Block copolymers of poly(ethylene terephthalate–polybutylene terephthalate). I. Preparation and crystallization behavior

Block copolymers of two crystallizable compounds, poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT), were developed with PET as the major component and the amount of PBT varying from 1.0 to 20.0 wt %. These block copolymers were prepared by end-group coupling of preformed oligomers. All polymers prepared were of equivalent molecular weight as determined by the intrinsic viscosity method. Thermal properties were determined by differential thermal analysis (DTA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). With increasing PBT content, the block copolymers showed a general decrease in the values of glass transition temperature, melting temperature, initial decomposition temperature, and maximum decomposition temperature. The heat of fusion and heat of crystallization first increased and then decreased slightly. Rates of crystallization were determined by measuring density as a function of time of isothermal crystallization carried out at 95°C. It was found that small amounts of PBT increased the crystallization rate considerably over that of PET. Random copolymers did not show this phenomenon and behaved more like pure PET. The crystallization behavior of block copolymers was analyzed by the Avrami equation and Avrami exponents were determined. Results were explained on the basis that the faster-crystallizing PBT blocks crystallized first and provided built-in nucleation sites for the subsequent crystallization of PET, thus resulting in a relatively fast-crystallizing copolyester.     

Block copolymers of styrene,isoprene, and ethylene oxide prepared by anionic polymerization. I. Synthesis and characterization

Anionic polymerization has been used as a technique for the synthesis of five-block copolymers of polystyrene (PS), polyisoprene (PI), and poly(ethylene oxide) (PEO). Two types of such polymers, PEO-PI-PS-PI-PEO and PEO-PS-PI-PS-PEO with varying PEO block length, have been prepared, using potassium naphthalene as the initiator and tetrahydrofuran as the solvent. The polymers were purified by extraction with ethyl acetate, diethyl ether, and water. After the addition of each monomer, a sample from the living polymer solution was taken and analyzed by spectroscopy (infared (IR) and proton magnetic resonance (PMR)), osmometry, and gel-permeation chromatography (GPC) to obtain information about composition, molecular weight and molecular weight distribution of the intermediate polymers. The five-block copolymers have also been characterized by the same techniques and by elemental analysis.     

Organosilane polymers. III. Block copolymers

Chloro- and lithio-terminated diorganosilylene oligomers were coupled to form block copolymers that were soluble in common solvents and deposited coherent films from solution. Copolymer UV (ultraviolet) spectra showed a red shift in absorption maxima attributed to increased silicon chain length and phenyl-silicon spine interactions.     

Poly(ethylene terephthalate) copolymers containing nitroterephthalic units. I. Synthesis and characterization

The synthesis, microstructure, and thermal behavior of a series of poly(ethylene terephthalate) (PET) copolymers containing nitroterephthalic units are described. These novel copolyesters were synthesized by transesterification followed by melt copolycondensation of dimethyl terephthalate and dimethyl nitroterephthalate mixtures with ethylene glycol. The molar ratio of the two comonomers in the feed varied from 95/5 to 25/75. Furthermore, PET and poly(ethylene nitroterephthalate) homopolymers were synthesized with the same method and comparatively studied. Copolyester compositions were practically the same as in the feed, and weight‐average molecular weights ranged from 10,000 to 60,000. The two monomeric units were randomly distributed along the polymer chain, and the experimentally determined average sequence lengths were in accordance with ideal copolycondensation statistics. Melting temperatures and enthalpies of the copolyesters decreased with increasing content in nitroterephthalic units, and they all showed a single glass‐transition temperature superior to that of PET. They appeared to be stable up to 300 °C, and thermal degradation occurred in two well‐differentiated steps. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3761–3770, 2000     

Synthesis of ethylene copolymers

Summary Copolymers of ethylene with styrene, methyl methacrylate, acrylonitrile, and vinyl acetate were prepared by reaction in toluene in presence of tributylborine as polymerization catalyst.     

Block copolymers of poly(ethylene terephthalate)-poly(butylene terephthalate). II. Small-angle light-scattering studies

Small-angle light-scattering (SALS) studies were carried out on block copolymers of poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT), the synthesis and characterization of which have been reported in an earlier paper. Samples were crystallized isothermally from the melt at 95°C for predetermined crystallization times in order to follow the formation and growth of crystalline superstructure. During the early stages of crystallization, the block copolymers showed unusual H_v patterns with the four lobes along the polarizer directions, while at later stages they showed the usual H_v patterns with the four lobes at 45° to the polarizer directions. The unusual patterns are characteristic of PBT superstructure, while the usual patterns are characteristic of PET superstructure. These results show that PBT, which is the faster-crystallizing component, crystallizes first and provides nucleation sites for the crystallization of PET, which crystallizes later. Similar behavior was not observed in PET homopolymer and random copolymers of equivalent compositions. In each case the spherulite size increased with the time of crystallization. The ultimate spherulite size decreased with increasing PBT content in the block copolymer, thus showing an increase in nucleation density. It was demonstrated that light scattering is a useful tool to characterize block copolymers of two crystalline components which have different types of superstructure.     

