Anionic Synthesis and Rheological Characterization of Poly(p‐methylstyrene) Model Comb Architectures with a Defined and Very Low Degree of Long Chain Branching

Abstract

A method is presented for the synthesis of defined sparsely branched polystyrene-based homopolymer model combs. By the use of poly(p-methylstyrene) (PpMS) as backbone and side chains, a low, but well controlled amount of branching of typically less than 1 mol-% (e.g., 1 branch per approx. 200 backbone C-atoms) can be achieved. The used anionic synthesis offers full control of the molecular weight in combination with low polydispersity. Molecular weight and polydispersity were determined by SEC-MALLS, confirming the well defined synthesis with low polydispersity ($\overline {{\rm M}} _{{\rm w}} /\overline {{\rm M}} _{{\rm n}} $ < 1.07). The melt rheological properties of the synthesized linear and comb polymers were obtained in both oscillatory shear and uniaxial extensional flow. Using the so-called van Gurp-Palmen plot, clear differences between both synthesized topologies are clearly seen. The appearance of a second minimum for lower values of the complex modulus in shear is a clear indication of a second relaxation process attributable to the entangled side chains. The presence of the entangled side chains is responsible for the observed strain hardening obtained in extensional viscosity experiments, as compared to the linear polymers. These model samples open up the possibility to compare different advanced rheological methods, e.g., FT-rheology or extensional rheology, towards limiting sensitivity.

Comb and Bottlebrush Polymers with Superior Rheological and Mechanical Properties

“…Substantial experimental [11,[29][30][31] and coarse-grained simulation works along with scaling analysis [24,25,[32][33][34][35] have been done to classify graft polymers into comb and bottlebrush classes with distinct rheological and mechanical properties. [10,11,22,[36][37][38][39][40][41][42][43] While bottlebrushes generally were designed to control the elastic properties of polymers, e.g., the shear and extensional moduli, through independent variation of the DP of side chain, n sc , and their grafting density, g 1 n − . [24,25] Comb topologies have a backbone and side chains with an unperturbed random Gaussian conformation, while a densely grafted bottlebrush has a stretched backbone and side chains.…”

“…Side chains were introduced on comb polymers to mainly control the rheological properties of polymers melt and solutions, especially the extensional viscosity and strain hardening behavior under extensional deformations, through variation of Z bb , Z sc , and q. [10,11,22,[36][37][38][39][40][41][42][43] While bottlebrushes generally were designed to control the elastic properties of polymers, e.g., the shear and extensional moduli, through independent variation of the DP of side chain, n sc , and their grafting density, g 1 n − . [3,24,25,32,44] Side chains in comb polymers increase the friction of the backbone chain with neighboring molecules in the melt or solution state, which enhances the strain hardening (see below) of the polymer melt under processing conditions.…”

Synthesis and temperature gradient interaction chromatography of model asymmetric star polymers by the “macromonomer” approach

“…Star polymers with varying numbers of arms have been widely produced and studied [1][2][3][4][5][6][7][8] and branched polymers of increasing complexity and diverse structures have evolved. These include H-shaped polymers [9][10][11][12][13][14][15], comb-shaped polymers [16][17][18][19][20][21][22][23][24][25][26][27][28] and more recently dendritically branched polymers [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48]. Fundamental to all these studies is the ability of the synthetic polymer chemist to control structural homogeneity and produce branched ...…”

Branching structure and strain hardening of branched metallocene polyethylenes

“…They found that strain hardening became more prominent as the average number of side chains increased as long as the branches had masses greater than M e . Kempf et al (2010) and Kempf et al (2013) studied combs of polystyrene and poly(p-methylstyrene) having various structures and observed significant strain hardening when the length of the branches was on the order of twice the entanglement molecular weight of the polymer. Lentzakis et al (2013) studied carefully synthesized comb polymers and determined the effects of the length and number of branches and the length of segments between branches on rheological properties.…”