropanolamine hydrochloride (PPA.HCl) as a model drug. Crystallinity of the copolymer affected the release characteristics from the tablet. Tablets made with low-crystalline PVA-MA provided sustained release of PPA, both in vitro and in vivo in dogs. PPA absorption from the low-crystalline PVA-MA tablet formulation was biphasic. An initial rapid phase was followed by a second, slower absorption phase which continued over 16 hr. Plasma PPA concentrations then declined with a half-life roughly parallel to the oral immediate-release half-lives. Oral bioavailability from the low-crystalline PVA-MA tablet formulation was 78.8 +/- 3.9%.

Étude de l'état solide des copolymères du chlorure de vinylidène avec le chlorure de vinyle, l'acrylonitrile et le méthacrylate de méthyle, 1. Structure des copolymères, modélisation mathématique en relation avec la structure chimique des chaînes

AbstractThe properties of a random copolymer are not only determined by composition, but also by the repartition of the monomeric units along the chain. In order to explain the properties of such a copolymer it is necessary to know the sequence distribution or microstructure, each sequence by itself showing structural characteristics: length, relative position, etc. It is thus necessary to conduct a precise synthesis process, and to know the kinetic parameters of the polymerization reaction. Knowledge of the kinetic invariants and monomer feed composition gives access to the theoretical sequence distribution. By different physicochemical methods (NMR, IR and UV spectroscopy), the results obtained by calculation are confirmed. Specifically the effect of microstructure and composition on the properties of some vinylidene chloride (VDC) copolymers with acrylonitrile (AN), vinyl chloride (VC) and methyl methacrylate (MMA) is studied. VDC leads to a very cristalline polymer, whereas PVC generally shows very poor cristallinity, and PAN shows particular structural characteristics. VDC copolymers can easily crystallize when they are rich in VDC. Generally the polymers are semi‐crystalline with an amorphous phase. A theoretical model accounting for the lamellar structure and crystallinity of VDC copolymers is described. It utilizes the microstructural data, obtained by a kinetic study and some simple hypotheses, among them the possibility for molecules to slide along each other. This sliding brings together the material which is crystallizable in determined areas. It is thus possible to explain the presence of crystallinity peaks, or at least of paracrystallinity, up to a relatively high amount of comonomer MMA, AN and especially VC in the diffractograms of VDC copolymers with MMA, AN and VC. The paracrystalline domains are defined as areas which can present some degree of order at great distance, with a relatively high amount of comonomer defects.

Polyester‐Polyether Block Copolymers II. Thermal and Mechanical Properties of Poly(hexamethylene terephthalate)/Poly(oxytetramethylene) Block Copolymers

AbstractThe melting and crystallisation behaviour of crystalline phases in poly (hexamethylene terephthalate)/poly(oxytetramethylene) block copolymers have been investigated in relation to copolymer composition and polyether block molecular weight (m.w.). In contrast to that in corresponding homopolymer blends, the polyester crystallinity in the block polymers is greatly reduced by incorporation of polyether units, though some persists even at low polyester contents. Concomitant changes in the glass transition temperatures show part of the polyester component to form a homogeneous component of the amorphous phase.The mechanical properties change with composition in parallel with the changes in copolymer crystallinity and Tg. Copolymers with 20‐60 w % of poly(oxytetramethylene) units of m.w. 2000 are highly extensible elastomers. Those with higher m. w. polyether blocks have higher modulus and strength but suffer a serious loss of properties at 60d̀C.The observations are interpreted in terms of a model in which polyester crystallites (and polyether crystallites also, for the higher m. w. polyether blocks) are supported within an amorphous matrix by tie‐molecules whose nature changes with the copolymer compositions. The results are compared with those for analogous polyester‐polyethers having different structural components.

Structure of copolymers of ω-dodecalactam and ϵ-caprolactam

X-ray analysis and optical microscopy were used to examine the structure of ω-dodecalactam—ϵ-caprolactam copolymers obtained by anionic activated polymerization in the presence of a catalyst—Na-caprolactam and an activator—N-acetyl--ϵ-caprolactam. The hydrostatic method was used to determine copolymer density and calculate crystallinity and the density of amorphous polydodecane amide was evaluated for the first time ( ϱ a = 0·972 g/cm 3 ). It was shown that with a variation of copolymer composition a structural transition takes place from the hexagonal crystalline modification, typical of polydodecane-amide to the monoclinic modification typical of polycaprolactam. This transition occurs via an intermediate region, in which both crystalline forms coexist. It was shown that copolymer crystallinity decreases in proportion to approaching copolymers of equimolecular composition. Structural changes in copolymers are also noted on the optical level of investigation and are expressed by a variation of the dimensions and form of spherulites.