Block copolymers of polyacetals

The polymerization of 1,3-dioxolane was carried out using trifluoromethanesulfonic acid (triflic acid) as catalyst, in the presence of an oligomeric diol, α-hydro-ω-hydroxypoly(oxyethylene) (PEOG) or α-hydro-ω-hydroxypoly(oxytetramethylene) (poly-THF-diol). When PEOG was used, a linear increase of the number average molecular weight versus conversion was observed. A triblock copolymer was obtained as well as small cycles in their usual equilibrium concentration. When poly-THF-diol was used, fast transacetalization provoked the “polycondensation” of the diol through acetal linkages at the very onset of the reaction, leading to a very inhomogeneous mixture. After equilibrium was reached, through reactions involving all the various species present, a triblock copolymer was also obtained. In conclusion, this method is well suited to prepare α,ω-diol block copolymers in which the initial oligomeric diol constitutes the center block, while the outside blocks are made of polyacetal.     

Block copolymers of polystyrene and poly(dimethyl siloxane). I. Synthesis and characterization

The block copolymers of the ABA type, poly(dimethyl siloxane-b-styrene-b-dimethyl siloxane), were synthesized by the anionic polymerization of styrene and cyclic siloxane monomer, hexamethyl cyclotrisiloxane (D₃) or octamethylcyclotetrasiloxane (D₄), with lithium or sodium biphenyl as initiator. The effect of initiator concentration, gegenion, and the polymerization temperature for styrene on molecular weight distribution (MWD) was investigated. Gel permeation chromatography (GPC) data show broader MWD of polystyrene prepared by sodium biphenyl in comparison to that produced by lithium biphenyl. The block copolymers have been characterized by infrared (IR) and nuclear magnetic resonance (NMR) spectra. The influence of dimethylsiloxy units on thermal stability of the copolymers has also been discussed.     

Block copolymers with LC-segments

Liquid crystalline main chain polymers have outstanding properties concerning their modulus, thermal expansion, shear viscosity, and flame retardant behavior. It is of interest to introduce these properties into other polymers by the synthesis of block copolymers.     

Coionomeric mixtures of polyhydroxyethers and ethylene methacrylic acid copolymers. II. Compatibilizers for blends of polybutylene terephthalate and ethylene butyl acrylate copolymers

Blends of polybutylene terephthalate and ethylene butyl acrylate copolymers were studied at two extreme concentration levels so that each polymer would form, in turn, a particulate dispersed phase. The blends contained 5% by weight of a coionomeric compatibilizer, which was produced from 1 : 1 mixtures of a polyhydroxy ether of bisphenol A and the sodium ionomer of an ethylene methacrylic acid copolymer, using sodium ethoxide to enhance the formation of ionomeric clusters together with an A-B-A block oligomer to assist the solubilization of the two ionomeric polymers. In all cases the addition of the coionomeric compatibilizer mixture to the blend was found to decrease the size of the dispersed particles with a concomitant reduction in the interphase gap. It was also observed that the dispersed polymer exhibited a lower level of crystallinity and a slightly lower melting point than when it was present as a matrix, particularly for the case of the ethylene butylacrylate copolymer. The inability of the compatibilizer to completely prevent the formation of an interfacial gap which did not allow the blends to achieve more substantial improvements in mechanical properties, was attributed to the vast difference in crystallization temperature between the two polymers. © 1993 John Wiley & Sons, Inc.     

Photochemistry of ketone polymers. XIV. Studies of ethylene copolymers

Studies have been made of the photochemistry of ethylene copolymers with carbon monoxide (CO), methyl vinyl ketone (MVK), and methyl isopropenyl ketone (MIPK) in solid films. Infrared (IR) evidence is presented to show that a variety of unexpected ketone structures is present in these polymers as a result of 1,5-hydrogen transfer or “back-biting” during the high-pressure polymerization reaction. These additional structures complicate the analysis of the quantum yield data. The overall quantum yield for carbonyl disappearance (?-co) which increases from 0.074 to 0.24 to 0.26 in the series PE-1% CO, PE-2% MVK, and PE-20% MIPK reflects the increasing stability of the alkyl radicals produced from the type I process in the respective ketone structures. It is also shown that ketone groups located in the backbone of the polymer, as in the 1% CO copolymer, have lower quantum yields for photochemical reactions, particularly those that produce free radical intermediates. Studies of the gaseous products from extensive photodegradation under nitrogen show that in all three cases carbon monoxide is the major product (46-65% of the total). Acetaldehyde and methane, expected from the type I reaction, are major products only for the MVK and MIPK copolymers. Reaction schemes are presented to explain the major products observed.     

