Glass transition temperature of anionic polyisoprene

Widmaier, Jean‐Michel; Meyer, G. C.

doi:10.1021/ma50003a041

Cited by 68 publications

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“…In the same figure we plot the PS ring data 3 , along with an entangled linear PI for comparison and molecular dynamic simulations data of coarse grained bead-spring ring melts 24 . Due to the different glass transition temperatures T g for PI and PS, the data are compared at isofrictional conditions, i.e., same distance from T g (see also Table 1) 25 . In addition, a vertical shift of the PI data with respect to the PS data was performed, by the amount reflecting the ratio of the entanglement molar masses 26 .…”

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Viscosity of Ring Polymer Melts

et al. 2013

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We have measured the linear rheology of critically purified ring polyisoprenes, polystyrenes and polyethyleneoxides of different molar masses. The ratio of the zero-shear viscosities of linear polymer melts η0,linear to their ring counterparts η0,ring at isofrictional conditions is discussed as function of the number of entanglements Z. In the unentangled regime η0,linear/η0,ring is virtually constant, consistent with the earlier data, atomistic simulations, and the theoretical expectation η0,linear/η0,ring=2. In the entanglement regime, the Z-dependence of rings viscosity is much weaker than that of linear polymers, in qualitative agreement with predictions from scaling theory and simulations. The power-law extracted from the available experimental data in the rather limited range 1

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Viscosity of Ring Polymer Melts

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“…On the contrary, Tg's of homopolyisoprene are all near -70 ~ and their variation with molecular weight is slight and irregular. We examined this problem elsewhere [14] and it will not be discussed here.…”

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

Widmaier¹,

Meyer²

1982

Journal of Thermal Analysis

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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.

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“…The glass transitions of each component are widely separated. The bulk polyisoprene (PI) has a very low T g z À70 C [17]; the bulk atactic polystyrene has T g z 100 C [18]. In small volumes of micro-phase separated PS micelles of block-copolymer, the upper glass transition T g (PS) is suppressed, while the glass transition of PI is elevated.…”

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confidence: 99%

Vitrification and plastic flow in transient elastomer networks

Pritchard

Redmann

Pei

et al. 2016

Polymer

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a b s t r a c tWe investigate how the crossover temperature of the elastic-plastic transition, the 'vitrification point' T v , changes under load for isotropic vitrimers and exchangeable liquid crystal elastomers (xLCEs), using the thermoplastic SIS triblock polymer as a reference. In all these cases, the elastic network cross-links are transient: physical micro-phase separation in SIS and covalent transesterification bonds in vitrimers. From the analysis of SIS we define T v as the point when entropic rubber-elasticity contraction due to heating under load turns into the irreversible plastic extension due to cross-links breaking and reforming. In xLCEs, the response to mechanical stress is heavily influenced by the smectic liquidcrystalline order, which makes the material much stiffer than normal rubbery networks, and also leads to the shape-memory effect across the smectic-isotropic transition point. The vitrification in the isotropic phase of xLCE, and in isotropic vitrimers, was found to be independent of stress, which can be attributed to the thermal activity of the catalyst determining T v and it not being mechanically coupled to the elastic network. Beyond T v , with increasing stress the plastic extension rapidly increases with temperature, as cross-link dynamics becomes more apparent.

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Glass transition temperature of anionic polyisoprene

Abstract: We are currently investigating the glass transition temperature (Tg) of ABA poly(styrene-ó-isoprene

Cited by 68 publications

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Viscosity of Ring Polymer Melts

Viscosity of Ring Polymer Melts

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

Vitrification and plastic flow in transient elastomer networks

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