Molecular-weight dependence of the glass transition temperatures of rigid SIS triblock copolymers studied by DSC

Abstract

Differential scanning calorimetry (DSC) measurements have been carried out on a series of ABA poly(styrene-b-isoprene) triblock copolymers with 30% polyisoprene content and various molecular weights. The DSC data show an inward shift for the glass transition temperatures (Tg) of the blocks compared to the corresponding homopolymers. As a function of the molecular weight, one to three transitions were found. The additional third Tg gives some further evidence of the existence of an interphase between the microdomains.Numerous studies [1, 2] on multicomponent polymer systems have established the occurence of phase segregation and microdomain formation when two or more polymers are combined, in block copolymers, the factors governing the size of the domains depend on the number and length of the blocks and on their chemical nature.Meier [3] was the first to develop a theory about microphase formation for styrene-butadiene di-and triblock copolymers [4]. He showed that above a certain molecular weight, phase segregation takes place. Williams [5] and later Helfand [6] investigated the formation of an interphase: between the two pure phases, a region of mixed phases exists. These authors evaluated the influence of molecular weight and composition of the different blocks on the size of the pure phases and of the interphase. Particularly, the volume of the interphase increases with decreasing molecular weight. Toporowski and Roovers [7] as also Kraus and Rollmann [8] concluded that some low molecular weight block copolymers form a single phase. Through these investigations, block copolymers may exist in the solid state with morphologies going from a single phase to a completely organized two-phase structure.Glass transition temperatures (Tg) are commonly used to detect phase changes in copolymers. Two distinct Tg's corresponding roughly to those of the parent homopolymers appear when two well segregated phases exist in a copolymer. On the other hand, random copolymers known to exist as a single phase, show only one Tg, the value of which depends on its phase content. Thus, the number of transitions and the temperature at which they occur, provide information about the morphology of SIS copolymers.

Heat Capacity of Spider Silk-Like Block Copolymers

“…Several models have been proposed to predict block copolymer and polymer blend glass transition temperatures, such as the Fox equation, Gordon–Taylor equation, and Couchman equations . Although these equations have been successfully applied to certain blends and copolymers, for diblock copolymers and miscible blends, when specific interactions exist between components, these equations do not actually coincide with the experimental T g . Kwei’s equation adds in a term to the Gordon–Taylor equation corresponding to the strength of polymer chain interaction, which may include hydrogen bonding, in the block copolymer , or blend. , Therefore, it is the most popular equation applicable for systems with specific interactions: T normalg = false( W 1 T g 1 + W 2 T g 2 false) false( W 1 + k W 2 false) + q W 1 W 2 where W 1 and W 2 are weight fractions of pure components, T g1 and T g2 represent the corresponding glass transition temperatures, and k and q are fitting constants.…”

“…67 Although these equations have been successfully applied to certain blends and copolymers, for diblock copolymers and miscible blends, when specific interactions exist between components, these equations do not actually coincide with the experimental T g . 68 Kwei's equation 69 adds in a term to the GordonÀTaylor equation corresponding to the strength of polymer chain interaction, which may include hydrogen bonding, in the block copolymer 70,71 or blend. 71,72 Therefore, it is the most popular equation applicable for systems with specific interactions:…”

A pressure-sensitive adhesive made from macca carbon for medical use

“…The DSC thermogram in Figure 2 displays two distinct peaks at −60°C and 10°C, which correspond to the T g of polyisoprene and polystyrene, respectively. 26–28

Figure 2.DSC curve of PSA.

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“…The DSC thermogram in Figure 2 displays two distinct peaks at À60°C and 10°C, which correspond to the T g of polyisoprene and polystyrene, respectively. [26][27][28] The MWD of the purified PSA as determined by the GPC technique is depicted in Figure 3. From the calibration curve using a series of various MW of polystyrene as standards, the number-average molecular weight (M n ) and the weight-average molecular weight of (M w ) were estimated to be 1.45 × 10 5 and 1.59 × 10 5 Dalton, respectively, with a polydispersity index of 1.0966.…”

Stress–Strain Behavior, Elastic Recovery, Fracture Points, and Time–Temperature Superposition of an OOT-Possessing Triblock Copolymer

“…In this study, we studied Vector 4111, a SIS with 18.3 wt % of PS, which is known to possess several OOTs and ODT as described in Figure , where the ordered phases change from cylindrical, through BCC spherical, to lattice disordering spherical structures by changing annealing temperatures. − The relationship between the morphology and the mechanical properties of Vector 4111 through OOT and ODT was extensively studied to understand the linear as well as nonlinear mechanical properties of the triblock copolymer. In particular, G ′, G ′′, Young's modulus, fracture stress, fracture strain, and the time–temperature superposition were examined by DMA and by tensile testing.…”