Sequential reordering in condensation copolymers, 1. Melting‐ and crystallization‐induced sequential reordering in immiscible blends of poly(ethylene terephthalate) with polycarbonate or polyarylate

Abstract

Unlike previous attempts, the entire cycle of melting-and crystallization-induced reordering is realized in binary polymer blends in the following order: two homopolymers + block copol mer + random copolymer + block copolymer. Blends of poly(ethy1ene terephthalate) by (PET) and bisphenol-Npolycarbonate (PC) as well as PET/polyarylate (PAr) blends, are annealed directly in a differential scanning calorimeter at 280°C for various times. Scanning the samples in the heating mode reveals the complete disappearance of crystallization or melting in the blends where the ratio of PETPC repeating units is less than 5.7/1.0. Such an amorphization is attributed to the formation of random copolymers. This statement is confirmed by NMR measurements, by the observation of one glass transition temperature Tg in the range between the initial two Tgs, and by solubility tests. Once randomized, annealing the samples at 235 "C and 245 "C, i. e., below melting of PET, results in a Tg shift toward the Tg of PET as well as in reappearance of melting. This effect is accompanied by an eight-fold crystallinity increase in the equimolar blend, as compared to the randomized sample. The regenerated crystallization ability is explained by restoration of the blocks. According to previous findings, it is concluded that the considerable entropy increase is the main driving force of randomization. The rival trend to the formation of a block copolymer by sequential reordering is driven by the crystallization of PET blocks formed. The conclusion that the observed changes in the crystallization ability and Tg-values are based on sequential reordering is supported by experiments with samples containing increased amounts of transesterification catalyst leading to a much faster appearance of these changes. No randomization is observed with the blend composition ratio of repeating units PETPC > 5.7/1.0. When the annealing is performed for 300 min at 165 "C, where no significant exchange reactions are expected to occur, no restoration of the crystallization ability is observed.

A review on the potential biodegradability of poly(ethylene terephthalate)

“…Annealing of the randomized blend near to the melting temperature of PET usually results in a restoration of the multiblocked structure, and crystallinity is partially recovered. 18 The occurrence of transreactions in the blend strongly depends on the mutual af®nity of its components and on blending conditions. These include temperature, 24,28 duration of mixing, 24,28 preparation method, viscosity, and the presence of catalysts and inhibitors.…”

Sequence length determination in poly(ethylene terephthalate)-bisphenol-A polycarbonate random copolymers by application of selective degradation

“…Its NMR Studies inability to crystallize could be attributed to the fact that effective transreactions at the above conAmorphization of the PET-PC copolymer as revealed by DSC cannot be considered a direct proof ditions decrease the lengths of the PET blocks to sequences comprising, in average, less than 5 of randomization. Theoretically, even a block copolymer containing long PET sequences might be residues, which, as previously indicated, 3 would not be enough to form lamellae. It should be menfound unable to crystallize, owing to various reasons, such as hampered copolymer crystallization tioned here that the T g of 82ЊC registered for the amorphous copolymer obtained without melt mixdue to the presence of degradation products and improper crystallization time during the DSC ing (Fig.…”

“…3,4 Another important observation is ymer obtained by annealing of an equimolar mechanical blend directly in the DSC apparatus. 3 that the DSC traces of a PET-PC amorphous copolymer prepared by melt mixing at 280ЊC reveal After 45 min of such annealing at 280ЊC (curve c in Fig.…”

“…In some of these blends, transreactions can easily proven in numerous homopolymer blends. [3][4][5][6][7][8] Inrole of effective mass transfer in the molten homopolymer blend for the obtaining of amorphous cotensive research in this area has shown that the control of transreactions can provide a new polymers with a more or less random sequence distribution. method for preparation of copolymers within the processing equipment.…”

“…12 In the study of transesterification reactions in a molten blend of condensation polymers, it is often important to know whether the resulting product is a block copolymer, a random copolymer, or still a mechanical mixture of the starting homopolymers. To that purpose, the following analytic techniques are most frequently used in the PET-PC or similar systems: differential scanning calorimetry (DSC) [2][3][4][5] , 1 H and 13 C nuclear magnetic resoPreparation of PET-PC Copolymer Samples nance (NMR), 6 -8,10,13 -16 chromatographic methods, 10,17 and selective degradation of the PC The starting homopolymers were dried overnight in vacuum at 100ЊC and used without further pusegments with subsequent determination of viscosity. 18 The process of PET-PC copolymer preparification.…”