Syndiotactic Poly(methyl methacrylate) (sPMMA)−Polybutadiene (PBD)−sPMMA Triblock Copolymers:  Synthesis, Morphology, and Mechanical Properties

Abstract

A series of syndiotactic poly(methyl methacrylate) (sPMMA)-polybutadiene (PBD)-sPMMA triblock copolymers, or MBM, have been successfully synthesized by using dilithium initiators (DLi's) based on the diadduct of tert-butyllithium (t-BuLi) to either 1,3-bis(1-phenylethenyl)benzene (PEB) or m-diisopropenylbenzene (m-DIB). The efficiency of these DLi's in building up MBM triblock copolymers has been compared under the same experimental conditions, i.e., in a cyclohexane/diethyl ether mixture for the butadiene polymerization at room temperature and in a cyclohexane/THF mixture for the MMA polymerization at -78 °C. Although all the synthesized copolymers show a monomodal, symmetric, and very narrow molecular weight distribution, the MBM copolymers synthesized with the m-DIB/t-BuLi diadduct are pure triblocks and show a high tensile strength, in contrast to copolymers initiated by the PEB/t-BuLi diadducts that are of a lower tensile strength and contaminated by MB diblock copolymers. Solvent cast films of MBM prepared with the m-DIB/t-BuLi diadduct are two-phase materials as confirmed by DSC and dynamic mechanical analysis (DMA). Transmission electron microscopy (TEM) shows a spherical morphology at a low sPMMA content, that changes into a cylindrical and finally lamellar morphology upon increasing the sPMMA content. Phase separation is observed for MBM with M h n of the sPMMA blocks as low as 6000. Dependence of tensile strength on copolymer structure and sample preparation has been studied. The smaller sPMMA molecular weight, M h n(PMMA), required for high tensile strength depends on the PBD molecular weight, M h n(PBD), e.g. 12 000 for Mn(PBD) ) 36 000 and 6000 for Mn(PBD) ) 80 000. The upper M h n(PMMA) is ca. 20-25 000, whatever the Mn(PBD). The optimum tensile strength is observed for M h n(PMMA) ) 15 000, independently of Mn(PBD) in the studied range. As a rule, the tensile strength tends to level off and the elongation at break starts to decrease when the sPMMA content is increased beyond 35 wt %. At a constant sPMMA content, Mn(PBD) (>ca. 36 000) does not affect the ultimate tensile properties.

Silica reinforced triblock copolymer gels

“…Modification of the polydiene block in polystyrene-polydiene-polystyrene block copolymers has received much attention [35][36][37][38][39][40][41], including the selective hydrogenation of the midblock. Because the transition temperature from a rubbery gel to a plastic fluid (T P ) is too low for many applications, polystyrene has been either replaced by a higher T g block [42][43][44][45] or chemically modified [46][47]. An alternative strategy is the physical modification of one phase of the gel by appropriate additives.…”

Synthesis of poly(methyl methacrylate)-b-poly(n-butyl acrylate)-b-poly(methyl methacrylate) triblocks and their potential as thermoplastic elastomers

“…The use of diene-based TPEs is however limited by the poor oxidation resistance of the unsaturated central block and the relatively low service temperature (60-70°C) in relation to the glass transition temperature of polystyrene. Accordingly, efforts have been made to improve the properties of the outer [1][2][3][4][5][6] and/or the inner [2,7] blocks. Substitution of fully (meth)acrylate TPEs for the traditional SBS and SIS copolymers would be potentially beneficial due to the large range of properties of poly(meth)acrylates.…”

Synthesis and characterization of hydrogenated poly[alkylmethacrylate(-b-styrene)-b-butadiene-b-(styrene-b-) alkylmethacrylate] triblock and pentablock copolymers

“…Syringes and stainless steel capillaries were used in order to transfer solvents, monomers and initiator. Details of the experimental techniques and reaction conditions were reported elsewhere [23,29]. The triblock copolymerization consisted of 3 steps: (1) butadiene was polymerized in a cyclohexane/diethyl ether mixture (100/6, v/v) at room temperature for one night, using a diadduct of m-DIB and two equivalents of t-BuLi (deep red colour) as a difunctional initiator previously prepared in cyclohexane at 50°C for 2h; (2) end-capping of PBD dianions by diphenylethylene (DPE) at room temperature for 1 h; (3) addition of THF to cyclohexane (40/60, v/v) followed by alkylmethacrylate at -78°C.…”

“…It has been reported from our laboratory [23] that well defined triblock copolymers could be obtained by sequential living anionic polymerization of butadiene and methyl methacrylate (MMA) with the t-butyllithium (t-BuLi)/m-diisopropenyl benzene diadduct as a difunctional initiator. This method was also successful for the preparation of pentablock copolymers [26].…”

“…Finally, sPMMA has the additional advantage of forming a stereocomplex with isotactic PMMA (iPMMA), the melting temperature of which may be as high as 190°C [6,7]. Recently, we have reported the synthesis and characterization of well defined triblock copolymers consisting of sPMMA blocks associated with a central PBD block [23]. These copolymers have been prepared by sequential living anionic polymerization of butadiene and MMA by using a difunctional initiator soluble in hydrocarbons.…”