Determination of crystallinity of olefin copolymers and polyolefin powders by inverse gas chromatography

AbstractStudies of olefin copolymers by inverse gas chromatography show that the method is suitable for determining the crystallinity of compositions where a linear extrapolation of density determinations is not applicable. Satisfactory estimates of crystallinity were obtained on ethylene copolymers with carbon monoxide and vinyl acetate and on an emulsifiable polyethylene wax. Studies were also made in which the columns were packed with physical mixtures of GC support and polyolefin powders, either obtained direct or ground from film samples. It was shown that good estimates of crystallinity could be obtained if suitable allowance is made for variance in peak retention time with flow rate, due to the relatively slow rate of diffusion of the probe molecule in polymer particles of large diameter (>100 μm). If smaller particles are used it is usually unnecessary to correct for flow rate effects. This extends the usefulness of the “molecular probe” technique to any polyolefin sample which can be ground to a fine particle size and eliminates the need for solution coating of the column packing.

Remarks on copolymer sequence distributions

AbstractDistribution functions for the unit X in copolymers of the type equation image are given. These functions have been used to calculate the expected degree of crystallinity using the Flory theory of copolymer crystallinity. The calculations indicate that differences can be expected between polymers prepared from XA and XX on the one hand and A and X on the other when the kinetics constants of the polymer‐forming reactions are identical. In addition, it has been shown that the Flory results carry over to the terpolymer case with the propagation probability given in its terpolymerization form. The addition of more than one comonomer can lead to increased or decreased crystallinity with a given constant melting point, depending on whether the noncrystallizable monomers tend to alternate or “block” with one another.

Dielectric properties of vinylidene chloride–vinyl chloride copolymers

AbstractThe dielectric properties of vinylidene chloride—vinyl chloride copolymers prepared at conversions of less than 5% were studied. The magnitude of dielectric α absorption (absorption at high temperature) is not a linear function of the composition on account of the effect of the copolymer's crystallinity. On the other hand, a nearly linear relationship was observed between the dielectric glass transition temperature (Tg) of low‐conversion polymer and its composition, while the relationship in a high‐conversion copolymer system, observed by Boyer and Narita et al., is sigmoid. The differences in the temperature—composition relationship between low‐conversion and high‐conversion copolymer systems are illustrated in terms of the distribution of molecular composition. The dielectric β absorption observed in the copolymer whose vinyl chloride molar fraction is more than 0.5 was interpreted as the local motion of vinyl chloride sequences, and the vinyl chloride sequence of 2 or 3 units is sufficient to participate in the β absorption of the copolymer.

On the structure and properties of polyamides. V. Infrared spectra and crystallinity of copolymers of caprolactam with γ-methylcaprolactam

On the structure and properties of polyamides. V. Infrared spectra and crystallinity of copolymers of caprolactam with γ-methylcaprolactam

Physical properties of ethylene‐1‐olefin copolymers

AbstractWith the advent of the newer catalyst systems it is now possible to prepare copolymers of ethylene and 1‐olefins possessing useful physical properties. A wide range of physical properties is readily achieved through variations in the concentration and type of 1‐olefin used as the comonomer. The era of tailor‐making ethylene type polymers to fit any specification regarding stiffness, strength and melt flow properties is now at hand. A comparison of physical properties of ethylene/1‐olefin copolymers with those of the corresponding polyethylene/poly (1‐olefin) blends indicates true copolymers are formed.Decrease in crystallinity of copolymers is due to the number of branch sites introduced into the main chain rather than to the bulk of the comonomer or the length of side chain.

Differential thermal analysis of high polymers. V. Ethylene copolymers

AbstractMelting and crystalline properties of methyl‐and ethyl‐branched polymethylenes—models for ethylene‐propylene and ethylene–α‐butene copolymers—containing up to 20 branches per 1000 carbon atoms have been investigated by differential thermal analysis (DTA). The melting‐point depression is practically linear with branch concentration. However, ethyl groups are more effective than methyl groups. Cooling at different rates during annealing produces a wider melting‐point spread in copolymers containing more branches. Again, copolymers containing ethyl groups are affected more than those having an equal number of methyl groups. Copolymer crystallinity estimated by DTA also decreases linearly with the number of branches; ethyl groups disrupt crystallinity more markedly than methyl groups do. The effect of colling rates on crystallinity increases with branch concentration. Melting and crystalline behavior of two commercial ethylene copolymers agree with patterns derived from the models. The thermogram of a crystalline ethylene‐propylene block copolymer consists of two separate melting peaks corresponding to crystalline regions formed by ethylene and propylene sequences. Total crystallinity of this copolymer was estimated and used in calculating the copolymer composition. Restrictions for crystallization in the block copolymer are apparent from the thermogram.

A new synthetic elastomer based on a chlorophosphonated polyolefin. II. Effect of polyolefin structure on vulcanizate properties

AbstractThe paper describes the effect of ethylene‐propylene copolymer structure on the properties of vulcanized, chlorophosphonated ethylene–propylene copolymer. The crystallinity of copolymer has a marked effect on vulcanizate properties. The more crystalline the copolymer, the higher hysteresis values and permanent set are for the vulcanizate. The catalyst used for the copolymerization of ethylene and propylene affects crystallinity markedly, titanium trichloride as a catalyst component giving a more crystalline copolymer than does the use of vanadium salts. Copolymer molecular weight has an effect on vulcanizate tensile strength but no effect on heat stability, elongation, and hysteresis loss.