Relationships between the molecular architecture, crystallization capacity, and miscibility in poly(butylene terephthalate)/polycarbonate blends: A comparison with poly(ethylene terephthalate)/polycarbonate blends

Abstract

Poly(butylene terephthalate) (PBT)/polycarbonate (PC) samples, prepared via reactive blending in the presence of Ti-and Sm-based catalysts, resulted in block copolymers whose block length decreased as the mixing time increased. A single homogeneous amorphous phase occurred when the blocks had monomeric sequences shorter than 10 units. Otherwise, a crystalline phase of PBT developed. Also, in poly(ethylene terephthalate) (PET)/PC blends previously studied, the miscibility was strictly correlated with the crystallizability of the system. Therefore, the miscibility of the PBT/PC and PET/PC blends was compared with respect to the tendency of the PBT and PET blocks to crystallize under isothermal conditions. The crystallization rate of the PBT/PC copolymers was faster than that of the PET/PC copolymers with similar block lengths. Accordingly, the minimum crystallizable sequence length of the PBT blocks was shorter than that of the PET blocks (18 vs 31 monomeric unit sequences). This behavior was interpreted as an effect of the more flexible PBT units, which had a greater tendency to fold and crystallize than the PET units. Therefore, PBT, the blocks of which tended to crystallize even if they were very short and phase-separated, was characterized by a poorer compatibility with PC than that of PET. As a result, the block size had a fundamental role in determining the crystallizability and, therefore, phase behavior of the semicrystalline block copolymers.

Crystallization of Poly(ethylene terephthalate) in Poly(ethylene terephthalate)/Bisphenol A Polycarbonate Block Copolymers: Influence of Block Length and Role of the Rubbery Amorphous Component

“…The copolymers have wide Table 1. Analyzed PET-co-PC and PET-samples, code used in the previous works [27,28,30] indicating the catalyst and the mixing time in Brabender, the molecular weight (M n ) and molecular weight distribution (M w =M n ), the number of PET monomeric units (X n PET ) and the results of the thermal analysis performed by DSC in the cooling scan. These latter data refer to the curves shown in Figure 1.…”

“…[27] In particular, a single disordered phase is potentially present in the molten state, especially at short block length, while the presence of a mesophase-separated melt is unlikely. When these systems are cooled from the melt, two processes are in competition: block dissolution to form a homogeneous phase and phase separation by crystallization of PET and PBT blocks.…”

“…The PC blocks do not take part in the crystallization process and remain in the amorphous state, as observed previously during crystallization experiments. [27] This behavior is due to the difficulty of the polycarbonate units of reaching a crystalline order after cooling from the melt. The role of the block length on the competition between block dissolution and crystallization was therefore assessed in isothermal conditions after cooling from the melt.…”

Effect of compatibilizer on compatibility and pervaporation performance of PC/PHEMA blend membranes

“…Most studies on the compatibility in polymer blends involve the preparative method of melt mixing (without use of a solvent) [3][4][5]7,8,[11][12][13][14][15][16][17][18][19][20][21]; rather few researches deal with solution blending (use of a solvent to dissolve the polymers) [2,6,22,23]. These studies commonly utilize analytical and conventional techniques [1][2][3][4][5][6][7][8][11][12][13][14][15]22].…”

Carbohydrate-based polyamides and polyesters: an overview illustrated with two selected examples

“…Nevertheless, it is worth noticing that the same basic pattern regarding both spacing and intensities was shared by all the copolymers revealing that the triclinic crystal structure of PBT was retained in the copolyesters. 36 Whereas it is thought that a length of at least 15-20 BT repeating-units is the minimum required for crystallization, 37 other observations have revealed that certain PBT copolymers are able to crystallize for chain segments consisting of only two to five repeating units. 38 A question immediately arises with respect to the location of the pentitol units in the biphasic semicrystalline state.…”