Block and graft copolymers by selective cationic initiation. IV. Physical properties of bigraft copolymers

The physical properties of bigraft copolymers, i.e., Nordel-g-polystyrene-g-poly(α-methylstyrene) and Nordel-g-polystyrene-g-polyisobutylene, have been studied in terms of stress strain behavior, glass transition temperature, dynamic mechanical data, intrinsic viscosity versus temperature profile and solubility properties. These products are thermoplastic elastomers and show the presence of incompatible domains. T_g and dynamic-mechanical data indicate an aggregation of the polystyrene and poly(α-methylstyrene) phases.     

Block copolymers prepared by emulsion polymerization with poly(ethylene oxide)–azo-initiators

Poly(ethylene oxide)-b-poly(styrene) block copolymers were prepared in the form of latex particles by emulsion polymerization of styrene with poly(ethylene glycol)–azo-initiators as well as with the redox initiation system poly(ethylene glycol)/Ce⁴⁺. The emulsion polymerization can be carried out in the absence of additional stabilizers if the chain length of the poly(ethylene glycol) is greater than 40. The latex particles as well as the copolymers were characterized by capillary hydrodynamic fractionation, ¹³C-nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared spectroscopy. By ¹³C-NMR spectroscopy a side reaction of the primary radicals arising from the azo-initiator was found which can contribute to the low efficiency of azo-initiators in emulsion polymerization.     

Block copolymers as nanoscopic templates

Block copolymers self‐assemble into well‐ordered, microphase separated morphologies having dimensions on the molecular scale. The key to the use of these nanoscopic structures lies in controlling the spatial orientation of the morphology, particularly in thin films. The preferential interactions of the segments of the blocks with interfaces forces an alignment of the morphology parallel to the interface. Here we describe the use of controlled interfacial interactions and electric fields to manipulate the orientation of the morphology and subsequent steps towards the generation of nanoporous templates as scaffolds for nanoscopic structures.     

Block copolymers of ethylene oxide and phenyl glycidyl ether: micellization, gelation, and drug solubilization

Three triblock copolymers of ethylene oxide and phenyl glycidyl ether, type E(m)G(n)E(m), where G = OCH2CH(CH2OC6H5) and E = OCH2CH2, were synthesized and characterized by gel-permeation chromatography, matrix-assisted laser desorption ionization time-of-flight mass spectrometry, and NMR spectroscopy. Their association properties in aqueous solution were investigated by surface tensiometry and light scattering, yielding values of the critical micelle concentration (cmc), the hydrodynamic radius, and the association number. Gel boundaries in concentrated micellar solution were investigated by tube inversion, and for one copolymer, the temperature and frequency dependence of the dynamic moduli served to confirm and extend the phase diagram and to highlight gel properties. Small-angle X-ray scattering was used to investigate gel structure. The overall aim of the work was to define a block copolymer micellar system with better solubilization capacity for poorly soluble aromatic drugs than had been achieved so far by use of block copoly(oxyalkylene)s. Judged by the solubilization of griseofulvin in aqueous solutions of the E(m)G(n)E(m) copolymers, this aim was achieved.     

Nanostructured Thermosetting Systems from Epoxidized Styrene Butadiene Block Copolymers

Summary: Nanostructured thermosetting materials were prepared by modification of an epoxy resin with 30 wt.‐% epoxidized polystyrene‐block‐polybutadiene copolymer (PS‐b‐PepB). The copolymer self‐assembles into a well‐defined hexagonal nanoordered structure, of around 30‐nm diameter, thus establishing its use as structure‐directing agent to generate nanostructured thermosetting materials. The study confirms pathways towards tailoring interactions between thermosetting matrices and immiscible block copolymers by using the concept of functionalization to build nanostructured polymer matrices.

Structure of diglycidyl ether of bisphenol‐A/4,4′‐methylenebis(3‐chloro 2,6‐diethylaniline) cured blend containing 30 wt.‐% PS‐b‐PepB61 block copolymer.     

Syntheses of amphiphilic block copolymers. Block copolymers of methacrylic acid and p-N,N-dimethylaminostyrene

Amphiphilic block copolymers consisting of methacrylic acid (MA) sequences and p-N,N-dimethylaminostyrene (DMS) sequences were prepared by living anionic polymerization. DMS was polymerized by lithium naphthalene in tetrahydrofuran to yield a living polymer solution, to which trimethylsilyl methacrylate (TMSM) was added to allow the block copolymerization. The conversion of TMSM was dependent on the countercation, i.e., with Na⁺ as counterion, no quantitative conversion was reached owing to premature termination, whereas with Li⁺ the conversion was quantitative. The role of the counterion was discussed in some detail in connection with self-termination by the backbiting mechanism. The trimethylsilyl ester groups in the block copolymer were quantitatively hydrolyzed by treatment with aqueous methanol at room temperature, yielding MA sequences. The block copolymer of MA and DMS exhibited micellar properties in an aqueous solution.